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Old Jan 17, 2012, 08:45 AM
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Build Log
Hurst Bowers’ Lincoln Sport bipe

This is a “Built” log of a 30” span Lincoln Sport biplane model, designed by Hurst Bowers, published in June 1975 “Flying Models” magazine, and now built from my parts by Australian Dick Everett (“evvo” here on RCGroups).

First, a little background on the full-scale. The Lincoln Sport was a cute little (20’ span) 1-place bipe produced by the Lincoln Aircraft Co. in the mid-1920s. It was sold factory-assembled, as a kit, and as plans. They claimed 100mph with a 35hp engine! There’s only one known factory-built around, but several homebuilts.

-Dave Plumpe
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Old Jan 17, 2012, 08:52 AM
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About Hurst and this “kit”

Back in the early 1950s Hurst Bowers designed and built his model as a free-flight with a K&B .035. In 1975 it was recovered, converted to RC and published in FM.

By vocation an Air Force officer and by temperament a true Southern Gentleman, Hurst was a prolific modeler who readily shared his energy, experience and time with his many friends and the entire modeling community. He designed over 80 models that I know of, published many, and founded the popular Flyline Models kit company with partner Herb Clukey. He was the first curator of the AMA museum,started their archives, and was inducted into the Model Aviation Hall of Fame in 1992. I was fortunate to know him in the late-60s when we were both in NVRC (Northern Va. RC club) and again in the 1990s when I frequented the AMA archives in Reston, Virginia. Sadly for us, he passed away in December 2004.

To help preserve his contributions to our hobby I began archiving his model designs and now keep a list here. In the past few years I’ve developed lasercutting files and had parts cut for some of his models that I wanted to build. I thought I might share these files with the community once they’ve been proofed by building, but so far I’ve been able to finish only three - his Buhl Sport Airsedan, Flyline Kinner Sportster, and Flyline Farman Moustique. I’m slow. That left me with 5 others needing to be built. Happily, two fellas here on RCGroups have stepped up to build the Lincoln Sport and Flyline Great Lakes Trainer. Dick Everett has now completed his Lincoln Sport and I’m pleased to document his build.

-Dave Plumpe
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Old Jan 17, 2012, 08:56 AM
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Starting with the Fuselage, upside down on blocks

First of all, let me boast that Dick found no outright errors in the parts (whew!), though the slots were a bit tight and needed sanding, especially where his metric sizes were slightly larger than the fractional I designed for. His 1.5mm (.059”) stock fit snugly in the 1/16” (.0625”) slots, but 2.5mm (.098”) was too tight in 3/32” (.094”) ones. This was intended, to a point, since I originally laid out the parts for my own use, I like tight sand-to-fit joints, and lasercutting kerf is a bit variable. Still, I probably should open up the slots a thou or 2. He also made some mods, which I will point out as we go along. First off, he decided to decrease the lower wing’s incidence by raising the TE about 1/16” (note this requires minor mods to lower wing mount and wing struts). I talked him out of raising the stab incidence a couple degrees, but if he had it to do over he’d ignore me. Also, he’d give the motor some downthrust (after maiden flights he put in about 3 deg).

Dick started with the fuselage. He initially planned to build it in two half-shells and suggested I split the formers vertically. It would be super simple to split them, but instead he built it in the whole, raised on blocks. Another variation would be to slot the blocks to clear the bottom keel so all four could be installed while on the blocks.

Instead of the sandwiched 3/32” balsa and 1/32” ply formers 3 & 4, which take landing gear and cabane loads, Dick substituted 1/16” ply for both and added aluminum tubes (yes!) to accept the landing gear and cabane wires so they could be installed later, after planking & covering. He pre-bent the 4 keels and beefed up the lower wing mounting by making the tongue of 3/32 bass faced with 1/32 ply extending through F4 & F5. And he built a hatch in the top half from F1 back to F3 for motor & battery access.

I really like the way he arranged the clamp colors!

-Dave
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Old Jan 17, 2012, 09:00 AM
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Biplanes have tails & lots of wings

Wing & tail construction begin with laminating the outlines. Dick increased thickness of the stab/elevator & fin/rudder spars from the plan’s 3/32” so he could bevel them to get tight hinge gaps. Good move – it’s either that or large hinge gaps.

It helps to tilt the strut socket ribs (4T, 4B, and the ribs they sandwich) to match the dihedral. Speaking of struts, they’re not on my cut file since they require different wood (hard balsa) from the rest. Besides, if you change wing incidence, lasercut struts wouldn’t fit. Also, make sure the center bottom wing ribs are spaced right for the reinforced keel tongue.

