Flaps

[Bigglesworth]

Garry is currently developing electric flaps for the Sierra, which could also go on the Cheetah or Diamond. This is a very good idea, a cheetah will float about 500m if the approach speed is 50 kts. coming from a plane which can cruise at 110kts this is pretty good. But not good when trying to land short with one up and half fuel.

 

The flaps will require at least part of the wing to be metal covered which is probably a good thing, despite being a bit heavier.

 

I also hear that they are going to try a 2.2 jab in a Sierra, the nose will be made longer yet to balance it, that will make it a very long nosed plane.

 

 

[facthunter]

Landing speed decay.

 

That's a problem with a slippery aircraft, they will float forever in ground effect, especially if the engine idle speed is a bit high as well. The flaps,(depending on the design) will improve the view over the nose on approach, but not in the latter part of the flare if a tailwheel aircraft. You mention the situation of one person and a small amount of fuel. The reality there is that a slower approach speed should be used when you are lighter, and obviously, faster when you are heavy. Some pilots think the approach speed is fixed for the aircraft, when it should be related to the conditions, of which landing weight is but one. Someone with a bit more time & inclination than myself at the moment, may care to look at the likely variation of stall speeds to likely landing weight range for some of our more common types. Nev..

 

 

[Guest pelorus32]

Theoretical Stall Speeds

 

Warning: This is a theoretical calculation of a theoretical aircraft please don't make approach speed decisions or any other flying decisions on the basis of this graph.

 

Stall speed varies with the square root of the load factor. I have taken a theoretical aircraft - not dissimilar to many of the types we fly - and assumed a stall speed of 42 knots at 540kg. The results for other weights are as shown. This assumes a 1g, unaccelerated stall. Load factors due to acceleration can have a huge impact on stall speed - far outweighing the magnitude of these changes here.

 

 

Regards

 

Mike

 

 

[Guest pelorus32]

Just for some more fun, with the same warning as above.

 

This is the graph above with additional lines for 20, 40 and 60 degrees angle of bank.

 

Notice the substantial increase in stall speed with load.

 

Regards

 

Mike

 

 

 

[Bigglesworth]

That's a problem with a slippery aircraft, they will float forever in ground effect, especially if the engine idle speed is a bit high as well. The flaps,(depending on the design) will improve the view over the nose on approach, but not in the latter part of the flare if a tailwheel aircraft. You mention the situation of one person and a small amount of fuel. The reality there is that a slower approach speed should be used when you are lighter, and obviously, faster when you are heavy. ..

Stall is rated at 37kts (loaded) I was coming in at 40kts over the fence, and still floating forever, ended up slipping it to slow down just above the ground. And as for high idle; jab says it should be 900rpm, but I am here to tell you that below 1000 it dies. Ever had to restart a motor about 20 feet off the ground? Next time you are flying, try to reach the start button while on approach. Then you will know why I am going to have to adjust that idle a bit up.

 

 

[Guest pelorus32]

Stall is rated at 37kts (loaded) I was coming in at 40kts over the fence, and still floating forever, ended up slipping it to slow down just above the ground. And as for high idle; jab says it should be 900rpm, but I am here to tell you that below 1000 it dies. Ever had to restart a motor about 20 feet off the ground? Next time you are flying, try to reach the start button while on approach. Then you will know why I am going to have to adjust that idle a bit up.

G;day Bigglesworth,

 

Went to bed after reading your post and woke up this morning still thinking that that feels a little close for comfort.

 

So let's assume that you are about 120kgs under fully loaded - or about 5 knots of stall speed. Though with many a/c that last little bit may not be linear. That gives you a "theoretical" stall speed in light configuration of say 32 knots.

 

Next question is: that is the "rated" stall speed. What speeds does your a/c stall at? Is your ASI reading accurately? What about if it is over-reading?

 

So my question is...if you are coming over the fence at 40 knots what happens the first time you get a 6-7 knot wind gradient or a 10 knot wind shear or 5 knots of inattention or a 15 knot crosswind gust...coming over the fence?

