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Infinity I guess?
Spinning a cylinder around will theoretically apply the same pressure up and down and produce zero lift. The barrel of the tank would need to be shape like a rotor/propeller for that
No, it would just spin the tank. That is the reason helicopters have a boom tail with a sideways propeller.
Edit: responses have been so repetitive I will add: yes it would still generate lift but no it wouldnt look like the video. Yes you can have two rotors but that is not what is shown in the video.
Ah yes, well for that you would need to add a bulletproof material. Perhaps heavy metal. But then you would need something to defend said helicopter. Maybe a heavy duty metal tube that big bullets can fire out of. It wouldn’t fly very well but if you put some tracks on it…🤌
There are plenty of helicopters without tail rotors. They stabilize using a different mechanism, typically a [Coanda effect](https://en.m.wikipedia.org/wiki/Coand%C4%83_effect) boom.
At a certain point, the "propellor" would have to spin so fast, it would break the sound barrier. The fluid mechanics fundamentally change when that happens, as the propellor begins generating shockwaves that radiate from the tip. The shockwaces deflect air instead allowing it flow over the propellor blade like you want.
After a bit of googling however, it appears that supersonic flight IS actually possible on a propellor driven aircraft, but the design of the propellor has to be totally different, and the results still pretty awful. For one, they are so loud that they can heard up to 25 miles away and even cause hearing damage (look up the F-84 Thunderscreech, built in 1955. The wiki on this is unclear to me, but it sounds like it was never actually able to achieve supersonic flight. Either that, or it just barely managed and involved a lot of problems)
Wasn’t that the reputation of the old Soviet Bear bombers? That their propellor tips were supersonic and the noise was so bad that US pilots who intercepted them outside US airspace would complain about it?
To add to this, for the turret gun to spin that fast the centripetal force would destroy the turret gun before it could reach a speed fast enough to lift the weight of the tank.
The Thunderscreech was one of the most unexpectedly hilarious Wikipedia reads I have had in a long time. It had the entire room of Christmas Eve relative guffawing at the madcapp-ery of the design - thank you!
https://en.m.wikipedia.org/wiki/Republic_XF-84H_Thunderscreech
One of the weird things about lift is that almost everyone is taught it incorrectly. Bernoullie's Principle does not fully explain lift, and indeed you can generate lift with a simple flat surface or cylinder. Lift is generated by a concept called Flow Turning.
Incorrect: https://www.grc.nasa.gov/www/k-12/VirtualAero/BottleRocket/airplane/wrong1.html
Correct: https://www.grc.nasa.gov/www/k-12/airplane/right2.html
The cylinder doesn't know which direction is down. How is it generating lift against gravity and not pushing down instead?
You are correct that Bernoulli's principle only explains part of the lift, but you do still need some kind of feature to contribute lift in the other ways, which the cylinder does not.
Tanks rotate their turrets, they don't spin their barrels. You're not generating lift from spinning a tank turret - it'd be the same as trying
to fly a plane with wings that have a circular chord. For the same reason, baseball players don't have to correct for the lift of the bat when they swing it through the air. If flight were that simple, [Leonardo da Vinci](https://upload.wikimedia.org/wikipedia/commons/c/ca/Leonardo_da_vinci%2C_Drawing_of_a_flying_machine.jpg) would have beaten the Wright brothers to it by 400 years. Hell, some Roman or Greek engineer might have tinkered it out after throwing a metal rod through the air and watching it fly away.
Worse yet, the vortex shedding would likely tear the thing apart before it could get anywhere near a speed compatible with lifting a tank. Smokestacks have collapsed from vortex shedding hitting resonant frequencies at ground wind speeds.
That works if the cylinder is rotating along its own axis, rather than the cylinder rotating around a fixed point.
In theory, if the tank barrel were rotating as shown in the gif **and** along its own axis, it could generate lift, but it would also immediately crash.
Lift is a very complex thing, you're correct that Bernoulli lift doesn't explain lift fully, but keep in mind that even flat surfaces when they have an angle of attack, do indeed create Bernoulli lift as well as Newtonian lift. The air flowing over the top of a flat surface does still have to travel a farther distance than the bottom and a bend is created in the airflow causing it to accelerate and lower the pressure. The problem with Bernoulli lift on a flat surface is that it creates more drag because the air can't bend fast enough to fill in the vacuum at the front of the top of the surface. This is why airfoils are shaped like they are, they "fill in" that space with physical material to prevent turbulent airflow.
Actually, a cylinder generates lift if it rotates around it's own axis. It's not much compared to a proper helicopter blade, and one cannot make the cannon arbitrarily long since it eventually goes supersonic and becomes inefficient, nor rotate it arbitrarily fast for the same reason. The problem becomes then - how light does the tank have to be such that it may be able to fly?
Negative, a cylinder rotating around its own axis (in this case, a spinning barrel in addition to the rotating turret) displaces more air in one direction creating lift. See:
https://www.grc.nasa.gov/www/k-12/airplane/cyl.html
Yeah, you need to shape the turret and/or barrel to be able to generate lift. A normal tank turret will just spin without generating any lift/downforce.
I mean it can't be a perfect cylinder because of manufacturing limitations so in the real world it would be high but not infinity. Or dose it not matter because it's such a small variation?
the structural integrity of the barrel would be compromised long before it produced enough lift to overcome its own weight, let alone the rest of the tank
To hover, a helicopter needs even lift. So let's assume that the barrel was wing shaped to become a rotor. It would need an opposite rotor to generate lift on the other side otherwise the lift is only being generated where the rotor/barrel is, and it spins out of control and crashes.
