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Thanks, George, but actually, I “misspoke”
a bit. {:>)
It’s the increased velocity of the
exhaust gas gained by forcing it through a smaller area that spins up the
turbine blades at lower engine rpm and produces power there rather than the
exhaust gas flowing around or dodging the blades as I implied. Conversely enlarging
the exhaust area the gas is flowing through causes the gas velocity to slow
down and therefore does not spin the blades of the turbine as fast. But, the
conclusion is the same - smaller a/R for faster (response time) and lower rpm
boost and a larger a/R for slower spool up (response time) and higher RPM
boost.
The smaller a/R also tends to act more as
an exhaust gas restriction at high RPM plus it can over speed the turbine wheel
assembly - not to mention possibly blow your engine due to the higher boost
generated.
Ed
From: Rotary motors in
aircraft [mailto:flyrotary@lancaironline.net] On
Behalf Of George Lendich
Sent: Thursday, May 27, 2010 8:40
PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: a/R ratio
: [FlyRotary] Re: Rotary HP revisited
I've been trying to understand that for years - Thanks.
Ok, Chris,
If you are going to “blow”
your rotary, ya gotta use the correct terminology {:>). The correct
terminology is the a/R ratio or “ a R ratio” rather than
“aspect ratio – not bad” which is actually the ratio of
the exhaust area of the turbine outlet to the radius of the center of that area
from the turbine shaft. (see drawing below)
As you might imagine the more
“a” or area of your turbine exhaust compared to the radius of its
blades the more exhaust gas can “escape” around the blades without
imparting its full force. So with more “a” it takes more
exhaust gas volume to drive the blades to the same rpm. For a sports car
feel, a small a/R means the smaller area forces the exhaust gas to interact
more with the blades and gives you more Zoom at lower engine speeds.
Whereas for aircraft use you generally want more power at higher rpm (no need
at lower rpm {:>)) therefore normally an a/R of around 1.0 or close to it is
desired. Depends on a lot of factors, but that’s it in a
nutshell.
Turbocharger Area Ratio
A/R
The other consideration is the A/R. It determines when the turbine starts to
spool. The turbine housing A/R is the cross sectional area of the turbine
housing divided by the distance from the center of that cross section to the
center of the wheel. This makes sense if you look at the graphic.
If you take for example, the area in A1 and divide it by R1, you will have
found the A/R for this turbine housing. Each cross section and radius have the
same proportions so the A/R will be found by using any cross section/radius.
Common turbine housing A/R's are .58, .69, .81, .84, .96 and 1.00. The turbine
will start to spool sooner with a .58 A/R, and later with a 1.00 A/R. Lag will
be a problem if the A/R is too large, but if it's too small, the turbo will run
out of steam and be nothing more than a restriction.
If It works fine for John, it should
work fine for you.
Ed
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Chris Barber
Sent: Thursday, May 27, 2010 6:27
PM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Re: Rotary HP
revisited
When I ordered my prop from IVO I
pretty much had them send me exactly what John had. He actually
said..."you want what John Slade has?" At the time, IIRC, it
was a 68" at the time so that is what I believe I currently have.
I too have the 2.17 redrive.
I hav yet to order the module from IVO for it to regulate RPM.
May do so soon.
I think you and I have the same aspect
ratio of 96 (?). My first start with the turbo was with a six pound
spring but on advice of a trusted friend who has more experience, I replaced it
with a three pound spring to start out with. It was the three pound
spring that I ran yesterday. We are thinking that minor boost should be a
better starting point and reduce potential problems. Should we want more later
and determine it is prudent, we can increase it. The
"Performance" wastegate comes with various springs that can be
used individually or in combination from as low as 1.5 lbs upt to 25 lbs
+ (I believe).
The wastegate is located behind the
turbo. See the attached photo. Since this shot was taken about two
weeks ago, I have replaced the blue oil line with a stainless one with a 90
degree fitting. I have also fabricated and installed an additional weight
support to bear some of the load off of the turbo manifold.
I will post more pictures in separate
emails so not go over size limits.
From: Rotary
motors in aircraft [flyrotary@lancaironline.net] on behalf of
John Slade [jslade@canardaviation.com]
Sent: Thursday, May 27, 2010 9:40
AM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Re: Rotary HP
revisited
Hi Kelly,
My IVO is 66 (I found 68 gave too little ground clearance), 3 blade and the
higher pitch.
Yes, it's a 2.17.
