To the Collective,

Each aircraft has it's own "approved" procedures and each aircraft has it's own "operational" procedures. You know, the ones that have evolved over time largely out of OJT, myth or other means. I personal spent many years flying a DHC6 above 60N and the collective wisdom of the "operational" community was invaluable. Last Spring I treated myself to an early retirement toy, a 1952 170B and had a great Summer getting reacquainted with grass roots flying, the stuff we all grew up on as pilots and truly love. As I re-honed my craft, watched videos, read and listened to the collected wisdom of others I was struck by a "recurring" technique I've observed and truly wondered about the net gain vs potential risks. I've been well served over the years by listening and the wisdom of others, the "you can't live long enough to make all the mistakes yourself" is a truism that has real meaning in aviation.

So at great risk to my self worth here goes, how much is truly gained by making a flap position selection at a somewhat critical point in the take off roll, take off slide or across the water on floats. Its a technique that seems simple enough on first blush, apparently benign enough, if handled correctly no harm but to what net gain over just setting the appropriate flap position for the type of take off from the start. I full agree that different take offs, standard vs STOL vs off strip each have their own unique configurations but does this configuration need to be achieve at what could be deem as a "critical phase of flight". I did "experiment" a little bit on floats last Summer with this technique, flaps reconfiguration once on the step and while I'm admittedly reacquainting myself with floats I honestly found no perceptible benefit but that could have been my rust. I generally operate only on "big" water and long surfaces, no confined spaces for me at this point but look forward to this in the future. Presently I see no need to operate other then in the manor defined by the manufacturer in the aircraft flight manual. However with that said and as mentioned above I equally value the collective wisdom, knowledge and "learned" experiences of those who have gone before.

Thanks for listening, kind regards to all

Mapleflt

There is a lot more wisdom on this question that will certainly chime in but for what it's worth, I'll add what I know.

By starting with the flaps up you have the least amount of resistance to acceleration because without the flaps you have less lift (Lift = Drag). During the take off roll your purpose is to get the wing flying as soon as possible. Some use of flaps may be necessary (depending on airframe characteristics) as they may help guide the prop blast to the tail feathers allowing a tailwheel aircraft to get the tail off the ground sooner. Here again, the tailwheel is resistance to acceleration, so the sooner it is off the ground the better. Reserve the application of serious flap deflection for the moment the aircraft has enough airspeed that the additional lift will allow the aircraft to leave the ground, but not ground effect. Here, the additional lift may cause some stagnation in acceleration for the airspeed required for climb out. You will need to remain in ground effect and relax the flaps enough to continue to build required speed needed to leave ground effect. Once climb performance is established with enough speed, fly the plane.

This is only necessary in circumstances where there is a limited amount of rollable surface from which to take off from. It also requires that there are no obstructions in the ground effect phase. The timing for each phase will grow larger the heavier the aircraft is loaded. Although this technique is not necessary in 99% of our flying, practicing it could save your bacon some day.

Hoooooo, Boy......let the ramblings begin

The true answer to your question is: It depends. It depends on the type Aircraft, it depends on the type of undercarriage, it depends on the pilot’s skill and comfort in the Aircraft, it depends on the loading of the aircraft, and it depends on a half dozen other things I haven’t mentioned.

So, let’s narrow it down to your avatar photo....which appears to be a Cessna 170 on floats. Since the vast majority of floated 170’s on floats are equipped with EDO 2000 floats, I’ll assume that’s the case with yours. I can’t tell from the photo whether your airplane has the stock engine or has been upgraded, but I’ll assume it’s stock. I assume the 170 is a B model, with big flaps....a very significant factor.

Okay, now we’ve controlled the variables substantially. And, you’ve noted that you are returning to floats and the plane is fairly new to you. But, you also note you have operated commercially in the north in a Twotter, so you’re obviously not a low time type. So, more variables controlled....probably.

So, the stock engine 170B is a nice airplane, but it’s not a powerhouse, and on EDO 2000 floats, it’s pretty seriously underfloated. In fact the gross weight is restricted due to reserve buoyancy.....a fact that many if not most pilots of such craft seem to overlook on occasion.

Floats of any sort add significant drag to any airframe, particularly when on the surface, where the “hull speed” of the floats can be close to or even lower than the stall speed of the plane. Hull speed is essentially the speed beyond which it requires significant additional thrust to accelerate at all.....kind of like hitting a wall. Fortunately, the EDO 2000 floats hull speed is pretty generous, so that’s not a factor here.

