wiking

I have done some ground test on my JL F-15 and it has not gone so well.The outer tube sucks against the inner tube when it goes over 50% power does any one have any hint what the problem can be?
The engine is a Jetcat P80 and the distance between the outer cone of the P80 and the pipe is little more than 1" (27mm) see pic and the pipe has no bellmouth ring.
And the fiberglass duct gets warm from the end of the hatch and backwards in which direction should I move the engine?


Many questions from a newbie[8D]



Sorry for my bad english[:@]

Per Andersson
Sweden

bevar

My Feedback: (27)

Sounds like maybe the engine is too close to the pipe. Take off the bypass and take a pic of it that way.

Beave

wiking

Thanks for the reply Beave,
Here is some more pic,s of the installation.

Per Andersson

JMCJET

Your problem is not the engine position, but no air flow betwin the inner and outer tubes. At the rear end the outer tube must be, at least, 5 mm longer than the inner tube and they must be concentric all the lenght with 5mm gap betwin them. As far as I can see by the picture, the air can´t go betwin pipes. You can drill one or more holes in the outer pipe to allow more air circulation if the rear keeps hot.

Saudos

wiking

Saudos the outer tube at the rear end is about 8mm longer than the inner tube. does it still help to drill holes?

Per Andersson

JMCJET

You must be sure that the air can flow betwin the two pipes. The holes in the outer pipe are only needed if, for some reason, you have not enough air flowing betwin pipes. When the engine is running, the high speed of the exaust gases build depression in the exaust pipe. So, the air must fill the "space" free. If this doesn´t happen the pipe collapse. This is true for both pipes, but is more critical in the inner one. The gap betwin the two pipes in the rear end is a very smart idea because it sucks the air from the other side (turbine side). This air flow keeps the rear of the plane cold. Your problem is that the air can not go inside the gap of the two pipes and than you have depression and a collapsed pipe.

So: 8 mm gap in the rear end is OK. You must check why the air can not go inside the gap betwin the two pipes. Fix the problem and try again. If the rear end of your plane is still hot then you can drill some holes in the outer pipe to allow more air inside the gap of the two pipes.

Saudos is not my name, but our way to wish the best.

Saudos
JMC

jeff sewell

My Feedback: (1)

Hi,

I agree with the other guys but also ensure that the engine is aligned centally down the pipe and not pointing at the wall.

i've seen similar occurrences in other jets where this was the case...

Cheers

Jeff

wiking

Thank you guys for the help!
Sorry about the the name there JMC but the hot area is not at the rear end of the pipe its of the rear end of the fiberglass duct
behind the engine.
could it be that the outer pipe is so weak so it can not stand the pressure?
I am going to try and adjust the engine as Jeff said.

Regards

Per Andersson

jeff sewell

My Feedback: (1)

Hi,
The outer wall is just to duct air through for cooling. When the much thicker part of the pipe gets hot it causes this phenomenon. Not sure why but it does...!
These pipes have coped with 160 size engines with no problems.
Let me know how you get on...

Jeff

USSCAT

Wiking,

Does the outer tube fit tight in the fiberglass bypass? if so you may want to pull the tube out a bit and allow a gap between the outer tube and the bypass. I think you have a situation where the air is getting sucked out of the outer tube from both end hence collapsing the outer tube.

Hope that helps.

regards,
Mike

Rider-60

My Feedback: (17)

Get rid of the bypass, put a bellmouth instead and your problems will be gone.
I thought that JL pipes were now delivered with a bellmouth as standard?

Florent

757Driver

My Feedback: (90)

Hello gentlemen, I'm new to jets but I have to ask. Is the Bifurcated pipe mounted in such a way as to allow for expansion in the longitudnal (lengthwise, nose to tail) axis? If it is rigidly mounted at both ends and the metal pipe expands due to the increase in EGT at higher power settings this could be a problem.

afterburner

My Feedback: (18)

I have the JL F-15. My pipe didn't come with a bellmouth and I'm using a Jet Central Eagle and have not had any problems with the pipe. I'm using the bottom half of the bypass but like another poster said, I have a slight gap between the end of the bypass and the pipe. This might be the problem as well as making sure the exhaust is centered and straight.

