Use of Flaps on Takeoff...?

[codenamejames]

May be a bit of a Flying 101 question:

I was recently taking off in a Cherokee 140 and was right at the MAUW. I was advised by an instructor to not use any flap on takeoff.
(not sure if this was a performance suggestion or safety suggestion for my benefit?)

We took off ok, but just got me thinking on Flap use on takeoff.

I know that some aircraft specify 1 notch of flap on takeoff, presumably as they increase lift (and drag). What are the protocols on using/not using flap if you're heavy/hot/high/short field?

[pcx]

James
A serious question that deserves a serious answer.
Aviation is rife with opinions and statements that have been handed down from pilot to pilot or instructor to student often presented as gospel. A classic is " don't operate a piston engine over square". We won't go into that one here.
The answer to your question lies within the Flight Manual, Pilots Operating Handbook or whatever the equivalent document is called.
Look for the performance section and you should find some reference to take off and landing charts. These charts will specify the take off configuration required to produce the predicted take off distance.
There may be charts for nil flap and also for one stage of flap. If so, provided the runway is suitable, with the prevailing conditions, then either flap setting would be suitable.
I do not have a manual for the Cherokee available so am not able to provide you with a definate answer.
Always remember, the Approved Flight Manual (or whatever it may be called) is your aviation bible and should take precedence over any other source of information.
Enjoy your flying and never be afraid to ask a question if you are not sure of the answer. The true professional pilot, and I include private, glider and ultralight pilots in this description, will respect you for your honesty and integrity in attempting to improve your aviation knowledge.

[VH-BCY]

Flaps

If you are using any configuration other than what it says in the POH or owners manual, then the take off distance will increase and you are acting as a test pilot. Does your instructor thinks he is better than the very experienced test pilots who certified these aircrafts way back in the dark ages? Stick to what it says in the POH/owners/flight manual. Not all instructors know what they are doing and if you think they are wrong, question him/her and try and do your own research. If you are not satisfied with the answer, ask a more experienced instructor.

[go_soaring]

Case closed, top responses. I guess techniques for T/O is that all can be discussed now..


go_soaring! instead

[ForkTailedDrKiller]

If you are using any configuration other than what it says in the POH or owners manual, then the take off distance will increase and you are acting as a test pilot

With all due respect - that is rubbish!

The POH for the V35B states nil flap for take-off, but the reality is that by using flap you can get the aeroplane off the ground in a fraction of distance that you will with nil flap.

Apparently the POH for earlier models of the V-tail gave much more detail on short-field take-off technique and performance than do later versions - for essentially the same aeroplane.

My advice is to start with the POH for the aeroplane, then use your common sense, your growing experience as a pilot and with the aeroplane - adjusted where appropriate by advice from highly experienced pilots that you know and respect.

But it is true - if you prang it the ATSB report will probably make a big deal out of the fact that you used a technique not approved by the manufacturer - as indicated in the POH!

Dr

PS: Just yesterday I took the FTDK into an interesting little "house" strip on a Cape York cattle station - requires a curved approach to very short final to dodge a large mango tree that encroaches on the approach path, over a crocodile infested lagoon (will try to get some pics tomorrow!). Departed using what I consider a max performance TO for the Bo (20o flap) cause I wanted to see how much strip it used (less than half) - tomorrow I will depart near MTOW.

[Mach E Avelli]

I don't have a POH for a Cherokee so this is just guessing. Your instructor probably should have explained that the climb capability with flap hanging out would be less, particularly at max weight.
However, if flap is certified for takeoff, it is almost certainly certified to be used at maximum weight. I am not aware of any limitations based on weight for any single-engine type where flap is allowed to be used.
If use of flap is optional for takeoff, it is up to the pilot to decide what is more importatnt - takeoff distance or initial climb performance. One is often at the expense of the other.
In multi-engine aircraft the use of flap is much more defined because it is based on runway versus initial climb requirements, assuming an engine failure. In a single, an engine failure soon after takeoff is likely to have an inevitable outcome regardless of flap. But if runway length permits, less flap will usually reduce the time when you could be exposed to obstacles in the takoff path, so maybe that was what your instructor was getting at.

