HP/Prop pitch ratio??

Logan, I agree with M1. If you only make a few long trips per year, but want to get there faster, just push the rpm up higher to get the speed you want. The fuel flow is going to be higher either way. This way you will have the take-off/climb performance the rest of the time. Spend the $$ on gas instead of the prop.

I'll have to look at my notes, but from memory these are the results when I first started flying with the new engine and did some testing.

I get very similar climb rate at 60, 70 and 80 mph, these were timed climbs with the airspeed stable, started timing at 1000' stopped at 2000'.
Fuel burn rate is very similar from 2100 rpm to 2500 rpm, that is miles per gallon. At 2600 to 2700 the fuel burn per mile increases, full throttle will get me 2800 rpm. Testing was done with a gps, light winds, alternate tracks and JPI fuel flow, leaned to peak egt. In my installation 2400 rpm seems to be a nice choice, reasonable speed and fuel burn rates and the engine seems happy. There is more noise and vibration at 2500 without much if any gain in my installation.

Here is the real kicker. I went from a 150 hp O320 to 180 hp O360. The O360 can burn lots more fuel, but at similar cruise air speeds to what I flew with the O320 I get very similar fuel burn with the O360, in other words the same horsepower and same airspeed as before, and that was with a completely different propeller too. On climb the O360 burns lots more fuel than the O320, but I get a better rate of climb.

Your results are sure to vary from mine.

Another 2 cents

M1

Rob Murray said:

This may be a bit beside the point, but I just put Wip 2100 Amphibs on my 150hp Cub and have been pleasantly surprised by the performance. 100-102 mph at 2400 with a 74DM6-1-56 prop that Sensenich made for me.
T.O.s are a little bit longer than when I was on EDO 2000s, I keep the angle of climb a lot more shallow and don't make any steep turns until I have altitude and airspeed. Must admit I don't go into very many small lakes and most of the water I use is between 500 and 1000' ASL. Haven't bothered to calculate the fuel burn yet, but I'm glad to have the higher cruise on long X-countries. Any comments?

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Rob, Many years ago I did some comparison tests with several different props on a 7GCB on EDO 2000s and a PA-18 on EDO 339-JHS amphibs. I ended up with a McCauley 1A175GM80-46 which gave the same cruise speed of 100-103 mph as the 74-56. The rate of climb increased by about 30% with a reduction in take-off time of about 30%.

Thanks Skywagon. Interesting. So long as I don't loose the cruise speed, shorter T.O.s and better rate of climb might justify going to a different prop. (I see you are in S.E. Mass. Was that Dennis Burkes PA18 by any chance?)

Yes Rob, it was. He settled on a 82" with a little less pitch. The performance on both were the same. I felt that the extra 2" were just spinning around without producing anything. Couldn't document the difference just a feeling. We tried several different 82" and the one 80" on both planes. Besides the performance gains you will find that it runs a lot smoother.

Small world. Soon as I get the floats paid for, guess I'd better start looking for a new prop.

M1 said:

I tried this once, went from 41" to 43" - flew for a while and then went back to 41" since I didn't really see any better cruise performance,

That's what I'm (now) thinking. Originally I was just feeling that a bit more top end speed would be a GoodThing, but now, with the help of y'all here, I see that it comes at a cost. That cost is always present, even tho I'd only enjoy the speed a few times a year.

Logan: What RPM does your engine run when climbing, say at 70 IAS?

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I did a run for you yesterday. Air was cold, so prop/engine were more efficient, but holding 70mph indicated, she pulled 2500rpm, and GPS said 1200+ ft/min. That gave more fuel to the thought that I shouldn't change anything. Thanks for that, Mike.

skywagon8a said:

Logan, I agree with M1.

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I am in agreement with your agreement with M1.

How does the length vs pitch efficiencies work I imagine the lines of speed would cross somewhere.


The premise is that the longer the prop the more efficient it is...
the slower the prop the more efficient it is.....

if a longer prop slows the motor down and more pitch slows the motor down

where in the curve does the short pitched prop equal the long flat prop??

now that we are up moving through the air does the greater pitch of the short prop overcome the efficiency of the long flat prop and give more speed??

is there an aerodynamic point of no return on a cub that says it is so draggy at this (MPH) breaking point it begins to take exponentially more power and prop for very little gain??

OK, just in case this horse hasn't been beat enough...
AND to confirm my incredible fuel burn rate...

Just got back from a trip up to Atlin & Whitehorse, and flitting around the Yukon & northern BC. I saved all my gas receipts & divided by the GPS flight time & came up with 5.3 (Canuck) gals/hr. That's about 6.3 US gal/hr. & does not include the gas burned in runups, taxiing, etc. I'm quite happy, and believe it is because of: Bart's magic, couple of wing mods (Jerry B) and being as anal as possible about drag thingies.

My Borer is stamped as 41" but flying with another "160 - 0320" & a 44" Borer @ same RPMs we had identical airspeed. His is a highly modded '22 & mine is a slightly modded '18, both on EDO 2000's & similar loads. Anybody have a WTF on if the props are different or the same pitch?? I'm thinking that mine is NOT a 41.

Sure wish I understood what you're talking about!
I replaced the old tach with a new SW aircraft tach, and the RPM readings were identical, so I THINK it's accurate. Also think that over 20 hrs of flight time would give an accurate fuel burn, no? I consistently bought less fuel than the bud's 0320 - 160. (I used the total GPS time from all flights)

Pleeze advise where the doubt/inconsistency could be??

OK, I see what you meant (suspected that, so I included: "I used the total GPS time from all flights").

This just confirmed my fuel burn from when I flew 3 hrs to get to Kraploops & Bart poured in 15 gals. I asked him if that was possible, and he said yep. (paraphrased)

Aviator said:

View attachment 19133

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My IO-360 pretty much agrees with this chart when leaned.

Nimpo,
I would pitch your prop up to a 44" pitch as it sounds like you have a pretty strong engine, expect it to cost you an extra 50' getting off the water, I bet it climbs out 150' fpm better, and gains you around 3/4 mph, But I would expect to see around say 125 less rpm static.
I had a 82/44 on a cub that was a 160 narrow deck from an Apache, that we stuck 170 pistons in .
However it originally had a 82/41 same as you do, it got off good, but thats were it ended, if you didnt run it right up to 2500 for cruise it " dragged its ass in the air..... not cool. SO I put on a new 44 pitch, bingo ! Got off 99% as well, climbed better, cruised little faster, and set right up rock solid at 2350 no tail droopy jazz what so ever, nice tail high Cruise attitude, you will be pleased, (garanteed!)
E

An oft-overlooked way to get a bit more RPM - and pwr. - for just a few $$ is by getting the front-end dynamically balanced.