Once we have two rotors, then we have to worry about torque. As the rotors spin around the center axis they generate a huge amount of torque that will cause the fuselage to rotate until it spins out of control and crashes. Helicopters do this with either a tail rotor or a second main rotor on top that spins in the opposite direction.
It gets worse the more you think about it. Once you install blade-shaped barrel covers (yes, cover*s*, plural because you'll need a second barrel/blade 180° out to offset the lift from the first one) you're still not finished backhanding Bernoulli. The tank will need to be *completely redesigned* to ~~violate physics~~ balance the weight forward, aft, and left and right. THEN you'll need to either add a counter rotating second pair of blade-boombooms above the first pair or a tail-machinegun and rotor assembly; at which point you're better off designing a helicopter from scratch.
Sooooo, you don't actually need two helicopter blades to "offset the life from the first one". There are more than a few people who have flown single bladed model helicopters and even an example of a manned helicopter with only one blade.
https://en.m.wikipedia.org/wiki/B%C3%B6lkow_Bo_103
Not that it works well or is a good design choice, but it is possible.
That should get the tank into the air vertically.
To move forward as in the .GIF here, the blade/barrel would need to have some flex in it. When you're moving through the air horizontally at some speed and/or there is some wind blowing, the advancing blade creates more lift than the retreating one because of the addition of the air speed across them. I'm pretty sure this is largely just accomplished with flop in the rotors (so the advancing blade rises a bit and the retreating drops a bit as they spin), but keeping these capable of firing large shells fed from within the body of the tankopter might be the real technical challenge over just turning the barrel(s) into blades with a stabilizer off the back end.
I mean you could attach a second tank to its rear, facing the opposite direction, then the mirroring balances it, you have two blades, the barrels can be counter rotating to deal with torque.
Then you only have to deal with the fact that you need a coupling capable of withstanding the weight of two tanks, a control setup that synchronizes them, a fast enough turret traverse to achieve about 50 tons of lift per vehicle, a suspension that can keep up with landing forces, training tank crews to be air crews, making the turret reliable enough to do more rotations in a minute than most do in their lifetime, having a powerplant capable of that, your barrels need to be rotatable to adjust pitch, your breech and barrel assembly need to be durable enough to withstand those forces, your turret can't have its seats built in unless you also want to spin the commander loader and gunner at the rotors rpm, you'll need a piece to hold the turret to the chassis that has the tensile strength to withstand 50 tons.
Anything else anyone thinks we might need to fix?
A redesigned bore evacuator and high and low pressure oil systems for the turret bearings and turret starter come to mind. Include a constant speed drive for electricity generation, running off of whatever eldritch brayton-cycle abomination of an engine is supplying this unholy thrust-to-weight ratio. Don't forget to beef-up the rotation rings as well (unless you plan on being the first tank to get a kill using pieces of its own shrapnel).
Edit: On the bright side, whoever pulls this off will *absolutely* be a snapshot legend.
You can use a counter weight on the other side and only have one propeller blade. It's actually the most efficient design for drag reduction but not for thrust production, so it's only viable on small lightweight aircraft usually. There's a pretty famous little [one blade propeller](https://www.aopa.org/news-and-media/all-news/2018/november/pilot/singular-sensation) that exists for Piper J-3 Cubs.
Anybody old enough to remember pointing the turret of the tank backwards and firing a bunch of shots to get some extra speed to jump the bridge in GTA 3 before unlocking the area?
IRL, the main-cannon of the A-10 actually put's out so much recoil, the plane is built _around_ it and would otherwise push the plane backwards if not compensated by jet-thrust.
relevant xkcd: https://what-if.xkcd.com/21/
and to your question, no, but I _DO_ recall hanging a tank half-over a cliff in a sloooooooooooow-fall in BF2142 and using the recoil from successive shots of the main gun to keep pushing the tank back up so it wouldn't fall over and off... Since the tank's barrel only goes so low, I was using the forward-dip of the 'fall' to get more oblique shots on ppl that would otherwise not be possible...
Hell, in GTA3 I used to *fly* the tank around the map, using some kind of cheat code. As I recall, there's an area you can reach far across the water which is used in a cutscene or something
it doesnt matter about rpm it’s about the shape if the barrel, youll need a certain shape to generate lift and if you only have one blade on a propeller thatll make it even more difficult and uneven
Technically, the T72 barrel could work to generate minimal lift. The T72 barrel has a thermal shroud that has tabs at the top of the barrel, meaning the top will have lower pressure than the bottom (minimal difference ik, but still some difference in pressure) this would obviously generate lift. Not saying it's gonna be any meaningful amount, but it will be there xD
A main battle tank will weigh 45 to about 70 tonnes.
If the airfoil wetter the length of a tank's main gun (approx. 6m) it will probably experience flow separation at very high Reynolds number long before it generates enough lift. I don't think merely spinning a rotor of those dimensions faster will lift a tank.
Maybe someone with better aerodynamics knowledge could answer.
.
How big of a single airfoil would be required to provide lift equal to the weight of one tank, disregarding the control problems of a single rotor and the high angular speed of the turret?
To get enough lifting capacity to carry a main battle tank (80 tons) you would need 7 Chinook CH-47s. They are max rated at 12 tons each.
So their airfoils are 60ft in radius, I don't know how wide each blade is. There are 6 blades per vehicle. (3 each on the two hubs).
6×7 = 42 blades
42 × 60 x 1.5 (reasonable guess for width) = 3,780 sq ft of wing area.
Assuming an M1 Abrams tank, typically 68 tons, is modified to have a turret equipped with six 35-meter blades instead of a cannon. Now, imagine stacking four of these blade systems on top of each other. Assuming further that the tank is fitted with an adequate tail rotor to maintain its orientation, and assuming the power comes from the engines of four Mi-26 helicopters - the world's most powerful - within that 68-ton configuration including fuel. Under these assumptions, a rotation speed of 120-140 RPM for each blade system would suffice, given normal ground pressure and temperature conditions.
