Catapult lauch gliders, how to build and adjust

[Treetop]

Well, I have started something that I thought was quite easy, and find it very in depth. I have found some sites on building and adjusting gliders (freeflight), but thought someone on this forum may know a good book, or another forum, or feel like doing a tutorial on the building and trimming of catapult gliders.

Most of the info I have found assumes you know what wash in and washout is, and talk about things I don't quite grasp. I am looking for info about aerodynamics of the gliders, and why some have a longer fuse, and some have a wing lifter, how much incidence to plan for, and a troubleshooter for certain flight characteristics. Is this art leaving us, or are the guys who know this stuff just not on the internet? Hope it doesn't go the way of tight barrel coopering. Or wagon wheel makiing.

Thanks in advance for any help, direction you might can give. I have ordered several kits, to fly proven designs, and will take it from there, and wing it if necessary. Trial and error. I am really amazed at how much goes into the design of these little gliders, as having flown RC and rubber power, I bought a glider kit for $5 a few years ago, found it in my closet, built it, and I am hooked. Seems to require more aerodynamic knowledge, and minor trimming than the other planes I have built, trying to get that best flight. tt :eek:

[robert harik]

I am hooked too! Its hard when you first start looking for stuff on free flight gliders, it seems it is a lost art . I have some web sites I can give you , but there mostly hand launch. I am sure if you go through them you will find some stuff on catapult too. Also there is a news letter from down under(it seems to be bigger there) that I am expecting soon, I have been told its very good and has lots of building,trimming and flying info. Plus plans somtimes.
Sorry running out of time I will post the sites latter today.
Rob

[robert harik]

Treetop I just saw your thread on the free flight forum and it looks like you know alot more about it than I do.
I will keep a look out and if I find any thing interesting on catapult gliders I will post it on the free flight forum. Rob

[Mark Wood]

This sounds like a good thread for Modeling Science. It sure isn't Beginner stuff. ;)

mw

[Treetop]

Interesting you should say that Mark, in that gliders were the first step in getting into flying in the past.

However if it gets results...
tt

[Fingerless50]

I flew them some time ago and its fairly easy to get them up, just make sure its trimmed out ok, throwing it to see that it flys level, prefebably in long grass:))

As for launching, you will need a Bungee its surgical Rubber attached to line, about the length of a field. you stake it at one end, make sure the wind is in the right direction for take off, what i did was hold transmiiter in one hand, with glider in other, the bungee will tell you how much stretch to put on it, hold Glider up with right hand, then let go, it should rise right away if trimmed out, i never had to adjust much, its rather a nice sight, you can relaese the bungee when you have enough height, or it will come off anyway, and float down on the Parachute on it, happy flying

[Mike Taylor]

It is not a common subject anymore, but there is some discussion of HLG / CLG at smallflyingarts.com in the discusion forums (search for clg, hlg, etc), and there is an R/C CLG in the 'featured articles' area (http://www.smallflyingarts.com/Archives/Feature_Articles/Fleance/Fleance.htm)

[Treetop]

Thanks Mike.

I just bought a "straight-up" and a "cata-piglet" made by Campbell from Radical RC

http://radicalrc.secure-mall.com/shop/index.php?shop=1&cat=8&cart=194336

They are very nice kits. The straight-up has a lot of instructions, although I think flying these things will be the only way to become clear on it's performance. The kits are a bit pricey, $12, but come with good plans for me to make more, and the balsa is excellent, a real top shelf kit, and are ready for competition (once built). The wings even have the airfoil angle cut into them, so not much sanding will be needed to get them right. Also they have a dethermalizer included, as well as a nice big dowel and rubber band for the launch. Radical rc charges only $2 shipping, and I got them quite quickly.

I saw a "straight up" forum on the smallflyingarts site. tt

[BMatthews]

CLG shares a lot in common with HLG for trim. The biggest part is to get the CG back as far as you can to where it has the minimum pitch stability. If it loops over on launch then move the CG back a bit at a time. Hopefully the plans showed some stab tilt with the left side high (right side if you're a southpaw) by about 1/4 of an inch. The major part of the left hand glide turn comes from this tilt. The stab tilt has little effect on the launch so you'll also need to use just a little rudder trim to set up the proper pattern.

"And that is?" you ask? The launch should be roughly 30 to 40 degrees nose up with the wings tilted from 20 to 80 degrees based on previous launches. Start with a 20 degree bank. The launch should be a big 1/8 to 1/4 loop/spiral with a steady roll to the left thanks to the rudder trim. The model should reach the top of the climb with a strong left bank of around 45 degrees and some 20'ish degrees of nose up angle. From that hang point of near zero airspeed the model should sideslip to level flight and lightly accelerate to a stable glide speed with little or no altitude loss.

