FLAP RETRACTION AFTER TAKEOFF

[DCarlton]

I experienced a few differences with my flight instructor during a BFR today.  I'm curious what the prevalent thinking is regarding flap retraction after takeoff in a Mooney.  I tend to like to gain some altitude, let the airspeed build and then retract the flaps just before I reach the do not exceed speed.  So for me, it's gear up, scan, then flaps up around 100 mph, no rush.  My instructor suggested I get the flaps up much quicker.  I'm wondering why the rush.  At take off flap settings, at what speed does any benefit of increased lift get overcome by drag?  Just wondering when most folks get their flaps up.  Thanks.  

[Hank]

My normal takeoffs are No Flaps, initially at Vx for the first couple hundred feet then relaxing to Vy..

I use flaps for any of the following:  loaded near gross; short field; obstructions that I'm bothered by; soft field. In those cases, I climb at Vx until I'm looking down at the obstruction or at a couple or three hundred feet, then relax to Vy then raise flaps.

For my C, Vx = 85 mph, Vy = 100mph minus altitude in thousands, Vfo = 125 mph.

[A64Pilot]

I do like you, for several reasons, one is comfort as in the nose being lower makes it easier to see over the nose, and secondly I don’t want to be grabbing at too many things right after takeoff and running trim etc. where maybe my attention is best spent doing something else, for a few seconds.

But then under normal conditions I don’t climb at Vx or Vy either, I climb faster for engine cooling.

‘Some instructors have you get the gear as soon as you lift off, I don’t until a landing on the runway I’m leaving isn’t possible, I think the immediate get the gear thing is a carry over from days gone past where we were all supposed to eventually end up in a twin and single engine was just a stepping stone.

On edit, manual gear guys have different reasons when they do of course.

ANY flap setting other than zero increases drag, if it didn’t then of course we would leave them down. So many people instruct to use no flap for takeoff in any aircraft that the POH will allow it, I believe the Mooney POH calls for takeoff flap setting, where many aircraft allow no flap takeoffs. Takeoff flaps while they do increase drag allow for a shorter ground roll and lift off at lower speeds, but you will climb better and faster without them.

Certainly listen to your instructor, they may have a logical reason why you should change your ways, and don’t of course exceed any limits, but I would say don’t blindly do whatever your told, just because they have a CFI. 

Edited July 8, 2021 by A64Pilot

[steingar]

My take offs are busy.  Rotate, get the gear up fast.  Combination of pipsqueak and J-bar.  Get the flaps up.  Power down to 25 squared.  Probably folks to argue with each.

I get my flaps up quick because at full power it's really easy to blow through the low flap speed of my C.  I've already spent a lot on flap repairs, I'd rather not spend more.

[GeeBee]

Get it cleaned up as quickly as you can, your climb performance will be better.

 

I wrote this on 9-27-2020. 

It is a compromise. The best second segment climb comes with reduced to zero flaps. The shortest take-off run comes from increased flaps. 

Example 1. If you have the runway but you need the climb performance, use no flaps and come off the runway with extra speed and energy to quickly achieve Vx. Very commonly we would come off Guatemala City with Flaps 1 "Improved" which means we would accelerate to a higher than normal Vr speed to leave the runway with extra "smash" and reduced drag due to the low flap setting. The climb performance was spectacular but you needed intestinal fortitude to hold the airplane on the deck as the end of the runway came towards you fast.

Example 2. Taking off of PHOG nonstop to KATL in a fully loaded 767. OGG was only 7000', same length as LGA. Solution? Roll with the highest flap setting possible other than landing flaps, Flaps 20. Even with a 5 knot tailwind Rwy 2 works better than 20, because 20 has rising terrain, but 2 shoots you out across the beach. over the ocean, no obstacles, so climb performance is not critical, runway performance is the need. Sure she climbs slow, but you got her off the deck quick

With light airplanes it is similar but not quite so stark and in a Mooney, you may not have a lot of choices in flap settings, but suffice to say if you need climb performance, the cleaner you leave the ground, the better off you are if you got the runway. If you need to leave the ground quickly, higher flap settings, but be prepared for a slug in the climb due to as donkaye points out, high drag. Consider your climb performance in a aborted landing and that is what you would have at best with a full flap take off. If climb performance is not important, but the runway is really short it would help, but since you have no numbers in the POH you are really in test pilot territory and any mishap would be hard to justify the use of full flaps while sitting at the "big green table" assuming you survive.

[PT20J]

Flaps shorten the takeoff roll but decrease climb rate. Generally, the reduced takeoff roll is more advantageous than the improved climb to clear the FAA’s standard 50’ obstacle. Many light airplane POHs say to raise flaps after the obstacles are cleared because after that they are hurting rather than helping. I generally raise the flaps in my M20J accelerating through 80 KIAS. I don’t like to do it too low because I use the same procedures IFR and VFR. There is a significant trim change with flap retraction and I don’t want to be distracted unnecessarily at low altitude on an IFR departure. 

