FLYBOYJ
"THE GREAT GAZOO"
How far do you move the IFF? You need an exact distance in inches to know how its going to effect the c/g. It's not that simple, but please go on.
XP-39 II - The Groundhog Day Thread
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fastmongrel
1st Sergeant
An example of how things were similar but different. The UK at the same time had 29,000 locomotives, 0.75 million freight vehicles and 19,000 route miles 50,000 total miles of track. 1.2 billion passenger journeys and 92 million parcels. Clapham junction was (and still is I think) the busiest station in the world with a train movement every 5 seconds at peak times.
so much smaller but more intensively used. Mind you most British locomotives would have fitted into the tender of a UP behemoth with room to spare.
FLYBOYJ
"THE GREAT GAZOO"
And the weight and balance charts that show this? As a teacher once told me, "show me the math!"
I get the feeling that some people believe W&B and CG is a simple task, when there really is a science to it. You cannot simply take weight away from somewhere, and add some weight here. When I was on 2nd shift working as an A&P I had to work with QC quite a bit doing them after modifications had been performed. I always enjoyed it.
When at the end of May 1940 Italy was on the verge to declare war to G.B. and France, Italo Balbo was desperate, as in Italy public opinion clearly knew that U.S. would have not remained idle in supporting the British:
"The Duce has never seen the size of the phone book of New York!" he repetedly told his staff.
Probably the phone book of Rome in 1939 was some one hundred pages, that of N.Y. a couple of thousand if not more...
Peter Gunn
Master Sergeant
Gentlemen,
I believe you ALL are going about this issue of lightening the P-39 to get a better climb rate out of it the wrong way. I mean, I have no training in aerodynamics or engineering but ye gods and little fishes but you guys are dense. The answer is soooo simple:
I mean... DUH!
I believe you ALL are going about this issue of lightening the P-39 to get a better climb rate out of it the wrong way. I mean, I have no training in aerodynamics or engineering but ye gods and little fishes but you guys are dense. The answer is soooo simple:
I mean... DUH!
FLYBOYJ
"THE GREAT GAZOO"
I pulled some other charts from what I can find on the internet. It seems that the P-39N used a %of MAC for it's CG envelope, the P-39Q uses inches aft of a datum line which I believe is at the nose of the aircraft. I see similarities between both models and can probably "interpulate" a C/G range. I have more info but let's see what our friend comes up with.
wuzak
Captain
I still want to know why the Russians didn't remove the nose armour after they removed the IFF.
And I still believe the IFF was kinda important for operators other than Russia!
FLYBOYJ
"THE GREAT GAZOO"
Hard to say but from I got from the P-39D W&B chart, the CG range was between 23 and 31 % of MAC. The Chart shows 3 loading configurations operating between 28.9 and 29.5 % of MAC which is not only a tight envelope but shows the aircraft tail heavy. My guess would be to make the aircraft more nose heavy.
P-39 Expert
Non-Expert
CG location is shown on the drawing you furnished in post #286.
FLYBOYJ
"THE GREAT GAZOO"
Yes it is shown - So tell us, what's the value? You don't calculate W&B on a pictorial image with no value.
P-39 Expert
Non-Expert
Yes the Russians removed the IFF radio that weighed about 120lbs from the tail section and didn't remove the 100lb nose armor. According to some folks on here the plane should have immediately fallen out of the sky.
Why would the IFF radio be important to the AAF and not the Russians? I don't know.
I read somewhere that German spies in the US reported back to Germany on the size of American locomotives like the Union Pacific Big Boy and the Germans simply thought they were lying.
FLYBOYJ
"THE GREAT GAZOO"
It possibly can, but again the c/g calculation will show if this is possible.
Hello FLYBOYJ,
I did these calculations off the P-39Q chart a couple years ago when I was working on a design project for the P-39.
These numbers might be helpful in interpreting the values from the P-39Q chart:
The Leading Edge of MAC is at Fuselage Station 111.56 inch.
(LE Wing Root to LE MAC is 5.41 inch.)
MAC is 80.64 inch.
CoG at Basic Weight + 200 pound Pilot is at Station 135.88 inch.
That would make it 30.16% MAC.
I specified the pilot weight because it makes a significant difference and it ain't goin' nowhere without the pilot.
- Ivan.
FLYBOYJ
"THE GREAT GAZOO"
Excellent Ivan!!!
My calculations are about the same. I'm going to assume that the P-39Q carries the same CG range of 23.0 to 31.0% of MACas the P-39N. Assuming 23.0% of MAC = at station 111.56, 31.0% of MAC should be 140.98?
FLYBOYJ
"THE GREAT GAZOO"
P-39 Expert - If you understand any of this feel free to chime in.
Hello FLYBOYJ,
Station 111.56 is Leading Edge of MAC, so it would be 0% MAC.
Here is how I arrived at %MAC:
Station in inches - Station of LE MAC / Length of MAC
so
140.98 - 111.56 = 29.42 inch
divided by 80.64 = 36.48% MAC
31% MAC would be 24.9984 inch so it would be
24.9984 + 111.56 = 136.5584 inch.
- Ivan.
FLYBOYJ
"THE GREAT GAZOO"
Going back to check my math.
So the T/E of MAC would be Sta 192.2 (111.56+80.64)
So the most aft CG 31% of MAC is at 136.5584
so 23% of MAC would be 125.63~? (a rough calculation, I'm in a meeting)
23% MAC would be 130.1072 inch
80.64 inch * 0.23 = 18.5472 inch from LE MAC
18.5472 + 111.56 LE MAC = 130.1072 inch
My Daughter would be screaming at me for significant figures right about now!
- Ivan.
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