P-39C-D & 400

[Shortround6]

From the other thread on the XP-39.




I would note that most/all Spitfire IXs carried Five 17.5 ballast weights in the tail. How about just shifting the radio/s, battery and oxygen equipment further back and getting rid of some of the Ballast? Presto...... an improvement of climb of several hundred FPM?

 

[Tkdog]

...
You know there were literally thousands of people working on this stuff. Really smart people. While I'm sure they missed some tricks, it's likely safe to assume that easy obvious stuff they didn't do has less obvious reasons for not having happened.

 

[Shortround6]

A bit of sarcasm in my post. A lot of planes used ballast to get the CG where they wanted it, especially after modifications from original design.

But the P-39 seems to generate an awful lot of decades late armchair engineering (or re-engineering).

And the Bell engineers had two rather extensive do-overs. The P-39E/P-76 and the P-63.
So yes, there was hundreds of thousands of hours devoted to solving the P-39s problems.

 

[Elmas]

A transceiver radio of those times, using vacuum tubes, and therefore in a pre-transistor era ( not to mention microprocessors...)

could not be placed (length of connecting cables to change frequency, which induced "parasitic capacitance" problems and many other reasons), too far from the operator. So, there were reasons to place radios where they were located.
Let's remember that radio communications in those times were mostly on CW, expecially for medium to long ranges, as communications by voice required a complicated and often unreliable equipment.

 

[fastmongrel]

A transceiver radio of those times, using vacuum tubes, and therefore in a pre-transistor era ( not to mention microprocessors...)
View attachment 596268
could not be placed (length of connecting cables to change frequency, which induced "parasitic capacitance" problems and many other reasons), too far from the operator. So, there were reasons to place radios where they were located.
Let's remember that radio communications in those times were mostly on CW, expecially for medium to long ranges, as communications by voice required a complicated and often unreliable equipment.

Interesting I didn't know about the length of connection cables causing problems. That explains the location of radios as close to the pilot as possible even when it looks like another position would be better.

Maybe the designers knew what they were doing

 

[Elmas]

Interesting I didn't know about the length of connection cables causing problems. That explains the location of radios as close to the pilot as possible even when it looks like another position would be better.

Maybe the designers knew what they were doing

Exactly...

 

[Shortround6]

as a note to the various "ceilings" aircraft could operate at.

Please note that the following ceilings were usually figured out for "normal" gross weight (as in clean condition)

Absolute ceiling, almost always calculated based of the climb rates at lower ceilings. The was theoretical ceiling the plane could reach at full throttle (or max continuous power) and maintain for at least a few minutes. No zoom climb

Service ceiling, the altitude a plane could still climb at 100fpm (or metric equivalent) while using standard climb power setting/rpm. Please note that going above this altitude to try for absolute ceiling is going to tanke many minutes as the climb rate falls into the low double digit per minute range.

Operational Ceiling. Seldom listed and may be a British term. At any rate it is the ceiling at which the plane could still climb at 500fpm (or metric/air force in question equivalent). this was to allow for variations between planes in a small formation and for the worst plane to be on the outside of a turn. It was highest ceiling the planners thought the small formation could maneuver at and still keep formation.

Combat Ceiling, Again seldom listed and again may be British. It is the max ceiling at which the British figured a fighter could engage in combat (aside from a pure diving attack??) with enough surplus power for at least some combat maneuvers.

Please note that absolute and Service ceiling are near useless for figuring out combat capabilities except as a very rough benchmark. A Spitfire V could take 20 minutes to make it to about 35,500 and it took 4 of those minutes to climb the last 2000ft.

Some planes had the climb rate fall off faster than others.

 

[P-39 Expert]

as a note to the various "ceilings" aircraft could operate at.

Please note that the following ceilings were usually figured out for "normal" gross weight (as in clean condition)

Absolute ceiling, almost always calculated based of the climb rates at lower ceilings. The was theoretical ceiling the plane could reach at full throttle (or max continuous power) and maintain for at least a few minutes. No zoom climb

Service ceiling, the altitude a plane could still climb at 100fpm (or metric equivalent) while using standard climb power setting/rpm. Please note that going above this altitude to try for absolute ceiling is going to tanke many minutes as the climb rate falls into the low double digit per minute range.

Operational Ceiling. Seldom listed and may be a British term. At any rate it is the ceiling at which the plane could still climb at 500fpm (or metric/air force in question equivalent). this was to allow for variations between planes in a small formation and for the worst plane to be on the outside of a turn. It was highest ceiling the planners thought the small formation could maneuver at and still keep formation.

