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Hi Dave -While investigating a P-39Q crash site, it was discovered that the propeller had bullet holes in it and the plane shot itself down with its own .50 cal. The Plane was on a practice straffing run at the time. I have read that U.S. airmen complained about the P-39 slow synchronized rate of fire for the browning .50 Cal (12.7 mm) averaging around 300 r/m.
Questions: Anyone ever heard of a ww2 P-39 .50 cal. synchronization problem?
What is the synchronized rate of fire for the .50 cal in the P-39Q?
Anyone heard of a P-39 shooting itself down?
Yes, I do have the accident report. The P-39 was underwater until recently. It is in process of recovery now. They recovered the propeller and that is when the bullet holes in the prop were discovered. The official accident report only mentions that parts/debris were witnessed coming off the front of the plane before it dived into the lake. the official cause was listed as mechanical failure unknown cause.Hi Dave -
A few things - do you have an accident report that specified that this aircraft shot itself down? Just because the synchronization failed and a round went through the prop doesn't mean immediate failure. I read at least one occasion where synchronization failed on a fighter and a hole was shot through the propeller and the plane continued to fly (and was not immediately repaired!) This was mentioned in the book "Some Still Live" by Frank Tinker, the aircraft was Soviet I-15. Now if a major portion of the prop was shot away or if the prop strike resulted in the prop gearbox to fail, then absolutely.
I read somewhere about some synchronization issues with the P-39's nose .50s, but it was isolated and due to poor maintenance.
I'll try to look around for it, as you probably know we have a huge tread on the P-39, some good information, some gibberish, there might be mention about this happeningYes, I do have the accident report. The P-39 was underwater until recently. It is in process of recovery now. They recovered the propeller and that is when the bullet holes in the prop were discovered. The official accident report only mentions that parts/debris were witnessed coming off the front of the plane before it dived into the lake. the official cause was listed as mechanical failure unknown cause.
"I read somewhere about some synchronization issues with the P-39's nose .50s, but it was isolated and due to poor maintenance." I badly need this reference!
More on the accident and its historical importance: P-39Q, Serial Number: 42-21226, Pilot: Moody, Frank H, crashed into lake Huron. Moody was among the Tuskegee Airmen, America's first black military pilots.
The state of Michigan is doing a full recovery of the wreck. Pictures and story available upon request or I can post here.
The bullet holes are level with the guns at about 9 inches above the hub and in a limited area. see next reply including a picture.Also , if it was the synchronization issue the damages should be at the same level and quite limited area. If the bullet holes are not concentrated these could be caused by another factor rather.
thanks I also found that statement. You are most likely correct that it was during an interviewHI Dave -
I've been looking high and low and I can't find that piece about a synchronization failure on the P-39, I'm sure it was mentioned during a pilot interview. I found the same statement about the ROF from this site:
Bell P-39 Airacobra - fighter
The complaints by U.S. airmen about the slow synchronized rate of fire for the browning .50 Cal (12.7 mm) P-40B cowl guns averaging around 425 r /m made the P-39 look bad at 300 r /m while the Soviet synchronized 12.7 mm UBS fired over 800 r /m each!
A practical example of the effect of synchronisation is graphically provided by comparative tests held by the USN in 1926/7 of the .30 inch (7.62 mm) M1921 and .50 inch (12.7 mm) M1921, both on a test stand and in synchronised mountings. These also shed some light on the differences between claimed and actual rates of fire, and between different installations of the same gun. The .30 had a claimed RoF of 1,200 rpm, but proved capable of between 800 and 900 rpm on the test stand. When synchronised, the RoF went down to an average of 730 rpm (a fall of about 15%), with a range of between 667 and 818 rpm for different installations and propeller speeds. The .50 had a claimed RoF of 600 rpm, and did rather well to achieve between 500 and 700 rpm, depending on the recoil buffer adjustment (although a contemporary British report put this at 400-650 rpm, the difference possibly caused by belt drag when installed), but this fell to an average of 438 rpm when synchronised, varying between 383 and 487 rpm. As the synchronised guns were adjusted for maximum RoF, this represented a reduction of around 37%. There is no inherent reason why a larger calibre weapon would suffer a bigger reduction in RoF, so the synchronisation conditions must have been better suited to the .30 in gun's natural RoF.
message sent regarding this issueI have an article on aircraft gun synchronisation on my website here: https://www.quarryhs.co.uk/Synchro.pdf
This includes the following:
by all information that I have, the P-39Q was the slowest RoF for the synchronized guns and pilots complained about it. The question is what made it the slowest? It appears the design was at fault and different from the others.I do not know if the following information might shed light on the issue re the P-39's .50 cal synchronized gun ROF, but here it is:
P-400/P-39D/F
V-1710-35(E4) engine.
Propeller reduction gearing was .556:1 and synchronizer gearing was .556:1, both relative to crankshaft speed.
P-39K/L
V-1710-63(E6) engine and P-39M with V-1710-83(E18) engine.
Propeller reduction gearing was .500:1 and synchronizer gearing was .500:1, both relative to crankshaft speed.
P-39N/Q
V-1710-85(E19) engine.
Propeller reduction gearing was .449:1 and synchronizer gearing was .449:1, both relative to crankshaft speed.
All of the above P-39 engine arrangements have the following entry re the Gun Synchronizer Impulse Generator:
View attachment 677872
When compared with the other airframes fitted with the V-1710 and synchronization gear:
P-40B/C
V-1710-33(C15) engine.
Propeller reduction gearing was .500:1 and synchronizer gearing was .500:1, both relative to crankshaft speed.
View attachment 677873
View attachment 677877
Mustang Mk I
V-1710-39(F3R) engine.
Propeller reduction gearing was .500:1 and synchronizer gearing was .500:1, both relative to crankshaft speed.
View attachment 677874
A-36A
V-1710-87(F21) engine.
Propeller reduction gearing was .500:1 and synchronizer gearing was .500:1, both relative to crankshaft speed.
View attachment 677875
If we assume that the information posted up-thread by daveT (re the ROF for the P-40B nose guns is approximately 425 rpm) and by A.G. Williams (re the ROF range of 383 - 487 the British reported) then we get the following theoretical ROFs:
P-40B/C__________425 rpm
P-400/P-39D/F____473 rpm
P-39K/L__________425 rpm
P-39N/Q_________ 382 rpm
Mustang Mk I_____425 rpm
A-36A___________ 425 rpm
For a range of 382 - 473 rpm.
Maybe?