P-51 would be devastating weapon of war in this game.

[Emgy]

I hate to be a calibre police, but the 109 used 7.92mm MGs (.312in)

 

I'm in a pedantic mood, nothing personal :-)

Edited February 26, 2014 by Calvamos

[Venturi]

Technically, it's 8x57JS Mauser and 7.62x63 (.30-06) and .303 British / 7.7x56 rimmed. I can bust out my Hornady manual if you're interested in the bullet weights, powder charges, powder types, case dimensions, primer types, and muzzle velocities for each.

 

I just call them .30 cals to make it simpler, see?

[Venturi]

No, the Hispano fired fro a locked bolt. That's why it could have decent ballistics without being too heavy.

 

Actually, you're both right, let me clarify. The Oerlikon FF cannon was a blowback design, but the Hispano 404 cannon was a locked-breech design. But they both were open-bolt designs.

 

This is a very different discussion from an open bolt/closed bolt dichotomy. An open bolt design, versus a closed bolt design, differs in that the closed bolt design chambers a round and then waits for the trigger / firing mechanism to be activated before releasing the firing-pin, whilst the open bolt design waits for the trigger / firing mechanism to be pulled, this then releases the bolt to chamber a round and firing happens immediately after the bolt rams home. Both the Oerlikon and Hispano cannons were open bolt designs, as are most non-synchonized guns (too much lock time, from the trigger pulled, to the bolt ramming home, to firing, which can all be slightly different from shot-to-shot, for such weapons to be able to be sync'd with the propeller. This relates to another recent discussion on these forums...).

[Crump]

 

But they both were open-bolt designs.

 

Right, open bolt designs are for fully automatic weapons to aid in cooling.  It is one of the thing that gives them such high sustained rates of fire. 

[Sternjaeger]

Rate of fire trumps all against fast moving targets, relatively unarmored and small fighter planes. Against slow, large, armored targets, cannon were necessary for efficient takedown. This was one of the primary reasons for European air forces' switching to cannon/mg setups from the 4x 30cal mg bf109e-1 and 6x and 8x .30cal mg hurri and spit during and after the battle of britain. American air forces, when they faced Japanese bombers in the pacific, never found .50cals lacking, and by the time they were employed against the Luftwaffe, did not have to deal with bombers at all. Thus, standardization on .50cals was simply common sense given the problematic operation, mounting, and supply brought about by introducing the unneeded power but slow rate of fire 20mm cannon setups to aircraft designs that were already set up for .50cal mounting (recall that aircraft design took several years, the P-51 airframe for instance began development before the battle of britain, in 1939).

 

well I guess the fact that the Japanese didn't use self-sealing tanks meant that even an incendiary .50 cal could be quite devastating. The US Navy soon started to look into 20mm because they needed a more effective gun for ground attacks against semi-fortified structures and light tanks. And if memory serves, the P-51 prototype (NA-73X) was actually designed and rolled out in a record-breaking 120 days. 

 

Technically, it's 8x57JS Mauser and 7.62x63 (.30-06) and .303 British / 7.7x56 rimmed. I can bust out my Hornady manual if you're interested in the bullet weights, powder charges, powder types, case dimensions, primer types, and muzzle velocities for each.

 

I just call them .30 cals to make it simpler, see?

 

well no, the wartime military-spec rounds are definitely 7.92x57mm. 8x57JS is the civilian spec name (where "J" actually stands for "I" of "Infantrie" and "S" is for "Spitzer"), but if you measure them you'll see it's the same thing. 

 

Note that the civilian loads are much milder than the wartime ones, and the military ones varied according to the the kind of ammunition (infantry use, aircraft use, sniper etc...). Same applies to different kinds of bullets (and the 7.92x57mm had at least 10 mainstream varieties!).

Right, open bolt designs are for fully automatic weapons to aid in cooling.  It is one of the thing that gives them such high sustained rates of fire. 

 

yep, and they're much cheaper to produce, as they have less moving parts.

Edited February 26, 2014 by Sternjaeger

[Emgy]

I just call them .30 cals to make it simpler, see?

I know, and like I said, I was being pedantic :-) There are a few of us that get OCD about this stuff on forums - it was not meant as a correction.

