May 31, 2019, 05:09 PM
ƃuıʇɐǝʞ ʇʇoɔs
Quote:
 Originally Posted by MCarlton Is there an equation which can solve for altitude in terms of flight performance? Assume a typical slope glider, is it possible to determine the change in airspeed (without trim change), stall speed, max l/d, minimum sink rate and speed etc?
This webpage might help toward quantifying things. The associated calculator here is interesting to play with too. You can easily see how things change when you only alter the density altitude.

Important to note that they talk about actual aircraft speed and not indicated air speed, which to me more relates to to our thinking about models than performance charts with full scale aircraft.
Latest blog entry: Sagitta 600 build 2018
Jun 01, 2019, 03:36 AM
Registered User

theory and wind tunnel tests

i agree that having formulas to predict the results may save time, but at the end of the day, the only way to get the optimum results is by trial and error.
in other words, guess, build, and see what you get. and build another. until you get so close that the difference is so small that it really does not matter. which 1 of the closer to use.
that is why in real aircraft they end building whatever and see how it works.
wind tunnel tests are not so accurate. the pressure around the object is not the same as in the open.
which is why even with the largest and more expensive prototypes the owners tremble at the maiden flight. even sometimes after some time, things show variations that were not apparent before, making extensive testing necessary, but with everybody under pressure not done. an example are the recalls in the automotive industry.
Jun 21, 2019, 02:46 AM
Registered User

just an update

slimmer fuselage, lower t tail, rudder lower and longer (along), more carbon on the wing structure...
the only thing left is testing a wing with wider chord (lower wing loading) and same weight to check flight time.
will tell...
 Nov 21, 2019, 12:53 AM Registered User Phil: I think the issues you had with the free flight models might have been due to Reynolds numbers and the particular airfoils you were using. Trial and error may be the ultimate way to determine what's best, but correct application of theory ought to cut way down on the number of required trials. -------------- Turning radius at a given bank angle, in a steady turn, is proportional to the square of the speed. So that change might be somewhat more noticeable than the speed change. At 7,000 feet, using NC14310's figures,