Back-spinning conveyors instead of wings?

[WCOLtd]

Not yet, businesses are closed due to all the snow, and the holiday, so I'll try to find out tomorrow and Wednesday how much it will cost. Bearings are not an absolute necessity, I could have the belt just on a low friction surface and the belt could be bade out of a durable substance, it would be less preferential, but it should work - at least temporarily.

Also the problem of needing a high speed bearing is unique to the prototypes size. Meaning, this won't likely be a problem for larger aircraft - the bigger I scale up the prototype the easier it will be for me to overcome the problem, whereas the leading edge of this remote controlled aircraft is only 5/16 (less than a third of an inch in diameter), with a 3 inch diameter nose circle or more and only have tangential speed requirements of two to three times greater) - so for a larger bearing on a real aircraft the bearing RPM requirements could easily be below 8,000 rpm.

The thicker the leading edge of wing, the lower the rpm requirements will be for the leading edge roller.

Originally I had a really dumb idea of trying to maximize lift without worrying about whether the wing was aerodynamic or not, now I am trying to focus on reducing drag over the top of the airfoil. (It's probably still a dumb idea though because I am not entirely sure I know what I'm doing)

I have also settled on a design to have the entire upper leading surface of the wing be a conveyor belt - this is because of concerns over boundary layer conditions between the moving conveyor and the stationary wing. The surface of the wing will have lower viscosity than the stationary part of the wing, so air passing from the conveyor to the stationary wing will likely create a bunch of drag.

Again, I don't see how this design can lead to making an aircraft any less aerodynamic. All I am doing putting a conveyor belt over top an airfoil thereby reducing the velocity between the surface of the upper part of the wing and the surrounding air. It may be that it produces little to no benefit over conventional designs - I have no idea.

Simple as it sounds, as far as I know (which isn't very much) this hasn't been tried before, so I am going to try it! If you have already tried this or know someone who does, then let me know how it worked out - you'll save me a lot of time and money. Otherwise it really doesn't matter to me what your opinion is.

It's easy to be skeptical and tell me that it won't work or that it's dumb, but if you don't provide me with a reason based on the laws of nature and back it up with experiment, I don't see why I should listen.

 

[DaveC426913]

Again, I don't see how this design can lead to making an aircraft any less aerodynamic.

Well in an ideal scenario, yes. But you may have problems with deformation, fluttering, etc. Additonally, you can't ignore the added weight your design will inevitably have. Not poo-pooing the idea, just pointing out places where your design's performance will be mitigated by unavoidable side-effects.


Something else you might want to consider: a control. You'll need a plane of identical characteristics to your design sans your modifications. Results with this plane will serve as the baseline to determine how much improvement your design affords.

 

[WCOLtd]

Back Spinning Conveyor belts over top of wings

I just figured out another problem with having the entire upper surface as a conveyor belt. The trailing edge is normally a pointed tip, rather than a circle, at least part of the reason why that is is to reduce drag, the fatter the trailing edge is, the more drag I'll have to worry about. Having a roller at the end of the airfoil then, would likely increase drag. One unlikely solution is to get a 1/16 inch diameter pipe with enough structural integrity to not bend, and to have a bearing with speeds in excess of 120,000 rpm with an inner diameter or outer diameter of 1/16 of an inch. More than likely I would just have to try to have a fatter roller further up from the trailing edge and just have to worry about the change in boundary layer conditions between back of the conveyor (moving wing section) and the forward part of trailing edge of the airfoil (unmoving wing section).

Getting a bearing and roller to meet the requirements are highly unlikely - and I will probably have to concern myself with either having to determine the greater of two evils - a fatter trailing edge or a change in boundary conditions between the conveyor and trailing edge wing sections.

I am starting to design the structure to hold the series of rollers in the wing, the bottom of the conveyor will not be exposed, I will start with a three roller system, with one roller along the leading edge, a second roller slightly above and behind that, and the third roller - the big roller will be recessed into the airfoil and will be powered by a propeller engine sticking out from the side of the fuselage. (I still have to determine whether or not the direction of rotation can be reversed by reversing the direction of the current)

- the remainder of the upper surface of the airfoil will be a stationary wing section. Drag caused by the change in boundary layer conditions is my main concern with this prototype.

