IDIAMN 1 JG27 AFRIKA posted 12-16-98 09:50 PM ET (US)     

Picked up a book called "fighter: the true story of the battle of britain" and while reading it I came to this passage concerning turn radii:

quote:

"....pilots of spits, hurri's, and bf109's all claimed that their aircraft had the tightest turning circle, but the 32 foot wingspan of the bf109 gave it the advantage over it's rivals. In spite of it's high wing loading, it had a turn radius of only 750 feet (spitfire 880 and hurricane 800 feet), and this could be a vital factor in air fighting.

The first thing that comes to mind, of course, is the Luftwaffe conspiracy again filling the world with dis-information, but when I checked my top secret conspiracy agenda folder, I could find no such agenda listed, and since I AM a card holding conspirator, I am discounting the conspiracy theory.

Therefore I ask.... Why would this book that contains so much obviously well researched information contain this little tid-bit of information pertaining to the "emil" and it's abilility to out-turn it's rivals???

Is there something else involved in turn radii besides the wing loading of the aircraft??? Maybe some high speed flaps, or wing design or something???

Of course you can never believe what you read because there is allways a different fact or figure to either substantiate or discount a supposed truth, so I am not really taking it as fact that the old "emil" could actually out turn the "flies like its on rails hurricane and spitfire", I'm just curious as to the actual effects of wing loading.

Lemme know what you think.

C U above,

"Hey...nice cannons"

Idi

holst FT posted 12-16-98 10:17 PM ET (US)            

Wing loading is a useful guideline for these things because it is by far the most important factor. No matter how well designed the wing on a p-51 is (and it was incredibly well designed, btw), its not going to out turn a zero.

However, there are lots of other factors effecting the performance of a wing. So many, in fact, that I couldn't possibly cover them all here, presuming that I knew well enough what I was talking about, which is also sometimes a bit of a stretch

Two of the most important ones, however, are Aspect ratio and taper ratio.

Airfoil *section* properties (that is to say two dimensional considerations) are only part of the wing. This is the familiar province of angle of attack, etc.

However, planform can also be extremely important. The Spitfire wing, for example, is an example of an aircraft with a different (and in the spits case, very efficent) planform. As much as I hate looping dweebfires, the lower induced drag produced by an eliptical wing gives *some* merit to their energy retention. (Although to my eye, its still totally out of control in WB).

But I'm getting ahead of myself.

There are two general means by which the designer can change the planform of a wing, either of which will affect the aerodynamic characteristics of the wing. The first is to effect a change in the aspect ratio. Aspect ratio is the primary factor in determining the three dimensional characteristics of the ordinary wing and its lift/drag ratio. An increase in aspect ratio with constant velocity will *decrease the drag, especially at high angles of attack* (this is important for the turn performance of the 109) and increase the performance of the wing when in a climbing attitude. A decrease in aspect ratio will give a corresponding increase in drag.

The second means of changing the planform is by "tapering" (decreasing the length of chord from the root to the tip of the wing). In general , tapering will cause a decrease in drag (most effective at high speeds) and an increase in lift.

The 109 wing is both tapered and has a very high aspect ratio.

A bit about the spitfire...

The elliptical wing is the ideal subsonic planform since it provides for a minimum of induced drag for a given aspect ratio, though as we shall see, its stall characteristics in some respects are inferior to the rectangular wing. It is also comparatively difficult to construct. It has a tendency to weigh more than comparable tapered wings (spit vs 109).

So essentially:

The spit has an elliptical wing which is most efficent for a given aspect ratio

but

The 109 has a higher aspect ratio and thus (all else being equal, which it nearly is) better performance at a high AOA.

Apparently, WB has the spit coming out on top, just barely. I can buy that. OTOH, mere numbers in terms of wing loading don't tell the whole story...so its not inconcievable to me that the 109 is as good or even a little better.

As far as precision goes...I don't have the numbers or the expertise to say exactly what should happen...thats what we pay iMOL for. I can, however, say with assurance that wing loading is not all there is to turn performance.

------------------

holst-FT

(Flying Tigers)

worr posted 12-16-98 10:26 PM ET (US)            

Wing loading isn't the whole picture.

Sure you need apples to make an apple pie, but with good apples you can still burn the crust. There are many other variables to be added into the equation. The P-38 is a superb example of this!

As far as the 109 out turning spitfires...well always cross reference any comments like this. Get two people to say it working with different primary sources (mind you most of your reading books work with secondary and tertiary sources.)

Worr, out

epee posted 12-16-98 10:54 PM ET (US)            

Turn performance of aircraft are measured in several ways. Rarely is a single plane a master at all of them.