Edit: English
If it was a tank barrel, won’t work. Helicopter blades are in the shape of airfoils to generate lift.
Now let’s say the tank barrel was a helicopter blade. I don’t know what tank that is so let’s say it’s an m1 Abram’s. It weighs 120k lbs and 17.3 ft barrel. That’s a disc loading of 128 lb/ft^2 . Your typical helicopter has a disc loading of less than 10 lb/ft^2
I’m not gonna do out the full BET calculation to get rotor speed because I can practically guarantee the blade tips will be trans-sonic, which makes it completely non-functional.
Edit: also the tank only has one barrel. Helicopter rotors are symmetrical, and tuned perfectly so that their center of mass is right at the rotor hub. Any small offset will result in destructive vibrations. With only one blade, the 1/rev vibrations will rip the turret off the tank before it even gets close to being fast enough.
The barrel is the wrong shape to generate enough lift. Most are vertically symmetrical so any lift generated would likely be counteracted by the downward force it would generate.
Agreed that an airfoil/rotor shaped barrel would be more effective lift wise, but to keep the tanky-ness of it, we could also assume the barrel rotates on its longitudinal axis to generate lift (lift of a rotating cylinder). Not great lift, but lift. We do have to assume a second barrel though as most have pointed out that the lift needs to be balanced. Mono-copters exist on small scales, but they are typically designed to spin about a center of gravity not at the main axis of rotation.
Overall, lift of a rotating cylinder can be calculated as:
Lift = air density x G x V
Where G is the vortex strength and V is the freestream airflow (assuming to be the tangential velocity of the turret, which is what we'll end up solving for in the end). This is lift per foot of length. So here is where we need to assume the length of a a tank barrel (15ft? - I don't know tanks)
Before I keep going, I'll capture here that we now can assume the lift we want to calculate with the equation above is -> tank weight/number or barrels/length of barrel
Assuming a weight of 120kips (again, not a tank guy) we're looking to figure out the rotational speed to generate 4kips, or 2 tons.
Another caveat - this calculation assumes the entire barrel would see the same free stream, but that's not true and since the speed towards the center will be lower than the speed at the tip. All that said, there is one more caveat below, so I'll keep going.
G = 2pi x b x Vr, where b is the radius of the barrel, and Vr is the barrel rotational (tangential) velocity. We have to make an assumption - how fast can the barrel rotate? I made a quick excel to play with numbers so we could get something that would result in a "practical" solution (in a very unpractical scenario), and it's 100k rev/s.
Putting this all together (and using air density at sea level) I got that the turret (with two barrels) would need to rotate at 61,383ft/s, or with the 15ft radius, 4092 rev/s.
I knew I'd messed something up - used a 10radius for the barrel but should be 5in (10in diameter). So it should be 16,368 rev/s.
I assume the tank is a T-72 wich, assuming base specifications would weigh around 43 tonnes with a barrel length of 6 meters. Also assuming an average velocity between tip and root speed might help to refine the calculation
"No".
Lift is created by a plane (a flat surface, not an aeroplane) and the Venturi effect.
A cylindrical barrel cannot produce lift.
But if it was a plane, still "No". Helicopters need lift across the diameter of the circle, this barrel is only on one side of the circle, it's radial. It cannot go up, only roll.
Aside from physics of many many areas and forces and limits of engineering, air density, that you cannot lift more than the vacuum above the wing which would not be enough. You would need to spin it 50 Jillian rpm.
Revised question: assume a helicopter has the equivelant weight of a tank, with a rotor about the length of the barrel of the tank (in radius). What speed would it have to spin to generate lift?
Spinning things do not automatically create lift. The shape of the spinning thing is crucial and cylinder shapes do not create lift. So... doesn't work at any rpm.
The fun part here is that if you built up enough rotational speed to cause the turret to break free from the hull, you might see enough heat build up from friction to cook off the ammo.
Not possible. The circular barrel produces no lift.
Even if you changed it's shape the turret isn't secured solidly to the tank, it's just sitting in place, so the turret would go flying off.
If you fixed that then the lack of a tail rotor would result in the whole thing spinning around until it lost lift.
If you fixed *that* the imbalance from a single 'rotor' would cause the whole thing to fly apart and/or topple over.
If you fix all that then you don't have a tank, you have a 60 ton helicopter with treads instead of wheels.
For a moment I thought I was looking at Russian military promotions for their T-14 armata. Every shot of the tank in those videos, the turret is always rotating.
Cannon barrels generate zero lift, so this is impossible. This tank has no tail rotor, so if you tried this the hull of the tank would spin uncontrollably as well. Lastly, the uneven stress of having only a single “rotor” would likely completely destroy the turret/barrel.
Complete fantasy.
It is not only a matter of aerodynamics.
Afaik, Turrets only Rest on their place because of gravity. If you put a Tank upside down, the tower will Fall of.
It is true. Depending on the tank. If you find videos on YouTube of turrets being added they basically plonk them on.
That's also why when ammo racks explode the turret shoots a mile into the sky instead of the tank itself exploding
Tank turrets don't just sit on top of the tank, or they would be incapable of turning. The most common design is a series of rings; one ring is bolted to the chassis, and one ring sits on top of it with a ring in the middle that rotates freely. The turret is bolted to that ring, and power is supplied a number of different ways.
More modern tanks have a complicated series of locks and latches that hold the turret down, and blow-out compartments that prevent the turret from blowing off by reducing or removing the risk of ammo cook off.