 

[WCOLtd]

Limitations for design will be set by the maximum bearing speeds physical limitations of the belt and geometrical limitations inherent in a conveyor belt design.

I have already established that for 3/16 inch inner diameter ball bearings the maximum theoretical rpm is roughly 55,000 rpm, well above the 45,000 that I need.

This is based on the equation NDM / 1/2(bore+outer diameter)
found here:
http://www.phymet.com/calc.htm

The cost isn't very high either for these types of bearings - about $5 per bearing, and that should get me to a theoretical belt speed of about 50mph (I can more than double that speed if I use the outer surface of the bearing as the inner contact surface with the belt)

That means with a 3/8 of an inch diameter trailing edge, I can get the belt up to speeds of 100 mph! Significantly more if I increase the radius of the leading edge. infact I can increase the speed further by feeding one bearing into another, i don't see why I would be unable to exceed 130 mph maximum belt speed that way.

Now that that problem seems to be resolved, I will try and focus on the propeller motor see if the propeller can be reversed and whether or not it can get the larger diameter pipe to speeds fast enough to get the belt to speeds of 40-60 mph. (I don't anticipate this to be a problem). Although mounting the rotor onto the pipe will be a big challenge.

I will meet with the Hobby shop owner tomorrow and see what he says.

 

[Brian_C]

The Magnus effect can barely generate enough force to steer a sailboat, much less lift a plane off the ground. The torque required to spin the conveyor belt will generate a pitching moment, which would have to be corrected. In short, it's a horrible idea.

 

[Cyrus]

The torque required to spin the conveyor belt will generate a pitching moment, which would have to be corrected.

Hah, you're right. The question is how much.

 

[WCOLtd]

Pitching moment? Of all the trivial concerns that takes the cake.

The belt is made out of metallic wrapping paper for goodness sakes! Even at 120 mph tangential speed how much of a moment could that possibly create?

Pitch would only be effected while the belt is accelerated or decelerated! Pitch is the only axis which is unaffected by rotation of the belt and pipe. My concerns are the gyroscopic forces, yaw and roll and I don't anticipate that to be such a problem - but I could be wrong - I haven't done the calculations.

The wrapping paper and roller is super light, I don't see why a 1 inch pipe rotating at 15,000 rpm will generate that much of a pitching moment, especially when you consider that on a real plane, it will be accelerated as the relative windspeed increases. There is no way in the world that the pitching moment would be anything in comparison to the anti pitching resisting forces of the wing and tail wing.

Also magnus sail boats don't steer through the magnus effect, they steer through the rudder like all boats. And the boats do move through the water, even when a small sailboat is filled with 3 people! also the tangential speeds on those sailboats are 25 mph maximum with the wind, my belt will have relative speeds anywhere from 50 mph - 120 mph! The amount of force needed to lift a remote control airplane vs the amount of force to move a sailboat with 3 people is dramatically less.

On top of that, the belt is in the shape similar to a NACA 4 series airfoil, the geometry of the belt itself will generate part of the lift, I am not going for creating lift via the magnus effect. Unlike a back-spinning ball I am mainly focused on reducing the viscous forces over the top of the wing - maybe it won't produce all that much lift, I don't know, but as far as I know, my design has never been tried.

The design is not perfect, I will have a bunch of challenges making the thing work, but I am pretty sure it's going to fly.

 

[WCOLtd]

The biggest problem I could think of with this design was how I was going to center the rotor to the roller pipe - I figured that in order to prevent a wobbling I would need to somehow perfectly bind the rotor into the exact center of the roller pipe. However I think I have come up with a solution to that problem of rotational stability. It will be achieved by making a special mold for the 1 inch outer diameter bearing. The propeller engine will be behind a wall, with a hole drilled in it. The rotor poll will stick out of the fusalage or will be partially encased in the pipe itself, and the bearing will fit around the rotor, it will have a mold on it to attach the inside bore of the bearing to fusalage, and the outer bearing will be attached to the inside of the pipe - along with the rotor. Looking into the rotor, the mold will have to look something like one of those depictions of space-time curvature around a black whole.