Combat Ceiling, Again seldom listed and again may be British. It is the max ceiling at which the British figured a fighter could engage in combat (aside from a pure diving attack??) with enough surplus power for at least some combat maneuvers.

Please note that absolute and Service ceiling are near useless for figuring out combat capabilities except as a very rough benchmark. A Spitfire V could take 20 minutes to make it to about 35,500 and it took 4 of those minutes to climb the last 2000ft.

Some planes had the climb rate fall off faster than others.

Excellent descriptions of some often misunderstood terms. I think the Operational Ceiling was a USN term. Mainly because the Wildcat Combat Ceiling was pretty low.

 

[Micetro]

From the other thread on the XP-39.




I would note that most/all Spitfire IXs carried Five 17.5 ballast weights in the tail. How about just shifting the radio/s, battery and oxygen equipment further back and getting rid of some of the Ballast? Presto...... an improvement of climb of several hundred FPM?

Shortround, where did your information come from that says the MKIX required five ballast weights please?

 

[Shortround6]

Shortround, where did your information come from that says the MKIX required five ballast weights please?

Spitfire Mk IX Weights and Loading

 

[Shortround6]

duplicate post.

 

[MIflyer]

They did not route RF from component to component around the airplane by cable, so the length of cables did not matter. They did not use communications transceivers in WWII aircraft but instead used separate transmitters and receivers. In the case of the SCR-522 VHF comm radio the receiver and transmitter were in the same box with the power supply with its dynamotors in a separate box. When the US redesigned the SCR-522 to make the ARC-3, they went to using separate boxes for the transmitter and receiver, with the dynamotors mounted on a separate chassis. The ARC-3 not only made maintenance easier by enabling "Line Replaceable Units" so that only a bad transmitter or receiver could be swapped out rather than pulling the whole set, but also enabled the equipment to be distributed into a more favorable CG situation.

I have an SCR-522 receiver and transmitter and an ARC-3 receiver and transmitter as well as a number of SCR-274-N receivers and transmitters, if anyone wants any pictures or details.

 

[GrauGeist]

Mainly because the Wildcat Combat Ceiling was pretty low.

What do you consider low?

The F4F-3's ceiling was over 39,000 feet, the FM-2 was about 34,000 feet.

It wasn't the Space Shuttle, FFS...

 

[Micetro]

Spitfire Mk IX Weights and Loading

OK thanks, you might find there's a difference when the different mark Merlins are fitted due to the weight changes, also if the armour plate is fitted to the radiators for low-level ops because it all affects the CofG. In my experience with Spits I can never recall fitting five weights when all of the original equipment was also fitted when we did the weight and balance.

 

[Elmas]

They did not route RF from component to component around the airplane by cable, so the length of cables did not matter.
Omissis

Exactly. But how could you switch frequency, mode of operation, fine tune the coupling of the antenna etc. with a TX like this positioned far away from the pilot, without routing RF (or even AF) all around the airplane?
To operate a radio in a single seater in WWII was already not at all an easy thing, let's imagine to turn all that knobs (everyone is there on purpose...) with thick gloves at night, when landing, in a severe turbulence, lightnigs here and there and statics everywhere...
So, basically, RX-TX had to be positioned very close to the operator.

VHF transmitter T-23/ARC-5 and HF transmitter T-20/ARC-5 on rack MT-71/ARC-5.

 

[ThomasP]

re Operational Ceiling and Combat Ceiling

As far as I can find the UK started using the term Operational Ceiling (1000 ft/min climb) around 1941, it is mentioned in some of the tests done by A&AEE/RAE/AFDU, including the ones done on the Airacobra Mk I AH573 (operational ceiling of ~24,000 ft). Note that this is with 3000 rpm at FT.

Immediate post-war mention by Wade etal: "Comparitive Performance of Fighter Aircraft" under Operational Ceiling.

I have seen the US occasionally use the term operational ceiling in dispatches during the late-war, but the USN and USAF both formally started using the term Combat Ceiling (500 ft/min climb) after the war. You can find the US formal usage starting in their SACs about 1950.

examples for the US:

"http://www.alternatewars.com/SAC/F2H-2_and_-2N_Banshee_SAC_-_1_November_1949.pdf"
"http://www.alternatewars.com/SAC/F-51H_Mustang_SAC_-_22_March_1949.pdf"

 

[MIflyer]

No, the SCR-274-N and related ARC-5 such as you show were not anywhere near to the operator, nor did he have direct access to them. The same was true of the SCR-522. Those sets were located wherever they could be accommodated in the aircraft. In the case of the SCR-274-N, in bomber aircraft the sets were in the radio compartment, near the radio operator - who generally did not use them! Only the pilots used them, for communications such as landing clearance, "get back in formation,you idiot" and "there is a Zero on your tail". In the case of the transmitters they were set on frequency before the aircraft took off, and generally not adjusted in flight. While the SCR-274-N had the capability to send and receive CW we have found no evidence that feature was used very much or even at all.

