Are Flaps Over Rated?

[ground loop]

bob turner,
Lots of lift without drag seems like a formula for sucess on floats. At least for getting of the water; however, I wonder if no drag means less angle of attack? I think the new husky can beat a cub out of the water even without the 50 degree flaps.

 

[mvivion]

Bob,

I wouldn't doubt that the Husky flap deflection was dictated by a certification issue, but if so, it had nothing to do with a full flap go around. In this post, I was describing Cessna flaps, not Husky flaps.

Of course, certification issues could be CG limitations, stresses on airframe parts (try lowering that last notch of flaps on a Husky at Vfe-and bring a very strong left arm), etc.

My point was that I suspect that the Cessnas were limited for liability reasons, as opposed to certification. Then again, all the 206s have flap restrictions on floats, I believe. Again, it could be climb rate, cooling, stall/spin characteristics, or a whole menu of other issues.

The Husky flaps are HUGE, and just got bigger. They had to change the alloy of the rear spar to get to the gw they wanted, plus get a better flap speed. If they were to deflect the flaps to 50, they might have to put in two rear spars .

MTV
MTV

 

[Crash]

Flaps: You can do some amazing landings and take offs if you know how and when to dump them and when to yank them on. If you don't know how to use them, you're right, you might as well not have em. Crash

 

[Erik]

Yep! Still learning how to use them. The mindless/automatic deployment and retraction taught in primary training doesn't seem to yield such spectacular results. So, I'll keep experimenting. I will find their potential!

 

[bob turner]

My very limited experience on floats says to me that anything you can do to get the floats off the water is a good thing. Seems you need a neck brace to protect against whiplash when the floats lift off. That means flaps. Full flaps on the Husky certainly decreases ground roll; I assume the same setting is used for water takeoff.

 

[Aviator]

...You have to ask: if flaps are such good things for climbing, why is it that we train to clean the darn thing up before doing the engine fire/ failure checklist?

Not sure I agree with you Bob. Flaps are kept at T/O setting until top of 1st segment climb (min 400') to assure obstacle clearance performance. Clean up starts only during transition to 2nd segment climb (when clearing obstacles is no longer an issue).

 

[ground loop]

Gunny of Mike Butterfield,
Is the best angle of climb different with extended flaps a slot? Have you done a best angle of climb and cut power with that wing?

 

[bob turner]

Aviator: Your procedures called for fighting the fire during the first 400 feet? Ours started after cleanup, as I recall. (it has been a while) And while that 400 foot level-off was a minimum, the obstacle had to be really close to extend that upward. Reno was a case in point; you didn't want to go all the way to Washoe with the flaps out.

But I was referring to your average light twin, which probably doesn't climb at all with flaps extended. I am no longer current in twins, but as I recall the drill was gear up, feather, flaps up, blue line, checklist. The order varied, but the checklist was always after cleanup.

 

[bob turner]

Let me back up my assertions with some references. My all-time favorite aero book is NavWeps 00-80T-80, and if you look in the index, you will find climb angle. In mine, it starts on page 152, and goes on to state that max climb angle is obtained when T-D is greatest. I have a nice little book called Jet Airplane Performance, by Lufthansa Consulting, and on page 32, after giving the standard equation, it states "The smallest value for C(drag), and therefore the drag, are obtained with retracted flaps . . .. Thus, the climb gradient is greatest with flaps retracted." I have a neat book by Boeing designed only for folks who absolutely love the Calculus, (it took us six weeks to go through it!) and it gives the same equation on page 3.130. I can't find a succinct statement, but I did stick all the equations into a computer about fifteen years ago, and showed that, at max weight for a noise abatement takeoff, the 737-300 would arrive at 1000'agl about 150 feet sooner with flaps five than with flaps 15, even though with the greater flap setting, the ground roll was significantly less. Hence my hangup when folks say that flaps make you climb better.

By the by, that noise abatement climb gave me every bit as much of a rush as a good slow-roll. I loved it. But it was stupid - deck angles of 30 degrees were not uncommon! An engine seizure at that attitude in the sim challenged the very best!

 

[Aviator]

Bob, when you get into jets, factors other than flaps play a role in climb angle. E.g, swept-wings mean relatively high body angles and, consequently, a vertical thrust vector. In the extreme, if you stand an F-16 on its tail, its climb angle is purely a function vectored thrust.

Further, thrust increases with speed. At the low-end just after T/O, speed is constant (V2) and so is thrust. But as you accelerate to a lower flap setting, you'll have more power and climb angle will increase. But this increase is due to more power rather than less flaps.