 

And if you go to a hunting forum and use .25 as a blanket term for anything between .243 Win to .260 Rem, someone will most probably get OCD about that too :-)

Edited February 26, 2014 by Calvamos

[Venturi]

well I guess the fact that the Japanese didn't use self-sealing tanks meant that even an incendiary .50 cal could be quite devastating. The US Navy soon started to look into 20mm because they needed a more effective gun for ground attacks against semi-fortified structures and light tanks. And if memory serves, the P-51 prototype (NA-73X) was actually designed and rolled out in a record-breaking 120 days. 

 

 

well no, the wartime military-spec rounds are definitely 7.92x57mm. 8x57JS is the civilian spec name (where "J" actually stands for "I" of "Infantrie" and "S" is for "Spitzer"), but if you measure them you'll see it's the same thing. 

 

Note that the civilian loads are much milder than the wartime ones, and the military ones varied according to the the kind of ammunition (infantry use, aircraft use, sniper etc...). Same applies to different kinds of bullets (and the 7.92x57mm had at least 10 mainstream varieties!).

 

yep, and they're much cheaper to produce, as they have less moving parts.

 

Save me from the internet commandos.

 

Wrong, the 8mm mauser actually had two different caliber bullets that were used. However, it is still known as the 8mm mauser regardless (or 7.92x57, or any other of the 10 monikers the round has). Owners of old mausers know better than to take it for granted they have a .323" bore. BTW, this is a spitzer https://en.wikipedia.org/wiki/Spitzer_%28bullet%29  and I guarantee you that the JS was used in aircraft.

[Sternjaeger]

Save your sarcasm for your friends, and get your facts right. How does it work then, you can shred other people's statements, then when you're in the wrong, if someone corrects you then he's the internet commando?

 

In the military world it's always been known as 7.92 or 7.9, even if the bullet diameter is in excess of 8mm (I have some Luftwaffe-issued L-Spur and K-Spur which are respectively 8.21mm and 8.25mm in actual bullet diameter).

 

The 8x57 IS or JS is a SAAMI designation for the civilian market (same as calling .223 the 5.56 NATO), and even those are very close yet slightly different in measures from the original military spec one (they can still be used in your Mausers of course).

 

The picture you posted shows an M/88, which is the predecessor of the 7.92, together with a 7.92. I assume you took it from here, so you might as well look at it again and read it too this time..

 

http://en.wikipedia.org/wiki/7.92×57mm_Mauser

Edited February 27, 2014 by Sternjaeger

[FlatSpinMan]

Knock the sarcasm off, Venturi. Just post what you have to say without putting anyone down.

[Sternjaeger]

just to clarify things further: the ammunition used on Luftwaffe aircraft guns had to respond to strict regulations. Primarily it was the choice of materials, with brass being the only acceptable material for cases (brass cases for aircraft use are identified by the "S" letter and an asterisk logo). Second thing, they had a "hotter" charge, around 15% more than the average ammo, which was identified by the "V" letter and was not supposed to be used by conventional rifles (although snipers liked to use the "observation" rounds and other types according to what they needed to do).

 

Here are a couple of examples of Lufwaffe-issue ammunition (note the "7,9mm" description on the original box, which wasn't always applied)

 

P.m.K. which is an AP round

 

 

 

B (for "beobachtung", observation), which was an incendiary/explosive round, (snipers used this with devastating psychological effects).

 

below is a list of some of the other types of Luftwaffe ammo available: note the variation in muzzle speed not only among different kinds of round, but also if shot by different guns (the barrel heaviness came into play there).

 

Edited February 27, 2014 by Sternjaeger

[Sternjaeger]

As I said earlier, the bullet diameter was actually in the region of 8.21~8.25 mm, but I assume they stuck to the 7,9mm or 7,92mm designation to differentiate it from the other existing 8mm calibres of the time (i.e. the 8mm Hotckiss).

[HurlyBurly]

 Well data is being provided I can't help but voice my skepticism to the conclusions being drawn as they are rationalist in nature. Personally I question what value there is presenting opinions on this matter without evidence to support them. 

