Well, Paul

I have been trying for a week to get out and put the new gear box on. But, one thing after another has precluded that so far. But, If I encounter no unexpected problems I hope to be flying again in about three weeks. Since the propeller will be "tuned" based on the rpm my engine will generate, I may go back to the manifold that gave me the best performance - yes, I never throw one away - it might turn out to be the best one. Interestingly enough it is certainly the ugliest and heaviest one of the 4 I have made - but it do work well. Tracy told me he had an inch taken off the length of his first prop and later as he found more power, he wish he had that inch back.

So I hope to avoid that. We will see.

Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC

----- Original Message -----

From: paul

To: Rotary motors in aircraft

Sent: Sunday, August 22, 2004 9:03 PM

Subject: [FlyRotary] Re: Compressor maps
----- Original Message -----

From: Ed Anderson

To: Rotary motors in aircraft

Sent: Sunday, August 22, 2004 7:10 PM

Subject: [FlyRotary] Re: Compressor maps

Yes, no matter what anyone tells you - it takes fuel to make power. Its always a bit amusing to hear folks talk about making 200HP with a fuel flow of 10-12 GPH, just won't come close with our current state of the art in engines. Either their measurement incorrect, there math is bad or they are simply embellishing {:>).

Ed

Hi, Ed....I was unfamiliar with the term embellishing, so I looked it up in Webster's. Loose translation is: full of crap. On a serious note....just doing a progress check on your aircraft.....any idea when you might get airborne again? I'm sure you miss flying the RV, but hopefully you will have improved performance to offset the down-time. Take care, and thanks for all the great rotary info you have been sharing. Paul Conner

Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC
----- Original Message -----

From: David Staten

To: Rotary motors in aircraft

Sent: Sunday, August 22, 2004 7:07 PM

Subject: [FlyRotary] Re: Compressor maps

Thanks EVERYONE for the feedback....

Ed,
I used the 1.6 PR at 3000 and 222 CFM simply out of ignorance.. I didnt know what else to use. Truth is, I dont think I (or anyone else) needs much boost at lower RPM's but rather need it at the higher end since for aviation we are gonna be running in the 70-80% power on a continuous basis...

Something else I stumbled across is that when making these large amounts of HP I noticed that the fuel flow is astronomical.. I'm thinkin ok.. 8-9 gpm with the rotary at cruise... but for lets say 250 hp I'm getting something like 20 gph (again ballpark numbers..) so it looks like truthfully its all about getting UP off the ground and up to altitude and then at altitude maintaining 160-180 hp (more like 15 gph)... I've always know that turbos would increase the fuel burn but never really sat down and did the math before.

And as an aside.. the mitsubishi turbo I had the inside line on.. as a result of all this calculating, it appears that it will be unsuitable.. just too small.. and will be passing on it..

Ed Anderson wrote:
Hi Dave,

Yes, the compressor map only knows its input (not the engines input - lots of confusion out there on this point) Some folk use the engine's CFM which is OK IF you adjusted for the boost as you did. You appear to have the concept down.

However, I am a bit confused, I notice your have a 13B, yet you use 222CFM at 3000 rpm - which is about twice what you should be getting out of a 13B, I get about 153 CFM. Wait! 153*1.6 = 244 CFM, Ok I see where you are coming from. Now the crucial question is - does your engine produce enough exhaust mass flow to drive the T06H turbine wheel fast enough to produce 1.6 pressure ratio at sea level? If it does then 6000 rpm underload will likely produce much more than 1.6 pressure ratio. What I am saying is if you could get 1.6 at 3000 rpm then you would unquestionably need a waste gate to keep from blowing your engine at 6000 rpm under load.

Also notice I keep referring to Load. If you are not producing a load on the engine (like when you are at idle) then your exhaust mass flow is very low and therefore so is your turbine speed and boost (you may be getting some, but not enough to get your boost gauge much past atmospheric) in none existent.

That is what makes it difficult to predict exactly what is going to be the end condition.

Yes, you are correct, if you have to err then error toward the side of less efficiency - that means you air will run hotter, but surge can destroy a turbocharger and damage an engine if encountered, so I would stay away from the left side.

Now one thing about the T06 - its not the best match for the 13B in my opinion - not to say it can not be used. But, lets say you only want to run 2- 3 psi of boost on an extended climb to keep temps down (hypothetical case). That would gives a pressure ratio of (taking the 3 psi). of (14.7+3)/14.7 =.17.7/14.7 = 1.2 pressure ratio which is off the map for the T06 as you can see.

The T04 is a better choice in my opinion since we are unlikely to be running above 10 psi of boost - at least I would not in an aircraft application.

Selection of the compressor wheel is 1/2 of the challenge. Compressor maps and an understanding of your engine flow capability and how to compare compressor maps takes care of that part. The second half of the equation is getting the right turbine wheel and correct A/r size for your Turbine housing. The is no cut and dry formula for that although Corky Bell in his book "Maximum Performance" has some general guide lines to get you in the ball part.

