I am sure someone with more knowledge about fluid dynamics can say this better than I can, but it is NOT frontal area that determines drag. The drag increases faster than the frontal area when you lower the flaps and the drag increase from 60 degrees and 90 degrees is enormous, much more than the frontal area increase.
Anker ----- Original Message ----- From: "Harley Michaelis" <[EMAIL PROTECTED]> To: "Dieter @ ShredAir" <[EMAIL PROTECTED]> Cc: <[EMAIL PROTECTED]> Sent: Thursday, July 25, 2002 11:17 AM Subject: Re: [RCSE] Flap Deflection on Typical Moldie > Hi Dieter. . hope all is well with you. > > I did the drawing you suggested and it does clarify that more flap than > expected is exposed to the airflow. However, in other than a 90 degrees down > situation, the air is deflecting off the surface and the result would appear > to be not as effective. Taking the example of 45 degrees exposing 69% of the > flap area, I'm inclined to think that a flap with 69% of the chord but > positioned 90 degrees down would be more effective in causing drag because > it is "blocking" the airflow, rather than deflecting it.This seems to be > born out in practice. Something else other than just exposed area is > happening at 90. > ----- Original Message ----- > From: "Dieter @ ShredAir" <[EMAIL PROTECTED]> > To: <[EMAIL PROTECTED]> > Sent: Wednesday, July 24, 2002 10:16 PM > Subject: Re: [RCSE] Flap Deflection on Typical Moldie > > > > > > >Realistically, is there much difference in flap performance between 60, > > >and say 70 or 80 degrees of deflection? Thanks > > > > Simon, et al., here is an interesting exercise: > > > > On a sheet of paper, draw a 90-degree angle, one leg horizontal, the > > other vertical. Now insert a compass at the point of the angle and > > draw a 1/4 circle with a 100 mm radius intersecting both legs of the > > angle. Draw lines at 45, 60, 75, etc degrees from the point of the > > angle. Now draw lines perpendicular from the vertical leg so that > > they intersect where the 45, 60, 75 lines intersect the arc. > > > > Sounds complicated, but here is what you'll find, when you measure the > result: > > A 45-degree flap deflection exposes about 69% of the flap area to the > > airflow... Huh? > > A 60-degree flap deflection exposes about 86% of the flap area to the > airflow. > > A 75-degree flap deflection exposes about 96% of the flap area to the > airflow. > > > > Now, for you in Canada, 75 degrees may be fine, but here in the US, > > planes need "The Full Ninety," else they don't land worth shards... > > :o) > > > > Dieter > > http://shredair.com > > > > RCSE-List facilities provided by Model Airplane News. Send "subscribe" > and "unsubscribe" requests to [EMAIL PROTECTED] > > > > RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED] > > ################################################################# ################################################################# ################################################################# ##### ##### ##### ################################################################# ################################################################# ################################################################# RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
