Performance modifications done at Squadron level.

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Getting back to the OP about performance modifications done at a squadron level, the conversion of de Havilland two-pitch propellers to constant speed units on RAF fighter squadrons before and during the Battle of Britain springs to mind: an article called "Pitch Panic" from Flight Magazine, 7 December 1943, explained what happened. All-in-all, it was quite a feat of production and organisation. (Arguably, the CS unit should have been in universal use for RAF fighters well before June 1940, but that's another story.)




An interesting vintage film on installing the de H Hydromatic CS Airscrew... 1:21, for examples, shows the CS unit; 1:28 shows the quill shaft that's mentioned in the article.


View: https://www.youtube.com/watch?v=fvCmQAetyag
 
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Interesting post. The video is good, but note that it is for the later licensed Hamilton-Standard Hydromatic type propeller, not the earlier licensed H-S "Bracket" type propeller that is referred to in the Flight written article.
The Flight article has some detail of some aspects of the De Haviland work, but nothing on Rotol. I think there is an error in the "more than 7,000' increase in ceiling" claim. The early Mk1 Spit with 2-bladed wooden prop was tested with a service ceiling of 31,900'. A similar 1939 Spit, 200lbs heavier, with the De-Havilland 2-pitch airscrew had 34,400' and a similar early 1940 one with Rotol 3-blade constant speed prop gave 34,700' ceiling. All these with same boost limits on 87 Octane fuel. So, we are seeing only about 2,500' increase in ceiling. However, the time to climb from zero to 30,000' was respectively, 22m25s, 23m04s and 16m24s, a very definite win for the C-S prop!
BTW, an indication of the further improvement that the 100 Octane fuel made with increased boost in the climb is that a similar climb to 30,000' was 13m42s, some 2m42s faster than the 87 oct performance. The bigger factor then, was the Constant Speed function, although the 100 oct was a further improvement.

Eng
 
When comparing propellers it may be useful to think of a car transmission.
A Spitfire with a fixed pitch prop is locked in high gear. You can pick the gear so the top speed is very good.
Acceleration and hill climbing both suck.
Spitfire with 2 pitch has a transmission with two gears, a low gear for take-off (initial acceleration) and the high speed gear. Think 4-6 speed car with all the middle gears taken out.
Spitfires shifted to course pitch at about 140mph and climbed in course pitch with reduced RPM to keep the prop working (again think of boat cavitating) until the air got thinner and IAS different from actual airspeed and throttle could be advanced a bit more as the plane climbed.

CS props had a infinite range of gears (speeds) limited by the prop pitch limits 20 degree change in the DH props and 30 degrees in the Rotol props (P-40 props had 35 degrees?) But then we start talking about the speed range, minimum speed vs max speed.
The CS prop allowed for both a better match of propeller speed to air speed (better bite?) and allowed the engine to operate at full throttle or 2600-2850rpm while climbing instead of starting the climb at 2100-2200rpm and taking thousands of feet to climb to where even 2600rpm could be used.

Spitfireperformance.com used to have the climb charts for the Hurricane I and Spitfire I with some of the different propellers that showed the rpm and boost settings at altitudes like every 1000ft or 2,000ft. Trying to climb at about 2/3s power or even 75% makes for a slow climb.
 
These should be still available at the archive.
 
tomo pauk said:
These should be still available at the archive.
Click to expand...
Thank you.
Can't get it work, I can bring up the the main page but trying to get into the sub pages is working.
Like where it says "For more of this report see HERE" where the more detailed charts are and not the summery.
Some times it will work, like for the MK I Spit with the Rotol Prop but I can't get to the reports for the fixed pitch or the 2 pitch DH prop charts.
 
Don't know exactly what you mean by "performance" but if you are not talking about just engines there is a Spitfire story I have always thought interesting, as told by WingCo J.E. Johnson.

A new aileron was developed for Spitfires, made out of metal rather than fabric covered, and with a blunter trailing edge. This increased roll rate significantly, presumably by reducing the stick forces, very important in dogfighting the FW-190. The Spit was inferior to the Brewster F2A and Curtiss Hawk 75 in that regard. Johnson's squadron found out about the new aileron, and entirely without authorization, contacted the manufacturer and arranged to ferry their airplanes over to the factory and have the new ailerons installed, rather than waiting on a proper mod program to do it.

It was some time later before they were asked whothell had authorized that mod.

Farnborough also developed a new much improved aileron for the Mustang Mk 1 that upped the roll rate, but I don't think they ever did a mod program for it NAA developed one also and that was used on late production P-51's, although Winkle Brown thought that the Farnborough one was a tad better.
 
Try Here, at the back up page
 
This higher speed was likely the reason why one or two RAF pilots with the RAF in France preferred the fixed pitch wooden propellor. Doing so at the cost of climb rate. That suggests that the pre Battle of France RAF Hurricane sorties were less interception and more patrols. With the latter they would already be at height if they encountered German bombers so a higher speed may have been of more use then. A pure interception sends them up to reach the bombers arriving at height so climb rate was more important to such an interception. Also the fixed pitch propellor was lighter.

