Another A5 Icon crash 7/27/19

This forum is for safety-related discussions. Be safe out there!

Moderator: drseti

User avatar
FastEddieB
Posts: 2880
Joined: Wed Jan 07, 2009 9:33 pm
Location: Lenoir City, TN/Mineral Bluff, GA

Re: Another A5 Icon crash 7/27/19

Post by FastEddieB »

TimTaylor wrote:FastEddie, you are correct but have an over-simplified understanding of the situation. You are ignoring the effects of momentum (energy) of the aircraft that must be overcome, especially if the turn is quick.
It’s momentum relative to what? The air mass or the ground?

Analogy...

You’re walking down the aisle of a train moving at a constant speed of 60 mph. You stumble and fall. Is it relevant to your injury likelihood whether you’re walking in the direction the train is moving or in the opposite direction?

In the case of a plane, the only thing that matters is its momentum relative to the air mass. In a 60 kt wind, a 100 kt plane could be moving over the ground at 40 kts into the wind or 160 kts flying downwind. In both situations the “lift” and stall likelihood are identical. The plane has no way of knowing what the ground is doing*. In your scenario, something would change momentum-wise if the plane started doing 360’s in that wind as the groundspeed went from 40 kts to 160 kts. It doesn’t. Under a hood you could not feel anything different from doing the same 360’s in still air.

Back to the ICON, as it made the right turn in an airmass moving left to right in the video, it would behave exactly as it would in still air. A wing does not know or care what the ground - or water - below it is doing.


*The only way to determine what the plane is doing relative to the ground is via navigation sources - or to look.
Fast Eddie B.
Sky Arrow 600 E-LSA • N467SA
CFI, CFII, CFIME
[email protected]
Wm.Ince
Posts: 1080
Joined: Sun Nov 17, 2013 3:27 pm
Location: Clearwater, FL

Re: Another A5 Icon crash 7/27/19

Post by Wm.Ince »

FastEddieB wrote:
Wm.Ince wrote:A 15 knot loss of airspeed (as in a, non-microburst, wind shear event)...
Of course. Stipulated.
But not relevant to a discussion about the effect of a downwind turn on lift and/or stall.
On the contrary, I think it may be very relevant. Review what happens to the ICON just before contact with the tree.
Forget about what happens over the ground reference (water), that is irrelevant. But the airmass the airplane is surround by, that's what is relevant, especially at low speed and high angle of attack.
Last edited by Wm.Ince on Sun Jul 28, 2019 2:22 pm, edited 1 time in total.
Bill Ince
LSRI
Retired Heavy Equipment Operator
TimTaylor
Posts: 1594
Joined: Tue Feb 21, 2017 7:17 pm

Re: Another A5 Icon crash 7/27/19

Post by TimTaylor »

Momentum relative to the earth and the earth's gravitational field. If the aircraft had zero mass, you would be correct. However, it has mass and does not instantaneously change directions such that the relative wind is constant. It takes some time for the aircraft to "catch up" such that the relative wind is constant again. How long is proportional to the mass and power, I suppose.
Retired from flying.
User avatar
FastEddieB
Posts: 2880
Joined: Wed Jan 07, 2009 9:33 pm
Location: Lenoir City, TN/Mineral Bluff, GA

Re: Another A5 Icon crash 7/27/19

Post by FastEddieB »

Wm.Ince wrote:
FastEddieB wrote:
Wm.Ince wrote:A 15 knot loss of airspeed (as in a, non-microburst, wind shear event)...
Of course. Stipulated.
But not relevant to a discussion about the effect of a downwind turn on lift and/or stall.
On the contrary, I think it may be very relevant. Review what happens to the ICON just before contact with the tree.
It could have been a gust from the rear. It has nothing to do with whether the plane was turning upwind or downwind at the time - the result would be the same.
Fast Eddie B.
Sky Arrow 600 E-LSA • N467SA
CFI, CFII, CFIME
[email protected]
User avatar
FastEddieB
Posts: 2880
Joined: Wed Jan 07, 2009 9:33 pm
Location: Lenoir City, TN/Mineral Bluff, GA

Re: Another A5 Icon crash 7/27/19

Post by FastEddieB »

TimTaylor wrote:Momentum relative to the earth and the earth's gravitational field.
So doing the 360’s in a 60 kt wind can be felt by a pilot?

The earth’s gravitational field is “pulling” things straight down to the earth’s center. It is not somehow “pinning” things not in contact with the surface to a particular location to which things can be referenced inertia-wise.

Admittedly, I never took physics in school, so if I have something wrong I can accept that. But I still hold that we can set up an experiment on a day with a steady, strong wind: fly perpendicular to the wind, and do 90° turning stalls turning in either direction. I hold they will be identical, and such is my experience. I take it you hold the “downwind” turn will stall sooner. In that case I’m virtually sure you’re wrong.
Fast Eddie B.
Sky Arrow 600 E-LSA • N467SA
CFI, CFII, CFIME
[email protected]
Wm.Ince
Posts: 1080
Joined: Sun Nov 17, 2013 3:27 pm
Location: Clearwater, FL

Re: Another A5 Icon crash 7/27/19

Post by Wm.Ince »

FastEddieB wrote: . . . But I still hold that we can set up an experiment on a day with a steady, strong wind: fly perpendicular to the wind, and do 90° turning stalls turning in either direction. I hold they will be identical, and such is my experience. I take it you hold the “downwind” turn will stall sooner. In that case I’m virtually sure you’re wrong.
Using your logic . . . then why add "half the gust spread" to Vref.
Energy management.
Bill Ince
LSRI
Retired Heavy Equipment Operator
Wm.Ince
Posts: 1080
Joined: Sun Nov 17, 2013 3:27 pm
Location: Clearwater, FL

