f6f-5 vs 109

[Soren]

Hey Bonehead, what ou say we figure out how these two a/c compared ?

 

[drgondog]

Hey Bonehead, what ou say we figure out how these two a/c compared ?

Soren - my suspicion is that the 109 pounds the F6F in the horizontal and vertical but I am sooooo weary of screwing around with the spreadsheet when so much of the input data is either questionable with respect to facts that more than one source reliably points to.

I was having fun with HoHum because the P-38 would be a VERY interesting ship to look at close to stall in High G manuevers, particularly with manuevering flaps and two different airfoils.

The inboard secion (also completely immersed in propwash) has a much higher Clmax with the fowlers deployed - so what happens when the outboard NACA 4412 wing stalls out at a lower AoA -or is the effective AoA of the inboard section with flaps deployed high enough to stall the way it should - inboard to outboard?

And what effect does the counter rotating prop upwash have on the inboard section at high AoA?

I haven't looked at the twist on the outboard wing - if its a couple of degrees it might keep 'trucking' and not lose ailerons.

At any rate it is good to see you back and don't go humble on me - we both know I was part of a two dimensional problem

Regards,

Bonehead2

 

[Soren]

Yeah the P-38 discussion is interesting, and no doubt the maneuvering flaps would help raise the Clmax, but as with all kinds of trailing edge flaps they add a lot of drag. So I believe they'd be very handy at low speeds, one had to be careful about using them too early or one might loose potential energy way to quickly. The advantage the 109 has is first and foremost that it's a lot lighter and smaller, which is always a plus for a fighter, but also that it's got both the low drag + high lift LE slats and the split trailing edge flaps. (These compliment each other excellently) So if the P-38 tries to take it down low slow the 109 jocky could simply apply a little flaps and he'd be on the P-38's tail rather quickly.

That is my opinion atleast.

 

[drgondog]

Yeah the P-38 discussion is interesting, and no doubt the maneuvering flaps would help raise the Clmax, but as with all kinds of trailing edge flaps they add a lot of drag. So I believe they'd be very handy at low speeds, one had to be careful about using them too early or one might loose potential energy way to quickly. The advantage the 109 has is first and foremost that it's a lot lighter and smaller, which is always a plus for a fighter, but also that it's got both the low drag + high lift LE slats and the split trailing edge flaps. (These compliment each other excellently) So if the P-38 tries to take it down low slow the 109 jocky could simply apply a little flaps and he'd be on the P-38's tail rather quickly.

That is my opinion atleast.

I think about it in another way - independent of the speed in which both engage in a turning fight, they each have certain advantages which have to be looked at in a model.

The P-38 does not have the same degree of rudder feed requirement in a high G turn because of the counter rotating props and will be able to turn in either directtion with no distinct disadvantage.

The boosted ailerons of the J-25 and all P-38L gave this big beast excellent roll at all speeds and the power available vs power required gives it pretty good capability in the full spectrum of speeds.

It got very high praise in comparisons with the P-51 and P-40 in turn capability BEFORE manuevering flaps were installed and before boosted ailerons. The biggest flaw was sluggish roll to initiate or follow a turn before boosted ailerons.

The P-38J-25 and beyond had slightly better acceleration than a 51D but it had a lot more drag - and it has more drag than a 109 and it has a larger lift (wing) loading than either the 109 or the 51. The power loading for the 109G-6 (and beyond) was better than both the 51D and 38.

Both the 109 and the P-38 have a lot of drag when the manuevering flaps are down and the slats are out - but I suspect that the 109's only possible wing disadvantage is more potential asymmetric drag with the high wing than low wing with slats deployed - but would be difficult to account for that in the context of rudder trim drag to keep the nose on track. The 51 had a LOT less drag than both and I know this had a lot to do with the 51's ability to be comparable to the 109 in a turn.

The 38 was more forgiving on elevator forces in high G than either the 51 or the 109. I don't know what the metrics are, howver.

Intangible - The best air to air ratio in the 8th AF was the 479th when they were flying late model J's before conversion to Mustang in late Sept 1944 - but that also is when the 109 pilot skills were on the down slope. It was a very different beast from the ones that Expertens would use to train their wingman on the art of the kill.


There was something about the combinations of improvements in the P-38J-25 that made it a very formidable dog fighter beyond the metrics that surface in a model. If I had time I would really look at the wing.

 

[Soren]

I'm not really sure about the assymmetric drag, atleast I've never heard it mentioned by any pilots. The Emil had a lot of problems with its slats though, mostly due to frequent jamming of one of them, which could cause irrecoverable spins. The issue was solved completely with the F series though, the common consensus amongst pilots being that the a/c feels completely stable in turns and gives ample warning of an impeding stall, which comes a good deal after the slats deploy.