Similar effects were noted with Sea Gladiators in RAF service in Malta when the Sea Gladiator Mercury engines and fixed pitch 3 blade aluminium propellors were replaced with Blenheim Mercuries and matching two pitch VP propellors. The extra climb rate was notably improved (I have no quantified data) and tempted them to have the final extra two Browning machine guns fitted to the mountings already in the upper wings giving them a six gun complement. Two synchronised and four free firing.
 
Many thanks to bada.

From the chart for the Spitfire I with fixed pitch prop.

altitude..................rate of climb...................air speed mph...........................rpm.................boost.
0....................................2090.................................174.5..........................................2095...............6.4
1000............................2130.................................174.5...........................................2130..............6.4
2000............................2195.................................174.5............................................2165..............6.4
3000............................2215.................................174.5............................................2200..............6.4
5000............................2295.................................174.5..............................................2270............6.4
6500............................2355.................................174.5..............................................2320............6.4
10,000........................2490.................................174.5..............................................2440............6.4
13,000........................2300.................................172.5..............................................2475............4.45
16,500........................1890.................................174.5..............................................2460............1.75
20,000........................1480.................................174.5..............................................2440...........-0.4

I skipped some lines and stopped after 20,000ft but RPM and boost limits show the story.
The plane with two pitch prop took off using 2750rpm but at 2000ft an 171mph it shifted the prop and rpm dropped to 2080rpm and the climb proceeded much the same with the engine staying under 2400rpm for most of the climb, Speed was at 185mph.
When fitted with the Rotol prop they used 161mph as the climbing speed and the engine ran at 2600rpm and 6.4lbs of boost until in hit critical altitude for 2600rpm, At 20,000 ft the engine was still making +1.0lbs of boost instead of the -0.4lbs the fixed pitch prop was doing at 2440rpm.
Rate of climb started at 2810fpm at 1000ft and slowly climbed until it hit 2905 at 11,000ft. At 20,000ft the Rotol prop was giving 360fpm more than the fixed pitch prop.

Anybody that wants to can look at the charts for more details. The numbers really show the difference and why. The fixed pitch props could not use anywhere near the full power of the engines for anything less than full speed.
 
Wow so they made that front fuel tank self sealing finally on the Spit VIII eh? It really was a huge upgrade across the board.

Very interesting tidbits here! The whole issue of ailerons is underrated I think. It seems to have been a major issue with the early Mustangs as well as the Spits.
 
Hi,
You can look at variable propeller pitch in simplistic ways like "gears", but really, it is better to read-up on propeller theory and function, IMO.
With constant speed propellers it is easy to recognise that the propeller pitch control really functions as an engine rpm control, the throttle lever itself then being just a method of varying Manifold Air Pressure (MAP).

The early Merlin manuals describe several propeller versions: D-H bracket (licensed H-S) 10 degree pitch range or 20 degree pitch range, Rotol internal cylinder 20 degree pitch range,
Rotol external cylinder 35 degree pitch range (or 70 degree feathering for multi-engined). Later D-H Hydromatic (licensed H-S Hydromatic) 80 degree feathering pitch range. This is just in the early engines upto about Merlin XII.

Eng
 
Engineman said:
You can look at variable propeller pitch in simplistic ways like "gears", but really, it is better to read-up on propeller theory and function, IMO.
Click to expand...
I firmly believe that propeller design is a strange form of witchcraft
Bubbling cauldrons and all.


This is for fixed pitch props with quick and easy correction factors. Which quickly start to contradict each other
and make little or no account blade shape, airfoil, and so on. And since the right shape and form that works at 10,000 ft while climbing is not the best shape/form to use at 25,000ft for high speed things get real confusing real fast
Engines are simple in comparison.

Constant speed propellers allow the engine to work at engine speeds that make the most power or can be the most economical for the speed the aircraft is doing. A fixed pitch propeller is only going to the right propeller at on speed, at one altitude and at one throttle setting. Every other condition is going to be a compromise. Some small and some large.
A two pitch propeller is going to be right twice. The constant speed prop may not be exactly right in all conditions but it is going to have the least compromises in most flight conditions.
 

Certainly, the detail design of aircraft propellers is complicated, but the basics of function is not too bad.
I like the graph here, do you have similar for 3-blade?

Eng
 
Shortround6 said:
No,
just needed diameter down 8%, adjust other conditions to suit and leave sacrificial offerings on the usual stump in the dark woods.
Click to expand...

Thanks, missed the 3-bladed correction. You may be interested that the table gives almost exactly the result for the Bf 109 G.

Eng
 
Spitfire unrelated but to stay on the post's subject:

JG26 midification of the exhaust pipes, cancelling the overheating issues and allowing full boost?
 
tomo pauk said:
When?
Click to expand...
I think this was 1941. The unit Technical Officer (Behrens?) was doing development with aircraft in operations. I am not certain how much of the technical changes was coming from
the parent companies Fw and BMW, ie, were parts and modifications being sent to them for trial, or was the unit suggesting changes?

Eng
 
Yes, referring to Heinz J Nowarra's old book, Fw 190 A famous German fighter, a special detachment with Behrens and Borris was set up in March 1941 at Rechlin, with other pilots and personnel from JG 26 to do development. So, this does seem to have been more of development effort, rather than unit modifications.

Eng
 

Did they also debugged the 801D?
 
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