Noah-Moore

I am in the process of scratch-building a V-22 Osprey. If your not familiar with the Osprey it is a so-called "tiltrotor" aircraft in which the turboprop engines are in a vertical postion for takeoff and landing, but then tilt forward in flight to become a normal aircraft. What kind of motors/gearbox's/batteries combination would be suitable for a model like this? I'm thinking of a model with a wingspan of about 4 feet and wieght of not more than 5 pounds. Keep in mind that the motors must be powerful enough to swing a 3-bladed 16-8 or 16-10 Master airscrew propeller and do it fast enough to lift the model of the ground. I know the props are big, but they're in scale with the real plane. PLEASE any advice welcome!!

Thanks!

driegel

Nothing is impossible, but there are some difficulties to overcome. Suitable power plants are the first. Static thrust would have to exceed aircraft weight by a considerable margin for a vertical takeoff. Next on the list is the rotation mechanism for the engines. How much will they weigh? Another concern is control during hover. Even if the CG is centered on the vertical thrust lines of the engines, how would you provide roll control, use throttle differential? Yaw around the vertical axis is another concern. Eddie Weeks had some posts on here regarding his Rig, a VTOL turbine plane. Quite a while back I had seen some site with a guy building an Osprey, can't recall who it was. Lot of engineering problems to solve, but it would make for a VERY impressive model.

Don

gubbs3

My Feedback: (1)

I'm thinking electric would be the way to go. With engines, it would be hard to swing a large prop and hard to get them at exactly the same speed. With some large electric motors and 6:1 gearboxs, you would be able to swing some pretty heavy wood.

Noah-Moore

Any idea's on what motors?

Cactus.

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i was just about to say go brushless, you dont want a dead engine on this, i saw a good, and fairly cheap motor on a fun fly the other week, i guess it should now be at www.westonuk.co.uk
it swung a 12x3.75 prop nice
my other idea would be a central motor and drive system, but you want to be low in pitch, its a hoverer, not a speed ship.
i did think about this as an autogyro a while back.
roll control, motor speed
yaw, motor pitch,
pitch, combined motor pitch. tho moves forwards and backwards more than pitch.

that brushless motor i saw was on a standard Cougar meant for a 36, and it pulled vert, hung on 1/2 throttle, that was using 8 3000 Mah cells.
pic of motor at rcflyers site ( pilots6 )

Noah-Moore

Here is a quick drawing on what i'm thinking. PLEASE, any comments welcome!

Cactus.

My Feedback: (1)

Personaly i'd mount two mothers of servos in the wing tips, then mount the motor nacells to the output horns.
this would give you indipendant control of the blade angle to give all the yaw control you'll ever need, + forwards and backwards movement, sideways ( if you wanted to be flash ) would come from diffrential throttle settings.
from what i can tell of your system, not only is it complicated, but it dosnt give you the same degree of control.
you'll be wanting over 100 degrees of pitch movement.
*POSSIBLE* other idea for better pitch control in hover, have a small 400 motor within the fus and a fan/tube system, blow air from small holes at the nose and tail, motor turns one way, it blows nose, pitch up, turns other way, blows at tail, pitch down

MinnFlyer

My Feedback: (4)

Noah...

I used to be a machinist for the government and considered this project for many years. I had lots of high-tech machinery to make any parts I needed, but still I scrapped the project due to the many problems involved. Some of my conclusions were:

Use a single engine mounted in the fuse: this way there's no chance of a one sided flame-out.
Next: use two, helicopter rotors. let's face it, you have to be able to hover this thing as the rotors are too big for the plane to land in a rotor forward configuration. And if you're going to hover, there's no way to balance your plane without a rotor head. If you don't believe it, consider this: You have two propellers that lift the aircraft off the ground to a height of , let's say 3 ft. And by some miraculous luck, it is balanced perfectly fore and aft so it doesn't tilt. Now, you want to transition to forward flight, so you start to rotate the nacelles forward, but there's a problem... remember those two spinning propellers? There's another scientific term for them... GYROs. That's right! Those propellers are acting like two gigantic gyros, and they don't WANT to be rotated! But! Remember that miraculous balance? That means there's no problem tilting the fuselage, so... when you try to rotate the engines forward, what will actually happen is that you will tilt the fuselage nose-up.