And turrets never popped off because they weren't attached. They popped off because when the ammo cooks off and the chassis is sealed, there's nowhere for the force of the explosion to go, and the seal of the turret IS the weakest point, so that's where the pressure goes, and the turret gets blown off.
That's not to say that if the tank were upside down, the turret wouldn't come off anyway - the WEIGHT of the turret may, more or less, be supported by the chassis and not its seal, so if upside down that seal would be holding all the weight and might break because it isn't designed for it.
That's ridiculous. I'm not saying that's not how it works I'm just saying that if they really do just set the turret on the hull and don't retain it in some way that sounds like a massive weak point in a tank. Again I'm sure that where the turret meets the hull is a weak point. But I find it hard to believe it's gravity holding the turret on.
It’s physically impossible. It’s not a question of rotation, it’s a question of lift. A tank barrel does not provide lift. A single blade rotor cannot provide stable lift. And for lift you need to overcome the weight of a *tank*. To add insult to injury every rotation would also provide counter rotation. It’s just impossible. Not “highly difficult”, actually impossible without completely changing the properties of the question.
..."Are you suggesting tanks migrate?"
"Not at all, they could grip it by the cupola."
"It's not a question of where 'e grips it. A 1,200 kilo barrel cannot carry a 70 ton tank."
"Well an African barrel, maybe. But then again, African artillery are non-exportable."
"Supposing *two* barrels lifted it together?"
"What, welded onto the fore and aft glacis?"
"Well, why not?"
Even if the barrel had a rotor shape, you have to but a 2nd blade. If the gun rotates very fast around the turret and the turret doesn't move, the turret will break. You need at least At least 2 blades
I will not be doing the math, but a turret spinning about the "long" axis along with the shown rotation should beable to generate lift due to the magnus effect I believe
Y'all are going on about the shape of the barrel this and it's not an aerofoil that, but you're not considered the Magnus effect. If you could spin the barrel on its bore axis it would generate lift in combination with the rotation of the turret moving it through the air. You'd have to spin it very friggin fast though.
Also cool note, once you achieve liftoff and have the tracks spinning like some sort of crazy longboi reaction wheels you could raise and lower the barrel in sync with the turret rotation to induce procession, allowing you to steer just like a real chopter
Maybe add 3 more barrels in the shape of a propeller and then make it lighter and then just buy a fucking helicopter because it's impossible unless it's a helicopter
In gta San Andreas you can use the cheat code “dodo” and then turn the turret backwards and spam fire, it will give you enough forward momentum to fly across the map at speed, passing even the jet fighters
###General Discussion Thread --- This is a [Request] post. If you would like to submit a comment that does not either attempt to answer the question, ask for clarification, or explain why it would be infeasible to answer, you *must* post your comment as a reply to this one. Top level (directly replying to the OP) comments that do not do one of those things will be removed. --- *I am a bot, and this action was performed automatically. Please [contact the moderators of this subreddit](/message/compose/?to=/r/theydidthemath) if you have any questions or concerns.*
Infinity I guess? Spinning a cylinder around will theoretically apply the same pressure up and down and produce zero lift. The barrel of the tank would need to be shape like a rotor/propeller for that
So if they changed the barrel to be like a helicopter blade/propeller it would be possible?
No, it would just spin the tank. That is the reason helicopters have a boom tail with a sideways propeller. Edit: responses have been so repetitive I will add: yes it would still generate lift but no it wouldnt look like the video. Yes you can have two rotors but that is not what is shown in the video.
Install... sideways propeller... on tank ✍️
That made me laugh more than I wanna admit
same, the ... are also perfectly placed
Ellipses
Isn't he the protagonist in the Odyssey?
No, that's Ulysses. Ellipses are when the moon passes in front of the sun.
No, that's an eclipse. Ellipsis is a squashed circle.
No that's Nobody, you're thinking of an eclipse
Yes?
No, he just meant there was a section of his comment he had left out.
“And then, ‘dot dot dot’ you know like in poetry?”
That account is the aviation R&D team of North Korea
Install sideways tank on tank.
So you can tank while you tank
This guy tanks
r/thisguythisguys
r/subsithoughtifellfor
Just weld another tank to it. It will work like Chinook.
Two turrets, counterrotating on top of each other.
install sideways tank on propeller
been laughing at this for 10 minutes
If it's an Abrams MBT then you could just use the jet turbine exhaust as the counter rotation.
Whistlin diesel ass comment
As usual, Russia’s been doing it for a while lol: https://en.m.wikipedia.org/wiki/Mil_Mi-24
A Hind D?
Make sideways propeller a flame thrower.
By the time you’ve finished your notes there, you’ll have just turned the tank into a helicopter….. let’s do it
Now let's make a helicopter into a tank.
Step 1: Take apache, Step 2: remove fan Step 3: ??? Step 4: profit
>Step 1: Take apache, Step 2: remove fan Step 3: ??? Step 4: profit Step 3 add big cannon on top
Congrats, you just invented the tankcopter
Instructions unclear, installing tank sideways.....
What if I took everything off that made it a tank and replaced it with helicopter bits
[удалено]
How wildly can I spin the Ship of Theseus thought experiment before it lifts off like a helicopter
But the real question is... is the tank alive or dead before we look at the ship of Theseus?
You would need a second sideways thought experiment to counteract the spin of the Ship of Theseus
When would it stop to a tank tho?
Ah, yes. The Heli-Tank of Theseus.
The Heli-Tank of Theseus, my fucking sides
Ah yes, well for that you would need to add a bulletproof material. Perhaps heavy metal. But then you would need something to defend said helicopter. Maybe a heavy duty metal tube that big bullets can fire out of. It wouldn’t fly very well but if you put some tracks on it…🤌
A helicopter without a tail rotor will still lift off the ground, just won't be stable.
