Thorp Air Command - T18.net

I thought I would post the performance numbers with my new prop.

The previous prop was Great American 68x74. (also has 180HP stamped on it)
New prop is Ed Sterba 68x72.

The actual length of the Sterba is actually 5/8" longer than the Great American. The cord and thickness of the Sterba is definetly less.

I have a 150 horse 0-320.

Static RPM before was 2,100 now is 2,300.

Takeoff and climb is MUCH faster. I do not have actual data but it is a very noticable improvement.

No change in top speed or RPM! Four direction test WOPT at 7,500' is 154 knots at 2,550 RPM.

After seeing the increase in static RPM I expected to see an increase in top end RPM??? Thoughts...

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Matt Smith
Des Moines, IA
55RC

Hi Matt,
You say that the new prop is thinner... I'm wondering if you might be seeing a little "almost constant-speed" effect like we see with the Aymar-Demuth props, that isn't there with the thicker, possibly stiffer Great American unit. That's where the prop flexes and flattens it's pitch when under heavier air-loads (like takeoff/climb), then relaxes a little as speed builds in cruise. Just a thought.

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John Evens
Arvada, Colorado
T-18 N71JE (sold)
Kitfox 7 SS N27JE

Just had the same thought John, don't know what we are going to do with Mike being gone. I would hope that AD props will continue.....Dan

What happens to a prop buisness like AD when the builder/artist dies?
I have a Ted Hendrickson prop, as does my son Peter, on his RV-4.
Ted sold his prop buisness, and he is still alive.
But AD is different because Mike died suddenly.
Is there anything of value that still could be considered an AD prop enterprise?
I wonder if someone could get the data files and any tooling, and carry on?

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Scott Emery
EAA Chapter 326
T-18 N18TE

Good question Matt. Perhaps Spanky could give a more definite answer. I would say that you are comparing apples to oranges. The top end RPM is simply a function of drag versus horsepower. Since you have not changed your engine, I would assume that the drag is similar between the props at high subsonic speeds. Not uncommon. When changing between prop manufacturers, you can not compare numbers. They all measure pitch at different locations.
Cubes

At this level, the best way is to flight test and compare. Unless you've got many more specifics on the props, I don't think you just can't eye-ball them and make a WAG as to the exact impact each will have on the aircraft's performance. I assume Cubes is refering to the prop's tip speed and not the airplane's speed when he wrote "high subsonic." We saw what happens to a T-18 when it gets to just really low subsonic.
Spanky

Yeah, I was referring to tip speeds. Drag is drag. Matt may not have enough horsepower to effect top end RPM.
Cubes

Hi Matt,

You lucked out and got the best of both worlds with the new prop. Better takeoff and climb (higher rpm) with the same top end. Like John stated "almost constant speed". Some of the wood props seem to do this somewhat. If you had put a metal prop on that gave higher takeoff and climb rpm, you would also have higher rpm at top end (at the price of lower top speed) as the metal prop does not flex to a higher pitch at the faster speeds as some of the wood props seem to do.

Matt,

I had the exact same propeller on my 150HP RV-4 for 3 years. Over it's life I tested nine different props on my RV4. Airframe differences, drag reduction and engine performance all affect top end max RPM. Before you change anything, use a prop tach inflight to verify your information. I added electronic ignition to one side and REM 37BY plugs on my Mag side which greatly improved performance. Ed Sterba will actually adjust/trim your prop for you to get desired RPM.
My goal with a FP propeller is to receive rated RPM(2700) at 11,500 full throttle. This requires the prop to spin to roughly 2850 at SL full throttle. The only 2 props I flew that challenged this rule were Bernie and Margie Warnke's props, amazing "flex" inflight.

I currently operate a Catto composite, the finest FP I have tested thus far.

V/R
Smokey

Thanks everyone,

Not planning on changing anything, I was just currious about the limited top end RPM. I am really pleased with the results. Almost made it worth not flying the month of September. OK not even close, we had great weather the whole month, I really would have rather been flying. But I am glad it is done (I still have some interior work to finish), and now my conditional is good until after 2013 KY Dam.

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Matt Smith
Des Moines, IA
55RC

Smokey, what was your top RPM and speed in the RV4 with this prop?

I have tested my tach with and optical tach on the ground at three different RPM and my tach does read about 50rpm slow so really I am turning 2600 WOT at 7,500'.

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Matt Smith
Des Moines, IA
55RC

Matt,
Your above numbers appear to be right on. A little airframe/fairing tweaking and electronic ignition or hotter plugs(REM 37BY) would easily give you another 100 RPM. My RV4 would indicate (213 MPH) 172KIAS at 2840 RPM (WOT) at S.L. with the ND 150HP 0-320 and Sterba prop. 5500' cruise at 2500RPM/22" was 150 Knots. The Sterba performed very well for the price. Make sure you use 7/16" bolts and/or check the torque every 25 hours and avoid RPM above 2200 in rain. Refinish with light sanding and Spar Varnish. Also be very vigilant to inspect for cracks along the grain. One more reason to go composite, someday...

V/R
Smokey

PS: My current RV6"X" has a 150HP 0-320ND EI Electronic Ignition/Vetterman tuned Exhaust with Craig Catto's latest design 2 blade with nickel leading edges. A recent trip to W. TX and back showed 170 KTAS at 11,500 2700 RPM/18".

So, Smokey......let's open a can of worms...............do you use mogas in that 150HP O-320?

I do!

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Matt Smith
Des Moines, IA
55RC

Sir, I cannot tell a lie, YES I do...
I have been utilizing MoGas for over 20 years having grown up with an IA Dad who ran nothing but MoGas in our family STC'd 57' Cessna 182. Over the years I have used it in my T-Craft, RV4, HR2 and now the RVX. I have found some additives I like including CD3, Marvel Mystery Oil and even 10% 100LL.
Currently I have a local station that sells 91 Octane Non-Ethanol MoGas for $3.88 a gallon which I use regularly. When I use 100% 100LL, I can tell no difference, except a lighter wallet...

This site shows all the non-ethanol stations in the US.
http://pure-gas.org/

V/R
Smokey