Let's go back to that perfect hover, now a little breeze blows and you start being blown backwards, what do you do? Rotate the nacelles forward? As you now know, that will only tilt the nose up exposing more of the fuselage to the wind, and before you can say "There goes all my money" the plane is in little pieces on the runway.

No, my friend, under NO circumstances will two propellers work. You MUST have two rotor heads.

Next: If you don't already have one, be prepared to shell out big bucks for a very sophisticated radio. Think about it... In hover mode, the collective (changing pitch on the rotors for more [or less] lift) would be controlled by the throttle (to go higher) and mixed with the aileron (for lateral balance) and the elevator servos will actuate the forward and aft rotor control. But once you transition to forward flight, the actual ailerons on the wing must now be controlled by your aileron stick, and your elevator stick must now control the elevators and not the rotors.

As I said before, this was a pet project of mine for many years, and the more I thought about it, the more bugs I encountered.

I'm not saying that modeling one of these babies is impossible, but don't forget... The military scratched this project because there were too many problems with making this thing fly. Don't think you're going to stick two engines on an airplane wing and show them up!

Cadet

The Canadian military had a very successful tilt rotor/wing aircraft that was nearly operational. I believe it was the Canadair CL-84 Dynavert. Anyway the whole wing tilted which made it much less mechanically complicated, and the ailerons were still effective in hover. That might be a better scale subject to consider, that and very few people will know what it is.
Cheers,
Grant

P.S. Found a few good sites using google
http://www.aviation.nmstc.ca/Eng/Collection/sd024e.htm
http://avia.russian.ee/vertigo/canadair_dynavert-r.html

Cactus.

My Feedback: (1)

there was a design here in the UK, a high wing plane with two engines on either side of the fuz, the rotated upwards to slow the plane, not to hover it. it worked very well. if i ever find the article ( dont hold your breath ) i'll scan and post.
i think for radio you'll want that Multiplex set with its millions of mixes and i think my ducted fan idea in the fuz linked to a pitch gyro should work nice to combat the pitching caused by the rotors.

MinnFlyer

My Feedback: (4)

Something else you would have to consider is what you're going to rotate the nacelles with. A servo won't do, as the nacelles need to be rotated VERY slowly. As you can see, I could go on and on. There are MANY MANY complicated things that must be worked out on a project like this.

Cactus.

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Servos can be slowed to any speed you want, i thought of that before i posted it.
if your real lucky the tranny might be able to do this for the transission only, leaving responce for yaw and directional movement fast and you with more control. kinda like having super quick servos on the tail controls for hovering funflys.
personal thought...... i would rather have the nacells able to move quick, as i didnt spend millions using a super PC to work all this out. and if i get in trouble i want instant go, not watch it crash and the nacells still slowely moving back up or down.
you can worry about scale looks after you got it working.
i would also build a VERY simple prototype just to get all the systems working before commiting to a scale plane.
to do the hovering stuff, i wouldnt even bother with wings

MinnFlyer

My Feedback: (4)

You guys are still missing the boat here. If you rotate the nacelles quickly, all you are going to do is rotate the fuselage up-wards. What do you think is going to hold the fuselage in a lateral position?

This machine is essentially a helicopter. To move a helicopter forward do they "tilt" the rotor head? NO! That's why it is a "rotor head" and not a "giant propeller".

To transition from hover to horizontal flight, you give forward pressure on the stick. The rotor blades now produce more lift in the rear, which tilts the entire aircraft forward. Now, the aircraft starts to gain speed which means (horizontal) airflow over the control surfaces. BUT, remember the fact that the aircraft is tilted forward? That means that it is facing slightly nose-down. In a helicopter, this is not much of a problem, but on an Osprey, which has wings and a tail surface, the plane wants to fly to-wards the ground. So, you need to feed in some up elevator, but guess what? Until transition is complete, the elevator stick is also controlling the rotor head! And up elevator is the same as giving back pressure on the rotor head which is going to stop your forward progress.

