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H model question


SEFEGeorge
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One thing I've always been curious about but never asked. On the H models why is the left side skin above the wheel well not painted? Is is because of a heat problem with the APUs and using a different type of metal there?

You ain't the only guy who's wondered about this. Me being an A model troop and you haveing lots more experience in the 130 world, I don't feel so bad about not knowing the answer to this.

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One thing I've always been curious about but never asked. On the H models why is the left side skin above the wheel well not painted? Is is because of a heat problem with the APUs and using a different type of metal there?

All I know is that it gets very hot there and the material is either titanium or stainless steel.

regular alu plating or the honeycomb would melt in these extreme temps.

greets bonzo

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It's titanium. When we got the new H-models at Dyess, a Lockheed tech rep came with them. His name was George ???? and he spent the majority of his time in the NCO Club stag bar. He told me it was titanium.

Oddly though, the commercial Hercs titanium panel is painted over. Perhaps because the APU is not certificated for inflight use?

Don R.

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You ain't the only guy who's wondered about this. Me being an A model troop and you haveing lots more experience in the 130 world, I don't feel so bad about not knowing the answer to this.

All I know is that it gets very hot there and the material is either titanium or stainless steel.

regular alu plating or the honeycomb would melt in these extreme temps.

greets bonzo

It's titanium. When we got the new H-models at Dyess, a Lockheed tech rep came with them. His name was George ???? and he spent the majority of his time in the NCO Club stag bar. He told me it was titanium.

Oddly though, the commercial Hercs titanium panel is painted over. Perhaps because the APU is not certificated for inflight use?

Don R.

Yep, I have quite a bit of Herc experience but not on the 74 models and later. The 73 H models had GTCs. I figured it was titanium or SS because of heat but just wasn't sure.

Don't the commercial Hercs have the same APU? If so it would seem like the APUs would be certified for inflight use.

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Yep, I have quite a bit of Herc experience but not on the 74 models and later. The 73 H models had GTCs. I figured it was titanium or SS because of heat but just wasn't sure.

Don't the commercial Hercs have the same APU? If so it would seem like the APUs would be certified for inflight use.

It's titanium on the Hs and even the Js due to temps associated with APU. It can be painted, as it is on AFSOC acft (for the sake of tone down/camouflage) however the paint does stick to titanium well and the heat does take a toll on the paint, thus requiring reapplication. On a slick where tone down/camouflage is not a concern, it's just as easy to leave bare metal and not worry about it at all.

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Don't the commercial Hercs have the same APU? If so it would seem like the APUs would be certified for inflight use.

George, I have no idea why the APU's on commercial Hercs can't be operated in flight; they're the same. Of course my AOM reference is more than 20 years old -- it even has instructions for operating the Omega!. I'll check with a friend at Lockheed. Now I'm curious.

Don R.

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OK, for anyone who is interested, a friend at Lockheed told me that when they converted from the GTC to the APU on the commercial Herc, engineering didn't make any effort to get FAA testing and certification for the inflight use of the APU at that time. He also said that today it would be cost prohibitive to have it done.

Don R.

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  • 4 months later...

The APU is wired thru the touchdown relay switch. This only allows operation either on the ground or in flight with main gear down.

Todd,

I've prefaced many a reply with this statement -- "It's been a very long time, but...." Well, it has, but I don't think the gear has to be down for the APU to operate in flight. I'm sure I've started it in cruise without slowing to lower the gear. I remember a note in the 130H-1 saying that the APU may not start or operate above 20,000 feet.

Don R.

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The APU is wired thru the touchdown relay switch. This only allows operation either on the ground or in flight with main gear down.

lilzac,

Gear position has no function regarding the APU operation other than the APU door position. On the ground the APU door opens to 35 degrees, in flight it's limited to 15 degrees. Don R you are absolutly correct, the APU should operate up to 20,000 feet.

Ron

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My 2 cents - Gear does not have to be down for APU operation - touchdown switch on fwd strut (and relay in hog trough) allows full inlet door travel to 35 degrees with weight on wheels (strut compressed), limits door travel to 15 degrees with weight off wheels. Operation above 20,000 feet or 200 KIAS usually not possible due to inlet air density/flow.

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The APU WILL operate at 20,000 feet even upside down...

You say WHAT!

Marine aircraft 106 went inverted after the loss of one raft which hung up and (inflated) by the airflow which induced a rollover and "spin". The FE "hit" the APU control switch (with his head) as he departed his seat (wear your lap belt!) and it started and continued to operate until touchdown....

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