Regards,
John
Kelly Troyer wrote:
What is
your "IVO" diameter, number of blades and are your blades the 30
to 90 or 45 to105 degree pitch ? If I
remember correctly you have the 2.17 to 1
RD1B gearbox.................
Kelly Troyer
"Dyke Delta"_13B ROTARY Engine
"RWS"_RD1C/EC2/EM2
"Mistral"_Backplate/Oil Manifold
From: John Slade <jslade@canardaviation.com>
To: Rotary
motors in aircraft <flyrotary@lancaironline.net>
Sent: Thu, May 27, 2010 8:44:43 AM
Subject: [FlyRotary] Re: Rotary HP
reviisted....now that I know more about it all...kinda.
Hi Ed, Chris,
That all makes sense, but I can add something from experience with the IVO prop
- The minimum pitch setting seems to optimum for take-off power. When I changed
from a big fixed pitch prop to an IVO at minimum pitch the difference in
acceleration was very marked. I have never taken off with the pitch at a higher
setting than minimum, so I can't attest to the effect, but if you forget to put
the pitch on full fine on the downwind, a go-around is much less doable.
Something else about the IVO that might help, Chris, is that when you throttle
back on final the airplane will want to slow down quite quickly. This is
somewhat unexpected if you're used to a fixed pitch prop that tends to make the
airplane float on final. The combination of fine pitch at idle, both rudders
and the landing brake make a Cozy (or Velocity I would think) come down like an
elevator.
One way to check that you have enough power would be to measure how much runway
you use to reach, say, 70kts. If it's more than 2000' I'd say you're under
powered. With a turbo and an IVO the acceleration should feel like a good
sports car, and the increase from 70 kts to flying speed will only take a few
seconds.
My 2c.
John
to Ed Anderson wrote:
No easy answer – to all the nuances
of producing power, Chris.
200 HP is a possibility depending on lots
of factors (like your total induction system set up, however, I believe that
180 HP is more in line with the likely maximum on the older 13B. The
Renesis a bit more/
Fuel flow is as much an indication of
power as anything short of a dyno and/or extensive aircraft performance
numbers.
RPM (in my opinion) has too many
variables – like I have a 74x88 prop with a 2.85:1 gearbox and can
turn 6000-6200 rpm static – does that mean I am making more or less HP
than you at 6200 rpm at 35” Hg. It all depends on what prop load
each of our engines are seeing at that rpm. Generally as a rough rule of thumb you can figure 10 hp
per gallon/hour of fuel flow. So it you have a fuel flow of 16
gallon/hour then your engine could be producing around 160 HP. 18 GPH =
180 HP, etc. Now your power won’t be more than that, but it could
be less. The rotary can flow considerably more fuel without making useful
power than a piston engine, but it is a useful rule of thumb.
I street ported my 91 Turbo block myself
using a Mazdatrix street
port template. I went through 5 intake designs and several muffler
experiments before finding one that appear to give me the power I wanted.
On a cold morning with OAT < 50F, I can get up to 6200 rpm and 18-20 GPH
fuel flow with the 74x88 prop. So I feel I have my set up just about as
good as its going to get – short of a forced induction system.
With your prop set at max fine
pitch, you have reduced the prop load on your engine to a minimum – that
permits your rpm to be at a maximum – but, that does NOT mean you are producing the power and
more importantly - the thrust needed
for safe flight.
Don’t be mislead by rpm.
As an extreme example to make my point, Without
a prop (almost no load) my engine will turn 5500 rpm at idle throttle setting
– but I am only flowing something like 1.5 – 2 GPH which means
producing something like 15-20 HP even though the rpm without prop is higher
than my static was when I had my old 68x72 with a 2.17:1 gear box.
So even though the rpm is the same or slightly greater, the engine not
making any where near the 150-160 HP I made with the prop on at the same
rpm. Fuel flow is not a perfect indicator but much more useful than RPM
alone in estimating your power particularly with a variable pitch prop.
This is important, Chris. Years ago,
there was a long EZ builder who had a non-rotary auto engine who unfortunately
ended his first flight in a fatal crash into a cactus plant. He
understood the electronics just fine, but did not understand the relationship
between rpm and thrust. He set his adjustable pitch prop for maximum RPM – which mean minimum prop load, which in his case mean minimum thrust. He managed to get
airborne with this limited thrust, but could not apparently climb out of ground
effect with the flight ending on impact with a cactus.
