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F-104 white wings - alternative reason


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In April there was a thread in the Research Corner section          that discussed the reason for white wings on the F-104, a question that pops up regularly. That's also why I'm posting now in the 'Jet Modeling' section.

 

Back then I posted an alternative explanation, but I could not remember my source. It took me a couple of months to find my source again, but here it is, from rec.models.scale in 2002:

 

https://groups.google.com/forum/#!searchin/rec.models.scale/variable$20stator$20system|sort:date/rec.models.scale/htfUxmCm7sw/6xClpm_ypA8J

 

Maybe someone can find crash reports to check whether these Eglin accidents really happened, and were caused by the problem described? Then we can put this question to bed forever 🙂

 

Rob

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I would say that's a very 'alternative reason' but totally incorrect. The source has no idea what they are talking about and has no factual content or references.

 

There is a lot of misinformation in that post regarding the design and implementation of the J79 into the F-104 airframe. At no point were thermocouples installed in the wings in an effort to control the VSV system on the J79 due to airframe heating. The actual limiting factor for the airframe heating is the J79 engine front frame and generator cooling air temperature and not the aluminum structure. The effects of high speed heating on the F-104 were well understood by Lockheed engineers and the Aluminum used in the structure was more than sufficient to cope with this heating.

 

As for Eglin AFB accidents, there were only 4 F-104's lost at Eglin over the years and only one was a takeoff accident when the engine failed. 

 

Interesting F-104 accident list.

 

http://www.i-f-s.nl/F-104 Accidents/

 

Eglin AFB accident list.

 

https://en.wikipedia.org/wiki/List_of_aircraft_accidents_at_Eglin_Air_Force_Base

 

The majority of early F-104 accidents were due to engine failure/fire, hydraulic failure or electrical failure.

 

Cheers,

 

John

 

 

 

 

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On 11/25/2018 at 6:04 AM, CF104 said:

I would say that's a very 'alternative reason' but totally incorrect. The source has no idea what they are talking about and has no factual content or references.

 

There is a lot of misinformation in that post regarding the design and implementation of the J79 into the F-104 airframe. At no point were thermocouples installed in the wings in an effort to control the VSV system on the J79 due to airframe heating. The actual limiting factor for the airframe heating is the J79 engine front frame and generator cooling air temperature and not the aluminum structure. The effects of high speed heating on the F-104 were well understood by Lockheed engineers and the Aluminum used in the structure was more than sufficient to cope with this heating.

 

As for Eglin AFB accidents, there were only 4 F-104's lost at Eglin over the years and only one was a takeoff accident when the engine failed. 

 

Interesting F-104 accident list.

 

http://www.i-f-s.nl/F-104 Accidents/

 

Thanks for researching this theory! Indeed only one of four Eglin 104 crashes would match the , this one:

 

22 Aug 1957      F-104A         56-753              Air Force Operational Test Center (AFOTC)       'crashed about two miles from the end of an Eglin runway shortly after takeoff'

 

http://www.i-f-s.nl/accidents-incidents-1957/

 

The strange thing is that 56-753 is now in a museum at Hill. But I found that this is actually 56-752 painted as 56-753.

 

As for the thermocouples in the wing: I agree that this was not installed in the G version. But are you 100% sure it wasn't installed in the A version? Or maybe the AFOTC or Lockheed wanted it installed? Who knows. I'm not dismissing this theory yet..

 

Regarding the aluminum: I think the 104 could do M2.2, and I think that involves temperatures above 130 deg C, which is the usual limit for 2024-T3. I think it ages to T4 or T8 condition (all from the heart from 25 years ago, have mercy), so it would not be unusual to have some warning mechanism. Coupling it to the variable guide vanes is a bit drastic, I agree.

 

I may have found a way to contact the original poster on rec.models.scale, maybe he remembers the details.


