|
Post by callun on Feb 8, 2008 17:57:01 GMT 10
If only Ken had been around with his Alula too. That would've been ideal.
|
|
|
Post by Pij on May 16, 2008 14:25:17 GMT 10
I'm gunna chuck a wobbly too. Actually, did the first test chucks Wednesday and Thursday, and made changes today (Friday). Mine's a bit different, as you'd expect with this sort of thing. You get some bits of one of these: And some bits of one of these: You make up a mount to shift the wing WAY back, because you've ripped out the motor and replaced it with a bit of EPP and tape. Then you find the reduced tail moment had some side effects, so you make a new bigger fin, with plenty of rudder down low. And you get this:
|
|
|
Post by felix on May 16, 2008 17:55:06 GMT 10
hey pij i hope it doen't fly as well as it looks buddy seriously though looks like she'll be a good flier with little outlay,well done!......makes me wish i had of held onto my long suffering aerocommander *sigh*
|
|
|
Post by Pij on May 16, 2008 21:00:58 GMT 10
Thanks Felix. I think.
Sitting up on the high shelf, it doesn't look anywhere near so ugly, as I can see only white surfaces. I think the red and yellow makes it look unmatched.
From yesterday's flights, it seems that if I get the rudder authority fixed, including the adverse yaw, it should be OK.
It's pretty light. Has 4xAA receiver battery way up front, and no other ballast to balance. I may have to add some weight eventually, but super light is good for testing, to reduce damage. It's already hit a few trees and cartwheeled a couple of times, with little to show except for one crunched spot on the LE.
I made a couple of mistakes in the fin design, but it'll do for a prototype. I wanted a bigger fin, bigger rudder, longer tail moment, and more rudder down low to reduce adverse yaw (tell me please if I was on the wrong track with that last one - well actually it was to reduce adverse ROLL opposing the chosen yaw, caused by applying rudder force too far above the roll axis).
I didn't want to increase the moment arm or area of the horiz stabilizer or elevator, even though there effectiveness should have been reduced by shifting the wing back (reducing moment arm), because I also have put on a wing with less area, so a drop in horiz tail effectiveness should be appropriate. Anyway, the test chucks showed the horiz surface was OK.
Reasons for doing all this: I hated my Thunderbird powered glider, have Electrafun parts on hand and cheap to get more, and want a light-wind glider to play with and teach the kids on.
Yesterday showed something strange: I had to keep full down elevator during the chuck, then release it. That's funny, because it's similar to how I throw my Duck off a cliff in strong wind. Good practice, then!
|
|
|
Post by felix on May 16, 2008 22:26:23 GMT 10
sorry mate just having a light dig at you ,she doesn't look half bad and when she's flying no doubt will look the goods.....besides nothin better than a little (or alot in this case) modification to produce something that flies great! the idea with more area down low to reduce rudder induced roll is correct but with a high wing,dihedralled wing it is such a small force (basically due to the fact the centre of drag/roll axis is higher than a mid wing) it's not entirely necessary and may be more prone to damage. as for the tail moment decrease i wouldn't worry.there's still a large arm there and the only downside to a shorter tail moment is a less stable/more twitchy yaw and pitch response -a good thing for slope!! ;D another note here is it looks like you replaced the wing with one of lesser chord length? higher aspect ratio wings generally need less tailplane area (good example is modern fullsize sailplanes with tiny tailplane areas). the full down on launch is more than likely a cause of a high wing incidence.basically you are launching perhaps higher than it's normal trimmed flying speed causing it to "balloon" up in a launch.this is quite typical in a flat bottomed/under cambered/slow flying glider -my electra with a javelin type launch has ballooned directly up and then come straight down on top of me much to the amusement of onlookers as for the same thing happening with the duck? my guess is you fly at slopes with not great amounts of lift normally so have a large amount of reflex to keep it aloft? same thing applies here.....or i could be totally out here,haven't flown a duck lol. overall looks like a great trainer and an even better light wing flier in the bargain.well done
|
|
|
Post by Pij on May 17, 2008 4:23:35 GMT 10
The wing is only a couple of mm less root chord than the original, but shorter and more taper reducing area. Undercambered, so prone to overlift with overspeed. With no motor weight, that caught me by surprise a bit.
When I fine-tune the CG (after getting the decalage fine-tuned) I might have more rudder authority.
The Duck trims are currently set for high wind with (I think) 28 points of down (out of 40 possible) compared to first flights in low wind. Even so, I use some down-elevator on launch when throwing into vertical air, just to make sure it goes forward.
|
|
|
Post by felix on May 17, 2008 16:58:33 GMT 10
got you on the duck launch now....the bees do the same thing but i normally apply down after i launch.must learn to do this myself i reckon as my bee needs some speed or the first turn is a little scary ;D. (as in another long walk down the slope)
|
|
|
Post by Pij on May 17, 2008 20:45:04 GMT 10
Some test chucks in the nearby schoolground this afternoon. On the best throws, lovely long flat glide, but still need down elevator on launch. On the worst, stall and nose in. In between, still lacks rudder authority unless generous amount of elevator is used.
The fancy one-piece adaptor I made yesterday, to cover the hole of the original wing and mount the new wing - I had a thought that maybe it should have been in two pieces with further strengthening. It apparently had the same idea. I am now doing so. Didn't have to cut it in two - did that itself on a nose-in - all 4 rubber bands released and the wing shot off, the mount split in 2. Serendipitous.
I think it needs to be trimmed for higher speed. Glides lovely at almost zero speed, but no control so slow. Will reduce decalage and add nose-weight.
|
|
|
Post by felix on May 17, 2008 21:33:33 GMT 10
difinately sounds an incidence problem (what you refered to as decalage?).your rudder prob is rather odd though,all signs say it should be great! have you tried increasing the throws at all and maybe a more forward CG? also how much dihedral does the wing have?
|
|
|
Post by felix on May 17, 2008 21:40:46 GMT 10
looking at your pics again maybe the rudder is too small for this type of model.could try moving the rudder hinge line all the way forward to the elevator.should turn in it's own length then ;D
|
|
|
Post by Pij on May 17, 2008 21:48:37 GMT 10
Plenty of dihedral. Large rudder but set to small throws at this stage. Moving cg to gain rudder authority was part of my reason to trim for higher speed - also to gain higher airspeed over rudder. It has some control at speed, but lacks it at slowest glide. Has control when plenty of Elev used with rudder, but wipes airspeed. Yes, I tend to think in terms of decalage rather than incidence, but I'm basically on the same idea. Thanks for your thoughts. en.wikipedia.org/wiki/Decalage
|
|
|
Post by felix on May 18, 2008 18:18:55 GMT 10
decalage hey......can say i learnt something new today ;D.will add this one to the memory banks.
|
|