 

 Beyond this are pilots reliable witnesses to the destructive power of any weapons mounted on their aircraft, with regards to strafing runs. The velocity let alone distance that these runs occur at usually necessitates the use of forward observers to reliabley report the effect on targets.

[FS-HerraTohtori]

the P-51 is heavier, but the four-bladed constant speed prop does a great job at keeping her airborne. It's defo an energy fighter though, having said that, the clean lines mean it also gains speed faster.. it flies like nothing else, but you gotta learn her ways. One of the most interesting things about her though is that all the warbird operators and owners who I know or met who flew several kinds of warbirds, all unanimously agree that it's by far the best warbird they've ever flown 

 

When you're speaking of two aircraft as different as these, statements like "gains speed faster" are more than a bit ambiguous. There can be significant differences in low speed acceleration, high speed acceleration, and dive acceleration, and it is not generally easy to see if an aircraft is better than another type at all these situations where the airspeed is increasing.

 

And "clean lines" are not the only thing that affect acceleration. The biggest factor is actually the mass of the aircraft, or rather its inertia. If you have two P-51's with otherwise same configuration but other one is loaded with extra weight, the lighter aircraft will accelerate faster.

 

The key variables you would want to keep in mind are (corresponding to weight, lift, drag and thrust):

 

-mass of the aircraft

-wing loading (ambiguous; heavier wing loading is more efficient at high speeds, light wing loading is better at low speed maneuvering)

-wing profile and general drag coefficient of the airframe (more lift is better, but less drag is better - fuselage is relatively easy to make clean and low-drag, but with wings you always make a compromise between lift and

-thrust from the propeller

 

Generally you can say that less mass gives a better performance (if other variables are comparable).

 

Wing loading is more ambiguous because higher wing loading is typically more efficient at high speed, but low wing loading is much better at low speed - particularly while maneuvering hard.

 

General drag coefficient is pretty simple. Fuselage is relatively "easy" to make aerodynamically clean without much compromises, except regarding to engine cooling and to some extent pilot visibility.

 

Wing profile is always a compromise. A high-lift wing design typically produces a lot of parasitic drag (mostly due to thick wing chord). However, a low-drag solution generally produces less lift. However when you actually need a lot of lift, and you're flying an aircraft with a low-drag wing, you will need to pull more angle of attack than with a high-lift wing - and as you increase the angle of attack your wing can easily produce MORE drag than a high-lift design would in the same conditions.

 

Thrust is a factor of propeller design and the engine's ability to spin it at optimal speed. Engine's ability in this context is axial torque, but most of the time only the power outputs are compared... In theory, more blades gives the propeller more "wing area" - which increases the thrust at low airspeeds and especially at high altitudes where air is thin. However, more propeller blades means more drag as well, which starts to affect things at high speed - but, as you go higher, this problem is reduced because the drag in general is reduced due to less dense air.

 

 

Looking at Newton's second law it is relatively simple to define (in theory) what the acceleration of an aircraft would be. When the sum of forces affecting the aircraft is F, then acceleration a = F/m where m is the aircraft's mass.

 

If we make things easier and make the aircraft fly level, we can say that lift and gravity are equal and cancel each other out, which leaves us to deal with thrust and drag.

 

If an aircraft is producing more thrust than drag, it accelerates. If they are equal, it flies at constant velocity. If there's more drag than thrust, the aircraft slows down.

 

 

So if we're interested in how fast an aircraft accelerates, we get an equation something like a = (thrust - drag) / m

 

...which is, in practice, only solvable by flight testing because it's nearly impossible to actually know what kind of thrust and drag forces are affecting the aircraft. From the perspective of armchair aerodynamics, I can only make some estimations based on what I know of the aircraft and what my impressions are from various games:

 

Low initial speed acceleration, or "standing start", low altitude:

 

Bf 109 K-4 C3 will have better acceleration, and will reach its top speed (where thrust produced by the propeller is equal to drag produced by the aircraft) first. However the P-51 has slightly higher top speed, and naturally will continue accelerating after the 109 has reached its terminal velocity. The P-51 is initially hampered by its higher mass, need to keep the wings at higher angle of attack, and slightly lower engine power.