In bombers and transports there were two or more radio systems. SCR-274-N and SCR-522 were "Command Sets." They were used for communications with other aircraft and control towers. The radio operator operated the long range "Liaison Sets," usually using a BC-348 receiver (I have seven of them) and a large transmitter, such as the BC-375. They communicated with HQ units and other distant stations, usually employing CW. Typical communications by the radio operator would involve reports on targets hit, mission aborts, and secondary targets to be hit.

In the P-400 and P-39 the radios were located way back behind the engine. It appears that the P-400 had the SCR-283, which had one transmitter and one receiver, based on photos from Guadalcanal. Some kind of radio was added to the P-39's in the SWPA behind the cockpit, under the rear canopy, and over the engine; it probably was an IFF set; there was not room for it in that aft compartment.

 

[P-39 Expert]

What do you consider low?

The F4F-3's ceiling was over 39,000 feet, the FM-2 was about 34,000 feet.

It wasn't the Space Shuttle, FFS...

F4F-4 was 34000'. F4F-4 replaced the -3 in June 1942 at Midway. Introduced folding wings and 6 gun armament.

 

[Elmas]

No, the SCR-274-N and related ARC-5 such as you show were not anywhere near to the operator, nor did he have direct access to them. The same was true of the SCR-522. Those sets were located wherever they could be accommodated in the aircraft. In the case of the SCR-274-N, in bomber aircraft the sets were in the radio compartment, near the radio operator - who generally did not use them! Only the pilots used them, for communications such as landing clearance, "get back in formation,you idiot" and "there is a Zero on your tail". In the case of the transmitters they were set on frequency before the aircraft took off, and generally not adjusted in flight. While the SCR-274-N had the capability to send and receive CW we have found no evidence that feature was used very much or even at all.

In bombers and transports there were two or more radio systems. SCR-274-N and SCR-522 were "Command Sets." They were used for communications with other aircraft and control towers. The radio operator operated the long range "Liaison Sets," usually using a BC-348 receiver (I have seven of them) and a large transmitter, such as the BC-375. They communicated with HQ units and other distant stations, usually employing CW. Typical communications by the radio operator would involve reports on targets hit, mission aborts, and secondary targets to be hit.

In the P-400 and P-39 the radios were located way back behind the engine. It appears that the P-400 had the SCR-283, which had one transmitter and one receiver, based on photos from Guadalcanal. Some kind of radio was added to the P-39's in the SWPA behind the cockpit, under the rear canopy, and over the engine; it probably was an IFF set; there was not room for it in that aft compartment.

Myflier said:
"In the case of the transmitters they were set on frequency before the aircraft took off, and generally not adjusted in flight. "
So, a squadron of P-51s from Britain to Berlin used for the whole flight the same frequency, for take off, cruise, communicating with the fighter control, landing, emergency ditching, etc? Always VHF (short range) or HF (medium or long range)? Did they communicate with bombers or not? If they were distant from the base, their radio set on VHF and the operation was cancelled, how did they know?
The creation of Britain's Chain Home was much emphasized, but the whole of this organization would have been completely useless if Hurricanes and Spitfires had not had an equally efficient system of communication on board, a fact that is taken for granted and it is generally underestimated.
Of course,in my posts, I was not talking about planes with a dedicated radio operator on it.

 

[Micetro]

Exactly. But how could you switch frequency, mode of operation, fine tune the coupling of the antenna etc. with a TX like this positioned far away from the pilot, without routing RF (or even AF) all around the airplane?
To operate a radio in a single seater in WWII was already not at all an easy thing, let's imagine to turn all that knobs (everyone is there on purpose...) with thick gloves at night, when landing, in a severe turbulence, lightnigs here and there and statics everywhere...
So, basically, RX-TX had to be positioned very close to the operator.
View attachment 596839
VHF transmitter T-23/ARC-5 and HF transmitter T-20/ARC-5 on rack MT-71/ARC-5.

Elmas,

Frequency changing in single-seat fighters using the early War radios was carried out remotely using a mechanical Teleflex cockpit lever-cable-radio mounted lever system and later changed to electro-mechanical frequency changing, I'm not sure that fine tuning was possible as they were only short-range units compared to those used on the larger types