[john_tullamarine]

What some of the posts are hinting at is certification and design standards.

If you operate in accordance with the POH configurations and techiques then your operation previously has had the various certification ticks in the boxes addressed. This situation is far easier to argue after the accident both with the insurer and at the enquiry.

If you operate other than in accordance with the POH, then you are responsible for making sure that you could run a defacto certification exercise and achieve all the relevant ticks in the boxes. Herein lies the problem as the pilot, typically, doesn't have the certification details to hand. This situation is somewhat less easily argued after the accident ....

As a side note, in previous lifetimes, CASA had the performance view that the second option was acceptable, provided that the pilot could tick the boxes ... I don't know that that view ever was tested in court, though ...

[Jabawocky]

Just another thought or two

Cherokee 140 were all 140 ponies in good health? Did they have any Equine Flu or even Swine flu?? At 140HP they are blistering non performers. At any less .

Also with so few HP to play with, were your weights really at the prescribed limit? When was the last W&B for that plane? You may well find its gained weight over time. As have some pilots!

J

[codenamejames]

Thanks Jaba - and actually - you're not half wrong...140 isn't much, and it felt a lot less than that on the day.

Completely agree, the POH is the first thing to consult, and with my experience, the thing to stick to.

So a couple more details: From memory, the POH for the Chrokee 140 says 1 notch for a max performance takeoff.
In this case the runway is over 700m long, so I would've thought enough for a fat little PA-28-140.
The 'climb-out' was interesting - I felt like we were just missing the tops of trees, despite bing inside the calculated balance envelope.
So, in this instance, I'm guessing that it be obstacle avoidance rather than runway length that would be the critical factor.

[john_tullamarine]

So, in this instance, I'm guessing that it be obstacle avoidance rather than runway length that would be the critical factor.

However, you can't look at the two considerations independently. In general ..

(a) a bit more flap results in a shorter roll but degraded climb

(b) a bit less flap results in a longer (often quite a bit longer due to the extra speed you are going for) roll but improved climb

with the result that

(a) on a short strip without obstacles, flap is your friend

(b) on a long strip with far away obstacles, avoid flap

(c) on a short strip with obstacles .. go by car

About 35 years since I have been in a Cherokee so the memory is a bit scratchy but I would have thought 700m should be reasonably comfortable near sea level ?

When was the last W&B for that plane ?

An important point .. all aircraft grow heavier (accumulated dirt and rubbish in the bilges and, for some private aircraft, the odd unrecorded minor mod or refurbishment here and there).

Best anecdote I can relate .. we modded a Commanche, years ago, and I was going to run the sums to adjust the 6.2/6.3. However, I had the scales in the back of the ute so we figured .. why not run it over the ramps.

Weight was out by a couple of hundred pounds .. which we eventually tracked down to a couple of radio mods and, mainly, a total interior refurbishment including a bunch of lead wool for soundproofing ...

.. logbook ... what's that ?

[Mark1234]

I'm going to discuss the 160, just because I know it, and not the 140. I suspect the 140 may be similar, but I won't assume.

with a 160 you have 2 options - nil flap, or 2 stages (by POH)

Flap will shorten the ground roll, and reduce the climb gradient.
Additionally (and many seem to overlook this), the best climb gradient with flap will occur at a slower airspeed. I.e. if you climb at normal speed with flap you're doubly bu**ered.

To my mind, if there is ground run available, you use nil flap. This gives the best airborne performance, and (usually - unless the obstacle is close) the best obstacle clearance. Independant of temp, alt etc.

If the runway is short, or the hot and high conditions mean you need more runway than is available, then a flapped short field departure comes into the picture. Think about your obstacle clearance carefully (the POH gives distances to 50ft screen height as well as ground roll.)

Also consider whether you're cutting it too close.. and be aware of the reduced climb speed. Last time I did a short field departure for real was in an arrow 4 at MTOW, and if memory serves me the initial climb was about 65kts. Kinda slow..

It sounds very much like flap was the wrong decision in your case - adequate runway and poor obstacle clearance, but without running the figures I don't know.

[ForkTailedDrKiller]

If you need to get out of a tight spot, max angle of climb is what you are looking for, not rate of climb.

