Corsair vs. BF 109G,K or FW 190's

[drgondog]

Originally Posted by Soren

Hehe 127 mph is not the stall speed, the landing speed was lower than that. The stall speed of the P-51D with flaps and gear retracted is 109 mph IIRC, and the FW-190 around 102 - 105 mph under the same conditions.

The zero sink rate flight speed of a clean 51D is about 110 IAS - which means at that speed it loses no altitude in level flight.

The Stall speed - clean- is about 80 +/- IAS.

The 51 typically rolls slowly to right in a level flight stall and immediately recovers (if you have altitude) by simply letting go of the stick.

[Crumpp]

The 109G wing was stiffened over the 109F by increasing the skin thickness over main to aft spar.

Hi Bill,

Excellent point. As a former structure guy, I am sure you will agree with the following and is exactly why you made the point on the skins.

It is common in these type of discussions to look at design change and make assumptions that frankly cannot be made.

Everyone,

The German duralumin alloy had a lower cupric content than the US duralumin. This meant is some ways, the German duralumin was stronger but in other ways weaker.

Generally speaking the German duralumin had a higher tensile strength and much better resistance to corrosion. The US duralumin had a higher shear strength and was more vulnerable corrosion.

The German construction also relied on thicker skins. In some places, the FW-190 wing skins for example are 2cm thick.

Point is that there is little to choose in the results. Both sides aircraft construction resulted in airframes which had the same ultimate load factors. The construction techniques reflect the base materials chosen for the airframes.

Trying to compare strengths based on the shape of the I-beam is not going to get anyone very far.

It is a leap of logic that cannot be made given the facts behind the engineering.

All the best,

Crumpp

[davparlr]

Originally Posted by renrich

My reference show the P51 D with a sea level vmax of 367 mph, the P51B was slightly faster at SL. The F4U 4 was fastest of all at SL(US fighters) with Vmax of 380 mph. Same reference shows the P51D is introduced into the 8th AF in March of 1944. Same reference shows F4U4 could climb to 20000 ft in 6.8 minutes. Another reference shows the FW190D9 took 7min 6sec to climb to 19685 ft. The F4U4 was a significantly better climber.

In May, 1944, both North American estimates and AF flight test show that the P-51B with 150 grade fuel, pulling 75" Hg, could exceed 380 mph at SL (without wing racks).

http://www.wwiiaircraftperformance.o...rade-level.jpg

http://www.wwiiaircraftperformance.o...level-blue.jpg

[drgondog]

Originally Posted by Crumpp

Hi Bill,

Excellent point. As a former structure guy, I am sure you will agree with the following and is exactly why you made the point on the skins.

It is common in these type of discussions to look at design change and make assumptions that frankly cannot be made.

Everyone,

The German duralumin alloy had a lower cupric content than the US duralumin. This meant is some ways, the German duralumin was stronger but in other ways weaker.

Generally speaking the German duralumin had a higher tensile strength and much better resistance to corrosion. The US duralumin had a higher shear strength and was more vulnerable corrosion.

The German construction also relied on thicker skins. In some places, the FW-190 wing skins for example are 2cm thick.

Point is that there is little to choose in the results. Both sides aircraft construction resulted in airframes which had the same ultimate load factors. The construction techniques reflect the base materials chosen for the airframes.

Trying to compare strengths based on the shape of the I-beam is not going to get anyone very far.

It is a leap of logic that cannot be made given the facts behind the engineering.

All the best,

Crumpp

Crump - Agreed with one minor departure.

As a structures guy I want the main spar as close as possible to the Center of Lift- nominally at 25%, so that I am not adding a Lift Force to the existing Moment by moving the main spar, to say at 45% Chord, away from Center of lift.. like the 109.

In effect that 109 wing was a small, eccentric beam (leading edge) at zero chord, big beam and skin at 45% and another small beam at flap line. So the Center of Lift was approximately mid way beteen leading edge (small beam) and main spar with a big freaking hole in the bottom in the worst place - called a wheel well.

I can make that wing stiff in bending by increasing the structure (and weight) with thicker skins to give me more cap size for tension and compression (and shear) but as I get further out toward the tip, building a torque box with decreasing sectional thickness is a problem and the simple lift in level flight is creating an additional torque to aero moment.

I would love to see exactly what the analysis looked like... particularly for the asymetric load of a turn in a diving pullout

[Glider]

Certainly there were warnings to German pilots that if a yaw developed in a dive the wing tips tended to come off. Instructions were given that the wing tips should be checked so it would appear that the weakness is one that would build up over time, as opposed to one off catastrophic failures

[drgondog]

Originally Posted by Glider

Certainly there were warnings to German pilots that if a yaw developed in a dive the wing tips tended to come off. Instructions were given that the wing tips should be checked so it would appear that the weakness is one that would build up over time, as opposed to one off catastrophic failures

Interesting - in most cases a structural failure in Yaw would occur in tail area - either at the point of vertical stabilizer/fuselage spars or the Rudder itself. Usually the source of 'do not roll in a high speed dive' or snap roll or sideslip warnings

[Soren]

Originally Posted by drgondog

The zero sink rate flight speed of a clean 51D is about 110 IAS - which means at that speed it loses no altitude in level flight.

