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  #31  
Old 04-06-2005, 05:00 PM
martinkh martinkh is offline
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Quote:
Originally Posted by rv6ejguy
Audi puts out a turbo engine with torque peak at 1900 rpm and this is virtually flat to 5500. ...

The compressor density ratio, not pressure ratio, multiplied by the static CR would give you the effective CR under boost.
I may be 10+ years out of touch on turbo technology.
do you have a formula?

If you double the amount of a gas that you put into a given space, you would double both the pressure and the density. The only thing I can think of that would make it a non-linear relationship (voiding my calculations) is if desity ratios take temperature differences into account. I would imagine that as you compress air it heats, this can have the pressure ratio be a little higher than the density ratio. So where I calculated 15:1 it may be more like 14:1, based on how hot the compressor makes the mix. Now that you pointed that out, I think if I ever shop for a turb, I would look for one that does not increase the heat of the air too much.
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  #32  
Old 04-07-2005, 12:26 PM
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rv6ejguy rv6ejguy is offline
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Default Turbos

Quote:
Originally Posted by martinkh
Then I suppose the question is, when you give the engine throttle on the line, does it take a long time to get the engine up to speed?

If it takes a long time, then that is the bottom end torque. High HP at 4050rpm may get you off the ground, but does it take a coons age to get to 4050rpm? I'm asking, not assuming. I have no clue if the engine gets up to rpms quick or if the air resistance keeps this from happening.

A turbo uses the exhaust gas pressure to spin a vane. At low RPM, the turbo will not boost much (this is turbo lag, and if they got rid of it in the last 10 years, hurrah)because the vanes on the turbo are designed for higher RPM. Variable vane turbos are designed to spin more at low RPM, and then the vanes flatten out at higher RPM so they dont overspeed. In 1988 shelby went from the intercooled turbo that I had, which was very peaky and had plenty of turbo lag (which was very common) to a variable vane turbo on the shelby shadow. It did wonders to broaden the powerband.

Aircraft applications are very different from ground applications. Turbo response is not an issue as we don't nail the throttle and expect instant boost nor do we need boost at 2000 rpm as the engine does not operate here (Wankel, Sube etc.) I have the largest A/R on my turbo available and boost response is just fine on takeoff even with old sleeve type bearings. There is no problem making 40 inches at 4000 rpm.

As far as density ratio (DR) goes, this is a function of compressor efficiency and intercooler effectiveness. The turbo books go over this in detail with the math if you wish to calculate. Note that Hugh McInnes' "Turbochargers "book will soon be released in its third edition. I have been lucky enough to be asked by the editors to supply photos, text and updated info for this. I haven't seen the latest draft yet but the first two were the best ever written on the subject.
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  #33  
Old 04-07-2005, 12:40 PM
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Quote:
Originally Posted by rv6ejguy
Note that Hugh McInnes' "Turbochargers "book will soon be released in its third edition. I have been lucky enough to be asked by the editors to supply photos, text and updated info for this. I haven't seen the latest draft yet but the first two were the best ever written on the subject.
that is the book i have been reading for 2 years, i respect your opinion, and am glad i also found a good source. I will also buy the update
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  #34  
Old 04-07-2005, 04:07 PM
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John Slade John Slade is offline
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Quote:
Then I suppose the question is, when you give the engine throttle on the line, does it take a long time to get the engine up to speed?
No, and as RV6guy said, I don't really care about this anyway.
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  #35  
Old 04-07-2005, 11:12 PM
martinkh martinkh is offline
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Is there a good book on propellor theory & design? Sounds like I need an edumacation.
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  #36  
Old 04-21-2005, 11:12 AM
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Default Prop matches on Subaru EG33

Here is a classic example of the problems with fixed pitch props attached to an atmo auto engine. He has had 6 props on this Cozy to date , all with dismal performance. This engine has a lot more torque than an atmo 13B.

http://groups.yahoo.com/group/subaru.../message/20586
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  #37  
Old 04-21-2005, 11:19 AM
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Quote:
Originally Posted by rv6ejguy
Here is a classic example of the problems with fixed pitch props attached to an atmo auto engine. He has had 6 props on this Cozy to date , all with dismal performance. This engine has a lot more torque than an atmo 13B.

http://groups.yahoo.com/group/subaru.../message/20586
Sorry, I'm not a member ant therefore can't read the post.
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  #38  
Old 04-21-2005, 11:37 AM
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Default Props and ECUs

I should have said a classic case of tinkering/ fooling with OE ECUs and not knowing the effect, combined with a fixed pitch prop attached to an atmo auto engine. Hopefully this will be insightful to others and Keith has found a solution with the inflight adjustable IVO. It will be interesting to see what transpires with this prop/ engine/ ECU combo. I've copied the message here for others to read:

