YFM-1 Airacuda

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Zipper730

Zipper730

Chief Master Sergeant
4,320
947
Nov 9, 2015
I'm not sure where to start on this: I've heard so much conflicting data on the aircraft that I figure I should just start a thread and ask people what they know about it.

I've heard the following about it
  1. Flying-Gunship: There was an idea that, from what I remember, involved modifying a Martin B-10 series aircraft with extra gunners to allow it to provide better defensive firepower for bomber formations
  2. 1934 Combat Exercises: After these exercises, there seemed to be an interest in more firepower than speed in aircraft, possibly the ability to fire at greater ranges.
  3. Super-Fighter: In 1935, a proposal from Captain Harry Johnson was submitted that called for a heavily-armed super-fighter capable of destroying bombers. It would be called FM (Fighter Multi-place)
  4. Design C: It apparently was some kind of design that included a cannon-equipped aircraft, long-range for standing-patrols, and bomber-escort capability
That said, I'm curious if anybody has anything involving
  1. The details of the 1934 combat-exercises: Particularly those that entailed bomber-defense (assuming that wasn't the nature of the whole exercise), and why they would have arrived at the conclusion for firepower over speed? Almost all other air forces either focused on speed, or speed and firepower together...
  2. The exact specifications for the "Design C" called for by the USAAC? I'm curious what the design called for, so I can compare what came out of it (The Bell YFM-1, and Lockheed YFM-2)
  3. The heavily-armed super-fighter proposal capable of destroying bombers: Was this part of Design-C, a refinement of it, or something that was folded into it?
M MIflyer , S Shortround6 , W wuzak , X XBe02Drvr
 
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Zipper730 said:
I'm curious how much of this document is true: The size of the anti-aircraft bombs seem similar to the size of some anti-personnel bombs that were proposed for CAS missions by the USAAC.



GrauGeist GrauGeist , Micdrow Micdrow , M MIflyer , W wuzak , X XBe02Drvr
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It amazes me that anyone thought this Airacucumber would actually go 300 MPH. Fat Albert personified.
This must have been dreamed up by MacNamara's grandaddy. Another chapter in the eternal quest for the holy grail.
 
Note that the RAF thought up the Bolton Paul Defiant at the same time. Neither the US nor the U.K. thought it was possible that attacking bombers would have fighter escorts and they tended to see destroying inbound enemy bombers in naval terms - applying the most amount of firepower to the bomber formation. The RAF's standardized attacks were designed to do the same thing in order to put the maximum number of guns on the enemy formation.
 
I have long been a fan of the XFM-1/YFM-1 Airacuda because of it's uniqueness, not it's performance. I have downloaded a considerable number of photos, many from this forum, and have marveled over the many modifications done with the 13 airframes. May I call your attention to only the engine carb intakes for example. Some of the video shots show flush intakes (9:04) of six slots on top of the engine cowling. The engineers apparently didn't consider boundary layer. Elsewhere can be seen a simple scoop added which must have caused airflow problems. The final air intake is over the gunner's cockpit and blends into the nacelle. There are many still shots showing different nose shapes, different side windows/blisters and the top retractable turret mid fuselage. The nose wheel mod was from within the 13 only aircraft.
 
special ed said:
The engineers apparently didn't consider boundary layer.
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Yes, and neither did anyone else in that era. When the P-51 and the P-38 first came out there was no lip between the fuselage and the cooling air intakes. They did not appreciate the effects of a boundary layer. The lip they added to the cooling intakes of the P-38 enabled them separate the boundary layer and to get better cooling with the same sized radiators. On the P-80 they added a splitter plate to the jet engine air intakes to separate the boundary layer. By the way, the boundary layer on the P-80 was used to cool the air conditioning system.
 
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I recall an article from Wings/Airpower that I probably have somewhere that revealed that if they feathered the props they cut into the trailing edge of the wing. They needed prop shaft extensions.
 
What I'm curious about is the following, from a purely technical standpoint
  • Given that the gyroscopic system was based on an anti-aircraft gunnery platform: What kind of gyro did it use?
  • Was it possible to have produced a gyroscopic gun-sighting system with the technology of the time of the aircraft's development to the pre-production stage that could have allowed the system to be operated with simply the pilot alone?
  • The two gunners could operate the guns as a backup, but their primary role was to feed belts of 37mm rounds into the cannon: Was there any need for this? Did we have the knowledge in the United States to produce a feeding system that would have allowed the full ammunition capacity intended without the need for multiple belts to be fed into the cannon without jamming?
 
Zipper730 said:
Given that the gyroscopic system was based on an anti-aircraft gunnery platform: What kind of gyro did it use?
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Are we talking flight instrument gyros here, or some sort of fire control system? Remember, Jimmy Doolittle's instrument flying escapades were relatively recent history, and the technology was still in the development and tweaking phase.

