J250-powered Sei-Aerobatic

[Don Cooper]

Sometime back i experimented with a series of scratch design IPS-powered semi-aerobatic planes. They flew well, but there was a basic problem. Their size and responsiveness was not compatible with with my flying skills and aged reflexes and eyes. If I flew them high enough to allow some margin for error, I had trouble keeping them oriented. If I flew them low enough to keep them oriented, one error usually put them into the ground, so a given version typically didn't last very long and I gave up on them. I experimented with the J250 in other planes and was impressed by its perfomance, so, I took the plan for the most successful IPS-powered plane and scaled it up for the J250, hoping the result would be a plane big enough for me to see at altitude. Specifics for the plane are:

span = 38"
airfoil - WASP
motor - J250 with GWS 100 B gearbox
prop - still experimenting - so far 10-8 or 9-7 appear to work best
control - AERT
weight - 9.5 oz w/o battery about 1/2 oz over my target weight

Some pictures are contained in following posts.

[Don Cooper]

A picture during construction is attached. The body is built around a horizontal sturdy board crutch with a few foam formers attached to the crutch and sheet balsa attached to the formers and crutch. Vertical tail is sturdy board. Wing and horizontal tail are balsa.

[Don Cooper]

Here are a couple of pictures of the finished plane

[Don Cooper]

Another picture of the completed plane. Covering is Reynolds Wrap.

[Don Cooper]

In the process of launching.

[Don Cooper]

A picture of a flyby is attached.

It has been too windy to really wring it out, but so far it has done everything I have asked. Best of all,I can see it at altitudes high enough to provide some margin for error.

[MAXX-n around]

Wow!! Good work I really like it.

[miraclesailor]

Don:

That is a very nice plane, congratulations!

I have used the J250 alot in many planes and had very good luck with it. I have used it with gearboxes and without. The gear ratio that I like is something close to 5 to 1 with either a 7X5 or an 8X4 prop. Using it direct I will go with a Gunther style 5X5 prop. It works rather well either way. I love the price, cheap.

I am now ready to try some brushless and have been wrapping some cd motors to that end. I will have one one to experiment with soon. I am looking for a bit more power with a slightly longer flight time.

I have had 20 minute flights with the geared J250 using 2S LiPoly 1200mA, on an 8oz plane. Too good! I have had the best luck with the motors by initially running the motor submerged in distilled water connected to a 1.5 volt D battery, rotating in the direction you are planning to use it, until the battery dies, or about 30 minutes.

Later,
Dan

[Don Cooper]

Dan,

Thanks for the info. I haven't tried a prop smaller than 9". I will have to try the smaller sizes when the wind drops below double digits again.

Don

[NitroDad]

I am wondering? I've heard of using Reynolds Wrap, how do you get it to stay on? Basiclly how do you work with it?

[Don Cooper]

I use DAP non-flammable contact cement that I get at Home Depot to attach the Reynolds Wrap. You can also use BalsaRite. To attach the Reynolds Wrap, I paint the surfaces that I want the wrap to stick to with a light coat of contact cement, then let the cement dry for 30 minutes or so. Then use a standard covering iron to stick the Reynolds Wrap down and shrink it. One thing I like about Reynolds Wrap is that it will shrink a LOT. Even sloppy covering jobs can be shrunk tight by continuing to apply heat. It doesn't appear to have a 'grain' direction, but shrinks equally in all directions. It is light and surprisingly tough. The price is right also. The hardest part of using Wrap is keeping it from folding back on itself when you attach it to the frame. If it does, in most cases you might as well wad it up and cut another piece.

Don

[miraclesailor]

I have also used the permanent glue sticks that you get at the likes of Staples. I like the UHU best but the Avery also works. You put it on the balsa edges that you would like to stick down to and press it on. When you are over lapping the wrap use a bit on the underneath piece. It will shrink nicely even if you decide to use a hair dryer.

Later,
Dan

[Don Cooper]

A couple of other points about Reynolds Wrap. It has very little tensile strength, which is good in that it can be used on light structures without warping them. I have used it on tail surfaces made of 1/16 balsa sticks without problems. It is bad in that it doesn't add any torsional rigidity to the structure, and you can't use it to remove warps. The other thing is that you have to be very careful not to let the two sides touch when covering both sides of a thin structure (e.g. a tail surface). If they touch, you will probably not be able to separate them.

[TMaxxBenny25]

Looks fun !