In the Cherokee, I let them do a full-flap takeoff, to see exactly why: it basically starts flying ass-end first, and rides along on the nose wheel unless you maintain alot of back pressure.
The main reason is the excess drag. True, you do get more lift, but for the purposes of climbing the aircraft, the amount of drag makes it far less efficient for climbing purposes. The aircraft will climb with full-flap, but not as well as with less. And if you're aiming to get the airplane up to altitude in the most efficient manner, then full flap doesn't cut it.
It will get you off the ground real quick, but the climb performance is crud.
Full flap takeoffs: why not?
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Clodhopper
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Jimmy Mack
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One of the most "frightening" experiences I ever had was a full flap t/o
I didn't verify the flap setting and assumed they were in the t/o instead of down position and the bird starting flying at 50 mph...... then instead of the usual climb out at 80 she wanted to fly 60 and no faster.... i was sitting there thinking what the hell is going on here?!?!?! then it dawned on me that I was an idiot.
I guess that's why they have a flap gauge, eh?
I didn't verify the flap setting and assumed they were in the t/o instead of down position and the bird starting flying at 50 mph...... then instead of the usual climb out at 80 she wanted to fly 60 and no faster.... i was sitting there thinking what the hell is going on here?!?!?! then it dawned on me that I was an idiot.
I guess that's why they have a flap gauge, eh?
Flaps create lift, but they also produce drag.
Best to accelerate (at least, on a hard surface) with minimum drag.
Try taxiing with both doors pushed all the way open. You will be surprised how much power is required to move the aircraft!
An aircraft with sufficient thrust will use a modicum (10 to 20 degrees) of flaps for takeoff because they have enough thrust to overcome the drag of 10 to 20 degrees of flaps. example: Maule, C182.
Beyond 20 degrees, most flaps simply produce more drag, and little extra lift, which is useful during a steep approach over an obstacle to keep the speed down, but is not useful on takeoff.
Best to accelerate (at least, on a hard surface) with minimum drag.
Try taxiing with both doors pushed all the way open. You will be surprised how much power is required to move the aircraft!
An aircraft with sufficient thrust will use a modicum (10 to 20 degrees) of flaps for takeoff because they have enough thrust to overcome the drag of 10 to 20 degrees of flaps. example: Maule, C182.
Beyond 20 degrees, most flaps simply produce more drag, and little extra lift, which is useful during a steep approach over an obstacle to keep the speed down, but is not useful on takeoff.
Actually, if you have manual flaps like a cherokee I have heard that one way to achieve an extremely short takeoff roll is to accelerate with no flap, and then dump in full flap once the airplane reaches a speed where it will fly with flap (this will be below Vr). You get the benefits of no drag while accelerating, and the added lift from the flaps. Apparently people have used this technique to get cherokees off in 400' or so at full gross.
P.S. I've never tried this manouvre and don't just do it because some guy on the internet told you it would work. This is a disclaimer.
P.S. I've never tried this manouvre and don't just do it because some guy on the internet told you it would work. This is a disclaimer.
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Clodhopper
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Really? Deploying flap to suck the wheels up out of the muck is a technique which I am sure is older than I am.Never heard of that manoeuver
Look carefully at the flaps in the following sequence:
http://www.mauleairinc.com/Maule_in_the ... nonball_5/
Hedley makes a good point whereas flaps create more drag, and if you look in a 172 POH (there might be something similar in other POH) there is a little table with stall speeds with flaps. For instance, in the 1973 POH for a C-172
No flaps stall speed: 57 mph CAS
10 deg. of flaps Stall speed: 52 mph CAS
Ok, so with only 10 degrees of flaps you decrease your stall speed by 5 mph....
40 degrees of flaps Stall speed: 49 mph CAS
Add another 30 degrees over your initial 10 degrees and stall speed goes down only 3 mph...
So we can conclude for the C-172 at least, anything over 10 degrees of flaps is more drag than lift and therefore slows you right down for the take-off roll. And try climbing with full flaps on a marginaly warm day.... you'd probably hit de 3' fence at the end of the runway with full flaps.
Another thing to take into consideration. Climb is very poor with full flaps, and you will want to bring them up to 20 at least (again, for the 172) to accelerate and get somewhat of a better climb and eventually no flaps at all. A safety issue here would be the the flaps would be retracted too fast over the ground and the airplane would stall maybe 50' or even less over the ground (or whatever altitude the pilot brings the flaps up)
What about the overshoot, you could be fairly low and at the last minute a deer goes on the runway... well, keep in mind you have your approach speed already and you are not starting from 0 MPH, and you don't have the friction of the wheels.
