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Author Topic: New Embryo design  (Read 562 times)
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bobson
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« on: September 09, 2020, 06:21:34 PM »

I'm almost finished designing a new Embryo, probably going to call it the Swallow. Inspired by the Big Cat, Maxout, and Go Devil designs I've built and had a ton of fun flying. Made a geodetic plan for the wing as well, but I'll probably just go with hard wood for the spars and careful shrinking for the first build. Also thinking of doing a V-tail or biplane version, or maybe both. Airfoils are ruthlessly traced from a George Perryman glider plan.

Excited to get some wood down!

Oliver
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bobson
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« Reply #1 on: September 09, 2020, 06:22:08 PM »

Oops, here's a plan snapshot:
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bobson
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« Reply #2 on: October 08, 2020, 06:54:08 PM »

Well I finished the plans and it flew right off the board! 3 maxes with no CG or incidence changes, only issue was that with the thin LG wire I used ROG and initial climb-out are a little hairy. Contest times have been entered so the name's official, this Embryo is called the Nite Hawk.

The wing comes off and has a DT with a viscous timer, which seems to work well too. I'll attach a few pictures -- the DT mechanism itself is the same as what I have used in the past, with a pull-down wire going through 2 eyelets on the wing's leading edge, around a post on the fuselage, and to the spring and timer. The trailing edge of the wing is connected to a balsa block with a Tyvek hinge and CA, and the block comes in and out of the fuselage with 2 0-80 screws threaded into a couple layers of 1/64" ply (thanks Mike Kelly for the inspiration).

The wing has a hook extending up from close to the TE, with a small rubber band pulling down to the fuselage for DT activation. This pulling force doesn't need to be too strong, because the oncoming airflow encourages the DT to open after the timer pops -- unlike a tail DT, which can be pushed down if the band or spring isn't strong enough. The upward angle of the DT is limited by the spring itself catching on the left-hand eyelet, but could also easily be limited by a washer or bead.

I'll put the plans up soon in the Plans Gallery, and I'm planning on doing a build-slideshow-flight video up on YouTube.

Oliver
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bobson
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« Reply #3 on: October 08, 2020, 06:58:26 PM »

Some pictures of a trim flight from Tom Hallman, the CD of the contest at Wawayanda where I got to fly the model.
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MKelly
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« Reply #4 on: October 08, 2020, 10:58:17 PM »

Nice-looking ship Oliver, and sounds like it flies nicely - job well done.  I can't take any credit for the screws. Don DeLoach pointed me at them - I'm merely an enthusiastic adopter and proponent.

Mike

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Bredehoft
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« Reply #5 on: October 09, 2020, 11:52:06 AM »

Well done, Oliver!  The Kanone has been logged!

--george
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Yak 52
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« Reply #6 on: October 09, 2020, 12:37:48 PM »

Nice work Oliver  Cool

...The trailing edge of the wing is connected to a balsa block with a Tyvek hinge and CA, and the block comes in and out of the fuselage with 2 0-80 screws threaded into a couple layers of 1/64" ply (thanks Mike Kelly for the inspiration).

I'd be interested to hear/see more about the Tyvek hinge? Is it just like a mylar hinge used on RC stuff?

Thanks,
Jon
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bobson
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« Reply #7 on: October 09, 2020, 01:26:53 PM »

Thanks all.

Jon, it's Tyvek from a mailing envelope, thin 2-ply stuff that works either split or left as the original thickness.
Hopefully these pictures make sense, but here's a quick description of the process. Not sure who originally used Tyvek but I started building with it on Tom Hallman's recommendation.

I first cut out a rectangle of the Tyvek, and made a crease with the capped end of a square razor on the hinge line.

On the "block" that attaches to the wing, with thru-holes for the screws that thread into the fuselage, one side of the hinge is sandwiched between balsa and ply layers. Medium CA wicks into the Tyvek pretty nicely with a little burnishing, and with a CA bond on the top and bottom the hinge feels strong.

The other side of the hinge is CA'd and burnished onto the (hard balsa) center section of the wing's TE. I made sure to include a bit of room on the hinge so that it wouldn't bind up with the wing tilted upward.

