Design

[Less_Incidence]

The theory behind the dropped tail boom is that the low stab height keeps the stabilizer away from the turbulent air coming off of the wing, specifically the induced vortexes from the tips and dihedral joints. This allows the lifting tail to do its job a bit better. Also, I think that when I first built the plane, the tail incidence was slightly positive, which probably contributed to the stalling. When I dropped the tail I made sure to give the stab about 1 degree negative incidence, which stopped the stalling and fixed the attitude in flight.

[bonysteak]

Hey, I'm doing Wright Stuff for nationals. It's my first year in Science Olympiad. Last week I bought a freedom flight plane for the first time, because i used Osprey for regionals (didn't go to state -kind of a long story). My partner already bought a kit but broke one of them, and the one he built was working well but not nearly good enough to be competitive (best time was like 2 min). So stupid me thought I could build a plane that went better.


Aaaaaaaaand...

Well I wasted like $60 and tens of hours of my time. I went and tested it in my school gym today (large, circular, very high ceiling - probably like 30' no ac) and...well please don't judge but the plane wouldn't even fly for more than 10 seconds. I tried with all three types of rubber from the kit, I moved both the wing posts and the wing itself (not both at the same time). So quite literally I tried everything. The best it would do is fly smoothly but with no climb and it wouldn't even stay at the same level. At some point it even just dived straight to the ground. This is really retarded because partner and I medaled at regionals (and he medaled at state) I really don't know what to do, and any help would be greatly appreciated.

If this is of any help: I built the plane as exactly and precisely as I possibly can, and since (gonna brag a bit) I'm kind of good at building things it's almost perfect in terms of looks. I don't have any model cement so I used superglue. It has a 7 cm wing chord, 50 cm wing span, 6 cm stabilizer chord, etc. etc. The colored wing panel is already on it, I smeared about .05 grams worth of pink paint on it. I think the biggest problem is the mylar is kind of loose. It's not hanging off the plane or anything, it's only loose enough so that you can see it tremble ever so slightly if you shake the plane. Is that the problem? I tried 20-40 winds with all three rubber widths provided in the kit, moved the wing posts up (did absolutely nothing until it went so high that it started stalling/diving) moved wings forward, but nothing changed the flight pattern. Oh and the plane is kind of heavy - it's 8.5 grams with the propeller. The motors are all 1.92-1.98 grams.

Think I can make use of this plane? Thanks in advance!

-noob scioly scrub

[DoctaDave]

20-40 winds simply isn't enough. If you're using a 10:1 winder, the thickest rubber that comes with the kit, .094, should be able to take at least 1500 turns, or 150 winds. Try going for 100 winds and see how that goes, and after that start playing with the torque and dewinding etc.

[bonysteak]

Sorry, I wasn't being specific. I was only trimming, tonight was my first time taking the plane out for a ride. I didn't dare go more than 40 on a 15:1 if it wouldn't even work properly at such a low level.

[DoctaDave]

if your plane still goes straight into the ground, have you checked to see if your motorstick is bending? or if you have enough wing washin on the left wing? Without wing washin, the plane will probably bank too much during the beginning of its flight, and thus it won't get enough lift, so it could just go into the ground or not climb at all. If your motor stick is bending, it could give your propellor some downthrust, which would also send it to the ground.

[bonysteak]

Yeah, the motor stick is fine, at least at this low number of turns.

There is a very small washin but I have not had any problems with banking at the start of the flight.

I think the best I've gotten it to do tonight is to just glide slowly to the ground, almost as if I had just released the plane without a rubber motor (of course just lasting a tiny bit longer). It just won't climb, and I can't figure out why.

[DoctaDave]

when you release your plane, does it go quickly? or does it go at a velocity similar to if you just tossed the plane? If the plane is moving extremely slowly after you release it, I would definitely just try adding more turns to the motor. A video of your plane flying would be extremely helpful, if you could provide one.

[bonysteak]

I guess the best way you could describe the flight is just the exact same as tossing it gently without a motor - it just lasts a little longer. Or it'll go up, stall, then dive to the ground.

Sorry, I won't be able to get a video anytime soon - I don't have access to our school gym until Wednesday afternoon, what with all the AP testing going on.

[Less_Incidence]

That sort of behavior sounds like you might have a severe problem with wing incidence and/or a severely unbalanced prop. If the plane is shaking violently as it "glides to the ground", then that may be a sign of a very bad propeller problem like a bent shaft. If the prop isn't the culprit, check to make sure that your wing incidence is right around +3 degrees relative to the stab. If your wing incidence is negative then the plane will never fly.