Why airplanes were designed the way they were.

[EwenS]

The first FAA fighter squadrons to form in May 1933 combined existing flights flying single types. So

800 - initial equipment 9 Nimrod & 3 Osprey. Replaced by Skuas & Rocs in 1939
801 - initial equipment 3 Flycatchers (later replaced by Ospreys) & 6 Nimrods (removed 1936). Replaced by Sea Gladiator & Skua in 1939.
802 - initial equipment 9 Nimrod & 3 Osprey. Replaced by Sea Gladiators in May 1939.
803 - initial equipment 9 Osprey, later (1938) 6 Osprey & 3 Nimrod. Replaced by Skuas & Rocs in 1939.

Those were all the pre-war FAA fighter squadrons. The next, 804 didn't form until November 1939 with Sea Gladiators.

 

[Shortround6]

I will note that in May 1937 the Japanese issued the specification that lead to A6M. It was revised in Oct 1937 at which time they were requesting a top speed of 270kts (311mph) at 4,000meters (13,125ft). They were ahead of their time asking for 6-8 hours max endurance with drop tanks. One of the requirements was a take-off distance of 70 meters (230ft) with a 27kt head wind.
1st prototype flew in May 1939 succeeding in most things except speed with the Zuisei engine requiring an engine change. 1st Sakae powered plane flew in Dec 1939. Sakae engine had a single speed supercharger with 950hp at 4200 meters. Japanese use of pre production series planes in China in 1940 is somewhat deceptive. The decision to send the 15 pre-production examples was made 10 days before the A6M2 was officially accepted for production. While they did very well in combat there were some problems with the early aircraft including 2 structural failures which needed sorting out and modifications (and flight restrictions until things were sorted out).

Shifting back to the US. The XF4F-2 in the photo posted earlier was about 1500lbs lighter than the F4F-3 in service in late 41 or early 42.
In addition to just two guns (and corresponding ammo) it used a single stage supercharger on the engine and had a max speed of 288mph at 10,000ft. The engine in the prototype was good for 1050hp for take-off. The two stage engine gained around 180lbs and that does not include the intercoolers and duct work. The US was scrambling to improve the F2A Buffalo and the F4F Wildcat during 1939 and 1940. Let's not forget that Brewster and the Navy improved the landing gear on the early Buffalo just in time to increase the weight of the plane by about 1300lbs (not including extra fuel) which canceled out whatever beefing up they did. I will also note that a lot of the prewar (1939-41/42) US navy performance figures (except range/endurance) were done with 110 US gallons of fuel on board. It might be more realistic than fuel fuel but if everybody else is using full fuel and the USN is using part fuel it tends to skew the data.

 

[z42]

Circling back to the topic of seaplanes, it seems that for larger seaplanes the flying boat configuration was more or less universally adopted (yes, there were exceptions like the floatplane version of the He111), whereas for smaller aircraft the floatplane configuration seems to have been more popular than the flying boat. Of the major navies involved in WWII, it seems only the RN had a flying boat style scout plane whereas the others all had ended up with floatplanes.

 

[Shortround6]

Circling back to the topic of seaplanes, it seems that for larger seaplanes the flying boat configuration was more or less universally adopted (yes, there were exceptions like the floatplane version of the He111), whereas for smaller aircraft the floatplane configuration seems to have been more popular than the flying boat. Of the major navies involved in WWII, it seems only the RN had a flying boat style scout plane whereas the others all had ended up with floatplanes.

This may have been influenced by Geography/sea conditions. Italy had one flying boat in WW II. They had 7 float planes, either production or experimental. The Med has kinder sea conditions than the Atlantic or Pacific (or Indian Ocean)?

The other general exceptions seem to be converted landplanes or planes that could be converted.
US for instance had one/two float planes that were not convertible. Although the Grumman J2F was always an amphibian so where do you count it?

US float planes went from Ryan STM-S2 to a C-47.

France was rather prolific, in both categories. Flying boats went from 6 engines down to 6 different single engine designs of under 8000lbs.
For anybody wishing for a monoplane Walrus the French have answered your dreams

Loire 130. I will spare us all from the Loire-Nieuport 10. A plane that will turn the stomach of a Amiot 143 fan. A 30,000lb floatplane.
With the fall of France in 1940 the world was spared some of their more creative endeavors into maritime aircraft but they could honestly be said not to follow anybody else's trends.

I will close this out with the Yugoslavian Rogozarski SIM-XIV-H

3 man crew and a pair of 270hp Argus engines. 6 built, another 12 under construction according to one source. 2 of the 6 escaped and flew for the allies for a short period of time.

 

[z42]

This may have been influenced by Geography/sea conditions. Italy had one flying boat in WW II. They had 7 float planes, either production or experimental. The Med has kinder sea conditions than the Atlantic or Pacific (or Indian Ocean)?

Maybe. Then again seems the USN and IJN, as well as the KM, were happy with float planes for scouting.

