Lower rpm 2180

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karmarepair

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Check.

I like that video because Gene explains a lot of things that were quite obscure in the Valley Engineering website.

Another application of their VW redrive

I had not seen this one, which seems about the latest they were showing airplanes
.028 wall thickness - I hadn't heard that detail before. Gene was the grandfather and Larry was the son. Alaina Lewis is the granddaughter, and the proprietress of Culver Props.

And one more resources I hadn't seen till today, Valley had a YouTube channel. Lots of construction details. I think that's Alaina's husband welding and talking. https://www.youtube.com/user/jlewi555
 

cluttonfred

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One thing that strikes me about some "big bore" VW installations is that they often seem to be turning props that are smaller than necessary at RPMs that are higher than necessary. If the Aerovee torque curve below is any guide to a typical 2180cc engine then about 3350 RPM is the max you ever really need in terms of staying at the top of the torque curve. Especially for the low and slow crowd, I suspect you'd see better performance in takeoff and climb with a larger prop sized and pitched to hit that sweet spot on the curves, maybe 3300 RPM full throttle at climb speed? FWIW, Sonex recommends 54" props for the Sonex/Waiex/Onex and 56" for the Xenos motorglider, Bill Beatty recommends a 60" prop for the VP-2 in the Volksplane manual, and Leonard Millholland uses a 64" prop on his Cabin Eagle.

1664860466962.png
 

TFF

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Remember it’s not just diameter, it is diameter and pitch. A 56, 60, and 64 inch prop is not going to run the same pitches on the same engine, but the engine has to reach the same RPM to be in the horsepower range. Arbitrary numbers but if you can run a 56x45, the 64” prop will be a 64x37. The engine won’t see it as different, but the airflow character will be different. Diameter and pitch, not just one or the other.
 

Pops

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Gene at Culver prop got the dia and pitch for the 1835 cc VW engine perfect. A 60"x26". WOT is 3200 rpm. Cruise at 80 mph at 2650/2700 rpm with a ROC of 1200+ with my 235lbs on the SSSC.
Talked to him about an hour when deciding on the prop for the JMR. So far, I'm happy. That was a few weeks before he died. Seem like a very nice person.
 

Vigilant1

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If the Aerovee torque curve below is any guide to a typical 2180cc engine then about 3350 RPM is the max you ever really need in terms of staying at the top of the torque curve.

View attachment 130505
It's important to remember that propeller performance changes with airspeed. The effective AoA of the propeller decreases with increasing airspeed until, eventually, the prop generates very little thrust. If we have a fixed pitch prop, our options are limited, but one way to overcome this and get more thrust is to turn the prop faster. The increased thrust that results is not due to the HP curve of the engine, but because of the higher relative AoA of the prop in these conditions of high ambient airspeed as we take the same prop and turn it faster.
With a VW, we have the luxury of being able to use these additional available RPMs, because the engine"s "red line" (to the extent that term applies to E-AB aircraft) is pretty high. They don't seem to suffer ill effects at speeds up to (and over) 4000 RPM (don't try this with a stock O-200). 3600 rpm is certainly not a problem for the engine, but it becomes a problem for efficiency and propeller integrity if a wood prop is turned at extremely high tip speeds (generally, 850 fps or so is considered the practical limit). That's why big bore VWs on faster planes often use relatively short propellers: It allows them to turn the prop at high enough RPM so they can generate thrust at high airspeeds.
 
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cluttonfred

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Guys, obviously pitch is also a factor, I was just pointing out that for low and slow applications, larger diameter props than are usually used for direct-drive VWs are also an option.
 

TFF

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45-50% of cubic inches is the general air cooled target range for horsepower direct drive. If it beats this, it’s probably running a smaller prop. It’s how VW and Corvair users level the playing field as much as they can. A bigger diameter does not necessarily mean lower rpm. It’s the pitch that’s going to determine rpm once one selects the diameter. Having the horsepower, crossed with torque at a certain rpm to be a useful prop, pitch and diameter, is what we are after.

Pops with his bird selected to keep the engine not working hard. Besides not zinging away at the front, it’s going to last longer. He also regulated the plane to one person. Most people with that combo is trying to stuff two people in it. He kept it to standard airplane ratios instead of forcing it to be more than it should. It’s just designed choices, not a good or bad thing. Choices that can’t reach are what gets us in trouble.
 

Pops

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I think the LEAST marginal 2 place VW powered airplane is the Cygnet. Light weight , lots of wing area for a light loading. Other than the Cygnet, I would not be happy with a 2 place VW powered airplane. Two place would have a small cont engine in it.
An old friend gave me a Zenith 2 place 600 project that was designed for the 1835 cc, VW engine. I built an engine mount for a C-75 for it and had engine parts to build a C-75 and gave it to my grandson.
 

Map

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I have a 64" x 36" prop (2 blade) on my 2276 cc VW in my motorglider. This gives me about 2700 rpm on takeoff, 2900-3000 rpm in climb. Economy cruise is typical at 2700-2800 rpm (high altitude). Before that I had a 64" x 39" prop, which resulted in too low rpm for takeoff, but had about the same cruise performance. I have to add that my spinner is pretty large (15.5" diameter). I don't go over 3300 rpm.
 

ToddK

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I have a 64" x 36" prop (2 blade) on my 2276 cc VW in my motorglider. This gives me about 2700 rpm on takeoff, 2900-3000 rpm in climb. Economy cruise is typical at 2700-2800 rpm (high altitude). Before that I had a 64" x 39" prop, which resulted in too low rpm for takeoff, but had about the same cruise performance. I have to add that my spinner is pretty large (15.5" diameter). I don't go over 3300 rpm.

That's a pretty respectable prop.

On a 2332 engine that would be about 75hp on take off, 80hp in climb. That's Jabiru 2200 territory.
 
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