But power, expressed as a function of resultant thrust, is a huge factor here. To get airborne, you need to work thrust and lift against inertia, aerodynamic drag and that massive drag of the hulls through the water. And the bigger the load in the plane, the greater the inertia and the higher the hydrodynamic drag.....hulls deeper in the water....more wetted area.

So, I would start the takeoff run in this airplane with flaps set at 20 degrees, push the power up and get the plane on the step. Many seaplanes simply will not get on the step without some flaps extended, including some pretty powerful airplanes....like a Cessna 185. You might get there eventually, but it’ll take a LOT of lake. So, ON FLOATS, I always set the flaps at their mid range prior to starting the takeoff.

Once the plane is on step, the pilot’s skill in the fine touch of pitch is absolutely critical, and the 170 is very light in pitch forces, so easy to overcontrol here. A wee bit too nose high or a wee bit too nose low and the drag of those hulls will massively overcome the thrust from your propeller.

So, this is where the pilot’s steady and skilled touch will permit the airplane to accelerate. The key is, when is the plane going fast enough to fly? Airspeed indicators are nearl worthless at these low speeds, so this is a feel thing. But, once the pilot feels that the plane is near flying speed, it’s time to change control inputs to encourage the plane to lift off.

In the airplane we’re discussing here, AT A REASONABLY LIGHT WEIGHT, a very gentle pull on the yoke should increase the AOA sufficiently to cause a launch.

That is the ideal....simple, little special skill required, etc. But, often that doesn’t work for a variety of reasons....Density altitude, wind (or lack of same) and load being the primary culprits. So, now we start trying “other techniques” to effect a launch.

First of those is often to roll in full left aileron, coordinating with a touch of right rudder to compensate for adverse yaw, combined with a pull on the yoke. The theory here is to reduce the amount of hull in the water, thus reducing hydrodynamic drag. And, sometimes this does the trick. But this is where the pilot’s skill and fine touch really come into play.

Now, finally, we’ll try the procedure you questioned.....”popping” the flaps. So, we’re nicely on step, and about as fast as we’re going to get. Flaps set at 20 degrees prior to start of the run. Now, the pilot reaches down, gets a grip on the flap lever, briskly moves that lever up to the 30 degree setting, while at the same time pulling on the yoke to increase AOA, and hopefully yard the plane out of the water. This MUST be immediately followed by lowering the nose to allow the plane to accelerate in low ground effect. As in LOW ground effect. As the plane accelerates (you’ve just eliminated that massive hydrodynamic drag) in low ground effect, the pilot gradually reduces the flap setting back to the 20 degree setting for acceleration and initial climb.

This technique does work, without question....when performed by a very skilled pilot who has practiced the technique to perfection. But, one tiny misapplication.....the flap pull a tiny bit too soon, the pull miss timed, etc....will cause the plane to settle back into the water, and massively increase the water run.

In some airplanes and floats, I’ve used this technique, combined with a full application of aileron to yard a heavily loaded seaplane out of the water.

So, will this technique work for you, in your seaplane? With practice, it probably will.

But, every configuration is different, and different techniques may be required. And remember, different loading may require different techniques. That’s one reason that techniques used at STOL contests may or may not work in a heavily loaded plane.

I transitioned from flying Cessna 185s on floats to flying a 206 on 4000 straight floats....an airplane certified at 3800 pounds, compared to the 185’s 3350 gross.

This 206 has a RSTOL kit and an IO 550 engine. I spent quite a bit of time figuring out how to get this beast to launch heavy. Those huge floats create massive drag. The “popping flaps” thing doesn’t work on the 206, because the electric flaps are too slow to work well. So, I tried rolling one float out....nope. I tried very subtle increase in AOA while clean on step,...nope.

One day, while sliding along on step, I shifted in my seat for whatever reason, which caused a push on right rudder....the plane got slightly sideways, and......launched. I worked on that technique, and found that a shove on a rudder would push the opposite side float out of the water....so add aileron and a gentle pull, and the plane would crawl up into ground effect, and accelerate.

Turned out this odd technique worked even at high weights, and using that technique, I’d get out of the water within 50 to 100 feet of where I’d been getting airborne with a 185, at a much lower weight. After adopting that technique, I went everywhere in the 206 where I’d been going with the 185’s.

Figure out what technique works for you in your plane. Don’t be afraid to experiment, but the key is to develop your skills.

Finally, a technique that gets you airborne relatively quick iron floats may make almost no difference on wheels....two VERY different problems.

MTV

Good information DeltaRomeo.

From an instructional point of view, I find pilots less comfortable with using fairly aggressive forward elevator to get level in low ground effect prefer the flap application to both come off and level the airplane. Unless using Cary's nose down trim, most light and low powered airplanes will require forward elevator in addition to flaps to level the nose in low ground effect.

