Fabric over Guns?

[VALENGO]

I´ve seem many times an old film showing a close up of a Spit´s firing guns. Something that always have my attention is what seems to be a little piece of fabric in the gun´s mouth. This thing waves ahead with every shot (I guess that the plane was not flying, cause there is not wind backwards).
Well, yesterday I was looking some stuff of the Me163 and I noted this (see picture). If you see carefully you can see what looks like a ripped fabric cover (under a screwed ring) over the MK108´s mouth.
Here the question: any planes had fabric covers over the guns?.
If so, I guess that the support personnel musted replace them after every sortie.
If someone can put more light over this, thanks in advance.

 

[gumbyk]

I have seen the same. to me it looks like some fabric tape or somethign like that.
I had presumed that it was to keep water/dirt out of the gun barrells.

 

[VALENGO]

yes, a protection until the gun is needed.

 

[Airframes]

Quite right. In the R.A.F. at least, squares of cotton canvas fabric were doped over the gun ports (hence the dull red colour). This was not only to prevent the ingress of dirt and dust into the muzzles and barrels, but more importantly to aid in preventing the guns freezing at altitude, due to the effects of 'wet cold'. Basically, this is cold, damp air, being forced down the barrel(s) of the weapons, causing a vapour which froze around the breech and working parts, preventing the guns from firing, or causing a stoppage after one or two rounds had been fired.
Until an adequate gun bay/breech heating system was fitted to the Spitfire (and, of course, other types), this was the only way of trying to prevent the problems of gun operation at altitude. Even when heating ducts were fitted, the fabric patches were still used, and these were replaced after each sortie, during the re-arming and re-fuelling of the aircraft.
Depending on the type and arrangement of an aircraft's armament, the fabric patches were often replaced by discs of waxed, or similarly coated card, or thin rubber membranes, over the muzzles.

 

[VALENGO]

so, when we make a plastic model is allowed show guns covered with discs or squares.
Well, enough for me, thanks for the info, airframes.

 

[Airframes]

You're welcome. Just check reference pics for the type/size/colour etc of any patches/caps on the particular type of aircraft.

 

[Capt. Vick]

It would be interesting to see if someone could find an operational picture of the Komet with the "patches" clearly in place over the cannon ports.

 

[stona]

The square patches on the Spitfire were self adhesive fabric.They functioned exactly as described by Airframes,Spitfire guns being heated by exhaust heat,not electrically. When replaced they also served to warn ground crew that the aircraft was re-armed and the guns cocked. i.e. don't fiddle about in the cockpit and avoid walking in the line of fire. They also served to indicate to the ground crew whether the guns had, or had not, been fired after a sortie.
The cannon on British fighters wore rather fetching red "condoms" for the same reasons.
Steve

 

[Colin1]

It would be interesting to see if someone could find an operational picture of the Komet with the "patches" clearly in place over the cannon ports.

Me163A and B. Taken soon after the first of the Klemm-built aircraft was delivered to Bad Zwischenahn in January 1944. Masked cannon port visible on the nearer Me163B.

 

[VALENGO]

Colin1, I thought that I´ve seen every single picture of the komet, but the one you uploaded is new for me. Thanks.

 

[Colin1]

Colin1, I thought that I´ve seen every single picture of the komet, but the one you uploaded is new for me. Thanks.

It could have been better
but I need to buy some scanning software instead of running 30-day trials
I can scan it but can't save it, I then have to close the app, open MS Paint and take it from there.

There were actually two photos but the other one didn't come to much.

 

[wheelsup_cavu]

Cool photo Colin.


Wheels

 

[hawkeye2an]

That's a new one for me to, thanks.

 

[timshatz]

I always thought they used duct tape or something similar.

 

[ppopsie]

In case of the Spitfire NACA tested stall characteristics of the Spitfire V with and without tape covering on the wing gunports. The report says the characteristics became worse with the tape removed.
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930092582_1993092582.pdf

Also I believe the dimensions of the aircraft indicated in the report to be reliable.

 

[gumbyk]

Makes sense. The gun ports would set up turbulent airflow over the wings at high angles.

 

[drgondog]

The 355th used duct tape - strictly for keeping debris out of the barrels.