29 March, 2010

PROFILE 41: "OLD CROW" update

If it weren't for insomnia, I wouldn't make any progress'tall.

More than a few eyes are on this project, so I thought to post this newest update.  I'll mask in a new wing later this week and make whatever changes/suggestions that Bud says need to be done.

But, I did get some input from my friend Jim, an armorer who worked on B model Mustangs in England during WW2.   Unfortunately, his comments had nothing to do with the art, but with the structure of the actual airplane.  Specifically, the gun mounts in the wing.

The P-51 series featured a wing design strategy that created "Laminar Flow."   Without getting too geeky, on a traditional wing, turbulence between the surface and air flow creates drag at the bulky leading edge.  Laminar Flow philosophy moves the thickest part of the wing back towards the middle, creating a smoother surface for air to flow across, reducing drag and maintaining efficient lift at various speeds.

With me?  Yeah, I'm lost too.  Just nod your head.

Anyway, this wing design made it a challenge to effectively mount the 4 .50cal Brownings within the limited space created by utilizing Laminar design theory.  So, the engineers tilted the guns, lowering the height needed but also forcing the ammo belt to make a little "up and over" into the gun breeches.

These guns would fire at about 750 rounds/minute.  Some more, some less.  But you can imagine the the importance of having an uninterrupted, even flow of bullets.  The barrels truly were 'garden hoses that sprayed lead.'  Wings level, in warm air, the guns chattered just fine.  But, in twisty, high-g combat at altitude, the ammo feeds would get fouled and stoppages would occur that couldn't be fixed until the pilot made it back home.

Jim explains how various Groups tried to solve this problem in the field.  One took the motorized feed units from B-17 waist guns and put them into the wings (at a substantial weight penalty).  But he remembers replacing feed springs, cams and actuators with items of higher tolerance.  This work resulted in a feed mechanism that was less likely to deform during high-G stresses or react to the profound cold of 20,000 ft + altitude temps.

On a personal level, this info is so much more than anecdotal.  Understand, the P-51B was a major weapon of war with a serious flaw solved by the acumen and ingenuity of individuals.  When I hear - from the source - of a man's work, in the moment, on the spot, I get inspired that my own issues can be solved with the same application.

Cool, huh?

I'll be finished with this one in about 2-4 days.  Stay tuned...