RC Hang Glider by weight shifting

18 September 2017

2mm bamboo dowels, plastic bag and tape



$2 kite for future conversion?

 

 

 

Coffee stirrer, cotton bud, wire shaft, pushrods, rubber band, zip tie and hotglue

 

 

 

 

 

 

 

 

 

 

 

22 August 2017

On Sunday morning, the sky looked like it was going to rain when I left home. I detoured for breakfast at Chong Pang. By then the sky cleared significantly enough and I rode to the flying field. Choong was already at the field. He was flying his Skysurfer and I set up my gondola against the stretched rogallo wing. It was then that I discovered the negative wire lead has broken loose from the board. It wasn't as if I didn't check the gear, I tested it the day before. There was nothing I can do; I could return home to solder but that is a fair 20 minutes ride away. Choong came to the rescue: he was returning home so he soldered the wire for me at his place and cycled back to give it back to me before going off for his breakfast.

I would describe the first test flight as a 2m radius loop, it began once it left my hand, pitching up and looped into the tree behind me. It was obvious that I must not use much throttle. I couldn't continue because the coffee stirrer motor mount came off from the central column.

I waited until Eddy arrived at the field and borrowed his portable hotglue gun. This time round, at the suggestion of Thang, I glued it in with quite a bit of downthrust, maybe 25-35 degrees. Next time, if there is one, I could replace the glued joint with a small bolt/washer/nut assembly for adjustable thrustline.

Knowing that it looped the last time, I taped the "repaired" gondola slightly forward under the rogallo wing and used little throttle. This time it flew but it was going left all the time. After the "crash", one Z-bend wire came out of the heatshrank pushrod, so this was slipped back in and eyeballed for pro-right.

The next and last flight was much better, there is no persistent left turn. The model climbed easily and was very stable. The trim is too much to the right this time, left turn was hesitant but I can see that it is there. Too bad though that I lost control of it and it was trapped high up in a tree and remain there while I was there.

It really is to be expected, I know that gusty condition is not suitable for lightly loaded model. So I lost a receiver board and a new 7mm motor and prop. However, weight shifting roll control has definitely worked. I didn't have enough flight time to determine if the pitch/flap weight shifting control is workable. It would be great to try it indoors. Weight shifting control is possible but moving surfaces are more direct and effective.

Just today, Choong messaged me that he has the model, I'll collect this Saturday.

4 August 2017

April's idea has a central post, if shifted forward, the twin pushrods can simply be substituted with pull lines.

23 May 2017

Para-sail?

How to make a simple and effective para-sail?

• Totally flexible (the parachute) made from cut pieces of plastic from plastic bags?
• Flexible from simple piece of plastic (plastic bag) with CF rod (the wing sail)?
• Rigid from cut pieces of foam sheets (the short cut)?

27 April 2017

I thought about this for a day and could not come up with a simple and reliable solution for controlling pitch and roll axes of the wing.

The keyword is weight shifting and drag inducing motions are out. For example, instead of producing the desired pitching of the model, what could happen is that a portion of the movement produces lowering or raising of the CG which does nothing to the flight path; the pod is pitched but not the model.

I WhatsApp Thang and he showed me what he declared as an unsuccessful model of his past:

He said "the movement was quite ok but somewhat it has no effect".

There could be so many factors, maybe the CG of the wing didn't coincide with the trike although he said it glided ok, or, the wings are too heavy relative to the trike or maybe the geometry just didn't work out.

I could arrange the servos of the WLToys' board so that the elevator will slide the board (and battery and motor) front and back for CG and the other rudder servo to give vectoring to the motor. It has pros and cons and it seems to be a deviation to what I set out to do unless I have a 3rd servo for rolling control.

Here's an alternative that I think might work, I studied his photos and drew this up:

The motor could be mounted to the top platform so that the thrust angle relative to the wing doesn't change, but that means the motor weight is relegated to the wing and not the pod/trike.

One immediate problem is how can I get the CG of the wing to coincide with the hinge point and CG of the pod/trike? Maybe it isn't possible unless additional nose weight is added to wing? But if I don't get this coincidence, I strongly suspect that the servos will be doing the useless motions of lifting and lowering of CG?

The next thing to consider is the placement of the motor. Sure it could be fixed to the wing and so be unaffected by any servo movement, but this is not the path I am taking. And sure it can be trimmed to fly at set speed, no matter what. But the model could be more efficient and maneuverable if thought is given to its placement. When the servos pulled (shorten) in unison, the trike noses down but the CG is moved backwards so the entire model will climb and relative to the wing, the thrustline will be pointing down. If the thrustline is at or below total CG and drag centre (drag force will depend on speed), the model climbs. And vice versa when the servos pushed. It is important therefore to have the thrustline as close to the combined drag centre and CG. But in the case of roll, the thrustline will act against the direction of roll and this seems unavoidable but is minimized if the thrustline is close to the combined CG and drag centre. I don't know how to determine the combined CG and varying drag centre effect. Just thoughts without decisions.

11 November 2015

Flapping plastic will drag the plane, maybe just a fixed rigid wing?

5 November 2015

1. Make a wing to the planform and reflex of a hang glider and add keel.
2. Adjust with weight till it glides.
3. Mark the location of the CG location on the keel.
4. Assemble the WLToys receiver and battery as one unit.
5. Do up a triangle or a T shaped trestle.
6. Connect the two servos with pushrods to the trestle thus forming a single control unit.
7. Remove any weight from step 2 and lay the control unit on wing, place it so that the entire model (wing and control unit) still balances at the location marked on the keel.
8. Brace the trestle to the wing and suspend the receiver/battery to the keel.
9. Check that the model glides and is controllable in pitch and roll, adjust the hinge points of the pushrods at the trestle and choose the servo holes as appropriate.

Wing may be contructed of CF rods braced with strings and covered by plastic, or with foam sheets. The keel may be a solid piece or covered by plastic sheet. I think it would be more fun and 'realistically' scale, if the wing and keel are made from CF rods, strings, plastic, etc. This would probably mean that after the CF rod keel is doubleside taped or glued to the centre of the plastic sheet, a further doubleside tape or glue line is required so that the plastic sheet will glue on itself and form a small triangular keel. Maybe such a fin is not necessary, but it looks smart and I am only fiddling the aerodynamics slightly because the wing would then have a slight anhedral and I have some lateral area to counter the side areas of the hanging control unit.

If this all works out, how about plugging in a 6/7mm motor direct drive? Propeller could be at the nose of the wing, at the tail of the wing, or by mounting it to the rear of the dangling receiver/battery combo, I would have vector control as well! It would probably be more stable too, bringing the CG lower again and therefore improve response. To counter any shift of overall CG, just fix the battery to a new position to balance things out. I don't see loops are possible with this model.

If using a motor, angle of upthrust/downthrust? Observe the attitude of the glide, a horizontal line to that would be the zero-powered thrustline. It ought to pitch up on power, so long as full power is still controllable, I would settle for that, if full power is too much, then adjust the thrust angle. Similarly, I would allow the torque to do whatever it wants if it is not too much. It is unlikely that the 6-7mm motor would over power the model or make things too difficult if mounted at the hanging receiver/battery.

What size should it be? Maybe something with the same area as a rogallo winged Cootie is good enough. All depends on how much CF rods I want to use...And I think a rogallo wing is good enough, no point making anything more complicated then it needs to be.

I wonder if flying gliders is permissible at Bedok Reservoir. If it is not, then the model has to be powered to have any chance of fun flying.

This seems to be a real simple model to construct and fly. If I do this, it would be my first in weight shifting hang glider.