Even with our stock Mazda which is apparently excellent on the second generation Turbo engines turns out not be the right combination for aircraft. It was designed to produce lots of boost at low engine rpms (read low exhaust mass flow) and the engineers decided that most folks would not keep their foot to the floor for over a few seconds. Well, that turbine housing was specifically designed for low rpm acceleration rush, high engine rpms for long duration are simply pushing the stock turbo beyond its design and intended limits as configured for the auto. An Aussi company is making some modifications to the stock turbo which make it much better suited for our aircraft needs in my opinion.

John Slade should be receiving his in a week or so and hopefully we will see how it does.

In any case, Dave, you are on the right track. I especially like the fact your are considering the effect of "boost creep" caused by lessen ambient pressure at altitude - not everyone considers that important factor. They may luck-out or not.. Failing to do that can have you trying to use a turbo that is near or in its surge zone under boost at altitude.

Hope this helps

Ed

Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC
----- Original Message -----

From: David Staten

To: Rotary motors in aircraft

Sent: Sunday, August 22, 2004 11:39 AM

Subject: [FlyRotary] Re: Compressor maps

Ed,

I am trying to work my way through the compressor maps and formulae that I have stumbled across in the past few days, and looking at your formula, I am able to make sense of it.. and I am using a website with a calculator built in that reproduces your values...but the value of 277 cfm.. thats how much air the engine is pumping normally aspirated at wide open throttle.. right?

So plotting this at 1.0 atm and 277 cfm wouldnt event be on the "map" at all.. If I am understanding this at all.

Using the TD06H-20G map listed at http://cybrina.mine.nu/MR2_Docs/compressor_flow_maps.htm (and attached to this mail)
if I wanted to maintain 23 PSIA (8.3 PSIG) boost (48" map). which comes out to a presure ratio of 1.6..
. then I would need to calculate the CFM required at 1.6 PR..

At 3000 rpm I am getting 222 CFM and
At 6000 rpm I am getting 444 CFM... (1.6 PR),
which falls in the map on that site....

To take it further.. if I wanted to maintain that amount of boost (23 PSIA/8.3 PSIG) to say.. 12,000 feet..
Ambient pressure at 12k is a ballpark value 18"/9psi.. the pressure ratio there is 2.5...

3000 rpm, PR 2.5, comes out to 347 CFM.. appears to fall just left of where I'm told the "surge line" is
6000 rpm, PR 2.5 equals 697 CFM and falls to the right of the 65% efficiency island..

If I am interpreting this correctly that means that this turbo would be able to give the desired performance but would NOT be able to maintain 23" absolute boost to 12k feet....

5000 rpm at 2.5 PR gives 578 CFM and DOES fall within the map though...

I am throwing all this out there to see if I am grasping the concept clearly or not.. and to see what I need to adjust conceptually..

I am also guessing that the .55 value listed below by Mike, is BSFC.. correct?

I am trying to comprehend the "volumetric efficiency" concept as it relates to pressurized/charged intakes.. are we assuming a value of 1.0/100% or is this not realistic? What about porting... will that improve the VE? (I'm wanting to say YES) Iis it realistic or even possible to have a VE > 1.0/100%?

The reason for all the head scratching on my end is that I have several turbo 13b cores.. but none of them have turbo's attached.. so I get to pick what I want on there.. but I want to make sure I have a grasp of the concept before I start turbo shopping..

I must admit that this listserv group has been a literal gold mine of information. I have exposed to a truckload of data in the past 2 weeks and am just trying to organize it at this point.

Dave Staten
2nd Gen 13B rebuild in progress..

Ed Anderson wrote:
Mike makes a good point.  While the official displacement of the 13B is
1.308 liters (actually 1308 cc), for airflow/power purposes it acts the same
as a 4 cylinder engine of 40 CID (each cylinder) or 160 CID or 2.6 Liters.

CFM = (4*40)RPM/(1728*2) so for 6000 rpm, CFM = 160*6000/(1728*2) = 277.77
CFM at 100 Ve

Some compressor maps use CFM on the X axis and some use mass flow usually
Lbs/min.  My spreadsheet automatically calculates the lbs/min of air flow
for every rpm and power situation.  Or its easy enough to calculate.

Just multiply your air flow volume in CFM by 0.076 for sea level density.
So in this case 277.77*0.76 = 21.1052 lbm/min



Ed
Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC
----- Original Message ----- 
From: "Mike Robert" <pmrobert@bellsouth.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Wednesday, August 18, 2004 11:14 AM
Subject: [FlyRotary] Re: Compressor maps


  
John Slade wrote:

    
John, here is a URL to a pretty good discussion on reading compressor
maps with examples
 http://cybrina.mine.nu/MR2_Docs/compressor_flow_maps.htm

That's great, Ed. And you did it in one sentence. :)
Do you happen to know the engine capacity (in litres) and the
volumetric efficiency of an REW engine?
Regards,
John

      
John, the auto people use 2.6 litres and .55 for those turbo map calcs.

HTH, Mike

    
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