I did this all before covering the wing with preshrunk Mt Fuji, which I then shrunk again with the wing pinned down over spacers high enough that the TE block didn't interfere with the workboard. Whole process went pretty well, I've covered before hinge-ing in the past but I like to easily have a naked-balsa contact onto the Tyvek.

Oliver
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bobson
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« Reply #8 on: October 09, 2020, 01:32:53 PM »

Some more progress photos, and detail on the wing block - fuselage threads interface before I glued the pieces onto the wing and fuselage. The top of the fuselage threads is balsa, but as you can see on the underside I have 2 layers of 1/64" ply. Cut with an 0-80 tap, holds the screws pretty well.
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OneArm
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« Reply #9 on: October 09, 2020, 01:47:42 PM »

Looks like there is dihedral on the stab, is that correct? Let me know when the plans are up, looks like a great design!
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Indoorflyer
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« Reply #10 on: October 09, 2020, 04:11:33 PM »

Nice detail shots, Oliver.  Thanks for the info.  What is the "weight" of your Nite Hawk, with and without the rubber?   I like the roomy fuselage, without taper until aft of the motor peg..
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FLYACE1946
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« Reply #11 on: October 09, 2020, 04:41:26 PM »

Oliver you are really following a lot of famous flyers and designers. George Perryman, Herb Koth, and Al Backstrom. Let me know if I missed anyone. This is a well done design. Please add Josh Finn
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OZPAF
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« Reply #12 on: October 09, 2020, 06:03:12 PM »

Very neat Oliver and thanks for the info and photos.

John
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bobson
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« Reply #13 on: October 09, 2020, 08:14:27 PM »

Alright, plans are up in the Gallery and thanks everyone for the comments! (and to the admin who formatted the plans/parts sheet together). The sharp-eyed among you might notice that I built the rear wing spar on top of the airfoil but put it on bottom in the final plans; I think this will help the tissue hold the undercamber better, but everyone is welcome to build and modify how they choose.

There's no dihedral in the tail, but I'm sure my camera did weird things with those swept back tips. If I build another, I'm tempted to try a V-tail. I believe the empty weight is around 16 grams, will check with and w/o motor when I get to my workbench.

Oliver
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Indoorflyer
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« Reply #14 on: October 09, 2020, 11:27:38 PM »

Nice! Thanks for sharing your Nite Hawk plans!  Re: the rear spar--It could probably be "split" into two 1/16" sq hard strips, one on top, one on bottom at the same distance aft of the LE shown on the plan.
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OZPAF
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« Reply #15 on: October 09, 2020, 11:29:27 PM »

Oliver what sizeand pitch prop are you using - it appears to be quite a high pitch.

John
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bobson
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« Reply #16 on: October 10, 2020, 09:39:49 AM »

Good idea with the spars Indoorflyer. John, the prop is 8" dia x 10" pitch, and I used 1 loop of 1/8" and 1 loop of 3/32" 30" long to power it.

The empty weight is 17 grams, with a 9 gram motor. Not the lightest it could have been, but I used medium-weight 1/16" throughout and am happy with the trade-off of not breaking a longeron or wing spar every flight. My Go Devil was 10 or 11 grams with a 7 gram motor, and had amazing outdoor performance for a season or 2 before I warped and crunched it out of trim.

It'd be interesting to see how the Nite Hawk does with duration with different wing loading/power setup extremes... for example, the 7" prop and 3/16" rubber I usually run on Embryos and big dime scale models, and 2 loops of 1/8" with the 8" prop for a shorter and higher climb. With the big prop and fuselage, it almost feels like a 2-bit sized OT plane with small wings.
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Yak 52
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« Reply #17 on: October 11, 2020, 07:30:39 AM »

Thank you for the details Oliver. I must try something like that.

Jon
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AAdamisin
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« Reply #18 on: October 13, 2020, 06:09:02 PM »

Very nice looking model.  Glad to see you were able to fly it this year and enjoy some great weather.  I love your DT method.  I have used Tyvek in rc pylon models for aileron and elevator hinges.  Very tough stuff.

Archie Adamisin
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bobson
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« Reply #19 on: October 14, 2020, 07:34:15 AM »

Thanks Archie. Glad to see a new crop of outdoor embryo designs in 2020!
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