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Altitude considerations for Liquid cooling

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I am curious to know if the Rotary with its liquid cooling system has any altitude restrictions. I have looked around this forum, checked the Cozy Girrrls site, and poked around Slades' site but I cannot find anything relating to max altitude. I know that the Rotary and Subaru's can be turbo normalized for altitude, my concern is the secondary systems and altitude. like how they handle cooling at 19,000 or 20,000 feet. Do any of you have any information or good sites to point out for this kind of information? I am still in the research stage, I love the idea of an auto conversion, I have experience with Mazda's and Subaru's (in cars, not aircraft) and they are both great designs.

 

Thanks,

Robert

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Is your concern restricted to the water cooling issue?

I'm trying to think if the P-51 had such restrictions?

The cooling system is closed and under pressure so my best guess is it should not be a factor.

 

SUBNOTE:

If you look in wikipedia and get a list of aircraft engines ...... you'll find the wankel listed but not the subaru.

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Also, try the Mistral site. http://www.mistral-engines.com/ . They are the folks across the pond who are devloping the Wankle for FAA certification. There stuff started as a Mazda that they now create from the ground up due to the FAA requirements. Some parts....such as the intake I got from them a couple of years ago fits my 2nd gen 13b.

 

All the best,

 

Chris

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Also, even though you seem to be a bit far away. The weekend of May 29, 30 & 31, 2009 there is going to be a Texas Rotary Roundup north of Austin at a private field 40XS (Breakaway Park...which, btw, contrary to AirNav's report, is reportedly now paved).

 

The big names in rotary aviation are planning to attend depending on WWW (Wind, Weather or Whatever) including Tracy Crook, Ed Anderson and Al Gietzen.

 

They all have flying rotory's. Two have 13b's in RV's and Al has a 20b (three rotor) in a Velocity SE (the same plane as I have).

 

I hope it will prove interesting.

 

All the best,

 

Chris

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But does anyone know how the cold air up high was dealt with in the powerful old planes?

 

Cowl flaps? or other air restrictors in front of the radiators?

 

My motor got real cold! Yes I know, it's not like yours :-)

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Most WWII fighters that had liquid cooled engines (e.g., FW-190-D9, BF-109, Spitfire, Mustang) typically controlled airflow into/out of the radiator either at the inlet or the exhaust of the cooling system.

 

The P-51 has a huge 'cowl flap' at the aft end of the radiator tunnel to 'throttle' airflow. The 2,200hp liquid cooled Jumo inverted V-12 in the long-nose 'Dora' Focke-Wulfs had a self regulating shutter arrangement at the front of the engine, kind of like the iris on a camera as I recall, that regulated airflow into the radiator (which sat behind the prop).

 

A properly sized and operating thermostat will go a long way towards regulating engine operating temperature, but even the Titan T-51 Mustang has an operating cowl flap for the scale mounted radiator.

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Slight correction to my post above, the FW-190-D9 did use an annular radiator, but cooling was controlled by adjustable cowl mounted flaps around the periphery of the back end of the cowling, like a big radial.

 

The crankshaft mounted shutter arrangement I was thinking of was seen on the air-cooled Vedeneyev M-14P radial.

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Well yes ...... you can control the coolant temperature through either airflow or regulating the flow of coolant. Obviously if the coolant is not circulating through the engine (thermostat closed) then it's warming up.

 

As a young driver, when it got to be sub-zero F (-18 to -20 F) we would cram a piece of cardboard in front of the radiator to restrict airflow. Our thermostats are a lot better now.

 

Even the VW aircooled engines controlled airflow through a thermostat of sorts that would expand and contract thus pushing a rod up or down to change the position of vanes that controlled airflow.

 

Bottom line: Outside airtemp should not be a factor. Altitude could effect the contents of the resevoir but if it did, you would already be dead.

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Well yes ...... you can control the coolant temperature through either airflow or regulating the flow of coolant. Obviously if the coolant is not circulating through the engine (thermostat closed) then it's warming up.

 

As a young driver, when it got to be sub-zero F (-18 to -20 F) we would cram a piece of cardboard in front of the radiator to restrict airflow. Our thermostats are a lot better now.

 

Even the VW aircooled engines controlled airflow through a thermostat of sorts that would expand and contract thus pushing a rod up or down to change the position of vanes that controlled airflow.

 

Bottom line: Outside airtemp should not be a factor. Altitude could effect the contents of the resevoir but if it did, you would already be dead.

 

As a matter of fact, the "cold weather kits" that Cessna and others sell are nothing more than an aluminum plate that restricts air floage through the oil cooler.

 

Large trucks, in the winter, many times, have a fabric cover for the radiator which has a zipper for air control.