Because of the complexity mentioned by the OP, and the need in most airplanes to level with elevator anyway, I just set the flap, use elevator to get nose wheel or tailwheel off as soon as possible, use elevator to get the mains off as soon as possible, and use elevator to get the nose down and stay in low ground effect as long as possible. It's a hard sell but dynamic reactive elevator control brackets, insures, and controls pitch attitude extremely accurately and easily at each stage.

MTV is our local guru on floats. I defer to him on those.

As an instructor, I have found most pilots get the tail up slowly, don't keep the nose wheel just off, and resist smarty leveling the nose in low ground effect because they worry about the prop striking the ground. A five second demonstration of dynamic proactive elevator usage at each stage and voila! Pilot practice and voila! No more worries about prop strike.

FWIW I set flaps to 20 and go. Maybe I can squeeze a little more performance out of milking the flaps, but I don't see it as the highest priority during the take off roll, and I don't land places where that slight bit of performance is going to matter. That's on wheels with the upgraded engine...stock engine on floats I might have a different opinion.

You could write several chapters on how, when, and why flap use is important. Then add one on how you don't need them at all. I view the manual as a safe starting point. For many pilots I have found that if you ask why they do anything pertaining to flying the answer is "that is how I was trained". Then you get the guys like mike, contact, and others that usually start the explanation with "well one day there I was" When you examine the flying of the two groups you tend to find on has very strict limits on conditions (long runways, good weather, good equipment) The other group has flown in extremely difficult situations that the manual may not cover (short/poor runways, bad weather, high wind, or high atmospheric lead content) Nothing wrong with the first group, if they stick to the limits. they usually bend less stuff. The second group, well the view from the edge seems worth the risk!! The more tricks you keep in the hat the better the magic show.
DENNY

WOW,

Fantastic stuff from all, MTV and all others you have clearly expressed the kind of collective wisdom I was hoping for and I thank you for that.

I am moving forward slowly, season two is fast approaching. For now I'm in the "set 20" and go category, far more gain by managing the pitch angle once on the step at this point for me, in fact I purposely went out one day and did exactly that on the lake. I got out of the hole; on to the step and then "experimented" with pitch to evaluate the rate of acceleration, the net effect was remarkable !!! As MTV pointed out with the lighter pitch forces of the 170B it was very manageable and a great learning experience. In addition I've played with the "roll" a float off and clear benefit as observed. Rest assured I'll move forward in a measured pace after 28 years of OJT (and my fair share of tricks) I'm in no rush at all.

Thank to all, keep the "intel" flowing it may help others as well, cheers

Mapleflt

As I noted earlier, it depends on a lot of factors. In my experience with the Aviat Husky, on Bushwheel’s, about the best takeoff performance was with full flaps from the git go, neutral trim, full power and let it fly off. At least in calm winds.

As I said, it depends.

MTV

mtv wrote:As I noted earlier, it depends on a lot of factors. In my experience with the Aviat Husky, on Bushwheel’s, about the best takeoff performance was with full flaps from the git go, neutral trim, full power and let it fly off. At least in calm winds.

As I said, it depends.

MTV

I agree.

Kurt

I tried and tried but could never shorten the takeoff distance by yanking the flaps. I just leave them at 20 and ease them out in ground effect. All my takeoffs and landings are short soft field in the event I have to put her down I'll be savy.

No idea if it is shorter but I pretty much always yank in 20 degrees when I see the airspeed needle move off 40mph. Then push forward until I have speed. Its just fun. And (flame suit on) I have the EZflap handle so I don't reach for or look for the handle. Really did not like it much when I installed it, now I love it.

daedaluscan wrote:No idea if it is shorter but I pretty much always yank in 20 degrees when I see the airspeed needle move off 40mph. Then push forward until I have speed. Its just fun. And (flame suit on) I have the EZflap handle so I don't reach for or look for the handle. Really did not like it much when I installed it, now I love it.

That's my next purchase.

I don’t know how you guys do it without the EZ Flap.

Not first hand experience, because I'm not at a level where I'm willing to reach for the lever while on the roll, but a story worth adding:

A RSTOL 185 pilot liked to grab the flap handle and yank the flaps down, popping off the ground as he reached minimum flying speed. On his final flight, he did this as always, but a pulley in the floor ripped out the the bracket that it attached to. Only one, not both. Asymmetrical flap rolled the airplane. No survivors.

