What happened to Rare Bear?

[ebutner]

Re: What happened to Rare Bear?

Less.

A man of few words.

[AAFO_WSagar]

Re: What happened to Rare Bear?

A boil off system uses a finite amount of water to cool the engine. In a traditional system water is sent to the engine, then to the radiator to be cooled and then sent back to the engine. In a boil off system the water is sent to the engine and then evacuated from the aircraft as steam as it "boils off" this allows the plane to not have to use a radiator to cool the water thus reducing drag by not having induction scoops to force air through the radiator.

Kinda-Sorta right.. I'm not exactly sure on water cooled engines but on the radials, in a normal system, the oil goes through an air cooled radiator, air taken out of the slippery surface *somewhere* that is then slowed down by going through this air-oil heat exchange. Boil off takes that cooler and immersed it in "coolant", I think ADI fluid is used, as it is Alcohol and water mix and has lower boiling point. No air is used from the slippery surfaces of the airplane, so no cooling drag..

I believe, in a waterpumper, there are two radiators, one for the oil, one for the water, both immersed in a coolant bath... I don't think the ADI fluid is actually pumped through the engine, rather is used, instead of air, to achieve the necessary heat exchange to keep things in the green....

Tech guys, correct me where wrong...

[flyingjibus]

Re: What happened to Rare Bear?

I think you are right Wayne. after I posted that I started thinking and realized I defined it in car terms, which I am far more familiar with. The concept is the same I believe.

Thank you for correcting me without any pictures of Captain Kirk.

[flyingjibus]

Re: What happened to Rare Bear?

Also ,

Mr. Penny if you are still reading his thread, I cant stop laughing about what you wrote on my shirt under Skip Holm's signature. Thanks for the laugh and thanks for being available to us lowly pukes. You are a class act.

Someday I am going to go watch you play with some of Paul Allen's toys. It will be neat to see you turn right!

[marada mx3]

Re: What happened to Rare Bear?

Man this is great! This 'conversation' is absolutely riveting with the input from JP, BL, and others. Only thing better would be a discussion in person (dream sequence begin!). Thank you very much for the input. I don't recall there being this many posts from 'drivers' like JP, BL, WW, MJ(who am I forgetting), etc the last few years. Keep it coming!

Tommy

[Matt58]

Re: What happened to Rare Bear?

Kinda-Sorta right.. I'm not exactly sure on water cooled engines but on the radials, in a normal system, the oil goes through an air cooled radiator, air taken out of the slippery surface *somewhere* that is then slowed down by going through this air-oil heat exchange. Boil off takes that cooler and immersed it in "coolant", I think ADI fluid is used, as it is Alcohol and water mix and has lower boiling point. No air is used from the slippery surfaces of the airplane, so no cooling drag..

I believe, in a waterpumper, there are two radiators, one for the oil, one for the water, both immersed in a coolant bath... I don't think the ADI fluid is actually pumped through the engine, rather is used, instead of air, to achieve the necessary heat exchange to keep things in the green....

Tech guys, correct me where wrong...

Wayne, I think you hit the nail on the head here! Instead of using air to cool the oil in the oil cooler (radiator), it is put in a tank of ADI. As the temp, of the oil rises in the oil cooler, it heats the ADI. At a certain temp. it begins to boil, or close to it, and valves are opened (prob. automatic) to evacuate the steam (vapor). That travels down some tubes or pipes and is exited out of the tail, and i'm pretty sure out of one of the wings too on the Bear.

In the case of the Galloping Ghost, this is the case for the engine coolant radiator and the oil cooler.

Please correct if i'm wrong...

[Mluvara]

Re: What happened to Rare Bear?

Wayne, I think you hit the nail on the head here! Instead of using air to cool the oil in the oil cooler (radiator), it is put in a tank of ADI. As the temp, of the oil rises in the oil cooler, it heats the ADI. At a certain temp. it begins to boil, or close to it, and valves are opened (prob. automatic) to evacuate the steam (vapor). That travels down some tubes or pipes and is exited out of the tail, and i'm pretty sure out of one of the wings too on the Bear.

In the case of the Galloping Ghost, this is the case for the engine coolant radiator and the oil cooler.

