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

[drgondog]

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]

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]

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]

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]

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.

 

[Kurfürst]

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.

... that`s a faulty conclusion based on insufficent information. We know there was an instruction for the 109F wingtips. Do we know the 109G still had this problem? How we do the Mustang and Spitfire (La7, Yak3, Typhoon etc.) did not have similiar problems? They are less well documented? Of course. The less details we dig up on a plane, the fewer skeletons we find in the cupboard. But that doesn`t effect the actual number of skeletons overall. They are there, even if we don`t know about it.

BTW, ever wondered why the 'pointed', ie. tall vertical stabiliser was introduced to the Spitfire..? Stabiliser fin to the p51d..? Tall tail to the 109?

These aircraft had more in common than not. Designers kept bumping into the same limits, no matter the country. Physics are universal.

 

[drgondog]

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:


"Official" ??

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

at 10,000 feet, 96 at 8,000 close to 80 at SL

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.

Page 29 of the "Pilot's Flight Operating Instructions AN 01-60JD-1" has the reference to Zero Sink speed - clean.

Multiple references are made to this including the instruction to not start climb until flaps are up and airspeed at least 110IAS... and do not side .slip the Mustang below 110 IAS, etc..

Stall speed is contained in Appendix II and varies with load but I have flown the airplane several times at 80-90 mph at 5000 feet to coax it into a clean stall, notably because my dad 'insisted' that I learn how easy it is to recover from. The bird would have weighed in the 8900+ weight range.

You were looking at 106mph/10,000 feet in your Power Off Stall chart and failed to notice (?) that the stall speed in that chart was down to 94 mph for 8,000 feet and continues to drop with increased density.

Crumpp's figures are`'correct' for good assumptions in performance calculations.

 

[drgondog]

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 - ??

I made an assumption based on drawings I have seen of the 109 that the main spar is around 45% chord - not so? or, just as intriguing the Center of Lift actually at 45%??

 

[drgondog]

... that`s a faulty conclusion based on insufficent information. We know there was an instruction for the 109F wingtips. Do we know the 109G still had this problem? How we do the Mustang and Spitfire (La7, Yak3, Typhoon etc.) did not have similiar problems? They are less well documented? Of course. The less details we dig up on a plane, the fewer skeletons we find in the cupboard. But that doesn`t effect the actual number of skeletons overall. They are there, even if we don`t know about it.

BTW, ever wondered why the 'pointed', ie. tall vertical stabiliser was introduced to the Spitfire..? Stabiliser fin to the p51d..? Tall tail to the 109?

These aircraft had more in common than not. Designers kept bumping into the same limits, no matter the country. Physics are universal.

There were no wintip issues with 51 or control reversal issues due to aileron loads causing too much twist in wing.

Having said this, the P-51 had sveral 'skeletons', all were well documented and none remain as skeletons... as you (and Crumpp) said - they all had problems and all were fixed.

The big ones for the 51 were a.) wheel door uplock failing to keep landing gear where it belonged in a dive, b.) bad batch of heat treated bolts for engine mounts, c.) increasing yaw as speeds increased from .75 to .81 Mach, d.) structural failure of Tail/aft fuselage due to asymmetrical loads at high speeds (i.e rolling in dive, snap roll at high speed), e.) ammo door deflection at high speeds causing a local increased lift and spar failure in high speed diving pullout.

To the best of my knowledge Kurfurst, there is no conspiracy to keep those shameful secrets hidden?

 

[Soren]

Page 29 of the "Pilot's Flight Operating Instructions AN 01-60JD-1" has the reference to Zero Sink speed - clean.

Multiple references are made to this including the instruction to not start climb until flaps are up and airspeed at least 110IAS... and do not side .slip the Mustang below 110 IAS, etc..

Stall speed is contained in Appendix II and varies with load but I have flown the airplane several times at 80-90 mph at 5000 feet to coax it into a clean stall, notably because my dad 'insisted' that I learn how easy it is to recover from. The bird would have weighed in the 8900+ weight range.

You were looking at 106mph/10,000 feet in your Power Off Stall chart and failed to notice (?) that the stall speed in that chart was down to 94 mph for 8,000 feet and continues to drop with increased density.

Crumpp's figures are`'correct' for good assumptions in performance calculations.

What are you talking about Bill ??!

The stall speeds are given for different weights, NOT different altitudes!

What the chart says is that the P-51D stalls at 106 mph at SL at 9,700 lbs ! At 10,000 lbs its 108 mph at SL. There's no way the P-51D is ever going to fly at 80 mph clean, the real stalling speed is WAY higher than that!

Btw, is it me or are you saying you actually fly the P-51 ?? - suspiciously late to come forth with this IMO.