For the V35B, Vx (max angle of climb) is 77 kts. Now that does tend to get your attention because the nose is way up in the air from where you normally expect it to be for a normal TO and climb out at 90-100 kts, but stall speed in that configuration is down around 60 kts so you still have a reasonable margin to play with.

If I was trying to get the Bo out of a short strip with potentially troublesome obstacles to clear, I would use 20o flap and focus most of my attention on nailing the correct airspeed. I would retract the gear as soon as I had a positive rate of climb, but would leave the 20o flap down until I was clear of the obstacles. Chances are that trying to retract the flap will cause more trouble (with sinking) than it is worth.

Not in the POH, but what you learn from 600 hrs of playing in one aeroplane.

Dr

[RadioSaigon]

it's a loooong time since I've flown a 140 -they were an initial trainer when I started! From memory, 2 POB, 1/2-tanks and a wallet each and you would be close to 15lb over MAUW!

I've been lurking this thread and really, I'm wondering whats so hard about it all? Manual flaps, a good length of prepared T/o surface -sure, obstacles to be cleared- but really, it's a doddle!

This departing clean has me wondering a bit... Why would you want to do that??? The aircraft is going to be longer and faster on the ground before she flies -more stress/wear on the undercarriage and airframe. Use a notch (or two!) initially, let her fly when she's ready, accelerate in ground effect, rotate to a positive ROC -and clean up your flap!!! Rotate again to Vx or Vy as required and fly it out! Simple, simple stuff. If initial acceleration on the ground is your concern, start the T/o roll clean, then passing say 45-50KIAS drop a notch or more of flap on her and she'll pop straight off the ground, proceed as above.

The beauty of the manual flap too, is you can feel where you are getting the best lift from the flap without going into the high-drag flap-extension range. Often that's between 1st and 2nd notches on the 140's, if I remember correctly.

Your AFM will have figures for Vx and Vy clean and with flap. Personally I'd be going for the clean speeds unless there was a compelling reason to not allow the aircraft to accelerate in ground-effect initially and clean up.

BTW: it takes a helluva long time to get a 140 to FL100 and some creative flying -even in considerably better than ISA conditions -but boy, did we have some fun on the way back down!

[jamsquat]

Most PA28-140's, those manufactured after about 1965 are actually 150hp. The -140 was kept to differentiate between the base model and the PA28-150. Which had a baggage door. The Flight manual in the one i fly, which is all of about 5pages thick, states all take-off performance figures for nil-flap. Knowledge passed down to me from many white haired pilots, and in practicing for myself, shows one stage of flap gets it off the ground much quicker but doesn't add much to the climb rate.

JS

[harrowing]

popping flap for take-off?

RadioSaigon
Surely the difference in drag and initial acceleration between zero flap and a notch or two for the initial take-off roll would be so small as to exist in theory only. At the risk of being cynical, this sounds like a myth. Playing around with flaps just before rotation would require a hand to come off the throttle.
I am not trying to be antagonistic, but perhaps I am out of touch with GA and just a little more cautious these days.

[RadioSaigon]

Fair call harrowing, and yup I agree. Any advantage gained by the lack of aerodynamic drag during initial acceleration in a 140 is going to be absolutely minimal. Lets face it, a 140's acceleration is fairly minimal under the very best of circumstances! I can't point you to any qualitative studies of the techniques' worth, was just throwing it out there in a thread that seemed to be going into a circular, theoretical discussion that's making something very hard out of something really very simple... another example of that was the recent thread about the legalities of a C172's configuration...

Again a fair call re hands off the throttle during the take-off roll. I know what's being taught and that some people take these 'teachings' (would I dare go as far as saying OWT's?) as absolute gospel that simply must not be contravened under any circumstances... as I'm sure you are aware, there are very few 'absolutes' in aviation -or for that matter, life in general. Every action and decision should be evaluated in the light of current circumstances and required performance. This technique is definitely one of those. It's a valid technique which I have used many times -and used to be taught pre-PPL in whatever airframe you were in! Is that no longer the case? I gaurantee it's a technique used by many C180/185 drivers operating from strips etc.

