kevinh

kevinh

Well Known Member
Hi ya'll,

When I built my RV I did a couple of things to increase my heater performance:

* pushrod boots
* Tossed in a choir boy pad into my (single) heater muff

I was feeling pretty pleased with myself with the few cold weather trips before I took my plane to the paint shop. However, the flight down to Texas was at about -4C at altitude and I was cold.

For the return flight I tried a tip I had read on the matronics archives: I slipped some foam pipe insulation into the slider rails (from the inside, during the flight). This made a huge difference. And since the outside temps were identical and I only changed one thing I think this offers a good test of the idea.

The difference was light and day - the trip down I had two layers of fleece over some fancy inner liner. My legs were okay but my chest was cold. I started off the return trip with the same fleeces, but was down to just my thin bottom layer within a few minutes. I only had the heater knob out a few clicks.

Someday I may try sealing the little gaps in the baggage bulkheads. I'm no longer considering adding a second muff. Slipping in these little foam tubes is not super elegant but it sure does work.

For an example of the stuff I'm describing see:

froogle entry
 
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cockpit heating

Kevin,

I read your post and it made me smile because I made you same bone chilling trip and remember it well. In fact my father in law went with me to pick up my airplane and he kept talking about how he was cold soaked and the hours it took to warm up after we landed. It turns out the passenger side of my airplane is colder than the pilot side and I flew the last 3 hours while he sat over there and froze.

Reading your post gave me an idea which I plan to try that just might be a good bandaid for the sideskirts on cold days. My thought is to run a line of velcro on the horzontal surface just below the canopy sides, on the flat top of the canopy frame. Then cutting out some sort of light material such as what windbreakers are made of into strips the lenght of the side skirt and about 4" wide and attaching velcro to the edge of these. These strips could be rolled up and stored easily in the plane, would be very light, and would go on easy on cold flights and virtually stop all air from leaking on the sides as the vacumn pulled them snug into place. Basically a small removable curtain that the air can not get through to escape. I'll let you know how they work in a week or so.

Bryan
 
Here is some collected wisdom from flying both my RV-6 and Rocket in a cold weather environment. Let me preface my comments by saying they are based upon my experience flying in the Midwest. I found that normal operations are tolerable down to about 20 F. Below that, the cold is really noticable and sun warming through the canopy was not effective at keeping me comfortable.

1) The key to keeping warm is to keep air infiltration to a minimum. The push rod covers are a must. The worst area is the fit of the slider canopy and anything you can do to stop the sides from gaping is worth it.

2) You pretty much need to use two heat muffs, connected to one another in series. One muff won't cut it. Also, stuffing the heat muff doesn't do anything either. The problem is that you muff is already capturing all the heat it can from the exhaust. If you want to prove it to yourself, go flying in the cold, land, and then grab the exhaust pipe with your bare hand. It will be cool to the touch. To get more heat, you need longer muffs and more of them.

3) Neither of the above will keep your butt and back warm. For that, you need supplemental heat source, like electric seat heaters. Heat distribution is spotty at best from the heater valve so you may be warm, but your passenger may be cold. The seat heaters really make the difference.

Currently, I've flown the Rocket in temps below zero and have been toasty warm. I have dual heat muffs customized by Rick Robbins to be as long as possible, and so that they can connect in series with a minimum of bends. I also have dual electric seat heaters in my cushions with two power settings and pads for both the bottom and back cushions. It takes about 15 minutes for them to heat up, but they really take all the chill off of me. Also, my canopy seals very tightly against the side so I have very little air infiltration.

I played around with all the options on my RV-6, and these are the things I learned to do to actually fix the problem. YMMV.
 
Aircraft Exhaust Technologies

Call them and they can weld on heat transfer studs to your exhaust. I think they will do it even if it is not their exhaust pipe or Muff, although they make custom heat muffs as well. As Randy said two works, but if you have room a longer one with the studs may do it. http://www.aircraftexhaust.net/

Last is air IN and air OUT. Many find a reverse belly scoop (aft of the wing trailing edge, and some vents in the aft baggage helps draw air out, which promotes the HOT air (hopefully) getting into the cabin, improving the heat in the cockpit. I have seen vents in the elevator bell crank covers (way back under the Horz Stab). Not sure how well this location works.

George
 
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I am still on the wings. So with that, I have a question: On the heat muff, is the cabin air taken off the port closest to the engine and does the inlet air enter the muff at the end that is closest to the exhaust outlet?

Here is my point, if the muff is set up such that the cabin heat is pulled off the muff closest to the engine, then it is a "Counterflow heat exchanger" if it is set up such that the cabin inlet is coming off the muff closest to the end of the exhaust (furthest from the engine) then it is a parallel flow heat exchanger.

Conterflow HX is way more efficient than a parallel flow HX.

http://www.engineersedge.com/heat_exchanger/counter_flow.htm

Can anybody give me andy feedback as to how they have their heater hose routed?

Alton
RV7A
skinning the left wing.
 
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AltonD said:
Can anybody give me andy feedback as to how they have their heater hose routed?
Click to expand...

Mine is routed with the aft hose connection going to the firewall - exactly opposite of what you propose. But what you write makes sense! I think I might try changing things around a bit the next time I have the cowl off. Thanks!
 
Go with the flow, or against?

AltonD said:
Conterflow HX is way more efficient than a parallel flow HX.

http://www.engineersedge.com/heat_exchanger/counter_flow.htm

Can anybody give me any feedback as to how they have their heater hose routed?

Alton RV7A skinning the left wing.
Click to expand...
Heat Transfer! My pet topic when I was an undergrad engineering student. As far as how to route hose, it all depends on where the heat muff is located, the cabin / firewall valve is and where you are getting fresh air.

Try to route the cabin heat counter flow if at all possible. There are basic principals at work, temp differential, flow and surface area, but the short answer is what ever is easier to route and counter flow if at all possible. It would be easy to test the differnce between counter and parallel.



Bottom line, a crap heat system will not become fantastic changing to counter flow. There is a lot more going on than just the direction the air moves in the muff.

I am all for efficiency, but there are many factors, heat muffs are too small, the flow is too fast, insufficent surface area, cabin (cold) air leakage too great, cabin exhaust air is stagnated and hot cabin air pressure too low.

The best thing you can do is seal the cabin from cold air getting in, have a controlled place for air to egress. If the cabin is air tight, no air in or out, that would also be bad. Even in Jets have an OUT FLOW valve in the aft fuselage to get airflow.

Folks have found running two heat muffs in series solves their freezing issue in the winter. Also left baffle inlet ramp just aft the cowl inlet give the most air. There are 100's of variations.

George
 
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