 

The real question is, "under relatively normal flight regimes, is controlling the airflow necessary.

 

As a side (foot)note, cowl flap arrangements can be designed to create a low pressure area at the air exit and increase airflow when open. This would benefit high power, low airspeed situations such as climb.

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You might have to consider the pressure cap on the cooling system. Intuitively it seems that the radiator would boil over at a lower temperature because the absolute pressure would be lower at high altitude. The pressure cap can only regulate relative pressure in the radiator relative to the atmospheric pressure.

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Another safety factor used in the water cooled rotary installations is a water pressure gauge so you should see it coming before you pop the pressure cap.

...Chrissi

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Yea.. You guys touched on many of my concerns.. I live in the PNW, and I know that its possible to get real cold up at altitude (-40 and lower) while being real toasty on the ground. (Yes, standard adiabatic laps rate is 2c for every 1k feet, so if its 20c at sea level it would be -20c at 20k) It sounds like using water is not a problem as long as you have a way to regulate airflow through the radiator. I guess I would be afraid that the thermostat which allows flow when the water is hot enough might cause a problem if it doesn't pop before the liquid in the radiator freezes and restricts fluid flow causing the engine to overheat at altitude, (which could probably be handled through proper mixture of Antifreeze.) The other thought I had was water boiling at lower pressures so you would have to make sure the cooling system could handle higher pressures then it would at sea level so the water would not boil over at altitude and pop the radiator cap pressure valve or (heaven forbid) blow a seal in the engine. Boiling at 20k is roughly 86C or 186F, I guess putting a 30psi radiator cap on would solve the problem as long as you were warmed up before reaching altitude. (Cozy Girrrls recommendation for a Pressure sensor is a must then I guess)

 

The problem I am seeing is I could leave Sunny Oregon on a 70F day and make it to Juno at -32F, if I take the high altitude route then when I am over the water coming into Juno I could be looking at -40 or more.

 

Of course.. I think as a Pilot I would probably look a lot like Frosty the snowman after a trip like that.

 

I forgot the P51 was liquid cooled, It had a service ceiling of over 40k.

 

Robert

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Trying to get the Rotorhead out of my head......

 

At those extreme range temperatures for your Oregon to Juno flight, what happens to the air cooled Lyconentals.

 

I addressed the oil cooler blocker before, but -40 degree air hitting the hot cylinder heads and other private parts can't be doing a world of good. Can you keep the aluminum hot enough??

 

Anybody have an idea of the boiling point of H2o at 13 PSI (with antifreeze in it.)

 

There is a waterless coolant, EVANS NPG, that is available, which runs without pressure. Does this change the equation?? .

 

Any rotorheads have experience with it?? (eggenfellner makes it available on his engines.)

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At those extreme range temperatures for your Oregon to Juno flight, what happens to the air cooled Lyconentals.

 

I addressed the oil cooler blocker before, but -40 degree air hitting the hot cylinder heads and other private parts can't be doing a world of good. Can you keep the aluminum hot enough??

 

That is not a pretty thought! :) an A&P mechanic friend of mine was telling me how he was nursing a Lycoming from Northern Alaska to Washington, at one point they had to land (somewhere in the tundra) due to icing and he made the mistake of putting his hand on the cowling. While the mistake dawned on him, the pilot reached over and ripped his hand off before it became a permanent fixture to the airplane. As I recall, the main problem of the trip was the Oil kept freezing. They had the air holes blocked so as to prevent shocking the engine, but they were starting in a colder area. I would think that if you were flying a Lycoming North, one would have to be careful with running too low throttle to prevent shocking the engine.. Of course, once the engine stopped and cooled, getting it started would require some winterization.

 

I guess that might be another consideration, but considering that Rotaries are Notoriously "Hot" engines freezing the oil would be more difficult to do.

 

Robert

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..... yes, and you are not running 50-60 weight oil in a rotary.

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Maybe I am acknowledging a complete misunderstanding, but I did not think rotary coolant was what was "nortoriously" hot. Yes, cooling can be an issue as it is in all/most conversions.

 

Also, about 30% of the rotary cooling is via the oil, thus another "difference" that can be very open to interpretation.

 

What IS hot, in this context, is the exhaust. But since the rotary is blowing directly out its combustion chamber and has no valves ect to pass by first, it EGT would naturally be hotter, or such is my understanding and experience.

 

All the best,

 

Chris

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Chris, Agreed, its not any hotter than any other, can't really change the boiling point of water all that much except by pressure and not good to monkey about with that too much.

