Hi all.

I think i had asked a similar question before, so i apologize if it is a repeat. Does anyone actually take a temperature reading on the outside of the fuselage
during the engine run to see how hot the fuselage's surface actually get? After several coats of BVM heat shield, mine still pretty hot when i let the engine idle
for about 3 minutes. I am seriously thinking about putting additional heat blanket despite the additional weight to protect the area around inside fuselage.
Thanks all.

Make sure the distance from engine to pipe is correct (very critical). Sounds as if you have restricted air flow...thus the rise in temperature. What engine and pipe are you using?

Tell us what airplane you have and what engine is installed, bypass , etc. There can be allot of reasons the fuse can get hot. Most come down to lack of proper air flow like Lewis said.

It should be warm to the touch in most cases but if you can't hold your hand on the fuselage you probably need to figure out why.

I noticed you live in California, what are temperatures your flying in this time of year?

The engine is Simjet and the pipe was the older BVM single wall bi-pipe. The pipe is connected directly to the bypass shroud.
It seems that there is plenty of air rushing by between the bypass and the engine case.

What airframe?

The problem at idle is primarily radiant heat from the pipe and on a lot of applications there just isn't going to be enough airflow at idle to do provide adequate cooling. If you add a ceramic blanket that will slow down the heat transfer such that you now might have to idle 4 minutes before it gets too hot.

A much more effective way to deal with radiant heat is with a reflective surface. I recommend that you get some aluminum tape and install it where the fuse is the hottest. The hottest section is near the engine exhaust cone, and as you get further away from the engine the pipe gets cooler. I usually install tape inside the fuse from about the center of the engine to about the middle of the pipe, depending on how long it is.

If you do a search you will find several threads on insulation and heat protection.

Joe

Hello Gary.
The airframe is Rafale from AD. Seems like the hottest section wasn't right after the exhaust cone of the engine, but
rather closer to the last 1/3 of the pipe's end near the end. I think it will be adequate for a short taxi to the runway, but i just
like to ask all of the experts here to be sure and safe. It is warm enough for me to keep my hands there for about a 45 seconds
to a minute or so. However it was hot enough to make the fiberglass little bit softer then normal when it is not running.

Well, looks like after a search as you experts suggested, the solution to this seems to lies within Home Depot store then. I will try
the aluminum tape tomorrow and will update as to how it went. Thank you so much everyone. It always a great help from all of you.

Best regards.

You stated the pipe is connected directly to the shroud. Still the distance from engine to pipe is very critical. <span style="font-size: medium">The engine may have to be moved forward in the shroud to get the correct distance.</span> If the enging is close to the pipe opening, move it forward. Jet Central requires 1 1/2 inch from the end of the pipe. More power and cooling at this distance. My hand held infrared detects a cooling of the fuse once the engine starts. Note the separation of the engine conefrom the pipe in the photo. I can actually place my hand on the pipe at full throttle without any harm. Good luck on this problem.

<span style="color: rgb(255, 0, 0);">It is warm enough for me to keep my hands there for about a 45 seconds
to a minute or so. However it was hot enough to make the </span><span style="color: rgb(255, 0, 0);">fiberglass</span><span style="color: rgb(255, 0, 0);"> little bit softer then normal when it is not running.</span>

Not sure what a single wall bi-pipe is exactly but if the fiberglass is soft that is definitely too hot!!

Is it a single wall pipe or a double wall pipe? The steps you take to fix this problem will likely be different for the two types of pipes. Getting air to move out of the fuse might be different for single wall pipe depending on a number of factors; whether you are running an enclosed bypass or open bypass, whether the pipe is attached directly to the bypass or are you using a bell mouth (as mentioned by Lewis), etc. I have found that in most cases adding more insulation is more of a band-aid than a fix.