My name is Keith and this is my first post to this group. I have a Cozy IV with a Subaru EG33, Ross 1.85:1 redrive. I've been flying for about a year now but the entire time I have been struggling with getting enough RPM, both static and high speed. Naturally, I've been mostly looking at prop pitch changes. However, it is very difficult to separate a low engine power problem from an over pitched prop problem. I have had a total of 6 props on the airplane. The first 5 ranged from 90" pitch to 84". All but one gave me 3600 RPM static (+/-100). The same 4 also gave me WOT level flight RPM of 4900 +/-100 RPM. The exception to these was a 90" 3 bladed prop that gave me 3800 static but only 4500 high speed. The 90" pitch was very interesting. It turns out that a large part of the disk is stalled at static. This produces actually less drag than the unstalled condition. So it turns 3800 static but as soon as you get up to around 30 kts, it starts unstalling and the RPM drops to 3400. All of these props have awful to God awful takeoff and climb performance. They are actually not too bad at the top end but could certainly be better if I could get up to 5400 RPM. I'm still working the prop issue. The 6th prop was an IVO ground adjustable. I had to crank the pitch down to 21 degs (72" IIRC) to get 4200 RPM static. I could not fly that prop due to other issues but I measured the thrust and got 608 lbs. I think that would be great for takeoff and climb. I measured one of the other props and only got 360 lbs at 3600 RPM. I just got an IVO in flight adjustable prop that ought to solve this problem once and for all. But I'm still not sure I'm getting all I can out of the engine, especially at the mid range RPMs around 3600.

My question is, is it possible that I have been operating in some degraded mode all this time? I have jumpered the park and neutral computer pins so that the computer does not think it is in either of those positions. I have simulated the vehicle speed input so that the computer reads about 35-40 mph at high RPM. I resolved all the error codes by simulating missing pieces with resistors (smog equip that I don't use). I don't have the IRIS installed. I tried it but it didn't make any difference. I'm burning 100LL. I've measured the timing. At idle it is 20 BTDC per the book. It increases to about 38 by the time it gets to 3000 RPM but then reduces to about 28 by the time it gets to 5000. The only error codes I get anymore is from one of the O2 sensors. The right one crapped out from the lead, I suppose, so I replaced it with resistors too. Those work most of the time but not at all RPMs. I'm told that the O2 sensors only effect the mixture at low RPMs. True? What else do you all suggest I look at to determine if the computer is operating to give the best power?

Keith
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  #39  
Old 04-21-2005, 12:48 PM
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scary - can't imagine running that blind, it would be very frustrating. With what little i know, could not even guess at what to do, i mean a wide band ox sensor would be a start to at least know what the a/f ratio was, but beyond that, having who knows what being done to the timing?
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  #40  
Old 04-21-2005, 06:55 PM
Craigbeee Craigbeee is offline
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Default WD?????

Anyone have any experience with Warp Drive props? They make some interesting claims RE their "constant speed" models. Very affordable,too.

http://www.warpdriveprops.com/
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  #41  
Old 04-23-2005, 10:15 AM
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Quote:
Originally Posted by Craigbeee
Anyone have any experience with Warp Drive props? They make some interesting claims RE their "constant speed" models. Very affordable,too.
I don't recall these coming into a discussion, you might take a look at the double-Suzuki Cozy of Venezuela with conter-rotating props. The props look like Warps or Ivo's.
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  #42  
Old 04-23-2005, 11:10 AM
argoldman argoldman is offline
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Quote:
Originally Posted by Craigbeee
Anyone have any experience with Warp Drive props? They make some interesting claims RE their "constant speed" models. Very affordable,too.

http://www.warpdriveprops.com/
My experience is with Warp drive props is mixed. I used them in my constant speed (airmaster) hub with my dragonfly, being turned by a Midwest (Norton)rotary. The blades are well made, however since they were originally designed for ultralights, suffered at high speeds. When my blades hit the ground they cleanly broke off saving the prop hub and engine.

If memory serves me correctly, the "constant speed modification" comes from when we were spinning the props past sonic speed on the tips. The guy that was the crue chief for pushy-galore modified the tips so that they woudn't react as a normal tip would at supersonic speed, allowing higher than normal T.O RPM and its increased power to be used.

There was a prohibition against using the warp drive props with a 4 cylinder engine (at that time it was VWs since there was a fairly high incicence of crank shaft failures with that combination.

The other problem that I ran into was that the blade area of the Warp is not enough to absorb the increased HP of larger engines. One of our boys that put a Sube in his D-fly ended up with a five bladed fixed pitch. (he now flies a O200 and I think he is converting to a Corvair For me to absorb the 115 HP of mine, the 3 blades stalled on TO until about 40-45 MPH, and at cruise were over pitched. I used them because they were the only blades that were available for the Airmaster hub, at the time.

I cannot speak to the high HP blades but would be careful in your assessment.

An other comment is that they are, I believe, heavier, although stronger. They are neat looking, however

Honey dos and donts prevent me from working on the Aerocanard today!
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