The MOSQUITO fighter

[Karnak]

AH Mosquito would fall apart before it would get anywhere near the speeds needed to dive with success on a V-1. So the Spitfire 14 was the fastest plane in the world then?

Not remotely true, though I do think it sheds parts when it shouldn't.  I have many times taken it past 480mph, which is far, far faster than the short dives after V1s would have reached.

Remember, the Mossie on 150 octane is faster than a V1, the dive is just to speed the overtake up.

The Spitfire Mk XIV on 150 octane will do about 390mph on the deck, as I recall.  That is slower than the Tempest Mk V using 150 octane on the deck and far slower than the Meteor or Me262.

[Jabberwock]

Jabberwock,

Sorry, but you are in error.  The NF.Mk 30, the fastest production Mosquito at 430mph, couldn't break 430mph on the deck.  Down low the Merlin 25s produce more power than the high blown Merlins.  The 350-355mph on the deck speed for a Mosquito FB.Mk VI is for one with ejector stacks, +18lbs boost and no external stores, though the bomb/DT hangars would still be there.

I never claimed any Mosquito could exceed 430 mph on the deck, I think out wires are getting crossed as I don't get that assertion from re-reading what I posted (or, indeed, even mentioned the figure).

Any wartime (or other) testing evident to support the assertion that the Mk VI with Merlin 25s at 18 lb. boost could do 350-355 mph at sea level? From my reading of Rolls-Royce engine hp charts, the Merlin 25 is just pipped by the two speed, two stage Merlins at low altitude.

I could be wrong, and most of my Mosquito data is on another computer at the moment, but the fastest sea-level tests speed I have seen for the FB Mk VI was are 354 mph with a Mk VI with Merlin 25s at 24 lb. boost (admittedly with ducted exhausts and 2 x 50 gal drop tanks) and 361 mph from a RAAF document, but the condition of the aircraft (exhausts, stores, tanks), is not given.

Best performance in RAF testing at + 18 lb. boost at sea level was 333 mph (again ducted exhausts and 2 x 50 gal drop tanks), while RAAF testing with a FB Mk VI gave a sea level speed of 340 mph with a Merlin 25 at + 18 lb. boost, again condition unknown.

I'm disinclined to believe that the saxophone exhausts cost the Mosquito 15-25 mph. More like 8-15 mph.

I'd also check that the NF Mk 30 is the "fastest production Mosquito", as testing I have seen suggests that it struggled to make 400 mph with Merlin 72s, and only about 10-15 mph better with Merlin 113s. I believe that the NF 30 was slowed somewhat by flame dampers on the exhausts.

The PR Mk 34 or B Mk 35 seem to me to be the fastest production Mosquitos, at approximately 432 mph, with the Merlin 114 and stores out.

I'm not trying to get into an argument over Mosquito performance, I was just trying to correct what I saw as ignorance over the Mosquito's relative performance to S/E fighters from the initial poster, and the losses it suffered at low altitude (which were actually quite high during daytime operations). In my experiance, the superiority of the Mosquito in speed is often mis-represented (or over-inflated) by many enthusiasts, and then they are disappointed when they are overhauled by enemy fighters in a stern chase.

[Karnak]

Low level operations always produce much higher loss rates, due to two main factors.  1) The primary cause of increased losses is to ground fire.  2) The other cause of increased losses is that you are ceding the altitude advantage to the enemy.

The Mosquito Mk VI was marginally faster than the Fw190s and Bf109s in service when it was introduced in mid 1943.  Numerous encounters confirm this.  The speed advantage was not so much that the Mosquito was remotely immune to interception.

Of course later Bf109s and Fw190s are significantly faster on the deck than the Mk VI, or any other Mosquito, was.

As for documentation, RAE tests found that it was capable of accelerating from a cruise to maximum speed to pull away from a Spitfire Mk XII, the fastest Spitfire at low altitude then in service (340-345mph), before the Spitfire could gain a favorable firing position if the Mosquito spotted the Spitfire if it were no closer than 800 yards and 1000ft above when the Mosquito went to +18lbs boost.