Skip

[Ricky_231]

Takeoff flaps, takeoff power (in my case 38"/2700RPM), rotate, gear up when no runway left to use (which is not to say when you're past the departure end, but when there's no way you'll make it back to the runway if you lose an engine), stable climb (500+ FPM) flaps up, climb power (33"/2600RPM).

[kortopates]

I agree with your instructor and teach rasing them based on airspeed - as soon as your airsppeed is sufficient such that you will not experience any nose drop. That airpseed varies with the airframe model but 80 kts in the mid-body's is what I teach to raise them. A second reason why I really dislike keeping them out beyond that airspeed is that once you do raise them the airspeed will accelerate in the climb and quickly allow your to get your airspeed up above Vy by a min of 10-20 kts where you're keeping the cylinders cooler with the faster airspeed and still have a great climb rate. I could go on about your reduced options if you loose the engine below the altitude you normally raise the flaps but when you think it out there is no good reason to keep them out like that.  

[DCarlton]

Excellent discussion and feedback from everyone.  Thanks.  Definitely helps me clarify my thinking and my takeoff procedure.  Appreciate your time.  

Edited July 8, 2021 by DCarlton

[RobertGary1]

I also suggest picking the flaps up in increments. If you pull them all up at once you get a sink. Pull up 1/2 way, wait, then the next 1/2 and no sink.

 

-Robert

[jlunseth]

231 here. Gear up as soon as I have a positive rate on the VSI, regardless of runway left. Flaps up when the gear is in the wells. Then pitch for midway between Vx and Vy to gain maximum altitude with minimum risk, as close to the airport as possible. Vx risks an inability to get the nose over in time if the engine quits. It is for performance takeoffs but not everyday takeoffs. Vy gains altitude too far from the airport to make it back if the engine quits. My initial climb in my aircraft is 85 KIAS. Getting the gear and flaps stowed helps to accelerate to that speed faster and allows a steeper climb at that speed.

I use takeoff flaps for takeoff in my aircraft, that's half flaps.

[Shadrach]

On 7/8/2021 at 2:24 PM, RobertGary1 said:

I also suggest picking the flaps up in increments. If you pull them all up at once you get a sink. Pull up 1/2 way, wait, then the next 1/2 and no sink.

 

-Robert

From the take off position? One must be pretty slow when raising to get sink. I experience a moderate pitch change when raising (above 80mph). I’ve not experienced much in the way of sink after take off. On a go around transitioning from full flaps, yes. On the other hand my flaps are set up to retract gently in flight

Edited July 21, 2021 by Shadrach

[carusoam]

Now is a good time to review how quickly your flaps retract…

Mine are programmed to move slowly between T/O and stowed… electric.

No way to stop half way… 

 

With hydraulic flaps… many have become misadjusted over the years … and move too quickly….

 

PP thoughts only, not a mechanic…

 

Best regards,

-a-

[RobertGary1]

2 hours ago, Shadrach said:

From the take off position? One must be pretty slow when raising to het sink. I experience a moderate pitch change when raising (above 80mph). I’ve not experienced much in the way of sink after take off. On a go around transitioning from full flaps, yes. On the other hand my flaps are set up to retract gently in flight

Usually around 90-100mph. I’ve seen the sink with my students in all the short and mid bodies. 

[donkaye]

My mentor instructor, who was an aeronautical engineer, said that approach flaps (takeoff flaps) provide ⅔ as much lift as drag while full flaps provide ⅔ as much drag as lift.  So, gear up at 50' or no more runway to land on and flaps up no less that 300' (to account for sink when flaps are raised) or after I'm done with a takeoff turn (for added safety margin).  That's the way I teach it.

[Hector]

In my C engine cooling is an issue so I do use takeoff flaps but quickly raise them after takeoff passing 80 so I can accelerate to cruise climb for better engine cooling.


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[PT20J]

I think it's good to remember that every airplane has it's own characteristics. 

I flew a friend's C last year. First time in a C in 25 years. First thing I noticed is that it was a lot harder (at least for me) to raise the Johnson bar gear from the left seat and that the airspeed builds quickly in the climb making it even more difficult. So, I went for the gear as soon as I was sure I was climbing. Second thing I noticed is that the CHTs went quickly over 400 unless I let the airplane accelerate, and the top of the white arc comes up quickly. So, immediately after gear I raised the flaps.

The Beaver floatplane will not get off the water without takeoff flaps and will not climb well until the flaps are raised to climb. So the drill was takeoff with takeoff flaps and stay in ground effect accelerating to 80 mph while raising the flaps to climb and reducing the power to climb power.

In the Cherokee (the best mannered airplane I have ever flown -- too bad they are so slow), I would take off with two notches of flap and reduce to one notch passing Vx and take off the last notch passing Vy. 

