Why the heck did they design it that way?

michael rauls · Jul 17, 2018

I would verry much like to hear everyones thoughts on design on issues pertaining to a particular plane that kept ok planes from being good, good planes from being great, and great planes from being darn near perfect( or at least as close to it as could be humanly expected at the time of its design). The obvious picks for me are two great planes that could have been darn near perfect , the Bf109 and the spitfire, both for the same two issues. Those being the narrow undercarriage and limited fuel capacity. I'm sure there are many examples so " why the heck did they design it that way"

pbehn · Jul 17, 2018

michael rauls said:
I would verry much like to hear everyones thoughts on design on issues pertaining to a particular plane that kept ok planes from being good, good planes from being great, and great planes from being darn near perfect( or at least as close to it as could be humanly expected at the time of its design). The obvious picks for me are two great planes that could have been darn near perfect , the Bf109 and the spitfire, both for the same two issues. Those being the narrow undercarriage and limited fuel capacity. I'm sure there are many examples so " why the heck did they design it that way"

The Spitfire was an interceptor, speed and rate of climb were paramount, also very important was the take off run with 1000HP and a fixed pitched prop (about 660HP in practice, on take off). In order to get a thin wing for speed with all the "stuff" in it Mitchell used an elliptical wing, with the narrow track wheels folding out. The whole thing was about getting a lightweight design to take off climb and the fly as fast as possible. The Spitfire was designed with a thin wing for low drag, later advances in aerofoils actually produced less drag from thicker wings so inward folding gear wasn't so much of a problem. The Bf 109 had a similar philosophy, its landing gear was attached close to he engine which saved a lot of weight, also allowed wings to be changed just with the plane on its landing gear. In 1936 when the Spitfire was being designed there wasn't actually a war being fought. The plane was designed and the first order placed for 300 aircraft, other allied designs that came after the war started had different requirements but as far as an interceptor goes, range isn't important.

Shortround6 · Jul 17, 2018

Opinions differ
Mine is that was what you were going to get given the power plants available at the time of design (several years earlier than going into service and even longer going into combat).

The 109 was designed around the Jumo 210 engine of roughly 700hp. It didn't even make 300mph as it was (and I believe the Jumo powered machines only held 270 liters of fuel?) so trying to turn it into a fuel truck would not have had good results. They built hundreds of Jumo powered 109 B, C & Ds before building DB 601 powered 109Es which got stuck with the physical size of the 109. It then started on the trying to stuff a quart into a pint jar path.

The Spitfire and Hurricane had a better basic engine but ran into two problems as to power plant. 1. was that the Merlin III had the highest critical altitude (FTH) of any production engine (in large numbers) in the 1930s but that meant they had to throttle it down at sea level for take 0ff to 880 hp. Then the Air ministry attached shackles, leg irons and cannon balls to them in regards to take-off by insisting on two blade fixed pitch props. Take off was done at just over 2000rpm on the engine instead of the 3000rpm the engine was capable of (and where the 880hp was).

Both countries had requirements about take-off runs and distance to 50 ft (or 20 meters for the 109) and given the engine/propeller combinations there was only so much weight the designer was going to get off the runway in the distance desired. Doesn't matter how long ranged the fighter plane is if it can't use the majority of airfields in the country (which got a lot more numerous and larger both before the war and during the early years of the war.)

michael rauls · Jul 17, 2018

pbehn said:
The Spitfire was an interceptor, speed and rate of climb were paramount, also very important was the take off run with 1000HP and a fixed pitched prop (about 660HP in practice, on take off). In order to get a thin wing for speed with all the "stuff" in it Mitchell used an elliptical wing, with the narrow track wheels folding out. The whole thing was about getting a lightweight design to take off climb and the fly as fast as possible. The Spitfire was designed with a thin wing for low drag, later advances in aerofoils actually produced less drag from thicker wings so inward folding gear wasn't so much of a problem. The Bf 109 had a similar philosophy, its landing gear was attached close to he engine which saved a lot of weight, also allowed wings to be changed just with the plane on its landing gear. In 1936 when the Spitfire was being designed there wasn't actually a war being fought. The plane was designed and the first order placed for 300 aircraft, other allied designs that came after the war started had different requirements but as far as an interceptor goes, range isn't important.

I had considered some of the things you point out. Although many I was unaware of runway length takeoff requirements for example. But as it pertains to the Bf 109 specificly seems like the germans forsaw the posible meed for longer range fighters( hence the 110) and doesn't seem like it would add much wieght and impact performance much to increase fuel capacity 10 or 15%. If I have my numbers and math right( always a big if) a 10% increase in fuel capacity would be about 90 lbs for the 109. Especially once somewhat more powerful engines were in the plane doesn't seem like 90 lbs would impact performance much and think what a 10 or 15 % increase in flight time would have meant to the Luftwaffe durring the battle of Britain for example.

