Fokker D.XXI in Dutch service

The Performance for the Hawk with the 1830-17 engine would be with 100 octane fuel. (due to the low critical altitude, and high low-level speed)

And the He 112 was suposeddly somewhat superior in performance to the Bf 109 with the same engine. (~20-30 km/h faster, 510 km/h for the B-2 with Jumo 210G) And also had significantly better range.
The main disadvantage to the Bf 109 being much greater parts count and elliptical wing making it more difficult to construct. (and possibly more difficult to repair)

The Hawk would still have significantly better range though.


Interesting "Super Hawk" concept, somthing I've thought about before, but in combination with a tight fitting cowling with latge spinner and cooling fan. (of the final version used on the XP-42)

Hi Juha,

>I have never heard on Hawk 75C, but both P-36A and C used R-1830-17 engine.

Problem is, I didn't do the research myself and the board on which the discussion was is inaccessible now so that I can't go back and look. At the time I thought the information looked quite well-researched, but I don't recall what exactly the Hawk 75C was. I guess it was one of the Hawk batches acquired by the French.

>Max speed for P-36A was 313 mph at 10,000 ft and 311 mph at 10,000ft for P-36C (it had 2 wing mgs added to 2 mgs in nose which was A's armament)

This seems to match my data, but if I recall correctly there were some internal contradictions in the source data (as so often - sigh!).

Regards,

Henning (HoHun)

Hi Juha,

>Test flight report of CU-503 after engine change from Cyclone to Twin Wasp R-1830-SC3-G. Speed 372 kmh IAS at 2350m.

Thanks for the data sheet! The speed looks rather disappointing compared to the factory figures, or am I missing something?

Regards,

Henning (HoHun)

Hello HoHun
French versions were A-1 - A-4. But french used text
Curtiss
H75-C1
No. XX

in the rudders of their Hawk 75A-1 - A3, A4 was for French H751.
The C1 in Frech Hawks only means 1 seat fighter. C came from Chasse fighter. But French Hawks didn't have 1830-17 engines but civil versions like 1830-SC-G or 1830-SC3-G or 1830-S1C3-G or 1820-G205A.

Juha

On CU-503
Yes Finns noticed that and even if they only used 87 octane in tests FAF concluded that only way the factory figures were possible was that in addition of the use of 100 octane fuel a/c had to be waxed, mgs, antenna and other projecting equipment removed. IIRC RAF also got worse performance than those in Curtiss' procures but on the other hand French got more or less same performance as Curtiss.

Juha

BTW
Curtiss figure for 100 octane engines were for 1830 423kmh at SL and 520 kmh at 4650m and for
1820 413 kmh at SL, 467 kmh at 2500m (max for low blower gear) and 488 kmh at 5790m. Which after all is nearly same as what British got for Mohawk IV that is 486 kmh at 4300m. Brewster B-239 with lower powered Cyclone 1820-G5 was fastest at appr 4900m. So a bit variation for max speed altitude of Cyclones.

But now we had hijacked Marcel's excellent Fokker D. XXI thread, sorry Marcel.

Juha

Juha

No problem, we were discussing alternatives to the D.XXI.

Hello HoHun
these test flights were normal tests after major repairs not special tests to clarify the performance of certain a/c type.
I checked a couple more similar tests

CU-502 25.6.41 992mb +22C 385 kmh IAS at 2810m, engineWright Cyclone GR-1820-G-205A
my rough estimation appr 452 kmh TAS, and I'm a historian not an aerodynamist.

CU-502 28.7.43 1003,7mb +25,8C 385 kmh IAS at 2350m, engine P&W R-1830 SC3-G
my rough estimation appr 431-444 kmh TAS.

CU-575 31.7.43 1006,4mb +19,8C 388 kmh IAS at 2350m. my rough estimation appr 435-448 kmh TAS.

Juha

Here a few pictures of the D.XXI replica at Soesterberg. Gives you an idea of the colours. The camo is not entirely correct though:

7./JG 3 Uffz. Massman Rotterdam (Sgt. Looijen 225)
7./JG 3 Uffz. Springer Rotterdam Waalhaven (Lt. Bodaan 238 )

5./JG 26 Stafferabschuss Amsterdam ?

3./JG 51 Oblt. Leppla Zevenbergen (Maybe actually Fokker G.1 330?)

5./JG186 Lt Hevler De Kooy
5./JG186 Ofw. Ubben De Kooy
5./JG186 Ofw. Thaut De Kooy
5./JG186 Uffz. Kaiser De Kooy
These 4 probably all claim the same a/c, 241 Lt. Bosch, destroyed while landing

3./JG 26 Oblt. Seifert Rotterdam
6./JG 27 Fw. Kreuz Rotterdam (? no D.XXI in the area at the time (14.20h))
1./JG 51 Lt Strehl Rotterdam (? no D.XXI in the area at the time (14.20h))
1./JG51 Ofw. Sicking Rotterdam ?

Hello Marcel
Thanks for the German claims and for the analyze of their victims.
This thread has been really amazingly informative.

Juha

Juha said:

Hello Marcel
Thanks for the German claims and for the analyze of their victims.
This thread has been really amazingly informative.

Juha

Click to expand...

