Groundhog Thread Part Deux - P-39 Fantasy and Fetish - The Never Ending Story (Mods take no responsibility for head against wall injuries sustained)

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I am assuming they are not M2's, but some sort of gas operated alternative. Or a very light and modified barrel, light enough to cycle the gun with only gases leaving the barrel
 
Without the resistance of the bullet being driven down the barrel by the expanding gasses, the cyclic rate of the weapon will be affected.
The barrel restrictor helps to maintain a certain amount of gas pressure needed to properly work the MG's firing cycle.

*edit* just saw SR's post with the link - that should have better info than my post
 
In this video, you can see the size of the shell casings. They look like .50s to me. I've shot M2s before.


Compare this to a pyrotechnic replica .50 doing simulated shooting via propane and O2

 
Quite a few restored warbirds have original weapons installed and are functional (where allowed by law).
Their blanks will be actual casings with fully functional primers (electric in the case of German weapons) with a gunpowder load appropiate for blank firing topped off by a wad and are loaded into the belts just as if it were live ordnance.
The weapon functions the same as if it were live: the blank round is loaded from the belt, the blank discharges and the shell is ejected and the next round is loaded into the chamber from the belt during the cycle.

It looks realistic because it is - the only difference is that the aircraft isn't hurling several hundred rounds downrange. The "bang", smoke and cascade of casings is genuine.
 
Milosh said:
But, did Expert use it?
Click to expand...
I had saved the chart for future use, but it would no longer let me make any adjustments. Said my excel subscription had expired, which I never had. Great chart and fun to play with, wish the radio could be included.

As I remember it, as the nose ammunition was expended the CG moved back but never got past the aft limit.
 
Excellent work, and very thorough. Just a note, the radio location issue is only for the 1942 P-39-D/F/K/L models with the lower powered V-1710-35/63 engines to save weight. The 1943 N/Q models had good performance at normal gross weight, no reduction was needed. Although the Soviets did delete the wing guns and IFF radio on most of their P-39s.
 

Thank you - A couple of things

If you get the station of where the radio compartment is located you can calculate the removal of the IFF unit. BTW, you were confusing me calling this area a "tail cone." It's actually an aft fuselage or empennage.

I believe on US aircraft, one of the reasons why you had all or part of the radio unit moved to the shelf behind the pilot was because of the IFF installation. There was only so much room in the radio compartment so the remainder of the comm system had to go somewhere. I believe the area behind the pilot was initially ignored for radio installations were because of RF and heat issues, but that's my opinion.
 
In it's original configuration yes.

Remove the nose armor, expend all the nose ammo and allow fuel to go below 1/4 tank - No
 
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I worked Greg's CG chart again and deleted the nose armor, nose cannon and MG ammunition, wing guns and wing ammunition and the CG was one half inch past the aft limit before any adjustment for the radio in the aft fuselage. Was not able to delete the fuel but it is located on the CG. For some reason was not able to attach the graph to this post.
 
Here's an accurate scale representation of the P-39Q and P-63A.


The P-39Q is 30" 2" long and the P-63A is 32" 8" long. In the above pic, I lined up the front of the exhaust manifolds since they are bolted to the engine. I went to the aft part of the air intake. Note the length added to the P-63 is aft of the windscreen.

As it happens, we have a P-63 in the final stages of work just before first engine run. We also have a P-39, complete with external engine and nose case. I volunteer every week on Tuesday, so I was there yesterday, but I was working on parts for another aircraft. Next week, I'll get measurements of the same areas shown above. Now, our P-63 is not using a 2-stage V-1710, but the engine compartment is stock. The engine we are using is a 100-series and makes about 1,600 hp at full MAP. Of course, it will very rarely see 1,600 hp and will likely be operate at the 1,200 - 1,400 hp max limit when it flies, and only at an airshow at that. Most of the time, it should see that limit only on takeoff and initial climbout.

Easy since we have the subjects right there. Talk with you then.

Cheers.
 

22Gallons of fuel (1/4) tank puts it out of C/G

Now something to consider - This data was taken from the P-39Q flight manual. The manual did not show what radio (or IFF) was installed for weight and balance purposes, that would be specific to the aircraft and found in the maintenance records that follow the aircraft.
 
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