Please correct if i'm wrong...

Couple of comments - Boilers do not trap the steam from the boiled off fluid. They simply have a "chimney" that lets the vapor exit. The only switches inside are for the fluid level, letting the systems know when to fill the tank back up.

ADI is typically referred to as (anti detonation injection). ADI fluid is the water/methanol mix injected into the engine. The same mixture of fluid used for ADI may also be used for boiler fluid, so the terms are mixed together at times. The mixture of water/methanol can be tailored independently of the ADI mix for the desired boiling point.

A good reference that I posted previously - http://www.enginehistory.org/Convent...te/Cooling.pdf

Michael

[AAFO_WSagar]

Re: What happened to Rare Bear?

Something I'd like to know, regarding using pure water v methanol-water for the boiler. Many years ago (about 12, I think) Vlado Lenoch brought his Mustang to Reno, since he was not really running that high power settings, he was having troubles using the ADI system he'd had installed. His engine was running too "cool" when he ran ADI.. he turned to using pure water and way less of it than used when at very high race power settings.

My question, since water boils at something around 220deg F... a bit less at Reno altitude.. (try following recipe cooking times at anything other than sea level.. ) At less than race power, would a boiloff system be able to use "just water" for the boiler, say for ferry flights?

We know water really will not get higher temp than its boiling point, so what's immersed in it, likely, would only be higher than what heat could be transferred to the 220 degree water. What is that ratio?

Say your boiler is running at 215 deg at altitude, you're running oil in it that can try to reach 300 degrees or higher.. I think anything over 250, at least for automotive applications, is too high.. what's the ratio between the boilier "water" and the oil running through a radiator through it?

Bottom line of this question is, could you just use plain water for ferry flights and stay within limits?

[kiwiracefan]

Re: What happened to Rare Bear?

hmmmm that is a damn good question Wayne..... now lets see if one of the resident Guru's will answer for us...

[Rampman]

Re: What happened to Rare Bear?

Any of you experts - About how big of a tank are we talking about to cool the oil? Is the weight of the liquid significant, and does it effect the handling of the airplane as it's boiled off?

Also, wouldn't it take a much larger system to cool a liquid cooled v-12 since you have to cool the engine water as well as the oil?

[Mluvara]

Re: What happened to Rare Bear?

Bottom line of this question is, could you just use plain water for ferry flights and stay within limits?

Using sea level as a reference, water has a higher boiling point (212deg F) than methanol (~149 deg F). Mixing the two gives a boiling point somewhere in between.

So, yes, one could run water only, but the temperatures would be higher than with a mix. It all depends what temperature you are comfortable with. Also the burn rate of the fluids will likely change with the temperature that you set.

Lastly, don't forget that this temperature we are discussing is the oil temperature INTO the motor. What comes out is related to how much heat the engine is making.

Michael

[bruce lockwood]

Re: What happened to Rare Bear?

Wayne, excellent question. One of your other members and a friend of mine, Elliot Sequine has been after me for years to look at the Stiletto file IE Boiler info. My father in-law and I original engineered, designed, built and installed the boiler system in Stiletto. Pete Law was the instigator of the project and set me in the right direction for Thermal Number, The the rest I gleaned from weeks of research at Cal Tech going over NACA, Tech Notes, Restricted Notes and other Classified War time documents. By the way, virtually every speed mod used on all the real fast unlimited have roots from the NACA documents. Thousands of documents generated by millions of man hrs of research using the same mindset that built the A bomb.

I don't' have time to get into this whole thing, as its really a story for Warbirds WW or Airclassics, so I'll give you the meat of the info and theory.

1 lb of water raised in temp 1 deg F takes 1 BTU of energy....
so to raise H20 from 50 deg F to 212 deg F (Boiling point of water @ std Temp and Pressure) takes 162 BTU's of energy.

The energy in BTU's to convert water to steam is 970.4 BTUs. So in other words it takes apx 6 times more energy to actually boil the water than it does to bring it from tap water temp to 212, just were the water looks like it wants to boil but seems to take forever.

