1/12 Scale Reiher Sailplane foam

[bcarter1234]

The cap strips were bonded into the top and bottom of the wing. Glidden Gripper provided a better bond than PVA/white glue in a quick test using scraps. For an additional 9 grams the wing is noticeably stiffer. The current weight ballasted with battery is 96 grams.

Inboard ailerons are next. If the ready to fly weight is 110 grams that would work out to 2.8oz/sq ft or 8.5grams/sq decimeter. The 36" free-flight tow line Reiher is at 1.6oz/sq ft, 4.9grams/sq decimeter.

[lincoln]

Because if you cut too slowly to avoid drag, the hot wire melts more of the foam to a larger radius around the wire diameter, so you have to account for the bigger kerf when making the root and tip templates to end up with the correct aerofoil section and thickness once cut.

That's true unless you have a variable DC supply , and this is a major help. There were many approaches to achieve this - from Variac's to using light dimmers.


John

I have a light dimmer in my setup. However, measuring the current is probably a good idea.

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I doubt if it would be necessary to turn up the heat on the wire for cutting without touching. Just cut more slowly. Foam is a good insulator. I think it's probably a good idea to make a bunch of cuts to get the kerf figured out before making airfoil templates. As I recall, one way to reduce the problem with the kerf is to make the lower cut first and let the core drop down after the cut. The kerf will be thicker at the tip than the root of a tapered wing.

I should admit that I haven't done much cutting with my gravity feed setup. Long ago, I did a bit of cutting with someone else's user-unfriendly NC cutter.

I think a really long bow might be good for cutting a really flat foam top for a less than perfect workbench. I haven't figured out the catenary curve, though. Maybe it becomes unreasonable.

[bcarter1234]

The inboard ailerons are installed. I don't have differential programmed correctly yet but I hope to get that sorted through OpenTx soon. It has been about six years since I last messed with it, I've forgotten almost everything. Ready to fly at 101 grams, a 14 gram increase for ailerons and cap strips. 

[bcarter1234]

This morning's test flight was a success in terms of gathering information, not so much from a desired outcome aspect.

The internal ailerons added a very small amount of influence over the roll axis but not nearly enough. Back to the drawing board! ;-)

[OZPAF]

Are you using rudder with ailerons? Adverse yaw is a major issue on long glider wings.

John

[bcarter1234]

John,

An excellent question. As I was trying to get the first test glide to roll I realized I wasn't adding rudder. Adding rudder gave the tiny amount of roll response that was available. It seems ailerons on the inner panel, before the anhedral break, don't have enough influence even with rudder added. I'm going to add rudder to the aileron input on the TX. 

I'll try up only ailerons on the outer panel next. Spoilers are tempting. Any thoughts on which is likely to provide the greatest roll control with the least adverse yaw? If I did use spoilers they would probably be the flip up type so like an up only aileron near the spar instead of on the trailing edge.

The weather was amazing this evening so I got several flights on the 36" towline free-flight Reiher. It flew along as stable as you could wish. If I can just get the larger RC version to do the same...

[OZPAF]

I'm not sure how effective "flip up" spoilers would be at your low RE no's. I tend to think that you may lose too much lift and that the best solution is to use rudder.
don't be afraid to use a fair amount mixed in with the ailerons. Try increasing the mix to see if it will provide good roll control.

I have used coupled aileron/rudder for years on all my RC gliders from F3B to F5J and now DLG - it makes a large difference.

Good luck

John

[bcarter1234]

Step 1 of switching to outboard up only ailerons was bonding the inboard ailerons back to the wing. Once the Glidden Gripper dries I'll cut the outboard ailerons.

[bcarter1234]

The outboard ailerons are cut and hinged. The pull lines are routed. Only one servo will be needed for this installation. Boring the holes for the pull lines was an interesting project.

[bcarter1234]

Ready for a calm morning to test the new ailerons.

[bcarter1234]

Flew about a dozen test glides yesterday without incident. I now have roll control as long as rudder and aileron are both used. It is not what I would consider authoritative but I think it will suffice for the way this model is intended to fly. My biggest concern is if it will be sufficient when on tow.

I did program the Taranis to have switchable 100/50/25% rudder added to ailerons so I can see what is preferred.

Any pointers for tow hook location? I will need to use a high start rather than towline for this one as flying and using the reel both take two hands. ;-)

[OZPAF]

For best height on a high start with RC - the CG can go back till under the CG. However I would suggest that you make the position adjustable and start with a position that is 15deg ahead of the CG.

An easy way to have an adjustable hook is to use a small screw hook(1/16" wire) - 90 deg bend, screwed into a small section of ply - then adjustment only requires drilling a few more holes.I used this approach on a 1.5m glider launched on a heavy duty HiStart

John

[bcarter1234]

John,

Thanks for the pointers on hook location. I assumed more forward would be good since I can always add some up elevator.

With a split foam fuse moving the tow hook is simple. The hook is bent to look like a T-pin with an inch wide T at the top. The vertical portion of the T is given about an 80 degree bend 1/4" below the T to form the hook. The actual degree of bend is whatever is needed to make sure the rear of the hook diverges from the wing's horizontal centerline. Having the hook parallel on some of the towline gliders turned out not to be a great idea.

The horizontal T part goes in the groove between the two halves. Tape is put in front and behind the vertical portion of the lower loop. Moving it is just a matter of removing and re-taping in the new location. I'm finding foam an excellent medium for experimenting. 

[OZPAF]

That's a clever solution for your launch loads.

John

[bcarter1234]

Another eight or nine test glides were flown on Friday morning. With the coupled rudder it has what might best be described as sluggish roll control. The glide however is beautiful to watch. Distances ranged from 250 to 320 feet with roughly 20 foot of drop. 

A rotary servo will replace the linear servo in order to add a bit more aileron deflection. I'm considering a very small amount of elevator coupling as it seems to track better if a little down elevator is added when aileron is applied.

It feels like it has a tendency to weathervane in a crosswind. Any suggestions for that?