 

[bob turner]

The vector diagram, and the equation as well, take angle of thrust into account. The one factor that is usually ignored is the difference between the thrust vector and the flight path - due in part to engine mount, and in part to angle of attack. It is ignored because it has negligible effect in most circumstances.

Thrust is a subject all to itself. And propeller thrust can be complicated - a lot of induced drag enters that one. Let's ignore it here.

Since we are really talking about Cubs, let me assure you - you are welcome to join the majority of lightplane pilots who believe that flaps equal lift, and lift equals climb. I think I will quietly believe otherwise. And while I find full-flap climbs in the Cub exhilarating, a sudden engine stoppage at that speed and angle might well be fatal, assuming ground or an obstacle any place close.

I give up. I promise not to further pursue this unpopular opinion in this thread.

 

[Christina Young]

Bob, I used to think that flaps equaled lift too, until Damian Delgaizo demonstrated to me that they don't in his short field class at Andover. I found they just slow the plane down.

 

[StewartB]

Christina, serious question,

Relative to your statement, if you were to depart a 500' strip that had 100' trees on the end, would you select flaps for take-off, or not? Why?

SB

 

[pzinck]

S B I certainly would.

 

[Christina Young]

Christina, serious question,

Relative to your statement, if you were to depart a 500' strip that had 100' trees on the end, would you select flaps for take-off, or not? Why?

SB

Absolutely. Best Vx = flaps (you are flying slower and therefore have more time until you encounter the trees), best Vy = no flaps. I would use 1 notch, get into ground effect, accelerate, pull second notch and pop up over the trees. Practiced these last week, I might add, at a little private strip near here.

On the other hand, you will achieve a higher angle of attack prior to stalling with no flaps than with flaps. I didn't believe it either until Damian showed me in a lesson. You will stall at a higher airspeed, though.... as I said, flaps slow the plane down.

 

[StewartB]

So if Vx is achieved as a function of flaps "slowing the plane down", how does that relate to the fact that the AOA and airspeed are both higher at stall when not using flaps?

With flaps, you're climbing steeper, at a slower speed, with a reduced AOA.

SB

 

[Christina Young]

So if Vx is achieved as a function of flaps allowing you to "go slower", how does that relate to the fact that the AOA and airspeed are both higher at stall when not using flaps?

SB

I'm not exactly sure what you're asking here. The cub wing with flaps retracted stalls at a higher AOA than it does with flaps deployed. If you don't believe me, it's easy enough to find this out for yourself in your own cub.

Lift is a function of both AOA and airfoil shape, among other things. The flaps are simply devices that change that airfoil shape, and the cub ones are not very good high-lift flaps (unlike the fowler flaps of the Husky that actually increase wing area too), as others have pointed out, but rather high drag ones.

 

[StewartB]

Bob, I used to think that flaps equaled lift too, until Damian Delgaizo demonstrated to me that they don't in his short field class at Andover. I found they just slow the plane down.

Okay. We all learned that there are four forces that we encounter in airplanes. Thrust, drag, lift, and gravity. Let's go back to your statement that the Cub stalls at both higher speed and higher AOA when the wing's clean. Let's assume we're talking power-off stalls holding a constant altitude. Dismiss thrust, both configurations are utilizing equal thrust. Dismiss gravity, since that's also a constant. What's left? Drag and lift. Drag is there, but we can argue that drag doesn't keep an airplane in the air. Lift, on the other hand, does. So if the stalling speed is lower with flaps assuming zero or near-zero thrust, wouldn't one assume that flaps increase lift?

SB

 

[mvivion]

Christina,

Are you confusing Angle of Attack with deck angle? I believe, but one of the aerodynamic whizes on the site can address this better than me, that the Cub will reach a higher angle of attack with flaps deployed.

But, its not a constitutional issue, so I could be wrong :lol: ,

MTV

 

[Christina Young]

So if the stalling speed is lower with flaps assuming zero or near-zero thrust, wouldn't one assume that flaps increase lift?

SB

I think I said that both wing shape AND AOA affect lift. But I definitely mispoke when I said that flaps don't generate any lift at all. Maybe I should have had my coffee first. The amount they generate is definitely dependent on design. But my point is that there is a tradeoff between that generated by AOA and flaps.

 

[StewartB]

Fair enough. I also understood your inferral that Cub flaps kinda suck compared to other designs.

We actually had a civil discussion! That's one in a row!

