SAAB Fighter

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Expand view Topic review: SAAB Fighter

Re: SAAB Fighter

Post by drachen » Tue Jun 04, 2019 4:27 pm

Very nice work, staubkorb. The prop is exceptionally well carved. Beyond my capabilities.

Cheers,
Drachen

Re: SAAB Fighter

Post by staubkorb » Thu May 30, 2019 2:10 pm

Mounted the prop and fed a 10'" loop of 3/32nd Tan SS (hook to peg = 9 inches) and re-balanced for a midnight test at the Dustbin Industries Proving Grounds (back yard) this last Tuesday. The rubber motor is one of the ones from my peanut Mew Gull, chosen only to give the SAAB enough oompf to determine what, if anything, needed to be corrected (thrust line), and to see if the prop worked at all.

One-hundred hand turns and an already damp saggy airplane showed that the prop definitely works and that more "down" thrust needs to be worked in. Side (right) thrust is also needed - difficult due to the prop-to-boom clearance. The model climbed at a rather alarming rate and did a near "wing-over" into a dive, landing on the stone walkway. No damage other than a bruised nose plug. The model does seem to be stable, tho, and the prop will be relieved at the hub and thinned a bit more (weight reduction).

WA really surprised that the tiny motor was able to make the model climb at approx 30° angle to about 15 feet before the turns ran out :shock: :o !
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Re: SAAB Fighter

Post by staubkorb » Tue May 28, 2019 6:59 pm

Made up a pusher prop (fan method) for the SAAB and will try it out before fully finishing (relieving the hub). P/D about 1.4:1 using the article by Fred Hall and made it fairly wide-bladed to help compensate for the small diameter. Diameter is 5.8 inches, giving me about 3mm to boom contact - may have to shorten it a bit more. I thought I had a number of 1mm reverse "S" hooks but only one was found so I'll do the initial OtM prop testing with a '"diamond" version - to see if the prop works at all.

Will use a 4-strand 3/32nd inch motor for starters.

Re: SAAB Fighter

Post by staubkorb » Fri May 24, 2019 7:01 pm

Went outside last night (10PM) since it was dead calm for a test toss or two. First from a kneeling position (nice) and then from shoulder height standing. It went clear across the yard :D . Humidity was high and the covering ended up very limp.

This afternoon was again near calm in the back yard so I set up the camera for some vid. I wasn't able to quite duplicate the night flights (I was too nervous with the camera running :roll: ) and a small warp may have sneaked in, but was still satisfying.

https://youtu.be/QmqX-DOL3Kc

Re: SAAB Fighter

Post by staubkorb » Wed May 22, 2019 1:18 pm

The tissue on the booms runs lengthwise which tremendously helps trimming the waste off and I used this characteristic to advantage when covering the remaining open frame area.

I cut a handy sized scrap of tissue, smeared glue stick on the rough side. Then smeared glue stick on the spine, the two stringers and the formers, and centered the tissue over the spine - burnishing it down. A suitable length of 1/16th wood with a smooth straight surface was then drawn across both formers - while keeping some tension on the tissue - around and down to the wing surface. A thin line of white glue or dope is laid on the wing tissue in a straight line between the boom formers and the boom tissue then pressed into the glue with the straight-edge.

Trimming the excess has to be done before the glue is dry to reduce a marked edge. I used a steel 6 inch ruler that is about 1/32nd inch thick, laid edgewise on the wing, against the boom formers. Gripping the tissue, I (carefully!) tore the excess away. As the tissue contact to the wing is at a slight deviation to the grain (airfoil!), the tear will not be as clean as some would want. To counter this, simply draw a NEW razor blade over the tissue - along the ruler - using ONLY the weight of the blade (single edged blades are best for this) and then do the tearing bit. This nicks the tissue fibers enough (usually) to enable the bias tear.

A touch of glue along the edge and lightly burnished will usually result in a near invisible join.

Four or more hands is helpful with at least two of them steady :lol:. Good lighting, a MUST!

Oh yeah... a bit of patience works wonders ;)
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Re: SAAB Fighter

Post by staubkorb » Tue May 21, 2019 8:25 am

Used coloured note paper for the forward fuselage/wing closure (more of an experiment...) that turned out "adequate" - re-discovering the reason that I stopped using the method more than 60 years ago. Then I formed the fillets using my preferred method - balsa sanded to less-than-paper thickness (about 0.015mm) and less than 3 mg. Due to the relatively small size and multiple compound curves, they were done in two parts. Also managed to poke a few holes in the tissue during the process :x .

The open frame on the boom has been covered and the forward part will be filled with foam.

Then comes the prop... I still haven't made up my mind whether to go with a three-blade, can-formed or a normal two-blade carved prop (pusher). OR, make things easy (and heavier) using a commercial plastic one and remembering to wind backwards :? .
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Re: SAAB Fighter

Post by staubkorb » Tue May 21, 2019 7:41 am

One of my posts has gone AWOL :?: .

Had a wedding last evening (14 May)!
Booms joined to wing, horizontal stab attached and wing married to fuselage - all covered areas have two 50/50 coats of dope.


Balanced it out and gave it a few tosses to the bed - looks promising and then put the airframe on the scale... At first I thought the scale was in the wrong mode, but my back-up weighing utensil confirmed that the weight was correct at 14.92 grams as shown. The dope hasn't completely gassed off so it might even be a bit less.
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Re: SAAB Fighter

Post by staubkorb » Mon May 13, 2019 6:48 pm

Was not able to do much over the weekend - lots of rain, high winds and shopping.

Fuselage is covered to the point where I can attach it to the wing. I've left the upper rear portion uncovered to aid getting everything aligned, and the same applies to the booms.
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Covering has gone on OK in strips - using a variety of methods (wet and dry) and adhesives (glue stick and thinned white glue). Areas with sharp and/or compound curve were covered wet with the white glue (I've not had any luck with glue stick while covering wet), and ALL seams are sealed with wicked-in white glue and burnished prior to shrinking.

I just might give Eze Dope one last chance...
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Re: SAAB Fighter

Post by staubkorb » Sat May 11, 2019 12:59 pm

Covering is progressing, with the booms done except for the portions that go over the top of the wing (for ease of alignment). The nose portion of the booms was filled with StyroDur (green foam), which is easily shaped and then coated with thinned Titebond.

The fuselage is about 3/4 covered, aiming to have it ready for dope by Sunday (if it stops raining).

Re: SAAB Fighter

Post by staubkorb » Tue Apr 30, 2019 12:16 pm

More progress. Weight is climbing exponentially...
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