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Why don't they put all the prop blades together to leave more space to shoot through?It might. I don't KNOW one way or the other. However the Germans used electric synchronization. Electric currant feed through the bolt ignited an electric primer in the cartridge.
I think the theory was that it allowed tighter control of when the cartridge fired vs mechanical or hydraulic synchronization (which operated a sear that released the firing pin to hit the primer. more "dead time"? or variation?
In any case a DB engine turning 2700rpm and using a 0.53 reduction gear had a prop turing 23.85 rpm per sec while a MG 131 machine gun fired at 15 rounds per second. Or on shot every 1.59 revolutions of the propeller. This seems a bit odd and perhaps the gun fired every 1.66 revs ( between the 5-6 propblade to pass by?) Gun firing speed can vary due to spring tension and temperature so things get screwed up even more which is why positive control of the instant of firing is so important.
With a 20mm cannon the prop might make two full turns for each time the gun fires.
Granted 4 blade props give less "opportunity" but I don't really know if they fired the guns when ever the gun was loaded and space came up between blades or if the gun just fired an a certain spot in the crankshaft rotation. I don't know how the Germans did it but the Allison used synchroniser drives off the camshafts.
They also needed to fire a couple of heavy machine guns through the propeller disc. Using wider three blade propellers to absorb the increasing engine power, rather than increasing the number of blades may have made the armament more effective, and the interrupter system simpler or more reliable.
Part of the reason for picking a propeller with fewer blades might be the belief in the theory that a propeller with more blades is less efficient.
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The Spitfire used a NACA 2200 series airfoil which meant that it had decent lift and gentle stall characteristics but unfortunately also generated more drag than most.
The Yakovlev fighters typically used a Clark-Y with pretty similar characteristics to Spitfire.
Great post Tomo but it should be borne in mind that some of these were choices. The original prototype Spitfire had covered wheels, they reverted to covered wheels with the Mk 22. The prototype also didn't have an armoured windscreen, whereas the angle of the windscreen is known to be poor from a drag point of view we must remember you also have to see through it. The mirror was introduced and then removed. The finish of aircraft improved as things progressed but there is a financial and time cost associated, for example flush rivets are better but cost more and take more time. The fit up of panels became increasingly important but this is frequently part of the basic design and system of manufacture.Spitfire used the wing that was 13% thick at the root, it's wing was as of low drag as realistically possible on military aircraft designed in late 1930s. There was several posts and thread here where Spitfire was measured with highest dive speeds for non-jet aircraft.
Things that were slowing down Spitfire were items like external BP glass, not covered U/C, bad carburetor, bad layout of exhust stacks, presence of rear wiev mirror, sometimes sloppy fit and finish. As time went on, those things were rectified. The radiator system was to wait until the advent of Spiteful.
Yakovlev's fighters were small, this is where from the reasonable performance came from. Does not equate with low-drag wing.
I discussed this many years ago in another forum. More blades give an more even distribution of the power, but apparently they perform less well when it comes to compresibility in the blade tips. I never researched the subject more, maybe someone can provide more information.
We all know about CL. Yet the WWII designers were all trying to optimize their pet fighter, and the CLs were often very close. So, wing loading is a good indication of general maneuverability. Doesn't tell the whole story, to be sure, but can serve as a good indicator. If CL didn't matter, then maneuvering flaps and-or slats would not have been effective. But they were.
As for synchronizing guns though a 4-blade prop, the Germans had a VERY wide blade at the cowl arc. A 4-blade would cover a significant portion of the prop arc. Had they employed a more conventional-looking prop (more narrow at the hub), then maybe sure. Even a 5-blade, as in the late Spitfires (with narrow hubs).
Let's look at the MG 151 (15x96). The cyclic rate of fire is 700 rpm, or one every 85.7 msec. The blades pass by, as you said, every 16 msec, so you'd shoot once every 5.36 blades, or between the 5th and 6th blade pass. Unfortunately, the wide-chord hub might seriously interfere with that, causing you to miss that window and have to wait another blade. That's one shot about every 96 msec or so, plus the time to move to empty space. Call it one shot every 100 msec. That's about 10 shots per second in an ideal world and doesn't SEEM like it would affect the cyclic rate much (700 down to 600). The reality was that real gun synchronization rates made it MUCH slower, due to mechanical constraints and spring return rates.
The guns may have been electrically fired, but they weren't computer operated. Solid state components were decades away. It was done with cams and springs that have mechanical constraints. They got really slow with wide chord and more than 3 blades. Since the fuselage guns were the German pilot's primary weapons, that was not acceptable to the pilots or the Luftwaffe. At least, I have heard that..
Spitfire used the wing that was 13% thick at the root, it's wing was as of low drag as realistically possible on military aircraft designed in late 1930s. There was several posts and thread here where Spitfire was measured with highest dive speeds for non-jet aircraft.
Things that were slowing down Spitfire were items like external BP glass, not covered U/C, bad carburetor, bad layout of exhust stacks, presence of rear wiev mirror, sometimes sloppy fit and finish. As time went on, those things were rectified. The radiator system was to wait until the advent of Spiteful.
Yakovlev's fighters were small, this is where from the reasonable performance came from. Does not equate with low-drag wing.
Hello Tomo Pauk,
Most of the other fighters of the period used a 15% thickness at the wing root which is not that different. A for low drag, the NACA 2200 series airfoil is not. A high dive speed / critical Mach number does not necessarily mean the wing is low drag.
The Spiteful / Seafang used a laminar flow airfoil and gave up on the wonderful elliptical wing which shows what they thought of the value of the airfoil and wing planform on the Spitfire.
The Clark-Y airfoil used on the Yakovlev fighters is not a low drag airfoil either. It is a fairly high lift airfoil with very benign characteristics.
If you really want to see what can be done with a little (or a lot) of aerodynamic clean up, compare the Lavochkin La-5FN and the La-7.
The two are nearly identical in size weight and have identical engines and yet the La-7 is about 20 MPH faster.
- Ivan.
There was a report summing up the service of the FW190, it was very brief.Does anyone have any raw data concerning the FW-190's "military achievements", such as number of sorties flown, aerial victories, losses to both enemy aircraft and ground fire, etc.?
I would be interested in seeing them.....
There was a report summing up the service of the FW190, it was very brief.
20,000 produced, in service from 1941 to 45, not as good as the F6F. Inferior to anything with roundel with a star in it.
I think you misunderstood my point Adler. This whole thread was created to conclude that the FW 190 was inferior to the F6F, purely because of one comparative test quoted on another thread.Fixed for preconceived notional accuracy...
I think you misunderstood my point Adler. This whole thread was created to conclude that the FW 190 was inferior to the F6F, purely because of one comparative test quoted on another thread.