esteban wrote:
effects of shape, if I look at wiki, it shows even 0.04-0.09 for streamlined body,
Most GA aircraft will fall under tube, cylinder, sphere shapes although they get named lance, arrow 
All aircraft, will have drag shape factor from 0.01 to 0.1 region where most trainers are 0.02 (I just want to highlight the effect of the shape factor with my example)
https://history.nasa.gov/SP-468/app-a2.htm
The drag from wings design is interesting as unless you fly fast or you have huge wingspan you will get “vortex drag” (some will call it “induced/turbulence drag” when you put full flaps and fly slow or even stall), this is not part of the text books drag equations as no one has clue for formulas on turbulent airflow yet but streamlining helps a lot here…
At high airspeed, wings/tail will be on small AoA and laminar flow, and “parasite drag” is mainly from cockpit section and streamlining, note that at higher airspeed you will tend to get more contribution from cockpit section than from surface streamlining
So really difficult to tell unless you know the “class of the aircraft”
For fast touring aircraft, I bet all has to do with with the section
For slow aircraft, I can blame it one surface materials or short wings
For trainers, shape probably? they look ugly anyway, what do you expect
aart wrote:
No weight increase, only a minuscule increase in frontal area compared to the 135 HP version
Bathman wrote:
And although the UK insist that all aircraft used for flying instruction have to have their engines replaced at TBO (2000 hours for the 912), other countries in Europe are happy for schools to run on condition.
aidanf123 wrote:
50% more range, TKS and cheap Jet A when you land – the tecnam is designed for multi training – the diamond is a tourer
Ibra wrote:
esteban wrote: effects of shape, if I look at wiki, it shows even 0.04-0.09 for streamlined body,Most GA aircraft will fall under tube, cylinder, sphere shapes although they get named lance, arrow
All aircraft, will have drag shape factor from 0.01 to 0.1 region where most trainers are 0.02 (I just want to highlight the effect of the shape factor with my example)https://history.nasa.gov/SP-468/app-a2.htm
The drag from wings design is interesting as unless you fly fast or you have huge wingspan you will get “vortex drag” (some will call it “induced/turbulence drag” when you put full flaps and fly slow or even stall), this is not part of the text books drag equations as no one has clue for formulas on turbulent airflow yet but streamlining helps a lot here…
At high airspeed, wings/tail will be on small AoA and laminar flow, and “parasite drag” is mainly from cockpit section and streamlining, note that at higher airspeed you will tend to get more contribution from cockpit section than from surface streamlining
So really difficult to tell unless you know the “class of the aircraft”
For fast touring aircraft, I bet all has to do with with the section
For slow aircraft, I can blame it one surface materials or short wings
For trainers, shape probably? they look ugly anyway, what do you expect
The induced drag coefficient is the Cl^2/Pi*AR, the lift coefficient squared divided by pi times the aspect ratio.
At low speed the lift coefficient is high, greater than 1 so the the square of it is very high. At high speed the lift coefficient is low, leass tha 1 so the square of it is low. Thus lots of induced drag at low speeds. The aspect ratio effect speaks for itself, that’s why sail planes have a seriously high aspect ratio wing.
Peter wrote:
Speak to any busy FTO which runs a fleet of DA42s and work out how much profit each DA42 contributes each year. It’s enough to buy a new one every 2 years.
I used to put out DA42s at £410/hr for flight training, this included instructor. Net profit was £17/hr.
Net, sure. There are many ways to juggle the numbers, on the road from gross profit to net profit.
My point is that I only had £17/hr to think about putting aside for a new DA42 every 2 years. :). Most airframes in the training environment will give you 600hrs/yr.
Joe_90 wrote:
The induced drag coefficient is the Cl^2/Pi*AR, the lift coefficient squared divided by pi times the aspect ratio.At low speed the lift coefficient is high, greater than 1 so the the square of it is very high. At high speed the lift coefficient is low, leass tha 1 so the square of it is low. Thus lots of induced drag at low speeds. The aspect ratio effect speaks for itself, that’s why sail planes have a seriously high aspect ratio wing.
Yes, intuitively a large span/cord aspect ratio will give you low induced drag (e.g. no vortex at the end of the wing or “turbulence leaks” before the stall)
The physics are bit complicated near the stall to get a formula for the induced drag force, but the coefficient should be along the formula you mentioned…
Dave_Phillips wrote:
My point is that I only had £17/hr to think about putting aside for a new DA42 every 2 years. :). Most airframes in the training environment will give you 600hrs/yr.
You should put a side 400£/h *600h/y * 2y to get closer to Peter’s estimates to buy a new one unless they cost 20k£
