Chan,

I built mine from scratch using the on-line plans. Couldn't get a decent hand toss at all so decided to fly it and see what happens. Nice boost on an A8-3. Didn't really glide.....just kinda fluttered down. So I figure I need to add a little nose weight to induce the glide.

__________________
Don
NAR 53455
"Carpe Diem"

Sounds like my hand toss--sometimes a pathetic flutter, or when tossing into a light 3-5 mph breeze, pretty harsh nose-over arc (arc, not nose-down dive). I didn't really round my edges much, though, so might also go back and try that.

My hand tosses seem to be just like yours, either the nose over arc or flutter but on a couple of tosses (out of about 30) I got a reasonable looking glide for about 20 ft.

I decided to just try it but the day I tried was on the windy side. I used an A8-3 and when it was on the pad, the wind started blowing from the top side against the saucer which caused the launch lug to jam on the rod and it got up to about 15 - 20 ft before crashing and breaking the pod loose. It's since been fixed and I plan to try it again at the CMASS launch this Saturday.

Mine somersaulted under boost (1/2A6-2, comically low altitude). Looks like I had a slight nose-up angle on mounting the motor tube, which amplifies the glider's natural tendency to pitch. It clearly needs about a 1-2 degree nose-down thrust angle.

Try adding a little bit of clay weight under the tail to go along with the weight in the nose. Don't ask me why, but this seems to help. Because of all the weight in the nose, and because this nose weight is up above the wing's centerline, the Invader always wants to flip over and fly upside down during the glide (hence the erratic glides and the nose dives). The weight under the tail (centered and all the way back) seems to help to keep it flying in an upright orientation (where the wing's dihedral and the fin "rudders" can do the most good) and increases the glider's stability. What the Invader's design really needs is the addition of a small rudder under the tail.

Mark \\.

__________________
SAM # 0011

I tried to fly mine today on an A8-3.

It pitched over on boost and completed a nice half circle before burying the pod into the ground.

The engine ejection charge sent the expended motor higher than the rocket had achieved.

On my model, putting in nose-down thrust would only amplify the problem, I think.

Maybe I don't understand but wouldn't the nose-down thrust push the nose over even faster??

I tried to launch my first Invader clone on A8-3's three times in a row, and each flight was identical to yours. On the third flight, the impact with the ground tore the engine pod off, which effectively retired that model. After some analysis, along with some discussion on this forum, I concluded that the Invader had not been nosing down forward into the ground after leaving the launch rod, but instead had been doing a back flip into the ground. In fact, the process happened so fast that I never saw in any detail what actually occurred, but this explanation made excellent sense.

Imagine a springboard diver doing a backflip off the board; that's what my glider was doing, and that's what this design tends to do. The explanation that I received at the time was that the Invader's very large, circular wing produced so much lift that it overpowers the forward thrust provided by the motor, causing the glider to loop right over backwards and into the ground. Positioning the motor so that it has some incidence, i. e., angling it downwards slightly (2 or 3 degrees), is meant to give the motor more "leverage" to counteract this tendency.

I gave the motor pod in my current Invader clone about 4 degrees of incidence, and it seems to have done the trick. I can position the launch rod so that it is vertical, with zero tilt, and my Invader #2 travels straight up on an A8-3. I also made another modification, too. I glued the launch lug to the bottom of the motor pod, instead of in the crease in the wing. I felt that doing this would insure that the lug was in line with and parallel to the motor's thrust, and would bring the motor and the launch rod closer together, especially now that the motor was mounted at an angle to the wing.

I have recently done some additional testing and analysis that has caused me to suspect that the above "back-flip" explanation is not the whole story, though. It accounts for much of what I saw in my first version, but not all of it. Now, I don't know about anyone else, but I had to add a pretty hefty amount of weight to the nose to get each of my Invaders to balance in the right place and achieve any kind of glide during hand tosses. I ended up using solid pine car derby model round weights in my latest version. I installed a six-segment slug of 3/8" diameter weights into the nose cone, which amounted to about 11 or 12 grams of mass. This amount of weight in the nose did enable the Invader to glide in my hand tosses in my backyard, but it also consistently rolled over and glided upside down every time, when it did achieve glide, while still doing sharp nose dives into the ground in a troubling number of tosses.

