BPA parallel valve 382 engine

[Carl Froehlich]

Anyone have or know about this engine? Looking to put it in an RV-8.

Carl

[Raymo]

Might you be referring to the engine in this thread?

http://www.vansairforce.com/communit...d.php?t=114713

[DanH]

Great choice. 4.625" stroke crank like the XP-400, with the parallel valve 360's 5.125" bore. The crank has pendulum absorbers, so a lot of propeller concerns go away. Through-hardened steel cylinders. I could be easily be talked into one for my next airplane.

Check the width dimension. RV-8 cowl gets tight on the left side with a 390 at 34.25"W. I think the 382 is a little less, but I'm not sure.

[Carl Froehlich]

As you say - the counterweight crank is an attractive aspect for me.

I'm looking at 9/1 pistons and cold air induction, 200-205hp out the door @ 300 pounds. Still waiting on a price. That might kill the deal.

Carl

[rvisnext]

I also considered the 382 for my 8. I was concerned about the heavier 390/400. I was told multiple times about the heavier pitch stick forces with the heavier angle valve engine. Then I got some great advice...it was basically since I have never flown any version of an RV8, I would be none the wiser about what's heavy stick force for the RV8 and what's not.

As they say ignorance is bliss, and it is. I am still in phase one with my XP400 powered RV8 and loving the cool running angle valve CHTs. Just get the big oil cooler and also go with a composite whirlwind or hartzell and you will be all set.

For the price difference to go from the 382 to 400 with the better IMHO angle valve cylinders, it was really an easy decision. As Dan H said, it is a tight fit in the left front corner of the cowling. BTW, I have the Showplanes cowling.

[ccsmith51]

Originally Posted by DanH

... The crank has pendulum absorbers, so a lot of propeller concerns go away.

Are pendulum absorbers the same as the counterweights on the crank of say an O-360-A1F6?

[DanH]

Originally Posted by ccsmith51

Are pendulum absorbers the same as the counterweights on the crank of say an O-360-A1F6?

Yes. Lots of folks refer to pendulum absorbers as "counterweights", including the manufacturers. I prefer to be more precise with the terms I use, a habit pounded into my thick skull by an engineering mentor. Here's the deal.

Set the wayback machine for the 1930's. Everyone is trying to develop larger, more powerful radial engines, but cranks break and props fail. The cause is found to be vibratory twisting of the crankshaft. Along come three guys named Solomon, Sarazin and Chilton, who develop different devices all operating on the same principle...a pendulum to counter torsional vibration. Chilton's patent describes what we know today as a "counterweight", but how did it get the name?

In the case of a radial, the pendulum absorber is in fact located 180 degrees from the crankpin, and replaces one or both fixed counterweights. A pendulum arranged this way is both counterweight and absorber. Visit a university library and dig out the SAE Transactions from around 1938 or 1939. The engine designers were really excited; the new device meant they had a way to control an entire vibratory order, not just a frequency, and do so without adding any new weight to the engine. It was one of many developments which helped win WWII.

I think it was Continental who first published (again in the SAE Transactions) experiments with applying torsional pendulums to a small flat engine. The difference, as compared to a radial, was that the pendulums were applied in matched pairs, at 90 degrees to the adjacent crankpin. A flat engine has no counterweights; each piston assembly is countered by its opposing twin. The pendulums counter nothing but themselves.

Ahh, but the name. Imagine an entire generation of mechanics trained on big radials. That dangling thing on the radial crank? That's a counterweight. Says so right there in the textbook. Now along comes new postwar flat engines with more cylinders (i.e. longer, more flexible cranks) and more power; they need pendulums. Never mind that a flat motor doesn't need a counterweight. It's got dangling things on the crank, so they're counterweights, right?

No, but we're stuck with the name, however wrong.

[ccsmith51]

Thanks, Dan, great explanation. I still see it referred to as a "counter-weighted crankshaft."

I ask the question because I had an A1F6D on my RV-4 with a wood prop. Someone mentioned one time that the counterweights (I'll use that term for this discussion even though it is technically incorrect) were sized for a certain prop. My engine came out of a C177 with a CSP and I was told that the counterweights were sized to minimize the vibrations with that prop, on that engine.

So, I got nervous worrying that perhaps my engine was "tuned" to a certain prop and if I had something different I might find some vibration issues. I called Lycoming and talked to a tech. When I told him that I had an experimental with that engine and wood prop, he said there would be no problem with a wood prop. When I asked him if I would have any problem putting a metal prop on it, he said he couldn't give an answer.

Since I plan on building another plane with an O-360 and CSP, this is of great interest to me.

Do you think that there are any issues with any normal RV prop on a counter-weighted engine?

[DanH]

Originally Posted by ccsmith51

Someone mentioned one time that the counterweights were sized for a certain prop.

No, not really. The pendulum is there to reduce crankshaft vibratory twist at a particular order. "Order" means "how may times per revolution".

All the fours, best I know, have 6th and 8th order pendulums, regardless of propeller choice.

When I told him that I had an experimental with that engine and wood prop, he said there would be no problem with a wood prop. When I asked him if I would have any problem putting a metal prop on it, he said he couldn't give an answer.

Wood is fatigue resistant, and has a high damping coefficient; strike it and it doesn't "ring" like a tuning fork for very long. Aluminum props, on the other hand, have a steadily declining S-N curve and very little damping coefficient.

So, a wood prop is the safe choice for a drive system with unknown vibratory behavior. A metal prop is usually strain-gauged and run to determine if there are conditions of RPM and manifold pressure which make the prop blade resonate. If it does, that RPM/MP becomes a prohibited range. Without the vibratory survey, your technician could not give you an answer.

[ccsmith51]

Thanks again, Dan.

Thinking about what you said, if the only difference between an A1F and an A1F6, or example, is the pendulums, what do you think is the reason that they were included, if not to compensate for a particular prop?