 

To paraphrase Dirty Harry "are you feeling lucky....well are you?"

 

Too close for my comfort.

 

Kind regards

 

Mike

 

 

[Flyer]

Hi Bigglesworth

 

I'd be considering 1.3 x Vso for a final approach speed. i.e. 1.3 x 37kts = 48knots.

 

This is in still conditions.

 

If you have a gusty wind, add half of the gust factor to this speed. i.e. if the wind is gusting at 10 knots add 5 knots to your approach speed.

 

Just as a matter of interest, how long is the strip you are operating from and how short are you trying to land the aircraft ?

 

Regards

 

Phil

 

 

[WestCoast]

Bigglesworth....it might be a good time to review the basics again.

 

• Vref – the reference indicated (CAS) approach speed, usually about 1.3 to 1.5 times Vso plus 50% of the wind gust speed in excess of the mean wind speed. e.g.Vso = 30 knots, wind speed 10 knots gusting to 20 knots, Vref = 1.3 x 30 + 5 knots = 44 knots. Faster, heavier aircraft would tend towards the 1.3 times Vso end; lighter, slower aircraft would tend towards the 1.5 times Vso end. Normal landing procedure is to set up the approach so that an imaginary 15 metre [50 ft] high screen placed before the runway threshold is crossed at Vref and the airspeed is reduced to maybe 1.2 to 1.3 Vso – plus the gust allowance – when rounding out prior to touchdown. The ground distance from the screen to the touch-down point can be roughly estimated, using the 1-in-60 rule, from the approach slope. For example with a 6° slope – which is around the norm for most light aeroplanes – the distance will be 60/6 × 15 = 150 metres, to which must be added any float period plus the ground roll distance with normal braking, to give the total landing distance over the standard 15 m screen – in nil wind conditions.

 

Regards

 

Dave

 

 

[facthunter]

Approach speeds.

 

The point made about airspeed error is valid. If the instrument is not set up properly, it will not give an accurate figure. However it should give a consistent figure, which you can use. Before I land any plane, I will ask the owner what speed he uses on approach, in normal conditions, at differing weights OR I fly it upstairs (safe height) at slow speed, and you see how it flies at the speed INDICATED. You then have a reference. The aircraft should only stall when the wheels are virtually on the ground, (3-point tailwheel) and many pilots never get near the stall at any time. (land faster)

 

!.3 times the stall is considered to give a good margin over stall speed to allow some manoeuvering on approach. As I pointed out this does vary enough with weight to be significant. Gusts and possible windshear are other considerations. During the pre-solo training the instructor should constantly mention the way the aircraft will fly differently when the weight is reduced by the instructor not being there. In larger aircraft this is not so significant, as the proportional change is not so high. Mike, shouldn't those lines be curved ? Perhaps they are, but I would have thought that it would be more obvious. Nev..

 

 

[Guest pelorus32]

[snip] Mike, shouldn't those lines be curved ? Perhaps they are, but I would have thought that it would be more obvious. Nev..

Nev,

 

I don't think so. What they are is divergent - very slightly - but divergent.

 

The calculation, for anyone who wants to check it is this: Taking 540kg and a 42 knot stall speed as a "load factor" of 1. Then I simply calculate the weight as a factor of 540kg - so 1080kg would = 2 and 270kg = 0.5. Then I take the square root of that and multiply it by the stall speed at 540kg. That gives the 1 g line.

 

For the other lines I simply take the load factor for that AOB - 2 in the case of 60 degrees and take the square root of that and multiply that by the previously found answer for that weight at 1 g.

 

If my maths is wrong please let me know.

 

Regards

 

Mike

 

 

[Yenn]

Stall speeds are well and good but isn't the problem compounded here by ground effect. When within a wing span height there is extra lift generated due to the reduced drag. Flaps increase the drag to reduce landing speed.

