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 Post subject: Re: Bombardier ending Learjet production
PostPosted: 05 Mar 2021, 12:22 
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Taking the 31a to Rockford today for a visit with Mark Clark.
Details on that to follow...

The 31 definitely buzzes at high IAS in knots is when I notice it.
Fantastic handling plane.
I believe the 12Yr can be accomplished without removing the LE and certainly without removing the wing!

All that said, they are and have been dinosaurs in the market for some time. This “change” is not really a thing.


"The 31 definitely buzzes"

That's the problem with Learjets, aileron buzz, then aileron snatch if you don't quickly reduce speed and unload the wing. This is where the Falcon shines over the Learjet because in additional to the Falcon swept wing design, the flight controls are hydraulically powered, holding the ailerons firmly, where the Lear is cable controlled.

Looking at the trailing edge of the old Lear ailerons you can see a small 1/8" square metal strip running the span of the ailerons. Those are the "buzz strips". As the airflow starts to separate at high Mach, the last thing in contact with the turbulent airflow are the buzz strips causing them to induce a vibration or "buzz" into the ailerons which can be felt in the yoke. If corrective action isn't taken and the speed increases, the ailerons lose stability and yoke will go into a lock to lock oscillation , "aileron snatch." Then the plane tumbles out of control, coming apart.

This was discovered when Lears started disappearing off radar scopes from high altitude. The check haulers came forward and revealed that some were disabling the stick puller to get more speed out of the Lears then losing control when encountering turbulence or pulling too hard to slow down. Like some others, I rode with the Lear factory test pilot after a wing mod on our Lear, and he put it through all the flight regimes, including deep stalls and overspeeds. The stalls were with the stick pusher turned off in order to get deep into the stalls, but for the overspeeds, the stick puller did the recovery, other than closing the throttles. Edit: It's nothing to mess with, don't try it at home. ;)


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 Post subject: Re: Bombardier ending Learjet production
PostPosted: 05 Mar 2021, 14:07 
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Username Protected wrote:
Taking the 31a to Rockford today for a visit with Mark Clark.
Details on that to follow...

The 31 definitely buzzes at high IAS in knots is when I notice it.
Fantastic handling plane.
I believe the 12Yr can be accomplished without removing the LE and certainly without removing the wing!

All that said, they are and have been dinosaurs in the market for some time. This “change” is not really a thing.


"The 31 definitely buzzes"

That's the problem with Learjets, aileron buzz, then aileron snatch if you don't quickly reduce speed and unload the wing. This is where the Falcon shines over the Learjet because in additional to the Falcon swept wing design, the flight controls are hydraulically powered, holding the ailerons firmly, where the Lear is cable controlled.

Looking at the trailing edge of the old Lear ailerons you can see a small 1/8" square metal strip running the span of the ailerons. Those are the "buzz strips". As the airflow starts to separate at high Mach, the last thing in contact with the turbulent airflow are the buzz strips causing them to induce a vibration or "buzz" into the ailerons which can be felt in the yoke. If corrective action isn't taken and the speed increases, the ailerons lose stability and yoke will go into a lock to lock oscillation , "aileron snatch." Then the plane tumbles out of control, coming apart.

This was discovered when Lears started disappearing off radar scopes from high altitude. The check haulers came forward and revealed that some were disabling the stick puller to get more speed out of the Lears then losing control when encountering turbulence or pulling too hard to slow down. Like some others, I rode with the Lear factory test pilot after a wing mod on our Lear, and he put it through all the flight regimes, including deep stalls and overspeeds. The stalls were with the stick pusher turned off in order to get deep into the stalls, but for the overspeeds, the stick puller did the recovery, other than closing the throttles. Edit: It's nothing to mess with, don't try it at home. ;)

For an owner / operator.. I’d take the cables vs hydraulics.
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 Post subject: Re: Bombardier ending Learjet production
PostPosted: 05 Mar 2021, 14:42 
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Well then Tom, you might like an old DC-8; they had both. The ailerons were hydraulically powered, but if you lost hydraulics the plane could be flown in "manual reversion" where the aileron trim tabs were cable controlled, and you flew in manual reversion by controlling it with the trim tabs.

Compared to Boeings, the DC-8 handled like a truck, even worse in manual reversion. :D


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 Post subject: Re: Bombardier ending Learjet production
PostPosted: 05 Mar 2021, 15:13 
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This was discovered when Lears started disappearing off radar scopes from high altitude. The check haulers came forward and revealed that some were disabling the stick puller to get more speed out of the Lears then losing control when encountering turbulence or pulling too hard to slow down. Like some others, I rode with the Lear factory test pilot after a wing mod on our Lear, and he put it through all the flight regimes, including deep stalls and overspeeds. The stalls were with the stick pusher turned off in order to get deep into the stalls, but for the overspeeds, the stick puller did the recovery, other than closing the throttles. Edit: It's nothing to mess with, don't try it at home. ;)


I thought mach tuck was getting them? Operators were installing switches to disable the overspeed warning. Charter operator I worked for in Houston for a while lost one, I was told they had the illegal switch.


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 Post subject: Re: Bombardier ending Learjet production
PostPosted: 05 Mar 2021, 16:10 
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This was discovered when Lears started disappearing off radar scopes from high altitude. The check haulers came forward and revealed that some were disabling the stick puller to get more speed out of the Lears then losing control when encountering turbulence or pulling too hard to slow down. Like some others, I rode with the Lear factory test pilot after a wing mod on our Lear, and he put it through all the flight regimes, including deep stalls and overspeeds. The stalls were with the stick pusher turned off in order to get deep into the stalls, but for the overspeeds, the stick puller did the recovery, other than closing the throttles. Edit: It's nothing to mess with, don't try it at home. ;)


I thought mach tuck was getting them? Operators were installing switches to disable the overspeed warning. Charter operator I worked for in Houston for a while lost one, I was told they had the illegal switch.


