# Bubble canopies?



## vinnye (Oct 29, 2012)

I wonder why some fighter designs went from Razorback designs (Spitfire, P51 and P47) and some did not (F6F and F4U)?
The benefits seemed to be better all round visibility and possibly better aerodynamics?
So why did the two best fighters in the Pacific not follow suit?


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## wuzak (Oct 29, 2012)

The F2G version of the F4U was to have a bubble canopy.

I'm guessing that production won over potential improvements, including bubble canopies.


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## vinnye (Oct 29, 2012)

I was wondering if that may have been a reason?
They were both excellent fighters already and were getting the jod done as is - so maybe left that way?


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## MikeGazdik (Oct 29, 2012)

In reading some Grumman testing articles, I believe with Corky Meyer, they were dealing with problems of directional stability problems when testing bubble-canopies. With the U.S. Navy having a very conservative record, I think it may be they did not want to risk making a change for that reason, and interrupting supply as stated. The U.S. Navy would control the procurement of both the F5f and F4U.


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## CobberKane (Oct 29, 2012)

In effect, the Hellcat did get its bubble canopy - and a lot more besides. They called it the Bearcat. Bear in mind too that blown canopies can frequently be less aerodynamic than canopies that are faired into the fuselage, because they create a zone of low pressure in the space where the raised fuselage used to be. This can also cause directional instability. The Malcom hood P 51 was held by many pilots to be faster than the P51D, and the later model required the addition od a raised fin forward of the tail to restore stability. The trade off was massively improved visibility - vital for a fighter pilot.


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## davebender (Oct 29, 2012)

Too late to help the USN. However French pilots flying CAS missions in Indochina probably appreciated the F8F.


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## vinnye (Oct 29, 2012)

OK - I get the fact that the change to a bubble canopy changed the aerodynamics and affected stability. I am sure this happened with the Spitfire, P51 and P47 as well, and solutions were found to overcome this. The improved visibility was a benefit worth making the changes for. Unless you need quantity at all costs - which seemed to be the US Navy's primary concern.
It now seems worth asking why the LW did not copy this idea. I have seen a P51 pilot get into a Me109 and could not believe how poor the visibility was!


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## drgondog (Oct 29, 2012)

CobberKane said:


> In effect, the Hellcat did get its bubble canopy - and a lot more besides. They called it the Bearcat. Bear in mind too that blown canopies can frequently be less aerodynamic than canopies that are faired into the fuselage, because they create a zone of low pressure in the space where the raised fuselage used to be. This can also cause directional instability. The Malcom hood P 51 was held by many pilots to be faster than the P51D, and the later model required the addition od a raised fin forward of the tail to restore stability. The trade off was massively improved visibility - vital for a fighter pilot.



Cobber - The Malcom Hood P-51B-1 with high altitude Merlin 1650-3 was faster for equal load out than any of the P-51D's. The dorsal fin mod was applied to Both the P-51B and D. The yaw stability issue had nothing to do with either the canopy or the razorback (although it was thought so). It was only when the P-51H with 13" extended fuselage and re-designed vert Stab that yaw issues were resolved..

As to the adverse pressure gradient on the windscreen the P-51D was superior with greater slope. See the Lednicer report I posted in the P-51 performance Thread.

http://www.ww2aircraft.net/forum/flight-test-data/p-51-performance-thread-12670.html post #4


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## tyrodtom (Oct 29, 2012)

You really can't say the Luftwaffe needed to copy the bubble canopy, the Fw190 was flying in action with a bubble canopy before any allied fighters , I believe. But they never redesigned the Me109 for a bubble. The Me209 and Me309 both had bubble canopies, didn't they ?


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## zoomar (Oct 29, 2012)

I think the pure bubble canopy is one of those innovations that were really just cosmetic, and did little if anything to improve the planes that had them. Kind of like fins on 1950's cars. Since they were uniquely western (US and UK) and thus continued into the postwar jet age thay are also associated with modernity. I've read that many USAAF and RAF pilots preferred Mustangs with Malcom hoods to P-51Ds, while the A6M was lauded for its visibility from the many framed glasshouse canopy it had. No Soviet, Japanese, or German wartime fighter had true bubbles (all-round vision framed canopies such as those most Japanese planes had and which were on late war Yaks and Las as well as the Me-262 are not the same as bubble canopies), and only the prototype Fw-190 sported what we might consider a true bubble.


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## tyrodtom (Oct 29, 2012)

Making the bubble canopy was why most were slow to adopt it, not because they didn't care about fashion.

Getting a relately distortion free bubble wasn't easy, it took a lot of experimenting with materials and techniques to get it right. We take for granted all the things made with plastics today, in the early 40's, big, clear, bubble canopies, that you had good wision through and the sun didn't turn opaque in a few months, were new technology that not everybody had perfected.

When you speak of the Zero canopy, you need to know that all the flat panes in it were glass, not safety glass, not tempered glass, just common glass.