..Chrissi

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Golly gee Chrissi, I love ya a little more everytime you post:o

 

In that vain, answer me this. IIRC, the standard pressure radiator cap for the rotary is, I think, 13lbs cap. Howeve, the "conventional wisdom" seems to want to place a much higher capacity radiator cap on the rotary. 21lbs if I recall. I think John Slade, Tracy and Buly did/do so. I had to go to race shop to find one that high.

 

Why? Wouldn't the pressure inside the system still be held at bay with a 13lb cap even up high...as long as the internal pressure does not go over 13lbs. Does the pressure at altitude on the outside become so much less that the internal pressure is "fooled" thus blowing by the weaker cap?

 

I thought I knew the answer to this once, but when my engineer friend asked about it (he is installing a Eggenfieldern in his RV7 and is one of the brightest guys I know) I was at a loss. After all, I am just a cop :D

 

I have a 21lbs on mine...again, due to perceived "consensus". But, as a rule, I would like to actually understand "consensus".

 

Thanks to all would care to enlighting me....espcially you Chrissi;)

 

All the best,

 

Chris

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Golly gee Chrissi, I love ya a little more everytime you post:o

 

In that vain, answer me this. IIRC, the standard pressure radiator cap for the rotary is, I think, 13lbs cap. Howeve, the "conventional wisdom" seems to want to place a much higher capacity radiator cap on the rotary. 21lbs if I recall. I think John Slade, Tracy and Buly did/do so. I had to go to race shop to find one that high.

 

Why? Wouldn't the pressure inside the system still be held at bay with a 13lb cap even up high...as long as the internal pressure does not go over 13lbs. Does the pressure at altitude on the outside become so much less that the internal pressure is "fooled" thus blowing by the weaker cap?

 

I thought I knew the answer to this once, but when my engineer friend asked about it (he is installing a Eggenfieldern in his RV7 and is one of the brightest guys I know) I was at a loss. After all, I am just a cop :D

 

I have a 21lbs on mine...again, due to perceived "consensus". But, as a rule, I would like to actually understand "consensus".

 

Thanks to all would care to enlighting me....espcially you Chrissi;)

 

All the best,

 

Chris

the pressure on the outside of the engine will be about 8 psi less at 20,000 feet

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Chris,

Lynn's observation is correct, also you need the reserve for climb out. Since you get 30% of your cooling from oil consider a deeper oil pan, again for more reserve on climb out before the oil gets really hot.

Speaking of hot, Chris we really love ya but you are geographically undesirable, one of us would have to commute! :D

...Chrissi

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Well, I ain't a Rotor Head, I'm going with fins.

 

I live at 7400', water boils at ~190 degrees up here (ask me how to make a "three minute" egg). Combine this with Lynn's pressure/elevation data point, draw a line (straight?) ... Factor in the chart on the back of the Prestone jug, and...

 

Rick

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Maybe I am acknowledging a complete misunderstanding, but I did not think rotary coolant was what was "nortoriously" hot. Yes, cooling can be an issue as it is in all/most conversions.

 

Chris

Sorry, I was not more specific, the Rotaries I have experience with have a HOT exhaust. (enough so to chuckle at the surface of the sun) With so much heat in the exhaust I doubt anything in the vicinity will get daunted by even 0 Kelvin*

 

 

 

*Lame attempt at humor

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Speaking of hot, Chris we really love ya but you are geographically undesirable, one of us would have to commute! :D

...Chrissi

Why do you think I am building an airplane??????;)

 

All the best,

 

Chris:cool2:

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Well, I am confused by the use of imperial units (metric makes so much more sense), but indeed, at a higher elevation water will boil earlier due to the reduced outside pressure. Water boils at 100°C at normal atmospheric conditions (vapor pressure thus being 1 bar) and will produce an additional 1 bar at about 120°C. At reduced pressure it will boil earlier since its vapor pressure equals the outside pressure at a lower temperature. A cap which releases pressure at 13psi above outside pressure will therefore release pressure at a lower temperature.

(Does that make sense?)

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BrainF,

 

Pressure and temperature (as it relates to auto conversions) are 2 different things. Generally, the two move around hand in hand but not always. Soon after start up you can have a cool rad but a hot block and have high pressure. The thermostat will open, the pressure will drop some but the temp remains the same. Air in the cooling system will also have an effect on pressure independent of temp. In the rotarys there is a possibly of having a cracked side housing that may show as high coolant pressure even though the coolant temp is low.

 

I've always used a 20lb cap on the rotary to lower the boiling point but if the cooling system is working well, you normally don't see temps over 190F. For high altitude work there are a number of factors in the cooling systems favor. The outside temps are lower (you get better heat transfer) and the engine isn't producing sea level power (unless you're blown in some way:cool2: )

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