Performance of the Fw 190A on the Deck?

[Boomerang]

Gentlemen:

Are there comments about the report in Don Caldwell's excellent JG 26 War Diary Vol 2 that 'The survivors claim today that the Fw 190A could outrun any Allied fighter on the deck, regardless of the official performance figures'.

This statement occurs in the section of the book dealing with JG26's role in Normandy after D Day, so it would apply e.g. to performance of the 190 A versus the Spitfire IX, not the Spitfire XIV, and similarly for the other Allied fighters.

I was a bit surprised by this statement, but presumably getting this sort of this correct was literally a matter of life or death. This forum has also taught me that assessing aircraft performance is more complex than reading simplistic tables of numbers.

On a technical level, would excellent speed on the deck relate to the radial versus in-line engine issue?

Thanks

Don W (Boomerang)

[Graham Boak]

The maximum speed at sea-level is linked to the maximum speed at full-throttle height, and has no connection to the inline/radial choice. For a first stab at understanding more, plot a graph of airspeed (x-axis) against altitude (y-axis). Many sources will quote speeds at different altitudes, usually sea level and at the full throttle height of each supercharger setting. You can draw a straight line linking the sea-level value and the first full-throttle height point. The slope of this line will be the same for all types of similar performance. (Not quite true, but good enough to make the point.) Thereafter, plotting any max. speed point will allow you to find an approximate sea level speed.

Beware aircraft with two-speed superchargers (eg Spitfire Mk.IX), use the point for the lower full throttle height not the absolute best.

The statement is clearly made by the survivors, as there certainly are Typhoon pilots who succeeded in catching and shooting down Fw 190 low-level raiders. Also the Spitfire Mk.XII, of course. In practice the types were so close that the difference between individual examples was more important: a "good" Fw would run away from a "poor" Typhoon, and vice versa. More generally, of course, successful pilots will always believe that their aircraft is better than the opposition, as long as the types are broadly similar. For them, it has been.

[drgondog]

Originally Posted by Graham Boak

The maximum speed at sea-level is linked to the maximum speed at full-throttle height, and has no connection to the inline/radial choice. For a first stab at understanding more, plot a graph of airspeed (x-axis) against altitude (y-axis). Many sources will quote speeds at different altitudes, usually sea level and at the full throttle height of each supercharger setting. You can draw a straight line linking the sea-level value and the first full-throttle height point. The slope of this line will be the same for all types of similar performance. (Not quite true, but good enough to make the point.) Thereafter, plotting any max. speed point will allow you to find an approximate sea level speed.

Beware aircraft with two-speed superchargers (eg Spitfire Mk.IX), use the point for the lower full throttle height not the absolute best.

The statement is clearly made by the survivors, as there certainly are Typhoon pilots who succeeded in catching and shooting down Fw 190 low-level raiders. Also the Spitfire Mk.XII, of course. In practice the types were so close that the difference between individual examples was more important: a "good" Fw would run away from a "poor" Typhoon, and vice versa. More generally, of course, successful pilots will always believe that their aircraft is better than the opposition, as long as the types are broadly similar. For them, it has been.

Excellent points.

Objectively, the P-51B-15 for example, had a 1650-7 engine with better low altitude capability than the -3 and was extremely fast on the deck.

Based on flight test data, and assuming both engines were operating correctly it is hard to expect a 190A7 for example, or even a D-9 to outrun this Mustang on the deck.. and the -15 was plentiful during the Normandy campaign

I forgot to mention one other fact about the 51 - namely the extremely low wetted drag of the airframe in comparison with the Spit and Fw 190A. The D-9 was closer to the 51.

[Nick Beale]

I go along with Graham's comments: the more Allied pilots' accounts I see, the more confused I get. One day they'll say they could easily catch a given type of enemy aircraft, the next " these [whatever] were too fast" or "we were unable to close" etc. The performance figures we all use don't seem to apply!

I'm sure a lot had to do with the particular situation of a combat but I also wonder whether individual machines of the same type were much more variable in performance than we now realise? Certainly you read pilots saying that a particular aircraft they flew was aither a good or a bad one of the type.

[Boomerang]

Gentlemen:

Now that the forum is running again, I can thank you for your responses.

I must say (based I'm sure on a much smaller sample) that I share Nick's thoughts - there doesn't seem to be the simple correlation between reports of fighter versus fighter combat that you might expect from published performance data.

One final point - is there any possibility that the fuel status of an aircraft would have a noticeable effect on performance i.e. an aircraft low on fuel would have greater speed than one with near full tanks?

Regards

Don W

[yogybär]

Yes, fuel status definitely is very important, especially on a P-51!

