Bubble canopies?
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wuzak
Captain
What about the Whirlwind?
It flew earlier. Are you discounting that because it had a small frame to support the bubble?
GregP
Major
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.
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
Banned
- 706
- Apr 4, 2012
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?
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.
CobberKane
Banned
- 706
- Apr 4, 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?
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.
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.
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.
GregP
Major
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?
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
"THE GREAT GAZOO"
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.
CobberKane
Banned
- 706
- Apr 4, 2012
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.
GregP
Major
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.
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.
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.
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.
GregP
Major
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.
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.
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
Major
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.
In my mind, it probably qualifies as a bubble canopy but, then again, we have not discussed yet what constitutes a bubble canopy.
yulzari
Tech Sergeant
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.)
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.)
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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