Caravan crash in Ohio
12-16-2007, 09:04 AM
#22
Gets Weekends Off
Joined APC: Dec 2005
Position: pilot
Posts: 111
Cessna retained expert David L. Kohlman, PhD., P.E., in his expert report dated 10 Feb 2005.
"It has been alleged that the cause of the wing stall was first the stall of the horizontal stabilizer, causing the airplane to pitch up, resulting in a wing stall. This theory depends on two things. First, the tail must be producing an up load, contrary to the normal down load operating on the horizontal stabilizer. In fact, the certification criteria to test for tail stall address only the phenomenon of downward tail stall, not an upward tail stall. An up loading tail stall is virtually unknown to the flying community."
Cessna retained expert David L. Kohlman, PhD., P.E., in his deposition dated 7 June 2005.
Q Is there any information that you've received
2 at any point in time that suggests that the Caravan
3 tail has an upward lift?
4 A Oh, yes.
5 Q And where did you first learn that
6 information?
7 A From a Cessna engineer. I've forgotten his
8 name. But we were talking about the tail loads. He
9 confirmed that yes, it does have an upward load with
10 the aft CG.
11 Q So when was the first time you learned that?
12 A Oh, several months ago, at least.
13 Q Is that set forth anywhere in your report?
14 A I did not specifically say that in the
15 report.
16 Q Have you talked to [Cessna attorney] about the
17 fact that this tail has an upward lift?
18 A Yes.
19 Q When is the first time you discussed it with
20 him?
21 A I can't give you a specific date.
22 [Cessna Attorney]: Let me interpose an objection
23 to form, please.
24 BY [co-defendant’s attorney]:
25 Q So you say you learned this a couple of
00085
1 months back for the first time?
2 A Several months back. I couldn't give you an
3 exact date.
4 Q And where were you when you learned it? That
5 is, were you at the Cessna plant, were you at home?
6 Where were you when you first learned this?
7 A If I remember correctly, I was in my office.
8 Q In Colorado Springs?
9 A Yes.
10 (Off-the-record discussion.)
11 Q The next -- it's a trick question, Dave. Who
12 was it, again? I think you already told us you didn't
13 remember.
14 A I don't remember his name.
15 Q All right. Well, did you -- you can't
16 describe him because you were on the phone.
17 A That's right.
18 Q What was the reason that you were talking to
19 someone at Cessna about that subject or why -- how did
20 that come up?
21 A We were talking about a number of issues, and
22 I asked him to confirm that the tail did have an up
23 load, because I knew that allegation had been made, my
24 preliminary calculation said yes, it has an up load
25 with the aft CG. And I just wanted a confirmation
00086
1 that Cessna's calculation showed that there was an up
2 load.
3 Q And this engineer confirmed that?
4 A That's correct.
5 Q Has anybody ever at Cessna ever confirmed
6 that, other than this unnamed individual?
7 A Oh, I'm sure -- yes. There are a lot them.
8 Q To you.
9 A Oh, not to me, no.
10 Q Did the certification data that you have --
11 and you call them the TRIs [as spoken], I guess -- did
12 they indicate that it has an up load on the tail?
13 A I have a report here with me, which is a tail
14 load study that's done for certification. And it
15 confirms that yes, there's an up load on the tail.
Various Cessna representatives and experts have gone on to say that the pilot does not need to know whether the tail produces an upload or a download. The pilot simply needs to know that "the plane will go down when the yoke is pushed forward, and up when the yoke is pulled back."
"It has been alleged that the cause of the wing stall was first the stall of the horizontal stabilizer, causing the airplane to pitch up, resulting in a wing stall. This theory depends on two things. First, the tail must be producing an up load, contrary to the normal down load operating on the horizontal stabilizer. In fact, the certification criteria to test for tail stall address only the phenomenon of downward tail stall, not an upward tail stall. An up loading tail stall is virtually unknown to the flying community."
Cessna retained expert David L. Kohlman, PhD., P.E., in his deposition dated 7 June 2005.
Q Is there any information that you've received
2 at any point in time that suggests that the Caravan
3 tail has an upward lift?
4 A Oh, yes.
5 Q And where did you first learn that
6 information?
7 A From a Cessna engineer. I've forgotten his
8 name. But we were talking about the tail loads. He
9 confirmed that yes, it does have an upward load with
10 the aft CG.
