Need help on an odd experiment
 

A friend of mine and I have identical airplanes. I came up with the idea of attaching a string to the left wingtip of both planes so it might be possible to take-off and land in a very small area. Both planes are small electrics with pusher props, and we did this with no one else around, so there wasn't much of a safety issue. Well, the experiment worked - kinda. The planes took off and stayed in a nice circular formation. The problem was that they then just drifted with the wind. Rudder inputs did nothing but slow down the plane (due to drag, I guess) and caused the other to fly around it.
My question is, is there any way to control the planes once they are in the air? Altitude is completely controllable, but it seems that wind will decide where they will go.

RE: Need help on an odd experiment
 

Sounds like you have a helicopter rotor disc without the helicopter. You might try tilting the disk into the wind by haveing one airplane climb onthe down wind side and the other dive (SLIGHTLY!!!) on the up wind side.

Interesting experiment!

RE: Need help on an odd experiment
 

So this is like two tethered models so they fly attached like a barbell in the air?

Of course the rudder won't do anything. For the rudder to make a model turn it makes the model yaw to one side and then the air hitting the dihedral of the wing makes it bank into the turn. With the models tethered together the whole thing becomes a system rather than one model.

You've basically created a tip driven helicopter with the string and two models. To turn you need to treat it like a helicopter and coordinate your elevator actions to tilt the "disc" so the model folllows a tilted circle and then "climb' in that direction. I'm sure it was a fun experiment but it's doomed to be only an oddity that'll drift with the wind as there is just no practical way for you and your buddy to coordinate the inputs to work out the issues.

It DOES raise some interesting ideas about such a tethered pair as a UAV format .......

RE: Need help on an odd experiment
 

Thanks for the inputs. The idea of treating it like a rotor disc makes sense. The planes fly rather slow and I think it would be possible to tilt the disc, if only one person controls it. If one guy fly relatively level and the other fly up and down around him, it might work. I realize that there is no practical use for this as is, but this is just the first step. What I'd like to do is be able to disconnect the planes once airborne. My origional plan was for the planes to break the circular formation after takeoff and and fly conventionally in close formation. It now appears that the only way to break the circular formation is to break the connection.

As another idea, what if both models were controlled by the same controller? Could it work? It seems that with a little refinement, a person could make a pretty simple helicopter. But, I guess the biggest problem would be knowing where the models are in relation to the manuever you want to perfom. Just thinking out loud here.

RE: Need help on an odd experiment
 

so, I was sitting through a boring 3-hour art class and designed a "tip driven helicopter" as BMatthews put it. I got all the bugs worked out on it (on paper) except two things. First, although there is no torque on the rotor, wouldn't there be enough friction on the rotor bearing to cause the body to tend to follow the rotation of the rotor? Second, I plan to have the rotor blade fixed pitched, and control would be achieved by tilting the whole disc like a gyrocopter. The problem is that I would have to be able to control the speed of the motors on the tips of the blade. How would I route wires from the nonspinning body to the spinning blade? I considered using a telephone cord detangler. It's a thing that you plug inline with your phone cord that allows the wires to spin, but I don't know if A. the wires are large enough to take the power and B. if the device would hold up to constant high speed spinning.
Has anyone heard of a working tip powered radio controlled helicopter?

RE: Need help on an odd experiment
 

The detangler gizmo will NOT take the current of the drive motors but you're on the right thinking track. You'll need a set of slip rings and serious motor brushes from car motor. It's sort of like a motor commutator but instead of the three segments you use two full circle rings with a brush on each. In practice I'd tend to use two brushes onto each ring just to handle the current better through the running contacts.

Yes there will be some torque through the rotor bearing that goes into the body. You'll still need a tail rotor but instead of it pushing constantly it could be a small motor that goes on and off with a reversable power to push or pull as needed.

The tilt rotor in this case will work semi well but you'll want to put most of the heavy stuff in the bottom of the fuselage to assist with the pendulum effect. Otherwise trying to tilt the rotor will just tilt the fuselage. It'll still tilt as the rotor moves but with a tall shaft and low CG it shouldn't be too bad.

Will it fly? Not a clue. With this being a simple fixed rotor planform it may have "issues".

RE: Need help on an odd experiment
 

Exactly! In order to "hover" in a wind, you need to tilt the lift vector of the combined system upwind to compensate for it... the only way I know of is to tilt the plane of rotation in the upwind direction, which means the downwind airplane moves up and the upwind airplane moves down, tilting the plane of rotation...

Cheers!

Jim

RE: Need help on an odd experiment
 

Well, we tried it again today. This time, we attempted to control the planes' direction by tilting the "rotor disc". I've come to the conclusion that it is a frivolous experiment and control is impossible, but it was still fun. I guess I'll have to find some other silly way to try new things.
BMatthews, could you elaborate on the brush system? I know what you're saying, but where could I get the stuff I need for this project?

RE: Need help on an odd experiment
 

why not just fly one of the planes inverted once you're in the air?



dave

RE: Need help on an odd experiment
 

Good thought. Although I think that might be a little tough with these planes. They are electric trainers with alot of dihedral. I haven't tried, but I don't think they would sustain inverted flight. But, with different planes, you could have one inverted and they would fly side by side. When you wanted to land, just flip the one right side up and they'd go back to the circular formation. This experiment might just have life in it yet.

RE: Need help on an odd experiment
 

Cool experiment. How long is the connecting string? Not sure tilting the disc is going to work, since the string is not really like the blades on a heli, but...

Could you manuver the pair with throttle? To stay still in a wind the guy going into the wind adds throttle and the guy going down wind lets off throttle?

This is just about causing me to fall over laughing visuallizing you guys...I might have to try this if I get ambitions. Do you have video? You do HAVE video right...Get a video now! Right Now Damnit! Come to think of it this could make a new reality TV show![sm=lol.gif] Sort of like Myth Busters, where a couple guys go prove or disprove some wacky idea.

You should be able to do a half loop with one plane (maybe aim a bit toward center to loosen the string, I think loosening the string is key to getting full control.) then you would both be flying in the same direction. Then you could half-roll the inverted plane back to normal. Then you should be good to go, just keep both plane closer together than the string is long and don't get the string in a prop, that's all, easy as pie. ;-)

Better yet, maybe you both do a 90 loop to go vertical, that might make any problem of asymetry of the previous sugestion go away. Then one guys rolls to match the other and you're good to go.

Otherwise if you can fly the planes slow enough that they can hold that radius turn without the force of the string, you might have something there too.

Good Luck!

RE: Need help on an odd experiment
 

Well, we tried manuvering the pair with throttle, but slowing one plane down just made the other more or less fly around it. If we got our timing down, it might work, but we haven't had much success. The string between the planes is about 15'. Maybe if we used a longer string, there would be more time to try and control the planes. I like the idea of doing a half loop to get the planes going the same direction, the rolling to get them both upright, but the models we're using are only three channel and are unable to roll. I don't think they're even able to maintian inverted flight due to high dihedral and rudder only control. FYI we're using Wing Dragon's for this. We tried it again, this was the most successful attempt. After taking off and trying to manuever them for awhile the string broke. We both would've had successful landings, but we decided to try some combat since we now had strings trailing from our planes. The other guy was watching my plane, not his and hit pretty hard. These things are durable, he just picked it up and launched it again.
As for video, I do have one, but it is not digital. I could probably rip it to my computer, but I don't have the ability to host video.