SE5as and castor oil

Darryl · 8 September 1999, 05:09 AM

John L,

The earliest I have on a variable pitch prop is 1920, a great picture of an SE5a in Paul Hares book (thanks for the tip Ira). They of course offer the most efficient use of power as a fixed pitch is optimised for best AOA at cruising speed? (somebody??)
I was interested to see your calcs on the 6 foot prop. As to the Immelmann comment, that was just my little dig at the Psychic Friends Network that rears it’s head from time to time. I wasn’t suggesting that this was the cause of his misfortune.
I do tend to agree with you however that it is possible that upon shedding a tip the prop could become a liability. There are however numerous incidents of aircraft coming back with hits to the prop but without significant damage resulting from the out of balance motion.
For my own part I believe Immelmann was probably hit by enemy fire but you will always get an argument on that point and I certainly offer no proof one way or the other. I think ‘Under the Guns of the German Aces’ covers the various theories. I’ll happily drag it out and Email you the details if you haven’t seen it?

Brad,
Firstly, thanks for the coherent explanation of the Castor oil vs regular, wish I’d said that, that well!!. A couple of questions though from an amateur. The prop on the Cessna 206 would need to be about 7’ 8” for the tips to break the sound barrier at 2800. I don’t have the specs, but the pictures I have (nicely scaled by the door and people) do not support this. Are you sure this is the reason for the reduction of revs?
Secondly, you say that the Fokker is geared down to 1100 as these are the revs at which it produces most power. However the engine is still doing 1900. Why not spin the prop at 1900 too and put more air behind you? Do you have the dimensions of the prop?

As previously stated I am not an Aerodynamic Engineer but have always been told categorically that a prop can’t exceed the speed of sound. That is also one of the reasons that helicopters use such low rev counts.

Very best regards

Darryl

Darryl · 8 September 1999, 05:11 AM

John L,

The earliest I have on a variable pitch prop is 1920, a great picture of an SE5a in Paul Hares book (thanks for the tip Ira). They of course offer the most efficient use of power as a fixed pitch is optimised for best AOA at cruising speed? (somebody??)
I was interested to see your calcs on the 6 foot prop. As to the Immelmann comment, that was just my little dig at the Psychic Friends Network that rears it’s head from time to time. I wasn’t suggesting that this was the cause of his misfortune.
I do tend to agree with you however that it is possible that upon shedding a tip the prop could become a liability. There are however numerous incidents of aircraft coming back with hits to the prop but without significant damage resulting from the out of balance motion.
For my own part I believe Immelmann was probably hit by enemy fire but you will always get an argument on that point and I certainly offer no proof one way or the other. I think ‘Under the Guns of the German Aces’ covers the various theories. I’ll happily drag it out and Email you the details if you haven’t seen it?

Brad,
Firstly, thanks for the coherent explanation of the Castor oil vs regular, wish I’d said that, that well!!. A couple of questions though from an amateur. The prop on the Cessna 206 would need to be about 7’ 8” for the tips to break the sound barrier at 2800. I don’t have the specs, but the pictures I have (nicely scaled by the door and people) do not support this. Are you sure this is the reason for the reduction of revs?
Secondly, you say that the Fokker is geared down to 1100 as these are the revs at which it produces most power. However the engine is still doing 1900. Why not spin the prop at 1900 too and put more air behind you? Do you have the dimensions of the prop?

As previously stated I am not an Aerodynamic Engineer but have always been told categorically that a prop can’t exceed the speed of sound. That is also one of the reasons that helicopters use such low rev counts.

Very best regards

Darryl

Darryl · 8 September 1999, 05:12 AM

8 September 1999, 06:46 AM

Killratio, I would appreciate a copy of the text you mentioned. Don't "penny dreadfuls" sell for $4.95 and up today?
I remember using castor oil to break in a long series of Ohlsson 60 model aircraft engines in the mid '40's. Don't know about Castrol, but I think Slick 50 or a similar long lasting synthetic would work just fine.
E mail your writer's identity. I want to follow your work.

9 September 1999, 05:37 PM

The problem with prop rpm wasn't the sound barrier, pulling the engines out of the mounts, or throwing a copper blade tip. The problem was that a wood prop turning at more than 1800 to 2100 rpm literally tore ITSELF apart. They were laminated wood: very strong, but very massive/heavy. (They were also often a good deal longer than 6 feet long. I have one from the 1920's thats about 9 feet.) At higher rpm's the loadings multiplied the prop's own weight to the point that they literally tore themselves apart.

17 September 1999, 08:17 AM

A book titled The Rotary Aero Engine has just been reprinted, author Andrew Nahum, I got a copy in the post today. It deals with the oil question and has info on all? WW1 rotary engines. Also covers gearing, carburation and rotation speeds. A bit thin for the price, 64 pages about 16 US Dollars. Not bad though.