Dec 1941. Long range day fighter.

[fastmongrel]

Every aircraft is a compromise, whatever the technology of the day. In the 1930s the British were looking for firepower and performance in fighters. It was the quest for performance that led to the sacrifice of range.
The British were aware of the increasing performance of fighters and bombers in other countries. By 1934 views that the current fighter specifications might be lagging behind those being developed abroad (which in 1934/5 means Germany) were being openly expressed. This just drove the quest for greater performance at the cost of other capabilities.
It was in July 1934 that the Director of Technical Development (DTD, Cave) at the Air Ministry wrote to the Operational Requirements section that

"We receive from A[air]. I[intelligence]. reports of high speeds claimed for fighters built abroad. As our new Fighter Specifications F.7/30, F.5/33 and F.22/33 all sacrifice performance for other operational requirements the situation may arise shortly that our fastest fighter is very much slower than some foreign fighters."

He was probably referring to F.7/30s required night fighting capability and the low performance expected of twin designs. The story of how this quest for speed led to not one but two short range, high speed interceptors is well known.

Cheers

Steve

In the 1920s the RAF defence of London used a Three Zone Defence system. A coastal Gun Zone, then a Fighter Zone and then a final Gun Zone which was the suburbs of London. The Zone Fighter needed endurance as it would fly Standing patrols day and night, a High Frequency Radio so it could be guided by ground control, searchlights would be used to guide and control the fighters at night and night flying equipment which both needed electricity so a Generator and Battery which added weight. As a lot of the time would be at altitude a large and heavy oxygen system was also needed.

In 1927 the system evolved so that a few squadrons were stationed on the coast these were Interceptors that would not fly standing patrols but the pilots would be on 5 minutes standby to take off as bombers were spotted (or heard sound locating equipment was being worked on). The requirement for an Interceptor led to the Fury which was freed from the need to carry lots of fuel, radio, night flying equipment and a very large oxygen system. Everything was climb climb and climb with a light load of ammo.

These two seperate Zone and Interceptor fighters (Zone Bulldog then Gauntlet, Interceptor Fury MkI then Fury MkII) began to coverge from 1930 leading to the F5/34 8 gun Interceptor and F10/35 higher performance Zone fighter requirements where a heavier 6 gun armament and higher performance began to be contemplated with reduced endurance. Note endurance not range.

The Zone requirement for long endurance standing patrols declined and Interceptor climb and speed came to be more important as the Ground Control and Intercept system began to be formed. The Zone fighter requirement was expected to only have a speed around 280mph approx 40-50mph slower than the Interceptor fighter the F5/34 and F10/35 never lead to a service aircraft but I imagine the Defiant sort of filled the Zone part.

The Spitfire and Hurricane were components of a defence system and I doubt anyone expected to have to escort bombers to Berlin.

 

[stona]

If we wind the clock back a little further, it is also worth noting that while we are concentrating on aircraft for Home defence or offensive use in Europe (France, then Germany) the RAF had other roles to fulfill, notably Imperial policing, at which it claimed to be effective and cost efficient. This usually amounted to bombing remote tribesmen or some unfortunate chief's kraal. Nonetheless it did affect aircraft design.
In the 1920's the RAF's so called 'Air Control' responsibilities in the Near East and North West of India took precedence over just about everything else.
Trenchard bemoaned the fact that the ten year rule had led to a "general utility" machine for use in Iraq and elsewhere.

Malcolm Smith, in 'British Air Strategy' wrote.

"The work of the RAF in the 1920s required equipment that would be no use at all in a European emergency. In hot and undeveloped countries where there was no aerial opposition, lift, flight stability, low landing speed, ease of repair and fuel economy were the factors which governed the design of aircraft."

You are not going to get a high performance interceptor of any type, let alone long endurance, from parameters like that.

