Fixed wing flaps.

[jgdj19 10]

Hi, I want to check I understand flaps on fixed wing aircraft correctly.

Is it correct that you want flaps all the way down for landing and taking off? Currently, when parked, the aircraft have flaps up. So I want to get in, lower flaps, take off, raise gear and then raise flaps right?

[randir14 10]

It doesn't matter, the flight model in this game isn't even close to realistic.

[soul_assassin 1723]

In reality what flaps do is when extended they increase the surface area of the wing as well as its camber (the profile curviness). The lift coefficient of an aircraft is proportional to speed and surface area of the wing thus if you increase surface area you need less speed to get the same lift coeficient.

Standard practice is to have flaps set half way for take off and fully for landing (as you want to be flying as slow as possible before you land). Flying at these low landing speeds without flaps would make the wings stall and the aircraft to fall like a rock.

[b00ce 160]

It doesn't matter, the flight model in this game isn't even close to realistic.

It does matter though. ;)

[soul_assassin 1723]

indeed it does matter as on takeoff with flaps out you will lift off the ground faster and on landing will be able to come in much slower without stalling

[sunray 10]

Soul Assassin explains it well. Lift is increased, however drag is generally increased more, and all the more with larger amounts of flap set. This is important.

Aircraft performance depends only on excess power available. Not on lift. With flap hanging out, drag increases, so power must be increased, therefore with finite power available from a given powerplant, excess power (power available minus power required) will be less, and so, performance will be less. It may help you turn in a scrap, if you are flying a P-38 against a single engined opponent though I wouldn't recommend such tactics!

So why are flaps used then?

Wings are designed for efficiency in the cruise. Modern, especially swept wings all the more so. But these aircraft must takeoff and land. Flaps do the following:

1. Decrease the stall speed of the wing, so allow slower flight during landing. This simply translates to less runway length required.

2. Increase the approach angle, providing better terrain clearance during an arrival. Power setting during approach will be greater, but that's good for other reasons.

3. Lower the body angle of the aircraft. This provides better visibility during the approach. Mainly relevant in the old days. Now leading edge devices actually raise the body angle, but that's another story.

4. On takeoff the aircraft gets airborne at a lower speed. Needs less runway. Climbout suffers, but it's always a compromise. Flap use for takeoff will always depend on runway available v terrain or obstacles in the departure area. We use charts for this.

So in summary flaps are used for runway length considerations. The tradeoff is a performance penalty in the climbout, or the go-around. Flaps are retracted at a safe height and speed, generally 400-500 feet.

Before flaps were invented we used to use a 'sideslip' to wash off speed and steepen the approach path. Uncomfortable for passengers. But strangely elegant.

This info is probably redundant. And perhaps not entirely correct vis-a-vis OFP/ArmA/2. But I'm off flying duties with a damaged ankle and felt like offering some flap theory from my distant past.

Read Soul Assassin's last post, says it all. And use a bit of flap for takeoff, and all of it for landing.

Regards, T

Edited August 3, 2009 by Sunray

[soul_assassin 1723]

Haha talk about trip down the memory lane of aircraft performance class :)

[Vandrel 10]

much slower without stalling

Yup, this also proves quite true for tactical dog fighting. Dropping flaps creates drag which used with a proper amount of throttle combo you can create some good semi-vectoring on planes that cannot vector thrust. As crazy as it may sound, dropping the gear in some cases can also help in this tactic. The term "turn and burn baby" comes to mind.

[frederf 0]

Flaps for takeoff is pretty rare in real life.

[Thirdup 0]

(In game) I use them for landings, but rarely on t/o.

About the only time I've found that I really needed to deploy flaps for a t/o was on a short dirt strip.

[Vandrel 10]

Flaps for takeoff is pretty rare in real life.

I've been flying commercial for nearly 30 years, flaps are always used for take off. As mentioned, there's several different trim levels for the flaps which aid in lift but are not ment to remain extended for a long period of time as they also create drag

[cjsoques 0]

Flaps for takeoff is pretty rare in real life.

From that statement, you are obviously talking about something you know nothing about.

[frederf 0]

Really? My pilot's license would beg to disagree with you. Vandrel, what commercial aircraft are you flying with takeoff flaps? I bet a big arse Boeing with 0.5°, 1.0°, 2.5° and a million other tiny flap settings might be used. Cessna 172 doesn't use them except if you're doing some nutty short field T/O. F-16 doesn't use them (at least not pilot-commanded). We're not flying 737s in ArmA anyway. These are maaaajor flap settings like 15 and 30 degrees if not more.

[cjsoques 0]

Really? My pilot's license would beg to disagree with you. Vandrel, what commercial aircraft are you flying with takeoff flaps? I bet a big arse Boeing with 0.5°, 1.0°, 2.5° and a million other tiny flap settings might be used. Cessna 172 doesn't use them except if you're doing some nutty short field T/O. F-16 doesn't use them (at least not pilot-commanded). We're not flying 737s in ArmA anyway. These are maaaajor flap settings like 15 and 30 degrees if not more.

I've always been taught by various instructors with different teaching styles to use 10° flaps at all times when taking off except in heavy headwind or crosswind situations that affect the aircraft more with flaps down.

Then again I've never taken off on 10000ft. runways (only 5000ft. at the most IIRC). I've never heard of a reason why NOT to use 10° flaps for takeoff for a/c such as the 152/172 because it makes a world of a difference in takeoff distance, especially when you have a heavy passenger.

Apologies for saying you didn't know what you were talking about, but I can't think of a reason why your instructors taught you not to use flaps for conventional takeoff...never heard of that before in my career.