The issue will be whether or not I will be able to get a bearing to fit inside the pipe and 2) whether or not I will be able to strongly bond the rotor to the wing pipe.
A third problem will be the whether or not the prop engine will be able to handle the increased torque of the pipe.

 

[MotoH]

It seems to me that the lift to weight ratio would be very low, as all of these equipment to make the belt spin will have more effect on the aircraft than the lift generated.

or is this just proof of concept?

 

[WCOLtd]

It seems to me that the lift to weight ratio would be very low, as all of these equipment to make the belt spin will have more effect on the aircraft than the lift generated.

or is this just proof of concept?

Yes this is a concept design. My goal is to get a plane to lift off the ground.

After I have proven the concept I will focus on trying to get the weight of the conveyor system reduced as much as possible.

The key will be to find a lightweight and rigid roller. I am still looking around. The pipes on sale at a local RC hobby shop still seem like the best solution - they are designed to strengthen the leading edge of styrofoam airfoils so they don't dent when the plane crashes - I was delighted to find that the pipes are lighter and more rigid than solid aluminum rods of the same diameter. They are not ideal, but they are much better.

If the design is successful anyway, scaling up to reduce the weight will not be terribly difficult - carbon fiber rollers ceramic bearings, and some yet-to-be-discovered-by-me suitable belt likely already inside a DuPont catalog will all add up to reduced weight. Of course I'll cross that bridge if and when I get there.

 

[Cyrus]

Pitching moment? Of all the trivial concerns that takes the cake.

The belt is made out of metallic wrapping paper for goodness sakes! Even at 120 mph tangential speed how much of a moment could that possibly create?

Pitch would only be effected while the belt is accelerated or decelerated! Pitch is the only axis which is unaffected by rotation of the belt and pipe. My concerns are the gyroscopic forces, yaw and roll and I don't anticipate that to be such a problem - but I could be wrong - I haven't done the calculations.

The wrapping paper and roller is super light, I don't see why a 1 inch pipe rotating at 15,000 rpm will generate that much of a pitching moment, especially when you consider that on a real plane, it will be accelerated as the relative windspeed increases. There is no way in the world that the pitching moment would be anything in comparison to the anti pitching resisting forces of the wing and tail wing.

Also magnus sail boats don't steer through the magnus effect, they steer through the rudder like all boats. And the boats do move through the water, even when a small sailboat is filled with 3 people! also the tangential speeds on those sailboats are 25 mph maximum with the wind, my belt will have relative speeds anywhere from 50 mph - 120 mph! The amount of force needed to lift a remote control airplane vs the amount of force to move a sailboat with 3 people is dramatically less.

On top of that, the belt is in the shape similar to a NACA 4 series airfoil, the geometry of the belt itself will generate part of the lift, I am not going for creating lift via the magnus effect. Unlike a back-spinning ball I am mainly focused on reducing the viscous forces over the top of the wing - maybe it won't produce all that much lift, I don't know, but as far as I know, my design has never been tried.

The design is not perfect, I will have a bunch of challenges making the thing work, but I am pretty sure it's going to fly.

There will always be a pitching moment, not when it is "only accelerated or decelerated." Please be more careful when you make technical statements.

Second, a wing does not produce 'anti pitching moment'.

Your posts would benefit greatly from a diagram, as opposed to long paragraphs.

If the design is successful anyway, scaling up to reduce the weight will not be terribly difficult - carbon fiber rollers ceramic bearings, and some yet-to-be-discovered-by-me suitable belt likely already inside a DuPont catalog will all add up to reduced weight. Of course I'll cross that bridge if and when I get there.

... Let's not put the cart before the horse.

 

[WCOLtd]

I wrote it in the same erroneous way so that he could better understand it. I think you understand what I mean though, it won't have any effect on the aircraft's ability to pitch up and down. You said it yourself better than I did. Except I disagree when you inferred that there might be some legitimacy in the concern, it's really trivial.