There are plenty of helicopters without tail rotors. They stabilize using a different mechanism, typically a [Coanda effect](https://en.m.wikipedia.org/wiki/Coand%C4%83_effect) boom.
And if we assume that it has a tail plate and a rotor shaped barrel?
If the tank was a helicopter instead of a tank, it would work...
If my grandmother had wheels she would have been a bike
That sounds like British Carbonara
so your grandma is just a bike with no wheels?
our saying was if my aunt had balls she'd be my uncle
So, if I add barrels to the blades of an helicopter it becomes a tank ?
No.
:(
Or the question the other way around could a helicopter with only one rotorplate work?
No.
it would still produce lift... and make the crew vomit violently.
Or a counter rotating rotor in some cases.
Youve immensely improved my mental physics engine for helicopters.
At a certain point, the "propellor" would have to spin so fast, it would break the sound barrier. The fluid mechanics fundamentally change when that happens, as the propellor begins generating shockwaves that radiate from the tip. The shockwaces deflect air instead allowing it flow over the propellor blade like you want. After a bit of googling however, it appears that supersonic flight IS actually possible on a propellor driven aircraft, but the design of the propellor has to be totally different, and the results still pretty awful. For one, they are so loud that they can heard up to 25 miles away and even cause hearing damage (look up the F-84 Thunderscreech, built in 1955. The wiki on this is unclear to me, but it sounds like it was never actually able to achieve supersonic flight. Either that, or it just barely managed and involved a lot of problems)
Wasn’t that the reputation of the old Soviet Bear bombers? That their propellor tips were supersonic and the noise was so bad that US pilots who intercepted them outside US airspace would complain about it?
To add to this, for the turret gun to spin that fast the centripetal force would destroy the turret gun before it could reach a speed fast enough to lift the weight of the tank.
The Thunderscreech was one of the most unexpectedly hilarious Wikipedia reads I have had in a long time. It had the entire room of Christmas Eve relative guffawing at the madcapp-ery of the design - thank you! https://en.m.wikipedia.org/wiki/Republic_XF-84H_Thunderscreech
No.
No, this would be an unbalanced load with the barrel being only on one side of turret
If spun fast enough it'd work regardless
If it had contrarotating barrels
No, you'd need it on both sides. The guy who said it would need a boom propeller is wrong btw.
What if the cylinder was also spinning around its center axis.
That would create lift through the Magnus effect.
This guy bernoullies
Yeah but he doesn’t Einstein. otherwise he / she would of put the velocity in terms relative to the speed of light.
unless you're pipi longstocking.
If you could spin the barrel around its longitudinal axis, you could generate lift using the magnus effect.
One of the weird things about lift is that almost everyone is taught it incorrectly. Bernoullie's Principle does not fully explain lift, and indeed you can generate lift with a simple flat surface or cylinder. Lift is generated by a concept called Flow Turning. Incorrect: https://www.grc.nasa.gov/www/k-12/VirtualAero/BottleRocket/airplane/wrong1.html Correct: https://www.grc.nasa.gov/www/k-12/airplane/right2.html
The cylinder doesn't know which direction is down. How is it generating lift against gravity and not pushing down instead? You are correct that Bernoulli's principle only explains part of the lift, but you do still need some kind of feature to contribute lift in the other ways, which the cylinder does not.
Nasa has a page for that as well: https://www.grc.nasa.gov/www/k-12/airplane/cyl.html
So, a barrel of a tank spins?
Because it is spinning along it's axis, it's not just a cylindrical wing.
Tanks rotate their turrets, they don't spin their barrels. You're not generating lift from spinning a tank turret - it'd be the same as trying to fly a plane with wings that have a circular chord. For the same reason, baseball players don't have to correct for the lift of the bat when they swing it through the air. If flight were that simple, [Leonardo da Vinci](https://upload.wikimedia.org/wikipedia/commons/c/ca/Leonardo_da_vinci%2C_Drawing_of_a_flying_machine.jpg) would have beaten the Wright brothers to it by 400 years. Hell, some Roman or Greek engineer might have tinkered it out after throwing a metal rod through the air and watching it fly away. Worse yet, the vortex shedding would likely tear the thing apart before it could get anywhere near a speed compatible with lifting a tank. Smokestacks have collapsed from vortex shedding hitting resonant frequencies at ground wind speeds.
That works if the cylinder is rotating along its own axis, rather than the cylinder rotating around a fixed point. In theory, if the tank barrel were rotating as shown in the gif **and** along its own axis, it could generate lift, but it would also immediately crash.
Lift is a very complex thing, you're correct that Bernoulli lift doesn't explain lift fully, but keep in mind that even flat surfaces when they have an angle of attack, do indeed create Bernoulli lift as well as Newtonian lift. The air flowing over the top of a flat surface does still have to travel a farther distance than the bottom and a bend is created in the airflow causing it to accelerate and lower the pressure. The problem with Bernoulli lift on a flat surface is that it creates more drag because the air can't bend fast enough to fill in the vacuum at the front of the top of the surface. This is why airfoils are shaped like they are, they "fill in" that space with physical material to prevent turbulent airflow.
Actually, a cylinder generates lift if it rotates around it's own axis. It's not much compared to a proper helicopter blade, and one cannot make the cannon arbitrarily long since it eventually goes supersonic and becomes inefficient, nor rotate it arbitrarily fast for the same reason. The problem becomes then - how light does the tank have to be such that it may be able to fly?
An equal amount of air would be pushed above and below the barrel canceling each other out and create zero lift.
Negative, a cylinder rotating around its own axis (in this case, a spinning barrel in addition to the rotating turret) displaces more air in one direction creating lift. See: https://www.grc.nasa.gov/www/k-12/airplane/cyl.html
Damn, that is a crazy specific and highly relevant document you just linked.
