As always Gary you have a great theory, ( I love theories and formulas more than most flyers ) but if this was the answer the most successful flyers would be doing it that way and records would be broken. Practice developed over the last 40 or 50 years has resulted in times constantly increasing, most flyers I know try to use as little rubber as needed and adjust the amount ( cross section and length ) depending on turns used for the last flight and adjust launch torque for height of climb. The biggest increase of performance was the development of VP props and Tan 2 rubber, lighter covering materials and great cottage industry balsa cutters. I am not knocking the theories but they only work for certain in the formulas but don't always translate into long flights.
We should have a postal event of theories against common practice, limited penny plane or F1L would be good classes as the planes are strong and easy to build.
As for the mine and F1D the problem is limited allowed rubber .6 of a gram to be exact. This translates to a motor between 8 to 9.5 inches depending on the cross section allowing approximately 1300 to 1800 turns to fly with and a launch torque from .4 to .6 inch ounces. The motor sticks usually become a problem above .5 Jr. team member Nick Ray blew up at least one model trying to get enough torque to get his model to a useful altitude. Thus getting climb and cruise becomes a balancing act, many used too large cross section or too low of pitch to get climb and lost cruise time.
Fred
----- Original Message -----
From: dgbj_at_aol.com
To: Indoor_Construction_at_yahoogroups.com
Sent: Monday, March 19, 2007 5:04 PM
Subject: Re: [Indoor_Construction] Prop efficiency at high pitch (was: News from Roman...
"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?"
The important question for prop design is not about using it to control RPM,
but using it to convert torque energy into altitude energy with the greatest
efficiency. It is not getting there with the smallest number of turns, but
getting there with the smallest energy. If the plane climbs too fast with an
efficient prop, a thinner motor producing less torque is indicated. If the
plane is capable of hitting the ceiling, a motor of lower weight is
indicated. The ceiling, together with the weight of the plane, the weight and
specific energy of the rubber and the prop efficiency, imposes an absolute limit on
how much energy the plane may use. Spoiling the efficiency of the prop to
keep the plane from hitting the ceiling is making it necessary to carry more
weight of rubber than necessary. That extra weight takes away from duration
during the entire flight. The increase in sinking speed times the model weight
times the duration is the energy wasted by the extra weight, and you are
using less of the energy available from the rubber with the spoiled prop.
Gary Hinze
************************************** AOL now offers free email to everyone.
Find out more about what's free from AOL at
http://www.aol.com.
[Non-text portions of this message have been removed]
[Non-text portions of this message have been removed]
Received on Mon Mar 19 2007 - 15:04:16 CET