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A Few Performance Numbers

Ironflight

Ironflight

VAF Moderator / Line Boy
Mentor
Having survived a couple of days of fog, rain, and low clouds, I was itching to go flying in the clear blue of the Houston skies this afternoon. I had gotten a PM request from someone for my speed numbers the other day, and I was curious to see if they had changed any from my test flying a little over a year ago. While hardly scientific, I found that things matched pretty well, and since they are handy on my knee-board, I might as well let folks see them.

This data was taken directly off of my EFIS, which gives me real-time TAS derived from IAS, altitude, and temperature. My EFIS ASI and backup ASI are in agreement to within a knot, so either they are both off, or the numbers are pretty accurate (During Phase 1, I flew numerous wind triangles to work out the CAS corrections, and these numbers should be as close as we can expect to get in the homebuilders world). I stabilized the airplane at each altitude based on realtime Density Altitude, then took took the readings. And the Sea Level numbers were actually taken at maybe fifty feet - a slight error, and a benefit of living on the coast... :cool:

The percent power numbers are taken off the EFIS, which computed them from available data. All these readings were at Wide Open Throttle, and full RPM (2650). Engine leaned for peak HP above 5,000'

Sea Level, 29.0 inches Hg, 102% HP - 186 KTAS
1500', 28.1 inches Hg, 98% HP - 184 KTAS
6000', 24.1 inches Hg, 83% HP - 180 KTAS
10,000', 20.7 inches Hg, 70% HP - 175 KTAS

Out of curiosity, at 10,000', I then brought the RPM back to my normal cruise of 2350, and got:

10,000', 20.7 inches Hg, 65% HP - 170 KTAS


And then I decided I'd done enough boring data takes, and had some fun on the way down! Performance is pretty much what I got durign Phase I.

Data is worth what you paid for it.... :D

Paul
 
Ironflight said:
Sea Level, 29.0 inches Hg, 102% HP - 186 KTAS
1500', 28.1 inches Hg, 98% HP - 184 KTAS
6000', 24.1 inches Hg, 83% HP - 180 KTAS
10,000', 20.7 inches Hg, 70% HP - 175 KTAS
Click to expand...
and that 65-F, 50% RH weather this evening probably didn't hurt either! :)
 
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Ironflight said:
10,000', 20.7 inches Hg, 70% HP - 175 KTAS

Out of curiosity, at 10,000', I then brought the RPM back to my normal cruise of 2350, and got:

10,000', 20.7 inches Hg, 65% HP - 170 KTAS
Click to expand...
I noticed that the MP didn't change at all despite reducing RPM from 2650 to 2350. Is that a typo, or did it not change?
 
sprucemoose said:
I noticed that the MP didn't change at all despite reducing RPM from 2650 to 2350. Is that a typo, or did it not change?
Click to expand...

Nope, MAP didn't change while bringing the RPM back. Theoretically, that is what should happen (throttle controls MAP, Prop controls RPM), but it does seem like frequently, you get some coupling. In this case, I didn't. You do, however, see the %HP drop (%HP being a function of both MAP and RPM - as well as altitude).

Paul
 
Speed is life...

Hey Paul, Not too bad, would you like me to post my HR2 numbers, just for grins...:)

Smokey
 
smokyray said:
Hey Paul, Not too bad, would you like me to post my HR2 numbers, just for grins...:)

Smokey
Click to expand...

I'd love to see 'em!! I'm always interesetd in real-world numbers - no matter what they show. ;)

Paul
 
Got fuel...?

Pierre,Paul;
I know Doug doesn't really consider the Rocket an RV, but 85% of my airframe came from Vans..I tell all my RV friends that the Rocket will match RV performance with equal fuel burn. The problem is throttling the big six back to those settings, you just keep inching the power up!

2000 msl 69 degrees F (IAS with G-396/ASI +-5)

23/23= 188 knots 12.5 gph
24/24= 195 knots 13.5
25/25= 205 knots 14.5
27/27= 218 knots 15.5

Where it really shines is above 10K. 20"/2300 RPM is 195 knots true at 11.5-12gph. With 54 gallons that is right at 1000nm range. This in an airplane that lands at 65 knots on my 1900' strip, no worries. Gotta like it...

Smokey
 
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Simple Conservatism...?

William Slaughter said:
Paul, what happened to the other 50 RPM?
Click to expand...

Actually, my governor and prop came out of the box with a top end of about 2680, and I have simply never taken the time to go back and do any fine tuning. I'm not going to race any HR2's anyway.... :p

Paul
 
Ironflight said:
Actually, my governor and prop came out of the box with a top end of about 2680, and I have simply never taken the time to go back and do any fine tuning.
Click to expand...
Ditto. 2680 on the nose. Adjusted my prop governor, and now I get 2720. The takeoff roll was shortened by at least 250'. Just kidding. But I did adjust it up.
 
