Prop not a big factor but a factor, Tips on Racing
One of our rotary newsgroup bubbas (Dave Leonard) recently flew in the "Sharpie Speed and Economy Air Race" hosted by Dan Checkoway. The results can be found at this link:
http://rvproject.com/race.html
It would have been interesting to see what Dave could have done if he had a constant speed prop vs. his fixed pitch Cato. Maybe Ross and Dave will be able to hook up someday and fly side by side and then post the numbers of a turbo rotary and a turbo subie comparison of performance and efficiency.
Dave said he basically finishing tied for 2nd among the "side by side RV's" flying in the race, and that showed quite a few guys who were flying the race that the rotary doesn't necessarily have to drink a lot more fuel vs. a Lycoming while still posting good speed numbers.
Doug Lomheim
"Dave said he basically finishing tied for 2nd among the "side by side RV's flying in the race." What does that mean? Dave (Rotor) came in #7 fuel econ. Speed wise, mid-pack #5. He was close to #4, true. However the top 3 ran away from everyone. The top three, where 4.5 to 10.9 mph faster than Dave. But I agree, it was a nice show of Dave.
The
Side-by-side thing is my preference for comparative test. Its the best way to compare. In the race, they where two minutes apart. Really separate on the course. There was no side by side. There could have been some passing of slower planes by faster planes; don't get the "side by side" comment.
I don't think it (diff props, c/s) would made a difference. As you know c/s props have a substantial advantage for takeoff and climb. The airport L26 is 3390'. The highest terrain is 6,000', so we are talking about 3,000' min climb. I've done enough of these races to know, unless you know tailwinds at higher altitudes are a substantial benefit, don't waste time climbing. Its usually best to go low & fast, especially a short 111 mile long.
C/S props is not a big deal for this race. It does cost some economy. With that said, the fastest & most economical where all Hartzell's and the lowest three Econ planes where all composite props (MT-3 blade c/s, Catto-3 blade fixed and Whirlwind-2 blades c/s). The problem is must PSRU's can't use more efficent metal props, like the Sensenich.
In the racing world fixed props sometimes pose an advantage simply because the folks wrap their engine RPM way over RED LINE. I don't recommend it, unless its a dedicated racer & you have a chute on. Lycs & Continentals are over revved constantly, they seem fine. It's a way to make more power. Lyc gets mad when you start talking over 5% of Red Line or 2835 rpm.
As far as the Sensenich prop or even the Hartzell for that matter and the 2,600 rpm limit, that 100's is not going to make a whole lot of difference, may be 3-5 hp? so the diff in speed. may be 1%, about 1.5 or 2 mph? In this race it would be 0:30 seconds.
You can run your prop at 2,700 rpm for 30 minutes with out disaster. The reason is the design is for infinite fatigue life. Infinite in fatigue terms may be a finite number, like double/triple expected service life, may 10 thousand's in hrs, basically infinite for a GA prop. Most hartzell's do NOT have a high rpm limit unless you have electronic ignition.
In these races flying smoothly & straight (autopilot a big help). THis will save you minutes. Picking a good altitude and making the turn properly can help way more. The latter, turn procedure is usually a little wide, with the way point as the apex of the turn. Avoid steep banks.
Winds on the day? Headwinds and tailwinds on a two way run like this race, does not cancel. Headwinds act on you longer than a tailwind benefits, so no wind is faster. However you could play altitudes on each leg, flying lower to the gnd for headwinds (which are almost always lower close to the ground, aka, friction, coriolis affect) and higher on the tailwind leg (winds tend to increase with altitude).
Carbs are fast? YES! Carbs ROCK. They just tend to not be able to tune that last few ounces due to slight fuel distribution imbalance. Carb= HP. Watch the week end hot rod shows. Watch the drag races. You'll see Carbs a plenty. BUT WHY HIGH ON ECON? Well that red knob and pilot technique comes into it.
Pilot technique, skill, luck help, but the airframe makes a big difference. You might have the coolest engine and prop, fly it right, but the LOW DRAG airframe has the advantage from the get go.
LOW DRAG AIRFAME, is the gift that keeps on giving. It helps both SPEED & Economy.
Also interesting that the "best economy, ""best speed with economy," and "lowest cost" categories were the carb'ed, not the fuel injected. Only in "top speed" did the fuel injected do better.
Maybe this is because all the fuel injected folks thought they had a chance at the "top speed" award and burned the necessary fuel to prove it? (It would be really neat to hear what each of the pilots was trying to show. It would give the numbers more meaning.)
Take it all with a grain of salt, there where "strategies", as you suggest. Some traded speed for gas or vice verse. Some did very well on both sides of the coin, bravo, Brad "Wingnut" Peacock, Lyc 180HP and a Hartzell 7666!
Why are some slower or less economical? There does not seem to be any gross navigational error. I am not being funny, sarcastic or critical, it happens during races.
The course had two major turns at VOR's not observed. This can lead to some variations?
I'm not saying any one cheated. What I'm saying if you race you cut it close. If I knew there was a spotter and flying over the VOR 1-inch would give me a big penalty, I'd fly with a bigger margin and a longer course. Some may take it wide to make sure they don't cut it. Some may cut it close and shoot inside by 1/16 mile. It's not be cheating, but does affect the results. Two wide turns +90 degree turns can add what, 2 miles or almost 2% more course length.
This is why side-by-side comparisons are good. Racing is good but you have to include the race factor in the results.
Now with the aforementioned variation that can occur in racing lets look at the race:
Taking the top 4 econ winners the average is 17.57 mpg;
throwing out the median,
the average of the bottom 4, including the Wankel, 12.95 mpg.
That is a 37% difference.
Throw out top and bottom its 16.66 mpg for top 3 (top 4 minus highest)
Throw out the bottom, 13.49 mpg for the bottom 3 (bottom 4 minus lowest)
That is 23.5% for the top pack to bottom.
So there was a distinct dividing line
Speed with econ:
Brad "Wingnut" Peacock had fastest plus was 3 most Economical. The fastest being 209 mph, block from a standing start/ low fly by is not too shabby, with a 180HP Lyc and Hartzell 7666.
Larry "Hack" Hackney #2 on Econ, #9 speed, strategy? Sure.
David "Rodoc" Leonard Rotary did a nice mid pack #5 in speed and #7 in Econ.
Throwing out Brad "Wingnut" Peacock (great job), the top 5, minus Brad, the top speeds where fairly well packed, less than 5 mph. That tells me it was a well run and flow race with equal planes.
The bottom 4 where speed are also well placed, and two of the planes in the slower half where top econ performers.
Again issues with nav (flying further), technique, climbing higher for tailwinds which don't materialize, flying higher for more comfort/safety margin and possibly mixture technique?
## Of the three with lowest Econ they where all wood composite props. The fastest and most Econ where all Hartzell.
