Not under legs, but in the belly of the A/C, where the central tunnel for the air was on the P-47.
Allison V-3420- Anyone have information on it? It seems like it would have been perfect for the XB-42.
- Thread starter Kilkenny
- Start date
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GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
The pilot in Tomo's proposal would be better protected than in in a P-39/P-63, since the fuselage of a P-47 (or derivative) is much larger with the cockpit situated higher.
That might be true but I don't like the idea of a big piece of pipe spinning at high RPM running passed me.
GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
The P-47's cockpit floor (and other areas) is protected by face-hardened armor.
Something the P-39 did not have.
Additionally, a power take off shaft would not be as robust as the drive shaft used in the P-39/P-63, therefore being less of a threat to the pilot in the event of catastrophic failure.
Shortround6
Major General
The P-39s drive shaft went through a "donut" in the control column.
I sure hope there was a sheet metal tube around the drive shaft to keep anything floating around from getting tangles in it.
GregP
Major
It never was a problem in service.
Even though there were two output shafts emanating from certain versions of the V-3420, including the engine on the P-75, the shafts were internally linked by gears inside the case. Therefore, the independent control of the two propeller discs (feathering; reversing; rpm) and operation on a single engine would have been lost.Why would changing to a V-3420 change the propeller system?
The V-3420 could be configured with a single rotation propeller, or dual rotation, as in the Fisher XP-75.
The Fisher P-75 system is pretty much would have been used in teh XB-42 had they opted for teh V-3420 instead of twin V-1710s. The main difference being that the XB-42 was a tractor arrangement, the XB-42 a pusher.
The engine and driveshafts can be seen in the 3rd photo down on this page:
Allison V-3420 24-Cylinder Aircraft Engine
The Allison V-3420 24-cylinder engine was more than just two coupled V-1710s. The large engine showed promise, but other priorities and a lack of aircraft applications regulated the V-3420 to obscu…oldmachinepress.com
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wuzak
Captain
Pitch control (including feathering and reversing) of the propellers could still be independent. If it was desired.
Single engine out and different rpm would not be possible.
The P-38 could use differential throttle to help with turns, but this does not apply to the XB-42, since its props were on centreline.
The biggest issue with using the V-3420 (apart from availability) was the engine out situation.
GregP
Major
In actual operation, including training, and combat in U.S. service, no P-39 or P-63 driveshaft ever failed and injured a pilot. If the aircraft hit the ground nose first, the engine stopped as it passed through the pilot's body on the way to the ground, and if it hit other than nose first, the pilot was dead anyway. In accidents where the pilot survived, nobody was injured by a driveshaft. If a Soviet pilot was injured by a driveshaft, I have never seen or heard it described, and I have spoken with 6 Russian or former Soviet pilots about the P-39 / P-63. Two had flown both.
That said I'd like to have a sheet metal shroud over it, too, if I were going to fy it.
Just as info, Yanks Air Museum is very close to the first post-restoration flight on our P-63A Kingcobra. Starts and runs great. It has already done a high-speed axi run that raised the nosewheel. We're working on a few last-minute things that cropped up, including some brake work (slight dragging) and one aileron linkage that had a small issue. Almost there! Soon, now.
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pinehilljoe
Senior Airman
- 741
- May 1, 2016
When you look at the V-3420, and sheer complexity, I think Frank Whittle's invention came at the right time. Its hard to think of more complexity added to an aircraft engine, vs. Whittle's design with one moving part. The aircraft IC engine reached its peak.
wuzak
Captain
Gas turbines (jets) are internal combustion too.
GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
I read that as "piston powered" engines.
His statement, however, is true.
They could build the most powerful inline or radial in history, but unless the mach issues generated by the prop tips are solved, won't be able to provide any real advantage in speed.
His statement, however, is true.
They could build the most powerful inline or radial in history, but unless the mach issues generated by the prop tips are solved, won't be able to provide any real advantage in speed.
Shortround6
Major General
The V-3420 was small potatoes.
It was things like this that scared engineers into gas turbine engines.
3 tons, 36 cylinders, 7755 Cu in 5,000hp.
It was things like this that scared engineers into gas turbine engines.
3 tons, 36 cylinders, 7755 Cu in 5,000hp.
GregP
Major
And it meshes very well with late-model Merlins that were also run near the end of the war.
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GregP
Major
Why not? The Soviet Bear used BIG contraprops and they were at almost an absurd pitch angle. That aircraft, clean, could hit 575 mph. If the Merlin made more power, then they could run the propeller at higher pitch.
At 20,00 feet, the speed of sound is 706.9 mph or 1,036.787 ft/s on a standard day.
