Bockscar Navigator station

Ken · **Posted:** Fri Dec 20, 2013 9:40 am

I recently sent the NMUSAF link to the panorama view of Bockscar's navigator/radio operator station to a buddy who is a 20-plus year USAF C-130 Nav and I thought some of you would appreciate the detail of his reply. I added some edits in parenthesis for clarity.

Ken

The panoramas are found here:

http://www.nationalmuseum.af.mil/virtua ... ckpits.asp

"Nice.

There is an SCR-718 Radio Altimeter on the left side of the Nav's desk. The SCR-718 was used in the A and B model Herks and a refurbished version (I don't recall the model number, but I think it was the APN-133) was used in the E-model and 1974 H1-model Herks. These were replaced by the CARA (combined altitude radar altimeter, this replaced the more basic RA supplied from the factory in nearly all C-130s after 1991-93) when modified with the SCNS (Self Contained Navigational System, somewhat similar to an airliner's FMS, Flight Management System).

Both the SCR-718 and its updated version were in the depot spares inventory, so occasionally a 718 would find its way into an E or H1. There was a requirement in the Nav's preflight to determine if your plane had the old SCR or updated APN version of the radio altimeter. The old version could not be used in flight unless you were 50 miles offshore. It's frequency interfered with some ground based systems.

I remember this trivia because of that preflight requirement and the curiosity of what "SCR" meant--Signal Corps Radio. That meant it was surplus Army Air Corps equipment, purchased prior to the establishment of the Air Force as a separate branch."

mike furline · **Joined:** Wed May 05, 2004 3:45 pm **Posts:** 2629

I'm assuming it is in original/unrestored condition.....amazing!!!

Taigh Ramey · **Posted:** Fri Dec 20, 2013 11:25 am

In 1980 when my Dad and I were on the crew of the B-29 Hawg Wild we stopped at Loring AFB in Main for some maintenance before heading over the pond toward Duxford. A very nice B-52 Bombardier/Navigator named Jake Huffman took my WWII B-29 Navigator Dad and I on a tour of the base. We crawled through a KC-135 and I was astounded to see the indicator for the SCR-718 mounted next to the Nav station. Right on the side of the indicator wax it's original data plate with the DAY-45 contract code indicating 1945! I told Jake about that radio being installed in the B-29 too.

What was also interesting was when we crawled in a B-52 at the bombardier station was a bomb release intervalometer panel with identical controls on it as the one found in most WWII bombers including the B-29.

The SCR-718 was used in many B-29s in WWII and was mostly located on the floor of the bombardiers compartment just to the right of the bombsight. It seems unusual to see it at the Nav station.

Because of many post war mods to the Silverplate aircraft there has been some debate about the location of the SCR-718 in the Enola Gay and it is believed that it too was mounted to the left of the Navigator on the table which interfered with the wood map case. Bernie Poppert determined that the wood map case was relocated to the radar ops compartment in the aft end of the aircraft. This is one of the items on our list of things that we would like to fix on the Enola Gay in a proposed work session sometime in the future.

mike furline · **Joined:** Wed May 05, 2004 3:45 pm **Posts:** 2629

Enola Gay interior, http://airandspace.si.edu/webimages/col ... -2cmyk.jpg

Ken · **Posted:** Fri Dec 20, 2013 12:55 pm

mike furline wrote:

I'm assuming it is in original/unrestored condition.....amazing!!!

Although it is very nice, I've always heard that those airplanes stored outside for the museum needed quite a bit of restoration to get to this stage; maybe someone else can chime in with the details.

As for the configuration of the Enola Gay Nav station, with Dutch still alive, I guess he no longer recalls how it was set up?

Finally, I was primarily an C-130H2 pilot, so I did some searching on the SCR-718 and found this link for you guys:

http://www.tankernav.com/kc-97l-nav-equipment.html

Ken

Taigh Ramey · **Posted:** Fri Dec 20, 2013 1:11 pm

In the shot that Mike linked at http://airandspace.si.edu/webimages/col ... -2cmyk.jpg
you can see the SCR-718 in its mount sitting on the floor at the navigator's compartment at the bottom of the photo. This mount is the one that is common for the B-29 when the SCR-718 indicator is mounted just to the right of the bombsight. This is how it came in the Enola Gay hence the discussion and debate about where it would actually have been located on the August 6th flight.

Bernie is pretty certain that it was indeed located as seen in Bocks Car and the plan is to put it back there. Right now it is simply sitting on the floor awaiting proper mounting. One issue as I recall is reproducing the mount. I think Bernie may have measurements from the AFM but I can't recall.

