Jim Cattanach

Just had the first flight with my Skymaster F15. I have a Simjet 1700 turbine that has been uprated & puts out about 9kg thrust.
The flight was excellent & the plane was easy to fly & land.
The only problem I am having is getting it to lift on take off. At full power it uses about 200 yards to get airborne off a smooth runway, even using the maximum suggested elevator movement.
The CG is as suggested on this site.
I have 3.5 inch wheels on the mains & a 2 inch on the nose & the plane looks reasonably nose high.
Has anyone else had a similar problem?
Any suggestions are most welcome.
Regards
Jim.

SAP_2000

Hello Jim!

I also fly the SM F-15 with a 3000 engine and these are my settings.

I feel it is a bit nose heavy with the CG at the front former, so I have moved it back one inch or 2,5 cm. Nothing dramatic about that. Still drops the nose gently when it stalls, and does not feel tail heavy at all. I will probably move it a bit further back in the future.

I have also increased elevator movement to about 65 mm. I'm using 25% expo on the elevator. I use about half elevator on the take of roll, and it gets airborne in about 50-80 meters. Also no problem keeping the nose high during the roll out.

So try to move the CG a bit back and increase elevator bit and you will be fine. Even the CG shift alone would probably make a big difference on your take off roll. Last pic is of a roll out...

Also make sure you have the correct distance between your exhaust nozzle and the pipe for minimum thrust loss. about 1.5 to 2.5 cm.

Hope this helps.

Aero65

My Feedback: (2)

Hello Jim

Staale has it on the money, thank you for your help! Nice pictures too.

Im flying my Skymaster F-15's with the CG a bit farther aft than the rear most position shown in the directions. I will have to confirm the position before I post it.

BluFox

My Feedback: (10)

Jim:
I agree with Staale and Duke without question. I flew mine (FTE-750) for the 10th time yesterday under the watchful eye of my mentor Todd Witkoff. CG is just ahead of the forward aluminum wing mount by 1/4 inch. Rotation is smooth and crisp in about 200' or less. I could actually pull it off sooner. CG changes in flight as fuel burns off and OH MY the landings are beautiful. She comes in nose high ( I am on low rates) and very stable with 1 click of flap. Holding her off is no problem either. Remember to balance with gear down and NO fuel other than the UAT. Enjoy! OH, forgot to mention I am using stock wheels on the mains and nose.

BRG,
Eric

Jim Cattanach

Many thanks for all the advice, it is most welcome.
I noticed my tires on the mains were a little soft, this may have added some drag.
I have also fixed a quarter inch spacer under the nose wheel retract to lift the nose slightly to see if that helps.
Regards
Jim.

Jim Cattanach

I think I may have solved the problem of the long take off runs. I had fitted eurokit retracts,brakes, oleos & wheels I had for my Avonds F15. Due to problems with the wheels & tyres, I replaced all this with the proper Skymaster set up. Skymaster retracts when fitted are 1 inch further forward than the eurokit set so making the plane lighter at the front. This combined with the Skymaster mains oleos being shorter & increasing the angle of attack should help the plane rotate in a much shorter distance. If the weather is ok, I should find out this weekend.

Regards

Alexdu

My Feedback: (3)

Staale: What a great picture!!!!![sm=thumbup.gif]


Regards

Alex

EddieWeeks

The way you fix that problem is you shift the gear forward...

You may be able to put some washers in the back of the main gear to move
them some.. I don't know if you can do that with that plane but
it will most likely rotate much easier..

Eddie Weeks

Pyolet

I concur with Eddie. Please DO NOT change the CG of an otherwise good flying plane to fix rotation problems. Fix the rotation problem by the reducing the distance between the CG and tire contact point to lighten the nose on the ground, or raising the nose by lengthening the strut, etc. Otherwise you are putting the cart before the horse IMO.

sonic bang

Well said Pyolet

Irfan

SAP_2000

Thanks Alex!

That was a lucky shot...
My friend took that picture with my Canon SLR camera at our field this summer. I probably did around 30 fly-by's like that during that flight, and that was the only picture that turned out sharp enough and had both the plane and me in it....

Most of the pictures taken that day looked something like this:


I wish I had the climate you have right now...[&o] Here, there is nothing but sub-zero temperatures, freezing winds and snow falls.... And I want to go flying so bad...

cairoman

Staale,

You are more than welcome to come and fly here. 95% of the time, the weather is super in the winter. It's the summer that we can't stand!!!

Jim, the weather is bad today, but tomorrow will be full sunshine. Time to give the F15 one more try at LM.

Chris