notch of flap for take off

[johnm]

reading the latest sport pilot mag and a particular plane in that mag - it said one notch of flap to be selected for take off

 

I can't imagine any ultalight wouldn't get off the ground without flaps being selected (assuming the plane has flaps)

 

- is there an ultralight that won't leave the ground without flap - or is there some other issue ?

 

just curious

 

 

[facthunter]

There is a performance issue. It's not a matter of not getting off the ground. Most aircraft use flap for the take off (where fitted) unless it is of a type that just creates drag more than lift. Nev

 

 

[Guest Maj Millard]

Most aircraft with flap have a 'first notch' of flap that is generally recommended, and often used for take-offs and landings. The exception to this would be operations in very high winds or cross-winds. The first notch of flap allows the aircraft to leave the ground with a shorter ground run, and during landing, and landing approach, stabilisers the aircraft a bit for better speed control leading to a slower touchdown and shorter ground roll.

 

One exception to this that I have come across is with the Slepcev Storch, where the first notch of flap is full flap, at around 40 deg !!.....even thought the aircrafts' operation manual calls for full flap for both take-off and landing........there are only two stages of flap on Storches..off or very on !!..........Maj...

 

 

[Guest steve-nz]

I can remember once I actually to pull the first notch of flap during my runups, have never forgotten again.

 

But takeoff was bit flatter, slightly longer roll, had me wondering what was happening, but got off with heaps if room remaining.

 

That was in a Jabiru UL450, so heaps of wing area anyway, but now I check and recheck before entering strip for takeoff.

 

 

[Old Koreelah]

Pulling a notch or two of lap moves the wing's centre of pressure backwards, further behind centre of gravity. That should improve your safety margin, as long as the elevator has enough oomph to hold that angle of attack at these lower speeds.

 

 

[facthunter]

Not considered a good practice at high altitude aerodromes. (Obvious if you think about it) Nev

 

 

[Guest SAJabiruflyer]

When I did some time in a SportStar, I was told no Flap for Takeoff. Didnt appear to be any issues with it. I suspect it may be because the Vfe is pretty close to climbout speed of 60kts, would be easy to get close to, and exceed, Vfe, if you werent on the ball. In the Jabiru, taking off without Flaps works as well (as I discovered when I got distracted and forgot to Follow My Rules - didnt start my takeoff checks from scratch again). It just takes a bit longer to get off the ground and the climb out is a bit flat.

 

 

[eightyknots]

One exception to this that I have come across is with the Slepcev Storch, where the first notch of flap is full flap, at around 40 deg

:yikes:First stage = 40 degrees: yikes!

 

 

[kgwilson]

The POH for some aircraft with flaps don't recommend flaps for takeoff. e.g The C172 POH says zero flap for normal and short field takeoff and 10 deg flap for soft/rough field takeoff.

 

 

[Guest Maj Millard]

:yikes:First stage = 40 degrees: yikes!

Yeah blew me away also when I first read the POH.....but it does work amazingly........

 

 

[metalman]

Hey Maj, had a tour through Judy Pays hangar on Sunday, she's got a Fiesler Storch being restored to flying status, 275 HP inverted V8 54 foot wingspan 250 ft take off, not sure how much flap the original called for but it'll be great to see it flying in a few years time.

 

 

[Ryanm]

It's best to use what ever flap the POH says to use.

 

 

[David Isaac]

Correct Ryan,

 

Especially if you are relying on the P charts in marginal available take off distance.

 

 

[David Isaac]

The Cessna 182 is a classic example of how the application of flap on takeoff has a significant effect on takeoff performance. Does a C182 need flap to take off in a reasonable distance? He'll no, they go like hell even at MTOW. But all the performance charts are based on 20 degree flap for takeoff. So if you are doing takeoff calculations at marginal airfields you MUST use the recommend flap for minimum takeoff distance otherwise you may be in for a very nasty surprise.

 

 

[facthunter]

Stick to the POH, but have a notion of what flaps do. IF the field is soft or rough or very wet, you don't want to be on it any longer than you have to. IF you have a long paved runway and good wheel bearings tyres, let her roll. IF you are at high altitude don't use flap for take -of ( or use less) because you wouldn't be flying at altitude with flap and trying to climb.

 

A short length runway might need flap, but a lot of POH's won't have a lot of data. Nev

 

 

[Head in the clouds]

Not considered a good practice at high altitude aerodromes. (Obvious if you think about it) Nev

 

IF you are at high altitude don't use flap for take -of ( or use less) because you wouldn't be flying at altitude with flap and trying to climb.