 

Low-speed acceleration, high altitude:

 

Both the Packard Merlin and DB-605 had excellent high altitude performance, but very likely the Merlin engine would be performing better. Additionally, the four-bladed propeller helps a bit, although the 109 might be using a wide-bladed propeller as well. P-51 is still heavier and Bf 109 lighter. I'd say initial acceleration gives slight edge to the 109 (depending on initial velocity - the lower the better for 109) but the P-51 would probably out-accelerate the 109 before either aircraft reaches their top speed.

 

 

High-speed acceleration:

 

P-51 has a higher top speed. It'll maintain its capacity to accelerate longer, while 109's acceleration drops as it gets closer and closer to its top speed. Without exceptional circumstances I would give this to the P-51 in both low and high altitudes (although with less margin at low altitude).

 

 

Power-on dive acceleration, low and high altitude:

 

Starting from low initial velocity and low altitude, the 109's initial acceleration advantages still hold even if the aircraft are both diving. 109 should probably have a very slight edge at the start of the dive, but as the aircraft pick up speed, the P-51's lower drag and higher mass will (should) give it a clear advantage in a dive. At high altitudes, the P-51 has even more of an edge because effects of drag and engine thrust are reduced but the mass difference still favours the P-51.

 

Power-off dive acceleration:

 

P-51 wins. It has less overall drag and higher mass, so it simply has higher terminal velocity and it will accelerate to it faster. This applies to all dive angles.

 

 

Climb performance is closely related to low-speed acceleration, mostly because the same variables that make an aircraft accelerate well tend to also make it climb well. Namely, high thrust to weight ratio.

Edited February 28, 2014 by FS-HerraTohtori

[79_vRAF_Friendly_flyer]

Actually, you're both right, let me clarify. The Oerlikon FF cannon was a blowback design, but the Hispano 404 cannon was a locked-breech design. But they both were open-bolt designs.

 

You are right, I should have written "locked breech". I think the terminology varies between sources.

[LukeFF]

just to clarify things further: the ammunition used on Luftwaffe aircraft guns had to respond to strict regulations. Primarily it was the choice of materials, with brass being the only acceptable material for cases (brass cases for aircraft use are identified by the "S" letter and an asterisk logo). Second thing, they had a "hotter" charge, around 15% more than the average ammo, which was identified by the "V" letter and was not supposed to be used by conventional rifles (although snipers liked to use the "observation" rounds and other types according to what they needed to do).

 

What grain did the Luftwaffe use for their 7.92mm ammo? The Yugoslav stuff I shoot in my Mausers is all 196 grain (yeesh, and that kicks hard!).

[Sternjaeger]

What grain did the Luftwaffe use for their 7.92mm ammo? The Yugoslav stuff I shoot in my Mausers is all 196 grain (yeesh, and that kicks hard!).

 

according to the aforementioned wiki page and the descriptions on the boxes in the pics above, the special rounds used by the Luftwaffe had lower bullet grains than the average ammunition, but had slightly bigger load:

 

so the standard 7.92x57mm available today and which was the standard one for the infantry has a 197 grains bullet and a 45 grains charge.

 

The P.m.K.-V (AP) above has a 156.6 grains bullet and a 52.47 grains charge.

 

The B.-V (HE-I) above has a 167.4 grains bullet and a 50.15 grains charge.

 

Other special rounds had the same "lighter-bullet/heavier-load" combination, so it was considerably faster ammunition. Would it kick more? I don't know, as I've never shot anything different than the 197/45 grains round for that calibre, but my guess is no, although you'd have a much hotter barrel! 

Edited March 1, 2014 by Sternjaeger

[LukeFF]

Thanks, Stern! That's an interesting design there to get more energy out of the bullet. Do you know if the Russians did the same thing with the 7.62x54R round? I have read they loaded "hotter" rounds for their aviation MGs, but I'm not sure exactly what is meant by that. 

[II./JG27_Rich]

Dave Southwood:

 

[Sternjaeger]

Thanks, Stern! That's an interesting design there to get more energy out of the bullet. Do you know if the Russians did the same thing with the 7.62x54R round? I have read they loaded "hotter" rounds for their aviation MGs, but I'm not sure exactly what is meant by that. 

