Ray Tackett
(Top Gun)
01/18/16 11:54 AM
Center Line Thrust

This is an offshoot of the CPL PTS discussion.

Obviously, a Cessna 337 is a multiengine aircraft with center line thrust.

What about multiengine aircraft whose thrust is close enough to the center
line that one would not expect a huge yaw moment on engine failure? I'm
thinking of DC-9/MD-80 and B727. Shorter fuselages, such as A-10 and
Citation might well have significant yaw with one engine out.


sreyoB yrraL
(AVSIG Member)
01/18/16 12:07 PM
Re: Center Line Thrust

Quote:

What about multiengine aircraft whose thrust is close enough to the center
line that one would not expect a huge yaw moment on engine failure? I'm
thinking of DC-9/MD-80 and B727.



False premise.

A V1 cut in a DC9 takes full rudder, plus a little bit of aileron, to maintain heading as you climb at V2.

The DC8, with its four engines, required considerably less rudder when losing an outboard engine at V1. The V1 cut on the DC8 is a non-event in comparison.


Dave Siciliano (ADS)
(Top Gun)
01/18/16 02:59 PM
Re: Center Line Thrust

Larry would know those aircraft. For the Citation II and V I wouldn't say it's a non-even, but pretty manageable if above Vmc and more speed helps. V2 for us is always Vmc or more. Some of the AF folks had trouble with civil insurance with some of their fighters. The 337 of course, was centerline as was the Adam prototype that never came to fruition.

Jeff Hartmann CIC
(Top Gun)
01/18/16 03:41 PM
Re: Center Line Thrust

CJ-4 with 3600/side takes all the rudder.

Mase Taylor
(Top Gun)
01/18/16 03:58 PM
Re: Center Line Thrust

The F-4 Phantom is considered center-line thrust from the standpoint of a military pilot obtaining a civilian certificate.

sreyoB yrraL
(AVSIG Member)
01/18/16 04:14 PM
Re: Center Line Thrust

Quote:

CJ-4 with 3600/side takes all the rudder.



Yep.

What people forget is that the designers give each airplane just as much rudder as it needs to meet the most restrictive certification criteria. For most twins that is the V1 cut. For the DC8 it was a two-engine-out (on the same side) go-around. The design must not only handle the situations where rudder is needed but it must handle situations where there is a rudder hard-over and the more authority the rudder has the more difficult that requirement will be to meet.


Bill Bridges - 9S1
(Top Gun)
01/18/16 04:32 PM
Re: Center Line Thrust

Quote:

there is a rudder hard-over and the more authority the rudder has the more difficult that requirement will be to meet.





For a rudder hard-over is differential power a viable option?

the other bill


Ray Tackett
(Top Gun)
01/18/16 04:59 PM
Center Line Thrust

Thanks, yrraL. I asked seeking wisdom and found some.

sreyoB yrraL
(AVSIG Member)
01/18/16 05:07 PM
Re: Center Line Thrust

Quote:

For a rudder hard-over is differential power a viable option?



I do not know the certification requirements. I would not think that it would be based on using differential power for recovery.


Gil Buettner [KAUW]
(Top Gun)
01/18/16 08:51 PM
Re: Center Line Thrust

My multi-engine rating was limited to centerline thrust after graduating from UPT with only T-37 and T-38 time.

When I returned to civilian life I took my C-130 records to the FSDO and had a new certificate without the restriction.


Bruce Gorrell [EQY]
(Top Gun)
01/18/16 09:48 PM
Re: Center Line Thrust

The F14 is considered by the FAA to be centerline thrust. The engines (15,000 lb thrust) are 26 feet apart. I have seen them yaw 90° off the cat with a burner blowout.

Ray Tackett
(Top Gun)
01/19/16 04:20 AM
Center Line Thrust

Why am I not surprised to read of another disconnect between FAA and reality?

Thanks.


Ralph Jones
(Top Gun)
01/19/16 09:12 AM
Re: Center Line Thrust

Military aircraft certainly aren't their strong suit. Some years ago an FAA higher-up, who had a brief presence on Avsig, wanted to force civilian Warbird owners to disable their ejection seats. I made a sarcastic crack about it, and he, assuming I owned a Warbird, threatened to ground it for good...

Dave Siciliano (ADS)
(Top Gun)
01/19/16 10:59 AM
Re: Center Line Thrust

Quote:



What people forget is that the designers give each airplane just as much rudder as it needs to meet the most restrictive certification criteria.




