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Cox Engine of The Month
Fokker V.23 + MARZ 2.5D
Page 1 of 1
Fokker V.23 + MARZ 2.5D
Hello,
I hope this is the correct place for this topic.
I'm in the process of making a 1m (40'') Fokker v.23 (or maybe v.25 - we'll see, they both have the exact same wing, so I still have time to decide) powered by a MARZ 2.5 Diesel I bought factory new and manage to get running.

Here's the progress so far:



I hope this is the correct place for this topic.
I'm in the process of making a 1m (40'') Fokker v.23 (or maybe v.25 - we'll see, they both have the exact same wing, so I still have time to decide) powered by a MARZ 2.5 Diesel I bought factory new and manage to get running.

Here's the progress so far:



Last edited by dirk gently on Fri Apr 02, 2021 8:21 am; edited 1 time in total
dirk gently- Gold Member
- Posts : 416
Join date : 2012-02-03
Age : 38
Location : Poznań
Re: Fokker V.23 + MARZ 2.5D
I've always wondered how the Marz runs. I had a Meteor ( Glow version ) which I enjoyed a lot. I sold the engine and regret it. The Meteor was also made in a diesel version. It's to my understanding that many of these engines were used for teaching machine skills. Even my Chinese Silver Swallow does quite well once it was broken in. It seems to take a eternity.
Ken Cook- Top Poster
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Re: Fokker V.23 + MARZ 2.5D
The engines were made because modelling was a strategic activity in the USSR, being seen as a way to attract kids to engineering and military careers. There is a magnificent article by Adrian Duncan on this engine, giving a detailed historical perspective and many technical details: http://www.modelenginenews.org/ad/marz.html
As with many soviet artifacts, the design is pretty clever, but the manufacturing quality varies wildly. I hear these can go up to about 0.33hp swinging a 8x4 at 14000rpm, but I've also seen reports of much poorer performance. Mine seems to be somewhere in the middle, doing about 0.25hp at 12500rpm. This gives over 0.8kg of thrust, which should be ideal for this application. Weight, thrust and power- wise it's about equivalent to three Baby Bees, and perhaps I can squeeze a couple hundred rpms more from it.
As with many soviet artifacts, the design is pretty clever, but the manufacturing quality varies wildly. I hear these can go up to about 0.33hp swinging a 8x4 at 14000rpm, but I've also seen reports of much poorer performance. Mine seems to be somewhere in the middle, doing about 0.25hp at 12500rpm. This gives over 0.8kg of thrust, which should be ideal for this application. Weight, thrust and power- wise it's about equivalent to three Baby Bees, and perhaps I can squeeze a couple hundred rpms more from it.
dirk gently- Gold Member
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Re: Fokker V.23 + MARZ 2.5D
Guys,
looking at the first image at the top of the thread,
does it look to you like on the picture the top aft fuselage behind the cockpit is flat with a tall headrest fairing, whereas on the drawing the fuselage cross-section is curved there, with a much shallower fairing?
looking at the first image at the top of the thread,
does it look to you like on the picture the top aft fuselage behind the cockpit is flat with a tall headrest fairing, whereas on the drawing the fuselage cross-section is curved there, with a much shallower fairing?
dirk gently- Gold Member
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Re: Fokker V.23 + MARZ 2.5D
@dirk gently wrote:Guys,
looking at the first image at the top of the thread,
does it look to you like on the picture the top aft fuselage behind the cockpit is flat with a tall headrest fairing, whereas on the drawing the fuselage cross-section is curved there, with a much shallower fairing?
Looks that way. I like the curved upper decking better as it matches the upper fuselage in front of the cockpit.
Oldenginerod- Top Poster
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Re: Fokker V.23 + MARZ 2.5D
The cockpit opening is creating the illusion the rear decking is flat. It looks like the fuselage has constant cross section to the front of the cockpit.
If you saw my comment before, disregard it. Seems like it's virtually identical to the DVIII.