Here are two older posts, one by scherf and one by myself, explaining Mosquito Mk VI speeds.  (my post will be in the following post, too many characters to post both in this message) It is a messy issue.

OK, tried to get some numbers together. The graph is a touch "off" on the Y-axis due to mine own difficulties with Excel.

The original tables I've copied from are all available on Mike Williams' wonderful site.

First is the Boscombe Down test of HX908. They tested it to compare the performance of 150 octane fuel at +25 lbs boost to regular fuel at +18 lbs boost. The curve for the regular fuel speeds is at 95% of takeoff weight, with external tanks on and using saxophone exhausts.

HX809 is the starting point as the other FB.VI tested by Boscombe Down, HJ679, was described as being not representative in its tests there. I've used de Havilland's (not Boscombe Down's) tests of HJ679 as a reality check, though the Boscombe report for HJ679 does have useful information re: relative speeds with tanks on and off.

I'm trying to get from the speed curve from the HX809 tests (carried out with drop tanks attached and saxophone exhausts) to a speed with no tanks and with the ejector stub exhausts, then check it against another actual test.

So here's the HX809 test curve (note it's te left-hand one which is relevant; +18 lbs boost. The other, faster one is for +25 lbs boost, which requires 150-octane fuel, which is "another fine mess."

(Image removed from quote.)

The next step is to "add back" the speed loss from having the external drop tanks attached. Here's the relevant test numbers from HJ679 (see above). The average speed loss is 5 mph (5.1 mph if you want to pick nits), growing much larger at higher altitudes. I believe these were 50-gal tanks.

(Image removed from quote.)

The full test with the full range of speed diffrences at altitude is on Mike Williams' site - report for HJ679.

The next step is to find a value for the speed loss associated with sexophone vs. ejector stubs. I've posted the resulting graph on here before. The exact numbers for the speed loss for the range of altitudes tested is here, again from Mike Williams' site. Test was done on DK290, a B.IV, with max +9 lbs boost. The Merlin 25s on the FB.VI can use +18 lbs boost - I'll leave it to greater minds to speculate on whether there'd be any real difference in speed gain as a result.

(Image removed from quote.)

(Image removed from quote.)

Average speed gain for changing the exhausts across the range tested is 15 mph, 15.4 mph for nit-pickers.

So, then I put together a graph containing the original HX809 test, then a curve for the gain from dropping tanks, then a curve from the gain from using the stub exhausts, then a curve for an aircraft with no tanks and stubs, using the raw numbers from the tests. It's as near as dammit to simply adding 20 mph to the HX809 speeds.

To check for reality, I then put on a curve for another FB.VI, HJ679, as tested by de Havillands with no drop tanks and with stub exhausts. (Boscombe Down, as noted above, had complained that HJ679 was not performing as expected, so dH took it back and ran some more tests, which confirmed it had been about 15 mph too slow at Boscombe. The test data from dH for HJ679 with no tanks and stubs is from April '43, before the aircraft went to Boscombe).

As you can see from the orange curve, my calculations give a result which is very close to dH's, in fact mine are a few mph on the conservative side. There's only one data point with any real difference, and mine is lower than dH's). As dH tested HJ679 at 19,000-odd pounds, instead of 21,000-odd, this may account for the difference.

(Image removed from quote.)

So, I get a deck speed of 352 mph, overall best TAS of 383 mph.

[Karnak]

I know many of you think the persistent fuss a few of us make about the Mosquito using saxophone ducts compared to ejector stacks is silly and that the speed gain doesn't matter.  I disagree with that position and would ask you to imagine how P-51D fans would take it if the Mustang topped out at 352mph on the deck, or how gracefully Bf109K-4 fans would take a top speed of 352mph on the deck.  I remind you of the reaction to the Bf109G-14 being 10mph slow on the deck.  15mph is nothing to sniff at, particularly in an aircraft which relies on speed for success and is being used in an environment filled with speed demons.