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## wuzak (Oct 29, 2012)

tyrodtom said:


> You really can't say the Luftwaffe needed to copy the bubble canopy, the Fw190 was flying in action with a bubble canopy before any allied fighters , I believe.



Westland Whirlwind


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## tyrodtom (Oct 29, 2012)

wuzak said:


> Westland Whirlwind


 You're right, the Whirlwind prototype did fly before the first Fw190, but close enough in time so that I would doubt Tank copied the Whirlwind's canopy.


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## yulzari (Oct 29, 2012)

Makes the Miles M20 canopy all the more impressive.


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## drgondog (Oct 29, 2012)

zoomar said:


> I think the pure bubble canopy is one of those innovations that were really just cosmetic, and did little if anything to improve the planes that had them.
> 
> *That would be wrong - the difference in rear visibilty was HUGE and important for tear drop (Bubble) canopies. The difference in the Malcolm hood versus birdcage canopy was important in the 5 O'Clock to 7O'clock visibility to such fighters as the Spit and P-51B.*
> 
> ...



There is a reason most top air combat fighters (F-22, F-15, F-16, MiG 35, etc) have Full 360 vision Bubble canopies...


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## CobberKane (Oct 29, 2012)

zoomar said:


> I think the pure bubble canopy is one of those innovations that were really just cosmetic, and did little if anything to improve the planes that had them. Kind of like fins on 1950's cars. Since they were uniquely western (US and UK) and thus continued into the postwar jet age thay are also associated with modernity. I've read that many USAAF and RAF pilots preferred Mustangs with Malcom hoods to P-51Ds, while the A6M was lauded for its visibility from the many framed glasshouse canopy it had. No Soviet, Japanese, or German wartime fighter had true bubbles (all-round vision framed canopies such as those most Japanese planes had and which were on late war Yaks and Las as well as the Me-262 are not the same as bubble canopies), and only the prototype Fw-190 sported what we might consider a true bubble.


 
Sorry zoomar, but this initial statement is plain nonsense. The designers did not go to all the hassle of developing blow canopy maunfacturing and then have to tackle the handling issues they caused just for the purpose of making their plane pretty - they did it becase bubble canopies provided significantly improved vision, particularly in the vital rearward quadrant. The many positive comments of pilots who flew such aircraft as the P 51 and P 47 after this modification indicate how important it was. I agree though that there seems to be a bit of confusion about the difference between a bubble canopy, as fitted to the P51D, and a raised framed canopy as fitted to the Zero. A bubble canopy consists of a large rear section of self-supporting blown perspex that secures against a much smaller framed foward section that usually incorporated a plate of armoured glass. A raised framed canopy is simply domed framework fitted with glass panels. it would provide better all round vision than a faired framed canopy, but nowhere near as good as a bubble canopy.


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## GregP (Oct 29, 2012)

There is a strong misconseption that switiching to a bubble canopy caused instability in the P-51D / K. Not so .... really.

There were a NUMBER of culprits:

1. Changing from the Allison to the Merlin resulted in considerably more area forward of the CG when they fitted the larger, 4-bladed propeller.
2. They ALSO put in the fuselage tank, and THAT moved the CG backward while simultaneously having more blade area forward of the CG. They were looking for solutions to that when they went to the P-51D and the bubble canopy. The dorsal fin extension helped cure the problem in the P-51D and it was retrofitted not only to many P-51D and K models that were originally shipped without it, but also to many P-51B and C models that also were originally shipped without the doral fin extension.

The main cuplrits were the new prop for the Merlin and teh fuselage tank; the bubble canopy was minor in comparision to the first two. 

Here is a drawing of a famous P-51B WITH the dorsal fine xtension: http://information2share.files.wordpress.com/2011/06/north-american-p51-b-mustang.jpg


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## CobberKane (Oct 29, 2012)

GregP said:


> There is a strong misconseption that switiching to a bubble canopy caused instability in the P-51D / K. Not so .... really.
> 
> There were a NUMBER of culprits:
> 
> ...


 
How about the fin on the P47N?


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## GrauGeist (Oct 29, 2012)

I hate to say this, but the Fw190 did not have a true bubble canopy and neither did the Me262...both had the trailing portion of the canopy faired into the fuselage where the P-51, Typhoon and P-47D (etc.) did not. These were bubble canopies.


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## gumbyk (Oct 29, 2012)

What I understand is that it was the reduction in vertical area aft of the C of G that caused stability issues, hence the fillet on the fin. It wasn't the bubble canopy (or whatever you want to call it)per se, but the other changes in the airframe as a result.


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## GregP (Oct 29, 2012)

The P-47 was not the P-51, and the bubble canopy did cause a slight instability. Since the P-51 drosal ahd already been tried and it worked, it was natural to try it out on the P-47, where it ALSO worked. A general rule of aerodynamics is that if you remove wetted area behind the CG, you must add it somewhere else to restore the lost directional stability. They could have accomplished the same thing if they simply increased the vertical fin area by a similar amout to the dorsal extension ... but that would have caused a production interruption ... a real no-no in WWII's middle to late stages for the U.S.A.