Alcohol boils at apx 147 deg. F (std Temp/press) and takes apx 0.6 Btus of heat energy to raise 1lb 1 deg F and apx 378.12 BTUs to boil once it reaches 147 deg F. But..... BIG BUT here......it can only absorb apx 1/2 the heat per pound compared to water. But it is lighter 6.8 lb/gal compared to 8.35 lb/gal. Now these are all round estimate, as this is for your general knowledge.

So my astute arm chair engineers, you can see that Alcohol boils at apx 60 deg F lower than water. So by blending the two ( water/alcohol) you can adjust the temp between 147f to 212f at which your mixture boils. If the heat exchanger is efficient it will cool what ever liquid you are trying to cool to within 5-15deg F above this boiling point. Now the heat exchanger in the boil off system is basically a radiator containing vital engine liquids IE. OIL or Coolant from the engine/supercharger after-cooler submerged in an enclosed/vented to the atmosphere tank of liquid replenished by pumps from storage tanks on the airplane). Heat exchangers come in many forms "air to air", "air to liquid", "liquid to air", "liquid to liquid"


The next is an interesting bit of info you can use to see how much heat is generated as an average over a range of power from idle to t/o for the V1650.

1 horsepower equal 42.4 BTU's of heat (they are all forms of energy, heat, HP, electricity etc.)

V1650 heat rejection:

1 HP at the prop shaft generates in heat per minute the following...

30% to the radiator (.30 x 42.4 BTUs = 12.7 BTUs Heat per min)
5% to the after-cooler (.05 x 42.4 BTUs = 2.12 BTUs heat per min)
5% to the oil ( same as above)

NACA reports (RESEARCH MEMORANDUM 1948) show that the engine heat sent to the radiator varies from 62% at idle to 24% at 3000Hp. The cylinder liner and water jacket can only transfer so much heat, so at race power more heat goes to the oil and out the exhaust.

Radial engines run at apx 7-10%+ of HP is generated as heat to the oil.

As a rule of thumb and to simplify all the math by not taking in outside temp variation, you will reduce the boiling point of a mixture of 50/50 water alcohol (167 deg f) apx 2 deg for each 1000 ft gained in alt. from sea level. So on the race course at Reno, 5250 ft our mixture will boil at 157 deg f.

Now to put all this to practical use and see how much 50/50 mix the Bear was consuming a minute in its oil boiler, we will assume it was making 3300HP for the Sunday race, so 3300HP x .10 (10% brake HP to oil as heat) = 330Hp to heat, multiply that by the conversion of HP to BTUs

330hp x 42.4 btus = 13,992 BTUs a minute. Divide that by 790 ( BTUs needed to heat/boil 50/50 mix) = 17.7 lbs of 50/50 Water/Alcohol boiled a minute or 2.33 gals per min. And the oil temp. should have stabilized at around 179-185 deg F or 82-87 deg C.

Thanks to Pete Law who whetted my appetite for this stuff and to Dave Cornell who told me were to find the answer.

Cheers, Bruce

[bruce lockwood]

Re: What happened to Rare Bear?

Rampman with -7 blower gears 3500 RPM/110 MP and 2905 HP, the V1650generated (using NACA math numbers) 30,261 BTU,s Min to coolant and apx 7000 BTU's to oil per min so figure 37,500 BTUs would boil (37,500 divided by 790) 47.5 lbs per min/6.27 gals of 50/50 water alcohol.

Mouse motor would apx 2 gals per min more.

Bruce

[AAFO_WSagar]

Re: What happened to Rare Bear?

Wow Bruce, thanks for the information! My head is spinning with numbers!

Anyway, what's max oil temp for an air cooled aircraft engine?Remembering my VW bus days... I had a '74 with the pancake engine (no upright fan) and had installed an oil temp gauge, which really was just something to look at and worry about because they got hot going up hills, just about no matter what you did to them.. I remember seeing temps in the 250 deg range on my old bus.. sometimes even higher... but someone told me, as long as it never got to 300-350, the oil would be OK...

I loved that old bus, but... hope the person who owns it now removed that damn gauge, and the tach and just keeps their eyes on the road and enjoys it!

Thanks again for participating here!

[BUD_XXX]

Re: What happened to Rare Bear?

Thanks for the Thermodynamics Refresher!

Amazing...the talent that chimes in.