When you are sure you have the engine to pipe gap right like Lewis indicated then try the following;

There is probably a former at the rear of the fuselage that centers the pipe. On both of my Aviation design airframes these are solid. If yours is the same then you can drill holes in the former around the diameter of the pipe to allow air to bypass and flow around the pipe and out of the back of the fuselage. The other thing you can try is to make sure the pipe sits inside the rear of the fuselage about 1/4" and this will create a vaccuum effect around the pipe to pull more air out of the fuselage.

Let us know if you are running a single or double wall pipe.














Gary

Gary,

He said in post 4 that it was a single wall pipe.

The pipe is a single wall bifurcated from bvm. It is situated about 1.5 inch away from the Exhaust cone. It is connected to the bypass tube.It is connected to the bypass tube. The rear of the pipe is located 1.25 inch insideOf the fiberglass exhaust cones. Yes the rear former is solid. It is a full enclosedBypass. Thanks. ByThe way, just in case I have to get a new double wall pipe. Which company would you guys suggest that makes high quality pipe?Thanks again guys.

I saw the post but it said single wall "bi" pipe. I didn't really understand what he meant but I see it is bifurcated.

\
That may be your problem, and would explain why the rear of the pipe is hottest. It should be more like 1/4 to 1/2 inch inside the exhaust cones. My quess is that you are not drawing air out the back and some exhaust gases may be getting released inside the fuse. My suggestion is that you clamp about a 1 inch extension on to the back of the pipe outlets and see if that makes it run cooler. If that's it then you should re-mount your pipe and engine rearward.

Good luck,
Joe

I agree with Joe that the clearance at the tail cones shoud be around 1/4", this creates a vaccuum to help pull air out of the fuse.

Additionally, if it is a single wall pipe with a fully enclosed bypass the only air flowing through the pipe is hot air. You need that outer wall on the dual wall pipe to remove the heat immediately as it comes off of the inner pipe, otherwise it builds up and just sits in the fuselage. With your system being totally enclosed there is no way for hot air to exit the fuselage. You might try drilling the formers as I suggested but that will only help if there is enough fresh air getting into the fuselage through other openings such as gear doors, etc.

You really need a dual wall pipe when you are running an enclosed bypass to get proper cooling.

Call Tam at Tamjets and I am sure he can make a pipe for your application.

<div style="margin: 0cm 0cm 10pt"><span style="font-size: 9pt; line-height: 115%">This is your problem. If I was setting this up I would drill 10mm or biger holes all the way around the former that surrounds both pipesandstrengthen with carbon/epoxy if necessary. Then make sure the bifurcated pipe ends about 3/4 inch before the fibreglass nozzles do and line the nozzles with some stainless sheet/ ally sheet or even heat shield might be enough. Doing this will draw cooling air through the fuse and things will stay cooler. Currently you seem to have made a very effective oven and I don&rsquo;t think any amount of foil, heat shield or ceramic blanket is going to keep it coolat idle.</span></div><div style="margin: 0cm 0cm 10pt"></div><div style="margin: 0cm 0cm 10pt"><span style="font-size: 9pt; line-height: 115%">Good luck</span></div><div style="margin: 0cm 0cm 10pt"><span style="font-size: 9pt; line-height: 115%">Jason</span></div>

Thank you all for the sugestions. I will try all that was suggested and will updates on how it went. Thanks a bunch again guys.

Hello all.

Ok, update time for this over heating issue. Thanks to all, i finally was able to control the heat in the aft bay. Only one layer of reflective aluminum foil does it.
I didn't have to drill holes around the rear former to let air out. After running the engine for about 5 minutes in direct sunlight, the aft end barely warm to the touch.
I put my fingers right by the gap between the pipe's end and the fuselage's fiberglass exhaust cones, i could feel all the warm air being pull out of the fuse and
rushing by my fingers with a considerable velocity. So i guess the pipe's end was located with the right gap inside the fuselage in the beginning, it just radiant heat
like Joe said and without it reflected off of the fuse to be draw out fast enough, it heated up the inside. So with the issue fixed, i thank all that had shared their expertise
idea. Good day all.