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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
Ed Anderson
RV-6A N494BW Rotary
Powered
Matthews, NC
----- Original Message -----
Sent: Sunday, August 22, 2004 9:03
PM
Subject: [FlyRotary] Re: Compressor
maps
----- Original Message -----
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 -----
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 -----
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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