 

well yeah, although it might have looked identical to the untrained eye, the ShKAS ammunition was in fact very different from the standard issue 7.62x54R.

 

First thing, like for the German counterpart, there was the choice of better materials (the Russians experimented mainly with two alloys combinations for the cases), case and primers were re-designed to improve reliability, but above all a different selection of rounds:

 

- Cartridge with armor-piercing bullet B-30;

- Cartridge with armor-piercing incendiary B-32;

- Cartridges with tracer bullets T-30 and T-46;

- Cartridge with armor-piercing tracer BT;

- Cartridge with armor-piercing incendiary tracer bullet BZT;

- Ammunition with incendiary bullet sighting CP and PP.

 

but that's pretty much where the similarities ended.

 

The table below compares a conventional ball round (cartridge A) with the four most common ShKAS rounds.

 

 

So the bullet weight varied, but the load was substantially bigger (or "hotter"), making it unsuitable for rifle use. Again, snipers apparently used some of these, just like the Germans, but it's a considerably much more powerful round. The result of this combination was generally a round with better ballistic trajectory (snipers had to take this into account when using these rounds).

 

Note how the bullet shape went from the conventional flat spitzer ball round to the boat-tail shape and longer semi-flat tail with and without gas checks as well.

 

 

1 - A, light

2 - D, heavy long-range

3 - B-30, armor-piercing

4 - B-32, armor-piercing incendiary

5 - T-30 (T-46), tracer

6 - BT, armor-piercing tracer

7 - BZT, armor-piercing incendiary tracer

8 - BZT upgraded (ST-46),

9 - CP (PP), observation-incendiary (like the German B-V round above)

 

 

I guess the real game changer was the ShKAS machine gun loading system, which allowed the vertiginous rates of fire we know of.

Edited March 1, 2014 by Sternjaeger

[sturmkraehe]

I personally came to the conclusion that - while there are categories of aircraft with categories that can be judged better or worse - inside a category it boils down to the preferences of the pilot. I think a lot of Luftwaffe pilots thought the 190 to be the better aircraft than the 109 some Luftwaffe pilots preferred the 109 and refused to convert to 190 ... Says it all I think.

[Sternjaeger]

I personally came to the conclusion that - while there are categories of aircraft with categories that can be judged better or worse - inside a category it boils down to the preferences of the pilot. I think a lot of Luftwaffe pilots thought the 190 to be the better aircraft than the 109 some Luftwaffe pilots preferred the 109 and refused to convert to 190 ... Says it all I think.

 

Yes, it is down to the pilot's skills and his capacity to adapt to the aircraft as promptly as possible, above all understanding quickly the limitations of the aircraft itself, so that you don't get yourself into unnecessary trouble!

[79_vRAF_Friendly_flyer]

Quite. Some of the Finnish pilots bemoaned the switch from the old Brewster to the 109, despite the latter being a lot faster and better armed. Then again, the Finns were the only ones to really turn that old bird into an ace-making fighter.

[Crump]

 

 In theory, more blades gives the propeller more "wing area" - which increases the thrust at low airspeeds and especially at high altitudes where air is thin. However, more propeller blades means more drag as well, which starts to affect things at high speed - but, as you go higher, this problem is reduced because the drag in general is reduced due to less dense air.

 

More blades = higher power loading

 

More blades = less efficiency = less thrust horsepower for a given shaft horsepower.

 

The reason is more blades equals more interference.

Edited March 2, 2014 by Crump

[sturmkraehe]

I admit that I do not understand thoroughly the rationale behind selection a specific number of blades but from what I know of aerospace engineering (and I understand quite a lot as I am in that business) almost everything boils down to find the best compromise with respect to the given objective and most often conflicting constraints. One has to realize that quite a few aircraft passed from 2 blade to 4 blade like the Spit did. The supermarine engineers had their reason to do it. My assumption is that the number of blades responds to some sort of balance betweend different conflicting constraints. For them increasing the number of blades made sense while it did not for the Messerschmidt engineers.

 

I guess there is no absolute criteria applicable in a general way.

[Crump]

For the answers, we turned to Jeremy Kinney, a curator at the National Air and Space Museum, who explains that the use of four blades on World War II aircraft (such as the North American P-51 Mustang) increased the blade area, which produced more thrust, without increasing the overall diameter of the propeller.