What I meant by "anti pitching moment" was really "anti pitching torque", and due to the length of the distance between the rear wing and the surface area of the rear wing, the resistance to pitching motion is far greater than any motion induced by torque from getting the wrapping paper belt and the 1 inch diameter roller up to speed. Not to mention the fact that the belt will be accelerated to top speed while on the ground. I don't see what would have to be corrected or compensated for relating to the pitching axis of the plane.

You're right I suppose the issue is that I need to post my design up for people to be able to correctly critique it - he might imagine just a giant roller in the front absent a conveyor in which case he would be more correct in worrying about the pitching torque, and the tendency for the plane to want to tilt up and down. I suppose he just didn't read the entire thread.

I wish I had a scanner to post my designs. It would simply take way too long if I used a computer image software like photo shop.

...let's not put the cart before the horse

that's analogous to saying "I'll cross that bridge if and when I get there" which basically means "lets not get ahead of ourselves - let's worry about that if we ever will need to."

 

[Brian_C]

Yes, because a conveyor belt will keep spinning forever once its set into motion. No torque required.

 

[Cyrus]

I wrote it in the same erroneous way so that he could better understand it. I think you understand what I mean though, it won't have any effect on the aircraft's ability to pitch up and down. You said it yourself better than I did. Except I disagree when you inferred that there might be some legitimacy in the concern, it's really trivial.

You can't wish away problems in engineering. If its trivial, then show that its is. You are incorrect if you do not think it will cause gyroscopic coupling moments. Now, the magnitude of those couplings (and how they scale from your model scale to a prototype size) are an entirely different story. Do you really think spinning belts on a full size aircraft would also produce "trivial" moments?

As for the pitching moment on the belt - yes, there will be one. The rollers will have a reaction torque on the airframe - in pitch - all the time.

 

[WCOLtd]

To me, this just seems so absurd, the main propeller engine on the front will be producing far more torque than the rotors along the belt. According to this way of thinking I should be far more concerned with the plane doing perpetual barrel rolls through the air than I should be concerned with pitching.

 

[Cyrus]

To me, this just seems so absurd, the main propeller engine on the front will be producing far more torque than the rotors along the belt. According to this way of thinking I should be far more concerned with the plane doing perpetual barrel rolls through the air than I should be concerned with pitching.

The angular momentum of the propeller lies along the longitudinal axis of the aircraft, the rollers are on the lateral axis. Why do you think these two are directly comparable?

My point is that you need to stop "this way of thinking", and dig into a textbook on flight dynamics because a lot of what one may think and what really happens is counter-intuitive.

Also, a course correction: what is a "propeller engine"? There is a propeller and an engine, not a propeller engine.

 

[RonL]

The biggest problem I could think of with this design was how I was going to center the rotor to the roller pipe - I figured that in order to prevent a wobbling I would need to somehow perfectly bind the rotor into the exact center of the roller pipe. However I think I have come up with a solution to that problem of rotational stability. It will be achieved by making a special mold for the 1 inch outer diameter bearing. The propeller engine will be behind a wall, with a hole drilled in it. The rotor poll will stick out of the fusalage or will be partially encased in the pipe itself, and the bearing will fit around the rotor, it will have a mold on it to attach the inside bore of the bearing to fusalage, and the outer bearing will be attached to the inside of the pipe - along with the rotor. Looking into the rotor, the mold will have to look something like one of those depictions of space-time curvature around a black whole.

The issue will be whether or not I will be able to get a bearing to fit inside the pipe and 2) whether or not I will be able to strongly bond the rotor to the wing pipe.
A third problem will be the whether or not the prop engine will be able to handle the increased torque of the pipe.

Pretending like your idea might work, you can picture your belt sections like 'very wide fan belts' or conveyor belting. Your wing surface might consist of 80-90 % moving belts (3 or 4 feet wide each) and the remainder would be non moving support sections.

There are numbers of options to connect the tubes,(some type of flex connector) finding the least weight method will be the hard part.

Offsetting the pipe torque should not be a problem, sense we are in such a fictional process, why not have an offsetting spin of electric motor/generator power system spread as far out into each wing as needed?

 

[DaveC426913]

Devil's Advocate:

My point is that you need to stop "this way of thinking", and dig into a textbook on flight dynamics because a lot of what one may think and what really happens is counter-intuitive.