There's instantaneous turning ability, i.e. the ability to change your direction vector quickly. The FW 190, believe it or not, is very good at this when hauling ass.

There's turn radius, the amount of sky you need to turn in. The ability to ride the edge of stall is very important here and the 109 is good at it.

Then there is sustained turn speed, the speed you can maintain while continually turning 360 degrees without stopping. The Spitfire is a champ at this. That's why it's so easy to blackout in a Spit.

So while a 109 can loose speed to gain angles on a Spit he'd better kill it quick because the fast turning (not tight turning) Spit will soon be in behind him with more energy.

Wells posted 12-16-98 10:58 PM ET (US)            

Wing loading is only a guide (wing area is only one factor in the lift equation). A shorter wingspan has nothing to do with it as in that quote! The airfoil chosen has a LOT to do with it as well. For example: The P-38 uses an airfoil that is capable of pretty high lift coefficient without stalling. This is partly due to the thickness of the wing and the camber (curvature) of the airfoil.

Induced drag is directly connected to aspect ratio (ratio of span to average chord), so a high aspect ratio makes for lower induced drag and higher turning speed (more G's).

A plane that has a higher top speed will also have a small advantage, due to it's ability to overcome drag with thrust. Anything that will maintain a higher turning speed will allow for more G's to be pulled.

Good turning performance favours a wing that is ample in area, has a low aspect ratio and a low maximum lift coefficient (induced drag is also figured from the lift coefficient squared). This is exactly where the Spitfire is at. It has a thin wing (low Clmax), low wing loading (ample area) and reasonable aspect ratio. The 109 uses slats (higher CLmax and a slightly higher aspect ratio to give it's turn performance while also allowing for higher speeds). The modified clark-y airfoil has one of the best lift/drag ratio's as well, which helps climb performance.

Also, look at the stalling speeds for the planes. A lower stalling speed will allow a plane to pull more G's for any given speed.

Planes with good flaps that increase wing area (P-38, Ki-84) can benefit from a notch for better turn performance.

Pyro posted 12-17-98 03:42 AM ET (US)            

Wells,

First, I have to say that I've always admired your posts. I really like the scientific approach you take and the fact that you're willing to check things out for yourself rather than just accepting that something stated as factual is actually true. Anyway, I just wanted to say that.

Now to chime in on the wingloading issue. To the original poster, the statement that the 109 could turn better because of its wingspan is pure bunk. The author seems to suggest that because the Spitfire had a longer wingspan, the 109 could outturn it. That's just ridiculous. Wingspan doesn't have crap to do with figuring something like that out other than the fact that it is relational to aspect ratio and wing area, both of which are detrimented by a shorter wingspan, all other things being equal.

Wing loading is simply weight/wing area. Without knowing more about the airfoil characteristics of a particular airplane, this provides a good ballpark reference, but it totally excludes the lift coefficient.

The formula for lift is simply (Wing Area)(Lift Coefficient)(1/2 air density)(velocity^2). Since you're going to be comparing aircraft under the same atmospheric conditions and WB just uses a standard atmosphere(29.92 in. Hg, 59 degrees @ SL), you can throw that out and pare down the lift formula to the following statements:

1- Lift is proportional to the square of the velocity.

2- Lift is proportional to the wing area.

3- Lift is proportional to the lift coefficient.

Therefore, you can see that a wing with an area of 200 square feet and a max lift coefficient of 2.0 will produce the same amount of lift at an identical velocity as a wing with an area of 400 square feet and a max lift coefficient of 1.0(200*2=400, 1.0*400=400).

This illustrates that while wingloading can give a lot of insight to the lift characteristics of an airplane, it does not take into account the lift coefficient of the airfoil which has the same relationship as wing area with regards as to how much lift is produced.

Induced drag should also be mentioned here, but the formulas are just a bit more involved than lift and potentially a lot more misleading. However, you can break it down to the following statements:

1- Induced drag is inversely proportional to the square of the velocity.

2- Induced drag is proportional to the square of the lift coefficient.

3- Induced drag is proportional to the wing area.

4- Induced drag is inversely proportional to the aspect ratio.

5- This is fairly minor, but the elliptical wing such as that on a Spitfire is the most efficient wing shape when determining the induced drag coeffiecient.

So here's the interesting part. Using the two hypothetical wings I used in the lift example, the 200 sf wing would produce twice as much induced drag as the 400 sf wing at their max lift coefficients even though both are producing the same amount of lift. BTW, this does assume both wings have the same AR and shape.