Typically new comers to CLG/HLG try to fly with too much pitch stability and suffer from looping over on launch and bad stalls at transition. Moving the CG back fixes a LOT of evils. If you go a little too far the glider will soon tell you because it'll stall once and then never pull out of the resulting nose down. In worse cases it'll actually nose over into a steeper dive and lawndart itself. You need SOME pitch up with excess speed but it needs to be JUST ENOUGH.

Catapult launch is a real hoot as it doesn't wreck your arm and shoulder and simple ones can be built in an hour and for about $2 in materials if you don't bother with a DT.

[Treetop]

Thanks, Bruce. That is one of the better explanations for launch and trim that I have seen. Some of them being 3 pages, and leaving me more confused than when I started.

To clarify, a right hander will hold the catapult in his left hand, and tilt the glider 20-80 degrees to the right on launch. With the mentioned trim of stab and rudder, the plane will "corkscrew" about 1/8-1/4 turn to the left, "hopefully" stalling with the left wing low, and nose up, and this can be achieved by the launch angle adjustment. All the while pointing the plane up towards the sky 30-40 degrees. Is this correct?

As to wind, I believe it is correct to launch to the right of the wind? By about 15 degrees?

As to incidence, are most or all of your CLGs built with zero incidence?

Thanks Much, tt. :)

[BMatthews]

Pretty darn close there Treetop. The model ROLLS through about 1/4 to 1/2 (I said 1/8 to 1/4 but that wasn't really right) to the left during the climb depending on how much you tweak into the rudder. At the same time it climbs in a turn that starts slightly to the right and then comes around to the left and should finish up at over your left shoulder with the model pointed to the left and downwind. Some models that end up requiring a little more up tab than others may need a bit more turn in the climb to keep from looping over. These models may do a complete turn and end up pointed back into the wind overhead, or close to it.

I mentioned that the models need to be VERY close to the neutral stability point to perform this sort of climb and pullout. Along with that edginess comes a problem where the lifting stab can cause the model to fly well on one flight and tuck to a dive on the next. In that case you can try fixing that by blunting the leading edge of the lifting stab to reduce the stab airfoil's effectiveness. It's a trick I picked up from a HLG guy a few years back and it saved one model that was giving me fits.

HLG/CLG stability and setup. Yeah, we put the lower wing and stab surface at 0-0 but any model NEEDS some form of stabilizing effect such that when the model noses down and picks up speed there's some aerodynamic force to pull it back to level. Decalage is one way but there's other factors as well. A high located drag center can provide this speed sensitive stability and that's primarily what we rely on. The high drag center comes from the drag of the wingtips that are above the true CG location. The lifting wing airfoil also provides some of this as long as the tail airfoil doesn't over power it (that tuck and dive again). And finally we often need to breath in a little bit of uptrim. That and the others are all it needs to fly stabily.

To test fly CLG's I like to start with just a few inches of pull at first for an extended test glide more than anything but it can also show up some bad twitches. Work the stretch up to about 1/2 power and now you can start banking and lifting the launch to look for the groove you want for the max power flight. At this point there isn't enough power to drive it up and through the whole pattern so you actually need to over elevate the launch angle to simulate the angle at mid full power. Work on the roll out during these to find the sweet attitude that makes it flip to the glide. If it keeps zooming over in a loop or has a bad transition then keep moving the CG back in small increments and retrim the elevator tweak for a new glide then try again. When you've got your transistion then raise the power towards full stretch and reduce the launch angle and increase the bank to keep the pause and transition. The final elevation should be anywhere from 5 degrees to 50 degrees upwards with whatever bank it needs to make it work.

I like to always launch directly into the wind. If you set up a launch method that depends on some wind it can cause problems on those rare calm days. It'll be fine. After all it's going to S turn in front of you so you don't need to worry about catching a wingtip and spiralling in.

[Treetop]

Thanks again Bruce. You have helped me a lot. By the way, was in Vancouver in 1976, loved it. Went to Vancouver Island, and saw some people totem pole carving in old WWII airplane hangars. Great place, beautiful. tt

[BMatthews]

If I've helped another soul learn the joy of free flight for even a short time then I consider my time well spent. Best of luck with your CLG's. PM me if I can be of any further help. This applies to anyone else that wants to step up to the Free Flight challenge.

And as already mentioned if this sort of play intrests you check out www.smallflyingarts.com for more.

[bleriot 11]

in the indoor and micro models thread,you have:catapult launch micro glider.
it is a 12 gr micro rc glider.
patrick.

[Treetop]

Yes a good thread to follow, thanks patrick, tt.