Apart from that some technical factors on the not exactly, maybe even misidentified Luftwaffe AC which influence these "races":
- subtypes of 109G-x; 109K; 190A-x; 190F-x 190D-x(MW-50 yes/no) with different engine-subtypes
- did the german use WEP-systems like MW-50 or GM-1 or "erhöhter Laderdruck" (if available&working on his plane).
- maybe the german had external loadouts like MG151/20-gondolas, a droptank, bomb(s) - bombracks themselves can cause ca. 15km/h difference in v_max!
- status of the german A/C's surface due to bad painting, dirt, bad repairs, removed covering etc. pp.
- trim status
...

We can see: A lot was possible.

[Graham Boak]

Actually, fuel state is not that important with regard to maximum speed. Drag is made up of two components, the lift-induced drag and the rest, or zero-lift drag. Weight has no effect on zero-lift drag. At cruise, the two components are equal. The lift-induced drag increases with the lift coefficient, which is high at low speed and low at high speed. So at high speeds, and at sea-level, the lift-induced drag would only be a small proportion of the overall drag (of the order of 15%, perhaps). Lift-induced drag goes up with weight (because the aircraft needs greater lift to equal this weight) but you are only looking at the difference in weight of the fuel, compared with the overall weight of the aircraft. So you are only looking at a small proportion of the smaller part of the drag.

In most combats the opposing aircraft will be at similar fuel states, around half: after such a jabo attack the escaping aircraft might well be at a lighter state, the interceptor heavier. This sort of difference might show in a long steady chase, as did occur over the Channel after some Jabo attacks, but a few mph would not normally be noticed.

Weight is much more important in manoeuvre and climb, there the fuel state could be more important. Most of all near the ceiling.

[Crumpp]

Actually, fuel state is not that important with regard to maximum speed.

Hi Everyone,

Weight very much affects our aircrafts envelope. It has a direct relationship with velocity.

V2/V1 = SQRT(W2/W1)

There is no real mystery to the variation in pilot accounts. If you examine the aerodynamic properties, all of these designers very much knew what they were doing. Aircraft must be viewed as a system and not one or two isolated characteristics. Aircraft performance is always a percentage variation over a mean average as well. Fit, finish, and conditions of flight make all the differences. Pilot skill is another factor.

In the FW-190 vs P51 it very much depends on the particular aircraft set up and conditions. You can make no blanket statement at low altitudes without knowing this information.

Here is the 8th USAAF assessment made during the war. Credit goes the Smithsonian NASM archives:









Here is a comparison chart of a variety of flight tested data that overlays the altitude range of the bomber stream. It closely matches the 8th USAAF conclusions.




What does this information tell us about specific aircraft performance? Nothing. What it does say is that given a 3% normal variation there is very little to choose between any of these aircraft with a few notable ranges. Generally speaking at low altitudes, the FW190 was the fastest aircraft in the theater. At high altitudes, the P47 reigned supreme. All of these aircraft were continually upgraded by their perspective design teams.

The most important factor in aircraft performance is going to be the pilot. It is not a cliché. The ability of the pilot to properly trim, smoothness of the control input, and operation of the aircraft make a huge difference in performance. Pilot inputs can vary measured stall speeds as much as 30 mph IAS in "level flight".

The Allies had an overwhelming superiority in both numbers and quality of pilots. A USAAF pilot received ~8 times the flight experience in operational type aircraft before being posted an operational unit. The majority of Luftwaffe pilots were poorly trained for the job they were asked to do. The ebb and flow of the entire air war exactly matches the amount of training given to the pilots comprising the force. Type of aircraft is simply irrelevant.

The importance of pilot experience can be easily verified by picking up the phone and calling any aviation insurance company.

All the best,

Crumpp

[Crumpp]

If we examine the shape of the L/D curve for each of these designs, then we can see some important differences in the combat qualities.

All the best,

Crumpp

[Graham Boak]

[quote=Crumpp;70205]

Weight very much affects our aircrafts envelope. It has a direct relationship with velocity.

V2/V1 = SQRT(W2/W1)

[End quote]

No. Weight affects the envelope, indeed, but the direct relationship is wrong. For aircraft of this vintage, it is probably true that induced drag has a linear relationship with weight, but induced drag is only part of the story. The effect of weight on speed varies with altitude, because it varies with induced drag only, and induced drag increases with altitude (at any given speed). At low altitude and high speed, the drag term is dominated by the zero-lift drag. This is made up of skin friction drag, profile drag and excrescence drag, none of which vary with weight.

For high altitudes and low speeds, the effect is reversed, as the drag is dominated by the lift-induced drag, and the top left corner of the envelope is notably smaller at higher weight. The bottom right is hardly affected.

I made my living doing these sums. There's a lot about aircraft performance I never knew, but I think this is fairly basic.

The rest of the posting is sound, and a very useful addition.