We were winning with the tools in place at the time, so we didn't want to interrupt the flow of war materiel to the various fronts. It turned out to be the correct decision, didn't it?


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## R Pope (Oct 30, 2012)

Grumman's method of manufacture could have had a bearing on why they never went to a bubble. The fuselage was built up of rings of simple-curved sheet metal with rivetting flanges bent inward so the rivets were inside. Simple and strong, but requiring much redesign to make any changes. Not just a question of swing off the formers and reskinning.


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## CobberKane (Oct 30, 2012)

GregP said:


> The P-47 was not the P-51, and the bubble canopy did cause a slight instability. Since the P-51 drosal ahd already been tried and it worked, it was natural to try it out on the P-47, where it ALSO worked. A general rule of aerodynamics is that if you remove wetted area behind the CG, you must add it somewhere else to restore the lost directional stability. They could have accomplished the same thing if they simply increased the vertical fin area by a similar amout to the dorsal extension ... but that would have caused a production interruption ... a real no-no in WWII's middle to late stages for the U.S.A.
> 
> We were winning with the tools in place at the time, so we didn't want to interrupt the flow of war materiel to the various fronts. It turned out to be the correct decision, didn't it?


 
Sounds good to me! I believe Hawker went through pretty much the same process with the Tempest, although they redesigned the whole fin rather than sticking a fillet on it. How about the
FM2 compared to the F4F ? No bubble canopy, obviously - a design reaction to compensate for the extra torque of the more powerful engine?


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## bobbysocks (Oct 30, 2012)

as i understand it the dorsal fin was more to address an issue the 51 had from the beginning even with the razorback. the eppenage had a structural issue and would break away from the fuse either in a high G pull out ( or turn ) ...or a high speed roll...like a snap roll. i cant remember which it was or if it was both. but it was a result also of the higher HP and torque of the merlin over the allison. the airframe had been designed witht he allison rating and was not modiflied in the tail section once the engines were swapped. IIRC the mod was after D-15 and retrofitted to all war fit ac...Cs and Bs ( if they still had any ). to address the stability they increased the size of the rudder and the horizontal stabilizer but that was later.


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## GregP (Oct 30, 2012)

The tail did not break away in a high speed roll ... it was simply not stressed for snap rolls, which are almost always lower speed rolls anyway. NOBODY snap rolls from cruise speed! A snap roll is basically a horizontal spin, and nobody enters a spin from crusie speed either.

If the P-51 did a very high speed aileron roll, there was no problem, nor were point rolls or slow rolls, just snap rolls, usually called a flick roll (1 snap roll) or a vertical reverse (1/2 snap roll) in WWII. The P-51 was also not to be aerobated if there were any fuel in the fuselage tank ... it was suppose to be empty or nearly so since the fuselage tank effectively moved the CG too far aft when it was significantly filled.

For more explanation of my earlier post about an increase in blade area forward, the Bell P-63 used a 4-bladed prop and was designed for it. Some people tried to retrofit a G-series Allison and a 4-bladed prop to the P-39 for racing. When they did, it became alost unflyable due to the increase in blade area forward of the center of lift. Think of the Mike Carol P-39 accident in California. I know I said CG eariler, but I believe it is area ahead and behind the CL, not the CG. They are close to one another, but not the same.

Drogondog, do I have that right, increasing the blade are ahead of the CL requires compensation behind the CL with an increase in fin or rudder area, or moving the existing fin and rudder area back to create proper directional stability balance, right? That would mean yaw and pitch stability, not roll stability, which is unaffected by blade area ahead increases of the CL.


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## barney (Oct 31, 2012)

bobbysocks said:


> as i understand it the dorsal fin was more to address an issue the 51 had from the beginning even with the razorback. the eppenage had a structural issue and would break away from the fuse either in a high G pull out ( or turn ) ...or a high speed roll...like a snap roll. i cant remember which it was or if it was both. but it was a result also of the higher HP and torque of the merlin over the allison. the airframe had been designed witht he allison rating and was not modiflied in the tail section once the engines were swapped. IIRC the mod was after D-15 and retrofitted to all war fit ac...Cs and Bs ( if they still had any ). to address the stability they increased the size of the rudder and the horizontal stabilizer but that was later.



"Unless a dorsal fin is installed on the P-51B, P-51C and P-51D airplanes, a snap roll may result when attempting a slow roll. The horizontal stabilizer will not withstand the effects of a snap roll. To prevent recurrence, the stabilizer should be reinforced in accordance with T.O. 01-60J-18 dated 8 April 1944 and a dorsal fin should be installed. Dorsal fin kits are being made available to overseas activities"

A U-boat sank the ship carrying these first kits.

