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  #61  
Old 01-17-2005, 05:46 PM
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David Staten David Staten is offline
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Default Yes.. BUT...

Quote:
Originally Posted by rv6ejguy
Mass flow at 25,000 feet would be closer to 1/3 that of SL at same TAS. You won't be able to indicate anywhere near the same AS at 25,000 as at SL even with turbocharging. So in a nutshell, you will have far less mass flow available for cooling up there as at SL.
You are correct and I agree with you... but the examples I used were based on IAS not TAS... for a specific IAS, you should get essentially similar cooling air flow (pounds/min.. etc).

So.. if you have an IAS of 100 in the flight levels, you should be having the same mass of cooling air flow at an IAS at sea level. Now.. TAS is a whole different ball game. I think that we are both right, but are risking mixing up apples and oranges here.

Dave
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  #62  
Old 01-17-2005, 09:34 PM
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mplafleur mplafleur is offline
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Default

Quote:
Originally Posted by David Staten
You are correct and I agree with you... but the examples I used were based on IAS not TAS... for a specific IAS, you should get essentially similar cooling air flow (pounds/min.. etc).

So.. if you have an IAS of 100 in the flight levels, you should be having the same mass of cooling air flow at an IAS at sea level. Now.. TAS is a whole different ball game. I think that we are both right, but are risking mixing up apples and oranges here.

Dave
Hmmm... I said the same thing, kinda. Or at least I was trying to...
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  #63  
Old 01-17-2005, 09:58 PM
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we have all said it

IN PSI

sea level IAS 200 = 15 psi = 3000

25000 feet IAS 200, TAS 300 = 10 PSI = 3000

rv6ejguy - what are we all missing
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  #64  
Old 01-18-2005, 12:23 PM
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rv6ejguy rv6ejguy is offline
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Default IAS/TAS

Yes, at the same, IAS mass flow will be the same. I was just pointing out that in the real world at 25,000 feet you will not see 200 knots IAS in a Cozy and to climb at a constant IAS of say 120 knots means you won't be climbing at all at 25,000 feet because the nose is going to be level.
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  #65  
Old 01-18-2005, 12:34 PM
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Quote:
Originally Posted by rv6ejguy
because the nose is going to be level.
Why? Are you saying that all i will be able to indicate at 25000 is 120 knots?
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  #66  
Old 01-18-2005, 02:37 PM
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Default TAS/IAS

Well, you'd need to see 120 knots IAS at 25,000 roughly to true 180 knots. Don't think your rate of climb would be more than 2-300 feet/min. at this speed.
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  #67  
Old 01-18-2005, 03:24 PM
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It's stupid because I mix it upp with other expressions all the time

metric... like the old Volvo boss said (my translation) "The americans are accepting the metric system inch by inch"

Quote:
Originally Posted by Kumaros
Mr. Control.
now why does a perfectly good Greek word like "adiabatic" sound stupid to you?
Isn't it nice though, when almost all science is based on Greek words?
Now I only wish you would all start using metric and I would be perfectly happy
Oh well, back to the plans ordering process.
Kumaros
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PS For what it's worth, I wholeheartedly hated heat theory too.
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  #68  
Old 01-18-2005, 08:12 PM
Fred N. Fred N. is offline
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Quote:
Originally Posted by John Slade
Thanks, Mike.

I'm almost sorry I asked.

So.... with a turbo running at a pressure ratio of 2.3 I have 230% VE - right?
This would be theoretically correct at SL, IMHO.

I have also been considering the T-61 for my RX8. True it is a larger turbo, but because of the reduced pressures and MAF at 20,000 MSL, I wonder if it will be enough woomph up there.

A technical advisor said I should plan as though the RX8 is a 2.6 litre engine (about double the official displacement of a 13B). I was O.K. with this because I expect to be operating at 20,000 MSL & 6600 RPM. To avoid detonation, I do not want any more than sea level pressure on the engine at any altitude. I was amazed that my PR came out at 2.5 to obtain that. The PPM flow required for that was 42.7. The T-3 simply could not supply that. A selected few of the TO4s could. The T-61 came out in the upper center of the map island (75%) efficiency. Now RV6ejguy says that could all be out the window since I was using 80% efficiency charts. He's right if I'm 100 to 120% VE.

John, what turbo are you using? What is the highest manifold pressure you have operated with?
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  #69  
Old 01-18-2005, 09:25 PM
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Mine is the stock Mazda 89 single stage turbo modified by turbonetics in Australia. They call it a "hi-flo". They tell me it's now equivelent to a T04-V1. Unfortunately the main advantage of these modifications is effective at higher rpm than I can get (thus far) with my prop the way it is.

See http://www.turbonetics.com.au/ for details of the mods.

I don't have many hours on the new turbo yet and have been taking it fairly gently while I sort some other issues out. I did boost up to 50 MAP on one take off, but mostly I'm sticking below about 46.

I may end up trimming the prop back once I get some altitude and cruise numbers on the new turbo with wheel pants. Right now I'm getting 4050 static engine rpm (2.17 ratio) which gets me off the ground in around 1000'. Target WOT rpm at altitude is 6300. With the old turbo I got to about 5300 and around 190 kts TAS, just before it blew up
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  #70  
Old 06-12-2005, 11:40 AM
DustinD DustinD is offline
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If you are flying at 25,000 feet indicating 200 MPH you will be doing about 295 mph TAS. The air pressure will be about 5.4 psi, not 10 psi.

The reason you only gain 95 mph is because of air compressibility. If air did not compress in front of your airplane you would gain about 99.5 mph and thus fly at a TAS of 299.5 mph. Give or take. This does not take into account a few important factors such as what speed the airplane's aerodynamics where tuned for.

The formula for TAS is... TAS = sqrt(IAS * IAS / (air pressure / sea level pressure)) But that formula does not take into account the compressibility of air.

http://www.f1-rocketboy.com/AirData9a.exe This program takes compressibility into account, and has some nice features.

Keep in mind that these are just estimates, and I am not an expert.

Last edited by DustinD : 06-12-2005 at 11:53 AM.
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