 

[Crumpp]

Btw, is it me or are you saying you actually fly the P-51 ?? - suspiciously late to come forth with this IMO.

When your father is a P51 Ace, you think he might take you flying?

All the best,

Crumpp

 

[drgondog]

What are you talking about Bill ??!

The stall speeds are given for different weights, NOT different altitudes!

What the chart says is that the P-51D stalls at 106 mph at SL at 9,700 lbs ! At 10,000 lbs its 108 mph at SL. There's no way the P-51D is ever going to fly at 80 mph clean, the real stalling speed is WAY higher than that!

Btw, is it me or are you saying you actually fly the P-51 ?? - suspiciously late to come forth with this IMO.

You are right about the chart Soren - I was braindead on the quick glance at your chart.

As to a/c command time in the 51 - You haven't been paying attention. You have made more than a few 'not true comments' that I corrected based on my own experience with the ship. I have also commented that my own experience with cross wind landings does not co-incide with Manual just because it has a wide track gear!

I have 100 dual and 56.6 solo in a P1D-25 and -30.. I think I first mentioned it in June timeframe in a conversation with Joe about preferred landing speeds (I favored 110+ IAS Power on at 2700 rpm and 15-20 degrees flaps depending on how fast I wanted the sink rate.)

And Crumpp is correct on stalling speeds although I am reasonably sure he is talking about a bird at near max gross or at least combat load.- and yes the 51 stall speed for 8000-8500 pounds is somewhere in the range of 80-90 mph clean, power on, depending on a lot of factors... but much less than 110 IAS.

 

[drgondog]

When your father is a P51 Ace, you think he might take you flying?

All the best,

Crumpp

G - LOL - I'll tell You the story -it's worth it. Via email. The net is "there's nothing wrong with a fix - if you are in on it"

The USAF auctioned a lot of 51's when they got out of the biz in 1957-1958 and dad bought one.

He got a 51D-25 that had been completely overhauled, and included a spare 1650-7 with less than 25hrs on it. He traded that to Cavalier in return for a two seat TF-51D conversion..

He was one hell of a fighter pilot but perhaps an even better instructor. I miss him still and it's been 28 years.

My last time in the bird was back in 1985. If I was a biilionaire I would buy off the FAA docs and have one today.

Regards,

Bill

PS - both Jeff Ethell and I got our pilot's license before we got a driver's license - go figure. And Jeff's dad Irv was a squadron CO when my father was Gp CO of 35th in Japan - we grew up together, starting in Japan in 1948 - and I miss him.

 

[Crumpp]

I made an assumption based on drawings I have seen of the 109 that the main spar is around 45% chord - not so? or, just as intriguing the Center of Lift actually at 45%??

Hi Bill,

The AC has to be forward of the CG as you know. The limits of the CG are measured from Bulkhead 1 not from the LE of the wing. The main spar is located 1003.2mm from the LE and the most rearward CG location on the Bf-109G2 is 69.2cm from Bulkhead 1 <firewall>.

As you know, the most rearward portion of the CG has to in front of AC. The AC is in the vicinity of the spar were it should be as far as I can tell.

So I am not confusing you. Center of Lift and Aerodynamic Center are interchangeable terms today. You are probably used to Center of Pressure calcs where M = Lx.

Center of Pressure is seldom used today. The math gets hokey. As we approach zero lift mathematically our x reaches infinity and the Cp moves backward to infinity. This is of course impossible. You're probably thinking Cp is Center of Lift instead of AC. It used to be when we did Cp calcs.

AC is the point where all the torques of the Aerodynamic Forces are located.

To Soren's credit, Bill, there are plenty of folks who prowl these kinds of boards whose sole motivation is to up their game score and live out their ace fantasy. There is more than one BS artist around.

So readers will be able to follow what we are discussing.

Aerodynamic Center

All the best,

Crumpp

 

[drgondog]

Page 29 of the "Pilot's Flight Operating Instructions AN 01-60JD-1" has the reference to Zero Sink speed - clean.

Multiple references are made to this including the instruction to not start climb until flaps are up and airspeed at least 110IAS... and do not side .slip the Mustang below 110 IAS, etc..

Stall speed is contained in Appendix II and varies with load but I have flown the airplane several times at 80-90 mph at 5000 feet to coax it into a clean stall, notably because my dad 'insisted' that I learn how easy it is to recover from. The bird would have weighed in the 8900+ weight range.

You were looking at 106mph/10,000 feet in your Power Off Stall chart and failed to notice (?) that the stall speed in that chart was down to 94 mph for 8,000 feet and continues to drop with increased density.

(Wrong - I misread the chart - each condition for stall i power Off and different gross weights - called a brain fart on my part
Crumpp's figures are`'correct' for good assumptions in performance calculations.

correction made as noted