 

I don't have flaps and when the speed gets down I get a much greater rate of descent, so carry speed to prevent that. I then have to flare and dissipate the speed while in ground effect leading to a long hold off. All good fun especially for the by standers.

 

 

[Admin]

The CT is well known for its glide so a lot of times coming in on final at idle and at 55kts I have actually been climbing - the CT is the best aircraft I know to practice your go-arounds . I know of one CFI that said he knew what he was doing when he was coming in high and trying for the right glide slope only to find out the hard way with two go-arounds and being left with egg on his face.

 

I found that with the CT it was actually better to fly her in lower then the right glide slope and with a trickle of power on - driving her in - and then just feel the flare and let her come down when she wanted to. I found this was far safer then to lower the airspeed closer to the stall as anything can happen then. If there was any wind of any kind I wouldn't go near the 40deg flap setting and I always preferred the 15deg rather then 30 or 40 in the CT - mind you sometimes I would start the decent at 30deg and switch back to 15deg at a safe height to control the "flyin" better.

 

 

[Flyer]

Flaps have a multitude of functions. By lowering flap you also change the camber of the wing, thereby increasing lift. This will also increase the drag. It also gives you a better view of the runway.

 

With the extra lift generated by the flap allows you to slow the plane down further than it would if the wing was clean.

 

You can approach with a steeper angle and have a more pronounced flare which in itself creates more drag. All in all everything flies slower and stops quicker.

 

Just as a note, the Piper Saratoga (6 seat 300hp aircraft) can be a real problem aircraft to land if you choose to play the fool with it. If you get it low and slow on approach, you wont have enough energy to flare but you can/will float the full length of the runway with not enough energy to land and so far behing the drag curve you can't go around. This is to do with ground effect.

 

The only way out of it is to firewall everything, hold it in ground effect and accelerate to climb speed. (got myself into this situation once...scary)

 

My 2 bobs worth

 

Regards

 

Phil

 

 

[Bigglesworth]

Getting back to the topic, ( and to calm some earlier commentors down) I think the cheetah will really benefit from flaps, since it normally (as yet I can only speak about light loading) refuses to:

 

a: descend

 

b: slow down

 

c: stall (not really related to flaps)

 

All 3 of these situations it has to be forced into and doesn't like to stay that way. Someone earlier said that 40kts over the fence sounded dangerous, it isn't. It still floats 200 metres, and with a 400m strip, that is a long way. Take off no problem, but to get those wheels to touch the ground, that is a bit harder.

 

Also, having done comprehensive stall/slow practice at height, I would be confident that a stall due to wind gusts would still be that gentle that it would be a piece of cake to pick it back up. Not that I ever want to try.

 

Also with one up and half fuel I am about 180kgs below max (stacks of payload here) and that is below the earlier graph and into very low stall speeds.

 

PS, don't try to land a Saratoga down home, I won't be answerable.

 

Sounds like fun to land, engine failures must be dangerous, when you try for low speed in a short paddock,and then............

 

 

[Guest Flygirl]

The Cheetah wont float 200m at 50 kts more like 50m, and at 40 kts it will not float much at all

 

 

[Ultralights]

if the view over the nose is already good without flap, and its only required to produce drag, then a simple Split flap will suffice.

 

 

[Guest Flygirl]

Morgan Aero Works flaps

 

John Bale has his Cheetah Sierra 100 flying, it is powered with a 2.2 jab, with flaps. It does give a steady sink rate, no trim was needed when the flap was fully extended, there was very little pitching. He is still flying off the hrs so not a lot more info at this stage.

 

 

[BigPete]

Bum! - Mike I can't see your graphs - just a red cross - I'm using Explorer V7.0.

 

Any Ideas?

 

regards

 

 

[Garry Morgan]

Flaps now avaible

 

Flaps have now been fitted to a few aircraft, I find that they do give a greater rate of decent, but better landings are made with up to 1/2 flap.

 

The Sierra 100 should have its cert. done by spring.