ME-163 Komet

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burkefj

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I did a profile komet a while back, but did it single ply for the wing. The problem with a komet is that the motor mounted in the tail is pretty far back relative to the CG location and the nose is short, so you wind up having to put a lot of nose weight in place. It got too heavy and had a bit of wing flutter at high speed. That's why most people do a tractor motor in the front, or do ducted fan/jet as you can put the weight forward where you need it. I had been meaning to go back and do a doubled wing/lower fuse to remove that problem.
Anyway, here it is. Got about 20 flights on it so far. Due to where I had to put the rail buttons to clear the radio equipment, they are pretty far off center, that causes a bit of pitch over off the rod, then a gentle pull up and it will climb. I was trying to trim out the pitch up, but then it would keep trying to go past vertical and the boost would sort of look like a rollercoaster as I tried to damp it out. I finally went back to no trim on boost and just pull up once off the rod and let it go. Glide is pretty good even at 14 ounces. The airframe weight is 4.5 ounces, needed 3 ounces of lead in the nose plus a 1.7oz battery for CG to be correct. As it gets really slow it does run out of elevon, but it settles flat. If you keep speed on you can flare before landing. Anyway, hope it's interesting. Video coming later this morning.......

Markings are trim monokote I cut myself, used a silver sharpie for the panel lines. Model master gray and OD for the paint.

Build thread with lots of pictures...

https://www.rcgroups.com/forums/showthread.php?t=2356237#post30912060


Frank

WP_20150226_006.jpg

WP_20150226_008.jpg
 
Thats one for the to do list! Those rail buttons are a pain, could they not be mounted under the wing?


Richard
 
The hard part about mounting them on the wing is that the bottom of the wing is not a single thickness, you could mount the on the top of the wing or on the top side of the fuse where there isn't any blockage from components...I've done that on others, but on other planes I don't see the pitching unless the motor thrust is off axis, I'm surprised it is so pronounced on this plane. It could be that for boost the CG is just very far back and it is extremely pitch sensitive and that is exacerbating the lug location issue....but for glide I don't really want it more nose heavy...

Frank


Thats one for the to do list! Those rail buttons are a pain, could they not be mounted under the wing?


Richard
 
I read you. Flying wings and deltas are very CG sensitive. I've a number of things on the fire but this is one I will build maybe in the summer.


Richard
 
I t could be that it isn't the rail buttons so much as the CG is right on the rear edge for boost and it is just twitchy, I tried putting a bit more nose weight for the first flight and boost was ok, but I ran out of elevon on glide....It's sort of a compromise....
 
Have you ever seen the old technique using a rear-mounted motor, front-mounted ballast weight, and connecting body tube or spar?
You use enough ballast to make the complete rocket stable for boost. The whole motor-ballast thing ejects after boost to re-trim your vehicle for glide, and descends under parachute. Designs using this feature usually require a tube through the length of the rocket to house the motor and ballast, and extend as far forward as possible to make the ballast more effective.
This system has the advantage of dumping a lot of weight at apogee that is necessary for safe boost but non-optimum for gliding flight.

Edit: Good-looking Komet, too! Any more pics?
 
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Of course, but I like to see if I can get them to work without having to drop anything or shift balast, keeps it simple and faster to turn-around for flight....but of course that will give the best glide weight....The E-6 motor does not have ejection anyway, so you'd have to release it some other way.

Frank

Have you ever seen the old technique using a rear-mounted motor, front-mounted ballast weight, and connecting body tube or spar?
You use enough ballast to make the complete rocket stable for boost. The whole motor-ballast thing ejects after boost to re-trim your vehicle for glide, and descends under parachute. Designs using this feature usually require a tube through the length of the rocket to house the motor and ballast, and extend as far forward as possible to make the ballast more effective.
This system has the advantage of dumping a lot of weight at apogee that is necessary for safe boost but non-optimum for gliding flight.

Edit: Good-looking Komet, too! Any more pics?
 
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