Zipper730 said:
Was it possible to have produced a gyroscopic gun-sighting system with the technology of the time of the aircraft's development to the pre-production stage that could have allowed the system to be operated with simply the pilot alone?
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Fully functional remote control turrets were still nearly a decade in the future. I suspect the only viable option might've been fixed forward firing cannons as in conventional fighters of the time.

Zipper730 said:
The two gunners could operate the guns as a backup, but their primary role was to feed belts of 37mm rounds into the cannon: Was there any need for this? Did we have the knowledge in the United States to produce a feeding system that would have allowed the full ammunition capacity intended without the need for multiple belts to be fed into the cannon without jamming?
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I think we might have had the conceptual knowledge. Whether that would translate easily into reliable hardware is another question entirely. When I went to work at GE, the trash bins were littered with the detritus of failed iterations of feed mechanisms for the Vulcan cannon and Minigun. Every new application required a reengineered feed mechanism, and every new feed mechanism developed it's own unforeseen catastrophes. When feedpath turning sprockets start punching holes in 20MM cartridge cases and spraying propellant around next to a gun firing 6,000 rounds/minute, it makes a mess. The insides of the test range firing stand shelter huts looked like war zones.
 
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I would assume that any control system for the 37MM guns on the Airacuda was similar to that used on ships, where the gyro platform defined "Level" and adjusted the guns to compensate for the rocking of the ship. You would see the guns moving up and down before they fired and in reality that was the barrel remaining "level" while the ship moved under it. This same approach was adopted for tank guns. Our tanks did not have to stop to fire but could fire on the move even as the tank pitched and rolled over rough terrain.

Of course later in the war the K-14 gyro stabilized gunsight for fighters was installed in some aircraft, and that automaticaly computed the required lead on the target. After WWII the APG-30 was used on the F-86 and F-84; it used the radar to determine the distance to the target for computing the lead.

I recall reading about the difficulty they had using the turret on the P-61. They could not hit anything with it, but then a highly experienced enlisted man had an idea. When firing at attacking fighters the normal procedure was to lead the target. But the P-61 was moving faster than the target so you had to aim BEHIND the target aircraft.
 
XBe02Drvr said:
Are we talking flight instrument gyros here, or some sort of fire control system?
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Fire-control system: It was used for controlling the guns. While I could be wrong, the turrets were generally controlled from the cockpit, but as a backup, could be controlled from the nacelles.

MIFlyer said:
I would assume that any control system for the 37MM guns on the Airacuda was similar to that used on ships, where the gyro platform defined "Level" and adjusted the guns to compensate for the rocking of the ship. You would see the guns moving up and down before they fired and in reality that was the barrel remaining "level" while the ship moved under it. This same approach was adopted for tank guns. Our tanks did not have to stop to fire but could fire on the move even as the tank pitched and rolled over rough terrain.
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Was this gyro a gimbal system? Was there ever serious issues with the matter of tumbling the gyro?
 
Zipper730 said:
Was this gyro a gimbal system? Was there ever serious issues with the matter of tumbling the gyro?
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If this was based on a shipboard artillery stabilizing gyro, I would expect it to have those issues. The range of motion of a fighter plane is a bit broader than that of a battleship. OTOH, the Airacucumber looks more like a battleship of the sky than a fighter plane, so maybe not an issue. The early 50s gyros in our club's T34 would tumble at the drop of a hat if you exceeded 60° in roll or 30° in pitch and forgot to cage them.
 
There are basically two kinds of gyros:

1. Rate gyros, that can tell how fast you are going in a particular direction. Turn Rate indicators in aircraft are rate gyros. They don't really tumble very easily.

2. Integrating Gyros that have to be set to a reference and can tell you how far you have turned, side to side and up and down. They can be tumbled.

It should be theoretically possible to analyze the data from the integrating gyros to compute the turn rate but that does not always work.
 
Zipper730 said:
M MIflyer

Do you know which type of gyroscopic system would have been used for the fire-control system?
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If you think about it a bit, the answer becomes obvious. Rate gyros (aircraft rate of turn instrument) rely on the gyroscopic property of precession, while the integrating type utilize the property of rigidity in space. Now which do you think would more useful in providing a stable platform for aerial gunnery?
 
XBe02Drvr said:
If you think about it a bit, the answer becomes obvious. Rate gyros (aircraft rate of turn instrument) rely on the gyroscopic property of precession, while the integrating type utilize the property of rigidity in space. Now which do you think would more useful in providing a stable platform for aerial gunnery?
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Given that you used the term "stable platform for aerial gunnery", I'm guessing integrating type.

That said, the British did use rate-gyros for gunnery.
 
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