As I recall, the reinforcement of the horizontal stabilizer amounted to the installation of larger diameter rivets.


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## drgondog (Oct 31, 2012)

GregP said:


> The tail did not break away in a high speed roll ... it was simply not stressed for snap rolls, which are almost always lower speed rolls anyway. NOBODY snap rolls from cruise speed! A snap roll is basically a horizontal spin, and nobody enters a spin from crusie speed either.*Greg, IIRC there was a cautionary put out regarding slow rolls also but I'll have to research that*
> 
> If the P-51 did a very high speed aileron roll, there was no problem, nor were point rolls or slow rolls, just snap rolls, usually called a flick roll (1 snap roll) or a vertical reverse (1/2 snap roll) in WWII. The P-51 was also not to be aerobated if there were any fuel in the fuselage tank ... it was suppose to be empty or nearly so since the fuselage tank effectively moved the CG too far aft when it was significantly filled.
> 
> ...



Greg - I do not know. Offhand I can't see any reason why switching from three blade to four would alter stability in any way. It was not a factor for any of the P-51 series including experimenting with a five blade prop - Ditto Spitty. It shouldn't alter thrust axis, could affect some characteristics of the prop vortex, but can't see how it affects stability around X, Y or Z axis.


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## wuzak (Oct 31, 2012)

drgondog said:


> Greg - I do not know. Offhand I can't see any reason why switching from three blade to four would alter stability in any way. It was not a factor for any of the P-51 series including experimenting with a five blade prop - Ditto Spitty. It shouldn't alter thrust axis, could affect some characteristics of the prop vortex, but can't see how it affects stability around X, Y or Z axis.



But the extra power would cause the change?

Rolls-Royce's conversion was found to have very poor stability, until they added fin area. NAA altered more than Rolls-Royce did in changing to the P-51B. IIRC teh wing was moved relative to the fuselage.

I'm not sure with the XII, but the thrust line for the Spitfire XIV did change - the engine was angled down to give a better view over the nose for the pilot, which in turn required a smaller diameter prop and the need for 5 blades to absorb the power.

The engine in the XII wasn't angled down, but I am unsure as to the relative position of the thrust line.


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## drgondog (Oct 31, 2012)

gumbyk said:


> What I understand is that it was the reduction in vertical area aft of the C of G that caused stability issues, hence the fillet on the fin. It wasn't the bubble canopy (or whatever you want to call it)per se, but the other changes in the airframe as a result.



It was the addition of the 85 gallon tank aft of the seat which caused the aft cg issue. The vertical stabilizer for P-51A-D was slightly inadequate in low speed when the Merlin engine replaced the Allison. The aft fuselage structure was marginal at design load limits in asymmetric flight conditions (High speed roll) as well as a snap roll at any speed.

While the notion that loss of the turtleback was the cause of yaw issues in a dive, the primary reason was that the rudder was neither sized nor stressed for the major jump in torque for the Merlin version. The P-51B/C had these same issue to a slightly less degree at high speed. 

The P-51H specifically addressed the associated problems when they introduced the vertical stabilizer/rudder`increase in size and Lengthened the airframe aft of the CG by 13". The P-51H had Very few common parts with any previous P-51A-D.

The ventral fin did slightly improve yaw characteristics but that was it. I will have to scratch my head and see what if anything NAA did to improve the structural capabilty of the eppenage section - but I doubt that increasing rivet size in the elevator was performed. Rivets are there to introduce shear loadpaths for skins and loss of the eppenage should not have anything to do with shear panel buckling per se - the buckling, if any occurred, would have been due to the primary load path (Spar/bulkhead) failure. IIRC the observed failure mode was first the vertical stab/rudder failed along with the aft section of the fuse where the vert tail main spar connected to the fuselage. 

Candidly I never heard of an elevator/horizontal stabilizer being the cause of any structural failure - although the fabric covered elevators were replaced by metal elevators beginning with the P-51D-10 (when the dorsal was introduced in production) and both were retrofitted to all Mustangs (P-51B-1 through P-51D-5) as field kits.


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## drgondog (Oct 31, 2012)

wuzak said:


> But the extra power would cause the change?
> 
> *Wayne - the extra torque of the Rolls was the root cause of directional stability issues with the P-51B-D. Additionally the 4 blade Hamilton Standard prop was 5" greater in diameter and obviously with greater mass distributed radially away from the thrust axis.*
> 
> ...



Additionally, the wing plan view (Root Chord to WS 61.5) changed from the B/C to the D series to accomodate new wheel cover doors and gear uplock re-design. Zero change to the airfoil, span, tip, flap, etc.


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## GregP (Oct 31, 2012)

Adding power always decreases stability since the aircraft is most probably flying with the power it was designed for to start with.