Techniques such as these are particularly useful in poor performing aircraft -they help to wring every last ounce of performance out of it when you don't have enough power to simply grunt through it. As with any other unfamiliar technique, before you try it seek instruction from someone that knows what they're doing and practice it in a place that doesn't need it before you use it in anger.

[remoak]

Having just started flying light aircraft again after many years just flying jets for a living, I find this quite interesting. However, my take on the POH is a little different.

Since the days of product liability suits in the US, POHs have been quite restrictive and are more of an exercise in limiting liability to the manufacturer, than a helpful document to the pilot. There is an awful lot that isn't in there, because the manufacturer wants to limit risk and would prefer that you only ever flew straight and level, and took off and landed from large concrete runways on sunny days with no wind. Therefore, the true capabilities of many aircraft are never properly laid out in the POH.

I would take the view that you should never do anything that is specifically prohibited in the POH, but by the same token you are free to do anything that isn't specifically prohibited, as long as you apply prudence and good airmanship. I don't agree that this makes you a test pilot - that is a standard saying in GA that has little basis in fact, and is just used by instructors to scare students into behaving themselves. Most light aircraft are absolutely benign unless deliberately provoked by serious mishandling. For example, if you were to ask a group of ten bush pilots about takeoff and landing techniques, you would probably get ten different answers - all valid and all of which work for the person concerned (and probably none of them in the POH). Some topics, like mixture control/leaning, have been endlessly argued by proponents of many different methods, none of them specifically approved by the manufacturer but all of which work.

So my point is... use common sense, take the POH as a starting point, and develop your own techniques. Don't do anything specifically prohibited by the POH, but by the same token don't not do stuff that is sensible, just because it isn't written down. Most of what you need to know in aviation isn't written down!

And on the subject of takeoff technique, you can take off with any flap setting you like... you will always get airborne... but some settings are sensible and some aren't. I once accidentally took off in a 172 with 40 degrees of flap after the electric flaps failed during a touch and go... we got airborne OK (with virtually no ground roll!), but if we had lost the engine, we would have been dead meat.

And just to illustrate that point a little more, the BAe146 that I used to fly could take off with flaps at 18, 24 or 30 degrees. Full flap was 33 degrees, so a 30 flap takeoff was virtually a full-flap takeoff. In terms of performance, when taking off from a short field (around 1200m), Flaps 30 was mandatory. Went up like an elevator!

Use common sense!

[RadioSaigon]

Very well spoken remoak; a thoughtful, insightful and very very valid response!

Couldn't agree more with your comments re POH's -they're a disgrace and at best, minimally useful document. That the regulators allow continued use of the manufacturers POH speaks volumes more about their political acumen & stance than it does of their responsibility to administration of safe, sustainable aviation.

[RadioSaigon]

Originally Posted by remoak

Since the days of product liability suits in the US, POHs have been quite restrictive and are more of an exercise in limiting liability to the manufacturer, than a helpful document to the pilot. There is an awful lot that isn't in there, because the manufacturer wants to limit risk and would prefer that you only ever flew straight and level, and took off and landed from large concrete runways on sunny days with no wind. Therefore, the true capabilities of many aircraft are never properly laid out in the POH... I once accidentally took off in a 172 with 40 degrees of flap...

A magically pertinent example! As I'm sure you're aware, Cessna haven't produced a 172 (or any other light-single?) with 40deg flaps for quite some years now... if memory serves, the J models were about the last, somewhere in the early- mid-80's. The reason for that was the mind-boggling number of Yanks killing themselves when they attempted a go-around in a 172 with 40deg hanging out, stalled it and killed themselves. This despite the fact of the AFM of the time stating specifically that flaps had to be reduced immediately after application of power for the missed! The crazy civil liability laws of the US meant that the families of the deceased were able to bring suit against Cessna -and win bizarre damages, despite the patently obvious mishandling by the PinC. The whole debacle very nearly sounded the death-knell for the whole GA manufacturing industry!

Personally having flown both the 40's and the later model 30's, gimme a 40 every day!!! There are things you can do with that aircraft that very few others will ever come near.

[CoodaShooda]

Pulled out my 1977 vintage Handling Notes for the PA28-140/PA28-180.

Take off weight calculation charts mandate 0 degrees flap for the 140 and 10 degrees for the 180.

Power v drag?