For example, you would get your
highest rpm with a prop that absolutely no pitch which would produce minimum
load on the engine – however, I think you would agree there would not be
much “push/Pull” by such a prop set up. With a variable pitch
prop, you need to find the optimum balance between rpm and thrust. Too
much rpm could indicate too little pitch (and too little thrust), too low rpm
could indicate too much pitch (and too little thrust) – neither condition
gives you maximum thrust.
The only way I can think of to find that
optimum balance between rpm and thrust is to attach your airframe through a
scale to an anchor. Then measure the pull on the scale at various rpm and
prop pitch settings. This should help you find where combination of
engine rpm and prop pitch provides maximum thrust (at least maximum static
thrust – which is a good start). Perhaps someone else can offer a
better and easier method. Yes, you should be able to get a feel during
taxi test – although some folks frown on the idea of high-speed taxi
test. Theoretically you could use an accelerometer, some accurate speed
measurements the weight of your aircraft and calculate the effective HP
– that has been done with automobiles.
In cases were folks are using fixed pitch
props with parameters similar to those used by others, you can make a
comparison and get a rough feel for engine performance based on RPM.
Unfortunately, with a variable pitch prop making such comparisons is more
difficult and questionable. Now if you can find someone using the same
variable pitch prop you are using and compare your rpm and prop settings, that
is certainly something worth checking into.
Just continue to ask these kinds of
questions and to think about the issues in producing power and thrust –
you’ll be ready.
Ed
.
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net]
On Behalf Of Chris Barber
Sent: Wednesday, May 26, 2010 9:51
PM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Rotary HP
reviisted....now that I know more about it all...kinda.
I know this must have been discussed,
but perhaps more in passing or in some of Tracy
's literature (now kinda dated, especially with some of the strides he
continues to make), but what is the conventional wisdom as to rotary
horsepower? I know when I first started looking into it, oh many years
ago, it seemed the impression I got was that you could pretty easily achieve
200 hp, however, that is now a bit lower. Some of the tricks to get the
higher HP was mild and medium porting, bridge, "J" and "P"
porting. Then there was the option of turbo...the one, in combination
with a medium street port, I chose.
When started today, mine was turning
about 6200 rpm at 35 MP (with a 3 lb spring in the wastegate).....it surged
forward against the chocks and breaks. IVO prop full fine. Nice feel
of power even if it likes to heat up fast in 90 degree weather like this.
Also, I think this was discussed before
too, when I go WOT my engine develops up to about 6250 rpm, but then
drops a couple/few hundred rpm to usually just under 6000....sometimes just
above. Thoughts? Ed, (perhaps Al)it seems you may have chimed in
before. Regrettably, when I search the archives I tend to get
frustrated due to thread drift.
I heard a lot about porting when I was
initially investigating all this and I chose to use a medium street port.
I let Mazdatrix do the work. That being said, I have read all but
nothing on others porting their engines (other than a LOT
from PL on P ports). Since standard porting does not reportedly effect
reliability, only, potentially low low idle (I can idle as low as about
1300 rpm when warm smoothly) why is it not discussed and/or utilized more?
Just curious guys/gals. Discuss
<g>
Always loved the lines of a Tailwind
– in fact, I have the plans and license to build a W-10 sitting on my
book shelf. Unfortunately, I doubt I’ll ever get around to it.
Ok with thermostat in the system holding
it at 190F – we really won’t know how much reserve capacity you
have in your cooling system until the power goes up.
I agree with George, 200HP out of an N/A
13B is really pushing it. I think 180HP is a more realistic expectation
– but, hey you never know. It amazing how power goes up when things
come together.
Enjoy and fly safe.
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net]
On Behalf Of John
Sent: Wednesday, May 26, 2010 2:36
PM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Emailing: 3
view w-10 003, first flight
My most humble thank you to flyrotary and
all you fine folks that have helped bring my project to flight.
Ed and many others whom I won't try to name here because I would miss
many. The plane is a Wittman Tailwind W-10, empty wt. is 981 and it is a
tri-gear, Wt. is within 6 #'s of similar trikes w/ 0-320 engines. I
have the thermostat in the engine because most of the year it is not very hot,
if we get 50 days with the temperature over 70, we have had a hot summer, not a
lot of beach bunny activity. 7-1 I'll be 74 and have realized my dream,
now it's all gravy. Again, thanks guys!! JohnD
Your message
is ready to be sent with the following file or link attachments:
3 view w-10 003
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