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  #31  
Old 05-04-2005, 10:22 AM
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Kumaros Kumaros is offline
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Default Time shifting my time away

Quote:
Originally Posted by David Staten
I hate to admit it, but as a whole 1) the public is ignorant of technical matters and 2) the public is indignant and offended when you remind them of #1.
snipped ...
Dave
Dave, you just uttered a universal truth, unfortunately as true in Greece as in the US. I had hoped that CNN with its only news coverage would cater to a more upscale and alert audience.
Things in Greece ar just as bad or worse, we used to lament that we only had two state run TV "networks", now we have x private "networks" and there are times I'd like to smash my TV. I time shift like crazy.
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  #32  
Old 05-04-2005, 11:51 AM
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Quote:
Originally Posted by JonC
The common way to do that is just pipe the air through a seperate intercooler that is enclosed in a plenum with a flapper on the intake. Look at the leading edge of a C421 wing root and you will see what I mean.... better yet, I'll take pictures tonight/tommorow.



You may have hotter air at those points, but you are also working the turbo harder and harder as you get higher. 50 scfm might not be much for a turbo at low altitude, but the higher you go the more likely you are to overspeed trying to keep up your bleed air as well as 30 inches in the manifold.

It is a very real solution to do, however I'm not sure it is worth the extra engineering time when you can just pipe air through an oil cooler and get the same effect without risking your turbo(s).

Overspeeding the turbo is no concern at 24,000 feet and 30 inches, about 2.5 pressure ratio, about 105,000 rpm on a TO4 E-50, max 125,000. 50 SCFM equates to about 3.8 lbs./min. which is only about 10% more flow for this compressor under these conditions. I agree that is is easier though for a non-pressurized aircraft to use waste heat off one of the existing heat exchangers- oil or intercoolers for cabin heat. Could bleed air heat the cabin? Yes. Is it the best solution? Probably not.
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  #33  
Old 05-04-2005, 01:10 PM
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Señor rv6ejguy, ifin i was in a tractor, with the items you have in front of you, i would agree, but in a pusher, with a built in heat duct that is about 2"x3" from back to front and the need to move allot of hot air 12 feet forward, i respectfully choose to disagree.

thats not to say that when i actually get to doin it i won't find that i am totally mistaken of the ability to do it, but through my rose colored not doing it yet glasses - it appears to be the simplest and most effective way to get allot of hot air to my tosies

always appreciate your input and really think thrice when i do not agree with you
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  #34  
Old 05-04-2005, 06:57 PM
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A few pages ago....
Dust said ...
" The amount of heat available to me will increase as altitude increases, i have the "formulas" of turbo output air temps at all boost levels and since i am going to only boost to normalize, the available heat will be meager at sea level

at take off i will start off with just about 4 IM boost to bring manifold to 31.5 MAP, this will not create much heat

The turbo bleed air will work best at high altitude cruise, my biggest concern.

If i need help at lower levels, then I'll just have to figure it out".

If you were to have a manual wastegate, and a manual bleed from the turbocharger prior to the intercooler; then at low levels you should experience the greatest mass flow of air, and the greatest rise in temperature of that air.

As altitude increases, the mass flow will decrease, as the engine now uses it, and bleed air temperature will drop, due to the fall in outside air temperature.
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  #35  
Old 05-04-2005, 07:06 PM
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Most of the heat from the turbo anyway is not from pressurizing the air but heat transfer from the exhaust.
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  #36  
Old 05-05-2005, 11:35 AM
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Default Bleed air temps

No4 says that compressor discharge temps will drop with increasing altitude. Just ain't so. As ambient pressure decreases, pressure ratio across the compressor must increase to mantain the same MP. Higher PR means higher discharge temps. The higher mass flow requirements simply more the operating range of the compressor to the right on the map. This may mean higher or lower efficiencies depending on how the compressor is matched under those conditions. Max efficiency is in the middle of the island with lower efficiencies to the right and left of that island.

We have done extensive compressor temperature studies on two different compressors and even built a 304 stainless backplate to try to reduce conduction from the center section to the compressor air. This surprisingly made no difference in compressor discharge temperatures. 304 stainless has 18 times less thermal conductivity than high silicon aluminum normally used for turbo backplates. The jury is out on how much conduction is happening here vs. straight adiabatic temperature rise from the compression of the air. We do see temps quite a bit higher than predicted mathematically supporting the conduction theory but if this were true, the 304 backplate should have made a big difference. ????? Compressors are tested not attached to the turbomachinery but to an electric motor. This allows only the adiabatic portion of its characteristics to be studied and documented.