The other general exceptions seem to be converted landplanes or planes that could be converted.

Not needing to design an entirely new plane might be the big advantage of the float plane layout.

Drag-wise, I guess for a single engine aircraft, at least by looking at the frontal area, a floatplane should be in the same ballpark compared to a flying boat with the engine and potentially the wings as well, mounted high over the body with struts.

Whereas for a bigger multi-engine aircraft, with a high mounted wing and a deep fuselage you can avoid these struts altogether (except for the side floats, obviously). Like the H8K or the Short Sunderland.

 

[Shortround6]

Maybe. Then again seems the USN and IJN, as well as the KM, were happy with float planes for scouting.

It may have been designers preference, However in the case of the USN, ALL of their catapult scout planes were also flown from land bases with fixed landing gear. A lot of times for training. The Japanese don't seem to have done that in most cases. As noted by others a lot of the British 1920s/30s torpedo planes could be fitted with floats for catapult recon duty.

Germans had about 16-17 ships (not including raiders) fitted for float planes. They also waited until the early 30s to start. WW I floats were rather crude.

Not needing to design an entirely new plane might be the big advantage of the float plane layout.

Very true although sometimes it doesn't work out in practice. The Float C-47 flew fairly well, the floats didn't give any problems. It was an amphibian (wheels in the floats) but they decided it was too hard to load and unload and with plethora of US bulldozers carving out jungle airstrips in short order and covering them with Marston matting (PSP) the need for float cargo planes was very limited.
PBYs and Martin PBMs could handle the limited missions needed.

Drag-wise, I guess for a single engine aircraft, at least by looking at the frontal area, a floatplane should be in the same ballpark compared to a flying boat with the engine and potentially the wings as well, mounted high over the body with struts.

It also may depend of the crew set up. If, for some reason, you want two of the crew to sit side by side a lot the drag stuff changes. Small flying boats have been built, problems include keeping the props out of the water Solutions include using twin engines with small props or sticking the engine on a pylon over the top of everything. Loading crew/passengers/cargo in the flying boat may be easier than using ladders, even built in, on a floatplane. Post war DH Beaver

What can you deal with on lakes, rivers and harbors may not what you want to deal with in more open waters. Also note that even a small radial engine is about as wide as two people sitting side by side so a lot of times "streamlining" gets more attention than it needed.
During 20s and 30s more attention was given to flying boats and float planes because they had longer runways available than land planes did. Heavier planes for the same power engines. WW II killed the market for large flying boats/float planes with the hundreds/thousands of air strips built all over the place and rather sizeable ones compared to pre-WW II air fields. Also turns out for commercial use you are safer over-powering the plane and flying to land after an engine failure on fewer engines than landing in the ocean and trying to repair the engine.
Building large water tight hulls was harder than building 2/3 floats and the float planes were easier to repair depending on damage, unbolt damaged float and bolt new float on and fly away.

 

[elbmc1969]

I would have thought so. A Roc with floats. Why not add a drogue 'chute too, to get a more stable platform?

The Skua and Roc were equipped with drogue 'chutes.

 

[swampyankee]

It may have been designers preference, However in the case of the USN, ALL of their catapult scout planes were also flown from land bases with fixed landing gear. A lot of times for training. The Japanese don't seem to have done that in most cases. As noted by others a lot of the British 1920s/30s torpedo planes could be fitted with floats for catapult recon duty.

Germans had about 16-17 ships (not including raiders) fitted for float planes. They also waited until the early 30s to start. WW I floats were rather crude.

Very true although sometimes it doesn't work out in practice. The Float C-47 flew fairly well, the floats didn't give any problems. It was an amphibian (wheels in the floats) but they decided it was too hard to load and unload and with plethora of US bulldozers carving out jungle airstrips in short order and covering them with Marston matting (PSP) the need for float cargo planes was very limited.
PBYs and Martin PBMs could handle the limited missions needed.

It also may depend of the crew set up. If, for some reason, you want two of the crew to sit side by side a lot the drag stuff changes. Small flying boats have been built, problems include keeping the props out of the water Solutions include using twin engines with small props or sticking the engine on a pylon over the top of everything. Loading crew/passengers/cargo in the flying boat may be easier than using ladders, even built in, on a floatplane. Post war DH Beaver
View attachment 778101
What can you deal with on lakes, rivers and harbors may not what you want to deal with in more open waters. Also note that even a small radial engine is about as wide as two people sitting side by side so a lot of times "streamlining" gets more attention than it needed.
During 20s and 30s more attention was given to flying boats and float planes because they had longer runways available than land planes did. Heavier planes for the same power engines. WW II killed the market for large flying boats/float planes with the hundreds/thousands of air strips built all over the place and rather sizeable ones compared to pre-WW II air fields. Also turns out for commercial use you are safer over-powering the plane and flying to land after an engine failure on fewer engines than landing in the ocean and trying to repair the engine.
Building large water tight hulls was harder than building 2/3 floats and the float planes were easier to repair depending on damage, unbolt damaged float and bolt new float on and fly away.

