What kind of aerodynamic calculations do you perform?

[Igwe Aneke]

I'm curious what kind of aerodynamic calculations fellow modellers perform when designing a scratch built project.
Personally I calculate each of the following parameters:

- Geometric data like wingarea, Aspect ratio, Taper ratio, Sweep, Tail Moment Arm and Tail Volume Ratio
- The all important wingloading
- Aprox. flying speed (based on the pitch and rpm of the prop used, or in the case of EDF the eflux-velocity)
- Reynoldsnumber for inflight- and landing-speed
- MAC and (graphical) CG calculations
- Cl required for the desired lift
- Planform-adjustmentfactors for AR/TR
- Total of section and induced AoA's
- Pitching moments and the required horizontal tail incidence


In the future (but only after i found a way to fully automate all of the above calculations)i would like to extend these calculations to also include drag-figures and centrifugal loads (and the implications of this on the required Cl and possible high speed stalls).

[Tom Harper]

You are very thorough!

To what extent are you able to verify these calculations when you get the model in the air?

[Ollie]

Tom,
Performance under power is mainly high thrust/weight ratio. When more power is simple but reduction of drag is hard. In R/C power planes, high energy brings it along.

Performance under soaring is mainly high L/D ratio. Reduction of drag is very complex. In R/C soaring, low energy is found thru air mass conditions.

[Ollie]

TK was dragged out to a power field on a Sunday morning to see an old
friends immaculate 1/3 scale Piper Cub that he had just finished over the
winter fly for the first time. Well after they got the motor and
everything straightened out on the ground, he asks TK to take the first
flight, "just in case". He wasn't expecting to do the test flying as it
was a big power club and there were lots of "experts" in attendance, but he
didn't want to see his friend break his model either so he agreed to take
the first flight. So here is a senior guy, a brand new 1/3 scale Piper
Cub, a glider guy to do the test flying, and the club "experts" have now
broken away from running gas thru their engines on the ground to checking
this out like a bunch of vultures.

TK taxis the Cub out, takes off, trims it out, starts backing off the
throttle a bit and the engine sputters and quits. Next thing he knows guys
are screaming up and down the flight line, "DEAD STICK - - DEAD
STICK" He's like thinking to himself, no big deal, got flying speed, got
altitude and over the field, why are these guys screaming... so he goes to
set up an approach and the wing gives a bobble. He sets the Cub in a
thermal turn and spends the next 10 minutes specking it out. Brings it
back down, sets up a nice approach on their paved strip, and rolls it out
to his feet... and yells DEAD STICK.

[Sparky Paul]

Ollie, i LOVE to do that! :)

[ImaBiggles]

as a scratch builder, I put together something I think will fly, put a motor on it and toss it into the air under full power!

[Sail 'n Soar]

I'm curious what kind of aerodynamic calculations fellow modellers perform when designing a scratch built project.
Personally I calculate each of the following parameters:

- Geometric data like wingarea, Aspect ratio, Taper ratio, Sweep, Tail Moment Arm and Tail Volume Ratio
- The all important wingloading
- Aprox. flying speed (based on the pitch and rpm of the prop used, or in the case of EDF the eflux-velocity)
- Reynoldsnumber for inflight- and landing-speed
- MAC and (graphical) CG calculations
- Cl required for the desired lift
- Planform-adjustmentfactors for AR/TR
- Total of section and induced AoA's
- Pitching moments and the required horizontal tail incidence


In the future (but only after i found a way to fully automate all of the above calculations)i would like to extend these calculations to also include drag-figures and centrifugal loads (and the implications of this on the required Cl and possible high speed stalls).

In addition to your calculations I calculate lift distribution and local CL as a function of plan form and washout to achieve a good Cdi/Cdi elliptical while maintaining fpleasant stall characteristics.

[gymguy]

In addition to your calculations I calculate lift distribution and local CL as a function of plan form and washout to achieve a good Cdi/Cdi elliptical while maintaining fpleasant stall characteristics.

I'm really impressed by the design knowledge you guys have amassed. Are you Aeronautical Engineers by trade or did you pick this up on your own? Are there good texts or online tutorials that might help me understand more about this subject?

[Igwe Aneke]

I'm really impressed by the design knowledge you guys have amassed. Are you Aeronautical Engineers by trade or did you pick this up on your own? Are there good texts or online tutorials that might help me understand more about this subject?I can't speak for the other guys, but I'm no (do wish so :D ) Aeronautical Engineer...I don't even have a technical occupation. Maybe this is the reason I just like to be technical in this hobby. ;)

but I personally learned (still learning though) it myself...I just bought two great books on the subject. 'Basics of RC Model Aircraft Design' by Andy Lennon (easy read) and 'Model Aircraft Aerodynamics' by Martin Simons (though but doable read).

You are very thorough!

To what extent are you able to verify these calculations when you get the model in the air?
Good question. I just recently started with scratch building and designing my own models so I don't know to be honoust. I simply trust on the experience of the authors and the (proven) scientific calculations involved.

edit: How could I forget. :o I also learned a GREAT deal by simply searching thru Ollie's post-history here on rcgroups. :D (Let me use this oppertunity to thank you for sharing your knowledge with us Ollie!)

edit2: @ gymguy: I would strongly advise you to just buy (at least) Andy Lennon's book, but you can also take a look at this thread:http://www.rcgroups.com/forums/showthread.php?t=404570

There are some great references posted there.