"Steere, John" wrote:
Paul;
The pictured engine is in my BD-4. Our discussion at Oshkosh
sprang from my wish that I had an in-flight adjustable pitch prop.
My pitch is currently set to redline the prop (2700 RPM) at full
power at my normal cruise altitude of ~5000 ft. In climb out at
90 mph, I can achieve 1667 FPM at ~2300-2400 Prop RPM [4080 engine
RPM] at my normal flying weight. 1600 FPM isn't too bad at 2100
lbs, but if I had a variable pitch prop, I could develop full
power during climb and get closer to 2000 FPM.
I wasn't thinking what this "hand grenade sounded like running at
full power" when you suggested looking at a higher PSRU ratio.
All I
could see
was $$$$$. The engine is very smooth at full power and emits a
pleasant,
masculine supercharger whine.
The 3.8L SC engine is rated at 210 HP in the car. While I have
never had it on a dyno, I have no doubt that I am achieving
something in that range or better. I'm very pleased with the
performance of this engine, but I would be even happier if it had
a two speed transmission.
Before buying an in-flight adjustable prop, I will change the
pitch on the Warp drive from 17 to ~12 degrees of pitch at the
tips, then record the climb performance.
Keep up the good work on the NG. I'm learning a lot lurking in
the bushes.
John Steere
Thanks for clarifying the numbers John.
Yes on your SC HP. I was referring to the normally aspirated V6
mentioned by Holger. I was not clear on that point. I am looking
forward to the data at 12 degrees of pitch on the Warp drive prop.
1600 FPM is 26.6 FPS straight up with 2100 pounds is 56,000 pound
foot per second or 101 net HP required for climb alone. This is net
HP out of the prop so giving the prop the benefit of the doubt at
80% efficient that is 127 HP out of the engine. This is just the
climb HP required to lift that weight at that rate so the
aerodynamic drag is not included in this calculation however it is
rather low at only 90 MPH.
Calculating the drag... giving things again the benefit of the
doubt. At a flat plate equivalent of three the drag would be 90^2 X
.0026 X 3 or 63 pounds of drag. 90 MPH is 132 feet per second so 63
pounds of drag times 132 FPS is about 8300 pound feet per second
or about 15 net HP out of the prop. Out of the engine it is 15 HP
dividing by .8 or 19 HP for a total of about 146 HP out of the
engine. Probably a bit more as induced drag from lift is a factor
at 90 MPH. 90 MPH is usually a bit below the bottom of the drag
bucket MPH.
I still think you need to get the RPM up to at least 4500 on the
engine somehow. I think you would still be better off cutting down
the diameter of the prop.
What is your top speed so far John?
Paul Lamar
Having owned & flown a Lyc 180hp/cs prop 'stock wing' BD-4, I can
tell you that his climb rate is much better than I would have
expected hauling that kind of weight if he has the stock wings (not
longer span). I flew mine to OSH a couple of years ago with a
neighbor in his C-182. He was at gross weight & I was at my gross of
around 1900 lbs. We would break ground at around the same spot, I
could rather easily outclimb him and pass him on climbout (100mph vs
120mph climb speed. I could outrun him below about 6k feet & he
could outrun me up higher. Neither of us had wheel pants & our
cruise was around 150-155 statute mph. I don't think I saw more than
1300 fpm when fully loaded. If John is doing 1600 fpm at 2100 lbs
with a fp prop pitched for cruise, he's beating a 180 Lyc. My plane
was rather dirty, but at 100mph climb speeds that wouldn't make a
lot of difference.
Charlie England
What are the two spans? What is the cord?
Paul Lamar
Paul;
My span is ~29 ft, a 22 inch extension on each side. The BD-4 chord
is 48".
John Steere
Wing area is 116 square feet
Dynamic pressure at 90 MPH is 21 psf
Lift is 2100 pounds at 90 MPH.
Lift coefficient is 1.16 at 2100 pounds.
Lift coef. squared Cl^2 is 1.35
Wing aspect ratio is 7.25
Drag coefficient due to lift is 1.35 / (7.25 X 3.1415)
or 1.35/23 or .059
Drag due to lift alone is 143 pounds.
Net HP 143 times 132 feet per second or 18,876/550 or 34 net HP.
Engine HP is 42.5 with assumed prop eff. of 80%.
Total HP is now up to 146 + 42 or 188 HP at 4000 RPM.
Check my numbers. Always :)
These numbers are based on the reported climb rate. Lets check top speed.
Induced drag due to lift fades into the background as the Cl (the lift
coeff.) goes way down and we can go strictly on flat plate equivalent.
186 MPH is 272 FPS
Dynamic pressure at 186 MPH is 90 PSF
Flat plate equivalent area drag number is assumed to be 3
Drag is 270 at 186 MPH.
Pound feet per second is 270 X 272 FPS or 73,400
One HP is 550 pound feet per second.
Net HP out of the prop is 73,400/550 133 net.
Prop eff. is assumed to be 80%.
Engine HP is 166 HP
Check my numbers. Always :)
Looks like I underestimated the equivalent flat plate area. Probably closer
to 3.4. That error will hardly affect the HP required to climb however.
Lots of HP there John at only 4000 RPM with your super charged engine.
The Warp Drive prop is working pretty good too. You should bring it to
Sun & Fun next year and enter it in the Sun 100 race.
BTW did you modify that outlet duct on the intercooler?
Charlie, what was the top speed of your Lyc 180 HP BD4?
Paul Lamar
Paul;
I have not removed the outlet duct yet. I want to temporarily install a
thermocouple on both sides of the intercooler so I can record data with and
without the outlet duct. I'll let you know the results, but it may be
several weeks before I get it set up. Life gets in the way of my hobby at
times.
John Steere
OK John no problem. Also as I recall the outlet duct for the rad could
be bigger too. While you are at it. :) When you get time.
Paul Lamar
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