Fokker D.XXI in Dutch service

Marcel said:

Hi Viikate,


I hope it was worth it

I'm still not 100% sure. I found info from Fokker, claiming at the acceptance trials a speed of 435 km/h at 5000m. This was supposingly with full gear, although this was the 212, which lacked for instance the radio at the time, AFAIK. Clean, the D.XXI clocked 460 km/h at 5000, that's for sure. I could not read the whole report. I'm still planing for a trip to Lelystad, where the Fokker archieves are stored. There should be a wealth of info there.

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If a retractable undercarriage was incorporated how much speed could be gained? I expect about 5%.

Hello Siegfried
Finns modified 2 D.XXIs with retractable undercarriage, the results of the first mod were disappointing but the second mod was more successful. I'd have test info on those mods somewhere, if you are intrested in those, I'll try to dig the info up.

Juha

Juha said:

Hello Siegfried
Finns modified 2 D.XXIs with retractable undercarriage, the results of the first mod were disappointing but the second mod was more successful. I'd have test info on those mods somewhere, if you are intrested in those, I'll try to dig the info up.

Juha

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Please do, this would be good data on the effect of such an effort.

It seems that the retractable undercarriage system of FR-117, a Mercury VII powered D.XXI was deemed so unsuccessful that there were proper speed tests made only with skies before it was remod back to fixed u/c. But mod of a Twin Wasp Jr engined FR-167 succeeded better, its max speed at SL was 367km/h and at 3000m 387km/h, when the figures for a normal Wasp Fokker were 342km/h at SL and 350km/h at 3000m (when figures were corrected to standard atmosphere FR-167 was at SL 20km/h faster and at 3000m 50km/h faster than the control plane FR-143). Strange thing is when the MU's test pilot declared that FR-167 was not suitable to front-line service one of the COs of flight regiments disagreed and one of his subordinates organized new tests, according to which FR-167 max speed at SL was 408km/h and 423km/h at 2800m. I personally believe more the official tests, even if a daughter of the pilot who flew the later tests served many decades later as our Minister of Defence.

Juha

pauljos2001 said:

I am new on this forum and followed the great explanations about Fokker DXXI.
However some photobucket pictures are not visable any more.
Is it possible to renwe the link or post the pictures once more.

regards
pauljos

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I guess you're referring to the pictures with the Danish D.XXI's. Unfortunately I don't posess them, so I cannot repost them. The site where I linked to apparently hosted the pictures from photobucket. The site is still online, but the pictures are gone. sorry.

For the people interested: Last week a new book was released about the D.XXI. I know there is a version in Dutch, but I don't know if it's also published in other languages. I haven't read it, yet. Maybe it can clear up some facts in this thread. I'll let you know when I have the book.

Hi Marcel,

Can you provide me with an exact title and a publisher?

Thanx in advance.

Natuurlijk:
Lanasta // Violaero - Fokker - Fokker D.21 - Fokkers laatste eenmotorige jager.

1e JaVA Squadron BB - Powered by vBulletin

A forum just for the 1 JaVa. Might have some good stuff there.

Seems to be an Ill-2 forum, so only virtual flying. I rather go looking here: Nederlandse Luchtvaart - Dutch Aviation

oh well, looked good upon first glance.

Cool, new one to me.

MilSpotters.nl • Inloggen

Has some nice pictures too. Mostly jets though (but plenty of early jet stuff).

Okay, I got some more info on the performance from the new book I mentioned earlier. The story is like this:
The prototype with a less powerfull engine (Mercury IVS, 645 hp) and less refined clocked around 403 km/h (more or less, hard to get some figures). When Fokker made the final refinements, they claimed a topspeed of 460 km/h with a Mercury VII engine. The Finish version however didn't reach that speed, but clocked 418 km/h at 5100m on average. The Dutch NLL measured a max speed of 414 km/h on the FR-76. However, the Finns had requested a Ratier propellor. Fitted with a Havilant Hamilton propellor, the FR-76 could reach 430 km/h. One should note that the FR-76 was prepared for carying guns at Fokker and these fittings took a few kilometers from the topspeed. This explaines the difference for the FR-76.
The Dutch government asked Fokker to improve the topspeed of the D.XXI.
1. They were fitted with a 2-speed Hamilton propellor (like said before), therefore fitted with a Mercury VIII. This engine had the same output as the VII, but was better suited for the Hamilton propellor beacuse of the transmission.
2. They got slimmer leggs. The Finns had requested 'thick' leggs for the undercariage. This costed some km in topspeed as well.
3. The cowling was made smooth, the finns had bulbs at the heads of every cylinder.
4. The landinglight was replaced by lights that fitted in the leading edge of the wing, therefore not causing more drag.
5. All MG's were fitted in the wing, therefor saving the weight of the synchronisation gear.

When the first Dutch D.XXI, the 212, was tested, it reached a speed of 460 km/h at 5100m. When fitted with weapoms and radio, the speed dropped to 446 km/h, still 30 km/h faster than the Finnish version. The weight dropped from 1594 kg (Finnish version) to 1426 kg (Dutch version). THis also had a positive influence on the climbspeed. Climbing to 3000m took the Finnish version 3m27s while 3m06s for the Dutch version. for 5000m these are 6m23s (Finnish) and 5m18s (Dutch).