Re: No touch LPP flying in Cat I

From: John Kagan <john_kagan_at_hotmail.com>
Date: Wed, 08 Jun 2011 02:41:40 -0000

--- In Indoor_Construction_at_yahoogroups.com, "Yuan Kang Lee" <ykleetx@...> wrote:
>
> John, I understand that centering the torque curve is a good rule of thumb, but I can't quite understand why it makes sense. What is your thought here?
>

Don't know if it's a good rule of thumb, but it's the one I use (for fixed pitch, anyway) :)

Basically, I think it is better to fly on the flatter part of the torque curve. The slope increases at both ends.

Take the extreme cases: no backoff with lots of turns leftover, or lots of backoff and deadstick. In both cases you are doing a bunch of flying on a quickly changing part of the curve, and maybe not even reaching the roof or flying all the way to the floor. Here there is a pretty definite advantage to adjusting the motor size.

Centering the flight on the curve even further probably has less signficant advantage, but I still think there is some.

In your example of a flaring prop, I think it might be better to give up a little peak torque (backoff), fly for a longer period of time
on a higher average torque (thicker motor), and use more turns at the end.

I don't use this rule of thumb for VP props though - not directly anyway. There are more factors involved that need attention. For example, as Mark mentioned, there is a limit to the high pitch and low pitch (he phrased it as a min and max rpm), beyond which thrust is lost without enough return on RPM control to make it worthwhile. Also, a goal is to reach a target altitude and fly all the way to the floor. With a VP this involves more prop adjustment than is available in a flaring prop. Another one is is to use all the energy you can pack in the motor - 5 turns at the end of a wound motor is worth way more than 5 at the start. They carry a huge amount of energy - the difference between a good flight and a great flight.
Received on Tue Jun 07 2011 - 19:41:45 CEST