P-51 Service Bulletin Issued

[Dan K]

http://www.warbirds-eaa.org/news/2013%2 ... Issued.pdf

[Mike]

I notice that this bulletin makes the dorsal fin installation mandatory on P-51Ds. Are any currently flying without it?

[WIXerGreg]

Failure of the elevator trim tab and loss of control of the aircraft has been experienced by a North American Aviation (NAA) P-51 aircraft. Contributing factors were worn fiber lock spline nuts at the elevator trim tab hinge attach fittings and the installation of non-structural screws and hardware.

Could this be related to the Leeward crash? Or has the trim tab come off another Mustang recently?

[John Dupre]

What authority does Cal Pacific Airmotive have for issuing a service bulletin? Are they the type certificate holder? Service Bulletins are only advisory in nature, for most operators, regardless of anything written in the service bulletin itself. Does this service bulletin presage an Airworthiness Directive from the FAA, which would be mandatory for most operators? Experimental registered aircraft are immune from service bulletins and ADs from the latest guidance from the FAA. So how will this SB affect most of the Experimental registered Mustangs?

Now I think given what happened to Galloping Ghost and apparently to other Mustangs this Service Bulletin is a good idea and any operator would be foolish not to follow it.

[JohnTerrell]

I notice that this bulletin makes the dorsal fin installation mandatory on P-51Ds. Are any currently flying without it?

Mike, that has already been a requirement of airworthy P-51D/K's, at least that is what has been stated on this forum in the past (when the question once arose about the possibility of restoring and flying a Mustang with the original P-51D-5-NA tail configuration). There aren't any P-51D/K's flying without the dorsal fin fillet added. I believe the mention of it in this service bulletin has more to do with the rudder trim tab rather than the dorsal fin fillet itself, as the installation of the fin fillet and de-boost rudder tab are both one in the same technical order, having been introduced together.

And John, yes Cal Pacific are the type certificate holder, which is mentioned in the "Background" paragraph of the service bulletin.

[PinecastleAAF]

Failure of the elevator trim tab and loss of control of the aircraft has been experienced by a North American Aviation (NAA) P-51 aircraft. Contributing factors were worn fiber lock spline nuts at the elevator trim tab hinge attach fittings and the installation of non-structural screws and hardware.


Could this be related to the Leeward crash? Or has the trim tab come off another Mustang recently?

Pretty much has to be.

[gale_dono]

Failure of the elevator trim tab and loss of control of the aircraft has been experienced by a North American Aviation (NAA) P-51 aircraft. Contributing factors were worn fiber lock spline nuts at the elevator trim tab hinge attach fittings and the installation of non-structural screws and hardware.


Could this be related to the Leeward crash? Or has the trim tab come off another Mustang recently?

Pretty much has to be.

How is it possible they own the type certificate, but Boeing still owns the actual copyright to the design (and can dole it out to people making plastic models?)

/minor derail

[51fixer]

Failure of the elevator trim tab and loss of control of the aircraft has been experienced by a North American Aviation (NAA) P-51 aircraft. Contributing factors were worn fiber lock spline nuts at the elevator trim tab hinge attach fittings and the installation of non-structural screws and hardware.


Could this be related to the Leeward crash? Or has the trim tab come off another Mustang recently?

Pretty much has to be.

How is it possible they own the type certificate, but Boeing still owns the actual copyright to the design (and can dole it out to people making plastic models?)

/minor derail

Type Certificate dealt with the FAA only. The Limited TC was pretty easy to acquire at a point in time and was independent of the Mfg.
Probably why it was a system that didn't last.

[HawkerTempestMKII]

P-51 D has a bubble canopy which could disturb the air flow over the tail and that probably created a need for the dorsal fin for correct stability.