Actually, the stick shaker, pusher and puller are part of the stall warning system and powered from the hot battery buss through two switches on the glare shield panel, and could just be turned off, cancelling all stall warning and overspeed functions through the autopilot pitch servo. No secret switch to turn off. At least that's how I remember it after not flying the plane for 35 years, when I can't remember what I had for lunch yesterday. :D

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 Post subject: Re: Bombardier ending Learjet production
PostPosted: 05 Mar 2021, 17:12 
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^ unless you spend a lot of time past the pole all of that talk about buzzing and tucking is merely recurrent training discussion stuff. Non issue.

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 Post subject: Re: Bombardier ending Learjet production
PostPosted: 05 Mar 2021, 17:38 
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Actually, the stick shaker, pusher and puller are part of the stall warning system and powered from the hot battery buss through two switches on the glare shield panel, and could just be turned off, cancelling all stall warning and overspeed functions through the autopilot pitch servo.


Don't I know. I once left the stall switches on and my customer called me the next morning with dead batteries.....


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 Post subject: Re: Bombardier ending Learjet production
PostPosted: 05 Mar 2021, 18:26 
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[/quote]
For an owner / operator.. I’d take the cables vs hydraulics.[/quote]

The old Falcon 20 that I flew had push pull rods in an addition to the hydraulics. Triple redundancy, two different hyd systems plus the rods.


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 Post subject: Re: Bombardier ending Learjet production
PostPosted: 05 Mar 2021, 19:42 
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Actually, the stick shaker, pusher and puller are part of the stall warning system and powered from the hot battery buss through two switches on the glare shield panel, and could just be turned off, cancelling all stall warning and overspeed functions through the autopilot pitch servo.


Don't I know. I once left the stall switches on and my customer called me the next morning with dead batteries.....


Yes, that's because the stall warning is powered by the hot battery buss, any time the stall switches are on, they are drawing current.

Terry, you might have seen a Lear in a hangar or on a ramp leaning over on one wing tip fuel tank. That's because somebody forgot to close the cross feed valve, and fuel migrated from one side to the other. Don't ask me how I know. :D

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 Post subject: Re: Bombardier ending Learjet production
PostPosted: 05 Mar 2021, 20:14 
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For an owner / operator.. I’d take the cables vs hydraulics.[/quote]

The old Falcon 20 that I flew had push pull rods in an addition to the hydraulics. Triple redundancy, two different hyd systems plus the rods.[/quote]

When I was instructing for JAL their initial jet trainer was a Falcon 20 at Napa. I didn't fly it, but the guys who did said it was a dream machine.


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 Post subject: Re: Bombardier ending Learjet production
PostPosted: 05 Mar 2021, 20:16 
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I fly both a falcon 20 and Lear 45/75 , the Arthur Q hydraulic system is amazing in the falcon 20


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 Post subject: Re: Bombardier ending Learjet production
PostPosted: 06 Mar 2021, 06:54 
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Terry, you might have seen a Lear in a hangar or on a ramp leaning over on one wing tip fuel tank. That's because somebody forgot to close the cross feed valve, and fuel migrated from one side to the other. Don't ask me how I know. :D


Seen it many times!


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 Post subject: Re: Bombardier ending Learjet production
PostPosted: 06 Mar 2021, 07:25 
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I thought mach tuck was getting them? Operators were installing switches to disable the overspeed warning. Charter operator I worked for in Houston for a while lost one, I was told they had the illegal switch.


Actually, the stick shaker, pusher and puller are part of the stall warning system and powered from the hot battery buss through two switches on the glare shield panel, and could just be turned off, cancelling all stall warning and overspeed functions through the autopilot pitch servo. No secret switch to turn off. At least that's how I remember it after not flying the plane for 35 years, when I can't remember what I had for lunch yesterday. :D


From NTSB-AAR-81-15

"N125NE was equipped with an overspeed warning horn cut-out switch, an unauthorized modification. (See figure 2.) The Northeast Jet Company reported the existence of the switch when a similiar one was located under the pilot's instrument panel in the company's other Learjet 25D, N911MG."

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 Post subject: Re: Bombardier ending Learjet production
PostPosted: 07 Mar 2021, 22:34 
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Terry,

The report is an interesting read. The clandestine switch only inhibits the overspeed warning horn, not the stick puller; it's controlled through the left stall system switch I mentioned earlier, and as stated in the NTSB report. So, in order to exceed MMO, they only needed to turn off the left stall switch, then if they didn't want to listen to the horn or have it overheard in ATC communications, they used the clandestine switch to silence it.

The clandestine switch didn't get them, it was exceeding MMO with the stick puller disabled through the stall switch being turned off, then encountering moderate to severe clear air turbulence, losing control. I tried to post the full text of the NTSB report, but it didn't work.


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 Post subject: Re: Bombardier ending Learjet production
PostPosted: 08 Mar 2021, 01:45 
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Flew the 31a a total of 3287 miles over the last week.
Such a trouble free time machine.
I still can’t get over the climb rate passing FL350 consistently over 3400ft/min.

Fantastic approach back to SOCAL this evening through the puffy clouds.
Magical sweet spot airplane.

Now for a short cocktail and long night sleep.
Tj

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