Marty

USSCAT

[sm=thumbup.gif][sm=thumbs_up.gif]

thumbnstick

My Feedback: (169)

I have the exact setup on an older version of the F-15. I had to leave a gap between the bypass and the pipe. This allows the outer tubing to get the air it needs. No bell mouth. My gap is about 3/8". I also had to use BVM Heat shield on the bypass do to the heat after shutdown. The gap also helped with that cooling. The best solution would be to not use the bypass and use a bellmouth. The bypass is just a little bit small for the P-80 can. You can see mine fly on SKS Video's Florida Jets 2008. I flew it with the tanks and missles, which made the CG go tail heavy. I mistakenly say 'nose heavy' in the video. It is a great flying jet, let me know how it goes.

jroth

My Feedback: (60)

Hi,

I am finishing my JL F-15 and currently working on the bypass, pipe, and engine installation.
I want to use the bypass because I think it helps keep the engine separate from the rest of the plane wiring, tubing, etc and FOD from the wheels wells.
I removed the bell mouth from the exhaust tube because I am using the bypass, if I was not using the bypass I would use the bell mouth. The inner pipe is about 1/2" inside the bypass and the outer pipe is about 1" away from the bypass.
I am cutting into the inlet to allow the electric start motor to approach the front fuel cell, which will allow me to leave a 20mm gap between the engine and the pipe inlet. This positioning will also allow the pipe to remain inside of the tail cones by 13mm to allow the venture effect to help the pipe cooling.

I am not an expert, but after checking around this seems to be the preferred installation method.

John

Steve Collins

My Feedback: (8)

This probably has nothing to do with this problem but my understanding is that the type of turbine tail cone shown in the picture was most suitable for installations where the turbine is hanging out in the wind, similar to a Bobcat or a Hotspot style installation. I have been under the impression that it is best to use the larger, outer tail cone in a bypass installation.

I am wondering if this is why there is a heat problem at the rear of the bypass?

I am not familiar with the thrust pipe on the JetLegend F-15 but, on my dual wall pipes, the outer wall does not come all the way up to the bypass.

thumbnstick

My Feedback: (169)

Each installation will have its own problems. We are dealing with some very high flows of air here. This causes differential preasures throughout the inner airframe. Ones mans answer is not always anothers soution. The gap between the bypass and the pipe should relieve the effect on the outer wall of the pipe that you are having. It does not take much of a pressure difference here. Just handling the pipe makes is cave in easilly. Its a no wonder everything doesn't suck in the engine. You might try starting and running the engine with the top cover off the bypass and see if the additional air to the pipe relieves the problem.
Keep plugging, this is a nice flying airframe! The bifurcated pipe makes it sound awesome in the air! A deeper roar than most.
Jack

wiking

Jack,
All the pic,s is with the hatch off and it got worse when i put the hatch on.
I have picked up a bellmouth ring as a last solution if something else does not work.
Thank you all for the support i will report how its going.

Regards
Per Andersson

thumbnstick

My Feedback: (169)

Here is a Pic of my P-80 in the JL F-15. No bellmouth, but good spacing between the pipe and the bypass. ( if the Pic doen't go up right, I will e-mail it to you)
Jack Graham

thumbnstick

My Feedback: (169)

i'll try the pic again

thumbnstick

My Feedback: (169)

The full pic of the F-15, the JL T-45's

wiking

Thank you every one!
I had not solve this problems so quick and easy with out you guys.
The only thing I did was to open up vent holes in the duct and its working

Best regards
Per Andersson

Molnar142

My Feedback: (38)

Jack,

Did you sell your F-15? The used one I bought over the weekend looks awfully similar!!!
I'm thinking this one must have been yours after watching the SKS video of you at the 2008 Florida Jets.

Regards,
Mike

Sorry for the messy room...it's clean now. I promise.

thumbnstick

My Feedback: (169)

No mistaking it. That was my paint job. My buddy and I did the blue/grey job at his shop and I did the weathering and all the decals. I sent you my ph#s by email.
Jack