On that note, I submit this set of data that I believe strongly supports the idea that we have sufficient data for HTC to boost the Mosquito VI's speed when the 3D model is redone.


Report No. 74 on the Tactical Trials - Mosquito VI tested Mosquito VI No. HJ.666 which was powered by Merlin 23s fitted with ejector stacks.  The addendum, which I will transcribe in full, tested Mosquito VI No. HJ.821 powered by Merlin 25s fitted with ejector stacks.  The addendum is as follows:

_____________________________ _____________________________ _________________

ADDENDUM TO REPORT NO. 74 on TACTICAL TRIALS - MOSQUITO VI

INTRODUCTION
   A Mosquito VI, No. HJ.821, has now been made available by No. 418 Squadron by arrangement with Headquarters, Fighter Command.  This aircraft differed from the one used for the earlier trial only in having Merlin 25 engines instead of Merlin 23 and was flown in the same condition.  The relative performance with fighters near the ground was investigated.

TACTICAL.

Performance.
2.  The aircraft was flown both with and without the long range external jettison tanks.  It is thought that only about 5 m.p.h. is lost by fitting the tanks when operating at low levels.

3.  Full throttle heights are about 5,000 ft. in M.S. gear and 12,000 ft. in F.S. gear.  No actual speed measurements can be quoted as the position error for this aircraft was unknown.

4.  When cruising fairly fast (2300 r.p.m. + 4 boost) near the ground, the Mosquito was "jumped" by a Spitfire XII (Griffon IV) which is the fastest mark of Spitfire at low altitude in use at present.  It was found that provided a good watch was kept, it was possible to pull away from it before it could close to range to shoot effectively.  This of course depended considerably upon the height from which the Spitfire was attacking and the range at which it was first observed, but at the Mosquito's fast cruising speed the Spitfire usually had difficulty in positioning itself to attack and was seen in time.  Even if not seen till 800 yds, and about 1,000 ft. above, it was possible to accelerate and pull away if the Mosquito was opened up to full power (3,000 r.p.m. + 18 lb. boost) immediately.  The indicated airspeeds were 250 m.p.h. for cruising and 340 m.p.h. at full power.

5.  The Mosquito accelerates from 250 m.p.h. to full speed in 1½ minutes.  If height allows, the acceleration can be helped by a slight dive through 500 - 600 ft., in which case this speed can be reached in one minute from fast cruising.  The hight must, however, be lost slowly.

6.  The climb has also improved considerably at full power so that the Mosquito can pull up from low level into a cloud 2,000 ft. above it in less than 30 seconds from fast cruising.  Near the ground the rate was approximately 3,800 ft. per minute in a steady climb.

CONCLUSIONS.

7.  The Mosquito VI with Merlin 25 engines is slightly faster than the Spitifre XII at low level.  On intruder work with good search it should accelerate away from the majority of enemy attacks.

8.  The good climb at full power allows the Mosquito an excellent chance of reaching cloud cover quickly.

AFDU/3/20/46
4th August, 1943

_____________________________ _____________________________ _________________

What can we infer from this report?  We can, in my opinion, infer that the Mosquito VI HJ.821 did something like 350mph on the deck.  The report says 340mph was indicated, but it also says the position error was unknown so speeds could not be quoted. According to the performance chart for the Spitfire XII ( http://www.spitfireperformance.com/spitfire-XII.html ) the Spitfire XII does ~345mph on the deck.  If the Mosquito VI was out running it slightly that would put the Mosquito VI at about 350-355mph.  This number is right in line with both de Haviland's claims and pilot claims as to the speed obtained by their Mosquito VIs.  It would also put it right in the region expected if 15mph were gained by replacing the saxophone ducts with ejector stacks when compared to the charts we have for a saxophone ducted Mosquito VI, which put it at 338mph on the deck.  This chart:

demonstrates in hard numbers the performance gain of a Mosquito IV with Merlin 21s going from saxophone ducts to ejector stacks and gives the 15mph gain in speed claim a basis in hard fact.

