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Air Conditioned RV6!

Radioflyer

Well Known Member
I recently had the pleasure of meeting a VAF member who goes by the handle "hgerhardt", name omitted to protect the innocent ;-). Since I was in the area, I had asked to check out his RV6. His plane has to be one of the more spectacular builds in the fleet and sightseeing over Catalina Island and the stacked-up shipping fleet in the bay was a treat. However, what surprised me the most was that we flew in air conditioned comfort...in the tiny RV6.

The AC was turned on for about an hour from first engine start, taxi, takeoff, low altitude cruise, landing, and shutdown back at the hangar. I forget what the OAT was, but under the bubble canopy it would normally have been at least in the mid 80's F. In the cockpit, it was about 65F. After we landed and got out of the plane I noticed a wet spot on the ground and for a moment I was a bit concerned thinking it was fuel dripping. I had to be reminded it was AC water condensate just like you find on the ground under a car with air conditioner running. Upon request, the plane's top cowl was effortlessly removed to show me the components of the AC system. The components were less cumbersome than I expected, mechanically beautiful, and looking like a well-versed factory installation.

There seems to be nothing kludgy about the setup or its development. The system has been tested on an "iron bird" for many hours and in his plane for quite some time now. I was shocked that it only added 24 pounds to his basic empty weight. I later learned that it is capable of about 16,000 BTU of heat extraction, draws only about 2 hp from the engine, and doesn't noticeably impact overall performance or fuel.

Live and learn! Until that flight, I had thought that an AC system would have been a stupid, expensive, unacceptable weight/performance drag in our little two seaters. The system is called called "PlaneKool". Apparently, there has been mention of this in much earlier postings, but this was my first knowledge of it. As a retired engineer, he's not sure he wants to get back in business, but I for one can applaud his contribution to experimental aviation.
 
I was shocked that it only added 24 pounds

So am I, though I would omit that word "only". It might be an engineering feat to trade A/C against only 24lbs additional fat on a "tiny RV6", but for most builders trying to save every gram (or ounce) on their build to maintain the promised performance figures and agility of the design, it might be less than impressive.
Still, we are all experimenting, and tailoring one's machine to one's requirements is one of the freedoms homebuilts afford :cool:
 
“Only” 24 lbs.

Hmmmm, Our RV-6 runs tailheavy with the fixed Catto prop and lightweight starter. Yeah, 24 pounds up there could be a boon, and so much more useful than just iron ballast. Then if the cabin heat would just work…
 
Yeah, I hear you. However, I deem 24 pounds as a reasonable amount for where one can make a judgemental choice as to what to trade for. From what I've learned, aircraft AC has typically added 40 -60 pounds. If I lived in a year round hot climate, it would be a worthwhile tradeoff. If I was overweight, as the American population is statistically known to be, it would be another trade off for cool comfort and health to loose some body fat. Replace your typical AGM battery, or heavy Comforfoam cushions, etc. with a lighter alternative and you have mitigated at least some of the 24 pounds. Not to belabor the point, but just want to say it is a practical tradeoff and a choice. With 180 or 200 hp engines in RV6s, there doesn't seem to be too much of a negative impact for the gain in luxury.
 
I recently had the pleasure of meeting a VAF member who goes by the handle "hgerhardt", name omitted to protect the innocent ;-). Since I was in the area, I had asked to check out his RV6. His plane has to be one of the more spectacular builds in the fleet and sightseeing over Catalina Island and the stacked-up shipping fleet in the bay was a treat. However, what surprised me the most was that we flew in air conditioned comfort...in the tiny RV6.

The AC was turned on for about an hour from first engine start, taxi, takeoff, low altitude cruise, landing, and shutdown back at the hangar. I forget what the OAT was, but under the bubble canopy it would normally have been at least in the mid 80's F. In the cockpit, it was about 65F. After we landed and got out of the plane I noticed a wet spot on the ground and for a moment I was a bit concerned thinking it was fuel dripping. I had to be reminded it was AC water condensate just like you find on the ground under a car with air conditioner running. Upon request, the plane's top cowl was effortlessly removed to show me the components of the AC system. The components were less cumbersome than I expected, mechanically beautiful, and looking like a well-versed factory installation.

There seems to be nothing kludgy about the setup or its development. The system has been tested on an "iron bird" for many hours and in his plane for quite some time now. I was shocked that it only added 24 pounds to his basic empty weight. I later learned that it is capable of about 16,000 BTU of heat extraction, draws only about 2 hp from the engine, and doesn't noticeably impact overall performance or fuel.

Live and learn! Until that flight, I had thought that an AC system would have been a stupid, expensive, unacceptable weight/performance drag in our little two seaters. The system is called called "PlaneKool". Apparently, there has been mention of this in much earlier postings, but this was my first knowledge of it. As a retired engineer, he's not sure he wants to get back in business, but I for one can applaud his contribution to experimental aviation.

So what happened? Is it in production or kits available to the flying experimenters? It seems that Kool and the Gang have captured the Google search engine for PlaneKool?
 
