High DA; no flaps

[GravityHater]

I am having a hard time explaining the aerodynamics of why some aircraft manuals command a no flap takeoff in higher DA conditions when some is called out for all lower DA situations.
Not sure how 0 flaps would benefit the takeoff.
I have follow up questions as well, but lets start there!

 

[midlifeflyer]

Flaps add both lift and drag. When the air is thinner, like at high density altitudes where both the engine and the airfoils (including the propeller) are less efficient, the net effect is that the increase in drag of even minimal flaps is greater than the lift benefit. The drag will actually extend the takeoff roll under these circumstances rather than decrease it.

 

[Doc Holiday]

The use of no or less flaps is to improve climb performance after takeoff, not to decrease the takeoff roll. For example, in many transport category airplanes a reduced flap setting is necessary to meet required climb gradients when PA/DAs are high. This usually requires more runway due to higher takeoff V speeds as a tradeoff to improved initial climb performance.

To try to answer your question, reduced flaps settings do not improve the takeoff roll, they increase the runway required to lift off. Reduced flaps tend to improve aircraft performance throughout the takeoff path (which is defined in general as ending 1500' AFE). This is because of the reduction in induced drag, which allows for an improved climb gradient (altitude gained for the distance traveled). Thus the airplane would reach a higher altitude over a shorter horizontal distance traveled, which is sometimes necesary to clear obstacles.

 

[minitour]

What he said...plus in some places with some planes, even if it does decrease your ground roll, what is it doing to your initial climb?

The 172RG, for instance, commands 0 flaps for a short field takeoff...too much of a drag hit in the climb.

Good question!

-mini

 

[cobraman]

To try to answer your question, reduced flaps settings do not improve the takeoff roll, they increase the runway required to lift off.

Really????? I am showing anywhere from 300ft to 1500ft better performance using 50% flaps in a C-130 as opposed to NO FLAPS. Yes I am talking about ground roll... (ground run) same animal.:bomb:

 

[Doc Holiday]

Really????? I am showing anywhere from 300ft to 1500ft better performance using 50% flaps in a C-130 as opposed to NO FLAPS. Yes I am talking about ground roll... (ground run) same animal.:bomb:

Isn't that what I said? Reduced flap settings (NO FLAPS as opposed to 50% flaps in your example) increase the ground roll/run. I would imagine that your second segment climb gradient is reduced using 50% flaps instead of zero flaps though.

That is the tradeoff I have seen in aircraft certificated with more than one takeoff flap setting. More flaps will get you a shorter ground roll and reduce the second segment climb gradient. Less flaps increase the ground roll, but will result in a better second segment climb gradient.

 

[cobraman]

That's not what I understood from the first post or yours. Using flaps on takeoff will DECREASE your ground roll. And assist in climbout. My bad.:0

 

[midlifeflyer]

What he said...plus in some places with some planes, even if it does decrease your ground roll, what is it doing to your initial climb?

The 172RG, for instance, commands 0 flaps for a short field takeoff...too much of a drag hit in the climb.

Good question!

It is indeed. In those "some places" with those "some planes" (and many piston singles without the advisory in the POH), the use of flaps will =increase= the takeoff roll and =decrease= climb performance. There's just not enough power/thrust to overcome the added drag of the flaps.

 

[VW Pilot]

This is an interesting question...Does it lead to the performance/capability of the aircraft flown or temperature and weather conditions???

 

[Doc Holiday]

I'm having a hard time with the logic that the use of flaps can increase the takeoff roll...induced drag doesn't happen until an airfoil creates lift. Using flaps during the takeoff will enable the wing to create lift at a lower airspeed which would equate to the airplane breaking ground in less distance.

You could argue that the wing is creating lift throughout most of the takeoff roll, just not enough lift to enable the airplane to fly. I don't believe that this is of enough consequence to affect performance in any measurable way. The act of the airplane rotating and beginning to break ground is when induced drag really begins to occur. After all, the textbooks tell you to note the point of rotation of the preceding airplane when avoiding wake turbulence.

On top of it all, induced drag is drastically reduced while the airplane is in ground effect. People flying light aircraft in high density altitude conditions have demonstrated this several times when they took off too heavy and were unable to climb out of ground effect.

To sum it up, using reduce/no flaps for takeoff is so the airplane will have better initial climb performance.