Say you are in P-51D mustang (11 foot diameter prop) going 450 mph true airspeed, turning 3,000 rpm, with a prop reduction gear of 0.5, making Omega equal 157.0796 radians per minute.
Your forward velocity is 660 ft/s ([450*5280]/[60*60]). Your radial velocity is 495 ft/s (V = omega r, with r = 5.5 ft). Square them both, add them up, and take the square root to get tip velocity, which turns out to be 825 ft/s., or Mach 0.7957. You could hit 514 mph before your prop tip speed reaches Mach 0.87, which is nearly ideal, assuming you have the power to turn the engine at 3,000 rpm with the prop pitch set to give 514 mph. Since the prop has an efficiency (assume 0.90 or so), it would likely have to be pitched to give 560 mph or so, making it even harder to turn, but that is just power. We are assuming a more powerful Merlin, V-1710, V-3420, etc., so let's say we have the power.
Let's say we go 450 mph with a Merlin making 1,490 hp. Using the old tried and true formula for new top speed with new power, assuming no increase in drag, I get that we'd need 2,220 hp to go 514 mph. That's possible. The Mustangs at Reno were making 512 mph or so around the Unlimited course (8 miles) making about 3,800 hp, but that course is NOT a straight line. It's pear-shaped and the power required goes way up as you load the airplane. Real in-cockpit camera recorded up to 4.5 g's or so around the course, so the 2,220 hp for 514 mph in a straight line at 20,000 feet sounds plausible to me. The P-47J went almost that fast on similar power, and the P-51H and lightweight Mustangs weren't far from that speed.
Just thinking out loud, Graugeist, not trying to argue.
I've been wrong enough times before to make that a non-starter.EDIT:
I checked both the Merlin 61 specs and my spreadsheet. I'm not the world's best typist and made an input error (shock). Also, the actual Merlin 61 reduction gear was 0.42 : 1, not 0.50 : 1. That moves the Omega to 131.9469 rad/s. Multiply that by 5.5 and you get 725.7079 ft/s. Square that and the forward speed (660 ft/s), add them up and take the square root to get a tip speed of 980.944 ft/s, or Mach .946. The Mustang is unlikely to go faster without changing the reduction gear to decrease the prop rpm a bit. That would be possible, but only by Rolls-Royce. The average field unit didn't have different reduction gears to put into the nose case. They had spare engines, and factory parts, but not custom reduction gears.
To get to Mach 0.87 at the prop tip, you'd need to have a reduction gear of 0.3565. Possible, yes, but unlikely during wartime when jets were showing such high-speed promise. The alternative would be to decrease the prop diameter. To get to Mach 0.87 tip speed with the standard reduction gear, you'd need a prop with diameter of 9.338 feet. Now THAT would be possible in the field, assuming the prop pitch is or could could be adjusted for the new speeds. In fact, both Strega and Voodoo are running props that are undersized compared with a stock P-51 prop.
I've never measured either one or asked about the diameter, but HAVE heard they were shorter than what could be certified in the Limited Category. Hence, they are both classified in the Experimental Exhibition category, if only by propeller choice. Of course, they have both been modified to the point where they'd have to be rebuilt back to stock to be able to even THINK about a Limited Category certification, never mind the propellers.
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pinehilljoe
Senior Airman
- 741
- May 1, 2016
It also comes down to air for combustion. The amount of air and hence oxygen is limited by the cylinder displacement in a conventional piston IC engine. The jet engine's intake as a general rule of thumb brings in 80 times more air than a piston engine of comparable size, and horse power is enormous, all done with one moving part. Mr. Whittle's idea was really a paradigm shift.
GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
Whittle and Von Ohain were able to successfully build a working jet engine, but the design was proposed and patented in the early 20's by Maxime Guillaume.
Metallurgy and and the ability to machine materials needed, advanced considerably in the decade following Guillaume's patent - had the materials been available then, the French would have most likely had the first turbojet engine well before WWII.
Metallurgy and and the ability to machine materials needed, advanced considerably in the decade following Guillaume's patent - had the materials been available then, the French would have most likely had the first turbojet engine well before WWII.
GregP
Major
Here's the cockpit of a P-39:
The driveshaft is right there, between your legs. If your trousers get wrapped around it, you're in some difficulty, for sure. Didn't happen in practice, but the possibility was there.
Here's the cockpit of P-63:
The driveshaft is in the same place, but there is a sheet metal shield around it, making it much better from the standpoint of getting a strap or other item wrapped around it somehow.
Cheers!
SaparotRob
Unter Gemeine Geschwader Murmeltier XIII
Is that why the P-39 pilots were wearing shorts in all those phots?
See the best part of the conversation:
IOW - drive shaft specific to the P-39 is never mentioned.