That is a tiny compressor, is it driven off of the accessory drive? I looked up the name and he got a prize for the design. Any way we could get some pictures of the components installed?
 
I did take a picture, but only of the top cowl removed. It shows the compressor and the plumbing heat exchanger (round silver tubing under the top cowl hinges) which, if I recall, accounts for significant efficiency gain. Hopefully, I'll do the pic upload correctly for it to show.
PS-I did ask permission to show this pic.
 

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I did take a picture, but only of the top cowl removed. It shows the compressor and the plumbing heat exchanger (round silver tubing under the top cowl hinges) which, if I recall, accounts for significant efficiency gain. Hopefully, I'll do the pic upload correctly for it to show.
PS-I did ask permission to show this pic.

Compressor off of engine accessory case? That is a lot of load on the gear train. Also what if compressor seizes? I assume it has a fused coupling.
 
Oh, good sleuthing. That is a cool article and it shows the iron bird. An interesting aspect of that test bed is that it was configured to develop stronger power pulses across the compressor to engine coupler than would normally be experienced.
 
Very interesting A/C system. Can't imagine why it isn't still available. Tried to find some info (not much there).

Came across this article. Found it interesting....

https://web.csulb.edu/colleges/coe/news/?p=10804

This is the one I found .. . apparently the compressor is not smaller, but the test bed engine must be larger. It appears to be using the drive mechanism in vacuum drive adapter. The vee-band clamp on the RV6 is larger than the test bed, presumably an area of improvement. I am still astounded at the 24 lb weight - -that is less than a parallel to angle valve engine weight. It sure look like more attractive design for a 10 to what I have seen (not much).
 
I recently had the pleasure of meeting a VAF member who goes by the handle "hgerhardt"..........

I'm glad you enjoyed your experience! And the pleasure was all mine to introduce you to my RV-6 and I hope you find a decent one to buy someday. And it looks like the cat's out of the bag now too with PlaneKool...

I developed this system starting about 8 years ago in hopes of improving the current commercially available A/C systems. You know, the ones which weigh 60 lbs and move CG forward by 1.1" and blow cool air at the back of the pilot's head. No way was I going to install one of those ungainly things in my -6.

By leveraging modern automotive and additive manufacturing technology, I've managed to achieve this: The all-up installed system weighs 24 lbs., CG shifts forward 0.15”, cold air is delivered through the RV’s original instrument panel-mounted vents, and has the cooling performance of a compact Toyota, even while on the ground with engine idling. The performance is outstanding, with a 40-50°F temperature drop seen between the blower intake and vent output and the system is typically used anytime OAT is above 65°F. A perhaps not-so-obvious, but huge benefit is the reduced humidity in the cockpit.

This system utilizes four large eyeball vents by alternately supplying recirculated-and-cooled or uncooled fresh outside air into the existing outboard panel vents (via air diverter valves), plus a second pair of vents under the engine controls. The evaporator is mounted above the copilot rudder pedals and is fed by a 200-watt blower. Ram air cools the belly-mounted condenser via a NACA inlet scoop cut into the engine cowl outlet fairing, reducing cowl exit area, but which is variably regained by a cowl flap and fixed louvers. The NACA inlet is also throttled by a diverter ramp controlled by high-side pressure. Compressor is variable-displacement and clutchless, allowing it to be directly driven from the vacuum pump pad. The compressor coupling includes a torsional damper and a frangible element (mechanical fuse) made from brittle cast iron to protect the engine in case of compressor failure. The existing heating system remains intact and does not interface with PlaneKool. The system in my -6 has been operational for almost 4 years now and still puts a smile on my face every time I turn it on. For me, it just makes the airplane so much more enjoyable.

3-view captions.jpg Side view.jpg 20200926_173021.jpg 20200926_173058.jpg 20200819_160912.jpg 20200815_093026.jpg20190628_151807.jpg
 
So am I, though I would omit that word "only". It might be an engineering feat to trade A/C against only 24lbs additional fat on a "tiny RV6", but for most builders trying to save every gram (or ounce) on their build to maintain the promised performance figures and agility of the design, it might be less than impressive.
Still, we are all experimenting, and tailoring one's machine to one's requirements is one of the freedoms homebuilts afford :cool:
Just leave 4 gallons of gas at home and you'll be back to original weight.

Hmmmm, Our RV-6 runs tailheavy with the fixed Catto prop and lightweight starter. Yeah, 24 pounds up there could be a boon, and so much more useful than just iron ballast. Then if the cabin heat would just work…
Sorry, CG only moves 0.15" forward.

So what happened? Is it in production or kits available to the flying experimenters? It seems that Kool and the Gang have captured the Google search engine for PlaneKool?
Ain't nothing happened... yet. Maybe kits someday if I can get the needed motivation...

Compressor off of engine accessory case? That is a lot of load on the gear train. Also what if compressor seizes? I assume it has a fused coupling.
It's actually less overhang moment than the bigger vacuum pump-mounted aux alternators. Torque and overhang are less than allowed by the Lycoming TCDS. And there's a frangible element in the coupling to protect the engine if compressor failed.

