Heat Loss In Small Aircraft 3

[drawoh]

We have some small aircraft used for surveying that are getting too cold for our operators in winter weather (-15°C). We are looking for ways to seal the holes we cut through the fuselages for our sensors. The aircraft are fairly old, and the seals for the various doors are not all that good. One of our aircraft is a Piper Aztec, which has little or no heating capability, even if we do seal the everything effectively.

Does anybody have a good idea of how much heat is lost through the aircraft skin?

At some point, I am going to try to work out a fancy sensor mount with a sealed skirt around it. I want to ensure this is going to accomplish something.

JHG

 

[GregLocock]

You can sssume the oter surface of the emtal skin is at ambient, and the inner is at cabin temp.

The rest is just maths!

Cheers

Greg Locock


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[drawoh]

GregLocock,

I tried that. It works out to around 15KW.

I have just worked out an air boundary layer due to 10mm insulation, and I am getting around 170W. The insulation itself conducts heat, and there is a boundary layer outside, so this is all quite crude. Does this match anybody's practical experience?

JHG

 

[GregLocock]

Your numbers are in the right ballpark. An 8 kW heater in a car will maintain the cabin at a delta of around 40 deg C.

But a car is better insulated than a plane, and the airspeed is less.



Cheers

Greg Locock


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[MikeHalloran]

Is the original cabin heat system worn out, removed, inadequate, or just turned off?


Mike Halloran
Pembroke Pines, FL, USA

 

[berkshire]

On that aircraft you should have a Janitrol Gasoline fired heater in the nose bay. If it is working properly it should keep the cabin toasty. The cabin walls should have fiberglass batt insulation to about R3 . I know its not much. The tail cone will have no insulation at all.

If the heater is not working, These folks can get you a nice new one.

http://www.aircraftheater.com/

B.E.

 

[drawoh]

Is the original cabin heat system worn out, removed, inadequate, or just turned off?

Inadequate.

Also, the -15°C is the thermometer on my front porch. The aircraft can be up at 10,000ft.

JHG

 

[MikeHalloran]

How big a hole did you cut for your sensors?






Mike Halloran
Pembroke Pines, FL, USA

 

[drawoh]

How big a hole did you cut for your sensors?

Around 20"x10". On one aircraft, they have sealed around most of the hole. The other aircraft appears to have a 1/2" gap between the floor and the mount plate on top of the hole. Most of our sensors are shock mounted, which requires a built-in flexible gap in our structure.

JHG

 

[MikeHalloran]

Okay, so get some soft weatherstripping and take care of the gaps.

After that, apply a small piece of black electrical tape to every interior surface of the cabin, go aloft, and record their temperatures with an infrared heat gun. Coolest large surfaces would benefit from more insulation.



Mike Halloran
Pembroke Pines, FL, USA

 

[berkshire]

Drawoh
Mike has pretty well covered the bases. The cabin air heater does not have a very high volume of air output, and holes in the structure will overcome it pretty quickly.

A source for additional insulation is Aircraft spruce in the States or Canada

http://www.aircraftspruce.com/menus/ap/insulation.html

There are other companies listed in Trade-A-Plane.
One thing I have done for camera mounts in bellies of aircraft, is to use 4" polyurethane mattress foam and custom cut a gasket to fit around the camera.
Hope this helps.
B.E.

 

[KENAT]

OK, not familiar with your specific aircraft but...

If the insulation doesn't cut it any way to try and duct some of what warm air there is to the camera?

Or, if you can afford the mass, how about a hot water botel;-).

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