Use of Bondo on wartime aircraft.

I remember hearing something about the leading edge of of PR-XI Spits being smoothed with *plaster* before being painted. There was def something that had to be dug out prior to removing skins when I was working on PA908.

Oh dear, this old P-51 dispute again. The blue was not only seen in the air from the ground, but also seen on the aircraft on the ground by a number of experienced British observers whilst on a tour of the base. These were close acquaintances of the great 8th AF historian Roger Freeman. If he found them convincing, that’s good enough for me. I agree that Olive Drab would be much more logical, but so what? I’m certainly not claiming that it was that particular shade of blue, however.

Don’t know about other P-51’s, but the consensus for “Lou IV” is that it was indeed green, and not blue as replicated on some warbirds. Correctly seen on these models:
britmoddeler/
ARC

I think SoBAC is the same as SBAC ie Society of British Aerospace Companies – basically the guys that came up with the standards.

Thanks for that Jed. I found the Britmodeller thread where Edgar wrote that and note that I took part in the discussion with the same quote from the RAE report. I’m getting old because I can’t remember doing that and its probably (the old age) why I raised the question again here. There remains one question; who or what was SOBAC?

Notes from the late great Edgar:

On the Seafire, this involved a coat of SOBAC primer, thinned 10-30% with SOBAC thinner “applying the thinnest coat possible consistent with complete covering,” with a minimum of 1 hr air drying. “Rivet recesses, joints, etc., require to be levelled by the application, with a thin bladed knife, of I.C.I. putty 147-524. Air dry at least two hours: longer may be necessary in some shops.”

After “dry scuffing” with grade 220 Gydro-durasil paper, two coats of I.C.I. grey filler 146-5 (not absolutely sure of the numbers, they’re almost illegible) thinned around 10% with SOBAC thinners. One coat required 6 hours drying time; if two coats were needed, two hours had to be allowed between them. This was rubbed down again, although a heavily thinned coat of camouflage colour could be applied, first, as a guide. On the Seafire “D.T.D.51 7” drawing, it states that SOBAC Hard Grey Stopper could be used instead of I.C.I. Putty 147-524, and SOBAC Grey Oil Filler instead of I.C.I. Filler 146-5.

I may have answered my own question with something found in another Farnborough report. A report on the trials on a Tempest, MkIX Spit and a Mustang MkIII to improve their performance against the V1 makes mention of the use of ‘Stopping’ and sanding the wing surface prior to repainting.
I use to use Stopping as a filler on the models I made (it was actually sold as a filler for furniture / wood working) as its Cellulose base keyed into the plastic and didn’t flake off when sanded thin. If I had to guess at what it was made from I’d say it was paste of China clay and Cellulose dope, well within the technology of the day of the original 1943 report.

I’ll need to dig but I remember reference to general surface fillers in the Horsa manuals. I think it had some stores references.

One thing I do know is that the Horsa and Hotspur where chock full of Bostik B!

The excellent documentary ‘Lancaster At Coventry’ which follows the last major service on PA474 shows filler being applied to dents in things like the engine cowlings, mainly the doubled skinned items like those for the radiators where it wasn’t possible to get on both sides of the metal to knock the dents out.

I am sure the Nakajima aircraft company used glues / bonding material to attach parts/structures in place of rivets, on many of their WW2, aircraft .
I just need to find the article.

Oh dear, this old P-51 dispute again. The blue was not only seen in the air from the ground, but also seen on the aircraft on the ground by a number of experienced British observers whilst on a tour of the base. These were close acquaintances of the great 8th AF historian Roger Freeman. If he found them convincing, that’s good enough for me. I agree that Olive Drab would be much more logical, but so what? I’m certainly not claiming that it was that particular shade of blue, however.

In the UK Aero Research Ltd pioneered resin adhesives back as far as the 1930’s. I am only guessing but some of their resin mixed with a filler material such as talc or flour would make a paste like substance for filling rivet depressions, nowdays micro balloons are used for that.
https://en.wikipedia.org/wiki/Aero_Research_Limited

Richard

Pop rivets on parts of the Valiant flaps were filled with a cellulose quick setting putty in order to prevent the stem from becoming loose & losing their shear strength of the set rivet. (One of my jobs as an apprentice at Weybridge). I can imagine that type of putty (normally in use for car repairs) as being used to fill dents on repairs.
One must also remember that during wartime there were not many skilled workers so quality of workmanship would be lower.
Keith

I have seen a picture of a museum fixing the droop tail SR71 with Bondo luckily it will never fly again.

Curlyboy

Yeah, the blue never happened

Which of course is nonsense, since by early 1944, metal U.S. aircraft were unpainted.
However, I would not be surprised if some (painted) restored Mustangs/Spitfires don’t have something to smooth their finish.

As you guess, the info on WIX pertains to restored Mustangs, especially those restored in the ’60s or thereabouts. A paintjob like the following could hide a multitude of Bondo sins, not that I’m implying that the following aircraft contains any.

I seem to recall a few comments that suggested no wartime P51s had that baby blue paint on them at all, and that it came from a fancifully misinterpreted description of the aircraft. As I’m not up to speed on US types I really don’t know.

On the P-51:-

The first 40% of the wing chord was sprayed with one coat of zinc chromate primer followed by enough coats of Acme Gray Surfacer No. 53N5 to cover all irregularities. Skin butt joints were then filled with Acme Red Vellunite glazing putty N 58485. The entire area was then sanded and sprayed with one coat of camouflage enamel. When camouflage was deleted, the forward portion of the wing (sometimes the entire wing) was sprayed aluminium.

I remember when we were restoring our Vampire F.1 VF301 at Baginton in the mid 1970s. Having been a ‘gate guardian’ (RAF Debden) for many years it had lots of layers of paint on it – which took lots of paint-stripper. Under the paint was filler – not just for rivet depressions but covering quite large areas. I’m sure I brought this up before but in a discussion on uses/reasons for filler. It’s use on the Vampire may well have been similar to the P-51 – the improvement in aerodynamics overcoming any reasonable weight penalty.

Roger Smith.

Bondo was introduced in the mid ’50s. Prior to that, body fillers contained lead.

That’s true of autos, but aircraft? Lead would seem to be too heavy. Perhaps a different material, after all something was used on aluminum bodied autos of the pre and immediate postwar period?

I’ve read a couple of threads on WIX that suggest a lot of P51s painted solid colours are hiding a lot of Bondo.

Which of course is nonsense, since by early 1944, metal U.S. aircraft were unpainted.
However, I would not be surprised if some (painted) restored Mustangs/Spitfires don’t have something to smooth their finish.

Bondo was introduced in the mid ’50s. Prior to that, body fillers contained lead. I’ve read a couple of threads on WIX that suggest a lot of P51s painted solid colours are hiding a lot of Bondo!