Well, there's a lot to be said for his putting his money where his mouth is...

What is wrong with him building his prototype? So he learns some things along the way. Far better that he follow it through than that we discourage him and he drops it.

Also, a course correction: what is a "propeller engine"? There is a propeller and an engine, not a propeller engine.

He is resetting context. Simply saying "engine" in the context of a discussion about wings might be confusing. Nitpicky at best, cheap shot at worst.

 

[Cyrus]

Devil's Advocate:

Well, there's a lot to be said for his putting his money where his mouth is...

What is wrong with him building his prototype? So he learns some things along the way. Far better that he follow it through than that we discourage him and he drops it.

Nothing - and I never said there was. What I did say; however, was not to make engineering statements with nothing to back it.

He is resetting context. Simply saying "engine" in the context of a discussion about wings might be confusing. Nitpicky at best, cheap shot at worst.

I am simply correcting him Dave, relax.

Would you prefer that he goes on using incorrect terminology?...

 

[DaveC426913]

I am simply correcting him Dave, relax.

Would you prefer that he goes on using incorrect terminology?...

I don't agree that he is using incorrect terminology.

If you can have a jet engine and a steam engine, you can have a prop engine.

 

[Cyrus]

I don't agree that he is using incorrect terminology.

If you can have a jet engine and a steam engine, you can have a prop engine.

Find me an aerospace book that uses that term and I will concede to you.

 

[DaveC426913]

Find me an aerospace book that uses that term and I will concede to you.

Appeal to authority. That does not make him wrong. Or me.

Don't tempt me to run around going "Cyrus (you know, the airplane expert?) He's never heard of a prop engine!"

 

[Cyrus]

Good luck with that terminology: let me know how it works out for you.

 

[WCOLtd]

The angular momentum of the propeller lies along the longitudinal axis of the aircraft, the rollers are on the lateral axis. Why do you think these two are directly comparable?

I thought that critique might come up, the reason I think It's not a problem is because;

1) the fact that the engine powering the belt is far less powerful than the main engine - I don't know exactly how much less because they don't keep track of the torque of the RC propeller rotors as far as I know.

2) Using mathematics it is indeed possible to relate the two axis to one another. Using just intuition - the forces normal to the longitudinal axis of the aircraft is equal to 4pi times the integral of the resistance across the surface area over the upper surface from the fusalage to the tip of the wing. (To calculate the resistance forces I assume I will need a more complete understanding of fluid dynamics)

My point is that you need to stop "this way of thinking", and dig into a textbook on flight dynamics because a lot of what one may think and what really happens is counter-intuitive.

Ok. you know more than I do - I'll concede that - so name a book and I'll buy it and I'll read it.

Also, a course correction: what is a "propeller engine"? There is a propeller and an engine, not a propeller engine.

A propeller engine is an engine that powers a propeller.

 

[Cyrus]

I thought that critique might come up, the reason I think It's not a problem is because;

1) the fact that the engine powering the belt is far less powerful than the main engine - I don't know exactly how much less because they don't keep track of the torque of the RC propeller rotors as far as I know.

Engine\belt power has absolutely nothing to do with angular momentum. What matters is the inertia and RPM of the belt. What is the formula for angular momentum?

2) Using mathematics it is indeed possible to relate the two axis to one another. Using just intuition - the forces normal to the longitudinal axis of the aircraft is equal to 4pi times the integral of the resistance across the surface area over the upper surface from the fusalage to the tip of the wing. (To calculate the resistance forces I assume I will need a more complete understanding of fluid dynamics)

This is not correct. I don't know where you got four pi times the integral of the resistance across the surface from.

Ok. you know more than I do - I'll concede that - so name a book and I'll buy it and I'll read it.

I don't want to waste your money on a wild goose chase, so I would look over these slides instead for now:

http://www.princeton.edu/~stengel/MAE331Lectures.html

A propeller engine is an engine that powers a propeller.

No, an engine powers a propeller. The engine can be reciprocating or a turbine. There is no such thing as a 'propeller engine'. (Or it can be an electric motor)