Flaps and slow fly by???
06-12-2013, 11:43 PM
#26
Member
Join Date: Feb 2010
Location: Slagelse, DENMARK
Posts: 46
Likes: 0
Received 0 Likes
on
0 Posts
RE: Flaps and slow fly by???
As an airline pilot and technical pilot I couldn't disagree more.
If you want to fly at the slowest possible airspeed, you need full flaps.
Indeed the lift/drag ratio with full flaps compared to take off flaps is lower but full flaps reduce the stall speed quite significant compared to take off flaps.
So why don't airliners take off with full flaps?
Airliners are certified to meet specific climb gradients in case of an engine failure during take off, and since the flap configuration may not be changed during take off it would simply not be possible to fulfill the required gradients with a higher flap setting than take off.
Usually airliners have two flap setting for take off. If the runway is short or there is a close-in obstacle the higher setting is used, since you want to get off the runway a early as possible.
The above does not apply with models having more than 45 degree flaps.
Above 45 degree flaps, the flaps act more like drag devices than lift devices.
Martin
06-13-2013, 08:07 AM
#27
RE: Flaps and slow fly by???
ORIGINAL: martin_wam
As an airline pilot and technical pilot I couldn't disagree more.
If you want to fly at the slowest possible airspeed, you need full flaps.
Indeed the lift/drag ratio with full flaps compared to take off flaps is lower but full flaps reduce the stall speed quite significant compared to take off flaps.
So why don't airliners take off with full flaps?
Airliners are certified to meet specific climb gradients in case of an engine failure during take off, and since the flap configuration may not be changed during take off it would simply not be possible to fulfill the required gradients with a higher flap setting than take off.
Usually airliners have two flap setting for take off. If the runway is short or there is a close-in obstacle the higher setting is used, since you want to get off the runway a early as possible.
The above does not apply with models having more than 45 degree flaps.
Above 45 degree flaps, the flaps act more like drag devices than lift devices.
Martin
fourth airline pilot to post here. He's asking about the best way to go slow,
and maximize his smoke with an RC jet here. Thanks for impressing us though.
06-13-2013, 05:38 PM
#30
RE: Flaps and slow fly by???
I need to give credit where credit is due. Martin is right and I am somewhat off the mark. Landing flaps do in fact give you a lower stall speed, up to a point. Once you get past a certain deflection; however, you stop adding lift and start adding drag. There is a point where lift is maximized at minimum drag expense, that would be a good setting, assuming you have enough thrust on tap to push yourself along in level flight!
I should have elaborated a bit about "takeoff flaps." Full size airplanes and especially jet airliners often have different takeoff flap settings. A lower deflection setting, say 5 degrees, which give a better climb rate due to a higher climb speed; and a higher flap setting, say 15 degrees, which allows a steeper angle of climb and allows for rotation at a lower airspeed because of the lower stall speed, hence a shorter takeoff roll. So I would go with the higher takeoff flap setting if I wanted to do a slow flyby.
There is definitely an amount of deflection you do not want to exceed. Short of that point, you will just have to play test pilot to find the best setting.
Now, if you are flying a Hotspot......
Don't worry gents, I know when to quit!
I should have elaborated a bit about "takeoff flaps." Full size airplanes and especially jet airliners often have different takeoff flap settings. A lower deflection setting, say 5 degrees, which give a better climb rate due to a higher climb speed; and a higher flap setting, say 15 degrees, which allows a steeper angle of climb and allows for rotation at a lower airspeed because of the lower stall speed, hence a shorter takeoff roll. So I would go with the higher takeoff flap setting if I wanted to do a slow flyby.
There is definitely an amount of deflection you do not want to exceed. Short of that point, you will just have to play test pilot to find the best setting.
Now, if you are flying a Hotspot......
Don't worry gents, I know when to quit!
06-14-2013, 04:35 AM
#31
RE: Flaps and slow fly by???
Gino,
For what it's worth,I use full flaps with crow on the Kingcat,to do the slow flyby with smoke. No gear though. The crow setup is draggy enough. More stable than takeoff flaps,and the engine is spooled more,so when I smack it to go vertical it's right there.
I think it depends alot on the jet. I don't know what Brian's using in the smokeout. good luck Brian!!
Erik
For what it's worth,I use full flaps with crow on the Kingcat,to do the slow flyby with smoke. No gear though. The crow setup is draggy enough. More stable than takeoff flaps,and the engine is spooled more,so when I smack it to go vertical it's right there.
I think it depends alot on the jet. I don't know what Brian's using in the smokeout. good luck Brian!!
Erik
06-14-2013, 12:55 PM
#32
RE: Flaps and slow fly by???
On the L29 we use 90 degree on all 4 Flaps, all less will only raise and not make em slow...
see video http://www.youtube.com/watch?v=Nzv7a_SB1Xc
see video http://www.youtube.com/watch?v=Nzv7a_SB1Xc