Kinney says the reason why in the late 1930s the designers of the Vought F4U Corsair used the inverted gull wing was to accommodate the big 13-foot, three-blade propeller—the largest used on a fighter up to that time. That propeller was right for the largest fighter engine at the time: the 1,800-horsepower Pratt & Whitney R-2800. When four-blade propellers came along early in World War II, they alleviated the problem of getting enough ground clearance for the tips.

 

Read more: http://www.airspacemag.com/need-to-know/are-more-propeller-blades-better-108981404/#ixzz2ulRh4d12

 

Read more at http://www.airspacemag.com/need-to-know/are-more-propeller-blades-better-108981404/#cDgZ9mWPea8omyOR.99

[Crump]

Here is a good discussion

 

http://www.pprune.org/private-flying/448912-2-propeller-blades-os-opposed-3-blades.html

[LukeFF]

well yeah, although it might have looked identical to the untrained eye, the ShKAS ammunition...

 

Very good stuff, thanks! It goes along with what I have read, that what we call "light ball" (147 grain) was meant for rifles, while the "heavy ball" ammo was meant for MGs (and the enterprising sniper).

[Crump]

 

My assumption is that the number of blades responds to some sort of balance betweend different conflicting constraints

 

 

Mostly engine power and ground clearance.

 

The most efficient and highest thrust producing propeller would have fewer but longer blades........

 

Long blades means you cannot load as much power due to blade twist and in the case of World War II, you run out of room as the propeller disk diameter is so large that ground clearance becomes an issue.

 

Thrust Horsepower(thp) = Propeller efficiency(n) X Shaft horsepower(shp)

 

n = .85

 

Three bladed propeller with an efficiency of 85% = 2000 shp X .85 = 1700 thp

 

Four Bladed propeller with an efficiency of 80.9% = 2200 shp X .81 = 1700 thp

 

I guess there is no absolute criteria applicable in a general way.

 

There is not any absolute criteria.  It is a balance.

[FS-HerraTohtori]

Mostly engine power and ground clearance.

 

The most efficient and highest thrust producing propeller would have fewer but longer blades........

 

Long blades means you cannot load as much power due to blade twist and in the case of World War II, you run out of room as the propeller disk diameter is so large that ground clearance becomes an issue.

 

Thrust Horsepower(thp) = Propeller efficiency(n) X Shaft horsepower(shp)

 

n = .85

 

Three bladed propeller with an efficiency of 85% = 2000 shp X .85 = 1700 thp

 

Four Bladed propeller with an efficiency of 80.9% = 2200 shp X .81 = 1700 thp

 

There is not any absolute criteria.  It is a balance.

 

 

Long blades also tend to have more problems with the tip breaking speed of sound, which causes excessive drag. To counter that, the propeller needs to spin slower, but that means the blades need to be larger to produce thrust, and larger blades produce more drag.

 

When you add more blades, you actually start to approximate a fan disk. Fans are better when they're surrounded by a fan housing, but your suggestion that adding blades uniformly decreases the efficiency of the propeller is simplified at best, and wrong at worst.

 

The thrust produced by a propeller is simply defined by three things:

 

-blade surface area

-blade profile

-blade velocity

-blade angle of attack

-air density

 

...in fact these are the same factors that determine a wing's performance, because propeller blades are wings just as much as any other aerofoil.

 

Now to actually estimate the thrust produced by an individual blade, you'd need to integrate over the length of the blade because velocity increases towards the tip - this is typically why propeller blades have a twist on them, with less angle of attack on the tip of the propeller.

 

If you want to increase the thrust of the propeller, you want:

 

-highest blade surface area

-thick chord blade profile

-move the blades at highest possible velocity

-maintain the optimal angle of attack (critical angle of attack really).

 

Unfortunately things get complicated at this point because all these things increase the propeller's drag... which means you need more axial torque to drive it at desired RPM - ie. more powerful engine.

 

For example thick chord blade profile means lots of drag - which has highest effect at high velocity; another typical reason why propellers have very thick profile at the base near the spinner, and thin out towards the tips that move at higher velocity.