Floatplanes tend to be draggier than seaplanes. Counter-intuitively, floatplanes with one float plus stabilizing floats are draggier than twin float ones.

A major source of drag is the bracing for the floats. Seaplanes can eschew that.

Incidentally, at the low speeds of sea- and floatplanes, frontal area isn't this issue: surface area and separation is, and both float- and seaplanes have steps, which are designed to produce separation.

 

[swampyankee]

The Skua and Roc were equipped with drogue 'chutes.

...and both were flying with the airbrakes locked in the "open" position.

 

[elbmc1969]

...and both were flying with the airbrakes locked in the "open" position.

I was serious. They were actually for spin recovery, bit it's so close as to make no difference.

 

[Reluctant Poster]

Flying boats rule. Amazingly these two buildings still exist

 

[Shortround6]

Getting back to why "some airplanes were designed the way they were" and what happens later.
The Hurricane and Spitfire were designed to meet certain requirements. If anybody has the full requirement I would be very interested as I am doing some guesswork here.
The earlier requirement that lead to the Supermarine 224 called for a landing speed (stalling speed?) of 50mph to fit into the typical English fighter fields of the early 30s. The type 224 doesn't seem to have used flaps. It also used a 600hp engine for a 4750lb plane.
The Hurricane and Spitfire were around 1000lbs heavier, and while their engines were supposed to give around 880hp (what they promised in 1934-35?)at sea level they had to throttle the engines well back because of the fixed pitch props so they were taking off using several hundred HP less.
The somewhat contemporary (first flight Aug 1935) French MS 406 was plagued with slow development. It was within a few hundred lbs and used a wing 70% the size of the Spitfire (66% the size of the Hurricane) BUT it used a two pitch prop and could use all of it's sea-level HP for take-off which made take-off shorter.
On the other end (landing) they all had flaps but primitive. Spitfire dropped 85 degrees from the wing with no intermediate position/s. Since when landing the nose was a little high and the flight path is a few degrees down this means that the flaps were pretty much 90 degrees to airflow. Zero extra lift but a great airbrake
On the Spitfire they were trying to kill the lift or create extra drag to get the plane to land in the distance available.
The MS. 406 used a much smaller angle on the flap

Swiss version, so any differences?

The MS 406, according to wiki, stalled at 84mph with flaps which is around 20-25mph higher than the Hurricane or Spitfire.

Now in 1940-41-42 (5-7 years after design) this meant that the Hurricane and Spitfire had enough size to fit more stuff in the wings, Could add more stuff (weight) without the landing speed going through the roof, and with better props and more powerful versions of the Merlin, get heavier pay loads out of the same length airfields or really (comparatively) heavy loads out of longer airfields. For the British was fortunate but completely unintended as the Sabre, Vulture and Centaurus powered fighters planned for in 1938-39 were supposed to have replaced the Merlin powered fighters.

The European fighters with their 170-190sq ft wings didn't have the same room for growth. Adding several hundred kg increased the wing loading by a higher percentage. More powerful engine helps get the take-off back. But may make the landing worse.

 

[Simon Thomas]

The Hurricane I with the fixed pitch prop used full throttle for takeoff. The reduced RPM was due to the coarse pitch and slow speed not allowing the engine to reach max RPM.

 

[Shortround6]

The Hurricane I with the fixed pitch prop used full throttle for takeoff. The reduced RPM was due to the coarse pitch and slow speed not allowing the engine to reach max RPM.

We may be stating things differently. The engine was rated at 880hp at 3000rpm using 6lbs (or 6 1/4 lb? ) boost.
The throttle on the engine was not fully open even though the throttle in cockpit was, the automatic boost limiter kept the throttle in the carb partially closed.

Even at sea level and doing 150-151.5mph the Hurricane was only using 2100rpm and 6lbs of boost.
Now we know the early Merlin can make 12lbs of boost at 9,000ft at 3000rpm and it can make 16lbs of boost at 5500ft at 3000rpm.

Even at 2100rpm the engine might have been good for 7-8lbs of boost. (Allison might have been good for 7lbs at 2100rpm).

The engine was operating at part throttle for some reason. But 6lbs at 2100rpm is not going to give the same power as 6lbs at 3000rpm.

 

[elbmc1969]

The MS. 406 used a much smaller angle on the flap
View attachment 781675

Swiss version, so any differences?

With the flaps? Not that I know of. There are others, of course. The fixed radiator is the biggest.

 

[Greg Boeser]

Good points. IMO, the Gloster F5/34 suffered in prototype trials due to the Mercury engine they were obliged to use instead of the not ready Perseus. Stick a Kestrel onto the Spitfire prototype and see how it goes.

Willi Messerschmitt used a Kestral in the Bf 109 prototype.