Thanks for your kind words and also a big thank you to you and Henning for your contributions so far.

If anyone knows more about those German claims, please contribute.

Very interesting thread! It is hard to find accounts such as these in the States (AFAIK). I love accounts of underdogs and how they fought with what they had. Also, I have been to the Netherlands twice and fell in love with the country. I didn't have time to visit any WWII sites. I wish I had the time to at least visit the Arnhem area.

Thanks Marshall! You won't believe it, but it's somewhat hard here as well. Luckily the sources are there, but it takes some energy.. Although I realise most people are more interested in Spitfires and Messerschmitts, I thought this could be interesting. It's good to know that it's appreciated.

I would like to see more of these minorities here on the forum, maybe IAR 80 planes by a Romanian, or the efforts of the Norway AF in 1940 etc. Maybe some-one will start one or two of these threads in future. I myself would like to start a similar thread on the G.1 as well. Maybe I'll do that in a few months.

Whenever you're in the neighbourhood again, please notify me. Maybe I could point you to some good WWII sites.

1. D.XXI at Soesterberg, combined JaVA
2. Prototype at Welschap airfield note that it's fitted with a 2 blade airscrew, contrary to productioen D.XXI's

Thanks a lot for this thread Marcel. I found it very interesting. I also love hearing about the lesser know aircraft of WW2.

I think the D.XXI was the correct aircraft to be chosen. It appears according to the statistics posted capable enough without being exceptional and the Dutch could have done a lot worse.

It's simple construction and ease of repair would of been crucial, when you consider how swamped the Dutch were. More sophisticated and therefore complex planes would have not been able to see the air as much as the D.XXI

Marcel said:

Hi Hohun,

Top speed: 460 km/h at 5100 m (at 2750 rpm engine), with full miliary load: 415 km/h.

Click to expand...

I happen to have a book in French: Profils Avions 009 - Le Fokker D.21, by Peter de Jong, full 223 pages on D.XXI

Fokker advertised D.XXI in early 1936 to be able to attain top speed 460 km/h with fixed gear and 475 km/h with retractable.
The promise obviously was not fulfilled in case of FR-76, which was capable of merely 414 - 418 km/h. But FR-76 was different to prototypes in:
- having Ratier prop, instead of Hamilton Standard (top speed with HS prop was 430 km/h, according to NLL!)
- having larger wheel covers, which could have wheels replaced with skis,
- bulges for Oerlikon cannons (without the guns),
- bulge for landing light,
- a little different cowling.

As we know the Finnish contract was the first one. After a while Dutch government was interested in D.XXI again, demanding it would reach 440 km/h. So Fokker made a number of slight, yet meaningful aerodynamical changes after which they calculated D.XXI top speed would be 447,5 km/h.
The first Dutch-ordered D.XXI, numbered 212 was first flown in 26 May 1938 and then was transferred to NLL or Nederlands Luchtvaart Laboratorium, that is - in my understanding - a STATE organisation. I'd like to stress that, because it means that following numbers are not Fokker advertising, but real performace. The 212 attained following speeds:
- 460 km/h without radio and armament and
- 446 km/h 'in full combat gear'.
I find those results perfectly reasonable, I mean the masts and wiring of radio antennas and gun ports/barrels should IMHO cause that kind of speed loss due to extra drag.

So I think HoHun can safely change his charts for performace of Dutch D.XXIs

Regarding climb the book says the following: "Avec l'helice au petit pas, l'appareil grimpe a 4000 m en 4 min et a 7000 m en 8 min 3 s. Le D.21 satisfait ainsi aux exigences: 5 min et 9 min 7 s.". Now, my French is almost non-existent so correct me if I'm wrong in thinking that it was surprisingly good 4 minutes to 4 km (btw.: the HS prop was not CSP but two-pitch), while the requirement was 5 minutes. I wonder if that very nice result, corresponding with relatively very low powerloading (lower than Bf 109E), was attained with or without radio and guns? Guns and ammo (300 rds per gun) would add like 80 kg and radio would mean some dozens kilograms more. Btw. D.XXI no 212 weighted empty 1426 kg, i.e. 26 kg less, than contract provided.

Hi Kocur,

Thanks for the info. Yes, the Luchtvaart Laboratorium is a state institution. I've also read these figures, but couldn't confirm them.
I'm planning a trip to the Dutch Military archives early next year. They're supposed to have additional test reports of the 212. Will be interesting to see the original findings.

Marcel

Hello Kocur
interesting info, even if I'm a bit doubtful.
Finns tested several D.XXIs and in average the max speed was around 415kmh.
On wheel covers, how much smaller were the Dutch ones? I have never noticed the difference.
According to Finnish tests the cannon bulges lowered the max speed only 1-1½kmh, so IMHO the effect of the bulge for landing light couldn't have been much bigger.
The effect of a different prop could have been more significant, maybe even the 15kmh mentioned.
IIRC Dutch D.XXIs were a bit lighter than FAF's, so a little better climb rate is entirely possible.

Juha

Juha,

The figures posted by Kocur sometimes pop up in books and internet when researching. Tha majority of the numbers however are lower, not much different of the Finn's numbers. Which one is correct, I don't know.