GrauGeist · Jul 17, 2018

The Bf109's landing gear was an innovation of Messerschmitt's, which allowed a savings in weight by the landing gear mount and engine mounts to share a unified assembly. It also made the aircraft easy to service or transport. While the landing gear geometry made it difficult for pilots, especially on hard/improved surfaces, it was not the narrowest of landing gears - this distinction should go to Grumman's F4F.

michael rauls · Jul 17, 2018

GrauGeist said:
The Bf109's landing gear was an innovation of Messerschmitt's, which allowed a savings in weight by the landing gear mount and engine mounts to share a unified assembly. It also made the aircraft easy to service or transport. While the landing gear geometry made it difficult for pilots, especially on hard/improved surfaces, it was not the narrowest of landing gears - this distinction should go to Grumman's F4F.

The landing gear thing makes alot more sense to me now but what do you think about a 10 or 15% increase in fuel capacity for the 109? About 90 lbs I think and like i was saying in my last post think what that would have meant to the Luftwaffe to have 10 or 15% more flight time during the Battle of Britain for example.

michael rauls · Jul 17, 2018

Or what 10 or 15 % more fuel for the spitfire would have meant to the British durring Dunkirk.

pbehn · Jul 17, 2018

michael rauls said:
I had considered some of the things you point out. Although many I was unaware of runway length takeoff requirements for example. But as it pertains to the Bf 109 specificly seems like the germans forsaw the posible meed for longer range fighters( hence the 110) and doesn't seem like it would add much wieght and impact performance much to increase fuel capacity 10 or 15%. If I have my numbers and math right( always a big if) a 10% increase in fuel capacity would be about 90 lbs for the 109. Especially once somewhat more powerful engines were in the plane doesn't seem like 90 lbs would impact performance much and think what a 10 or 15 % increase in flight time would have meant to the Luftwaffe durring the battle of Britain for example.

It is perhaps difficult to understand looking back at things, planes like the P-51 had huge range eventually but early in the war it wasn't very important. In the Battle of France the LW was getting to its limit at Dunkerque operating from Germany, the further your front line is away the fewer missions you can do in a day and the harder it is to communicate what is needed where. In the Battle of Britain the LW started to attach long rage tanks, but at the time they were being attached some in the LW thought the RAF were down to their last 50 aircraft. After the BoB, you could say the RAF needed longer range fighters, but they had to be much longer, there weren't many important targets in France that the Germans were compelled to defend, though Leigh Mallory could have done a much better job.

pbehn · Jul 17, 2018

michael rauls said:
Or what 10 or 15 % more fuel for the spitfire would have meant to the British durring Dunkirk.

Well Dunkerque was a success (of sorts) as it was, 10-15% more range may have been a help, but that was the first time the Spitfire was committed in numbers. At Dunkerque a major problem was actually seeing the enemy through low cloud and smoke, more fuel wouldn't solve that. Also pilots in action were as likely to turn back due to low ammunition as much as fuel.

michael rauls · Jul 17, 2018

pbehn said:
It is perhaps difficult to understand looking back at things, planes like the P-51 had huge range eventually but early in the war it wasn't very important. In the Battle of France the LW was getting to its limit at Dunkerque operating from Germany, the further your front line is away the fewer missions you can do in a day and the harder it is to communicate what is needed where. In the Battle of Britain the LW started to attach long rage tanks, but at the time they were being attached some in the LW thought the RAF were down to their last 50 aircraft. After the BoB, you could say the RAF needed longer range fighters, but they had to be much longer, there weren't many important targets in France that the Germans were compelled to defend, though Leigh Mallory could have done a much better job.

Verry good job explaining the why of these decisions. Thank you. I suppose whether they the best ones is a different and also interesting topic.

buffnut453 · Jul 17, 2018

michael rauls said:
Verry good job explaining the why of these decisions. Thank you. I suppose whether they the best ones is a different and also interesting topic.

They were probably the best decisions that could be made at the time, with the information available at hand AND within the constraints placed upon the designers and manufacturers. We've had countless threads on this forum about "could the Scruggs Wondaplane have been introduced 12 months earlier" and they always revert to the view that, if such acceleration of deliver were possible at the time, then it probably would have been done.

It's easy for people sitting comfortably in their armchairs in 2018 to be critical of decisions made in (insert year prior to 2018 here) but we have the benefits of hindsight that the people making decisions at the time did not possess.

pbehn · Jul 17, 2018

michael rauls said:
Verry good job explaining the why of these decisions. Thank you. I suppose whether they the best ones is a different and also interesting topic.

