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Oct 13, 2017, 06:23 PM
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Build Log

L2K F3b Model

This build log has been a long time in the making but it is finally time to do this project.
After the 2014 F3B team selections I started thinking of a better airplane than my Hijinks. I love the way that plane flies but it suffered in what some would say the 4th task of F3B... The launch. I decided to keep my original Hijinks as an F3F plane and start with a clean sheet of paper for my "B" model. One main focus was the airfoil. I looked around the internet and studied many of the older and new designs and airfoil choices. All of this led me to a very reputable source. I reached out to Dirk Pflug and he very graciously offered to help in airfoil selection and wing shape. **** Disclaimer... The airfoil is propitiatory and I will not be discussing anything about it ****. I say this build has been a long time coming as I fell ill and not able to do much flying or building until now. During this time of rest, I refined my design and have now started with making the tooling pieces. This will still take some time to complete as I have a full time job that keeps me very busy and making high quality molds take time as well. My planned schedule is to have one model flying by March of next year and two for next years Team selections. The model's name is L2K and here is a 3 view. Yes, it is a "T" tail... why, I love T tails and I have the technology to make it strong and light weight. besides. seems like every B model now is a V tail. Enjoy the build and I do welcome inputs.

3040 mm wingspan
1473 mm fuse length
58.44 dm2 wing area
15.89:1 Aspect Ratio
Last edited by Lutmi58; Oct 13, 2017 at 06:51 PM.
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Oct 13, 2017, 07:08 PM
Thermal Wrangler
DrFragnasty's Avatar
T-tail? Fantastic!
Can you describe the elevator servo connection? Is there a bell-crank? Curved nyrod?
Oct 13, 2017, 10:29 PM
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concreteman's Avatar
Oct 14, 2017, 12:23 PM
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The tail servo connection will be something like the drawing. It has not been finalized yet but will be of carbon fiber to be as light as I can make it as well and stiff enough for the loads. Slop from all the connections will be minimal with the help of G10 or Delrin bushings.
Oct 14, 2017, 01:35 PM
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Will be following along. Very cool - a T tail!
Oct 16, 2017, 05:30 PM
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It has been suggested that I do away with the pivot arm idea and mount a MKS DS65 or KST X08H servo in the tail. The technology of the new electronics is amazing. Guess an old dog can learn something new.
Oct 16, 2017, 08:53 PM
Thermal Wrangler
DrFragnasty's Avatar

Keep the extremities light

Just weigh the servo, long servo lead and linkage and compare it to the pivot arm/ pivot/ pushrod combo.

For every 20g at the arse end you need 80g at the front to compensate.

Whatever you choose keep the extremities light and keep the T-Tail at all costs ;0)
Oct 17, 2017, 05:26 AM
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I would use the MKS DS75k. Faster and stronger. That said, my guess is you can do linkages and pushrod lighter than a servo arrangement in the tail.

Oct 17, 2017, 08:30 AM
F3B and F3K
RetoF3X's Avatar
Besides weight, I would also consider aero-layout of the tails. If you want to use thin airfoils on the tails, it will be too tight for a servo and the bellcrank would be the better solution IMHO. Maybe the servo could be shoe-horned in at the intersection of the boom and vertical tail, but I would not constrain the design to make this possible if you can also go with a bellcrank.

The Altus and T-Warp from Dieter Perlick were very well done T-tails on an F3B ship and he kept things skinny on the rear. If Mike Smith still has his, maybe you can have a look how they solved it (all moving horizontal, though).

Latest blog entry: thoughts on contest flying
Oct 17, 2017, 10:19 AM
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Altus Tail

Here is a drawing Mike made of the Altus tail and how he fixed his double centering. Thanks for all the input. It's all good and happy to see there are many who are interested and wanting success with this project. Lots of data to go through. Still finishing up the fuse master so there still some time to work out more details.
Oct 17, 2017, 03:14 PM
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Avaldes's Avatar
Dean, I also love the T-tail! I agree that in all likelihood you can execute a pushrod-bellcrank lighter than a remote servo.

PS- I had looked at a broken Radical fuse years ago and had serious thoughts about making a mold for a T-tail. They just fly so purely.
Oct 17, 2017, 03:36 PM
satinet's Avatar
T tails do look nice!

The altus was a lovely looking model.
Very fond of the srtl.
Oct 20, 2017, 03:51 PM
Detail Freak
target's Avatar
Hey, Dean-
I don't visit this forum very much anymore, but I have a thought for the double centering-

Just add a torsion spring to the surface (like a DLG uses). Keep the push rod and bell crank.
So long as you are not DSing, I would think the spring should overcome aero loads, especially while in slower flight. I'm sure a Tom Keisling or other engineer type could calculate what amount of spring you need for airspeed assumed. Then you could figure out servo draw and requirements, but I think it would be fine.

You might test the theory on a flying model by introducing slop at the servo horn or some such thing, and adding a torsion spring to the surface.

Just a suggestion.

I love your builds!

Oct 20, 2017, 06:43 PM
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Primer on the Fuse Master

Busy day at work so I decided to shoot the first coat of primer on the fuse master.
Next.... Sand fill and prime again
Oct 24, 2017, 04:31 AM
registered user
Great looking model 👍🏼 I love the T tail too

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