Part of the fun has been trying to figure out what all was where for the August 6th mission as there isn't a lot of documentation or photos from the inside of the Enola Gay. You can imagine why.

Here is the shot from NASM that Mike referred to.

Ken · **Posted:** Fri Dec 20, 2013 2:22 pm

Excellent update, Taigh. Do you recall how high that unit would measure?

Most airline rad alt's come alive at 2500 AGL. The late model CARA in the Herk had a needle that came alive somewhere near 2500 AGL, however the face also contained a digital readout that remained continuously active with 5 digit spaces (although I doubt it worked out to 99,999'; I certainly never attempted that in the Herk)

Ken

Taigh Ramey · **Posted:** Fri Dec 20, 2013 3:04 pm

As I recall the unit could go up to 50,000 feet at least the scale went that high and it may have read higher. Not sure. I can dig out a manual and take a look.

It presented on a cathode ray tube in a circular format. I had one running about 30 years ago so my memory isn't what it used to be...

There would be a circle presented on the scope and it was graduated from 0 to 5 in thousands of feet. You could switch to a 10x scale and it would indicate up to 50,000 feet. Not sure if that was its actual capability. There would be a blip on the ring in the CRT that was the zero spot and I think you could adjust that for a zero on the scale. The other blip on the ring would indicate your altitude.

Ill try and dig out a manual and see.

These used the T shaped antennas commonly seen on the bombers and also the APN-1 radio altimeter used the same antenna. One antenna would transmit the signal down and the other would receive the signal that was bounced off of the ground or water. They had trouble with the system if the antennas could "see" each other then it would present false indications so they were ofete moved on opposite sides of the fuselage or tail area.

Taigh Ramey · **Posted:** Fri Dec 20, 2013 3:27 pm

Here is an excerpt from the Radar Observers Information File for the SCR-718.

Ken · **Posted:** Fri Dec 20, 2013 3:38 pm

Very cool, Taigh, thanks for sharing that. For anyone who has not flown with a good radar altimeter, it can be extremely handy. In combat it is an emitter, so that is a consideration, but, even for daytime low-level flying it is a great backup to what you perceive with your eyes. Of course they don't look forward, only down, so there's a limitation there unless you get really tricked out and start playing with terrain-following stuff.

Ken

Taigh Ramey · **Posted:** Fri Dec 20, 2013 4:43 pm

I have never had a good radar altimeter to play with in flight before. We have an APN-1 in the Harpoon that needs to be wired up. I even found the test equipment for it so it will be fun to get it running some day.

The APN-1 was a bit more user friendly with an instrument in the panel and a limit switch so you could set a warning area. A light on the panel and tone in the headset would keep you within the set range when in low level mode. I imagine that was handy when down in the soup under 500 feet in attack mode trying to fid the enemy in your Navy fighter or patrol bomber.

RAMC181 · **Posted:** Fri Dec 20, 2013 7:49 pm

Here's the indicator unit I bought back in July. It isn't quite as rough in real life as the photos make it seem:

I did consider picking up rest of the system while I was in Ohio in August, but I don't think my baggage allowance back to the UK would have been sufficient...

Does anyone have the installation drawings for how these were fitted into PFF B-17s?

Taigh Ramey · **Posted:** Fri Dec 20, 2013 8:01 pm

I have a few B-17 drawings so shoot me a part number and I will look for you Paul.

It is a simple hook up with a straight 7 conductor cable from connector to connector between the indicator and the T/R unit. The antennas are not too hard and should run straight coax.

Maybe you could bounce the signal off of a nearby mountain or building! Take out a local flying club Cessna (one with 24 volts) and hold an antenna out of each window

Actually it would be real simple to make a clamp for each lift strut...hmmm...

Taigh Ramey · **Posted:** Fri Dec 20, 2013 8:14 pm

Here is a photo from Mike Hanz's web site that shows the SCR-718 indicator still up in the nose of the Enola Gay before it was removed. You can see the corner of it on the floor just to the right of the bomb sight. This is the more common location for the indicator. I should check the B-29 parts manual to see if there is a serial number breakdown for the installation and see if any changes in location are mentioned.

Mike has a great web site and his page for the Enola Gay is here: http://aafradio.org/NASM/Enola_avionics_narrative.htm

RAMC181 · **Posted:** Fri Dec 20, 2013 8:19 pm

Thanks Taigh.

It would be a modification rather than a standard installation, so I'm afraid a drawing number has eluded me so far.
Having said that, Boeing Dwg. No. 15-17774 shows the RAF GEE Set B-17 installation Mod, so anything's possible.

I wonder if I could hook it up to my APN-1 Transceiver in the meantime...

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