11 Q So when was the first time you learned that?
12 A Oh, several months ago, at least.
13 Q Is that set forth anywhere in your report?
14 A I did not specifically say that in the
15 report.
16 Q Have you talked to [Cessna attorney] about the
17 fact that this tail has an upward lift?
18 A Yes.
19 Q When is the first time you discussed it with
20 him?
21 A I can't give you a specific date.
22 [Cessna Attorney]: Let me interpose an objection
23 to form, please.
24 BY [co-defendant’s attorney]:
25 Q So you say you learned this a couple of
00085
1 months back for the first time?
2 A Several months back. I couldn't give you an
3 exact date.
4 Q And where were you when you learned it? That
5 is, were you at the Cessna plant, were you at home?
6 Where were you when you first learned this?
7 A If I remember correctly, I was in my office.
8 Q In Colorado Springs?
9 A Yes.
10 (Off-the-record discussion.)
11 Q The next -- it's a trick question, Dave. Who
12 was it, again? I think you already told us you didn't
13 remember.
14 A I don't remember his name.
15 Q All right. Well, did you -- you can't
16 describe him because you were on the phone.
17 A That's right.
18 Q What was the reason that you were talking to
19 someone at Cessna about that subject or why -- how did
20 that come up?
21 A We were talking about a number of issues, and
22 I asked him to confirm that the tail did have an up
23 load, because I knew that allegation had been made, my
24 preliminary calculation said yes, it has an up load
25 with the aft CG. And I just wanted a confirmation
00086
1 that Cessna's calculation showed that there was an up
2 load.
3 Q And this engineer confirmed that?
4 A That's correct.
5 Q Has anybody ever at Cessna ever confirmed
6 that, other than this unnamed individual?
7 A Oh, I'm sure -- yes. There are a lot them.
8 Q To you.
9 A Oh, not to me, no.
10 Q Did the certification data that you have --
11 and you call them the TRIs [as spoken], I guess -- did
12 they indicate that it has an up load on the tail?
13 A I have a report here with me, which is a tail
14 load study that's done for certification. And it
15 confirms that yes, there's an up load on the tail.
Various Cessna representatives and experts have gone on to say that the pilot does not need to know whether the tail produces an upload or a download. The pilot simply needs to know that "the plane will go down when the yoke is pushed forward, and up when the yoke is pulled back."
12-16-2007, 09:06 PM
#23
Line Holder
Joined APC: Dec 2007
Posts: 27
Not defending Cessna here, but that sounds like hearsay from a paid witness.
It looks like maybe they were not deposing a Cessna employee, they were talking with a paid witness, who (IMO) will say whatever is needed.
In any event, dynamic stability is impossible with two lifting surfaces, unless it is a canard. If you believe otherwise, please explain how this can be?
It looks like maybe they were not deposing a Cessna employee, they were talking with a paid witness, who (IMO) will say whatever is needed.
In any event, dynamic stability is impossible with two lifting surfaces, unless it is a canard. If you believe otherwise, please explain how this can be?
12-17-2007, 04:39 AM
#24
Line Holder
Joined APC: Jun 2007
Position: CL-65 FO
Posts: 44
Originally Posted by Lost
Not defending Cessna here, but that sounds like hearsay from a paid witness.
It looks like maybe they were not deposing a Cessna employee, they were talking with a paid witness, who (IMO) will say whatever is needed.
In any event, dynamic stability is impossible with two lifting surfaces, unless it is a canard. If you believe otherwise, please explain how this can be?
It looks like maybe they were not deposing a Cessna employee, they were talking with a paid witness, who (IMO) will say whatever is needed.
In any event, dynamic stability is impossible with two lifting surfaces, unless it is a canard. If you believe otherwise, please explain how this can be?