And warbirds didn't have to meet certification criteria.


Terry Carraway
(Top Gun)
01/19/16 01:04 PM
Re: Center Line Thrust

This came up a number of years ago.

I think it was Rick Cremer who pointed out, the FAA considers any aircraft with fuselage mounted engines to be CLT.

And yes, the A-10 can generate enough yaw to lead to loss of control due to engine failure.

We will not discuss how I got my CLT restriction (from T-37/T-38) removed from Comm. :)


Randy Sohn
(Gradn Exlated Ordre of teh Fyling Fingres)
01/19/16 02:35 PM
Re: Center Line Thrust

Quote:

as it needs to meet the most restrictive certification criteria......And warbirds didn't have to meet certification criteria.




Not only warbirds, DC-3s. Seems to me (try'n to recall) I'd written a Warbird Note once about that exact situation.

best, randy


Dave Siciliano (ADS)
(Top Gun)
01/19/16 05:50 PM
Re: Center Line Thrust

Yep, you mentioned it when I got the B-25 SIC rating. I'm just repeating what you said before :)

nehoC hctiM
(Top Gun)
01/20/16 09:11 AM
Re: Center Line Thrust

As Captain B indicated,

The Crj 200-700-900 all take close to full rudder in a worst case engine failure, or v1- cut.
Same goes for the EMB-120, 170-175-190.

Just enough rudder to handle the situation, possibly some percentage over.

Not mentioned yet, if you have a Multi Engine rating, you can fly Any ME aircraft including clt. If you have a clt restriction, you are limited to clt aircraft only.


Andy Alson (HPN/NY)
(THE TOP GUN!)
01/20/16 10:08 AM
Re: Center Line Thrust

The following from 8900.1

E. Limited to Center Thrust Limitation.
1) The military aircraft listed below have no VMC established by the manufacturer. Other military multiengine airplanes may exist now or in the future for which there is no published data on VMC. Military pilots who can only show qualification in those kinds of multiengine airplanes may only be issued a multiengine airplane rating with the limitation “Limited to Center Thrust.”
a) T-2B/C Rockwell Buckeye.
b) T-37 Cessna 318.
c) T-38 Northrop Talon.
d) F-4 McDonnell-Douglas Phantom.
e) F-111 General Dynamics F-111.
Indicates new/changed information.
f) F-18 Northrop-McDonnell-Douglas Hornet.
g) A-6 Grumman American Intruder.
h) A-10 Fairchild Republic Thunderbolt II.
i) F-15 McDonnell-Douglas Eagle.
j) F-14 Grumman F-14.
k) F-117 Lockheed Stealth.
l) F-22 Boeing/McDonnell F-22.
Indicates new/changed information.
2) The “Limited to Center Thrust” limitation is not placed on a pilot certificate when the airplane has a VMC published on the airplane’s Type Certificate Data Sheet (TCDS) or approved AFM.


Terry Carraway
(Top Gun)
01/20/16 01:31 PM
Re: Center Line Thrust

Actually, there IS a VMC for the A-10A. But it is not written as Vmc.

The Dash 1 says, about an engine loss on take off:

Below 70 KIAS, flight control input may not be sufficient to maintain control of the aircraft with one engine at MAX and the other engine failed.

Also:

During single-engine operations, failure to use sufficient rudder can result in large sideslip angles and yaw rates. It is possible to create a condition where the yaw rate becomes so high that there is insufficient rudder available to correct it, and the aircraft will depart controlled flight.

The second is a Warning, which means the information, if not heeded could result in lose of aircraft or death of crew.


Richard Duxbury (Dux)
(Top Gun)
01/20/16 04:48 PM
Re: Center Line Thrust

Good post Larry.

I believe that we lost at least 1 (and perhaps 2) P-3 aircraft during training flights with two engines on the same side set at zero thrust -and in the early days with one actually feathered. Flying with just about max power on the other two engines could get you into a situation of close to VMC air -and a quick departure and upset. I know that one did get an upset, flat spin, and the FE restared an engine and the aircraft recovered close to the ground with very high "G" forces. I don't think that aircraft ever flew again

The USN S-2 that I flew had a short body and a big tail (rudder), which was augmented by an additional part of the rudder that you used for slow flight. I never flew that aircraft any where near close to full ASW weight, torpedos, and 4 crewmembers. I don't think it had a fuel jettison system -but I assume you could drop some of the bombs or torpedoes.