Different Data

Well, since we are posting data?? I left the RV8 at home and now piloting another craft that I operate about half the year. She burns a turbo charged 368 GPH and moves right along at 16 knts. Burn rate is high but she has good range. Her tanks hold 393,305 gallons which gives her a range of 17,100 NM. If you use the cargo area for ferry fuel, you can get 446,478 NM out of her. Sea level numbers. :p
 
OK then.......

How 'bout 47 GPH Jet A and 125 knots? Yep, I have burned near 400 gallons in one day with 9 tach hours on the Exterminator, my PT 6 powered Air Tractor (dot com). killing boll weevils :D

my.php
[/URL][/IMG]

Blue skies and tailwinds....er..tailwheels :D
 
Ironflight said:
Nope, MAP didn't change while bringing the RPM back. Theoretically, that is what should happen (throttle controls MAP, Prop controls RPM), but it does seem like frequently, you get some coupling. In this case, I didn't. You do, however, see the %HP drop (%HP being a function of both MAP and RPM - as well as altitude).

Paul
Click to expand...

Wonder why the designers of your engine monitor system decided MAP/RPM are the indicators of HP? The base constant of power is fuel consumtion, not MAP or RPM.

Maybe my thinking is contrary but I always flight plan and cruise on fuel flow - knowing what TAS is produced at a specific FF from experience. It can be at 2300 rpm, 2100 rpm, it doesn't matter. WOT is supposed to be most efficient due to least intake air flow obstruction, so that is also a factor, but sometimes the throttle is closed slightly to meet the flight plan fuel flow. RPM makes a difference due to prop efficiency. Altitude matters - from phase one testing at 2100 rpm WOT - @ 8500' (20.25 mpg) @ 12000' (22.35 mpg), a +10.3% at 12000'. (no wind, of course)

I guess I am stuck on fuel flow and speed rather than MAP/RPM because fuel is all that matters going anywhere. You've got to have enough to get there and be able to plan reliably, the percent of power used to do it is nice to know but not essential. X amount of fuel burn equals Y percentage of power, MAP/RPM matter not.

Maybe it all comes down the same, just a different way of looking at it. With my engine, 8 gph is a good cross country number, 6 gph is good for local loggy gagging. Anything above 8 gph is a waste of fuel in terms of efficiency. Above 8, the percent of speed increase does not match the percent of fuel burn increase. I wish it were better, but it isn't. Am more inclined to be low and slow these days as the engine will last longer and so does the shekel pile. :)


David Domeier
RV-7A N707DD
H6 Subby

By the way, Paul, your numbers are excellent!
 
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I think that your way of looking at it is quite valid David - there should be a direct correspondence between power and fuel flow - as long as you have the mixture at some known point.

I have said before that my favorite graph in the Lycoming manual is the one that shows a single line of "Minimum Fuel Flow vs. Percent HP". It has been my experience that I can set up a MAP and RPM and play with the mixture knob and vary the fuel flow quite a bit while maintaining the same airspeed (in level flight) - which tells me that within the accuracy of perception and instrumentation, I can get the same HP for different fuel flows if I operate off-peak on mixture. Some of us are still running these primitive engines with that silly mixture knob...you folks with computer controlled Subies are always on an optimum mixture curve I bet!

I think that GRT chose to use MAP/RPM for their Hp display (just guessing here) because that is how the Lycoming manual implies that it is done.

I think that your approach to flight planning is a good way of looking at things. I tend to look at it as a % HP exercise so that I know when it is safe to lean...(below 75%). I also tend to like to go fast, so I rarely throttle back to less than WOT in cruise above 8,000'. I spent a lot of years flying much slower airplanes, and the speed buzz hasn't worn off yet I guess...

Paul
 
pierre smith said:
How 'bout 47 GPH Jet A and 125 knots? Yep, I have burned near 400 gallons in one day with 9 tach hours on the Exterminator, my PT 6 powered Air Tractor (dot com). killing boll weevils :D

my.php
[/URL][/IMG]

Blue skies and tailwinds....er..tailwheels :D
Click to expand...
Love that pic! It's the new desktop on my PC after some crop and digital mojo:

arapp_combo.jpg
 
Hey Paul
Here's my numbers from today's first flight.
4000' PA, 11 deg. C, WOT 26.1 inches, 2650 rpm 182 KTAS.
My numbers fall right between your 1500' and 6000' numbers.
Aerosport Power 180 hp O-360 carb. 74" hartzell BA.
Jon
RV8
 
jthocker said:
Hey Paul
Here's my numbers from today's first flight.
4000' PA, 11 deg. C, WOT 26.1 inches, 2650 rpm 182 KTAS.
My numbers fall right between your 1500' and 6000' numbers.
Aerosport Power 180 hp O-360 carb. 74" hartzell BA.
Jon
RV8
Click to expand...

I guess it goes to show that if we build 'em like Van says, we get consistent results!

Paul
 
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