vtol_guy

Hi, i'm about to start flying my scratch built twin engined VTOL thing and i just need to know what the main differences are between flying a twin and a single engine. I hear that twin engine are meant to be a bit harder but that the only thing i really know, any help is greatly appreciated

Wayne22

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I can offer this from my brief experience with twins so far:
With both engines running, they fly just like a normal airplane......

I have not had anything but a perfect experience so far...

I have to admit that my knees were knocking and my ears strained to hear both engines at all times. My only contingency at this early stage in my twin career is to stay high, and be ready to throttle back if an engine goes to sleep.

I'm installing my computer radio this spring with separate channels for each throttle so I can experiment with simulated engine failures under very controlled conditions.

William Robison

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VTOC_GUY:
My pessimism has changed you from "Vertical Take-Off/Landing" to "Vertical Take-Off/Crash." Sorry. But I see many problems.

For take-off and landing I would strongly suggest you go to the helicopter area and search for entries about the twin rotor Hirobo.

I think I've seen several different twin rotor coaxial helicopters, but the only twin rotor NOT coaxial, which your VTOL, I assume is, is kitted by Hirobo. And due to the cost and complexity they haven't sold a lot.

I see two immediate problems, the first easy to fix, the second not so easy.

If the engines have the same rotation the plane will pinwheel the minute it comes off, easily fixed by going to counter rotating engines.

The harder problem to solve will be matching thrust, I just don't think you will be able to regulate the engines quickly enough to be stable in the vertical mode. Not just your reaction time, but also the engines wont respond fast enough. In normal flight this problem will go away.

And finally, for now at least, if you dont have enough wing to fly normally the loss of an engine guarantees a crash. Unless you have a cross drive system. And if you do, just use a single engine to drive both rotors. There! I knew we could solve your problems! Haw.

Now that all that's out of the way, let me say I'm awed by your project, and interested in how you do with it. Please keep us informed, and while you're "Sailing off the edge of the explored world," I'm sure that if anyone on RCU can help you, that help will be freely offered.

Lose power to one rotor...
. "MA! I want my motorrrrrrr!!!!!!

Bill.

twinman

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I know that twins make you crazy form personal experience, but a twin engine VTOL!! Got to love it!!
I cannot add to the above ideas beyond one more input. As stated above, controlling two engines will be more than a hand full. If you will go to a post I did concerning hovering with twins, I did do some experiments with the installation of a twin input and output gyro for one of my twins with a single tail, and was reasonably happy with the results. i would also voice that I am not sure the engines will or can react fast enough for this project, but I would stronly suggest discussion with the Helicopter guys about additional gyros for control.
Good Luck,
Send Pictures!!!!

vtol_guy

yeh, obviously a lot of problems which you've spotted just from me telling you which is pretty vigilant. Most of the problems as you were saying only really came to me while designing it and some throughout building but if there were no problems, then where would the fun be?

ok, about the torque problem. I've been told by a guy who already does VTOL's that since my engines are quite close into the fuse then it isn't a really big problem but i will still get torque. My initial plan is using control vanes to counter the torque reaction. I have no certain way of knowing if this will work but the design has been copied from Don Incoll's VTOL. As long as it turns out to be a good flyer and very entertaining then i will get a gear box put in and a contra rotation prop. I don't really wanna be spending more money initially before i even know if it will fly.

Second problem, about stability, i'm planning to have at LEAST 2 gyros hooked up into the system. One to control roll and the other possibly to control pitch OR the other engine. All going well they should be ok with reponse times but again its something i'm going to have to have a look at when/ if it gets off the ground. Also i'm planning to intergrate a co-pilot/ auto-pilot into the system so it should hopefully be stable in some aspect in hovering.

If theres any more problems however small then please point them out, the chances that i've caught virtually all the problems is very small so the faster i get to know them all the better. Before embarking on this project i did do about 3 months of pure research. In that time i've gained a lot of info about it and its all gone into the design of mine. Most people i talk to are very pessimistic about this and most say that i should leave it for a few years. Others arn't so bad with their views like will robinson above, trust me on this, out of all the people who have said bad things about my project, you are by no means anywhere near the worst. Obviously these comments build up and drags me down a little but for the odd few people who are quite optimistic, its makes it all worth while.

In all honesty, i'm expecting more problems than what i can handle to go to light on the 1st real test flight of it. I'm having at least 2 people video record it so i can see it over and over again what goes wrong if anything does happen which it most certainly will.

Hopefully provideing everything goes well it should actually be in test flight phases by this saturday coming up. I'll keep all progress of it going on the Clubhouse forum but i'll post the same thing in this forum too since it is a twin engine craft. Tonight i'm installing the rotation mechanism, wish me luck!

William Robison

My Feedback: (3)

vtol_guy:

First, please note I have changed your name back. With the amount of thought you've obviously put into this thing there is a possibility, granted it's extremely remote, that it might survive its first ascent to the lofty altitude of six inches. Haw.

Twinman George has a good thought about a gyro on the throttles, but I still don't think the engines will respond either accurately enough, or quickly enough.

But when you said you'd gear one, for reversed rotation, don't. Gear both of them, roughly 5:1 ratio, that will get you down to an RPM where you can use heli rotor heads. Set them up with collective pitch only with your gyro controlling roll through variation of the pitch. Or for good maneuverability in a hover use cyclic control as well, couple a second gyro to control airframe pitch through fore and aft cyclic.

You could use a simple gyro for roll, have it in the aileron circuit, but if you left the pitch gyro working in forward flight you might get some nasty resonant vibrations from the uneven blade pitch in the top and bottom of the arc. Best would be the ability to switch them both off, could couple them to the rotor tilt control. Assume you are planning on the "Osprey V-22" basic layout.