Are you starting to see how difficult this is?

You would need a VERY slow rotation of the nacelles, so that you can flip a switch and wiggle your sticks like crazy and pray while you try to balance the thing as the nacells are rotating to the forward position. There's no way you are going to control it, AND manually rotate the nacelles at the same time.

I strongly agree with PhillyBaby when he says, " I would also build a VERY simple prototype just to get all the systems working before committing to a scale plane. To do the hovering stuff, i wouldn't even bother with wings"

But put the wings on it... it adds a whole new dimension to the problem.

Cactus.

My Feedback: (1)

i think the thing that stoped it in my own mind pitching was my little ducted fan and nose/tail ports. this is what controls the harrier.
i know its not going to work if you move the nacells though the whole movement in half a second, its going to fall out the sky, they need to match the flight conditions. what you want is total contro during the hovering stage.
rasies a point, how does the real one do it? can it even hang? i not sure it can. which would solve the problems of airflow over surfaces during slow flight. the Osprey i have on MSflight sim handles like a wet brick at slow speed.
your model will be doing the same.
getting back to harriers, the flying bedspread wasnt pretty, but it proved the point and lead the way.
Im not arguing with anyone, if you want a million dumb ideas and maybe a good one, ask me lol

Johng

My Feedback: (4)

Step one is research.

In the model world - there are a few models of tandem rotor helis with a single engine, belt drives to each rotor, couter-rotating ( a requirement for this app, I think). You should look at these setups and then think about how to adapt it to the tilt-rotor world.

Rotor heads are indeed a requirement, if for no other reason - roll control. There is no way to change the speed of a prop fast enough to effectively control roll. Response would be sluggish because of inertia as the system tries to speed up and slow down on command. Directly controling pitch of the blades can happen fast enough to control roll though.

THe rotor heads might be expensive, but nowhere near as expensive as trying to develop other more complicated schemes that would be more expensive when all is said and done.

As for actually tilting the nacelles, a jackscrew drive is the way to do it. It allows a standard servo to give plenty of authority, at a naturally slow speed. Also, it only fedds a small amount of reaction force back to the servo connection when the nacelles aren't moving.

Eddie weeks built his turbine hovering "rig" with an engine that tilts. He uses a servo-driven jackscrew to control it. Check it out:

Noah-Moore

WOW!!! :stupid: I didn't realize this was such a hottly-contested debate. I'm begining to see where some the detractors are coming from. I know this is a extemely difficult subject to model, but you have to admit it, if it worked it would sure be cool! I would of course build a prototype first to see what i'm up against. I think the idea came across that i was building an absolute scale model of the osprey that could do anything the real one can. That is not what i designed this project to be. My intention is to make a model that can take off vertically, then transition into forward flight almost instantly. Total time in actual hover would be under 5 seconds. I just want the ability to take-off and land vertically, not spend large amounts of time in an actual hover. Would i still need all of those complicated systems for something like this? Was Cadet on to something when he talked about he Dynavert? I'm intrigued by the idea that the whole wing moves in one piece and that the control surfaces stay active because of the prop wash.

Cadet

If you look at the drawings for the Dynavert you will see that it had a vertically mounted tail rotor to control the pitch, thereby removing the need for rotor-heads on the wings. The real aircraft was so stable that it didn't really need it's autostabalizing system and was indeed flown without it.
Cheers,
Grant

driegel

No matter how short of a time you plan on being in hovering flight, you will want and need full control of the model. In the 5 seconds you are talking about, the model is going to have to accelerate from zero forward velocity to sufficient airspeed. During that fast acceleration you will need to be in complete control. It isn't that there is a debate over it, it would be a VERY diffucult project for anyone to pull off. Nothing is impossible, but it would be a lot of work and problem-solving. You said you didn't want it to perform everything that the real one does, but by necessity has to. To take off vertically you will need rotors. For ground clearance on landing, you will have to land from a hover. So you really do need the model to perfom everything that the real Osprey does.