-Pyro

Bombom posted 12-17-98 04:48 AM ET (US)            

quote:

"....pilots of spits, hurri's, and bf109's all claimed that their aircraft had the tightest turning circle blah blah"

While Len Deighton is an excellent writer of spy stories and handles the BoB narrative rather well, he's no expert on aerodynamics or period aircraft :-)

It's a good read, but it's aimed at the general public.

-bmbm-, CO Royal Swedish Air Force

Fighting for Bullens Pilsnerkorv and lukewarm beer worldwide

kats Jg27 posted 12-17-98 10:00 AM ET (US)            

There has never been debate over the Bf109 having a tighter turn radius than the spit. All sources agree, (even Imol sources).

The is spit has a faster turn rate though, dang!@#$%^&

wulfer posted 12-17-98 10:20 AM ET (US)            

In that same book, commenting on the structuraly integrity of the aircrafts' wings, Len Deighton says something like: One's claim that a plane can out-turn another is really just a reflection of how foolhardy one's opponents have been.

An interesting thought.

wulfer

from out of nowhere! Check six ya'll!

cuda posted 12-17-98 01:14 PM ET (US)            

Thanks Kats for observing that Deighton never argued that the 109 was a better turning aircraft but only that it has a tighter turn radius.

I would be interested to hear what Wells and Pyro has to say about turn radius. I guess it is a factor of max AOA without stalling.

Pros, speak up!

cuda out

Cuda, CO 99th Dragons

Cuda's Warbirds Resources

http://www.99th.org/cuda/

IDIAMN 1 JG27 AFRIKA posted 12-17-98 03:22 PM ET (US)         

Thank you for all of your informative responses.

AGAIN, let me RE-EMPHASIZE that I am not holding this "len deighton" dudes word as truth but was just curious as to what involved the ability to have a tight turning radius. I am fully aware of the MANY inaccuracies that occur in undertakings of history and such, and unlike SOME people I never take anything as fact but mere "strong possibility".

My question has been answered thank you.

C U above,

"Hey...nice cannons"

Idi

Wells posted 12-17-98 06:26 PM ET (US)            

Pyro,

Thanks man!

Turn radius is a function of the square of the velocity and G-force.

r = (Mass * V^2)/Force (lift)

IMO, it's turn rate that is more important. A higher turn rate aircraft should 'always' be able to get it's nose on it's target while avoiding being shot.

ik Jagdgeschwader 77 posted 12-17-98 09:56 PM ET (US)            

hehe, despite all the great posts i think kats was the only one to dispell the myth with the correct approach

NOWHERE, did the author say the Emil turned faster (faster turn rate), he said that it had a smaller turn radius, which i think is true! I would say though that the Author is wrong when he said that having the smallest turning circle is vital to combat, that' SPEED.

Tchüß

ik

"I fly close to my man, aim well, and then he falls down." -Oswald Boelcke

Pyro posted 12-18-98 03:16 PM ET (US)            

k wrote:

NOWHERE, did the author say the Emil turned faster (faster turn rate), he said that it had a smaller turn radius, which i think is true! I would say though that the Author is wrong when he said that having the smallest turning circle is vital to combat, that' SPEED.

t's not the what in his statement that I object to, it's the why(I have read the report that he cites). It's that he attributes that performance to the wingspan and infers to the reader that a shorter wingspan leads to a tighter turning radius. My original post convoluted things because I didn't keep it specific to radius. But when discussing how the wingspan would affect this, it doesn't matter whether you are talking about rate or radius. All other things being equal, a shorter wingspan will not give you a better turn rate nor will not give you a smaller turn radius.

Wells wrote:

Turn radius is a function of the square of the velocity and G-force.

r = (Mass * V^2)/Force (lift)

To illustrate my point let's look at Wells' formula here and discuss the elements in it that would be affected by the wing. If you want to decrease your turn radius, you could either increase your lift or decrease your velocity. Velocity has a much greater effect on radius since it is the squared term. But again, it is the plane with better lift characteristics that will be able to fly at the lower speed and therefore have the smaller turn radius.

This is only part of the picture because it totally ignores thrust and drag, but it's only my point that attributing that smaller turn radius to the 109's smaller wingspan is totally incorrect.

-Pyro

worr posted 12-18-98 07:41 PM ET (US)            

IK wrote:

hehe, despite all the great posts i think kats was the only one to dispell the myth with the correct approach

With all due respect the title of this tread was the point of departure for me and many others. As has been pointed out there is more to turn performance--radius or rate--than one factor.

For example, take a very heavy air craft like the P-38 that also has higher wing loading, there is still the tremendous lift of that wing as well as the thrust two enginges produce. No one characteristic either as a strength or weakness will be the telling result.

Worr, out