Unusual Trim Change Problem
 

The old setup is now out of the plane. I am waiting for delivery of the P-120 in order to reinstall and do some more running and see if I still experience the same thing. What I was really looking for was to identify the problem and take steps to avoid it with the new installation. I thought there might have been another pilot who may have wrestled with this situation before me and who had found a solution. I am planning to do the heat gun on the servo test and see if that is the cause. It cannot be an expanding pushrod or sleeve for that rod as that would push aft on the elevator control horn and give a down elevator change.

The Jet-Tech by-pass is considerably larger in diameter and appears to have about double the airspace between the by-pass and the turbine. It was specifically ordered for the P-120 and made to work with that engine. When I ordered the old pipe from Tam, it was specified that it was to be used with the RAM 1000 so I am sure Tam made a pipe of the correct diameter. The outer pipe stuck out of the tail of the plane nearly an inch. I had paid particular attention to getting the location of the RAM in the bypass in accordance with the recommendations in the RAM manual. The fuselage is not painted yet but it never got hot enough to blister or discolor paint. A friend of mine has an F-18 which is painted black on top(a NASA color scheme) that gets much hotter than mine did just sitting out in the sun. He has never noticed a trim change such as the one we experienced with mine. He uses Futaba servos in his plane and my T-33 uses JR with the elevator servo being a digital 8411.

It remains to be seen whether the phenomenon re-occurs with the new setup. I have got my fingers crossed until then.

small bypass?
 

aptar, you say old bypass is much smaller than new Jet-Tech! this maybe a clue...what size turbine was the original bypass designed for?
keep us posted as this will be an interesting test, Another thing to try would be to install your turbine without the bypass and see if heat is still high, only if the problem persists. Of coarse be sure to check your turbine positioning within bypass, allowing good flow of air around engine and into pipe...

Trim Change
 

It was designed for a RAM750 which is the same physical size as the 1000.

Call me on my cell
 

Aptar,

If you run hot at idle. There isn't enough air drawing to cool the pipe. Try run with the hatch open and check the temperture. Close the hacth and check the temperture again. If the temperture make a big jump. The problem is no air can get in the fuse to cool down the pipe. This problem can be solve very easy.
Find good location to get air in the fuse. I normaly cut two vent on each side of the inlet. You can also cut some vent from the bypass. This will feed air in when model is flying.

As for trim change. Try out with different servo, rx and module.
This kind of problem happen to me once. And it happen on the prop airplane. I put in new RX. The problem was solve.

BTW, Ram 1000 and Jetcat P-120 are the same diameter.
You don't about getting another pipe.

Brg,
Tam

More heat...
 

apter, Tams right re- fuz venting, try cutting small triangular vents similar to naca ducts, one in either inlet! about 1" long, place these inside, closest to fuz center. Also if there are any scale grill vent locations on the T33 you can open these up and make functional.

Also you mention original by-pass was for RAM 750, although of similar size to the RAM 1000 its the through put of air volume that we are interested in here, as the 1000 will be requiring a greater volume of air to operate efficiently/cooler, this larger by-pass I believe will help the situation greatly... in fact I would bet on it! : ) - Good luck with the new P120 set-up

Cheers