Very interesting A/C system. Can't imagine why it isn't still available. Tried to find some info (not much there).

Came across this article. Found it interesting....

https://web.csulb.edu/colleges/coe/news/?p=10804
Yeah, it did well as my senior project! And it's never been available, much less "isn't still available".

This is the one I found .. . apparently the compressor is not smaller, but the test bed engine must be larger. It appears to be using the drive mechanism in vacuum drive adapter. The vee-band clamp on the RV6 is larger than the test bed, presumably an area of improvement. I am still astounded at the 24 lb weight - -that is less than a parallel to angle valve engine weight. It sure look like more attractive design for a 10 to what I have seen (not much).

The different couplings you saw on the iron bird show the engineering evolution to creating a robust coupling, which is now on version 4.10. Yeah, the compressor coupling was the biggest engineering challenge. 1st iteration was simply using a COTS plastic vacuum pump spline drive like the aux alternator crowd uses. That worked well on the iron bird but failed immediately on the Lyc at anything below 1000 rpm. As I found out, the back of the Lyc crankshaft twists/untwists so much at idle speed that if you don't have a quite torsionally-soft coupling, the torsional loads are such that over 35 lb-ft load is generated at the spline drive even though the compressor only requires 4 lb-ft to rotate. The COTS plastic spline drive breaks at ~35 lb-ft from my testing. The current 4.10 coupling has several hundred hours on it now and is holding up great with pretty much no wear evident on the rubber blocks.
 
I'd SERIOUSLY look at retrofitting this into my -10. Not much weight penalty at all vs the Icy Breeze I'm currently plumbed for in my overhead ductwork.

Can you elaborate on the clutchless compressor? What kind of load does it apply to the engine when A/C is not required? Is there some way besides a clutch to cycle it on and off?
 
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After witnessing PlaneKool in operation, I looked into the type of compressor that was being used. It is known as a clutchless, variable displacement compressor. It is Very common in automobiles. If I understand it correctly, it is spinning continuously. Its operation and thus true load on the engine is controlled by the refrigerant pressures in the cooling circuit as determined by the demand for cooling. This is where the 'variable displacement' function of the compressor comes in.
 
To add to Radioflyer's comment: the compressor is an axial 5-cylinder with a variable swashplate, controlled by a PWM signal. PWM width determines swashplate angle, which determines the actual displacement. With no power to the compressor, the swashplate goes to 1-2% to maintain a tiny bit of pumping for oil circulation to keep the compressor lubricated. You can spin the shaft by hand in that condition, so no detectable load on the engine.
 
Very clever Heinrich, nice clean installation.

Interesting, I can see some real advantages for variable swashplate compressors, for example, soft starting a RV (Camping) type air conditioner.The starting inrush current would be reduced allowing it to operate on a much smaller generator.
 
Could you elaborate a little bit on the cowl shapes and ducting that you did? It's a very clean, good-looking system.

Dave
 
Very cool. Pun intended. Great job engineering each part of the system for light weight and performance.
 
+1 on all the kudos. Well deserved!

The rotary diverter valves are a real piece of virtuoso engineering too.
 
Quote:
Originally Posted by JDeanda View Post
Hmmmm, Our RV-6 runs tailheavy with the fixed Catto prop and lightweight starter. Yeah, 24 pounds up there could be a boon, and so much more useful than just iron ballast. Then if the cabin heat would just work…

Sorry, CG only moves 0.15" forward.

It's only 0.15" CG change on your RV-6 with an angle valve engine and Hartzell CS prop. The added A/C system weight will have more impact on the CG of a -6 with a lighter engine and prop and further aft empty CG. It'll still be small, though.

Ain't nothing happened... yet. Maybe kits someday if I can get the needed motivation...

Time to quit being lazy in retirement and get producing :p

Skylor

p.s. I have seen Heinrich's system up close many times and it is VERY well done!
 
Could you elaborate a little bit on the cowl shapes and ducting that you did? It's a very clean, good-looking system.

Dave

The NACA scoop is cut into the cowl exit and has a 6" x 2" outlet. The condenser housing tapers outward to the width of the condenser, which is 12" wide and 20" long. I also added turning vanes to the condenser to help turn the air into the fins. I figured out on a ground test with a big blower on the condenser housing inlet and using Kleenex tufts that the vanes help a bunch.

The NACA floor diverter ramp I added after flying for a few hours. At normal flight airspeed, the high side pressure was too low, indicating too much condenser airflow. It has a PWM-controlled actuator to move it and it's made from stainless spring steel. Works great at keeping hi pressure between 190-210 PSI. I copied that idea from A320 ECS inlets which work on the same principle.

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I learned a lot about this type of compressor/hydraulic pump that was brand new to me!

Great piece of engineering. Would definitely be interested in an aftermarket kit for the 10 if it ever came to fruition.
 
Put me in line for purchasing a future kit.

Been considering an AC for a long time. This looks really good.
 
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