No flaps stall speed: 57 mph CAS
10 deg. of flaps Stall speed: 52 mph CAS
Ok, so with only 10 degrees of flaps you decrease your stall speed by 5 mph....
40 degrees of flaps Stall speed: 49 mph CAS
Add another 30 degrees over your initial 10 degrees and stall speed goes down only 3 mph...
So we can conclude for the C-172 at least, anything over 10 degrees of flaps is more drag than lift and therefore slows you right down for the take-off roll. And try climbing with full flaps on a marginaly warm day.... you'd probably hit de 3' fence at the end of the runway with full flaps.
Another thing to take into consideration. Climb is very poor with full flaps, and you will want to bring them up to 20 at least (again, for the 172) to accelerate and get somewhat of a better climb and eventually no flaps at all. A safety issue here would be the the flaps would be retracted too fast over the ground and the airplane would stall maybe 50' or even less over the ground (or whatever altitude the pilot brings the flaps up)
What about the overshoot, you could be fairly low and at the last minute a deer goes on the runway... well, keep in mind you have your approach speed already and you are not starting from 0 MPH, and you don't have the friction of the wheels.
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goldeneagle
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Re: Full flap takeoffs: why not?
My question, if you couldn't answer that, was the student actually getting what they were paying for?cpl_atc wrote:When I was instructing, there was a question that I hoped students would never ask. And fortunately they didn't. However, it is a question (legitimate, not trolling here) for which I have never received a satisfactory answer, and thought I'd try here.
The first part of the correct answer is, it depends on the airplane. There are a lot of different ways flaps can be attached to an airplane, and different configurations produce different results. Example, on our 421 it's a split flap design, flaps create drag, and do NOT create lift. All takeoffs, all conditions are done flapless because they dont create lift. A long time ago, I flew a seneca with a robertson stol conversion on it. Flaps were fowler design, full span (no ailerons). For short field performance, you used all 40 degrees for takeoff, rotate at 'needle alive' and hold 40 knots indicated till clear of obstacles. With an empty airplane, it was quite impressive, often didn't bother to turn down the runway, just takeoff strait ahead from the hold line, easily cleared that snowbank on the other side of the runway, and climb away with about a 50 degree deck angle. It was actually fun, especially if there was a twin otter waiting to go behind you....
Most modern trainers use a flowler design for the flap track, and during the first 20 degrees of extension, it's also moving rearward, so, it's increasing wing area as well as the angle of attack on the inboard section. Net result, small increase in drag, huge increase in lift. The second half of the flap track actually makes the thing extend 'down' rather than 'back', resulting in a DECREASE in wing area, and a huge increase in drag.
And, in case it hasn't become obvious yet, that bit about lift and drag is what matters, but no so much the absolute values of each, it's the ratio of the two. If that first 20 degrees of extension produces more lift than drag, then the L/D ratio for the entire airplane goes up, and ultimately, that means it requires less power to maintain level flight, so, more power is available to provide climb. It's all about the ratio of lift and drag, maximize the L/D ratio, and you minimize the power needed for level flight, hence maximizing the 'excess power available'. The math is more fun for a fowler design because wing area is also a function of how far down the track the flaps are extended, and lift is directly proportional to wing area (simplistic first approximation, in reality, somewhat more complex). You can make it even more fun doing the math for a soft field, where the objective is to get airborne at minimum airspeed rather than maximum efficiency. Crunch all the numbers and you will quickly discover, that point on the fowler track where wing area is maximized works out to be the 'magic' spot. When you go out and play with a real airplane in the real world after doing all the math, you will discover, the math is correct.