 

And, it turns out that when you spin your propeller faster and faster you start getting diminishing returns as the blades approach speed of sound in the relative airflow. This typically causes instabilities that can wreck the blade, and also shock drag and reduction of lift coefficient - which means that it requires more engine power to spin the propeller, but it may actually produce less thrust. So you want to also keep the velocity of propeller blades in an optimal range (whatever that turns out to be, depends on propeller blade design).

 

So, if your propeller disk diameter is constrained, the only real thing you can adjust to make a propeller produce more thrust (acceleration) is increasing the blade surface area. In theory you could make the propeller disk larger by longer blades - but the blade tip speeds still can't exceed speed of sound which means your propeller would have to spin slower. A better choice is to make propeller blades wider, and that is in fact what many high-performance propellers did in WW2, good examples being late Bf 109, Fw 190 / Ta 152 and P-47 models with "paddle props".

 

Another choice is to keep individual blades the same, but increase their number. This effectively increases the combined surface area of the propeller blades, but the problem is that the blades are now closer to each other and disturb each other more; typically this means that air is moving through the propeller disc at higher velocity which reduces the propeller's thrust.

 

The compromise you have to make here is actually between low-speed performance and high-speed performance.

 

At low speed, propellers with very wide blades or very many blades produce more thrust simply due to higher surface area.

 

However at high speed where drag forces start to become more significant, a propeller with fewer and thinner blades will provide better performance.

 

An aircraft needs both, though - high surface area propellers produce good acceleration and climb rate, both very important for combat aircraft. Low surface area propellers are low drag propellers and are at their best at high speeds.

 

But wait! Air density also affects the performance of the propeller - and it turns out, you need large propeller blades to retain performance at very high altitude. Luckily, thin air also reduces the drag forces that slow the aircraft down! That's why planes like Ta 152 H-1 used wide propeller blades instead of the earlier, thinner blade propellers. And that's why this is commercially viable and efficient:

 

 

 

 

Also there's no such thing as thrust horsepower. Thrust is a force. The engine is producing axial torque and rotates at certain speed which gives you the axial power, but the power of a propeller - as it pertains to the aircraft's "power" - is not a constant.

 

In fact when the aircraft is stationary, all the work done by propeller is entirely used to move some air backwards. Whereas when the aircraft is moving at its top speed, very little air is thrown "backwards" as "propwash" and instead the propeller's thrust force is doing work against the equal but opposite drag forces.

 

As pertaining to the propeller's ability to accelerate and maintain the aircraft's velocity, "thrust horsepower" is not a meaningful quantity.

Edited March 2, 2014 by FS-HerraTohtori

[Bladderburst]

I really think you are living in a dream if you think that .50 caliber is somewhat effective against heavy tanks.

Don't get me wrong, the M2 is a great weapon, but when I read someone saying that it's a tiger killer, I can't help but roll my eyes and think "not again".

[Sternjaeger]

perhaps "tiger crippler" is more adequate as a description ;-)

[6./ZG26_Emil]

Tiger tickler more like

[Sternjaeger]

as said earlier, you could break its tracks, and if hit properly from the top rear, you could go through the engine grille.. it wasn't easy, but it was not as invulnerable as you might think.

[6./ZG26_Emil]

I don't buy it, maybe the odd lucky hit but I really doubt it.

[Sternjaeger]

well that's the point: we're not talking about a single M2 HBT, but 6/8 AN/M2 with higher rate of fire, incendiaries, APs and tracers, coming down at faster speed and converging to a single point of impact. They did do A LOT of damage when they hit stuff!

[Bladderburst]

Tracks are vulnerable, but it's nothing that can't be fixed in an hour by the crew. I don't know what is the chance of actually breaking a link with a .50 bullet, my guess is that it's pretty slim. If .50 could easily break tank tracks, those vehicle would be very vulnerable against most ground forces they would encounter.

Put it this way, if .50 bullets were effective at dealing with armor, we would see tons of guns specialized for this task using this caliber, which we don't. If .50 caliber was effective against tanks, we would see systems armed with similar weapons tasked with anti-armor duty. Guess why Germans and Russians resorted to big guns mounted on aircraft to deal with tanks? Because machine guns and machine cannons usually don't cut it. 