Rob

 

 

Edited by Rob de Bie
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23 hours ago, Rob de Bie said:

 

Thanks for researching this theory! Indeed only one of four Eglin 104 crashes would match the , this one:

 

22 Aug 1957      F-104A         56-753              Air Force Operational Test Center (AFOTC)       'crashed about two miles from the end of an Eglin runway shortly after takeoff'

 

http://www.i-f-s.nl/accidents-incidents-1957/

 

The strange thing is that 56-753 is now in a museum at Hill. But I found that this is actually 56-752 painted as 56-753.

 

As for the thermocouples in the wing: I agree that this was not installed in the G version. But are you 100% sure it wasn't installed in the A version? Or maybe the AFOTC or Lockheed wanted it installed? Who knows. I'm not dismissing this theory yet..

 

Regarding the aluminum: I think the 104 could do M2.2, and I think that involves temperatures above 130 deg C, which is the usual limit for 2024-T3. I think it ages to T4 or T8 condition (all from the heart from 25 years ago, have mercy), so it would not be unusual to have some warning mechanism. Coupling it to the variable guide vanes is a bit drastic, I agree.

 

I may have found a way to contact the original poster on rec.models.scale, maybe he remembers the details.


Rob

 

 

 

 

I've been collecting F-104 reference materials for the better part of 30 years and this is the first instance of thermocouples installed in the wing to control the engine to prevent overheating the airframe that I've heard of.

 

I can't find any reference to this supposed system in any of my F-104A materials which includes both Maintenance T.O.s and the Structural Repair Manual. Also the J79-GE-3B manuals have no reference to this system. The only thing controlling the VSV system on the -3B is the Main Fuel Control and an external input from the gunfire system to close the vanes when the gun is firing.

 

The majority of the structure on the F-104 is 7075-T6 with high carbon steel forgings in the center fuselage/engine bay area. There is modest use of 2024-T4 in some fairings and internal structures. The aft fuselage is primarily Stainless Steel structure with some Titanium skins. There really is no chance to overheat the aluminum structure as the time the F-104 can spend at Mach 2.0 is very limited. Both 2024-T4 and 7075-T6 have very similar thermal strength properties and are mechanically stable to well above 130 deg C. As far as the F-104 is concerned, it's the engine that is the speed limiting factor at altitude and high mach numbers. The compressor front case is made of cast magnesium and that's why the SLOW light comes on at 121 deg C Inlet Temp.

 

I Would be interested in hearing the details from the other post if the person remembers them.

 

Regardless this is a bit far off course for this forum so I'll take this back to the Research Corner.

 

Cheers,

 

John

 

 

 

 

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13 hours ago, CF104 said:

I've been collecting F-104 reference materials for the better part of 30 years and this is the first instance of thermocouples installed in the wing to control the engine to prevent overheating the airframe that I've heard of.

 

I can't find any reference to this supposed system in any of my F-104A materials which includes both Maintenance T.O.s and the Structural Repair Manual. Also the J79-GE-3B manuals have no reference to this system. The only thing controlling the VSV system on the -3B is the Main Fuel Control and an external input from the gunfire system to close the vanes when the gun is firing.

 

The majority of the structure on the F-104 is 7075-T6 with high carbon steel forgings in the center fuselage/engine bay area. There is modest use of 2024-T4 in some fairings and internal structures. The aft fuselage is primarily Stainless Steel structure with some Titanium skins. There really is no chance to overheat the aluminum structure as the time the F-104 can spend at Mach 2.0 is very limited. Both 2024-T4 and 7075-T6 have very similar thermal strength properties and are mechanically stable to well above 130 deg C. As far as the F-104 is concerned, it's the engine that is the speed limiting factor at altitude and high mach numbers. The compressor front case is made of cast magnesium and that's why the SLOW light comes on at 121 deg C Inlet Temp.

 

I Would be interested in hearing the details from the other post if the person remembers them.

 

Regardless this is a bit far off course for this forum so I'll take this back to the Research Corner.

 

Good point about the limited time that the aircraft could so M2 - I was thinking along Concord lines.. I also checked Mil Handbook 5H, and indeed above ~130C / 266F the strength goes down with hours exposed for 2024-T3 and T4. See figure 3.2.3.1.1 and further if interested. I agree that the 'Eglin theory' is now quite unlikely.

 

Rob

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