Mig 19 RC RG

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A quick mass model I did playing with wing sweep to minimize required nose weight with components placed looks like this with a rtf weight of 9.5 oz and a wing area of 108 sq inches....
I'm going to use a fully movable elevator which means I'll have to mount the motor higher in the tube so that the pivot rod won't interfere with the motor mount. That should compensate for the assymetric drag of the vertical stab and maybe avoid any boost trim.

mig19.ork.jpg
 
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Did the wing drawing and frameup this morning, just about everything that could go wrong during building did, just a string of stupidity...Fortunately nothing that ruined the model, just my attitude.....

I played with the wing sweep and tail surfaces till I got something as large and swept as possible while still looking like a mig 19. I mid mounted the horiz stab for simplicity which meant I had to put the motor tube up above the carbon pivot rod. In fact this was helpful to offset the vertical stab drag by having the thrust line above the wing, at least that was my thought.

I inserted the motor mount backwards, realizing it just before the CA set, pulled it out and tried to clean up and redo it. Made the canopy from laminated foam and decided it was taking too long to shape by hand so used the belt sander and it grabbed it and flung it on the floor and ruined it so I had to do another one. I thought my wing fillets were set but they weren't so got some glue on my pinkie which promptly stuck to my new shirt...you get the idea....

Got it framed up at 5.5oz dry without electronics, and did some glide tests inside, my boost CG turned out to be 3/4" ahead of where I had initially thought, so It took 1 oz of noseweight instead of 1/2 oz, so my final rtf weight was 10 3/4 oz. Final wing area was 120 sq inches.

Got it all ready to maiden and one of my new servos started to twitch uncontrollably, so I had to pull it and exchange it at the hobby shop.


Got out and it was pretty windy, 10-12 mph but the model handled it very well. I set up the model on the rail and found I had just barely enough clearance to the servo and stabilizer control arm, but there was enough so I was ok.

Did the countdown and the model pitched forward a tad off the rail into the headwind, but a quick pullup to near vertical and it only needed a tad of roll trim, pushed forward as it burned out and it settled into a near perfect hover in the headwind. It was a bit sluggish in roll on downwind but made a nice slow landing. I gave it a bit of up trim for boost, reduced the glide trim a few % and put in two clicks of left aileron. Next flight was near perfect even in the high wind, but as I flared a gust of wind just held it about a foot of the ground and then it died and plopped like a pancake, but no damage. In high wind it's bettery to just fly it down to the ground instead of trying to flare. Last flight was really good, boost and glide were perfect, did nice gentle s turns into the wind and let the wind take the model back to the downwind end of the runway and set up for landing and did a nice gentle flare. We'll see how she does in dead air, but the windy flights were pretty good considering the small wing.

I took her home and started some panel lines. I decided to do sort of a mashup between russian and czech markings using what colors of trim vinyl and monokote I had. I got too tired to finish the left side panel lines tonight, I have to get up early and do a rocket glider demo at a school after the eclipse tomorrow and I need to get an early start.

It looks pretty good in the air with the highly swept narrow chord wings and tail.

Here it is so far.
 
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Got in three great flights this morning, with video, camera shut off on one flight so we lost the boost but got the landing, I'm pretty happy, it really has a Mig 19 look, and for the small wing area glides pretty well and has a nice easy controllable flare. With the higher mounted motor, it pitches forward slightly off the rail but then as speed increases the tail drag pulls it up vertically on it's own pretty well.

[video=youtube;wqfIJ8m_GEQ]https://www.youtube.com/watch?v=wqfIJ8m_GEQ&feature=youtu.be[/video]

Frank
 
Since I ran out of nose cones, I had to do a model without a nose cone obviously! I decided to revisit the Mig 19 but I couldn't find any of my sims or drawings, so I had to just re figure things out based on the pictures. I decided to do this one a bit smaller for the 18mm D2.3's and hopefully come out under 6 oz rtf. I decided I would use 2.5mm spars instead of 3mm and do hinged tail surfaces instead of fully moving surfaces.

Some quick sketching and simming for balance and this one came together in a few hours this evening. I had to slot the wing slot on one side a bit longer and leave some of the slot attached and bent backwards and after getting the wing in place rotating it and trimming the slot tab and folding it back forward to fill the gap on that one side, I've done this before and it works well. The stab was installed with only one elevator installed and after gluing in place the other half was hinged in place. The motor tube if centered would still hit the stab spar so again the motor tube was placed just above the wing and the little down thrust due to the high thrust line relative to the wing should be compensated by the tall tail.

Bt-80 was used for the fuse with the rear end trimmed a bit to mimick the shape.
588566-eb7f9a1cbc04ecf09256e5bfe8e3005b.jpg588567-d943d3f74e28c2fd394e559a1af43df8.jpg588568-18b734e9e4ac2a47b789e10b61f15c86.jpg588569-5b358854472699b583fb40f6b9eef1fe.jpg588570-0af639fc5f781d619946bf4f1e76ea0c.jpg588571-ecdaf0b78042c02002ba034be0a524aa.jpg588572-a03c07402e593162f32f32b4119fc11d.jpg588573-093b2bc8dea5f9d34cd8227e2d1c3050.jpg588574-645d7010635b1161e2422d586cee2ad9.jpg588575-d9a0a1ffcc4e98658dd7c70e52d4ca6d.jpg
 
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Again, like my larger model my glide % MAC was closer to 25% instead of 30% for this model after glide testing, so I added longer pushrods with some guide tube to prevent flexing IMG_20241014_103428073.jpgIMG_20241014_103422947.jpgand moved the servos forward to save 10-15 grams of nose weight.

I really enjoy building these, working out the complexities of how they will go together trying to minimize nose weight, figuring out glide cg position, the little details and markings and they don't take very long to assemble due to the simplicity of the designs. Since I never took build photos of the larger/heavier version this will serve as the design/assembly is nearly the same except for the full pivoting tail which is heavier and more complex and doesn't really buy anything at the speeds these fly at compared to the new hinged version
 
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Here is a quick pic of the MAC calculation and the stability margin that was confirmed by glide tests, further back(static margin less than 5%) which would be closer to 30% of MAC seemed marginal. 25% of MAC would be 1.47 back, with 7% static margin and the distance from LE to MAC LE is 4.67 yielding 6.14 back from LE for boost CG, I could maybe get by with a little further back for launch because by the time it leaves the rail the propellent has burned off a bit. Moving the servos forward look like it may avoid any nose weight needed. MAC can be geometrically found by adding the root chord dimension to the LE of the wing tip and Tip chord to the TE of the root chord and then drawing a line from the new Tip plus root location to the TE of the root and tip length and another line from the middle of the root chord to the middle of the tip chord and where those lines intersect will be the MAC, draw a line parallel to the root at this point and it will give the MAC location and length.

Mig19CG.jpgScreenshot 2024-10-14 110611.jpg
 
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Found good photo/drawings of a Mig 19S Czech model so did a mashup of the three that I think looks nice.

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Maiden today was really nice, just a bit of up trim needed for boost, consistent 45 second glide times which isn't bad considering the boost weight, dragginess of the open tube and small wing area.

 
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