I forgot to say, the LWs role was mainly as a close support tactical force, not only was the LW at its limit in range at Dunkerque, the German army too was in need of rest re supply and consolidation. At D-Day the Allies had the planes with the range to fly across the Channel to Normandy, but within days of the landings, engineers were constructing mesh air strips for planes to operate from France, it is easier doing close support when you are close.

michael rauls · Jul 17, 2018

pbehn said:
Well Dunkerque was a success (of sorts) as it was, 10-15% more range may have been a help, but that was the first time the Spitfire was committed in numbers. At Dunkerque a major problem was actually seeing the enemy through low cloud and smoke, more fuel wouldn't solve that. Also pilots in action were as likely to turn back due to low ammunition as much as fuel.

I know your write about Dunkirk being a success given the circumstances. I was trying to give an example of where even a small increase in range could have helped(maybe alot) its my understanding that the Spitfire had verry limited time over the crucial area. Seems even another 10 or 15 minutes could have saved lives. Maybe quite a few but perhaps the didn't foresee the need.

michael rauls · Jul 17, 2018

buffnut453 said:
They were probably the best decisions that could be made at the time, with the information available at hand AND within the constraints placed upon the designers and manufacturers. We've had countless threads on this forum about "could the Scruggs Wondaplane have been introduced 12 months earlier" and they always revert to the view that, if such acceleration of deliver were possible at the time, then it probably would have been done.

It's easy for people sitting comfortably in their armchairs in 2018 to be critical of decisions made in (insert year prior to 2018 here) but we have the benefits of hindsight that the people making decisions at the time did not possess.

All your points are verry good but my idea for this thread was not an acussitory pointing of fingers at Willy Meschershmit for example but more of an honest asking of the question" why the heck did they make it that way" and an hopefully interesting discussion of such as well as the of course inevitable was it the rite decision discussion. Also usually interesting.

pbehn · Jul 17, 2018

michael rauls said:
I know your write about Dunkirk being a success given the circumstances. I was trying to give an example of where even a small increase in range could have helped(maybe alot) its my understanding that the Spitfire had verry limited time over the crucial area. Seems even another 10 or 15 minutes could have saved lives. Maybe quite a few but perhaps the didn't foresee the need.

It was not foreseen in any strategic planning that France would be in danger of falling to Germany in weeks, let alone a huge British force being encircled at Dunkerque. Dunkerque gets all the headlines, it was a sort of miracle, in most circumstances it should have been a disaster, however it is often forgotten that over 200,000 troops and civilians were returned to UK from other ports on the west coast in a more orderly and less dramatic fashion. (Operation Ariel)

pbehn · Jul 17, 2018

michael rauls said:
All your points are verry good but my idea for this thread was not an acussitory pointing of fingers at Willy Meschershmit for example but more of an honest asking of the question" why the heck did they make it that way" and an hopefully interesting discussion of such as well as the of course inevitable was it the rite decision discussion. Also usually interesting.

One decision on the Hawker Hurricane and later Typhoon that was wrong, because it was based on incorrect advice/thinking was the thickness of the wings. It was thought that thick wings were better, this turned out to be completely wrong and a major disadvantage on the Typhoon, which required new wings as the Tempest Oh and a new engine and better fuselage, the canopy was changed too lol

Shortround6 · Jul 17, 2018

It is a bit more than failing to see the need. Peace time airworthiness standards were different than war time.
Adding fuel sounds easy but was often rather difficult.The fuel tank behind the pilot in the P-36/P-40 being a prime example.

In early US service with the P-36 this tank was an overload ferry tank. Used for moving the aircraft form one airfield to another. performance trials were done with the tank empty and restrictions were placed on the plane as far as allowable maneuvers when the tank was full. The French crashed at least one Hawk 75 and maybe more by ignoring that restriction.
Early P-40s also used it as an overload/ferry tank and performance numbers were obtained with the tank empty. I don't know if restrictions were placed on the early P-40s as far as flying with the tank full. When you get to the P-40E and F something a little strange happens. It is not spelled out as a restriction but in the P-40E the sequence the tanks were used was the forward wing tank first for take-off, then the belly tank if carried, then the behind the seat tank, then the rear wing tank (under the pilot) and then and finally back to the forward wing tank. On the P-40F the difference was that the rear tank (behind pilot) was to be drawn down to 35 gallons and then that fuel was to be left there while the fuel in the other tanks was used. Instead of the fuel in the forward wing tank being the reserve, get home, bad weather safety fuel like the E on the F the forward fuel was used sooner and the 35 gallons behind the pilot became the reserve.
I am guessing but it might have to do with the Merlin engine being several hundred pounds heavier than the Allison and they were using the 35 gallons (210lbs) as ballast to keep the CG where they wanted it. Not sure what happened when they made the fuselage 20in longer
Sometimes adding fuel is easy and sometimes it makes the plane somewhat squirrly in handling. Some planes tended to tighten up a turn on their own once in a turn, not really a good trait. Post war both Mustangs and Spitfires with rear tanks wound up with restrictions on allowable conditions for filling/use of the rear tanks. With the need for combat gone accident prevention became a priority once again.
Ask the private pilot members about one of the major causes of single aircraft crashes, fuel management and the selection of the proper tank/s at the proper time. The more tanks/positions on the fuel selector valve the more problems per 1000 or 10,000 hours of flight.