As far as the different fighter types, nicely explained by fastmongrel above, it should be noted that the concept of the 'Advance' or 'Interception' fighter was discredited in the Air Exercises of 1931 when it was shown to be unworkable. The Fury squadrons, then the RAF's interception fighter, were moved back from their advanced bases into the Aircraft Fighting Zone where they served as day zone fighters.
There is a small but vital difference in the requirements of the two types of fighter. Zone fighters needed a high rate of climb to achieve their patrol height whereas for the interceptor speed and distance covered in a pursuit climb were important. Why a Fury replacement was ordered when the interceptor concept had been discredited is difficult to explain. It was largely because the Fury was still regarded as a successful aircraft.
It did however constitute the first step on the road to a blurring of the differences between the two types.

Cheers

Steve

 

[Shortround6]

I have stayed out of this due to in-depth ignorance regarding the FW 187 relative to identifiable and reliable flight test and drag data.

Hermann has produced good works on the FW 190D and others. Does he have similar background data for his treatment of the FW 187?

With reliable drag calculations validated by wind tunnel testing and reliable horsepower specs, the flight tests should validate (or repudiate) the preliminary engineering projections.

The problem/s here seems to be that the FW 187 was "designed" for a DB 60_ engine. The _ is because I don't know if it was a "normal" DB 601 for which we do have decent power numbers or an experiential "evaporative" cooled model for which there don't seem to be good power numbers. I have no desire to get into arguments about the "evaporative" cooling. The prototype used some sort of surface radiator arrangement and long radiator/condenser in the engine cowling. I will leave it at it was NOT a standard cooling system.
All but one prototype flying with the low powered Jumo 210 engines (of several different models) with some pretty dismal looking radiator installations in regards to drag but I have no idea what they were really like.
The one prototype that did fly used the above mentioned 'special' engines and the only speed result for it simple says "low level" for altitude.
Given the difficulty in matching power level (could be 1300PS, could be ???) to altitude (sea level or 1000meters?) and drag (engine installation/radiators way different than the pre-production series aircraft) everything just seems to be estimates/guesses.
One page in the book is a reproduction of DB specification sheet for a DB 601H engine showing power numbers but the test is not clear on IF this was the engine installed in the prototype or if those engines were experimental development engines for the "H" model.

One page in the book lists 3 "possible" armaments of the V4 and zero-series. these range from two MG 17s with 1000rpg, two MG/FF with 60 rounds per gun and a single MG 81 with 1000rpg up to four Mg 17s with 1000rpg, two mg 151s with 600rpg and one MG 181 with 1000rpg. These aircraft were the Jumo powered ones and the MG 151 and Mg 81 were not in service (although in development) at the time and obviously the weight difference (and drag) could screw things up.

There are 3 pictures of the DB powered V5 in the book but from the angles it is impossible to tell the gun outfit, as in number of guns let alone type.

There is just way too much "grey" in the book.

 

[Shortround6]

I would also note that none of the performance figures in the book seem to come from actual flight tests. Even the V-4 and A-O performance numbers are calculated and calculations include both a calculated higher full throttle height including RAM and a 13% increase in power due to engine thrust. Which is fair enough on the surface.
I would also note that R-R never claimed a 13% increase in power due to exhaust thrust during experiments with a Hurricane II with Merlin XX engine. It could very well be that FW or Junkers exhaust manifolds were better than the ones RR was using but exhaust thrust depends on two things. #1 is the mass flow, air plus gasoline (plus water/alcohol mixture if used) and the carburated RR engines ran richer than fuel injected German engines at full power meaning more mass for a given HP #2 exhaust gas velocity which is dependent not only on exhaust nozzle shape and size but the air pressure of the air at the outside of the nozzle. The RR figures may also be calculated but they figured exhaust velocities varying from 1395fps at 15,000ft to 1901fps at 30,000ft. due to the back pressure. RR was NOT figuring things at lower altitudes as they were interested in high altitude performance at the time and were looking at data with the supercharger in high gear.
Using a blanket correction factor seems a bit optimistic.

 

[davparlr]

That is the sole reason the average top speed in a P-51D for same boost/same engine/same RPM was approximately 4mph TAS slower than the P-51B.

I don't think that the weight increase was the sole reason the P-51B was faster. It had cleaner canopy, two less machine gun (insignificant?), and no fillet on wing leading edge (impact?).