Heads Up: Dick started with the 3/32” x 1/4" wing spars shown on the plans, but covering and doping pulled the wings up into very pretty, but hardly scale, banana curves. I’m sure he thought long & hard before removing the top covering and letting a 1/16”sq. hard balsa spar into the ribs across their tops. Probably the spars should be spruce or of thicker or taller hard balsa than the rather skimpy ones on the plan.

He considered adding ailerons but didn’t want the weight, so stayed with 3-chan and the plan’s dihedral. I’d love to see the Lincoln slip in for an approach, but agree this is a pretty small model to burden with ailerons.

-Dave
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Old Jan 17, 2012, 09:10 AM
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Fuselage Planking & Misc

Dick didn’t comment about planking the fuselage. I might not want to talk about it either - nevertheless it has to be done. He took care to locate the cabane and L.G. sockets before losing them forever to the deep dark fuselage recesses. And he didn’t lose the hatch, either – actually planned how he’d cut it free! He also wisely installed servo rails and planned linkages before planking the top.

-Dave
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Old Jan 17, 2012, 09:14 AM
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Bones

I think my favorite part of a build is when it all comes together in the bones. It FITS and looks like an AIRPLANE!

-Dave
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Old Jan 17, 2012, 09:16 AM
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Giving it Substance

Covering is what you do to keep the inside air and outside air from meeting and conspiring against flight. Dick used silkspan, modelspan & dope.

Paint is what you add to make an airplane YELLOW! Rattlecan lacquer. Wheels are Peter Rake style, tires to come.

-Dave
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Old Jan 17, 2012, 09:21 AM
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Pull-Pull

Rudder servo (HXT 500) is raised and elevator motion run through relay shaft “so as to have the control cables exit in somewhat near the scale location while keeping the cable runs straight.”

-Dave
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Old Jan 17, 2012, 09:25 AM
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Details, details, details

If it’s going to fly, it needs a motor, prop, battery, wires going to the right places, etc, etc.

To quote Dick on the dummy engine, “The cylinders are made from balsa dowels double wound with thread, then one thread removed. Some bits of thin ply & styrene sheet, a tiny rivet and a spring make up the valve gear with bits of aluminium tube for intake & exhaust.”

They look great and add much, but “The panel is only stained ply with cut out paper instruments. Cockpit coaming is just drawn on with a black felt pen.”

-Dave
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Old Jan 17, 2012, 09:34 AM
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Finished!

Put it all together and Dick has a model he should be rightly proud of! I only wish it were in my hemisphere

Some specs:
Span: 30” (or, in Metric-speak, 762mm). Area approx. 243sq.in. WCL approx 7.62oz/cu.ft.
Motor: Tower Pro TP 2406/21, 35gm, 1650Kv, does 50W on 2 cells with the 7x5 prop “and this seems quite sufficient urge”.
Battery: started as 2S800mah, later increased to 2S1000mah for added noseweight.
Servos: 5gm HobbyKing HXT 500
Weight: 16.3oz at first, 16.7oz after adding post-maiden noseweight.

He originally planned on working rigging, but structure turned out so stiff, it’s now “cosmetic”.

-Dave
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Old Jan 17, 2012, 09:45 AM
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Does it fly?

YES
Dick said: “First flights were a bit of a handful but I was immensely impressed at how robust she is. Several arrivals on the nose and no damage besides a bent motor shaft!”

“ …needs some trim changes, more downthrust, and balance a bit further forwards.”

“Yes she has attracted her share of interest at the field”

-Dave
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Old Jan 17, 2012, 09:48 AM
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Post-Maiden Mods and Final Thoughts

Mods
After the maiden flights, Dick pointed the motor down about 3 deg and moved it forward to make room for 1oz lead added to firewall. Now she weighs 16.7 oz and balances at lower wing L.E.

-Dave
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Old Jan 17, 2012, 09:51 AM
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Acknowledgement

I offer Dick my heartfelt gratitude for his build. I was after someone to check my parts for fit, but he went much farther and built a model anyone including, I think, Hurst would be proud of

THANK YOU, Dick Everett!

-Dave Plumpe
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Old Jan 17, 2012, 10:43 AM
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Very nice!. I still have the Monocoupe plans and parts for when I get a rountoit.
Gotta build another General Aristocrat from the kit in my stash.
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Old Jan 17, 2012, 10:45 AM
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Cute little plane. I have a couple of Flyline models still in the box waiting to be built, but I never knew the history. Thanks for sharing.
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