Have a nice week, I'm going fishing. Keep the boys on their toes.

SB

 

[Christina Young]

Christina,

Are you confusing Angle of Attack with deck angle? I believe, but one of the aerodynamic whizes on the site can address this better than me, that the Cub will reach a higher angle of attack with flaps deployed.

No, absolutely not. Try it for yourself! Go out and try a stall with no flaps, then one with flaps. Which one stalls with the higher AOA?

Also, if you want to get technical, the classic aerodynamics text, Introduction to Flight by John Anderson, has a very interesting graph in the flaps section. I have the 2nd Edition from my Aero 101 class when I was in the academy..... it is on page 222 (I don't know what page it's on in subsequent editions). It is titled "Illustration of the effect of flaps on the lift curve".

In the illustration the x axis represents the AOA, and the y axis the coefficient of lift. There are 3 lift curves plotted, one with no flaps, one with 15 deg of flaps, and one with 50 deg of flaps. It is supposed to represent a typical jet transport configuration.

The interesting thing is that the one with no flaps shows the wing stalling at a AOA of 15 deg. The one with 15 deg of flaps at an AOA of about 13 deg, and the one with 50 deg of flaps at an AOA of about 11 deg!

This would confirm what Damian showed me that one time in the cub.

If I can figure out why my scanner's not working right anymore, I'll scan this page in and post it, and you can see for yourself.

 

[bob turner]

Christina - I'll fly with you or Mike any day. Did you do Jet Transport performance at Andover, or just Cubs? I did mine at Boeing, with an incredible guy who drove a 1951 Chevy, and could derive every single aerodynamic equation from memory, on the blackboard! Unfortunately, half his students were not beyond high-school algebra, and were lost on the first day. (it was a six-week course, eight hours a day!)

This guy (I am ashamed to admit that his name is not popping up in my woeful short-term memory) probably had a bachelor's degree in aero, but he could teach circles around my profs at UCSD, many of whom were world-renowned physicists.

I would love to take a bush flying course - especially that Husky course from Mike. I envy folks who can learn that way - without the dangerous trial-and-error of our early bush Cub drivers.

 

[Christina Young]

Did you do Jet Transport performance at Andover, or just Cubs?

Uh, some slight confusion... I didn't mean that I took the Aero course at Andover Flight Academy........ I don't think jets would do too well there, it's those water traps again Here is Andover:

I actually took the aeronautical engineering 101 course at some "academy" out in Colorado ........ quite a few years ago. I took Cubs at Andover!

Going back to SB's question on his strip with trees example, here is one. This is a 600' private strip across the river in Bucks County, Pennsylvania. It has 75 ft+ trees at each end. What techniques would YOU (I mean SB, MV, everyone?) use to get into/out of it?

Do not be fooled by the hangar. It is a very small one, a single ultralight inside.

(I took these pictures in the spring before the leaves were back on the trees).

 

[harneymaki]

Go out and try a stall with no flaps, then one with flaps. Which one stalls with the higher AOA?

Are we talking the true ANGLE OF ATTACK of the wing or the nose high ATTITUDE of the aircraft?


Paul

 

[Christina Young]

Go out and try a stall with no flaps, then one with flaps. Which one stalls with the higher AOA?

Are we talking the true ANGLE OF ATTACK of the wing or the nose high ATTITUDE of the aircraft?


Paul

Well the aero engineering text book I referenced above talks about the true angle of attack of the wing. I assume that the angle of attack of the wing on a cub doesn't change compared to the nose high attitude (i.e. the wing can't somehow "rotate")?

 

[Aviator]

Maybe we're beating a dead horse here, so just a little fine-tuning.

Flaps are not designed to increase lift: They're designed to allow the airplane to fly slower. Less overall drag at lower speeds, in turn, offsets flap drag--more or less. If flaps are used to increase lift, then higher than minimum speed (for that flap setting) will be needed. Lift will then increase, but flap drag will not be offset and overall performance will suffer. So while it's comforting to have bags of speed to clear trees at the end of the runway, this technique gives a false sense of security as the airplane will be closer to the ground for the same distance covered than climbing with flaps at minimum speed for that flap setting.

 

[Fortysix12]

With 50 ft'rs at each end and a 600 ft. strip,thats a tight light strip by any standard.

 

[harneymaki]

The first chapter of Stick And Rudder seems to clear things up for me.

Paul

 

[Crash]

With 50 ft'rs at each end and a 600 ft. strip,thats a tight light strip by any standard.

A piece of cake with room to spare. Crash