According to Pete Law, several test pilots, and my aerodynamics courses way back when the earth cooled, adding blade area ahead of the CL will decrrease stability. The additional power wouldn't have any effect until the original power level was exceeded. That is, if the Merlin were to be operated at the Allison power level, then the only destabilizing force would come from the additional blade area ahead of the CL ... which is one of the factors in the case of the P-51B/C versus the P-51A.

The combination of extra blade area ahead of the CL, more power, and fuselage tank were enough to make it a real handful early in the escort flight. At takeoff, they could not fight effectively at all, and needed to at least burn off most of the fuselage tank before they were effective or very maneuverable.


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## bobbysocks (Oct 31, 2012)

when based in england engaging the enemy shortly after take off was a slim chance. shortly after take off they would burn fuel in the fuse tank until it was down to ~35 gal ( ~50 min flight time ) and then switch to drop tanks. that 50 minutes was generally forming up and gaining alt while heading across the channel. now for 51s based in europe after d-day that is a different matter. they were closer to the front and actally in the case of y-29 they got into battle shortly after take off. in those planes did they even used the fuse tank as they really didnt need the range?


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## barney (Oct 31, 2012)

drgondog said:


> Candidly I never heard of an elevator/horizontal stabilizer being the cause of any structural failure - although the fabric covered elevators were replaced by metal elevators beginning with the P-51D-10 (when the dorsal was introduced in production) and both were retrofitted to all Mustangs (P-51B-1 through P-51D-5) as field kits.



Google "T.O. 01-60J-18 dated 8 April 1944" to find many references to this modification.


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## drgondog (Oct 31, 2012)

barney said:


> Google "T.O. 01-60J-18 dated 8 April 1944" to find many references to this modification.



Found many references but could not find the Technical Order itself. Still skeptical about solving the problem with a larger shank rivet. That would reduce shear stress on both a supporting doubler/spar as well as the shear panel - but don't see how that solves a structural failure that almost had to be due to bending.


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## Milosh (Oct 31, 2012)

bobbysocks said:


> when based in england engaging the enemy shortly after take off was a slim chance. shortly after take off they would burn fuel in the fuse tank until it was down to ~35 gal ( ~50 min flight time ) and then switch to drop tanks. that 50 minutes was generally forming up and gaining alt while heading across the channel. now for 51s based in europe after d-day that is a different matter. they were closer to the front and actally in the case of y-29 they got into battle shortly after take off. in those planes did they even used the fuse tank as they really didnt need the range?



They took off with a full fuel load.

From Bodenplatte, pg 152: ".... went into dogfights with all tanks full."


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## drgondog (Oct 31, 2012)

GregP said:


> Adding power always decrfeases stability since the aircraft is most probably flying with the pwoer it was designed for to start with.
> 
> According to Pete Law, several test pilots, and my aerodynamics courses way back when the earth cooled, adding blade area ahead of the CL will decrrease stability. The additional power wouldn't have any effect until the original power level was exceeded. That is, if the Merlin were to be operated at the Allison power level, then the only destabilizing force would come from the additional blade area ahead of the CL ... which is one of the factors in the case of the P-51B/C versus the P-51A.
> 
> ...



I have never flown a fully loaded 51. I have had many hours of interested 'shop talk' about the Mustang during WWII escort operations. Nobody considered it a 'real handfull' early in the escort flight simply because there were no high G maneuvers experienced in takeoff rool, formation assembly and climb out - and by the time they were crossing the channel the aft c problem was not a problem. As to fight effectively maybe JC Meyer was lucky when he shot down an FW 190 before his gear was fully retracted, then another one 5 miles out from Asch - all with full fuselage tank.

Fully understood that they were not high G manuevers - just a skillful pilot managing the fight with full understanding of his current limitations.

I would love to hear Pete Law's theory on the stability issues created by higher disk density - and help me understand why there seems to be no common ground for consistency?


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## Milosh (Oct 31, 2012)

I think GregP has been reading too many of Gaston's posts.


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## CobberKane (Oct 31, 2012)

GregP said:


> Adding power always decrfeases stability since the aircraft is most probably flying with the pwoer it was designed for to start with.
> 
> According to Pete Law, several test pilots, and my aerodynamics courses way back when the earth cooled, adding blade area ahead of the CL will decrrease stability. The additional power wouldn't have any effect until the original power level was exceeded. That is, if the Merlin were to be operated at the Allison power level, then the only destabilizing force would come from the additional blade area ahead of the CL ... which is one of the factors in the case of the P-51B/C versus the P-51A.
> 
> The combination of extra blade area ahead of the CL, more power, and fuselage tank were enough to make it a real handful early in the excort flight. At takeoff, they could not fight effectively at all, and needed to at least burn off most of the fuselage tank before they were effective or very maneuverable.