I came to the conclusion that the roll overs and the nose dives were caused by the same problem. The nose weight that I had added, which was intended to balance the glider on its pitch (nose up, nose down) axis, was unbalancing it on another critical axis (I can't decide if it is the roll axis or the yaw axis). This was because all of that additional weight was positioned well above the top of the wing and forward of its front edge. Because of that, simple gravity was causing the Invader to roll over during the glide. In my model, the amount of nose weight was enough to cause an immediate and obvious roll over. Other builders may not be using as much nose weight, so their gliders may not show as obvious a tendency, but the tendency would still exist in their gliders, too. It would just have more subtle effects, causing erratic, fluttery glides, along with all-too-frequent nose dives into the ground.

Now I think that some (maybe all) of the "back flips" that occurred when I launched my first Invader may not have actually been backwards loops into the ground off the launch rod. Instead, I suspect the the Invader did leave the rod (which was inclined) in a straight up orientation, but instead of endlessly "climbing" until it looped right into the ground, I think that it barrel-rolled into an upside-down orientation, then "lifted" right into the ground. IOW, it made a severe nose dive under power, doing the same sort of thing that I and others have seen so often during our test hand tosses. Thus, the problem is a bit more complicated than the original "back-flip loop into the ground" explanation.

To remedy this, I added a 1" diameter blob of modeling clay underneath the tail, centered over the back end of the keel. I added and subtracted minute amounts of it following successive hand tosses, until I got the results I wanted. I eventually found that forming the clay into a sort of rudder-shapped wedge gave the best results. In hand tosses, the Invader now goes in nice, level and LONG glides (at least 30 feet each time, and over 40 feet in one toss), staying upright the whole time. Contact with the ground deforms the clay a little bit, so I have to re-form it each time. I get the best results when the clay is formed roughly into a small rudder, as far back as I can get it.

I need to add that I have not yet "proven" this latest change in an actual launch yet, though. I'll try to do that later today (Sunday).

Mark \\.

__________________
SAM # 0011

Mine was definitely a back flip, not pitch forward.

The weight being on a higher plane theory makes sense, though I would think the motor/casing represents a whole lot more weight up there than the little bit of clay we're using. Not much we can do about that except possibly shorten the motor mount legs, which gets us closer to burning the wings. I do sort of like the idea of counterweight at the tail, though this would make the glider even heavier.

I'm going to tweak the motor tube thrust angle a bit this week and see how much improvement I get there.

Thanks for the tips/dialogues, guys. I'm really glad to hear there are folks building and flying these things (or at least trying to).

--Chan Stevens

Ya'll know mine did exactly the same thing, the somersault and all, flipping over as the Invader cleared the rod and burying into the plowed ground. With my experience with R/C, a motor NOT mounted with down and right thrust will cause all kinds of stability problems and very often, a crash. I remounted my engine tube with about 1 degree of downthrust to try. I'll probably find I'll need more than that, though.
I like the idea of a small rudder at the ventral trailing edge; would making a small one out of, say, ply add the needed weight back there AND add stability? I think I'll try it, once I eliminate the launch issue.
It might be interesting to talk to Vern Estes about the initial stability problems he encountered while prototyping the model. Surely, those flew as poorly as the clones do 'out of the bag'.
Allen

Bill E. and I both built several K-19 clones a few years ago, and went through this little problem. The solution is the downthrust in the motor tube. I wound up with about 2-3 degrees and got near-perfect boosts. One of my clones had three great launches, three great flights, and two great recoveries...

__________________
Craig McGraw

BARCLONE Rocketry -- http://barclone.rocketshoppe.com
BARCLONE Blogsite -- http://barclone.wordpress.com
BARCLONE Forum -- BARCLONE Forum

BARs helping BARs

SAM 0044
AMA 352635