Anyway considering the much lower weight and smaller size of the 109, as-well has its higher Clmax and power to weight ratio, I am certain the 109 has a clear advantage in the horizontal compared to the P-38... and F6F, although the F6F would be closer. As for against the P-51, well at slow speeds its no contest, the Bf-109 easily beats the P-51 in a slow speed low alt turn fight. But at high alts, a P-51 is gonna have the advantage over a 109G-6 as its simply got loads more power available plus a lot less drag. Those are my observations at least.

At any rate a low wing loading (Or "lift loading") pretty much lost its importance at around 1942 where most fights took place at speeds exceeding 450 km/h, and at that speed most fighters could pull well over 6 G's, which is around the limit for a pilot. Thus light harmonious controls became more important than a low wing loading.

 

[drgondog]

I'm not really sure about the assymmetric drag, atleast I've never heard it mentioned by any pilots. The Emil had a lot of problems with its slats though, mostly due to frequent jamming of one of them, which could cause irrecoverable spins. The issue was solved completely with the F series though, the common consensus amongst pilots being that the a/c feels completely stable in turns and gives ample warning of an impeding stall, which comes a good deal after the slats deploy.

You know from your own experience two things - one is that you have to use rudder to carve a turn (best illustration is soaring and watching the tuft of yarn in front of cockpit). And you know the reason for that is the 'high wing is achieving more slightly more lift, and induced drag, on the high wing which gets us back to the first note.

My sense is that the 109, because of the slats creating creating more lift on the outboard half of the wing, is slightly more influenced by the upper wing than a P-38.

Hence my comment.

The second intuitive point is there is no "torque roll" with the P-38 which requires more rudder feed in one turn direction than the other as in example of a P-51/P-39

Anyway considering the much lower weight and smaller size of the 109, as-well has its higher Clmax and power to weight ratio, I am certain the 109 has a clear advantage in the horizontal compared to the P-38... and F6F, although the F6F would be closer. As for against the P-51, well at slow speeds its no contest, the Bf-109 easily beats the P-51 in a slow speed low alt turn fight. But at high alts, a P-51 is gonna have the advantage over a 109G-6 as its simply got loads more power available plus a lot less drag. Those are my observations at least.

I agree and we finally arrived at those conclusions after many months of debate. I also suspect the point you make below regarding control forces at high speed made a difference.

I remember dad remarking that the 109 in a high G turn required 'more' rudder pedal force (subjective) than a 51 in the similar manuever. Having said this, it can not be anything but a subjective comment as relative G would be impossible to establish and what exactly was 'more'?

At any rate a low wing loading (Or "lift loading") pretty much lost its importance at around 1942 where most fights took place at speeds exceeding 450 km/h, and at that speed most fighters could pull well over 6 G's, which is around the limit for a pilot. Thus light harmonious controls became more important than a low wing loading.

I agree with only a few mental reservations... and the P-38 is squarely in the strike zone where the lighter controls in high speed than the 109 may have been a 'plus' for the 38J-25 and above - if not necessarily a deciding factor.

Wing (lift) loading is stiil a relative factor of merit because it describes to a degree that when all things are equal (including airfoil/twist, fuselage, engine, weight) except the wing area, that the lower wing loading should enable a steeper bank angle for the same relative AoA (and velocity) to the wing...

or conversely for the same bank angle and velocity, the lower wing loading Wing has more lift (same Cl, same AOA, same airfoil, same velocity - more wing area) enabling a sustained turn at same radius and velocity as the higher wing loading ship - but over a greater range of velocities.

Taken further the lower wing loading ship can go slower at a greater bank angle to shorten the radius and maintain the same G level

All generalities and pardon me for rambling on the subject that you already know... i just needed to think through my caveats.

This analogy is why I still believe intuitively (w/o knowing what the 'blended CLmax for the 38 wing is) that a 109 in a sustained turn with a P-38 will out turn the P-38 (latest and greatest version) to the same g level tolerance of the pilots

Then we change the game to reflect a different wing, different Aspect Ratio, different drag charactristics, different engine, different control forces, etc and try to calculate turn performance.

 

[Soren]

My sense is that the 109, because of the slats creating creating more lift on the outboard half of the wing, is slightly more influenced by the upper wing than a P-38.

I don't see how as the slat on the lower wing is also creating more lift.

But again it depends on what kind of turn it is, cause if its a directly flat turn then both wings create the same amount of lift. The slats, which work by means of airpressure, should by themselves "sense" when extra lift is needed or not.

 

[drgondog]

I don't see how as the slat on the lower wing is also creating more lift.

