Take off roll flap deployment

Started by FlyingPig, November 24, 2022, 05:28:13 PM

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FlyingPig

During take offs in high DA or high altitude airports, or even under normal conditions, how many people have worked with the technique of starting your take off roll with no flaps, then at take off speed, lower your flaps to 10-20 or whatever your aircraft calls for?

It was something I was shown years ago. Ive never really been able to do it and collect data other than you can reach take off speed slightly sooner with your flaps up/less drag. 

Pros:
Achieving take off speed with less distance.

It can assist you with cross wind or gusting wind conditions and allow you to accomplish the take off roll without flaps, which can be a pain.

Cons:

increasing drag as you're attempting to accelerate, but with flaps, your take off speed is reducing so it tends to be a wash (unofficial aviation term)

Improper trim setting could create issues if not set for a flap take off

Although rare, the possibility of an asymmetric flap deployment could create issues

Ive never seen any legit data on it, but its something Ive seen missionary pilots do, Ive done it myself many times and its something I've been shown in mountain courses.  My experiences with it have been in the C182 and 206.  Ive flown other aircraft where I wouldnt do this, like a Kodiak.

Like anything, as you get more advanced there starts to be tricks of the trade passed along.   But that doesnt mean its good.  Like I said, Ive done it a lot and I think it can buy you some distance. Ive seen this in a mountain flying book as well, but cant find it to reference further.

Any experiences or thoughts?
Robert Steht, Capt.
Mission Pilot/CD Pilot
CFI Airplane / CFI Helicopter
Former Sq. Commander

FlyingPig

Robert Steht, Capt.
Mission Pilot/CD Pilot
CFI Airplane / CFI Helicopter
Former Sq. Commander

FlyingPig

Crash attributed to flap deployement during climb out.   In my scenario, the flap deployment takes place during the take off roll.

https://agairupdate.com/2021/12/01/mid-field-flap-extension-during-takeoff-deemed-improper/
Robert Steht, Capt.
Mission Pilot/CD Pilot
CFI Airplane / CFI Helicopter
Former Sq. Commander

Blanding

What exactly do you think you're saving in terms of takeoff distance here? One has to wonder, if the margins are that thin, should you be flying that mission at all?

I've not heard of this technique, but I typically stick to operating the airplane IAW the AFM/POH.

Pinecone

How much drag is there from the flaps at speeds below 50 - 60 knots?

FlyingPig

#5
If you choose to fly strictly in accordance with the POH, that's fine.  There are a lot of useful techniques out there that aren't in the POH that you can learn.   That's why there are specialty courses for mountain flying, bush flying, etc.  Don't just take someone's word for it.  Study it, see if you can find any red flags.   Which is one if the reasons I posted it here.  The aviation section here is all but dead, so its just a discussion.  I've been flying and instructing in airplanes and helicopters for going on 20 years now in several different sectors of aviation, so I run across a lot of ideas that I'm presented with.  For example, you can do a backwards auto rotation in a helicopter, but you'll never find that in an RFM, but I've taught it to students, and been taught that technique at Flight Safety and factory courses and done it in flight and in Class D Sims.   So again, just because youve never heard of it, or its not in the POH doesnt make it unsafe or prohibited.

I've been to a couple mountain flying courses over the years where it was presented, but I've never seen any data on it.  I've done it several times in a 206 and 182 and it "seemed" to get me up faster, but the conditions were always different and uncontrolled.  I've talked to a couple AK State Trooper pilots who use the technique as well.  It was even discussed when I went to the Kodiak factory course. You wouldn't do it in a Kodiak for a few reasons but I wont explain that here.  But that technique was mentioned to warn against doing it in a Kodiak specifically in case they were familiar with the technique.  The DOI pilots I attended the course with were aware of it.  It was presented at the CAP mountain course I did in CAWG several years ago.  I don't recall if it was in the course presentation but we did it out during the flying phase out of Hemet, CA.  So its not some wild anomaly.  Pilots do it.  There's nothing unsafe about it but be aware you are removing your hand from the throttle briefly on your take off roll and "flipping switches" during a critical phase.  The things I caution people on is insuring you are aware of your trim as the flaps change and the rare possibility of an asymmetric flap deployment.

Robert Steht, Capt.
Mission Pilot/CD Pilot
CFI Airplane / CFI Helicopter
Former Sq. Commander

Blanding

You answered my point about the procedure not being in the AFM eloquently, and I appreciate your insight.

What I come back to is whether there's any actual benefit from doing the procedure vs. taking on the four risk factors you identified.

To restate it for emphasis, if the only way I thought I could safely takeoff and climb from an airfield was by using this procedure, I'd be driving.

FlyingPig

Im not really sure what your point was that I made.  Like I said, there are an infinite number of techniques used in aviation that arent in the POH.  But, enjoy your drive.
Robert Steht, Capt.
Mission Pilot/CD Pilot
CFI Airplane / CFI Helicopter
Former Sq. Commander