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Jun 19, 2006, 09:14 AM
Registerd Beaver
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Build Log

Warbirdkits Yak 9D

Thought I'd share a quick build log on a little gem of a kit from
The ubiquitous Yak 9D...
This was my first laser-cut kit and I'm pretty impressed!
I've done many kits & scratchbuilds - Guillow's, Dumas, Aeroflyte & foamie planes before but none come close to this for going together so nice & true.
'Tis a credit to Tom Jacobys design skills that when this one maidened, it just got up and bolted like a racehorse from the gate.
Following just two clicks of down elevator it received howls of approval from a very excited pilot. [early morning at park & no dog-walkers]
Now, Steve St. Martins thread on the same kit was extremely helpful, very informative and covered extremely well, the stages in the stock assembly.
With mine, I digressed from stock setup in that I had a particular brushless drivetrain & battery configuration that was waiting for a home.
The Tower-Pro BP2408-21, I got off E-bay for $0.99c+$12 postage, ESC was $29.00 so the brushed sp400 option went out the window quite quickly.
So as not to bore everyone by repeating Steves pics, I'll just put up the main ones where I deviated. (also I'm on dial-up & we might all slip into a coma waiting for the uploads).
In the end, field requirements & my eyesight dictated some of the variations from stock like white tail & spinner.
I'm glad of that too as this little bird is very very quick!
Right - down to business, first pic shows the plane ready to fly. actually it had 1/2 an hour air-time on it by this time as I like to de-bug before committing to hours of painting etc. glad I did but more on that later.(huge crash)
Second pic is the wings - how easy were they? quickest I've ever done, no kidding and very robust design too.
Pic three shows the top of the forward fuze which is the hatch. doesn't show shows the stubby engine mounts as per text but they are about 3/4" shorter than sp400 version.
The BP2408-21 has a long 3mm shaft so the motor must be set well back.
The penalty for this setup is 1.5oz of lead weight to get correct CG.

more pics to follow
Last edited by Smokin' Beaver; Jul 04, 2007 at 03:24 AM. Reason: pic3 details edited
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Jun 19, 2006, 10:01 AM
Registerd Beaver
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Pic 1:
Here it shows the Ailerons top-hinged using So-Lite.
Doing it this way I was able to get good differential movement using a single servo as per stock location. Up movement is about 3/8" & down is about 1/4". Certainly paid off as the roll rate is crisp and axial, virtually no elevator input required. This is one of the best features about the model. The wings are really slippery in the air with low drag.

Putting the big bits together. I was a bit unsure of this step but it turned out to be quite easy. Thanks again to Steves thread for help here. Instructions are good, just it was my first attempt at foam fillets. Just as easy as soft balsa in the end. Hatch fits well too.
When the plastic engine cowling goes on, the front end of the hatch slides in underneath it by 3/16". rear of hatch is held down by magnets. simple & practical design already built in.

Close up of the motor. This is a newer version of the BP2408-21 motor which I changed out later on for the original version.
The diff is the yellow anodised back end of the bell, the version1 motor has no rear bell (exposed stator windings) so cools much better, given the spinner blocks 90% airflow, any improvement is worthwhile.
My experience with this motor is it will happily swing a GWS 8040HD and haul around a 17oz model with authority but once you block airflow, the motor will expire quite quickly. for this reason I went down 2" in diameter, up 1" in pitch and a SF prop will bite OK when shrouded with a spinner. this has proved worthwhile. no failure yet & it has been worked hard at times.

This one shows an overlay onto the plans.
Pretty self explanitory. The adaptor for the GWS prop onto the Du-Bro spinner is dury-rigged until I can get a wide diameter 3mm washer.
In my box of bits I found 3 solutions. final configuration pic later.

Time for a coffee now.

Last edited by Smokin' Beaver; Jun 19, 2006 at 10:10 AM.
Jun 19, 2006, 12:21 PM
Build it again, Sam!
Harpye's Avatar
Seems that everyone is searching for a JAK9 !

This is mine

-scratchbuilt - 420gramm AUW

Jun 20, 2006, 06:55 AM
Registerd Beaver
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Thread OP
Nice job Harpye.
what motor/battery combo?
Jun 20, 2006, 10:02 AM
Build it again, Sam!
Harpye's Avatar
Weight is 426Gram AUW - 1250 ETEC 3S - Hacker A20M and 8x3,8APC or 8x6APC- 2xMultiplex Servos and Schulze RX

Bye Hansjoerg

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