 
You would have to to think that by the end of the war the torque effect of increasingly powerful engines was really pushing conventional airftames and airscrew systems to the limit and if the jets hadn't come along things like contra-rotating props would have become virtual neccessities. When the Tempest was in it's development stage the torque effect from the engine was so strong that test piolts would start facing in the opposite direction from the intended take-off run, do a sweeping torque induced 180 degree turn onto the runway, by which time there was enough airflow over the rudder to compensate and hopefully they would be pointing in the right direction. Not exactly ideal practice for the average pilot on a crowded runway!


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## barney (Oct 31, 2012)

drgondog said:


> Found many references but could not find the Technical Order itself. Still skeptical about solving the problem with a larger shank rivet. That would reduce shear stress on both a supporting doubler/spar as well as the shear panel - but don't see how that solves a structural failure that almost had to be due to bending.



Sorry about that - try here
TO 01-60J-18 Reinforcement of horizontal stabilizer and fin - P-51B, P-51C, P-51D and P-51K


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## bobbysocks (Oct 31, 2012)

i dont remember reading anything specific about separation of the eppenage that i can remember. i do recall is reading the terms "structural failure" and "catastrophic failure of the horizontal stabilizer" in relation to this subject which gave no specifics. so, i erroneously filled in the blanks as meaning separation. my main crux i was trying to get across was the dorsal fin is more often that not attributed to the streamlining of the fuse when the bubble canopy is used and not to fix the problems that existed prior to that. mention was made about the replacement of fabric with metal skins.... looking into to it a little more i found this...its the first time i heard of the crafts tendency to "porpoise"

Note on Dive Tests on ‘Mustang IV’


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## nuuumannn (Oct 31, 2012)

> Makes the Miles M20 canopy all the more impressive.



Beat me to it - the first British one anyway.


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## wuzak (Nov 1, 2012)

nuuumannn said:


> Beat me to it - the first British one anyway.



What about the Whirlwind?

It flew earlier. Are you discounting that because it had a small frame to support the bubble?


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## GregP (Nov 1, 2012)

Hi Drgondog,

Airplane Stability and Control: A History of the Technologies that Made ... - Malcolm J. Abzug, E. Eugene Larrabee - Google Books

See page 53 about propeller balde area from the side as a desabilizing effect in aircraft stability ... all Reno racers know this and are very careful to creep up on it. In a tractor aircraft, if you increase the blade area, you MUST incresae the aft vertical tail area or moment to compensate for the loss in stabilizing effects of tail area and keel area for the power being employed.

It happens even in jets. The original F-100 was unstable in yaw and had to have the fin area increased when the production verion had more thrust than the prototype.

It happens in RC models, too. I have had it happen to me in RC moderls when I put an Kraft 60 on the nose of a Midwest Sweet Stick that was normally powered b y a 40 two-stroke, loop-scavengenged RC engine (usually a K&B 40). The plane flew almost OK, but not quite when at low power, but was VERY unstable in yaw at high power, regardless of speed. When I added a tuned pipe, it got much worse, but DID perform wonderful fast-rotating, slow-falling flat spins that were recoverable after 4 - 5 turns. I later went back to a K&B 40 and liked it a lot better whehn flying it as far as flying characteristics wee converned; but it WAS much slower ... 

If I were still flying RC, I'd make another 60 version if the kit were still available, and it isn't. You don;t have to be a GREAT RC pilot to fly it, but you DO have to on your toes and aware.

Much the same can be said of a full scale aircraft with a new, more powerful engine and bigger prop with more blade area.


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## CobberKane (Nov 1, 2012)

wuzak said:


> What about the Whirlwind?
> 
> It flew earlier. Are you discounting that because it had a small frame to support the bubble?


 
So far as I can recall all WWII bubble canopies had a framed forward section. I’ve always assumed this was to fix the plate of armoured glass most fighters had in front of the pilot. Modern jet fighters don’t have this – perhaps because such a feature would be pointless in the era of air to air rockets and rotary cannon?


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## Siegfried (Nov 1, 2012)

tyrodtom said:


> You really can't say the Luftwaffe needed to copy the bubble canopy, the Fw190 was flying in action with a bubble canopy before any allied fighters , I believe. But they never redesigned the Me109 for a bubble. The Me209 and Me309 both had bubble canopies, didn't they ?



Neither the Me 209 II had a bubble nor the completely different record plane Me 209 ere bubbled. The Heinkel He 112, which was in a fly of competition with the Me 109 and almost became the Luftwaffe's frontline fighter had a bubble canopy.

Had the bubble canopied Me 309 been pushed through it would likely beaten the P-51D into service. It was flying in June 1942 and even had a laminar flow wing and a range similar to the P-51. 

Clearly, as you point out with the FW 190, the Luftwaffe was thinking in terms of bubble canopies. Later Fw 190 had an enlarged canopy. The Me 262 had it from the beginning.