 

[drgondog]

CORRECTION - 6-5-16

Dave - the P-51D cockpit enclosure had lower profile/parasite drag than the P-51-1,A-36, P-51A/B, , primarily due to the windscreen. The P-51H had slight;y lower drag for its canopy than the D and the B. During our many philosophical discussions' with Soren, I covered this ground pretty thoroughly and included Lednicers VSAero supported Drag Report that is included in this Tech Forum.

The weight of the guns and ammo were the sole incremental factors between the gross weight of the B/C and D/K. That incremental weight is the manifested increase in Induced drag. The introduction of the re-designed bomb rack for the D/K brought the two versions to parity on drag/top speed for 1650-7 engine.

 

[drgondog]

Shortround - a blanket 13% is, as you note, not a 'reliable' factor for the reasons you mentioned as well as the alignment of the exhast stack relative to the Thrust axis - for a Mustang the angle is 8 degrees - ot Exhaust Thrust x Cosine 82 degrees. In Horner's Fluid Dynamic Drag study of the Bf 109, he states 10-14% as commonly found factors and used 12% IIRC to add to calculated Thrust Hp

 

[GrauGeist]

Bill, have they ever determined how much drag was caused by a weapon port (MG or cannon) in the leading edge of a wing?

 

[drgondog]

Bill, have they ever determined how much drag was caused by a weapon port (MG or cannon) in the leading edge of a wing?

Yes. the gun port openings were a pretty small delta for parasite drag, but the four cannons on the P-51-1 was significant and comparable to the early style P-51A/B external bomb racks. NACA started with a clean and polished scale model, replaced with live airframe with prop removed, all gaps sealed, including ailerons, flaps, rudder, elevator, exhaust stacks removed and covered, radio masts removed, etc. Then one by one, such gaps and interference objects were added back and contribution to drag recorded.

 

[Shortround6]

I could be wrong but I seem to remember something about gun ports/gun muzzles also disrupting airflow over/under the wing and hurting lift. Obviously a single gun port is going to affect a much smaller area than a group of 3-4 guns. Perhaps the tunnel test took into account the loss of lift, I don't know.

 

[drgondog]

I could be wrong but I seem to remember something about gun ports/gun muzzles also disrupting airflow over/under the wing and hurting lift. Obviously a single gun port is going to affect a much smaller area than a group of 3-4 guns. Perhaps the tunnel test took into account the loss of lift, I don't know.

There would be some degradation to the airflow, particularly when firing, but the more consequential effect is incremental parasite drag.

 

[Shortround6]

OK, thank you.

Ejection ports may be a source of drag also, many test results mention if either Gun ports or ejection slots are taped over or covered or are open during the test.

 

[drgondog]

Virtually All openings. gaps, slots, holes, protuberances, wire, wavy surfaces, rivet heads, grainy paint, etc are sources of either parasite or friction drag.

 

[pinehilljoe]

I always thought the Grumman XF5F Skyrocket would have been interesting. It was developed in time to have been able to have been deployed to the Fleet and the Air Corps by early 42

 

[Shortround6]

Interesting yes, useful no.

as listed by Tomo in an early post in this thread.

Standard Aircraft Characteristics Arcive

scroll down to the F5F entry and read the three entries. A range of 1170 miles at 172 mph doesn't really look good for a "long range" fighter. Please remember that an early P-47 was rated at being able to fly 880 miles at 200-210mph at low altitude on internal fuel.
Also look at the expected speeds. the 383mph at sea level listed by wiki seems to be pure fantasy or a misprint/typo from 283mph at sea level. Also initial armament was two .50 cal guns and two .30 cal guns.

 

[davparlr]

Dave - the P-51D cockpit enclosure had lower profile/parasite drag than the P-51D,

little error here, did you mean the P-51B cockpit enclosure had lower profile/parasite drag than the P-51D, or the P-51D cockpit enclosure had lower profile/parasite drag than the P-51B?

 

[drgondog]

I meant that P-51B had the highest profile drag compared to the D, and the D was slightly higher than the P-51H.
The windscreen of the series through the 51B was more inclined in vertical direction from thrust line, and like the Spits, had a stagnation pressure increase at the base of the windscreen. The P-51D, like the FW 190 solved that issue. The P-51H extended canopy combined with the windscreen further improved free stream pressure distribution