[CrazyAviator 10]

I teach commercial pilots how to fly. So far I've heard some good explanations of what flaps do and some poor ones. Flap settings (to a degree) increase lift but it also increases load factor (the measure of stress on the wing when increasing back pressure. i.e. pulling up) This is not noticeable on most GA aircraft but on something a little larger with higher capacity fuel tanks and low profile swept back wings it becomes a problem, especially when you start loading armaments. Now as far as flaps on take off, yes generally you do want some small amount of flap settings as they increase the camber of the wing (and length of the chord line on some designs). You could get into co-efficient of lift but alot of it has to do with where the air seperates from the wing (turbulent boundry layer). A longer wing = more lift because of less seperation.

That being said there becomes a point where flaps decrease performance by increasing drag, generally anything beyond say 10 to 15 degrees. In our cessna's we only use flaps at 10 and thats for performance takeoffs (shorts/softs). Its considered inappropriate to use 10 when doing a normal takeoff. In our piper multis however we never use flaps, even on shorts.

So it really just depends on what the hell you are flying and how your flying it. I do agree that the flap settings in ARMA 2 appear to be too great for T/O settings, I havent experimented enough to see if they are incremental or if there is only an up and down setting.

My .02

[sunray 10]

CrazyAviator: "Flap settings (to a degree) increase lift but it also increases load factor"

Not quite, though it may seem so. Flaps do not increase load factor. Load factor is an increase in apparent weight 'g' through manoeuvring. This is temporary.

Flaps increase lift. Flaps increase drag. They also reduce lateral stability. They reduce performance. They lower the stall speed. Load factor remains unchanged. Wing loading will decrease when flap is deployed, remember LIFT=WEIGHT. Flaps alter (increase) the camber and area of a wing, changing its characteristics into that of a lower speed aerofoil. This necessitates a trim change, sometimes dramatic for just the first 7-15 degrees.

CA there are some good explanations there. Additionally, flap is used for takeoff in airline operations every day. Turboprops typically use around 15 degrees. Some types (eg. Metro 23) for every takeoff, others (eg. Saab 340) when runway requirements dictate. I have flown both these types. As for landing, Boeing (737) recommend Flap 40 for CAT II/III approaches. The reduced deck angle provides better vision when breaking visual at the minimum. Some operators are restricted to Flap 30 though.

Edited August 4, 2009 by Sunray

[CrazyAviator 10]

Very nice sunray! I agree that the load factor would really only increase during takeoff roll and is not permanent. I also wanted to correct myself about the increase in chord line - the amount of wing surface with good lift characterists changes, not the air seperation. Again, this revolves around the amount of pitch and AoA being used.

Oh and I wasnt imposing that big jets dont use flaps on t/o - just mean it depends on the design and shape of the wingfoil being used. My friend flies the Hawker 20 and he says 15 degrees of flaps is good for up to 26,000 lbs t/oW. If they need 27,000 lbs they have to use 0 degrees- atleast thats what the tabulation requires. Not sure whats so special about the last 1k lbs?

[LeftSkidLow 1]

I've always been taught by various instructors with different teaching styles to use 10° flaps at all times when taking off except in heavy headwind or crosswind situations that affect the aircraft more with flaps down.

Then again I've never taken off on 10000ft. runways (only 5000ft. at the most IIRC). I've never heard of a reason why NOT to use 10° flaps for takeoff for a/c such as the 152/172 because it makes a world of a difference in takeoff distance, especially when you have a heavy passenger.

Apologies for saying you didn't know what you were talking about, but I can't think of a reason why your instructors taught you not to use flaps for conventional takeoff...never heard of that before in my career.

I have a PPL ASEL, and CFI Rotorcraft, I rarely used flaps on takeoff in a Piper Cherokee. Most of my time is in helicopters but for whatever reason my instructor never had me use flaps unless it was a short field takeoff. I've also had better luck ingame with the C-130 ingame without flaps on takeoff. All aircraft in arma respond terrible at low speeds.

[sunray 10]

CA. Performance was never my strong point. The Hawker takeoff flap thingy might be something to do with performance during the climb out phase, a sort of weight/altitude/temperature (WAT) thing. It might even be a structural thing (???). He'll probably dig it out of the manuals for you. If you were remotely interested (!)

Like propellers, performance is a black art.

:bounce3:

[LeftSkidLow 1]

I can understand it with faster aircraft because the wing is designed to be low lift, like a fighters wing is pretty low lift so that induced drag won't slow it down. It makes sense with a wing like that you would need flaps for takeoff.

[frederf 0]

Apologies for saying you didn't know what you were talking about, but I can't think of a reason why your instructors taught you not to use flaps for conventional takeoff...never heard of that before in my career.

Apologies certainly accepted. From what I've read since apparently it's very split what instructors will teach. I have flown a C-172N out of KRHV's 3100' runways without flaps every time I wasn't simulating a short field takeoff. 3000' is plenty even over a 50' obstacle on a hot day. The POH says to use "between 0-10° flaps for normal takeoff." Of course the POH is pretty much the Bible when it comes to what you should do. If the POH says to pull the yoke back with your toes, then that's what you gosh darn do.

I'm pretty sure the thoughts behind using no flaps for takeoff involve the dangers of one flap getting stuck when raising them along with the risks of sudden and poor performance envelope changes if they are raised at the wrong time. It probably puts less strain on the structure, uses less fuel, and gives better engine cooling as well. On a short field T/O you better believe I hang the tail out over the approach pad, stand on the brakes during power application, and put in my 10° of flaps.

[sunray 10]

In multi-engine ops, it's generally better to take-off without flap. Unless of course the performance tables or charts or FMS say otherwise - due to runway issues. They go better with an engine out when clean. (My first training captain: We're gonna lose one on this take-off son, it'll be a bonus if we don't)