In summary, we have the following pieces of evidence:

1) Hard numbers for a saxophone ducted Mosquito VI.
2) Hard numbers for the speed gain of a Mosquito IV going to ejector stacks.
3) Hard numbers for the Spitfire XII.
4) A tactical report in which a Mosquito VI with ejector stacks slightly outruns a Spitfire XII, a number which exactly matches the data in points 1, 2, and 3.


This very strongly indicates that a deck speed of 350-355mph and a F.S. gear altitude speed of 390mph would be an accurate model of the Mosquito VI's speed with Merlin 25s and ejector stacks.

Sources:
Mosquito; C. Martin Sharp & Michael J. F. Bowyer, ISBN 0-947554-41-6
Mosquito B. Mk. IV DK.290  Comparitive level speeds with ducted saxaphone and multi stub exhausts A. & A.E.E. Boscombe Down
Mosquito VI Tactical Trials at http://www.wwiiaircraftperformance.org/
Spitfire XII at http://www.wwiiaircraftperformance.org/

[Scherf]

I'd post a lnk to the thread we had a while back, where I uploaded a ton of official testing stuff. Telstra (ptui!) has unilaterally canned my webspace, so the links no longer work.

Sorry.

Either way, the prototype on Merlin 61s in mid-42 (basis for "fastest in service" claim) does not equal F.B.VI on M25s in 1945.

Edit - Does photobucket allow hotlinking?

[Charge]

"4) A tactical report in which a Mosquito VI with ejector stacks slightly outruns a Spitfire XII, a number which exactly matches the data in points 1, 2, and 3."

It has no relevance unless you know exactly what XII that was. Could well be the worst aircraft in the squadron.

Looking at the speed diagrams would indicate 330mph NOE.

DK290 also had the smooth glass nose i.e. no gun openings for .303s or 20mms so it may have less drag than the fighter config.

The trials were flown with 19.700lb as corrected standard load but that is in bomber config? For a fighter version that would be around 17000-18000lb?

-C+

[Karnak]

"4) A tactical report in which a Mosquito VI with ejector stacks slightly outruns a Spitfire XII, a number which exactly matches the data in points 1, 2, and 3."

It has no relevance unless you know exactly what XII that was. Could well be the worst aircraft in the squadron.

Looking at the speed diagrams would indicate 330mph NOE.

DK290 also had the smooth glass nose i.e. no gun openings for .303s or 20mms so it may have less drag than the fighter config.

The trials were flown with 19.700lb as corrected standard load but that is in bomber config? For a fighter version that would be around 17000-18000lb?

-C+

The difference in drag would not affect the speed increase from the exhaust thrust any more significantly than the increased exhaust thurst of the Merlin 25 over the Merlin 21 would.  We still end up with the same 350-355mph on the deck estimate.  That speed matches all known data points.  No other speed does so.

[RASTER]

It seems the concept of a bomber faster than fighter is difficult for some to grasp but it was not a new concept. Two early 1930s German light bombers, the Heinkel 70 and Dornier 17, and the Russian Tupolev SB-2, were faster than their contemporary fighters and proved almost impossible to intercept during the Spanish civil war. Once again the history does not seem to coincide with the representitive statistics being put forward. The first operational flight, in September 1941, demonstrated that the Mosquito, on a photo reconnaissance mission over southern France, simply outran the German Me-109 fighters sent to intercept it, leaving them behind at over 400mph.

And about the test results that are being presented...I want to point out that there are exceptions to official reports, and you might do well to consider this, I am quoting Group commander Donald Bennett "At a meeting at the Air Ministry on the subject, Bomber Command and the Air Ministry both very strongly opposed the adoption of the Mosquito.They argued that it was a frail wood machine totally unsuitable for Service conditions, that it would be shot down because of its absence of gun turrets, and that in any case it was far too small to carry the equipment and an adequate Pathfinder crew. I dealt with each one of these points in turn, but finally they played their ace. They declared that the Mosquito had been tested thoroughly by the appropriate establishments and found quite unsuitable, and indeed impossible to fly at night"

And take careful note these published tests were done " by the appropriate establishments" and read and understood by Bomber Command and the Air Ministry. We look back and say, well what blundering idiots. But we fail to see ourselves making the same mistake. Common sense would tell you that something does not jive here.