As for some of the 'tricks', well, they rely on a dynamic system rather than a static system. If you set the flaps, then start the roll, your geometry is static. Start the roll with no flaps, then at about 40kt, pull on full flap, suddenly you are restricting the airflow under the wing. That sudden restriction will cause an increase in pressure, which applies to the entire underside of the wing along the length of the flaps, with a resultant lift force that will 'pop' the airplane out of the muck, or off the water. The thing to remember, once it pops, then the airflow isn't restricted as much any more, and the lift drops off rapidly again. The key is to apply flap such that the increase in aerodynamic drag from the flaps is less than the decrease in rolling/sliding drag from the gear popping off the ground/water so it accelerates rapidly on the pop. The way I've always done it, pull hard to full flap, and as soon as she pops, start bleeding that flap off again back to the optimum settings. In a Cessna with a fowler track, that's typically 20 degrees, where the fowler track starts to angle down, but on stuff with split or strait flaps, it's often back to zero. For those that say you gotta have manual flaps, i call horsepucky, its a technique that works well getting a 206 off the water, hit the flap switch when you are getting close to the top of the swell and you will vault off the top like a ski jump, now fly the damn thing to make sure you dont clip the top of the next one.
Never ceases to amaze me how often this kind of question gets asked though, especially by instructors. This is theory thats SUPPOSED to be taught at the ppl groundschool. I started to sit in on an instructor groundschool earlier this year, contemplating getting the rating back. I had to stop going, because it was becoming painfully obvious, forgetting everything you learned at ppl and cpl groundschool was a pre-requisite to the instructors course, and all the rest of the candidates had that pre-req down pat.
I don't know why cessna does not recomend it, but here is my shot at why it works.
On a takeoff run on wheels, at rotate speed you pull the nose up a bit, this creates the AOA that along with your speed produces enough lift to get you off the surface.
On floats the problem is a bit different. If you try and rotate the nose up the way you would on wheels, you will drag the back of the floats, create drag on the water and slow you down.
With a bit more flap set for t/o, you now have in effect increased the AOA a bit which along with your speed produces enough lift to get you out. The bonus is that the a/c attitude with this flap setting is such that you are sitting on the sweet spot on the step that gives the minimum water drag.
This is my guess anyways. I have not read this in any textbooks to back this up though.
Thoughts anyone?
On a takeoff run on wheels, at rotate speed you pull the nose up a bit, this creates the AOA that along with your speed produces enough lift to get you off the surface.
On floats the problem is a bit different. If you try and rotate the nose up the way you would on wheels, you will drag the back of the floats, create drag on the water and slow you down.
With a bit more flap set for t/o, you now have in effect increased the AOA a bit which along with your speed produces enough lift to get you out. The bonus is that the a/c attitude with this flap setting is such that you are sitting on the sweet spot on the step that gives the minimum water drag.
This is my guess anyways. I have not read this in any textbooks to back this up though.
Thoughts anyone?
Wahunga!
cpl_atc, did you have a poh supplement for the float? because it does say for WHEELS no more than 10... how about floats? usually a few things changes when you go from wheels to floats..
Now, one thing we must all remember, if the POH says no more than 10 degrees, we cannot use more than 10 degrees lest we be linched by TC... If the runway is too short, don't go there
Now, one thing we must all remember, if the POH says no more than 10 degrees, we cannot use more than 10 degrees lest we be linched by TC... If the runway is too short, don't go there
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goldeneagle
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Re: Full flap takeoffs: why not?
Was the plane on edos, caps or whips ?cpl_atc wrote: - The performance gain on water, at least, is indisputable. So why doesn't Cessna recommend using 20 degrees for float operations? Or all operations, for that matter?
Again, it's basically the same answer (short version this time), and that is 'it depends on airplane configuration'. I've never flown a 172 on floats (not sure I ever want to either), but, done my share of time (years ago) on 185s. I dont remember the gory details, one was on small floats (I _think_ they were 2960 edos) and the other was on the bigger ones (cap 3500 ??). The point is, the floats were radically different, otherwise identical airplanes. Both had strenghts and weaknesses, but, at the end of the day, you used completely different techniques with them when trying to drag a load out of a short lake.
172 POH float supplement still states flaps 10.. however is does state to further reduce the take off run you can drop the flaps to 10 after you are up on the step, and lift one float at a time.
Now just excatly how accurate your weeble wooble flap gauge is .. seems to be +/- 5 degrees in the one i've seen, and how close you get it to 10 or 20 while on the step at 40mph who's to say. From what i've experienced at gross weight you get a signifigantly shorter takeoff run when the flaps are closer to 20.. BUT according POH its 10.. so thats what should be taught.
160hp, edo 2000, floatprop
Now just excatly how accurate your weeble wooble flap gauge is .. seems to be +/- 5 degrees in the one i've seen, and how close you get it to 10 or 20 while on the step at 40mph who's to say. From what i've experienced at gross weight you get a signifigantly shorter takeoff run when the flaps are closer to 20.. BUT according POH its 10.. so thats what should be taught.
