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SAAB Fighter

Posted: Thu Mar 07, 2019 7:29 pm
by staubkorb
An aircraft that has long intrigued me is the SAAB J/A 21 pusher fighter that was further developed into Sweden's first jet fighter. I was aware that Pres Bruning had built a rubber powered version sometime around 2004 and wrote to him if a plan was available ( assumed it was his design). A few weeks later I received a letter with a tiled print of the hand drawn (sketched!) plan by none other than the late great Nate Sturman!

The scan was/is fair/good, but the penciled in notations were all but illegible and masked some critical areas of the drawing so I re-scanned and loaded the pages into my TurboCad 4 (!) and started to redraw and stitch the tiles together.

Fast forward to last month, I completed a rough drawing (going thru TC4, v8, then v12.5 and finally v21) to what I hope will work for a viable model. I'm presently cutting wood.
220px-J-21-Intro.jpg
220px-J-21-Intro.jpg (6.53 KiB) Viewed 3127 times


Scale is 1/24th which translates to about a 19 inch span, assuming my scaling didn't go AWOL, makes a lot of the parts quite finicky. If it all works out, I'll probably go to 3/4" inch/foot scale for a span of 28 inches.

Re: SAAB Fighter

Posted: Fri Mar 08, 2019 12:14 am
by kittyfritters
Personally, I would go for 1:16 scale. It would be structurally less dense, have more wing area, a longer motor and likely be easier to trim. But, that's my view. It will be interesting watching how yours develops.

KF

Re: SAAB Fighter

Posted: Sat Mar 09, 2019 3:18 pm
by staubkorb
A fair idea, Howard! Bigger does generally fly better. 1:16 would put it at about 30 inches (I'm lousy at converting these scales even tho I studied aircraft design :oops: ).

I've started building the easy parts - stab and rudders - to let them fully "cure" as I've found that letting the flat gubbins age a bit helps reduce warpage (assuming the joints are square). Fairly slow going atm as I'm fighting a bad cold.

Re: SAAB Fighter

Posted: Sun Mar 10, 2019 6:36 pm
by staubkorb
Here are photos of the prelim plan that I'm using to check the buildability of this puppy.

Re: SAAB Fighter

Posted: Sun Mar 24, 2019 2:45 pm
by staubkorb
Started gluing up one of the booms and the fuselage to check parts fit and found a few areas that need adjustment - a couple of formers are a bit too short. Lot of work in this puppy, but otherwise is shaping up well. Pictures soon.

Re: SAAB Fighter

Posted: Mon Mar 25, 2019 3:38 pm
by staubkorb
Slow work due to too many other projects, but here are two pics. The "issues" with fitting are more to do with poor cutting - on these smaller models, a half millimeter makes a BIG difference! The one fuselage former (F3) was traced from the original hand drawing and I neglected to check the dimensions with the fuselage side-view :oops: . The rest are within tolerance (but not for laser cutting - have to work on that...).

Re: SAAB Fighter

Posted: Sun Mar 31, 2019 11:30 am
by staubkorb
Slow going (as usual for me :| ), but cutting, test fitting, modifying and adjusting takes its toll.

A number of the stringer notches as drawn in the rough plan were off quite a bit plus the two height errors on formers 3 and 4. The only notches that I pre-cut were on the nose former (the others were simply marked) and I used the string plumb method to get the rest to line up. The string is visible in the photos.

Three stringers still need to be added - One on the upper rear and two lower forward.

Haven't made up my mind whether I'll incorporate a plug-in landing gear...

Re: SAAB Fighter

Posted: Sun Mar 31, 2019 9:10 pm
by Sky9pilot
Love this plane Pete...I look forward to your progress. Hope you make the plan available when you get it all finalized. I'll have to add it to my "To Do List"!!!

Re: SAAB Fighter

Posted: Mon Apr 01, 2019 12:21 pm
by uhu
impressive plane, and nice build too!

Re: SAAB Fighter

Posted: Mon Apr 08, 2019 2:17 pm
by staubkorb
The majority of the fuselage and one boom is done plus the horz. stab. One thing about twin-boomed aircraft is the necessity of building essentially THREE fuselages :| . Weights are, at present, quite reasonable.

I've a lot of modifying on the plan to do that would have been obvious had I been even halfway proficient with 3D CAD - will be working on that next.