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## CobberKane (Nov 1, 2012)

So where does the He 162 fit in? The canopy is slightly faired into the fuselage but much less than the the Fw90, and it is cleary 'blown'. Furthermore, it does not have a framed forward section like the P51D, Tempest etc - the forward section is also a single blown unit, much like an F-16 or any number of other modern jets. The most advanced and forward thinking of WWII canopies?


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## zoomar (Nov 1, 2012)

Interesting point. It had a one-piece blown canopy (similar in concept to that of the Me-163 as well, I suspect), but it was not an all-round vision canopy so it's not a true bubble canopy, of course - while the modern jet canopies are. Most Fw-190 Ds as well as Ta-152s, Fw-190Fs and Fw-190s also had blown canopies but these were also not true all-round vision bubbles. None of the all-round vision canopies fitted on operational Luftwaffe fighters as well as prototypes (He-112, Me-309, Me-262) could remotely be called bubble canopies. The only complete all-round vision and frameless (and I presume blown) canopies were on the Fw-190V1 and Fw187V1, I believe.


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## tyrodtom (Nov 1, 2012)

That little bit of sky blocked by the solid part to the rear of the Fw190 canopy gives nothing but a view of the horizontal tail assembly, a full "bubble canopy" wouldn't increase it's practical view any.
I was just thinking of true to the rear view canopies, no matter how you manage to achieve it, 1-part, 2-part, 3-part or multipane canopy, what does it matter. A " bubble" canopy is just a manufactors improvement to get a 360 view canopy out of one easy stamping.


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## GregP (Nov 1, 2012)

Looking at an He-162 from 10 feet away would make you think twice about whether or not it has a bubble canopy ... it is so close to being one that I think the distinction is hard to make in this case. Also, in the case of the He-162. using a complete bubble canopy would be a bit pointless since all you could see directly rearwards would be the jet engine intake.

Maybe we could agree on exactly what constitutes a "bubble" canopy and at what angle the sliding portion of the canopy has to be in order to be disqualified as a bubble canopy.

What if a canopy looks just like a bubble canopy, but opens in a sideways clamshell fashion instead of sliding straight back? Is that still a bubble canopy?


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## FLYBOYJ (Nov 1, 2012)

Also consider that although some of these early transparancies were one piece, the quality of the field of vision left something to be desired, especially around curved surfaces where you would have distortion. In the post war years Soviet canopies were horrible.

Reactions: Agree Agree:
1 | Like List reactions


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## nuuumannn (Nov 1, 2012)

> Are you discounting that because it had a small frame to support the bubble?



Was it a frame or was the bubble in two seperate sections?


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## CobberKane (Nov 1, 2012)

zoomar said:


> Interesting point. It had a one-piece blown canopy (similar in concept to that of the Me-163 as well, I suspect), but it was not an all-round vision canopy so it's not a true bubble canopy, of course - while the modern jet canopies are. Most Fw-190 Ds as well as Ta-152s, Fw-190Fs and Fw-190s also had blown canopies but these were also not true all-round vision bubbles. None of the all-round vision canopies fitted on operational Luftwaffe fighters as well as prototypes (He-112, Me-309, Me-262) could remotely be called bubble canopies. The only complete all-round vision and frameless (and I presume blown) canopies were on the Fw-190V1 and Fw187V1, I believe.



Note that while the conopy of the ME163 is obviously of blown manucacture it follows the usual pattern of having a heavily framed foresection incorporating armoured glass. The HE 162 has entitrely dspensed with this.


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## tyrodtom (Nov 1, 2012)

That heaviy framed armored section is separate from and inside the canopy on the Me163, it stays stationary when you raise the one piece canopy.


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## GregP (Nov 1, 2012)

The Me 163 isn't even close to being a bubble type; it fairs right into the fuselage lines.

The He 162 has a one-piece moving portion of the canopy; it rasises from the back with a pivot pin at the rear part of the canopy frame.


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## tyrodtom (Nov 1, 2012)

Maybe they though since the Me163 was the fastest thing in the sky, it didn't need to see behind it. 
Just a joke. But the Me263 redesign did have a pretty good 360 view. I think they decided once the Me263 was a glider coming down a good all round view might be useful.


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## GregP (Nov 1, 2012)

Hi Cobberkane, Reference post 38. 

By the end of the war everyone WAS pushing the limits pretty hard. By simple example, if you look at a Spitfire 21, look at the area of the fin when referenced to a Spitfire I or even a Mk V. MUCH bigger. Likewise the Spitfires that went to the bubble canopy had an even bigger fin to offset the loss of keel area when the turtledeck was cut down. Same with Seafires and Seafang.

The Hellcat never needed to since it started life (at least the R-2800 portion of its life) with 2,000 HP already and only grew by about 150 - 200 HP or so, not especially significant. The Bearcat also never neeeded to grow the fin becasue it started with the 2,000+ HP R-2800, too. One glaring exception is the Reno racer "Rare Bear." When it was fitted with the 3-bladed prop from cut down P-3 Orion blades, it had horrible flying characteristics. Both Lyle Shelton and John Penney remarked that they could not fly it "seat of the pants" with the big 3-bladed prop because the plane felt the same if were flying coordinated, slipping or skidding. They had to look at the turn and bank indicator to tell ... and these were both superb pilots. When Rod Lewis bought Rare Bear, they went bak to a normal 4-bladed prop for better flying characteristics, and got what they wanted.