160hp, edo 2000, floatprop
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goldeneagle
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If you KNOW that using 10 is wrong, but want to teach it that way because it's 'written in a book', then you shouldn't be teaching to begin with. I'd actually go a step further, and suggest, you should know why it says 10 in the book, but 20 _appears_ to work better, and you should be able to explain it to the students the reason for the discrepancy.buck82 wrote: From what i've experienced at gross weight you get a signifigantly shorter takeoff run when the flaps are closer to 20.. BUT according POH its 10.. so thats what should be taught.
The answer to why it's 10 in the POH is actually quite simple. Takeoff on floats consists of 3 phases, start of slide, on the step, climb to 50 ft (35 ft if you are in a transport category). 20 will dramatically reduce phases 1 and 2, but she doesn't climb well, and it lengthens phase 3, resulting in a shorter slide, but a longer complete takeoff. 10 will increase the slide, with a better climb, and a shorter total distance to 50 feet. The POH pablum is written with the consideration that re-configuring flap settings during the takeoff is far to complex a procedure for mere pilots, so 10 is the reccomended setting as it is the shortest route to clearing that 50 foot obstacle in the POH conditions (sea level, flat calm, yada yada).
Out here in the real world, well, water has waves, and a 172 with 2 pax and full tanks on floats is already starting to get a little heavy, even before you toss the fishing rods and lunch in the back. Most new pilots dont have optimum aircraft control on the step, and tend to spend a lot of extra time sliding because of it. You may be 'safe' teaching your students to regurgitate the pablum out of the POH, but, your students will be a hell of a lot safer if you teach them how to get that thing off the water. If they dont have optimum aircraft control on the step, they will be way better off climbing with 20 flap than sliding with 10, and be up over the trees quicker.
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Cat Driver
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Goldenone, you are close to correct however there are many other factors involved in getting airborne in a fully loaded sea plane.
I just run and hide under my bed when I read some of the comments here on the instructors forum.
Anyhow I will not bother to make anymore comments other than repeat that I run and hide under my bed when I think of the general quality of flight instruction especailly sea planes and tail wheel airplanes.
I just run and hide under my bed when I read some of the comments here on the instructors forum.
Anyhow I will not bother to make anymore comments other than repeat that I run and hide under my bed when I think of the general quality of flight instruction especailly sea planes and tail wheel airplanes.
The hardest thing about flying is knowing when to say no
After over a half a century of flying no one ever died because of my decision not to fly.
After over a half a century of flying no one ever died because of my decision not to fly.
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Cat Driver
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Walker staying alive is not the only benchmark of how to fly, there is also the various techniques one learns over the years.
I have been flying sea planes since 1954 and can't even remember how many different types.
It is statements like this one that bothers me.
" From what i've experienced at gross weight you get a signifigantly shorter takeoff run when the flaps are closer to 20.. BUT according POH its 10.. so thats what should be taught. "
So based on that mindset some poor young pilot shows up at xxx fishing lodge for his / her first float plane flying job and the owner should just ignore the fact that his airplane is roaring down the lake at full power and taking forever to get off because the new pilot does not have the foggiest idea of how to get it in the air?
But as far as I am concerned what you should do is phone TC in Vancouver and ask that fu.kin TC guy who has made sure I can not teach sea plane flying in this area, ask him to clear up this matter.
When you are talking to him tell him I have not forgotten who he is.
PM me and I'll give you his name.
Cat
I have been flying sea planes since 1954 and can't even remember how many different types.
It is statements like this one that bothers me.
" From what i've experienced at gross weight you get a signifigantly shorter takeoff run when the flaps are closer to 20.. BUT according POH its 10.. so thats what should be taught. "
So based on that mindset some poor young pilot shows up at xxx fishing lodge for his / her first float plane flying job and the owner should just ignore the fact that his airplane is roaring down the lake at full power and taking forever to get off because the new pilot does not have the foggiest idea of how to get it in the air?
But as far as I am concerned what you should do is phone TC in Vancouver and ask that fu.kin TC guy who has made sure I can not teach sea plane flying in this area, ask him to clear up this matter.
When you are talking to him tell him I have not forgotten who he is.
PM me and I'll give you his name.