Johng

My Feedback: (4)

OK, when you said V-22, that's what everyone started talking about. If you just want to do a hovering prop-driven aircraft, it can be made alot simpler. In fact, the tilt-wing design, where the wing rotates up on a hinge, would be alot simpler for full scale as well. THe tilt-rotor concept was committed-to in the 80's and hasn't changed even though engineering studies have shown the tilt-wing to be superior.

Anyway, if you don't need to be scale, you can get away with a regular prop(s). You can hang control vanes in the propwash to deflect the air. Just as the dynavert uses the ailerons to deflect air, a couple perpendicular surfaces could also be used for all-axis control.


Do you need to have a twin, or can it be driven by a single prop? THere was an article printed a few years ago in MAN about the Vertigo - a plane with a single DF unit on a swivel that could hover or fly like a plane. It used the control vanes. That would be worth looking into.

Phil Cole

Here's one person who has a flying tilt-rotor. No swashplates in sight!

http://www.rcwizard.com/incoll/

Noah-Moore

What i meant was i am in fact building a V-22 Osprey-just not absolutely to scale.

v22

My Feedback: (8)

Noah
Check out what I have done with the V-22 :

Http://geocities.com/v22chap/vtol.html

This is a heavy twin nitro engine powered full scale operating R/C tilt rotor.To date I have not be able to do a successful transition,but I am still trying.I have used single engine/gearboxes and the recent twin engine and really like the twin set best.The working weight of the two engines on the wing tips help the roll axis in windy conditions,although the newer piezo gyros might take care of that as my single version was back in the days that we didn't have good gyro's at all.

I also have other guys projects on my webpage and some are trying electric v-22's and one is using airplane props.

The first big problem to R/C vtol is the power to weight ratio .All the tilt mechanics and bearings and such add up quick.
The next problem area is pitch axis control.With the long fuse of an airplane you need either cyclic helicopter swash plate control or a horizontal tail rotor like the candiair tilt wing, or a short fuse and a well balanced vtol like Tom Hunts vertigo.Then this leaves the problem of what happens to the pitch in transition.Some have hit on that fact.When you transition the fuse wants to rotate around the two large gyroscopic rotor disc that want to stay in the same plane they already are.That is the reason the real v-22 has an inverted airfoil elevator that helps to push the tail up thru the transition .

What little experimenting that I have done with control vanes and flaps yielded not good enough control to hover for a long time.You might be able to jump into the air and transition and do the same for a landing but to hover for more than 6 sec. wouldn't work.
I hope this helps and good luck on your project.

Homebrewer

My Feedback: (8)

Something like this has been successfully flown by Don Incoll

http://www.rcwizard.com/incoll/

Check out the VTOL link on the above page.

v22

My Feedback: (8)

Yes I know and have talked with Don.I have built and flown his XV-1 Salamon tailsetter.
The one that you are referring to is his Grumman design 698.He used two airplane engines and props with vane controls.It doesn't hover long and I don't think that he made a full vtol landing before he moved on to other things.As I remember he had trouble in the transition area with bad pitch up too.

I have his birds on my webpage with links to his page also.

Cactus.

My Feedback: (1)

far to complicated, fun flys hover, no swashplates, large heli set ups weight ect ect.
either go brushless and 12.5 x3.75 or 2 36's APC 10x4 ( engine cuts will kill you )
pitch control, i will say this once more, just use nose and tail jets, it works for harriers.
go back to the drawing board and design a fun fly, that has twin engines that can rotate on the wing tips. keep it light.
if you want to go the heli route do like they do to move, tilt the rotor forwards ( swashplate thingymejig) not the engine, then when you got some speed you can rotate the nacells forwards and have pitch control from the tail. whens the last time you saw a heli with a pitch stablising rotor at the rear?