A teachable moment

[FastEddieB]

Those are flap extended speeds.

I totally misread that. Oops!

Stall speed with 40° flaps is listed as 39kts, and with 0° flaps at 42kts. They don't specifically list a number for 15°, but it is closer to the 39 than the 42.
In the CTLS adding full flaps pitches the airplane very nose down, and they do add drag. However the glide path does not seem to change significantly. With exception to the nose down pitching, it is more like full flaps in a Cherokee compared to full flaps in a old Cessna 172. One thing for certain is during the round out and flare the airplane will lose its energy more quickly. If you are not spot on you altitude above the runway you will drop it in. It doesn't provide that little bit of extra cushion for a mistake that 15° flaps provides.

Thanks for the perspective. Seems weird that with both the flaps and flaperons in play, there's only a 3 kt difference in stall speed. I'm used to seeing a bit more. A Cirrus shows about a 10 kt difference, though my Sky Arrow just shows 4 kts - sounds like not much, but it is about 10%.

[MrMorden]

Take all those speeds with a grain of salt. I'm sure there is a CT somewhere that stalls at 39kt with full flaps at gross weight, but I've never seen such a thing. As with many manufacturer numbers, those are very optimistic. I bet at gross with full flaps my airplane stalls closer to 45kt than 39kt.

[FastEddieB]

Take all those speeds with a grain of salt. I'm sure there is a CT somewhere that stalls at 39kt with full flaps at gross weight, but I've never seen such a thing. As with many manufacturer numbers, those are very optimistic. I bet at gross with full flaps my airplane stalls closer to 45kt than 39kt.

Could be. Just make sure we're not confusing IAS with CAS.

[3Dreaming]

Take all those speeds with a grain of salt. I'm sure there is a CT somewhere that stalls at 39kt with full flaps at gross weight, but I've never seen such a thing. As with many manufacturer numbers, those are very optimistic. I bet at gross with full flaps my airplane stalls closer to 45kt than 39kt.

Could be. Just make sure we're not confusing IAS with CAS.

Most likely that is the case with Andy's numbers. To throw a bigger wrench into the mix stall speed with -6° flaps is 44kts. The FAA considers this to be the clean configuration for meeting the speed requirements of the CFR 1.1 definition of a light sport aircraft. That is the reason we have -6° flaps here in the states, and they have -12° everywhere else in the world. With that -6 number the swing between -6 and full flap stall speeds is over 10%, but still only 5kts.

[MrMorden]

Take all those speeds with a grain of salt. I'm sure there is a CT somewhere that stalls at 39kt with full flaps at gross weight, but I've never seen such a thing. As with many manufacturer numbers, those are very optimistic. I bet at gross with full flaps my airplane stalls closer to 45kt than 39kt.

Could be. Just make sure we're not confusing IAS with CAS.

I'm sure the numbers are CAS. But I don't have a CAS indicator in my airplane. My only point is that if you are slowing down and expecting a stall at 39kt, you will be in for a rude awakening at about 45kt on your airspeed indicator.

[FastEddieB]

I'm sure the numbers are CAS. But I don't have a CAS indicator in my airplane. My only point is that if you are slowing down and expecting a stall at 39kt, you will be in for a rude awakening at about 45kt on your airspeed indicator.

That sounds odd. I'm pretty sure the arcs are supposed to show the IAS for each speed. At least since the mid-1970's - before that they were CAS so you had to convert.

At max gross, full forward limit, power off, the plane should really stall pretty close to the bottom of the white or green arc as appropriate. Any other condition is more favorable, so the stall speed should be even lower than the arcs show.

If yours is stalling 6 kts faster, that again sounds odd - and potentially dangerous.

[3Dreaming]

For whatever reasons, it looks like the pilot came in too fast and landed too far down the runway. He also turned off the runway (on purpose or not) at too high speed. As a result of all this, he was probably also braking too hard. He could have prevented this by using a slower approach speed, touching down sooner, less braking, maintaining lateral control down the runway, and not exiting the runway until slowed down. He should have used the proper aircraft configuration for this, whatever it is.

I don't disagree.

[roger lee]

For whatever reasons, it looks like the pilot came in too fast and landed too far down the runway. He also turned off the runway (on purpose or not) at too high speed. As a result of all this, he was probably also braking too hard. He could have prevented this by using a slower approach speed, touching down sooner, less braking, maintaining lateral control down the runway, and not exiting the runway until slowed down. He should have used the proper aircraft configuration for this, whatever it is.[/quote]

I don't disagree.

I have first hand knowledge of the accident and the original video and you are absolutely correct.

[drseti]

Seems weird that with both the flaps and flaperons in play, there's only a 3 kt difference in stall speed.

In both of my SportStars with vortex generators, the difference in (indicated) stall speed between zero and 50 degree flaps is all of one knot! Of course, those planes use a split flap design, so the flaps function more as speed brakes (i.e., drag devices) than conventional flaps would.

BTW, regardless of what the indicated stall speed may be, I can almost guarantee that any SLSA's calibrated stall speed (clean) will be precisely 45 kts. That's because it's an engineering challenge and an economic burden to lower stall speed, so designers will tend to take it only as low as ASTM rules require.

[FastEddieB]

In both of my SportStars with vortex generators, the difference in (indicated) stall speed between zero and 50 degree flaps is all of one knot!

A curiosity!

This confirms what you just said:



As an aside: I have never before seen a red line at the low end of an airspeed indicator!

[drseti]

As an aside: I have never before seen a red line at the low end of an airspeed indicator!

Me neither, Eddie. Must be a Czech thing.