Center line thrust was the norm with the B-727 -yes some rudder was needed with the loss of an outboard engine but not like the B-757/747 or the USN P-3. Yes, that old Neptune P-2 also had a big rudder.

Watched some A-10 training flights today while shopping at the BX at Davis-Monthan. As someone mentioned, those engines are not on the centerline for sure.

Regards,

Dux


Ray Tackett
(Top Gun)
01/20/16 05:05 PM
Center Line Thrust

Interesting. It seems to be based entirely on having or not having a Vmc
specification. I wonder about the spookier stuff like F-117 or F-22, where
the military might want as little hard data as possible out in the civilian
world.


Ray Tackett
(Top Gun)
01/20/16 05:05 PM
Center Line Thrust

>>> but I assume you could drop some of the bombs or torpedoes.

Could make life way too interesting for waiting rescuers.


Randy Sohn
(Gradn Exlated Ordre of teh Fyling Fingres)
01/21/16 07:17 PM
Re: Center Line Thrust

Quote:

wanted to force civilian Warbird owners to disable their ejection seats




T'was a problem, indeed. When I was the Chief of Flight Safety at the CAF I had the KSFO unit appear before me to describe how they wanted to fly that newly restored T-33 (that many of you, I'm sure, have seen. Beautiful restoration, shiny/pristine/really great). The only problem, I quickly found out when questioning them was that it had cold seats and cold tips. Both! Either one was gonna be enuf for me to say NO! FAA requirement , they insisted! I could easily have some bad dreams if I didn't have that option back when I was flying T-birds. Can't recall what you USN guys called it, the "TV-2" or something like that? Anyhow, guess you'd share my feelings.. Anyhow, had a big argument with the feds over it, I really don't/didn't much care about their regs or something when it's MY rear end that's on the line, told them that. I have no idea today what they're doing with it, I quit. Gotta be able to get out or to get rid of a tip tank when I can't control the thing. Always will recall something (Bob Robins, one of the original Boeing test pilots on the B-29 told me once) in regard to max lateral fuel imbalance when I was in test pilot school -"Randy, when you lose control, you've just exceeded the limits".

best, randy


Randy Sohn
(Gradn Exlated Ordre of teh Fyling Fingres)
01/21/16 07:27 PM
Re: Center Line Thrust

>> VMC air <<

Chuckle Dux, you remember that we had also a VMC(g) on the 747?

>>The USN S-2 that I flew had a short body and a big tail (rudder), which was augmented by an additional part of the rudder<<

Dux, did'ja know that we lost a Stoof (an N numbered one) at Reno when a chum had part of the rudder wired off?

best, randy


Bill Bridges - 9S1
(Top Gun)
01/21/16 07:42 PM
Re: Center Line Thrust

Randy,

My Army buddy who flies a civilian OV-1 said it had cold seats in it.

the other bill


Tom Charlton
(Top Gun)
01/22/16 09:27 PM
Re: Center Line Thrust

Quote:

The only problem, I quickly found out when questioning them was that it had cold seats . . .


Hi Randy and others,
Back in the mid 80s lost a friend to his Folland Gnat with cold seats. Cross country flight, ran out gas after going missed in the clag. IIRC it was determined / thought they might’a tried climbing overboard for a manual extraction. Seems also I recall they often landed on fumes just doing local circuits at KISM. Darned if’n I can even remember his name at the moment. Gary something? We both had sailboats over in Port Canaveral. Nice guy.

Regards,
Tom Charlton


Randy Sohn
(Gradn Exlated Ordre of teh Fyling Fingres)
01/26/16 12:01 PM
Re: Center Line Thrust

Quote:

flies a civilian OV-1 said it had cold seats




Death wish!

best, randy


Rick Cremer
(AVSIG Member)
01/29/16 06:01 PM
Re: Center Line Thrust

Quote:

This came up a number of years ago.

I think it was Rick Cremer who pointed out, the FAA considers any aircraft with fuselage mounted engines to be CLT.




I don't believe that "Rick Cremer" ever said that "the FAA considers any aircraft with fuselage mounted engines to be CLT."

I think that Rick Cremer would have said that the FAA's position is that the “Limited to Center Thrust” limitation is placed on a pilot certificate if the the airplane does not have a VMC speed published on the airplane’s Type Certificate Data Sheet (TCDS) or in an approved AFM/POH. A speed determined during the certification process as defined in FARs 23.51 or 25.105 and 25.107.

Rick Cremer knows, for example, that his DC-9 AFM has a published Vmc(a) and Vmc(g) speed. He also knows that the Cesnna 337 does not have a published Vmc speed.