As for the Tempest / Sea Fury, it is NOT the increase in the number of blades that casuses instability, it is the increase in blade area forward of the CL. If you fit a 5 blade to an aircraft that formerly had a 4-blade, and if the net blade area doesn't change much, thebn there will be no loss of stability. Only with a significant increase in blade area will that happen.

In the case of the P-51, each balde of the 4-bladed Aeroproducts or Hamilton-Standard units had more area than any single blade of the 3-bladed Curtiss Electric prop used with the Allison-engined variants. That means more than a 33% increase in blade area forward of the CL, making for deteriorated handling. Add the extra power and the bubble canopy with attendant loss of keel area, and you have the issue defined. The Dorsal fin expention corrected the issue handily, or at LEAST made it acceptable, depending on who you believe.

Drgondog, the main reason this doesn't come up in most aerodynamic texts is that most texts deal with design of an aircraft, not modification of an existing aircraft to add a significant amount of extra power and blade area forward of the CL. The only people that typically do that are the military and racing people in the unlimited class. In the Sport class, say we are talking abiout the Nenesis NXT racer, it was designed from the outset for 600+ HP since Jon Sharp knew he would be doing that.

In the Piper Comanche, the original 180 HP unit had the same airframe as the Comanche 250. When they went to the 260, the overall lenth was increased by 6 inches ... they moved the tail back 6 inches to compensate to the extra power and loss of stability. When they went to the Comanche 400, the vertical tail has NOTHING in common with the 260, is balanced completely differently, and has a higher thickness ratio (increased tail volume). The horizontal tail has extra ribs and is beefier, too, along with a higher thickness ratio (increased tail volume).

If we want to continue this, and I don't particularly since the people doing this sort of thing these days are almost nonexistent, then I suggest we start another thread about it. I'll stick to bubble canopies in here going forward.


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## Siegfried (Nov 1, 2012)

zoomar said:


> Interesting point. It had a one-piece blown canopy (similar in concept to that of the Me-163 as well, I suspect), but it was not an all-round vision canopy so it's not a true bubble canopy, of course - while the modern jet canopies are. Most Fw-190 Ds as well as Ta-152s, Fw-190Fs and Fw-190s also had blown canopies but these were also not true all-round vision bubbles. None of the all-round vision canopies fitted on operational Luftwaffe fighters as well as prototypes (He-112, Me-309, Me-262) could remotely be called bubble canopies. The only complete all-round vision and frameless (and I presume blown) canopies were on the Fw-190V1 and Fw187V1, I believe.



The FW 190 canopy WAS frameless single piece unit, the metallic strip running down the middle only went halfway in most cases. It was a conduit and reinforcing attachment for a radio aerial cable that anchored between canopy and the tip of the vertical tail rather than a joining strip for two canopy halves. From latter models eg later Fw 190A-8, D9 the canopy were a new type that was far more bulged.

The 190 tail drooped quite low so by craning around the pilot should get a good view down behind and low.


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## GregP (Nov 1, 2012)

The FW 190D-9 that is in the Museum of Flight (used to be in Doug Champlin's Fighter Museum), has a one-piece sliding canopy and it is VERY narrow. If you had a helment on, you might not be able to turn your neck around to check your six!, but, if you COULD, the visibility was there. That partituclar unit was restored with the help of Kurt Tank, the original designer. There are some very interesting stories about it, but they are not related to bubble canopies ...

In my mind, it probably qualifies as a bubble canopy but, then again, we have not discussed yet what constitutes a bubble canopy.


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## yulzari (Nov 2, 2012)

There are 2 possible criteria for defining a bubble canopy.

1. Is it a single blown piece of plastic that covers the pilot aft of the windscreen. i.e. does it have the form of a bubble?

2. If the pilot looks back down can they see the base of the fin. i.e. does it have the function of a bubble?

Common useage seems to favour the first criterion (even if I prefer the latter.)


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## Milosh (Nov 2, 2012)

Siegfried said:


> The FW 190 canopy WAS frameless single piece unit, the metallic strip running down the middle only went halfway in most cases. It was a conduit and reinforcing attachment for a radio aerial cable that anchored between canopy and the tip of the vertical tail rather than a joining strip for two canopy halves. From latter models eg later Fw 190A-8, D9 the canopy were a new type that was far more bulged.
> 
> The 190 tail drooped quite low so by craning around the pilot should get a good view down behind and low.



The metal strip was to allow for the canopy to flex as it was rolled back. The canopy tracks narrowed. The radio antenna was attached behind the metal strip.


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