Fokker D.XXIII, Marton X/V & Other Push-Pull Aircraft

[rickshaw]

On the subject of the DXXIII, I built a resin kit of it some years ago, and very nicely it turned out too, but one thing always puzzled me. What's the almost vertical towel rail thingie for that's on the starboard side of the front engine? Piccie below.

Could be a hand-rail to help climbing into the cockpit but I suspect that its more than likely an exhaust guard to prevent people putting hands/things where they shouldn't.    Must have been interesting climbing in with the engines already running.

[elmayerle]

Elmayerle, you are right: the Walter Sagitta engines used on the D-XXIII were air-cooled.

That's quite a surprise; I don't think I've seen an aircooled V-12 before. Cooling the rear cylinders must have been a nightmare.

What's surprising?  There were a variety of such made before WW II in a number of countries.  They became rare postwar as flat or round air-cooled engines came to predominate for some reason.

[Hobbes]

Surprising mostly because despite having seen the Fokker D.23 before, I never realized it had aircooled engines. Plus as I said, cooling 6 rows of cylinders with air must be a headache. Even if you get adequate cooling, there's a temperature gradient over the engine with the rear cylinders operating hotter (closer to detonation), limiting the ignition and injection settings for the remaining cylinders, so there's power left untapped at the front of the engine while the rear is on the limit.

[dogsbody]

Surprising mostly because despite having seen the Fokker D.23 before, I never realized it had aircooled engines. Plus as I said, cooling 6 rows of cylinders with air must be a headache. Even if you get adequate cooling, there's a temperature gradient over the engine with the rear cylinders operating hotter (closer to detonation), limiting the ignition and injection settings for the remaining cylinders, so there's power left untapped at the front of the engine while the rear is on the limit.

How well did the cooling work on an Argus As 410 or an Isotta Fraschini Delta R.C.35 ?

[kitbasher]

According to info at http://www.aviastar.org/air/holland/fokker_d-23.php:
'The D XXIII single-seat fighter was unusual in employing a fore-and-aft tandem engine arrangement, the prototype being powered by two 528hp Walter Sagitta I-SR engines and flying for the first time on 30 May 1939.
Versions of the D XXIII were also proposed with Hispano- Suiza 12Xcrs, Junkers Jumo 210G and Rolls-Royce Kestrel XV engines, and although all-metal construction was intended, the prototype was fitted with a wooden wing of greater thickness/chord ratio in order to expedite the test programme. Owing to various problems, including rear engine cooling, only four hours of flight testing had been completed when the invasion of the Netherlands brought the D XXIII development programme to a halt. The proposed armament comprised two 7.9mm and two 13.2mm FN-Browning machine guns.'
So if Kestrels and Jumos were being considered, Merlins aren't too great a leap into the realms of the possible.

[Mossie]

Merlins were considered according to this article from Flight, DB.601's too:
Article from Flight including proposed engines

Which goes back to my question near the top of page 2 that's got a little swamped & related to a comment Evan made.  How would you go about it with water cooled engines such as the Kestrel, Jumo 210, DB.601 & Merlin?

[dogsbody]

[quote
Which goes back to my question near the top of page 2 that's got a little swamped & related to a comment Evan made.  How would you go about it with water cooled engines such as the Kestrel, Jumo 210, DB.601 & Merlin?
[/quote]

Wingroot radiators, like the SAAB J-21?

[elmayerle]

Merlins were considered according to this article from Flight, DB.601's too:
Article from Flight including proposed engines

Which goes back to my question near the top of page 2 that's got a little swamped & related to a comment Evan made.  How would you go about it with water cooled engines such as the Kestrel, Jumo 210, DB.601 & Merlin?

Well, wing leading edge radiators between the center fuselage and the booms for the front engine and either a Mustang-style or a Pfeil(Do-335)-style scoop and radiator for the rear engine.

Hobbes, it's very much a matter of proper baffling and plenum design to get the cooling system to work properly.  The IV-12 concept has the advantage of a plenum between the two rows of cylinders in the inverted V and thus a better shot at a more even thermal gradient than, say, between the first and fourth row of a R4360.  It's somewhat like cooling an air-cooled opposed engine where you establish the plenum and positive pressure above the engine, use cooling baffles to direct the air around the cylinders, and exhaust the air from the cowling in such a way that it's going into a low-pressure area and flows out easily.

[Mossie]

A problem for wing root radiators, specifically for the D.XXIII is that ammo feed for the guns is in the fuselage & runs on a conveyor through the leading edge.  I imagine the ammo feed could be relocated relatively easily.  If you introduced cannon, I guess the drum would go with the weapon & remove the problem.

See second photo in on the second row on this link, quite a lot of other detailed shots of the D.XXIII too:
http://www.letletlet-warplanes.com/2008/05/06/fokker-dxxiii/

[Weaver]

Wing leading edge radiators are normally mounted ahead of the wing leading edge proper, so that wouldn't neccessarily be a problem.

Neat ammo feed, isn't it?  Nicely avoids twisting the belt or piling it up in a box.....

[rickshaw]

Wing leading edge radiators are normally mounted ahead of the wing leading edge proper, so that wouldn't neccessarily be a problem.

Neat ammo feed, isn't it?  Nicely avoids twisting the belt or piling it up in a box.....

A single layer though, limits the number of rounds which can be carried.  Now, it has potential if a spiral was utilised.

[redstar72]

Here are blanks of D-XXIII projected versions with different engines. This picture is from Czech Aero Revue magazine, Vol. 65 (1997). Those who want can do some profiles of them...

Also I attach a cutaway from the same magazine.

What about the rear Sagitta cooling - it was really a problem. Even during slow climb, the rear engine valves heated up to 320⁰C, while maximum allowable temperature was 270⁰C. The high-speed climb was impossible at all. This problem wasn't solved until the end of the whole program...

[jcf]

Surprising mostly because despite having seen the Fokker D.23 before, I never realized it had aircooled engines. Plus as I said, cooling 6 rows of cylinders with air must be a headache. Even if you get adequate cooling, there's a temperature gradient over the engine with the rear cylinders operating hotter (closer to detonation), limiting the ignition and injection settings for the remaining cylinders, so there's power left untapped at the front of the engine while the rear is on the limit.

The cooling air for the Gipsy Twelve engines used on the De Havilland Albatross and Don flowed from back-to-front.
http://www.flightglobal.com/pdfarchive/view/1938/1938%20-%200919.html

[Mossie]

Here are blanks of D-XXIII projected versions with different engines. This picture is from Czech Aero Revue magazine, Vol. 65 (1997). Those who want can do some profiles of them...

Also I attach a cutaway from the same magazine.

What about the rear Sagitta cooling - it was really a problem. Even during slow climb, the rear engine valves heated up to 320⁰C, while maximum allowable temperature was 270⁰C. The high-speed climb was impossible at all. This problem wasn't solved until the end of the whole program...

I did some profiles of the other engines myself, I didn't post them before as I haven't spent as much time on them as the Kestrel, but here they are.  Although I've come to similar conclusions with the Kestrel & 210G (intakes being different), we differ on the 12X.  I admit I've got mine a little high & he's gone for a more appropriate version of it.  Like I say, I hadn't spent much time on them. 

Redstar, is there any explanation in the book as to the ventral hump that's been included in those profiles?

Jumo 210G


Hispano 12X (actually a brs, rather than the crs it should be)

[rickshaw]

Radiator for the rear engine (in the liquid cooled variants)?