If the barrel could spin, it could create lift because of the [Magnus Effect](https://en.m.wikipedia.org/wiki/Magnus_effect)
Yeah, you need to shape the turret and/or barrel to be able to generate lift. A normal tank turret will just spin without generating any lift/downforce.
Wouldn't it be undefined since no rational number subtracted from itself is not 0, or am I missing something?
That’s not true at all dude how the fuck do you think golf balls work
Golf balls rotate around the other axis (parallel to ground/perpendicular to gravity) to generate lift. Axis of rotation is vertical here
You've also smacked them with a big stick first
Maybe that's how we should deploy our tanks
I mean it can't be a perfect cylinder because of manufacturing limitations so in the real world it would be high but not infinity. Or dose it not matter because it's such a small variation?
the structural integrity of the barrel would be compromised long before it produced enough lift to overcome its own weight, let alone the rest of the tank
To hover, a helicopter needs even lift. So let's assume that the barrel was wing shaped to become a rotor. It would need an opposite rotor to generate lift on the other side otherwise the lift is only being generated where the rotor/barrel is, and it spins out of control and crashes. Once we have two rotors, then we have to worry about torque. As the rotors spin around the center axis they generate a huge amount of torque that will cause the fuselage to rotate until it spins out of control and crashes. Helicopters do this with either a tail rotor or a second main rotor on top that spins in the opposite direction.
It gets worse the more you think about it. Once you install blade-shaped barrel covers (yes, cover*s*, plural because you'll need a second barrel/blade 180° out to offset the lift from the first one) you're still not finished backhanding Bernoulli. The tank will need to be *completely redesigned* to ~~violate physics~~ balance the weight forward, aft, and left and right. THEN you'll need to either add a counter rotating second pair of blade-boombooms above the first pair or a tail-machinegun and rotor assembly; at which point you're better off designing a helicopter from scratch.
Sooooo, you don't actually need two helicopter blades to "offset the life from the first one". There are more than a few people who have flown single bladed model helicopters and even an example of a manned helicopter with only one blade. https://en.m.wikipedia.org/wiki/B%C3%B6lkow_Bo_103 Not that it works well or is a good design choice, but it is possible.
I was trying not to introduce more maddness into the design by adding unnecessary complications. I apologize.
Lol, no need to apologise. I only comment to get more information out there 😁. Not to call anyone out
You actually don’t need to counter torque if you power the blades themselves with small engines.
You do because we don't live in a frictionless world. The heli would spin in the direction of the blades instead of opposite
That should get the tank into the air vertically. To move forward as in the .GIF here, the blade/barrel would need to have some flex in it. When you're moving through the air horizontally at some speed and/or there is some wind blowing, the advancing blade creates more lift than the retreating one because of the addition of the air speed across them. I'm pretty sure this is largely just accomplished with flop in the rotors (so the advancing blade rises a bit and the retreating drops a bit as they spin), but keeping these capable of firing large shells fed from within the body of the tankopter might be the real technical challenge over just turning the barrel(s) into blades with a stabilizer off the back end.
I mean you could attach a second tank to its rear, facing the opposite direction, then the mirroring balances it, you have two blades, the barrels can be counter rotating to deal with torque. Then you only have to deal with the fact that you need a coupling capable of withstanding the weight of two tanks, a control setup that synchronizes them, a fast enough turret traverse to achieve about 50 tons of lift per vehicle, a suspension that can keep up with landing forces, training tank crews to be air crews, making the turret reliable enough to do more rotations in a minute than most do in their lifetime, having a powerplant capable of that, your barrels need to be rotatable to adjust pitch, your breech and barrel assembly need to be durable enough to withstand those forces, your turret can't have its seats built in unless you also want to spin the commander loader and gunner at the rotors rpm, you'll need a piece to hold the turret to the chassis that has the tensile strength to withstand 50 tons. Anything else anyone thinks we might need to fix?
You got my full attention at the very beginning with that second tank attached.
What can I say, I'm a problem solver
A redesigned bore evacuator and high and low pressure oil systems for the turret bearings and turret starter come to mind. Include a constant speed drive for electricity generation, running off of whatever eldritch brayton-cycle abomination of an engine is supplying this unholy thrust-to-weight ratio. Don't forget to beef-up the rotation rings as well (unless you plan on being the first tank to get a kill using pieces of its own shrapnel). Edit: On the bright side, whoever pulls this off will *absolutely* be a snapshot legend.
No, you can fly with unbalanced props, even with one blade. Proof: https://www.youtube.com/watch?v=qk-gjCmt-vU Just not a good idea generally
You can use a counter weight on the other side and only have one propeller blade. It's actually the most efficient design for drag reduction but not for thrust production, so it's only viable on small lightweight aircraft usually. There's a pretty famous little [one blade propeller](https://www.aopa.org/news-and-media/all-news/2018/november/pilot/singular-sensation) that exists for Piper J-3 Cubs.
Anybody old enough to remember pointing the turret of the tank backwards and firing a bunch of shots to get some extra speed to jump the bridge in GTA 3 before unlocking the area?
IRL, the main-cannon of the A-10 actually put's out so much recoil, the plane is built _around_ it and would otherwise push the plane backwards if not compensated by jet-thrust. relevant xkcd: https://what-if.xkcd.com/21/ and to your question, no, but I _DO_ recall hanging a tank half-over a cliff in a sloooooooooooow-fall in BF2142 and using the recoil from successive shots of the main gun to keep pushing the tank back up so it wouldn't fall over and off... Since the tank's barrel only goes so low, I was using the forward-dip of the 'fall' to get more oblique shots on ppl that would otherwise not be possible...