Lesson: RSTOL asks more of the flap actuating system than standard. You're using the same mechanism to activate not just the flaps, but ailerons at the same time. Even without the RSTOL, go easy on the flap lever. Next annual, when the airplane is all opened up, have a look in the middle of the floor where the flap cables turn 90° from the lever out toward the door posts and up into the wing. It'll be evident to you that your own strength could exceed the strength of the pulley attachments.

The CallAir A-9B had flaperons that worked well. I set a notch of flap and left it down throughout takeoff and working the field. My A-9B had a high time 235hp O-540 and I needed a notch to get the airplane level in the field with 15gal gas and 100gal in the hopper. My vegetable plots were close and I was putting on 10 gal per acre total volume, so about twelve minutes per load.

Prosaria wrote:I don’t know how you guys do it without the EZ Flap.

Set at 10 before rolling and long arms! How do you pull a full 40 from the ground with the EZ flap? I have to switch grabs to pull full flap with it, and there's no time to switch when popping flaps.

Pinecone wrote:Not first hand experience, because I'm not at a level where I'm willing to reach for the lever while on the roll, but a story worth adding:

A RSTOL 185 pilot liked to grab the flap handle and yank the flaps down, popping off the ground as he reached minimum flying speed. On his final flight, he did this as always, but a pulley in the floor ripped out the the bracket that it attached to. Only one, not both. Asymmetrical flap rolled the airplane. No survivors.

Lesson: RSTOL asks more of the flap actuating system than standard. You're using the same mechanism to activate not just the flaps, but ailerons at the same time. Even without the RSTOL, go easy on the flap lever. Next annual, when the airplane is all opened up, have a look in the middle of the floor where the flap cables turn 90° from the lever out toward the door posts and up into the wing. It'll be evident to you that your own strength could exceed the strength of the pulley attachments.

I know nothing about the accident you refer to, but I’d bet there was prior damage or corrosion in the area that failed. That is, however, an area that should be inspected regularly, on any of the Cessnas.

MTV

Hammer wrote:FWIW I set flaps to 20 and go. Maybe I can squeeze a little more performance out of milking the flaps, but I don't see it as the highest priority during the take off roll, and I don't land places where that slight bit of performance is going to matter. That's on wheels with the upgraded engine...stock engine on floats I might have a different opinion.

Almost all of my time is on straight floats and wheels skis. On floats, under ideal conditions with lots of lake in front of me, I set the flaps at about 20 (PA-12/18 clone, 160 hp on 2200's) and go. But when the load is heavy, the lake is calm and/or short, or density altitude is high, a pull on the flap handle seems to do the trick.

Same thing on skis; ideal conditions 20-degrees works well but when things get a bit "sticky" popping the flaps seems to help.

I generally just set flaps 20 on my C180.
Jerking the flaps (aka a "jump takeoff") can shorten the takeoff run, if done just right,
but although fun it usually isn't needed for my flying.
I have to lean down a ways to reach the flap handle at 0 so would start out at 10 for a jump takeoff.
Doing this does introduce the chance of being distracted at a critical moment,
or of the flap jerk messing up your steering or whatever.
Also need to get the nose down in ground effect to build a bit more airspeed,
so while it shortens the ground run I'm not sure if it helps all that much in clearing any obstacles taller than I am.

In my experience, if you do a jump takeoff just right you don't need to rotate-- the airplane just sort of levitates in a level attitude.
I cob the power, as tail starts to come up I jerk the flaps all the way,
then immediately retract flaps back to 20 or maybe only 10 after airplane levitates.
Then keep the nose down while I accelerate in ground effect to a safe climb speed. Then pitch the nose up for climb.
A lot more shit going on than a standard flaps 20 takeoff, with not all that much better performance.
But if do or die is a matter of a few feet either way, it can make a difference.

Pinecone wrote:A RSTOL 185 pilot liked to grab the flap handle and yank the flaps down, popping off the ground as he reached minimum flying speed. On his final flight, he did this as always, but a pulley in the floor ripped out the the bracket that it attached to. Only one, not both. Asymmetrical flap rolled the airplane.

A sad tale of course but the flap system on Cessnas does need the occasional look as MTW has noted.

One of my most thrilling rides was a 40 degree flap landing in a 172. I had 20' dialed in and looking good but a bit high so for grins I yanked the last 20 in and was deep in the flair when the handle dropped to the floor and I had a sudden change of attitude as a result. Anyway it was not by skill but self preservation that I pulled the yoke hard up under my chin and prepared for impact all in about a short second. It turned out to be one of the smoothest landings I ever made. I was sweating but looking good you know?

The detents on the catch thingy and the cog itself were badly worn. We replaced them instanter. Now when flying with manual flaps I pull what I need then give the handle a little push down just to be sure.