My advice is to fit the best intercooler you can abd duct lots of air through it. Our studies indicate that intercooler mass flow equal to the engine cooling mass flow is required for good results. This tends to be supported by looking at the duct work on WW2 turbocharged and supercharged aircraft feeding the intercoolers.
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  #37  
Old 05-05-2005, 01:04 PM
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Quote:
Originally Posted by rv6ejguy
My advice is to fit the best intercooler you can abd duct lots of air through it. Our studies indicate that intercooler mass flow equal to the engine cooling mass flow is required for good results. This tends to be supported by looking at the duct work on WW2 turbocharged and supercharged aircraft feeding the intercoolers.
Yes - cooling air will be extremly important, am not sure how i will get it yet, maybe from a top of turtledeck NACA or ??, will have to figure it out, but did not realize that THAT much air would be required, it will be interesting
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  #38  
Old 05-05-2005, 02:36 PM
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The use of the 304 was an interesting approach. But there are more issues at stake. Once the temperature on the front of the 304 and the back of the 304 are the same over time then the only remaining influence would be how much temperature you can conduct away with the mass of cooling air as Dust has addressed.

The requirement can be calculated

Check out this web site.
http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

It looks like you can use the factor for air, the factor for steel or aluminum if you prefer, the time and the delta T between the two materials.

I guess this would be an interesting approach.
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  #39  
Old 05-05-2005, 09:20 PM
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Hallo rv6ejguy,
you said "No4 says that compressor discharge temps will drop with increasing altitude. Just ain't so. As ambient pressure decreases, pressure ratio across the compressor must increase to mantain the same MP. Higher PR means higher discharge temps. The higher mass flow requirements simply more the operating range of the compressor to the right on the map."

I think perhaps you misunderstood my set up.
The manual wastegate is closed causing the turbocharger to work. The bleed air valve is opened. The correct combination of these two will give the desired manifold pressure, and the desired amount of heat to the cockpit.
The turbo is perfectly capable of a 3 : 1 compression ratio at sea level, and the increased outside air temperature, and mass flow means more heat.

Has anyone considered air to water intercoolers to reduce drag?
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  #40  
Old 06-12-2005, 01:11 PM
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The airplane I am planning on will have metal wings. I am planning on cooling both the engine and the turbo air (through a water air intercooler) with aluminum hard lines going through the fuel tanks in the wings.

I am also considering making another intercooler attached to the inside of the cowl or fusaloge skin to futher cool the air without adding any drag.
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  #41  
Old 06-12-2005, 07:13 PM
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Quote:
Originally Posted by DustinD
The airplane I am planning on will have metal wings. I am planning on cooling both the engine and the turbo air (through a water air intercooler) with aluminum hard lines going through the fuel tanks in the wings.

I am also considering making another intercooler attached to the inside of the cowl or fusaloge skin to futher cool the air without adding any drag.
I think you will find the heat flux from the charge air cooling is substantial and will raise the temperature of your fuel to unacceptable levels in a fairly short period of time. Liquid to air intercoolers are also heavy with the extra exchangers, lines, pump and generally less efficient than air to air.

Surface conduction cooling requires substantial surface area to be effective, probably in the dozens of square feet for an intercooler setup. Lots of tubing, effectively bonded to a skin somehow. Complicated and heavy.
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  #42  
Old 04-17-2006, 11:46 AM
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Dust,

You'll be happy to know that the new Cirrus SR22 turbo conversion by Tornado Alley replaces exhaust muffs for cabin heating with bleed air from the big twin Garretts.
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  #43  
Old 04-17-2006, 12:12 PM
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I'll be very curious to see how well it works.

I've always been curious as to why it doesnt work well in C421's... You have massive geared engines with massive turbochargers that are actually boosting, not just normalizing.... but yet when you close off the heat exchanger inlets the cabin temp barely increases.... and it is pressurized at that.

If only we had the same problems in our Merlin II... it bleedair heats it a little too well.
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  #44  
Old 04-17-2006, 02:47 PM
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Quote:
Originally Posted by JonC
I'll be very curious to see how well it works.

I've always been curious as to why it doesnt work well in C421's... You have massive geared engines with massive turbochargers that are actually boosting, not just normalizing.... but yet when you close off the heat exchanger inlets the cabin temp barely increases.... and it is pressurized at that.

If only we had the same problems in our Merlin II... it bleedair heats it a little too well.
Probably a matter of duct length with a twin and maybe the lower ambient temps at 25,000. They were seeing 190F CDT in the climb at 29 inches and 11,000 feet. They are still in testing so they may find that people get cold feet in the winter up high still.
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