According the FAA's current guidance in its inspector's FSMIS the following military aircraft have CLT restrictions:

a) T-2B/C Rockwell Buckeye.
b) T-37 Cessna 318.
c) T-38 Northrop Talon.
d) F-4 McDonnell-Douglas Phantom.
e) F-111 General Dynamics F-111.
f) F-18 Northrop-McDonnell-Douglas Hornet.
g) A-6 Grumman American Intruder.
h) A-10 Fairchild Republic Thunderbolt II.
i) F-15 McDonnell-Douglas Eagle.
j) F-14 Grumman F-14.
k) F-117 Lockheed Stealth.
l) F-22 Boeing/McDonnell F-22.

You may read that information here:

http://fsims.faa.gov/wdocs/8900.1/v05%20airman%20cert/chapter%2001/05_001_004rev1.htm

Best Regards

Rick Cremer
ATP DC-9


Rick Cremer
(AVSIG Member)
01/29/16 06:50 PM
Re: Center Line Thrust

Quote:

Why am I not surprised to read of another disconnect between FAA and reality?




There is NO disconnect. The reality is that civil aircraft in the U.S. are certificated by the FAA in accordance with FARs 21, 23, 25, etc. and military aircraft are not.

The FAA has no idea how military aircraft are certified. Nor, to be honest, did we give a rats ass.

The FAA relies on the manufacturers of military aircraft to tell the FAA what standards the aircraft meet that are equivalent to the same standard in an FAR. If the standards are similar enough then the pilot of a military aircraft can get, for example, an equivalent civilian type rating based on military experience. E.g. a C-9 is a DC-9, a KC-135 is a B-707, a C-40 is a B-737, a C-130 is a L-382. But, in the case of many, if not most fighter jets, there is no equivalent standards and, more to the point, if the manufacturer has not determined what the Vmc speeds are for a particular multi-engine aircraft then the FAA will be generous and give the military pilot a multi-engine rating but will limit it to CLT.

It's up to the military manufacturer to determine what the Vmcg and Vmca is for a particular airplane if it has more than one engine. If the manufacturer does not publish those numbers then the FAA puts a CLT limitation on the aircraft in question. I have given you the current list in another thread.

Best


Terry Carraway
(Top Gun)
01/30/16 08:19 AM
Re: Center Line Thrust

Quote:

Quote:

This came up a number of years ago.

I think it was Rick Cremer who pointed out, the FAA considers any aircraft with fuselage mounted engines to be CLT.




I don't believe that "Rick Cremer" ever said that "the FAA considers any aircraft with fuselage mounted engines to be CLT."

I think that Rick Cremer would have said that the FAA's position is that the “Limited to Center Thrust” limitation is placed on a pilot certificate if the the airplane does not have a VMC speed published on the airplane’s Type Certificate Data Sheet (TCDS) or in an approved AFM/POH. A speed determined during the certification process as defined in FARs 23.51 or 25.105 and 25.107.

Rick Cremer knows, for example, that his DC-9 AFM has a published Vmc(a) and Vmc(g) speed. He also knows that the Cesnna 337 does not have a published Vmc speed.

According the FAA's current guidance in its inspector's FSMIS the following military aircraft have CLT restrictions:

a) T-2B/C Rockwell Buckeye.
b) T-37 Cessna 318.
c) T-38 Northrop Talon.
d) F-4 McDonnell-Douglas Phantom.
e) F-111 General Dynamics F-111.
f) F-18 Northrop-McDonnell-Douglas Hornet.
g) A-6 Grumman American Intruder.
h) A-10 Fairchild Republic Thunderbolt II.
i) F-15 McDonnell-Douglas Eagle.
j) F-14 Grumman F-14.
k) F-117 Lockheed Stealth.
l) F-22 Boeing/McDonnell F-22.

You may read that information here:

http://fsims.faa.gov/wdocs/8900.1/v05%20airman%20cert/chapter%2001/05_001_004rev1.htm

Best Regards

Rick Cremer
ATP DC-9




Thanks for the clarification.

Did you see where I posted data from the A-10 flight manual that, while it does not say Vmc, talks about loss of control under certain airspeed?


Randy Sohn
(Gradn Exlated Ordre of teh Fyling Fingres)
01/30/16 03:14 PM
Re: Center Line Thrust

Quote:

loss of control




Heck man, at BPs today we discussed a few guys we know that can do that even without being in an airplane! <g>

best, randy



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