If you saw my comment before, disregard it. Seems like it's virtually identical to the DVIII.

gkamysz- Gold Member
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Re: Fokker V.23 + MARZ 2.5D
This should bee good looks like an interesting model of the error .

getback- Top Poster
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dirk gently- Gold Member
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Re: Fokker V.23 + MARZ 2.5D
Looking good !! That stick airframe sure looks delicate , but i am sure it will stiffen up after covered , what is the engine on the front ?

getback- Top Poster
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Re: Fokker V.23 + MARZ 2.5D
@getback wrote:That stick airframe sure looks delicate , but i am sure it will stiffen up after covered
Actually, the airframe is extremely rigid, both laterally and torsionally. I have added all the cross- and diagonal pieces and the fuselage is completely stiff, would probably break before flexing, and believe it would take a considerable force to break it. I originally planned on making the longerons out of 4mm square pine, but I'm happy I went with 3mm in the end. The fuse is much stronger than my typical balsa slab-sided fuses, and very light too.
I don't really like relying on covering to stiffen up the structure, as I believe that can be deceiving. The fuse or whatever seems fine on the bench, then you take it flying, the weather is a bit damp, the tissue slackens off and you know longer have the strength benefit of the covering. In my opinion, the airframe needs to be built in such a way that it's strong enough without the covering.
The name of the engine is in the title of the thread

dirk gently- Gold Member
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Re: Fokker V.23 + MARZ 2.5D
Cool , i feel the same way about the frame and Not relying on the covering to strengthen it up >> This is funny >>
getback- Top Poster
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Re: Fokker V.23 + MARZ 2.5D
It's funny when it happens to other people 
BTW, the sound on the video is very poor, but as far as I can tell the engine is hitting 14.5k RPM just before taking off, which is impressive.

BTW, the sound on the video is very poor, but as far as I can tell the engine is hitting 14.5k RPM just before taking off, which is impressive.
dirk gently- Gold Member
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Join date : 2012-02-03
Age : 38
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dirk gently- Gold Member
- Posts : 416
Join date : 2012-02-03
Age : 38
Location : Poznań
Re: Fokker V.23 + MARZ 2.5D
The Fokker is looking really good , has nice curves to it and you have brought them out ! So it will bee a mid wing ? Doing a good job with the weight also .

getback- Top Poster
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Re: Fokker V.23 + MARZ 2.5D
Hello,
this is probably the penultimate update before the model is completed:



Current weight is 580g, including all the gear.
I may need new wheels, the ones I have are 60mm, scale would be 80mm, but I can't find any that are light enough and the correct shape. I may need to manufacture a pair out of foam and some plywood.
this is probably the penultimate update before the model is completed:



Current weight is 580g, including all the gear.
I may need new wheels, the ones I have are 60mm, scale would be 80mm, but I can't find any that are light enough and the correct shape. I may need to manufacture a pair out of foam and some plywood.
dirk gently- Gold Member
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Re: Fokker V.23 + MARZ 2.5D
Great job Dirk. and colourful!
OVERLORD- Diamond Member
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Re: Fokker V.23 + MARZ 2.5D
Are these the wheels you're looking for?
https://modelisme-buggy-vintage.com/ROUE-WILLIAMS-80-mm-vintage
https://www.miniplanes.fr/scalebitz-18-scale-wwi-wheels-british-german-80mm
https://modelisme-buggy-vintage.com/ROUE-WILLIAMS-80-mm-vintage
https://www.miniplanes.fr/scalebitz-18-scale-wwi-wheels-british-german-80mm
OVERLORD- Diamond Member
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Re: Fokker V.23 + MARZ 2.5D
yeah, these would be perfect, but they're not available, and would be more expensive than the engine.
dirk gently- Gold Member
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Re: Fokker V.23 + MARZ 2.5D
You did another fantastic job on the covering , i think ur the one and only on the forum that does pretty much all your models in stick and tissue . Look forward to the maiden flight !


getback- Top Poster
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Re: Fokker V.23 + MARZ 2.5D
@getback wrote:i think ur the one and only on the forum that does pretty much all your models in stick and tissue
That's because I really suck at using film covering.
dirk gently- Gold Member
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