12-17-2007, 07:54 AM
#25
Gets Weekends Off
Joined APC: Dec 2005
Position: pilot
Posts: 111
he was cessna's witness
with flaps 20 the center of gravity is forward center of lift which produces a download on the stab
retract flaps and you lose 11 percent of chord and the center of gravity moves aft of the center of lift
the v/g's are on top of the stab. remember v/g's are always placed on a lifting surface
if you were to have an airflow seperation of the stabilisor or elevator when it is in a lifting mode the nose would pitch up
a pilots natural response would be to push the yoke forward calling for more lift
that makes the situation worse as the stab/elevator has a airflow problem to start with
when the pilot runs out of forward yoke the aircraft will then start a left turn because of prop torque and then the main wings stall and typically you are at about 6-900 feet and too low to recover
i have talked personally to three eyewitnessess that watched two seperate accidents and they described the exact description of this.
if i am in ice or during flap retraction i get a nose up pitching start i am going to redeploy 10 degrees of flap and gain as much airspeed as i can and get back on the ground
with flaps 20 the center of gravity is forward center of lift which produces a download on the stab
retract flaps and you lose 11 percent of chord and the center of gravity moves aft of the center of lift
the v/g's are on top of the stab. remember v/g's are always placed on a lifting surface
if you were to have an airflow seperation of the stabilisor or elevator when it is in a lifting mode the nose would pitch up
a pilots natural response would be to push the yoke forward calling for more lift
that makes the situation worse as the stab/elevator has a airflow problem to start with
when the pilot runs out of forward yoke the aircraft will then start a left turn because of prop torque and then the main wings stall and typically you are at about 6-900 feet and too low to recover
i have talked personally to three eyewitnessess that watched two seperate accidents and they described the exact description of this.
if i am in ice or during flap retraction i get a nose up pitching start i am going to redeploy 10 degrees of flap and gain as much airspeed as i can and get back on the ground
12-17-2007, 08:00 AM
#26
Gets Weekends Off
Joined APC: Dec 2005
Position: pilot
Posts: 111
cessna's test pilot also testified that during certification tests he had 4 times stalled/spun the caravan and was unable to recover without aid of a parachute they had attached to the tail which when deployed stopped the spin
i don't have a chute
i don't have a chute
12-20-2007, 03:50 AM
#29
Moderator
Joined APC: May 2006
Position: ATP, CFI etc.
Posts: 6,056
Originally Posted by Lost
As soon as CG goes behind the center of lift, game over, does not matter what you are flying - with the exception of those cool turboprops out of Italy.
As far as Caravan is concerned, what the tail does and when is beyond the scope of information currently available. A quick look at the approved CG range suggests it may have an uploaded tail at certain times. But one cannot know without access to tests and specific data. As far as I know the stability data for Caravan is not publicly accessible.
Last edited by Cubdriver; 12-20-2007 at 04:16 AM.
12-20-2007, 06:28 AM
#30
Line Holder
Joined APC: Dec 2007
Posts: 27
Originally Posted by lzakplt
Why can't a conventionally configured airplane have a lifting tail, because your Jeppeson private pilot manual said so?
I don't know you, you don't know me, or my education and experience. So instead of an off the cuff remark like that, how about explaining how what I posted is wrong?
"This is generally true but you have to distinguish between the center of lift as being that of the forward main wing, or taken as a combination of the main wing plus the aft-mounted tail. If the center of lift of the sum of the lifting surfaces is behind the center of gravity, then stability is maintained despite the possibility CG is behind the center of lift of the fore-mounted main wing.
As far as Caravan is concerned, what the tail does and when is beyond the scope of information currently available. A quick look at the approved CG range suggests it may have an uploaded tail at certain times. But one cannot know without access to tests and specific data. As far as I know the stability data for Caravan is not publicly accessible. Yesterday 08:38 PM"
The center of lift is always just that, the center of lift. I am not sure how you can include the stabilizer in the picture - the center of lift will show up somewhere about the MAC of the wing. I would LOVE to know how you can look at cg range and come up with the remark that at some point the *stabilizer* is responsible for some of the total lift force required.
Let me ask, do we agree that most (I say all) of the time, the stab is producing a down force? If yes, and you think at some point it produces a load supporting up lift, what happens right at the point where it transitions? Explain what you think stability will be like at that point? Or, what stability will be like if at any point in the flight will be like if the stab is actually lifting in the same direction of the wing? That would be one tough airplane to fly. I would think it would need a computer.
Your concepts of stability and control are far different than mine, and I am just asking for your explanation.
And no, thanks, I did not pick that up in a Jep Private pilot course, I got it by other means.
Thread
Thread Starter
Forum
Replies
Last Post
