thunderchief

I finally finished scratch building a 1/10 F-106A. The first run up showed high temperatures in the 26mm area where the turbine ends and the exhaust pipe starts. The epoxy paint actually bubbled on the fuse. I went in and put three coats of BVM heat shield. Today I ran a second test. Temps were running 85 to 95 F this time. Once I did get a 111 F reading. What is an acceptable temp. The plane was not moving. The epoxy resin I used is listed as 150 to 195. Here is a short video of my test, Any thoughts would be welcomed. ..
http://www.youtube.com/watch?v=eTvnS2eOdIg

Thanks
Glenn

bluescoobydoo

what is the distance between your turbine and tail pipe ? does it have a bell mouth?

thunderchief

Bluescoobydoo, I am using a Jet Central Bee II ks turbine, and a Wren single wall pipe. The distance is 26mm and the pipe does have a bell mount. There is no by-pass in the plane and because of the size 1/10 scale the turbine's exhaust is fair close to the fuse side,,,,,maybe 2 inches. The BVM heat sheild seems to be doing the job but I would like more insurance. . There are a couple of thermo tapes I am thinking of trying but the first one I tried would not stick to the BVM ceramic coating.

hmjets

Make a double pipe, in the seconde one you can use aluminium thick foil.

Joe Westrich

My Feedback: (95)

Sweet 106!

I would use ceramic blanket throughout the aft section of the airframe. I did it with my 1/8 F-16 and it took it from too hot, to just warm. The BVM stuff is good to keep stuff from burning but it doesn't insulate like the blanket. Dreamworks.... http://www.dreamworksrc.com/catalog/Ceramic-Blanket

Also, is that 26mm from the bell mouth or from the beginning of the pipe inside the bell mouth? It should be from the pipe inside the bell mouth.

Joe Westrich

My Feedback: (95)

Also, I wouldn't say 26mm (or about 1in) is way too far but it could be a little closer. Most of the time I gap them between 3/4 to 1-1/4. With a smaller turbine I would got on the lower side.

thunderchief

Joe, guys, thanks for the ideas. I tried to set up the pipe per the Wren instructions that came with it. Wren claims a 5% increase in thrust using their pipe. Moving the pipe and turbine closer might be the answer . Even a small lose of thrust would not hurt. The 106 weighted in at 15lbs 3oz and the bee II ks is rated at 15lbs 8oz. Naturally those numbers are at the factory. And the highest heat reading is the small open area between pipe and turbine. Thanks again

bluescoobydoo

if you want a heat blanket try a plumbers heat blanket that they use for soldering copper joints I use it to protect servos etc
http://www.screwfix.com/p/rothenberg...stid=21369#_=p

Jgwright

The gap you are working with is fine, I did the original tests with Wren. Also I did once had a JC Bee engine. On my smaller planes where the exhaust is close to the fuselage side I use sticky backed aluminium tape used for car exhausts to protect the area where you have had heat issues. More recently I have used BVM heat shield and that works very well. Alternatively the ideas for ceramic blanket are worth trying. Personally I would not have thought 111 F was a problem. When I read you post first I thought you were quoting C values. I would never start the engine with the hatch in place as that would be asking for problems with a tight installation. I was pleased to see that you had the fire extinguisher to hand. It is very common to see people getting very casual about starting their engines with the hatch closed and no extinguisher close to hand. I suspect your paint bubbling was caused by a hotter than expected start rather than normal running temperature.

I have had many small planes with the exhaust close to the fuselage sides. The key thing is to avoid the hot start. On some of my planes like the Savex L39, there was no hatch and starting always carried the possibility of a hot start damaging the paintwork above the engine.

Very nice plane by the way, nice to see something different. I would just go and fly it without worrying any more.

John

thunderchief

John, Thanks for the reply. I never start with the hatch on....although the idea has crossed my mind! You mentioned that you did tests with the original Wren exhaust pipe. What are your feelings on single wall vs dual wall pipes?
Thanks Glenn

hmjets

hmjets

Jgwright

Glenn

The single wall pipe is fine so long as you do not have a really hot start. I used single wall tubes in a variety of models like the Savex L39 and AMD Hawk. In my recent models like the 6 engine Arado I used single wall to start with but after a slightly hot start removed the pipes and fitted double walls. The pipes run very close to the epoxy making it much more susceptable to overheating the epoxy.

John

Harley Condra

My Feedback: (4)

Glenn,
A properly set-up pipe will remove heat from the inside of the airframe.

The aft end of the inner pipe should terminate about .700 to .750 forward of the outer pipe aft end. The high speed hot exhaust gasses coming down the inner pipe will suction the air inside the outer pipe and evacuate it out the back. In simple terms, this is called an augmentor.
Personally, I don't like plenum (non bypassed) installations as they are not as efficient, but they are much simpler to install.
See the photos of the aft end of a couple of airplanes...Super Bandit and Ultra Bandit. They are both bypassed, and have the type of pipes that I have described.

Best regards,