[JohnTerrell]

Just to extend the conversation, almost the same exact dorsal fin fillet/reverse rudder boost tab Technical Order was issued for the P-51B/C at around the same time the T.O. for the same modifications was issued for the P-51D/K, as it addressed the same issues with both aircraft - the potential for the tail coming off when a high angle of yaw was performed in some maneuvers at high speed. The reason why the dorsal fin fillet and the reverse rudder boost tab are in the same T.O.'s, is that they both worked together to solve that problem - to make it harder, at higher speeds, to inadvertently overload the tail. The fact that both are grouped into the same T.O., appears to be the only reason why the dorsal fin fillet makes a brief mention in the service bulletin, as it would appear to be only to do with the inspection of the reverse boost rudder tab.

Here is the P-51B/C T.O.: http://p51h.home.comcast.net/~p51h/sig/ ... 0JD-43.pdf
The same T.O. for the P-51D: http://p51h.home.comcast.net/~p51h/sig/TO/01-60JE-8.pdf

(The dorsal fin fillet was of a different design for the P-51B/C than it was for the D/K.)

It's interesting that, being a requirement on P-51D/K's flying today (as I recall it is), that it wouldn't be a requirement for P-51B/C's as well (though personally, I'm glad it's not, as it is nice to see the few P-51B/C's flying today in their original design).

[51fixer]

Just to extend the conversation, almost the same exact dorsal fin fillet/reverse rudder boost tab Technical Order was issued for the P-51B/C at around the same time the T.O. for the same modifications was issued for the P-51D/K, as it addressed the same issues with both aircraft - the potential for the tail coming off when a high angle of yaw was performed in some maneuvers at high speed. The reason why the dorsal fin fillet and the reverse rudder boost tab are in the same T.O.'s, is that they both worked together to solve that problem - to make it harder, at higher speeds, to inadvertently overload the tail. The fact that both are grouped into the same T.O., appears to be the only reason why the dorsal fin fillet makes a brief mention in the service bulletin, as it would appear to be only to do with the inspection of the reverse boost rudder tab.

Here is the P-51B/C T.O.: http://p51h.home.comcast.net/~p51h/sig/ ... 0JD-43.pdf
The same T.O. for the P-51D: http://p51h.home.comcast.net/~p51h/sig/TO/01-60JE-8.pdf

(The dorsal fin fillet was of a different design for the P-51B/C than it was for the D/K.)

It's interesting that, being a requirement on P-51D/K's flying today (as I recall it is), that it wouldn't be a requirement for P-51B/C's as well (though personally, I'm glad it's not, as it is nice to see the few P-51B/C's flying today in their original design).

This has been discussed at length several times in the past at wix.
There are some spirited conversations about the details.
The metal covered elevators change AFAIK came about as the fabric would bulge at times creating uncommanded control inputs like a trim tab.
The fillet and deboost rudder tab slowed the rate of input of rudder and rate of change to the yaw axis the over control of the rudder was linked to tail failures.
There were also modifications to the horizontal fwd spar assy, and each hinge point of the horizontal and vertical increasing their strength. At 1st it was reinforcements and later it was beefier components built into assemblies at the factory.
Their was also a change of the angle of incidence of the horizontal from 2 degrees to 1/2 degree.

[HawkerTempestMKII]

Did the B model have these problems too?

[b29flteng]

This past weekend I was preparing a friends T-6 rudder and elevators for recover and while removing the elevator tab hinge mounts I found lock washers under the head of the attach bolts. For you non-mechanics this means the fiber lock nutplates were worn out. Even though the T-6 doesn't fly as fast as a P-51, it's still scary.

[51fixer]

This past weekend I was preparing a friends T-6 rudder and elevators for recover and while removing the elevator tab hinge mounts I found lock washers under the head of the attach bolts. For you non-mechanics this means the fiber lock nutplates were worn out. Even though the T-6 doesn't fly as fast as a P-51, it's still scary.

I've found more issues of wear and cracks in T-6 tabs and their attachment components than any other of the A/C.
The arm the the pushrod attach to is like 1/8" steel and is riveted to an Alum rib that is .025 or so. This will work and open the hole around the rivet. The arm will show movement then. The tabs have a small bearing pressed into an Alum casting and its riveted to a rib in the same fashion and will lessen in the same way. I've also seen the false spar the tab attach brackets bolt on to crack near the nut plates.