OK Nev, you asked for it 'coz I've thought and thought about it and it hasn't become obvious to me ...

 

I've seen this come up on quite a few fora and the statement always starts out categorical but I've never seen a satisfactory explanation.

 

So, keeping the examples to below Flight Levels (and well below Mach numbers) and staying with take-off flap angles, say 10 degrees, why wouldn't you use 10 degrees of flap to get airborne quicker and shorter, and climb at a better angle at 10,000ft DA, rather than not use flap at all?

 

I'll state my position so you can all have a laugh at my expense when I'm shown to be wrong - I would use 10 degrees flap for shortest take-off at any density alt, and also keep them deployed for best climb angle, then retract them for best climb rate. I expect I'm wrong for high DA but I can't reason why, I would have thought that 10 degrees should give a greater increase in lift than the increase in drag regardless of DA.

 

 

[facthunter]

HITC just a concept. The higher the runway the less flap on any jet( for example) for take-off.. The 5 degree flap take off on a Boeing 727 where nosewheel braking has to be operating because the take.off groundspeed is so fast for accelerate stop situations. As you would know 5 degrees is almost just the Leading edge devices. The flap extension is small.

 

Reaching absolute or service ceiling, ( Both limits, not the same but similar principle) you do it without flap. reason . The wing is more efficient (L/D) and that factor plus power available will determine the altitude achieved.

 

Theoretically it would be possible with some hypothetical advanced fowler or other area altering devices to go higher with the devices deployed but this would not be a "normal" situation design wise, so I feel we ignore that as not applicable.

 

My approach is for the pilot to assess what the situation is. What variables to operating technique are available and how they would aid the situation.

 

Having flap out at high altitude can complicate stall recovery too.

 

The "shortest" take off will be with some flap always,. and for best climb ANGLE (obstacle clearance) just after lift off certainly. applies.

 

At limit High and Hot and Heavy (max weight for the conditions)" your plane will have little performance clean and always less with flap . Your limit altitude is lower with flap, and your RATE of climb will be less too.. This is because your L/D is less with flap extended.

 

When you lose engines you are not going anywhere till you clean it up, ( raise gear and flaps). either so I see this as similar situation in principle. Nev

 

 

[dazza 38]

Stick to the POH, but have a notion of what flaps do. IF the field is soft or rough or very wet, you don't want to be on it any longer than you have to. IF you have a long paved runway and good wheel bearings tyres, let her roll. IF you are at high altitude don't use flap for take -of ( or use less) because you wouldn't be flying at altitude with flap and trying to climb.A short length runway might need flap, but a lot of POH's won't have a lot of data. Nev

When I worked for BAE systems, I lived in a backwater called Khamis Mushayt, the joint is about 7300 feet above sea level, we flew Saudi Arabian airlines out of the place to Jeddah. In don't remember what model of aircraft we flew out of but I'm pretty sure it was a Airbus 330 or A320.Anyway to cut along story short, we took off with no flap. I remember it well because the first time I looked out the window as the engines were spooling up and I saw that no flaps were deployed. I had one of those oh Sh&T moments.

 

 

[facthunter]

Yeah .Don't think about the tyre speed. They probably lifted off at 190 knots.Nev

 

 

[Head in the clouds]

OK, thanks FH, so what you're saying is that since climb (any climb at all - rate or angle doesn't matter) is purely a factor of power in excess of that required to maintain height, then the total power available reduces as DA increases, and so the excess power available also reduces as DA increases. Therefore, as DA increases, we run out of of excess power available at some stage? If that's Ok so far, then since the plane requires a bit more power to maintain height (or rather, fly straight and level) with any flap at all, than it does without any flap (because there is a bit more drag with any flap extension), it would run out of excess power sooner (i.e. at a lower DA) with some flap, than without any flap.

 

OK, I can see that but we haven't factored in the wing performance issues and the 'cleanness' of the airframe. A little flap gives a relatively large increase in lift compared with the small amount of induced drag increase, and that allows the plane to fly slower than it would without the flap. So whilst the induced drag might be marginally higher, the parasitic drag at that lower speed is likely to be lower by more than the increase in induced drag because parasitic drag is a square function of speed and induced drag is linear with lift increase.