Skip

[DCarlton]

More good feedback thanks.  I do feel some sink.  My flaps are hydraulic and retract rather quickly.  I'll take that into consideration but probably try to get them up a little sooner as long as I have the altitude.  My annual is due soon too; perhaps I'll look into potential flap valve adjustments.  

[carusoam]

Just now, DCarlton said:

More good feedback thanks.  I do feel some sink.  My flaps are hydraulic and retract rather quickly.  I'll take that into consideration but probably try to get them up a little sooner as long as I have the altitude.  My annual is due soon too; perhaps I'll look into potential flap valve adjustments.  

The maintenance manual has the procedure for setting the flap retract rate…

Including the timing to expect while on the ground…

In flight conditions, everything speeds up…   
 

So don’t be surprised with how slow they go without any air pressure on them…

PP thoughts only, not a mechanic…

Best regards,

-a-

[Shadrach]

6 hours ago, PT20J said:

I think it's good to remember that every airplane has it's own characteristics. 

I flew a friend's C last year. First time in a C in 25 years. First thing I noticed is that it was a lot harder (at least for me) to raise the Johnson bar gear from the left seat and that the airspeed builds quickly in the climb making it even more difficult. So, I went for the gear as soon as I was sure I was climbing. Second thing I noticed is that the CHTs went quickly over 400 unless I let the airplane accelerate, and the top of the white arc comes up quickly. So, immediately after gear I raised the flaps.

Which begs the question, what were the raw take off EGT numbers for the C?

[Shadrach]

This thread is interesting and has me thinking about the “sink” phenomenon attributed to raising flaps.  Many here have mentioned it.  I experience a moderate but pronounced pitch change when raising take off flaps at climb angles of attack. I experience  a more dramatic pitch change when raising full flaps from a climb angle of attack. Sometimes this feels like sinking (losing attitude) but I don’t think it actually is (unless you’re raising flaps near clean stall speed).  I think what’s being felt is similar to the backward tumbling sensation that can be experienced in IMC with changes in pitch. Reconfiguring the wing will change the AOA, the effective AOI and pitch angle perceived by the pilot. There is no physical reason for an airplane traveling above clean stall speed to lose altitude unless AOA is negative or critical AOA is exceeded. If that’s happening to a pilot, they are reconfiguring close to the ragged edge.  I’m not picking nits here. I think that new pilots interpret the term “sink” as the airplane descending slightly and then regaining lost altitude as speed is gained. I can envision a scenario where that misunderstanding may cause problems. I would love to read @RobertGary1 and @donkaye thoughts on his.

Edited July 10, 2021 by Shadrach

[PT20J]

3 hours ago, Shadrach said:

Which begs the question, what were the raw take off EGT numbers for the C?

I was too busy to notice. 

[Shadrach]

1 minute ago, PT20J said:

I was too busy to notice. 

I bet.

If you talk to him again ask him to take note next time he takes off. I bet that offending cylinders are likely less than 200° ROP with EGTs in the mid to low 1400s. Unfortunately, it’s not an uncommon scenario 0360s. They seem to tolerate it well enough but it often forces pilots to trade climb performance for cooling

[GeeBee]

Absolutely sink can occur from raising the flaps. As the flaps are raised with no change in trajectory and thus angle of attack you go from an airfoil that has a fairly high Coefficient of Lift to one with a lower Cl for the given AoA. Thus the net lift produced is reduced. At this point the pilot usually pulls back to increase lift via AoA and that increases load factor, which further puts a strain on the lift-weight ratio creating a sink. Hopefully and usually the back pull does not exceed critical AoA. Until the airplane accelerates to generate a net lift comparable to its previous condition, there will be a sink. There is a reason why GPWS systems have a "Don't Sink" mode after take-off and if you never flew a 727 on one engine go around, you've never heard that callout 

[PeteMc]

51 minutes ago, GeeBee said:

Absolutely sink can occur from raising the flaps.

CAN sink sure, especially if you're a little to fast with the flap retraction and not paying attention (which may be the last time that happens....)  But if discussing a normal take-off, do you really think you actually SINK when you retract the flaps?  Plane is climbing AND accelerating and yes you do change the coefficient of lift as you said.  But do you actually think for that moment you're retracting the flaps you're behind the curve and loose all lift resulting in a momentary SINK?  (Again, assuming you don't do it right at the edge of stall.)

I agree with the others that have said you get a pitch change and I agree there is some REDUCTION in lift as the flaps are retracted.  But I don't think you loose all your lift and actually start sinking, aka actually loosing altitude.  But this slight slowing in the climb rate and change in pitch angle could make people think they are sinking.

Might be an interesting flight to hold specific climb angle and see what happens to speed and rate of climb as you raise and lower the flaps to TO position.  (But I bet the real numbers are in some flight test report at Mooney. )