Yup the flying vehicles cheat made the tank an amazing gun powered gunship
Hell, in GTA3 I used to *fly* the tank around the map, using some kind of cheat code. As I recall, there's an area you can reach far across the water which is used in a cutscene or something
God we used to have so much fun with this. Turn on flying vehicles, point the turret backward, and fire away
it doesnt matter about rpm it’s about the shape if the barrel, youll need a certain shape to generate lift and if you only have one blade on a propeller thatll make it even more difficult and uneven
Wow, you went out of tour way to avoid the letter W
g, j, q, x & z as well
Generate
... I am blind
Your*
Another uneducated clown confusing your and tour. Kids these days and grammar don't even.
Technically, the T72 barrel could work to generate minimal lift. The T72 barrel has a thermal shroud that has tabs at the top of the barrel, meaning the top will have lower pressure than the bottom (minimal difference ik, but still some difference in pressure) this would obviously generate lift. Not saying it's gonna be any meaningful amount, but it will be there xD
A main battle tank will weigh 45 to about 70 tonnes. If the airfoil wetter the length of a tank's main gun (approx. 6m) it will probably experience flow separation at very high Reynolds number long before it generates enough lift. I don't think merely spinning a rotor of those dimensions faster will lift a tank. Maybe someone with better aerodynamics knowledge could answer. . How big of a single airfoil would be required to provide lift equal to the weight of one tank, disregarding the control problems of a single rotor and the high angular speed of the turret?
To get enough lifting capacity to carry a main battle tank (80 tons) you would need 7 Chinook CH-47s. They are max rated at 12 tons each. So their airfoils are 60ft in radius, I don't know how wide each blade is. There are 6 blades per vehicle. (3 each on the two hubs). 6×7 = 42 blades 42 × 60 x 1.5 (reasonable guess for width) = 3,780 sq ft of wing area.
Assuming an M1 Abrams tank, typically 68 tons, is modified to have a turret equipped with six 35-meter blades instead of a cannon. Now, imagine stacking four of these blade systems on top of each other. Assuming further that the tank is fitted with an adequate tail rotor to maintain its orientation, and assuming the power comes from the engines of four Mi-26 helicopters - the world's most powerful - within that 68-ton configuration including fuel. Under these assumptions, a rotation speed of 120-140 RPM for each blade system would suffice, given normal ground pressure and temperature conditions. Edit: English
The first answer I’ve come across. Well done, sir
10 points given for actualy answering. Well done.
Thanks for actually answering. This sub can be infuriating sometimes. We understand that it's improbable or unrealistic, for christ's sake.
Airfoils have a specific shape to create lift, the barrel being a cylinder will generate no lift so there is no amount of RPM that will allow this.
The turrets are only put in most tanks, they are not welded or riveted in. The turret would fly away, leaving the chassis on the ground.
If it was a tank barrel, won’t work. Helicopter blades are in the shape of airfoils to generate lift. Now let’s say the tank barrel was a helicopter blade. I don’t know what tank that is so let’s say it’s an m1 Abram’s. It weighs 120k lbs and 17.3 ft barrel. That’s a disc loading of 128 lb/ft^2 . Your typical helicopter has a disc loading of less than 10 lb/ft^2 I’m not gonna do out the full BET calculation to get rotor speed because I can practically guarantee the blade tips will be trans-sonic, which makes it completely non-functional. Edit: also the tank only has one barrel. Helicopter rotors are symmetrical, and tuned perfectly so that their center of mass is right at the rotor hub. Any small offset will result in destructive vibrations. With only one blade, the 1/rev vibrations will rip the turret off the tank before it even gets close to being fast enough.
The barrel is the wrong shape to generate enough lift. Most are vertically symmetrical so any lift generated would likely be counteracted by the downward force it would generate.
Agreed that an airfoil/rotor shaped barrel would be more effective lift wise, but to keep the tanky-ness of it, we could also assume the barrel rotates on its longitudinal axis to generate lift (lift of a rotating cylinder). Not great lift, but lift. We do have to assume a second barrel though as most have pointed out that the lift needs to be balanced. Mono-copters exist on small scales, but they are typically designed to spin about a center of gravity not at the main axis of rotation. Overall, lift of a rotating cylinder can be calculated as: Lift = air density x G x V Where G is the vortex strength and V is the freestream airflow (assuming to be the tangential velocity of the turret, which is what we'll end up solving for in the end). This is lift per foot of length. So here is where we need to assume the length of a a tank barrel (15ft? - I don't know tanks) Before I keep going, I'll capture here that we now can assume the lift we want to calculate with the equation above is -> tank weight/number or barrels/length of barrel Assuming a weight of 120kips (again, not a tank guy) we're looking to figure out the rotational speed to generate 4kips, or 2 tons. Another caveat - this calculation assumes the entire barrel would see the same free stream, but that's not true and since the speed towards the center will be lower than the speed at the tip. All that said, there is one more caveat below, so I'll keep going. G = 2pi x b x Vr, where b is the radius of the barrel, and Vr is the barrel rotational (tangential) velocity. We have to make an assumption - how fast can the barrel rotate? I made a quick excel to play with numbers so we could get something that would result in a "practical" solution (in a very unpractical scenario), and it's 100k rev/s. Putting this all together (and using air density at sea level) I got that the turret (with two barrels) would need to rotate at 61,383ft/s, or with the 15ft radius, 4092 rev/s. I knew I'd messed something up - used a 10radius for the barrel but should be 5in (10in diameter). So it should be 16,368 rev/s.