 

This is why I don't think the recommendations for jet aircraft operations should be applied to our kind of aircraft. Jet aircraft are so clean that their parasitic drag is very small compared with their induced drag whereas our aircraft have exactly the opposite drag characteristics, parasitic being the main consideration.

 

From a practical point of view in our Lightwing for example, if we were taking off at a DA where we were so close to not having any power margin available for climb we probably shouldn't be attempting to fly, but if we assessed the conditions, strip length and all that, and considered that we could make it, but only just, would you use 10 degrees of flap or none?

 

 

[Guest Maj Millard]

Using 10 deg of flap for take off is standard in my GR Lightwing regardless of DA. The Clarke Y airfoil on the (GR not GA) Lightwing is a real good lifter anyway, and generally wants to fly before it should, at just above 40 Kts instead of the safety speed of 50-55 Kts recommended in the POH.

 

Using the 10 deg just makes the wing a bit more of a lifter and just gets you off the ground shorter, and gives an even more positive climb.

 

Flaps by the way on the GR -are only an option and most GRs (big wing) don't have them. All GAs have them standard(except for a couple of home built kits I've seen) and they do need them because the GA wing is more like a Saphire wing and 20 SqFt smaller in area....As mentioned before, I like 10 deg on final as it stabilises the aircraft nicely and allows for better AS control...........Maj...

 

 

 

[facthunter]

In the marginal condition you describe, sure, perhaps you should not fly. Often on a very hot day in draggy planes like gazelles drifter thrusters etc you can easily get to the situation where you really can't get the thing above 3,0oo feet. You slow it up to get a climb out of it and it just mushes along .. I've been in a C-150 that was virtually incapable of flying up to do a 1,000 ft circuit, that wasn't miles extended. in size.

 

Induced drag is worse with flap. ( for the same lift) Whether the parasite drag reduces enough to compensate for it I wouldn't say but as you have a plane fly slower and slower the protruberances affect it less. If you design a plane to fly at 50K for instance, you worry less about fairings and flush riveting than over 180 knots, where these things start to get really important. I really think the wing has more effect than form drag at slow speed as well. Nev

 

 

[kaz3g]

OK Nev, you asked for it [ATTACH=full]22752[/ATTACH] 'coz I've thought and thought about it and it hasn't become obvious to me ...I've seen this come up on quite a few fora and the statement always starts out categorical but I've never seen a satisfactory explanation.

 

.

http://www.free-online-private-pilot-ground-school.com/Aerodynamics_in_flight.html

 

During the takeoff phase of flight, ground effect produces some important relationships. The airplane leaving ground effect after takeoff encounters just the reverse of the airplane entering ground effect during landing; i.e., the airplane leaving ground effect will:

 

• Require an increase in angle of attack to maintain the same lift coefficient.

 

• Experience an increase in induced drag and thrust required.

 

• Experience a decrease in stability and a nose-up change in moment.

 

• Produce a reduction in static source pressure and increase in indicated airspeed.

 

These general effects should point out the possible danger in attempting takeoff prior to achieving the recommended takeoff speed. Due to the reduced drag in ground effect, the airplane may seem capable of takeoff well below the recommended speed.

 

However, as the airplane rises out of ground effect with a deficiency of speed, the greater induced drag may result in very marginal initial climb performance.

 

In extreme conditions such as high gross weight, high density altitude, and high temperature, a deficiency of airspeed during takeoff may permit the airplane to become airborne but be incapable of flying out of ground effect. In this case, the airplane may become airborne initially with a deficiency of speed, and then settle back to the runway. It is important that no attempt be made to force the airplane to become airborne with a deficiency of speed; the recommended takeoff speed is necessary to provide adequate initial climb performance.

 

Having flaps set increases the induced drag so the rule is to keep the aircraft as "clean" as possible

 

 

[facthunter]

I was going to say where did you learn all that and then I saw the link. Kaz if you fly a Noster on a rough strip and it bounces (as it does) on take off, and you lift it into the air (or give the take-off away) you will get plenty of practice at flying in ground effect. Anyhow that is a comprehensive well written article, very applicable to what we do. Have you had your new tyres fitted yet ? Nev

 

 

[pmccarthy]

I once completed a circuit in ground effect in a Piper Arrow 180 with the automatic gear feature. High density altitude and load and every time gear up was selected it would come up half way, spoil the lift, then go down again automatically. We were just clearing fences, fortunately in open desert country. Wasn't game to experiment with changing the first notch flap setting at the time.