Cat
The hardest thing about flying is knowing when to say no
After over a half a century of flying no one ever died because of my decision not to fly.
After over a half a century of flying no one ever died because of my decision not to fly.
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Cat Driver
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" I'ld have no problem explaining to people why more flap does work. "
Then why did you make this statement?
" From what i've experienced at gross weight you get a signifigantly shorter takeoff run when the flaps are closer to 20.. BUT according POH its 10.. so thats what should be taught. "
If you actually do teach float plane flying why not teach them what works best, or do you feel that by the book is the only way?
Then why did you make this statement?
" From what i've experienced at gross weight you get a signifigantly shorter takeoff run when the flaps are closer to 20.. BUT according POH its 10.. so thats what should be taught. "
If you actually do teach float plane flying why not teach them what works best, or do you feel that by the book is the only way?
The hardest thing about flying is knowing when to say no
After over a half a century of flying no one ever died because of my decision not to fly.
After over a half a century of flying no one ever died because of my decision not to fly.
Unfrotunately I don't have the authority to re-write 'the book'..
honest question here,
How do you deal with such situations cat? Is it possible to suggest different ways the aircraft should be operated in SOP's, ways that differ from whats written in the POH.. and then get transport to approve this variance?
honest question here,
How do you deal with such situations cat? Is it possible to suggest different ways the aircraft should be operated in SOP's, ways that differ from whats written in the POH.. and then get transport to approve this variance?
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Cat Driver
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" How do you deal with such situations cat? Is it possible to suggest different ways the aircraft should be operated in SOP's, ways that differ from whats written in the POH.. and then get transport to approve this variance? "
Buck82:
I will try and answer as honestly as I can.
Ever since I can remember we have used 20 degrees of flap as an aid to getting Cessna's off the water.
Some have manual flaps but most have electric, with manual you can select when you want quickly.
I have no idea of how many hours I have on Cessnas over the decades, but I do know the two best aids in breaking surface tension for lift off is with 20 degrees of flap and or lifting one float before the other.
This part of your question is beyond my understanding as I am not familiar with using the term SOP's to describe something as basic and logical as selecting 20 degrees of flap for shorter water runs in a Cessna.
" Is it possible to suggest different ways the aircraft should be operated in SOP's, "
It never occured to me to seek permission or to seek approval from Transport Canada to teach something I have been doing for half a century.
If you are that handcuffed by TC there is really nothing I can offer as advice except to feel sorry for your dilemma.
But look on the positive side of this 182, considering that I am not up to speed in the modern world of teaching float plane flying maybe I have been doing it wrong all these years and it is me who needs guidance.
I'm really sorry but the foregiong is all I can do to explain my position.
You take care and try to keep yourself out of trouble with the regulator and the best way to start is don't let them know that you sought my advice.
Cat
Buck82:
I will try and answer as honestly as I can.
Ever since I can remember we have used 20 degrees of flap as an aid to getting Cessna's off the water.
Some have manual flaps but most have electric, with manual you can select when you want quickly.
I have no idea of how many hours I have on Cessnas over the decades, but I do know the two best aids in breaking surface tension for lift off is with 20 degrees of flap and or lifting one float before the other.
This part of your question is beyond my understanding as I am not familiar with using the term SOP's to describe something as basic and logical as selecting 20 degrees of flap for shorter water runs in a Cessna.
" Is it possible to suggest different ways the aircraft should be operated in SOP's, "
It never occured to me to seek permission or to seek approval from Transport Canada to teach something I have been doing for half a century.
If you are that handcuffed by TC there is really nothing I can offer as advice except to feel sorry for your dilemma.
But look on the positive side of this 182, considering that I am not up to speed in the modern world of teaching float plane flying maybe I have been doing it wrong all these years and it is me who needs guidance.
I'm really sorry but the foregiong is all I can do to explain my position.
You take care and try to keep yourself out of trouble with the regulator and the best way to start is don't let them know that you sought my advice.
Cat
The hardest thing about flying is knowing when to say no
After over a half a century of flying no one ever died because of my decision not to fly.
After over a half a century of flying no one ever died because of my decision not to fly.
I completed a full-flap (40°) departure in a cessna aerobat the other day. It had about 190HP, though. We were comparing the ground run to a takeoff with just 20 flap. They are close in distance! It lept off the runway in a hurry. The bush STOL kit, vortex generators and drooped wingtips help a lot.
