Build Log Kyosho/Minium F15 Conversion

[Murdock-Monkey]

Latest play with the Minium kit - I've reduced Steve's F15 Park Jet plans (An Excellent set of plans by the way) down to approx 12" Fuselage/9" Wing.

Uses aileron and elevator control, plus pusher prop.

A few build photos and finished some of the finished thing. By having the battery compartment under the canopy the C of G is spot on, however it's a tad porky and needs more thrust. Can sustain level flight (Just) on a new battery however the second you roll/turn it loses too much height.

Need some advice/help please...

Do I,

a Change the motor/gearbox, if so, for what.
b Try and lighten it some more - replace surfaces for thinner depron etc.
c Enlarge the wing area slightly.

Any other ideas greatfully recieved - would really like to get this flying nicely.

[Pouncer]

What's your AUW ?

From the look of it you have a considerably higher wing loading than the original Cessna (18 g for 2,2 dm^2) I'd guess you have roughly twice that.

You can still make it fly, but at higher speed.
The easiest thing to try is to replace the prop with a higher pitched one, maybe with a cut back Plantraco 100*80?
Possibly a GWS 3030 if such a beast exists?

Next step is more power, replacing the motor with a 7 mm Super Slick, either an Orange with 4:1 gear and a 5030 prop, or a Blue with a cut back Plantraco Tri Turbo Fan.

The last option is probably your best bet, ask Ghostmechanic, he's done a lot of tinkering

All of the above is going to affect your CoG to various degrees so be sure there's enough room in the nose to compensate.

And good luck!

[Murdock-Monkey]

Thanks - advice much appreciated, never attempted a pusher/jet design before so all new to me.

[Pouncer]

Again, it all comes down to what the plane weighs ..

It looks like you've been using 2 mm Depron throughout and that can get a little heavy.
This may not be the answer you're looking for, but I'd consider making a second one a little larger, say 11 or 12" wingspan, and saving the 2 mm Depron for the wing and making the rest out of Ifoam?
I wouldn't be surprised if the new airframe weighed less than the old one, and your wing loading would drop significantly.
this would leave you with more breathing room when it comes to picking a working propulsion.

All of the items I've listed are available from Indoor Flyer in Harpenden.

[Chris T]

Very nice! Please do not enlarge the wings. It looks too cool as it is.

I would try a 7mm direct drive or similar or at least less gear reduction with a smaller prop. I think you need more efflux speed, not more thrust. I have had similar problems with too large props on fast planes. This prop is obviously too large for a fast jet.

Keep it going, it will fly...


Chris

[Mike Taylor]

That's a nice looking build.

I also think the foam could be thinner without losing strength. 2 mm for the wing is fine, but the boxed fuselage can be lightened a lot with split foam. There are two of each piece, and the weight does add up. Lighter foam would also let you do without the lightening holes which have to add a lot of drag.

A quicker solution my be a different prop. I have used the Plantraco 100x80 prop (I think they came in the starter pack) with the Cessna's gear in a 10" Skyray that was just too slow with the stock prop. The added pitch brightened its performance right up. It does draw more power though and taxes the stock battery. Cutting one down as Pouncer suggests may be a good idea. I have also heard the U-80 works well with this motor/gear combination.

[Murdock-Monkey]

If I can get it light enough, and get a better improvement with the Plantraco prop or 7mm motor, i'll cover the lightening holes with Tissue. Actually thinking about it - I could probably lighten up a fair bit of the structure.

It flys, just, but too many turns and it hits the ground.

If I can get it performing nicely i'll rebuild with thinner foam and learn by the mistakes on this build. Really does look nice on the desk, would be a shame to leave it a static model.

[pcolla1]

Looks sweet. You should make a kit and sell it, once you get everything sorted out. People would purchase in a hearbeat.

[Murdock-Monkey]

Originally Posted by pcolla1

Looks sweet. You should make a kit and sell it, once you get everything sorted out. People would purchase in a hearbeat.

As much as i'd love to - I could NEVER take credit the for Steve's plans, not charge people for something they could easily build themselves - however once I get it flying right - I will document everything and draw a plan to go with Steve's showing exactly what's needed to get it flying with the Kyosho kit.

More progress today (Due to lack of power, i've been launching from the 3rd floor at work and gliding under power across the carpark - needs must LOL) I found a problem - the wings were too short and when you tried a turn it actually stalled the wing making it almost impossible to control - I made a new set of wings - with a much better core shape - and just slightly larger, (Will try to get a photo up later). Have made the wing just 10mm longer with a slightly wider chord and it now glides and rolls 360degrees in the blink of an eye.

Just got to sort power - Epilot you'll have an order coming your way as soon as i've posted this ;-)

Anyways onwards and upwards - going to start MK2

[Murdock-Monkey]

PS - If anyone does attempt it - I used the non-tiled pdf plan and scaled it up 120%

[Murdock-Monkey]

Originally Posted by Mike Taylor

That's a nice looking build.

I also think the foam could be thinner without losing strength. 2 mm for the wing is fine, but the boxed fuselage can be lightened a lot with split foam. There are two of each piece, and the weight does add up. Lighter foam would also let you do without the lightening holes which have to add a lot of drag.

Mike what do you mean by Split foam?

[Mike Taylor]

Depron sheets that have been split with a hot wire to thinner thicknesses. I-foam is made like that, but you can do it yourself without too much trouble.

[Murdock-Monkey]

Cracked it :-)

Well, remade it is more like it.

Still got the original for when the new motor arrives, and i've had to use the gear that was in the flying wing.

1mm depron for the entire construction bar the wing that's fashioned from 2mm depron.

Only had a quick test in the garden (It's pitch black outside). Managed a circuit and brought it back to me, very twitchy, think I've got a little too much throw on the elevator

Rolls very quickly, will try to get a video up tomorrow. Picture of new fuselage attached.

This is only using the standard motor and gearbox, but i've chopped the prop down to almost half size and increased the pitch (Heating in boiling water and twisting).

[metroidrc]

nice!!! now if you can try putting that motor in a fan unit we'd be all set..

[Bugman Jeff]

Looking good Can't wait for the video.