[Plazus]

Raster, I think that you may be taking the historical records a bit too seriously. The information you are providing us is dated in early to mid war time of WW2 (1940-43). The Mosquito at that time was a marginally faster machine. But in 1944 and 45, you begin to see other aircraft beat the Mossie in the speed/manueverability category.

You must realize that in the Late War Arena, your Mosquito is going up against the likes of P51s, 109Ks, LA7s, and among other later war rides. The Mosquito cant outrun these late war machines. If you want a more historical feel, I suggest Mid War Arena, where the Mossie is a bit more competitive. I do, however, agree that the Mossie could use an overhaul. I personally would like HTC to create an early war bomber variant, along with a late war fighter variant. The current version in game just doesnt do full justice for the Mossie right now.

[Scherf]

Lemme test if I can get some images to appear.

Here's as far as I got for demonstrating what an FB.VI on M25s and +18 with no drop tanks and stub exhausts would look like. If it works I'll re-post the whole explanation, with snippets re: speed differences.




Hoo-fargin-'ray, it works.

Will try to reconstruct the whole post below.

As for the first sortie in '41, yes the Mossie outran intercepting fighters. No, I've never seen any claim that it did so at over 400 mph. I have Don Bennett's book upstairs and am familiar with the quote. In terms of the mathematics of modelling performance, it's a massive So What. The AH boys have to go off what can be demonstrated using original docs where possible. "Modelling by Anecdote" won't get anywhere.

[RASTER]

Modelling by Anecdote" won't get anywhere.

Thats very true Scherf, but there must be something we dont understand which places the Mosquito slower than history represents it.

I want to quote Canadian Mosquito pilot and air ace Russell Bannock because I am a Canadian and  (sadly) of the few planes made in Canada the Mossie was one of them. I saw my first V1 rocket on June 16, 1944,” he recalled at the ceremony, “over the English Channel below me at about 500 feet. I thought it was a burning aircraft.” “Mosquitos were the only plane able to do night patrols, carrying radar in the nose.” They were also fast, capable of more than 400 miles per hour, but even then, he said, they learned they had to attack from about 10,000 feet to get enough speed to intercept the low-flying missiles. He added, “We, (the Allies) were lucky that they didn’t get launched until near the end of the war.”

[W7LPNRICK]

I've heard you can't trust the history channel, but I watched a nice documentary on the mosquito before flying it and I was very disappointed. In AH its wings fall off with very light enemy fire. It's ENY reflects it's standing in the game. I still enjoy flying it when the ENY is low, mostly in attack mode. Personally I think it is misrepresented in the game & historical accounts are accurate, but what do I really know?   

[Scherf]

Here's my reconstructed post on FB.VI speeds below.

As for Russ Bannock's account, I've no doubt that the NF.30s he flew on 406 Sqn could have done 400 mph at altitude. But it's precisely for the sake of historical accuracy that test documents, not anecdotes have to be used.

Believe you me, if I could find a test for a 400 mph level-speed FB.VI, I'd post it.






OK, tried to get some numbers together. The graph is a touch "off" on the Y-axis due to mine own difficulties

with Excel.

The original tables I've copied from are all available on Mike Williams' wonderful site.

First is the Boscombe Down test of HX908. They tested it to compare the performance of 150 octane fuel at +25

lbs boost to regular fuel at +18 lbs boost. The curve for the regular fuel speeds is at 95% of takeoff

weight, with external tanks on and using saxophone exhausts.

HX809 is the starting point as the other FB.VI tested by Boscombe Down, HJ679, was described as being not

representative in its tests there. I've used de Havilland's (not Boscombe Down's) tests of HJ679 as a reality

check, though the Boscombe report for HJ679 does have useful information re: relative speeds with tanks on

and off.