The Stall speed - clean- is about 80 +/- IAS.

Exactly at what alt is this Bill and from where do you have this ??

The reason I'm asking is because the official figures are much higher.

This is from the POH:


As you can see the P-51D's stall speed in level flight was around 106 mph clean.

I don't have the official figure for the FW-190, I was hoping Crumpp would provide that, my guess is its lower though, esp. considering the much shorter take off run and distance to clear a 20m high object.

[Crumpp]

Certainly there were warnings to German pilots that if a yaw developed in a dive the wing tips tended to come off. Instructions were given that the wing tips should be checked so it would appear that the weakness is one that would build up over time, as opposed to one off catastrophic failures

AFAIK,

This does not show up in any of the high speed trials. That being said, any of these aircraft will suffer catastrophic structural failure if the limits are exceeded.

Hence we see the P51, Spitfire, and Bf-109 structural failures.

As a structures guy I want the main spar as close as possible to the Center of Lift- nominally at 25%, so that I am not adding a Lift Force to the existing Moment by moving the main spar, to say at 45% Chord, away from Center of lift.. like the 109.

The Center of Lift is located at the main wing spar in the Bf-109G. I can send you the ladeplan and the Ersatzteilliste. You might be thinking of the rearward CG limit. Remember that has to be just forward CoL if we want a controllable aircraft.

All the best,

Crumpp

[Crumpp]

my guess is its lower though

The FW-190A8's is about 110mph. The stall speed I used in my analysis are 89.5KEAS for the P51 and 94.4KEAS for the FW-190A8.

All the Best,

Crumpp

[Glider]

Originally Posted by Crumpp

AFAIK,

This does not show up in any of the high speed trials. That being said, any of these aircraft will suffer catastrophic structural failure if the limits are exceeded.

Hence we see the P51, Spitfire, and Bf-109 structural failures.

Crumpp

I hate asking this as it shows my age but what does AFAIK mean?

Re the reference to the wing tip failures, it was part of the Technical Instructions from Generalluftzeugmeister Berlin, 28th August 1942 so I have no reason to doubt its accuracy.

This would imply to me that it was a more common problem on the 109 as this was a general warning issued to all units.
I am not aware of similar warnings being sent to all Spitfire or P51 units.

Certainly I could be wrong on this and if anyone has a similar warning issued to allied units, I am happy to change my view.

[Soren]

Originally Posted by Crumpp

The FW-190A8's is about 110mph. The stall speed I used in my analysis are 89.5KEAS for the P51 and 94.4KEAS for the FW-190A8.

All the Best,

Crumpp

Roger, what about the Dora-9's then ?

[lesofprimus]

AFAIK = As far as I know...

[Crumpp]

Re the reference to the wing tip failures, it was part of the Technical Instructions from Generalluftzeugmeister Berlin, 28th August 1942 so I have no reason to doubt its accuracy.

Just as the P51's instructions found during the investigation into its wing failures.

Just as the Spitfire's longitudinal instability prompted similar warnings when plane started breaking up in flight.

The Spitfire's instructions go so far as to caution the pilot not to fly without bracing himself against the cockpit to ensure his stick inputs are very precise.

All of these were fixed in all of these designs. Including the Bf-109.

The Bf-109 developed a Dutch roll. A common stability issue even today. Fly a Pitts S-1 if you want to see some good Dutch roll. Normally this is a benign condition however any airframe pushed to the q-limits is going to come apart. Does not matter if it is a Bf-109, P51, Spitfire, or an SR-71.

Here is a page from the high speed trails. The results of this testing prompted a design change raising the q-limits of the Bf-109. Adding 13mm to the tail increases directional stability dampening the Dutch roll.

However even the small tail Bf-109's Mach number is unremarkable for a WWII fighter.

The small tail Bf-109's mach limit is placarded higher than the P51D's. Not that placard mach limits mean much in the WWII fighter. If you want to see that start converting British Airspeeds to the mach number listed. One day I am going to find Supermarine’s compressibility error standards in the National Archives, LOL.



Here is the P51D/K limit of Mach .75 with the elevator modification to correct the longitudinal instability:



Facts are all of the aircraft were limited to the vicinity of mach .8 simply due to the propeller. All of them would suffer catastrophic airframe failure if the q-limits were exceeded.

All the best,

Crumpp

[Crumpp]

Roger, what about the Dora-9's then ?

94.4KEAS

All the best,

Crumpp

[Glider]

Originally Posted by Crumpp

The Bf-109 developed a Dutch roll. A common stability issue even today. Fly a Pitts S-1 if you want to see some good Dutch roll.
Crumpp

We use something similar in a Glider when on a winch launch and the cable is to fast. To tell the winch operator that the launch is too fast you kick the rudder left and right, the secondry control effects ensure that there is plenty of yaw.
If your taking someone up on their first flight, it always causes deep gulps from the front seat.