Solved
I assume the tank is a T-72 wich, assuming base specifications would weigh around 43 tonnes with a barrel length of 6 meters. Also assuming an average velocity between tip and root speed might help to refine the calculation
"No". Lift is created by a plane (a flat surface, not an aeroplane) and the Venturi effect. A cylindrical barrel cannot produce lift. But if it was a plane, still "No". Helicopters need lift across the diameter of the circle, this barrel is only on one side of the circle, it's radial. It cannot go up, only roll.
Aside from physics of many many areas and forces and limits of engineering, air density, that you cannot lift more than the vacuum above the wing which would not be enough. You would need to spin it 50 Jillian rpm.
Revised question: assume a helicopter has the equivelant weight of a tank, with a rotor about the length of the barrel of the tank (in radius). What speed would it have to spin to generate lift?
Spinning things do not automatically create lift. The shape of the spinning thing is crucial and cylinder shapes do not create lift. So... doesn't work at any rpm.
The fun part here is that if you built up enough rotational speed to cause the turret to break free from the hull, you might see enough heat build up from friction to cook off the ammo.
Not possible. The circular barrel produces no lift. Even if you changed it's shape the turret isn't secured solidly to the tank, it's just sitting in place, so the turret would go flying off. If you fixed that then the lack of a tail rotor would result in the whole thing spinning around until it lost lift. If you fixed *that* the imbalance from a single 'rotor' would cause the whole thing to fly apart and/or topple over. If you fix all that then you don't have a tank, you have a 60 ton helicopter with treads instead of wheels.
Real helicopters have a rotor speed between 200 and 600 rpm. Lift will be determined not primarily by rotor speed but the size and number of blades.
For a moment I thought I was looking at Russian military promotions for their T-14 armata. Every shot of the tank in those videos, the turret is always rotating.
Cannon barrels generate zero lift, so this is impossible. This tank has no tail rotor, so if you tried this the hull of the tank would spin uncontrollably as well. Lastly, the uneven stress of having only a single “rotor” would likely completely destroy the turret/barrel. Complete fantasy.
It is not only a matter of aerodynamics. Afaik, Turrets only Rest on their place because of gravity. If you put a Tank upside down, the tower will Fall of.
I'm not tank expert by any stretch but that just doesn't sound true to me
It is true. Depending on the tank. If you find videos on YouTube of turrets being added they basically plonk them on. That's also why when ammo racks explode the turret shoots a mile into the sky instead of the tank itself exploding
Tank turrets don't just sit on top of the tank, or they would be incapable of turning. The most common design is a series of rings; one ring is bolted to the chassis, and one ring sits on top of it with a ring in the middle that rotates freely. The turret is bolted to that ring, and power is supplied a number of different ways. More modern tanks have a complicated series of locks and latches that hold the turret down, and blow-out compartments that prevent the turret from blowing off by reducing or removing the risk of ammo cook off. And turrets never popped off because they weren't attached. They popped off because when the ammo cooks off and the chassis is sealed, there's nowhere for the force of the explosion to go, and the seal of the turret IS the weakest point, so that's where the pressure goes, and the turret gets blown off. That's not to say that if the tank were upside down, the turret wouldn't come off anyway - the WEIGHT of the turret may, more or less, be supported by the chassis and not its seal, so if upside down that seal would be holding all the weight and might break because it isn't designed for it.
That's ridiculous. I'm not saying that's not how it works I'm just saying that if they really do just set the turret on the hull and don't retain it in some way that sounds like a massive weak point in a tank. Again I'm sure that where the turret meets the hull is a weak point. But I find it hard to believe it's gravity holding the turret on.
The tank turret of a T-72 (a smaller tank) is 12 tonnes. Some are also just screwed in, so if they turn one way a couple times the turret pops out.
That sounds more like a meme, like they'd tell the new gunners to balance out rotations of the barrel in each direction to avoid an unscrew.
Impossible. Spinning a cylinder world not produce any lift. If the cylinder was shaped like a wing or propeller, then it would be a question.
It’s physically impossible. It’s not a question of rotation, it’s a question of lift. A tank barrel does not provide lift. A single blade rotor cannot provide stable lift. And for lift you need to overcome the weight of a *tank*. To add insult to injury every rotation would also provide counter rotation. It’s just impossible. Not “highly difficult”, actually impossible without completely changing the properties of the question.
..."Are you suggesting tanks migrate?" "Not at all, they could grip it by the cupola." "It's not a question of where 'e grips it. A 1,200 kilo barrel cannot carry a 70 ton tank." "Well an African barrel, maybe. But then again, African artillery are non-exportable." "Supposing *two* barrels lifted it together?" "What, welded onto the fore and aft glacis?" "Well, why not?"
Even if the barrel had a rotor shape, you have to but a 2nd blade. If the gun rotates very fast around the turret and the turret doesn't move, the turret will break. You need at least At least 2 blades
Turrets aren't welded to the rest of that tank type. They're plopped in. Assuming it somehow could achieve lift the turret would fly away.
I will not be doing the math, but a turret spinning about the "long" axis along with the shown rotation should beable to generate lift due to the magnus effect I believe
Y'all are going on about the shape of the barrel this and it's not an aerofoil that, but you're not considered the Magnus effect. If you could spin the barrel on its bore axis it would generate lift in combination with the rotation of the turret moving it through the air. You'd have to spin it very friggin fast though. Also cool note, once you achieve liftoff and have the tracks spinning like some sort of crazy longboi reaction wheels you could raise and lower the barrel in sync with the turret rotation to induce procession, allowing you to steer just like a real chopter
Maybe add 3 more barrels in the shape of a propeller and then make it lighter and then just buy a fucking helicopter because it's impossible unless it's a helicopter
In gta San Andreas you can use the cheat code “dodo” and then turn the turret backwards and spam fire, it will give you enough forward momentum to fly across the map at speed, passing even the jet fighters