I'm trying to get from the speed curve from the HX809 tests (carried out with drop tanks attached and

saxophone exhausts) to a speed with no tanks and with the ejector stub exhausts, then check it against

another actual test.

So here's the HX809 test curve (note it's te left-hand one which is relevant; +18 lbs boost. The other,

faster one is for +25 lbs boost, which requires 150-octane fuel, which is "another fine mess."



The next step is to "add back" the speed loss from having the external drop tanks attached. Here's the

relevant test numbers from HJ679 (see above). The average speed loss is 5 mph (5.1 mph if you want to pick

nits), growing much larger at higher altitudes. I believe these were 50-gal tanks.



The full test with the full range of speed diffrences at altitude is on Mike Williams' site - report for

HJ679.

The next step is to find a value for the speed loss associated with sexophone vs. ejector stubs. I've posted

the resulting graph on here before. The exact numbers for the speed loss for the range of altitudes tested is

here, again from Mike Williams' site. Test was done on DK290, a B.IV, with max +9 lbs boost. The Merlin 25s

on the FB.VI can use +18 lbs boost - I'll leave it to greater minds to speculate on whether there'd be any

real difference in speed gain as a result.







Average speed gain for changing the exhausts across the range tested is 15 mph, 15.4 mph for nit-pickers.

So, then I put together a graph containing the original HX809 test, then a curve for the gain from dropping

tanks, then a curve from the gain from using the stub exhausts, then a curve for an aircraft with no tanks

and stubs, using the raw numbers from the tests. It's as near as dammit to simply adding 20 mph to the HX809

speeds.

To check for reality, I then put on a curve for another FB.VI, HJ679, as tested by de Havillands with no drop

tanks and with stub exhausts. (Boscombe Down, as noted above, had complained that HJ679 was not performing as

expected, so dH took it back and ran some more tests, which confirmed it had been about 15 mph too slow at

Boscombe. The test data from dH for HJ679 with no tanks and stubs is from April '43, before the aircraft went

to Boscombe).

As you can see from the orange curve, my calculations give a result which is very close to dH's, in fact mine

are a few mph on the conservative side. There's only one data point with any real difference, and mine is

lower than dH's). As dH tested HJ679 at 19,000-odd pounds, instead of 21,000-odd, this may account for the

difference.



So, I get a deck speed of 352 mph, overall best TAS of 383 mph.

[Neil Stirling]

I have a copy of Tech.Note. No. Eng. 316 AVIA6/5817.

This covering methods of increasing the speed of WW2 RAF Fighters in order to intercept V1,s  increased boost, ejector exhausts, NO2 etc.

The Mossi NF XIX (Merlin 25,s) is listed as gaining 15 mph by the use of exhaust thrust. The speed at 3,000ft 348mph +18lbs boost, 377mph full throttle (approx +24lbs) and 394mph full throttle and NO2.

Just for interest. Speeds at 3,000ft.

Temp V Sabre IIa +9lbs 390mph +11lbs 414mph

Mustang III V-1650-3 +18lbs 373mph
Mustang III V-1650-7 +25lbs 416mph full throttle 421mph

Spit XIV +18lbs 372mph, +21lbs 393mph and +25lbs 410mph
Spit VIII +18lbs 346mph +25lbs 381mph and full throttle 387 mph

[RASTER]

You are aware are you not that the Merlin engine only weights approximately 1500lbs and that the Mosquito was stressed skin. The skin was an ultra smooth laminate of Balsa wood. (take off 15mph for non reflective paint) It was a little larger than a P38 and you are giving speeds with a weight of approxmately 20000lbs with drop tanks added. Balsa weights only 170kg/cu m. while aluminum can be 1000kg/ cu. m. You would have us believe this plane weighed more than a P38 at 12500lbs (5800kgs) The added wind resistance loss of the drop tanks of 5mph. Come on the Mosquito was only marginally bigger and what about the loss in velocity. You trying to tell me the drop tanks removed 5 mph while the added size reduced the speed by 100mph? Wish I had more time....