michael rauls · Jul 17, 2018

pbehn said:
It was not foreseen in any strategic planning that France would be in danger of falling to Germany in weeks, let alone a huge British force being encircled at Dunkerque. Dunkerque gets all the headlines, it was a sort of miracle, in most circumstances it should have been a disaster, however it is often forgotten that over 200,000 troops and civilians were returned to UK from other ports on the west coast in a more orderly and less dramatic fashion. (Operation Ariel)

Verry enlightening answers to things I have wondered about. I'm sure there are many more examples like this like leaving the supercharger off the p39 or p40 but I want to leave at least a few picks for others.

pbehn · Jul 17, 2018

michael rauls said:
Verry enlightening answers to things I have wondered about. I'm sure there are many more examples like this like leaving the supercharger off the p39 or p40 but I want to leave at least a few picks for others.

It is easy to look at the P-51s range and think "why didn't they all do that" however if by a miracle of time travel you took a P51 airframe back to 1940 but with a 1940 Merlin and fixed pitch two blade prop......the first thing they would do would be to remove two of the guns and half fill the fuel tanks.

michael rauls · Jul 17, 2018

pbehn said:
One decision on the Hawker Hurricane and later Typhoon that was wrong, because it was based on incorrect advice/thinking was the thickness of the wings. It was thought that thick wings were better, this turned out to be completely wrong and a major disadvantage on the Typhoon, which required new wings as the Tempest Oh and a new engine and better fuselage, the canopy was changed too lol

Shortround6 said:
It is a bit more than failing to see the need. Peace time airworthiness standards were different than war time.
Adding fuel sounds easy but was often rather difficult.The fuel tank behind the pilot in the P-36/P-40 being a prime example.

In early US service with the P-36 this tank was an overload ferry tank. Used for moving the aircraft form one airfield to another. performance trials were done with the tank empty and restrictions were placed on the plane as far as allowable maneuvers when the tank was full. The French crashed at least one Hawk 75 and maybe more by ignoring that restriction.
Early P-40s also used it as an overload/ferry tank and performance numbers were obtained with the tank empty. I don't know if restrictions were placed on the early P-40s as far as flying with the tank full. When you get to the P-40E and F something a little strange happens. It is not spelled out as a restriction but in the P-40E the sequence the tanks were used was the forward wing tank first for take-off, then the belly tank if carried, then the behind the seat tank, then the rear wing tank (under the pilot) and then and finally back to the forward wing tank. On the P-40F the difference was that the rear tank (behind pilot) was to be drawn down to 35 gallons and then that fuel was to be left there while the fuel in the other tanks was used. Instead of the fuel in the forward wing tank being the reserve, get hove, bad weather safety fuel like the E on teh F the forward fuel was used sooner and the 35 gallons behind the pilot became the reserve.
I am guessing but it might have to do with the Merlin engine being several hundred pounds heavier than the Allison and they were using the 35 gallons (210lbs) as ballast to keep the CG where they wanted it. Not sure what happened when they made the fuselage 20in longer
Sometimes adding fuel is easy and sometimes it makes the plane somewhat squirrly in handling. Some planes tended to tighten up a turn on their own once in a turn, not really a good trait. Post war both Mustangs and Spitfires with rear tanks wound up with restrictions on allowable conditions for filling/use of the rear tanks. With the need for combat gone accident prevention became a priority once again.
Ask the private pilot members about one of the major causes of single aircraft crashes, fuel management and the selection of the proper tank/s at the proper time. The more tanks/positions on the fuel selector valve the more problems per 1000 or 10,000 hours of flight.

I've read that even during the war the British had restrictions on filling and use of the rear tank on the Mustang. Is there any truth to this as far as you know.

Why the heck did they design it that way?

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