'Best' Prop RPM

[David-aviator]

The chart is showing 220HP at 2000' ROP. That do make a difference. Nothing like power to go faster.

[nigelspeedy]

Note to self: "self don't post graphs with numbers on them". Rather than the absolute values what was of more interest to me was the trends with altitude and the sensitivity of the performance with speed changes.

Perhaps I miss used the term "Carson Speed", I'll have to go and re read his paper. If it is defined in terms of L/D then I am in error, as I used it as the speed that achieves the maximum value of the product of SR and TAS. The speed that gives the maximum SR in level flight is probably not the same as the one that gives the best L/D when gliding. In gliding flight the L/D of the airplane is not dependent on the efficiency of the prop or engine. In level flight the speed for maximum SR is the speed where the airplane as a whole (airframe, engine and prop) give the best efficiency. The SFC of the engine improves with increased power so speed for max SR in level flight is likely quite a bit faster than the speed for best L/D gliding. So I doubt if the best L/D speed of my airplane is 129knots, probably closer to 100 knots.
Cheers
Nige

[nigelspeedy]

So just re reading Carson's paper he does in fact define the cruising efficiency as the product of L/D and TAS, so my use was incorrect. Sorry for any confusion. That said, I buy fuel by the gallon (unfortunately at a unit cost of $5.29) so I am more interested in how far and fast any one unit of this fuel gets me than L/D.
Cheers
Nige

[tjo]

Originally Posted by nigelspeedy

Note to self: "self don't post graphs with numbers on them".

I appreciate the numbers, thanks for posting them.

Tim

[AX-O]

Nice work. Gouda would be proud of you.

[nigelspeedy]

G'day Axel,

How is the four going? You got your airworthiness certificate a week before me and I think the last post I saw you were working through some CHT issues, how is that going?
Cheers
Nige

[AX-O]

Originally Posted by nigelspeedy

How is the four going?

Sent you an email. I did not want to digress your thread.

[RVDan]

Originally Posted by nigelspeedy

So just re reading Carson's paper he does in fact define the cruising efficiency as the product of L/D and TAS, so my use was incorrect. Sorry for any confusion. That said, I buy fuel by the gallon (unfortunately at a unit cost of $5.29) so I am more interested in how far and fast any one unit of this fuel gets me than L/D.
Cheers
Nige

Interesting testing and data. As you say, the numbers could be scrutanized a bit, but the trends are nteresting. If ecomomy is what you are looking for, I think that your numbers support 2300 RPM at about 9GPH is the best for economy. It would be interesting to see how that worked out at altitude.

[hevansrv7a]

Originally Posted by brad walton

Carson speed is best lift/drag times 1.316.
A Carson speed of 170 knots means a best L/D of 129 knots? Seems high.

Carson speed is usually expressed in CAS.

Carson defines it but in fact, it is 1.316 x V L/D max. This is well established.

My beef is with the difference between a Carson speed derived from zero thrust glide data and a realistic number for in-flight. I don't think they are equal but I don't want to hijack this EXCELLENT thread.

[mike newall]

Every day - 23/23

Econ - 22/22

Fun - 24/24

Showing off - B8lls out

Simples