But still, without a cross drive system you are almost guaranteed destruction of the airplane. Sooner or later you WILL lose an engine. With full rotor pitch control, and an "Auto rotate" clutch you'd have a lot better chance of survival, but a cross drive is the thing that gives the best chance of avoiding a mad roll into the ground when one engine quits. It would let either engine drive both rotors.

Final note. Again, meaning for this post only. Haw. Why not, if using a cross drive, put the engine or engines inside the fuselage? Granted, you'd have to use a cooling fan, but consider the good points. You'd only need one heavy reduction box, the heavy bits [engine(s) and reduction box] would be closer to the center of gravity giving faster control response, the rotor tilt servo would have a lot less weight to swing, so forth and so on. this would also give you a lot of room in the "Nacelles" for the pitch control servos.

Build your own Osprey plane?
. The engineering, what a pain!

Bill.

vtol_guy

yeh, i think i forgot to mention this but its actually built so i can take off like a normal plane, i have a high U/C so i can have space for the props, thats one of the main things i was considering when building it. If i ever get an engine failure then i've got a lot of things in my favour, 1st being i can land normally, 2nd those control vanes will give me extremely good control on the roll rate if need be so i should be able to hold it off on a little engine throttle for the engine thats still active, if you think about it, its a 5.5lb plane and has a total of 12lb static thrust so i've got plenty of power if need be. So if i ever have a deadstick then i should be able to bring it down safely with some good piloting, hopefully

Also on the cross drive system and the heli setup. At the moment i don't have either money or or room for either of these so unfortunatly i'm gonna have to be out on these for the moment.

I've included a picture of what mine roughly looks like, this picture is Don's first design which i have copied from him,

twinman

My Feedback: (2)

This is absolutely awesome!!!!
Yes, it is welcome in the twins forum and I am sure all of us are pulling for your success.
I noted that you said use a gyro on the "Other engine".When I did my experiments, and the post is "Hovering with a twin", I think in page two now. The gyro I used was for two channel ailerons, except here I used it for the two channels to the throttles that were slaved together. It really did help. The problem I was trying to aid, was that with a conventional single tail plane, there was not enough prop blast for the rudder to work, and using the gyro on the two engines really did help. Completely successful for hands free hover, no. It is possible to keep the gryo on for normal take off. I used the hobbico aero for my experiments.
Please keep us posted.
Good Luck.!!!!!!1

vtol_guy

ok thanks again for the info. I've included below a diagram of my radio gear, i think everything is ok on it apart from the gyro setup which i'll have to revise. I'm on mode 2 so ya know what is what with the reciever channels ect.

I think with the way it is that i shouldnt need to turn off any gyros in plane mode. In plane mode i have the canard and the control vanes controlling pitch. The engine speeds and ailerons controlling roll, with optional roll control from vanes if i need it. Throttle is just both engine speeds again. I have no rudder control which just made things a bit easier for me and its not really neccasary in my opinion anyway.

My rotation mechanism too, is a modified servo. I've wired the pot. so its outside of the servo and replaced the servo motor with a 280. If you can sort of imagine the motor driving a leadscrew (spur gear) which moves an long nut back and forth. This then is attached to the rotation arm to pivot it back and forth. At the other end the pot. will be connected up so it'll be caliberated correctly so i should get the exact amount of movment that i need by operating a rotary switch.

William Robison

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vtol_guy:

What you have there is totally unlike what I had pictured in my mind. But while it looks like a lot of my cautions are negated by the design, I still have the feeling that a hover would be like balancing a needle on the point of a pin.

Your vectored thrust, I think, would allow extremely slow flight, but you'd still need the aerodynamic surfaces for attitude control. And since they did not show up in the picture, at least in a way I could understand, perhaps the "Vanes" you mention would be serving that purpose.

Maybe some pictures so we Yanks can see what you're doing?

Thanks.

Why bother with props?
. Use jets, pull out the stops!

Bill.

vtol_guy

apparantly Don Incoll's one had to be held by the rudder slightly in the hover but i think he experimented several times letting it go and having a little heli flight with it and it usually turned out okay. I think he was always quite cautionary about one of his engines failing so he didnt like to hover around much. The main reasons i built one was to explore something comlicated and try and make a cheap heli basically. I think so far the whole project has cost me about £270 approximatly which is about $460 i think, probaly a little less.

I dont know what prices of heli's are other there but if you add the price of a transmitter to mine then to kit yourself out with it will be about £320 in total, for heli's like that in britain will set you back usually at least £500, sometimes a lot more.

Considering that, and the fact it can transtion, as long as it works then i've made a very cheap basic heli and a plane. Someone who i know has said that if it flies like a heli and can do everything as planned then i should approach some manufacturers about making it into a kit. Don't think it would ever get that far but it'd be pretty good if it did

I've been making a site for my VTOL (called VeeTol, pretty cheezy i know) and that will have a lot of pics then so hoefully in about 2 weeks time i'll have a lot of pics on the net for everyone to have a look at, and a pic of it either flying or in a thousand different bits

For the first test flights i'm going to have it securely bolted to the ground and give it about an inch of movement with fishing line or something. First thing i'm lookin for is to make sure it does have enough thrust to get off the floor! As long as that bit goes okay then i'll gradualy let out an inch at a time until i can get an idea of how unstable she is and find someway of correcting it.

William Robison

My Feedback: (3)

vtol_guy:

Sorry, it's been done. The Vertol company, which is now a part of Boeing, beat you to it. But I doubt anyone would fuss if you used "Vee-Tol" again. Or just VeeTol as you wrote it.

Please keep us posted on your progress, both with the airplane and the web site.

I wish you successful development.

Lost a rotor from his V-22 Osprey,
. Was last seen flying a horizontal "3."

Bill.