But again it depends on what kind of turn it is, cause if its a directly flat turn then both wings create the same amount of lift. The slats, which work by means of airpressure, should by themselves "sense" when extra lift is needed or not.

For the wing to rise (by virtue of the aileron deflection) and the other wing to fall (by reverse aileron deflection) you are in a state of asymmetry.

For the wing that rises, independent of the slat, there is a local delta lift caused by the aileron - which in turn causes a local delta drag - tending to 'pull more' on the upper wing.

This is the reason you can't roll an a/c to the same point on the horizon without rudder input, or maintain a non yaw condition in the turn w/o rudder input.

The rudder is required to counteract the yaw created by the up wing.

When a slat deploys, say before stall is reached, it will continue to deploy slightly more on the upper wing ( theoretically for the reasons given above) as the upper wing is closer to effective AoA for stall due to the deflection of the aileron.

Think of the down deflection of the upperwing aileron as local hinged flap which gives both a higher local CL and CD.

 

[Soren]

I know but that could simply be offset by less aileron deflection to one direction. I really think it boils down to the same thing, which also seems to be confirmed by the pilots who express the a/c to be very stable in turns and a joy to push to the edge.

 

[drgondog]

I know but that could simply be offset by less aileron deflection to one direction. I really think it boils down to the same thing, which also seems to be confirmed by the pilots who express the a/c to be very stable in turns and a joy to push to the edge.

It has nothing to do with more or less stable.

If you reduce the side force on the stick and give the stick less deflection - resulting in less aileron deflection deflection -

It doesn't boil down to the same thing. Increase in lift for the wing - by whatever method - will increase drag on the wing.

If the high wing has slightly more lift (which it does) then it also has slightly more drag. As you 'decrease' the stick force gradually to center it, the airplane reaches the neutral yaw and roll (presumably) state - at which point the only rudder forces required are largely there to offset the torque contribution from the engine.

Without increase in Torque, but increasing aileron deflection more rudder force is required to keep the ac from a yaw to the upwing.

 

[Soren]

But it's the same for every a/c Bill, that's really all I'm trying to point out here.

The high wing will always be creating slightly more lift, and so wether it has slats or not wont make a difference, it just means an increased critical AoA for both wings. The slats start to extend at around 10 to 11 degrees AoA and fully extend at around 14 to 15 degrees AoA, so when pulling hard turns the slats are deployed fully symmetrically.

 

[drgondog]

But it's the same for every a/c Bill, that's really all I'm trying to point out here.

Soren - every wing exhibits same type behavior in a turn. Pause here and think about the relative chord angle from leading edge of each wing to the trailing edge of the aileron. They are at Different angles relative to the freestream AoA

The high wing will always be creating slightly more lift, and so wether it has slats or not wont make a difference, it just means an increased critical AoA for both wings.

Yes to the high wing having both a slight increase in lift, no to the low wing having a slight increase in lift.

The low wing has a lower critical AoA, particularly at the aileron area. It has an effective angle of attack due to the effective chord (leading edge of wing to trailing edge of flap) which Reduces the AoA to the lower wing aileron area.

The slats start to extend at around 10 to 11 degrees AoA and fully extend at around 14 to 15 degrees AoA, so when pulling hard turns the slats are deployed fully symmetrically.

Not likely.

With the lower effective freestream AoA (relative to aileron deflection change in effective chord) on the down wing it tends to enter the stall AoA for the aileron region later, after the high wing is already entering into stall AoA for the aileron region.

The high wing slat is activated by the impending stall before the low wing.

Statistically, because of wake turbulence that may be encountered in a turn chasing another a/c, the slat deployment may happen at the same time if the lower wing encounters indicial gusts which increase the relative AoA instantaneously over the freestream AoA.

 

[Soren]

I'm not entirely sure what it is you're trying to suggest Bill but it seems to go against what every pilot of the type says, and I certainly haven't experienced anything negative flying a slat equipped a/c. All I've experienced is a notable increase in turn performance, esp. a low speeds.

But to get back to the subject at hand;

Since the slats start to deploy already at 10 degrees AoA (On the 109 according to MTT documents) and are fully deployed at 15 degrees AoA (which is still 2 degrees from the original airfoils critical AoA), both slats will be fully deployed (aka symmetrically) in any form of high performance turn. The stall will occur at around 20 degree's AoA.

 

[drgondog]

I'm not entirelysure what it is you're trying to suggest Bill but it seems to against what every pilot of the type says, and I certainly haven't experienced any of that flying a slat equipped a/c. All I've experienced is a notable increase in turn performance, esp. a low speeds.

