L-39 Albatros, 1:25 Scale, Microfan, CD-ROM - RC Groups
View Poll Results: Bungee or Hand launch ???
Bungee 41 33.06%
Hand Launch 83 66.94%
Voters: 124. You may not vote on this poll

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Jul 24, 2005, 04:34 PM
Micro Jet Pilot
Chris T's Avatar
Build Log

L-39 Albatros, 1:25 Scale, Microfan, CD-ROM

Hi all,

finally I am posting my current project. It is a tiny L-39 Albatros. It is built from balsa, glas and some carbon. And it is scale!


Wingspan: 38cm (15'')
Weight: 145g (incl. battery)
EDF: WEMOTEC Microfan 50mm modified (shroud has been removed), pictures will follow...
Inlet / Outlet Diameter: 35mm
Motor: CD-ROM, 6 stator poles, 8 magnet poles (stock), 10 windings (I believe), turns up to 33000rpm, then gets out of sync (it's the controller limit I think). New motor with 6 magnets and standard stator in progress for higher rpm...
Battery: 3s Li-Poly 520mAh
Functions: flaperons, elevator, throttle, lights

To be discussed in this thread:

Modelling techniques
Optimization of fan, motor and ducting for top speed
Comparison with other nano scale models and setups
Best launching strategy
Flight report
anything else?

Have fun, and don't hesitate to give me feedback...

Chris T
Last edited by Chris T; Jun 03, 2007 at 01:57 PM.
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Jul 24, 2005, 07:10 PM
Watts your motivation
roccobro's Avatar

I like!

Jul 24, 2005, 08:45 PM
Having Fun!!!
FredN's Avatar

Jul 24, 2005, 08:52 PM
Registered User
Very nice job so far Chris, looks scale and great. I love this aircraft and I have about 30 miniutes flying one. I may have to get the plans from you and build one
Jul 24, 2005, 11:08 PM
Registered User
dapple63's Avatar
It is beautiful. You're quite a craftsman. Yeah, I'd be interested in the launch technique. Looks to me as a solid, but VERY fast bird. Getting up to the best speed....bungee?

I see no cheater, and even with the nice-sized intakes I wonder if you're going to grab all the thrust you can get.

Do you have a static thrust number as mounted?
Jul 25, 2005, 12:21 AM
Crazy Cessna Owner
Robbie d's Avatar
What stator are you using for the rebuild?
On my EDF-50's in my A-10 im running a 17mm Stator with 10 turns of 26gauge wire with 6 magnets per motor. Thrust is in excess of 150g per motor drawing 5.5A each.
Last edited by Robbie d; Jul 25, 2005 at 12:22 AM. Reason: forgot info
Jul 25, 2005, 04:05 AM
Micro Jet Pilot
Chris T's Avatar

Static Thrust

dapple63: static thrust as mounted is 70g at about 31500rpm. Power is around 60-70W (have to measure again). Static thrust goes up to 100g, when wing is removed -> big cheater hole at the bottom.
I intend to go up to 100W with new motor. Do you think cheater hole kills high speed performance?

There is still a gap between the rotor and the side wall as you can see in the photo (up to 2.5mm). That will be fixed and I expect thrust to go up more.

Static thrust seems to be low, but related to the total size of the plane and its weight, it is considerable. On the other side, a very high efflux velocity is created due to an outlet diameter of only 35mm and considering the slim aerodynamic shape, high top speeds are expected.

I wonder if I need the cheater hole at top speed. To my opinion it destroys more the aerodynamic than it helps the dynamic thrust. I will test it...
Inlet diameter is 35mm effective.
Last edited by Chris T; Jul 25, 2005 at 05:33 AM.
Jul 25, 2005, 05:30 AM
Micro Jet Pilot
Chris T's Avatar

Motor Specs

Robbie d, stators of both motors are 20mm. I will use 5x5x1mm magnets for the rebuild. Motor is integrated inside the rotor of the fan... fan and motor weigh roughly 1oz. (30g).
Last edited by Chris T; Jul 25, 2005 at 06:56 AM.
Jul 25, 2005, 05:45 AM
Claus at Area 52
clausxpf's Avatar
I would go for 4 magnet poles... not 6... on a 6 pole stator.
Jul 25, 2005, 06:50 AM
Micro Jet Pilot
Chris T's Avatar


Here is a nice 3-view...
Jul 25, 2005, 06:51 AM
Micro Jet Pilot
Chris T's Avatar
Originally Posted by clausxpf
I would go for 4 magnet poles... not 6... on a 6 pole stator.
clausxpf, the 6 magnets would be with a 9 pole stator...
Jul 25, 2005, 07:58 AM
Claus at Area 52
clausxpf's Avatar
The I can follow you.
Jul 25, 2005, 10:53 AM
Micro Jet Pilot
Chris T's Avatar

Modelling Technique

kdk, the 3-view is all you need to build it. I didn't use any other drawings. The body was built from 1mm balsa, that was bent over ribs. Then everything was coated with glas and in the end the ribs were removed using some brute force (didn't use so much glue here). So the duct was cleared. I think, this is a good method for prototyping (certainly not for mass production)...
Last edited by Chris T; Jul 25, 2005 at 03:15 PM.
Jul 25, 2005, 11:17 AM
veni,vidi, roto volubilis
Happy|Harry's Avatar
very nice work chris! , i hope you took construction photos as you built?

Jul 25, 2005, 11:34 AM
Micro Jet Pilot
Chris T's Avatar
...sorry Phil, no construction photos. But I will try to explain, how I did it...
... and I will show some close-ups so things get clear...
Last edited by Chris T; Jul 25, 2005 at 03:24 PM.

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