What I don't get also is that people expect an IL2 to survive being filled lead but expect to do significant damage with the same type of weapons on a 68 tons brick of steel. Get real, it's vintage aircraft machine guns, it's no GAU-8.

Edited March 2, 2014 by Boussourir

[6./ZG26_Emil]

well that's the point: we're not talking about a single M2 HBT, but 6/8 AN/M2 with higher rate of fire, incendiaries, APs and tracers, coming down at faster speed and converging to a single point of impact. They did do A LOT of damage when they hit stuff!

 

Not to the thick armour of a tank they don't.

There is only anecdotal evidence from pilots that they ever destroyed a tank.

 

The number of tanks knocked out by any aircraft (including rockets and bombs) in the western theater is very low.

Edited March 2, 2014 by JG5_Emil

[Sternjaeger]

Tracks are vulnerable, but it's nothing that can't be fixed in an hour by the crew. I don't know what is the chance of actually breaking a link with a .50 bullet, my guess is that it's pretty slim. If .50 could easily break tank tracks, those vehicle would be very vulnerable against most ground forces they would encounter.

there's quite a difference between one 50 cal round and a hailstorm of them.. besides, I'm sure you've heard of anti-tank rifles? Guess where they aimed at with them? Yes, tracks and side of the armours. You cripple a tank, you'll make it a sitting duck. Sure, it can be fixed, but we're talking about getting out of the tank to do it, which is not always possible. 

Put it this way, if .50 bullets were effective at dealing with armor, we would see tons of guns specialized for this task using this caliber, which we don't. If .50 caliber was effective against tanks, we would see systems armed with similar weapons tasked with anti-armor duty. Guess why Germans and Russians resorted to big guns mounted on aircraft to deal with tanks? Because machine guns and machine cannons usually don't cut it.

I'm not saying they're ideal anti-tank guns, I'm saying that the combined use of 6 to 8 high rate of fire M2s can cause considerable damage to a tank.

 

What I don't get also is that people expect to fill an IL2 to survive being filled lead but expect to do significant damage with the same type of weapons on a 68 tons brick of steel. Get real, it's vintage aircraft machine guns, it's no GAU-8.

first of all it's merely about armour thickness, it's NOT a brick of steel. Have you ever seen a real German tank up close? Have you ever knocked their hull? In any case, for the record, the Caliber .50, Ball, Armor Piercing round, has a penetrating power of 0.75 in (19 mm) at 500 meters and 0.39 in (10 mm) at 1,200 meters. A one second burst from a P-47 would have roughly contained 80 of these rounds. Eighty. Can you appreciate it's not quite the same thing as one single round? These things could do serious damage to rolling tracks and wheels.

 

Not to the thick armour of a tank they don't.

I'm not gonna repeat myself..see above.

Edited March 2, 2014 by Sternjaeger

[6./ZG26_Emil]

Show any evidence of a tiger being destroyed or knocked out by .50 cals?

 

13 Tigers destroyed by aircraft in Normandy, 7 of which to carpet bombing of high altitude aircraft and the rest to fighter bombers.

 

It is pointless to theorise show some evidence other than anecdotes. If a .50 cal equipt aircraft has ever knocked out or seriously imobalised a tiger or panther it is one in a million.

 

Aircraft were largely ineffective against tanks, both the RAF and USAF massively overclaimed their successes against them.

[Bladderburst]

Anti tank rifles are borderline effective against light armor. Guess why they were replaced by rockets or even magnetic mines? I don't think a 1944 aircraft can fire focused enough to pierce armor that a 6 pounder can't. On 80 bullets, no way that even half will hit its target, even less in a small region.

 

Sure, I'll give that to you, you can bust a lot of things with machine gun fire, you can break vision blocks, periscopes, with luck even a track as said before... but can you disable a tiger or a t34? No.

Anyway I don't get why this always comes up. The M2 browning is not a super weapon. It should not be treated like it is, we should not entertain the possibility of it destroying everything in sight with well focused hail of bullets. It's an excellent air to air weapon but is there anyone arguing if a FW190 could knock out an IS2 with its guns? It can't. It's the same thing excepted that the FW190 has even more firepower.