But to get back to the subject at hand;

Since the slats start to deploy already at 10 degrees AoA (On the 109 according to MTT documents) and are fully deployed at 15 degrees AoA (which is still 2 degrees from the original airfoils critical AoA), both slats will be fully deployed (aka symmetrically) in any form of high performance turn. The stall will occur a around 20 degree's AoA.

I believe the data. Where we are bogged down is visualizing the physics of the outboard span of the wing where the outer edge of the slat exists and the aileron exists. These are two extra lift devices for the wing in flight

Soren, take the slats out of the discussion for now.

Break this down to a 'local wing-upsdide' and a 'local wing-downside'

The LW-U has a 'flap (aileron) which deflects down. This 'new' condition for that LW-U is now experiencing is one of a.) increased Lift, b.) increased drag and c.) an increase in the 'local AoA' of the Freestream to the 'new' LWA environment.

Bring the wing back in for the outboard span area.

With the deflection of the aileron for LW-U the effective chord line of the airfoil/aileron ('flap') from leading edge of the wing (and slat) to the trailing edge of the aileron. For small to medium deflections this local effect increases Camber And Chord angle to the freestream.

For the LW-U this results in an immediate increase in local AoA to the freestream, increased Lift (just like a flap deflection in landing) and increased drag.

Bring the slat back in. It senses the pressure distribution behind the outer region of the slat as the AoA of the entire wing closes on 10 degrees.

But the slat on the LW-U will experience that change earlier because the local AoA of the aileron region (and outboard slat region) is higher than the inboard section of the wing. This upwing slat should start the deployment slightly earlier than it would if the aircraft was in level, symmetric flight.

The lift distribution on the inboard span does not change perceptibly, but the outboard span increases its lift (and drag) contribution from level flight with same AoA to wing and airframe.

The exact opposite scenario will occur for LW-U which has equal but Negative lift and the same drag - but the new 'effective chord' and angle to Freestream has the Opposite effect on local AoA, which reduces the local Lift/Drag of that aileron region of span relative to the inboard wing.

On the lower wing, the inboard span experiences no perceptible change in lift, but the outboard span decreases its Lift contribution in comparison to level flight.

Think of this in a different way. When the Up Wing Aileron deflects down - it is similar to locally reducing the twist of the wing and locally increasing AoA and locally increasing Lift and Drag - whereas the Down Wing aileron deflection Up Increases local twist and Reduces local Lift, Drag and AoA.

The Up wing will 'tug' on the airframe more than the Down wing and in parallel the Up wing slat should start to deploy slightly sooner than the down wing.

The pilot flying this aircraft should not sense anything unusual except he will be applying slightly more rudder than he would if the slats are 'wired shut'.

I don't know another way to describe this.

 

[Soren]

Oh I understood from the beginning, but I've never heard anyone comment about using more rudder than usual in slat equipped a/c, and I've never experienced it myself. But if it is the case then it is extremely minute and insignificant, so much so that it really can't be sensed.

 

[drgondog]

Oh I understood from the beginning, but I've never heard anyone comment about using more rudder than usual in slat equipped a/c, and I've never experienced it myself. But if it is the case then it is extremely minute and insignificant, so much so that it really can't be sensed.

>Since the slats start to deploy already at 10 degrees AoA (On the 109 according to MTT documents) and are fully deployed at 15 degrees AoA (which is still 2 degrees from the original airfoils critical AoA), both slats will be fully deployed (aka symmetrically) in any form of high performance turn. The stall will occur at around 20 degree's AoA.>

Where I underlined your comment would suggest that you didn't quite understand the concept of a modest asymmetrical early deployment of the high wing slat first. I am not suggesting it is a 'zero to full' slat deployment as they don't work that way.

Since you have to fly simultaneously in two exact same aircraft -one with/one without slats deployed - how would you know how much incremental rudder was required?

Which slat equipped aircraft do you have time in?

 

[Soren]

I haven't flown two otherwise identical a/c, one with slats and one not, but I fly the Cessna Aerobat, and I've tried several STOL a/c of the same weight, and they do turn a lot better.

Also we flew 3 STOL a/c in formation once, chasing each other, and I never felt any disturbance to the slats. Ofcourse I could feel the propwash, but so would I in any a/c.

And regarding what I said about the slats being deployed symmetrically, I was talking about a high performance turn where both wings have exceeded 15 degree's AoA, at that point both slats will be fully deployed and are therefore symmetric.

 

[Glider]

I only flew in an Aerobat a couple of times some years ago and could be very wrong, but I thought they had Fowler flaps, not leading edge flaps as in the 109 which would perform quite differently.

 

[Soren]

The Aerobat doesn't have slats.

 

[Glider]

Thats what I thought