Re: Another A5 Icon crash 7/27/19

Post by Wm.Ince »

FastEddieB wrote:
Wm.Ince wrote:
FastEddieB wrote: Of course. Stipulated.
But not relevant to a discussion about the effect of a downwind turn on lift and/or stall.
On the contrary, I think it may be very relevant. Review what happens to the ICON just before contact with the tree.
It could have been a gust from the rear. It has nothing to do with whether the plane was turning upwind or downwind at the time - the result would be the same.
I think that's possible.
"the result would be the same" . . . but not immediately!
And an immediate gust from the rear would result in a dropoff of airspeed, thus getting very close to critical angle of attack. Remember, he was at a very low speed to begin with, on his climbout.
Bill Ince
LSRI
Retired Heavy Equipment Operator
TimTaylor
Posts: 1594
Joined: Tue Feb 21, 2017 7:17 pm

Re: Another A5 Icon crash 7/27/19

Post by TimTaylor »

I took lots of physics, but not as much as Paul. So, how does inertial navigation work? Again, Eddie, you are looking at part of the issue and are correct for the part you are looking at. However, you are ignoring 1/2 of the situation or maybe less than 1/2. It depends on the mass of the aircraft and maybe some other variables.
Last edited by TimTaylor on Sun Jul 28, 2019 2:48 pm, edited 1 time in total.
Retired from flying.
User avatar
FastEddieB
Posts: 2880
Joined: Wed Jan 07, 2009 9:33 pm
Location: Lenoir City, TN/Mineral Bluff, GA

Re: Another A5 Icon crash 7/27/19

Post by FastEddieB »

You’re talking gusts. I’ve already stipulated that gusts and shear are real and have real effects.

What started this was an allegation that turning downwind can cause a loss of lift. That’s not true.

Yes, you approach at a faster airspeed when gusts are present. But it’s significant that you do not adjust approach airspeeds for headwinds or tailwinds. The way some are talking here, you’d expect to need to approach faster with a tailwind due to the “loss of lift”. You don’t, and there’s a reason for that.
Fast Eddie B.
Sky Arrow 600 E-LSA • N467SA
CFI, CFII, CFIME
[email protected]
User avatar
FastEddieB
Posts: 2880
Joined: Wed Jan 07, 2009 9:33 pm
Location: Lenoir City, TN/Mineral Bluff, GA

Re: Another A5 Icon crash 7/27/19

Post by FastEddieB »

TimTaylor wrote:I took lots of physics, but not as much as Paul. So, how does inertial navigation work?
Easy to Google. And irrelevant to any discussion of aerodynamics.
Fast Eddie B.
Sky Arrow 600 E-LSA • N467SA
CFI, CFII, CFIME
[email protected]
Wm.Ince
Posts: 1080
Joined: Sun Nov 17, 2013 3:27 pm
Location: Clearwater, FL

Re: Another A5 Icon crash 7/27/19

Post by Wm.Ince »

Paul . . . where are you? You need to weigh in on this issue.
Bill Ince
LSRI
Retired Heavy Equipment Operator
User avatar
drseti
Posts: 7227
Joined: Sat Nov 28, 2009 6:42 pm
Location: Lock Haven PA
Contact:

Re: Another A5 Icon crash 7/27/19

Post by drseti »

Wm.Ince wrote:Paul . . . where are you? You need to weigh in on this issue.
Where do you think, Bill? Been flying all day, and I'm now sitting with my feet up and a cold beverage in hand. Will weigh in after I cool down a bit.
The opinions posted are those of one CFI, and do not necessarily represent the FAA or its lawyers.
Prof H Paul Shuch
PhD CFII DPE LSRM-A/GL/WS/PPC iRMT
AvSport LLC, KLHV
[email protected]
AvSport.org
facebook.com/SportFlying
SportPilotExaminer.US
User avatar
Warmi
Posts: 1230
Joined: Sun Oct 16, 2016 5:35 pm
Location: Frankfort, IL

Re: Another A5 Icon crash 7/27/19

Post by Warmi »

Do you schedule your students , especially with very few hours, around midday ?
I wonder how do they take the usual thermals and bumps etc...

Now that I recall , due to my work and other commitments , pretty much all my lessons were either before 9am or after 5 pm - I never really experienced thermals until I started flying my own plane heh.
Flying Sting S4 ( N184WA ) out of Illinois
User avatar
drseti
Posts: 7227
Joined: Sat Nov 28, 2009 6:42 pm
Location: Lock Haven PA
Contact:

Re: Another A5 Icon crash 7/27/19

Post by drseti »

FastEddieB wrote: The plane has no way of knowing what the ground is doing
There you go again, Eddie, anthropomorphizing an inatimate object. You mustn't do that. They hate it!
The opinions posted are those of one CFI, and do not necessarily represent the FAA or its lawyers.
Prof H Paul Shuch
PhD CFII DPE LSRM-A/GL/WS/PPC iRMT
AvSport LLC, KLHV
[email protected]
AvSport.org
facebook.com/SportFlying
SportPilotExaminer.US
Wm.Ince
Posts: 1080
Joined: Sun Nov 17, 2013 3:27 pm
Location: Clearwater, FL

Re: Another A5 Icon crash 7/27/19

Post by Wm.Ince »

drseti wrote:
Wm.Ince wrote:Paul . . . where are you? You need to weigh in on this issue.
Where do you think, Bill? Been flying all day, and I'm now sitting with my feet up and a cold beverage in hand. Will weigh in after I cool down a bit.
Good!
Have one on us. :D
Bill Ince
LSRI
Retired Heavy Equipment Operator
Post Reply