1940's IFR Approach Capability (Fighters/Bombers)

Sat Jun 12, 2021 10:44 am

What kind of approach aids (if any) did the wartime aircraft have fitted? I rather imagine they didn't have much more capability than the four-legged radio range and maybe an ADF? Tough way to get home when the fog has rolled in.

Sat Jun 12, 2021 7:23 pm

While both the Instrument Landing System (ILS) and Ground Controlled Approach (GCA) systems were in existence during WWII, there were very few operating and most were in the U.S. The Automatic Direction Finder (ADF) was the most common form of radio navigation.

In England there were several airfields equipped with Fog Investigation and Dispersal Operation (FIDO). This was essentially pipes on either side of the runway with burner jets spaced along their length. Gasoline was pumped through the pipes and burned at the jets. This produced a "wall of flame" along each side of the runway which heated the air which evaporated the suspended droplets (fog) and cleared the air above the runway. This would clear away the English "pea soup" fog so aircraft could see to land. Having written this I realize that there had to be some sort of radio aid to guide aircraft to the now visible runway?

C2j

Sat Jun 12, 2021 7:52 pm

Here are some pages from the P-47 Pilot Training Manual that show the procedure for getting a DF steer to an airport or runway. This would work for a shot up or lost airplane, but more that a few would no doubt overload the system. I wasn’t really aware of how the system worked in WWII until reading this. At least I’d never heard of the Contractor Clock.

I’ve received DF steers from time to time so I know that they still work. When I flew explosives around the country in Twin Beeches in the 1970s I regularly made GCA approaches into Naval Air Stations because they didn’t use ILS and I didn’t have the UHF radios needed for their TACAN approaches.

92469F1F-C872-43B1-9FD5-6ED104E6C2BA by tanker622001, on Flickr

762D720B-5989-4157-8DF1-201DF2E31CD0 by tanker622001, on Flickr

1E248D27-481A-4CDD-8DCA-EA969256B00D by tanker622001, on Flickr

D5FDFD14-91A7-40A5-B90D-CBC029D1E1E5 by tanker622001, on Flickr

AABEF5F1-79B3-4F99-B3D6-EEB0BF7A9662 by tanker622001, on Flickr

Last edited by Larry Kraus on Sat Jun 12, 2021 8:24 pm, edited 2 times in total.

Sat Jun 12, 2021 7:58 pm

Thanks, Larry - that's interesting reading. I recognize some of it.

I always wondered how you'd feel, shot up, leaking fuel, and limping into a place with the FIDO system roaring away... Hopefully they could turn it on and off easily and quickly.

Sun Jun 13, 2021 4:55 am

Think MkV Spitfires started using Blind approach technology. :spit

Sun Jun 13, 2021 6:10 am

The RC-103 instrument approach equipment along with marker beacons and glideslope receivers were in use late in WWII. It can be seen in the B-17 photos showing the antennas for localizer and glideslope on top of the nose. It can also be seen on the instrument panels and is referenced in the Pilots Information file.

Number 18

The antenna for localizer and glideslope in front of the astrodome

Incidentally the frequencies used for the ILS, and even marker beacons in WWII, are the same frequencies used today. The present ILS system hasn't really changed that much since WWII.

Sun Jun 13, 2021 8:11 am

I am not certain of this, but I believe the following statements to be true about direction finding in WWII. This is the information I have assembled from PIF's, radio equipment I know equipped aircraft in WWII and general dates of installation, and interviews with various aircraft crew members. I am not a radio guy- I just sell the stuff! So what I write here might be disproven by further research.

1. Radio direction finding was very secret from the beginning of WWII. Knowledge of it was protected with the same seriousness as the Norden Bombsight information. Navigators and radio operators were specifically prohibited from talking about the capabilities. This was carried as far as scrubbing photos for antennae from aircraft in published photos. This is why you don't see much about it documented until the later WWII PIF's and Navigator's Information Files (NIF) and Radio Operators' Information Files (ROIF).

2. Non Directional Radio Beacons (NDB's), which were either specifically established or were existing radio stations, were in use from the early part of the war. Most of the radios based on aircraft using these frequencies were removable and not seen on the aircraft unless on transit for deployment or flying navigator or radio operator-specific training missions. This was the ADF capability carried on the aircraft, and is evidenced by the football or loop antennae. USN pilots trained on these in N3N's, as I have 1942-dated radios and literature which described their use.

3. The SCR-522 command sets, as shown, had the direction finding capability built into the system. But these were starting to be replaced by early 1944 with the SCR 274 (USAAF) and ARC-5 (USN).

4. The ILS system was in use and being trained on by mid- to late-1943. This consisted of the SCS ground system and the RC-103 radio sets on the aircraft. They were definitely deployed to ETO, as I have seen photos of the ground equipment on airfields at this time. I don't believe every aircraft was equipped with this capability until early 1944, and by then, it was in common use. But this doesn't appear in the PIF's until later 1944 or 1945. My guess is that this system was being very carefully guarded from widespread information dissemination because it could be used to home into flying fields by the enemy (if they knew the frequencies). As the SCR-585 IFF system came on board in later 1943 and early 1944, this was less of a concern, and that is why you see the ILS system described in the PIF's after this time period.

5. The late war ARC-5 and SCR-274 sets had DF built into the system and were carried even on the Stinson L-5 late in WWII. I don't believe that these sets made it into widespread use until the very end of WWII (in the field) but they were being use for training and were probably the intended radio sets for all tactical aircraft intended for use in the invasion of Japan. So every aircraft, down to L-5's was equipped with DF capability if it was headed to Operations Coronet or Olympic.

Sun Jun 13, 2021 12:13 pm

About thirty years ago I got to know an old guy who owned a fishing lodge/cabin business in northwestern Ontario and had been a B-17 driver in the ETO during the war. One day while looking in the -185 I flew he noticed the ILS head in the panel and asked me if I had an instrument ticket. When I said yes I did he asked me if I'd ever done an ILS. I was pretty young at the time and didn't have a lot of instrument experience but I said "yes, a few". He asked me "What are your limits?" and I said generally about 200', sometimes 250' depending on where you are. Then he said "We had first generation ILS in the Forts in England near the end of the war." When I asked him what his limits were back then he just kinda looked at me, smiled slightly, and said "The ground."

Did the ILS sets ever get put into the fighters?

Sun Jun 13, 2021 12:26 pm

Please don't take this the wrong way but I do not think that the ADF was secret as it was openly in use well before the war and was common in civil and military aircraft. Instrument let down procedures with the ADF and marker beacon gear were common and were about the only way to go with the AAF until the glideslope and glidepath or ILS gear started showing up.

The SCR-522 and the SCR-274N did not have built in direction finding capabilities. They were receiver-transmitters for communication and to be able to receive navigation signals but on very different frequency bands. They were commonly used together in the same AAF aircraft.

If you are referring to the P-47 manual excerpts posted above, the channel used for homing was meant as a common frequency to transmit to a ground station who would home in on your signal to identify you and determine your location in order to give you a heading back to base. Only the ADF had self contained homing capability.

Some Navy sets like the ARC-5 and RU/GF series of command gear had options for direction finding equipment that could be used in conjunction with the sets but as far as I know the standard AAF SCR-522 and 274N did not have stand alone DF capability without ground station help.