Re: Prop efficiency at high pitch (was: News from Romania)

From: Fred Tellier <fred-tellier_at_cogeco.ca>
Date: Mon, 19 Mar 2007 08:49:30 -0400

Hi Tapio

I don't think that a flare is more efficient, but at least much lighter. I used a VP in 2004 to finish 7th and a flare to finish 6th and I still haven't solved the mine flying equation. The only I use fixed pitch props is at Slanic so I have not real data for comparison but it is easier to control the flight pattern with a VP.

Fred
  ----- Original Message -----
  From: Tapio Linkosalo
  To: Indoor_Construction_at_yahoogroups.com
  Sent: Monday, March 19, 2007 7:44 AM
  Subject: [Indoor_Construction] Prop efficiency at high pitch (was: News from Romania)




  On Sun, 18 Mar 2007, Fred Tellier wrote:

> One of the biggest problems in flying the mine is getting enough climb
> without burning off all the turns while getting to the top. A lot of
> flyers at the world champs got great climbs due to high climbing rpm but
> not real long times because they wasted turns getting there. The trick
> is to get the model to climb with a lower RPM so that there is turns
> remaining for a long cruise. I used a flaring prop for that purpose but
> did not quite get it right, I think a little more launch torque was

  This is really interesting, and is related to a further question about
  prop efficiency.

  As a background, VP props have been the norm also in F1B for the past 10
  years or so. The common understanding is that they add 10 to 20% to the
  climb altitude. In recent years, however, the appearance of altitude
  loggers have questioned this (while also showing how prone to error the
  evaluation of model performance by the eye is). For example, in my own
  tests, models with a fixed pitch prop climb about the same as ones with
  VP. Some discussion about this thing has suggested, that even though the
  models with VP make the initial climb at lower speed, thus wasting less
  energy to drag, the increased pitch also reduces prop efficiency, which
  counteraffects the benefit from a slower climb. Thus all the gain you get
  from VP is possibly 5 to 10 seconds more time the climb lasts.

  This seems to come quite close to Fred's observation, that in the salt
  mine the question is not how to get to the ceiling, but how to get there
  with the smallest number of turns used. Sounds to me that this is
  precisely the same thing, how to keep the prop efficiency up at the high
  pitch setting. Am I right if I speculate from these messages, that a
  flaring prop might have a better efficiency at high pitch than a VP? If
  so, why?

  -Tapio-


   

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Received on Mon Mar 19 2007 - 05:49:37 CET