Build Log Hurst Bowers designs build

[DPlumpe]

Here's a photo off the web of the full scale Buhl Sport Airsedan. Last September I saw this plane at the Golden Wings museum in Minneapolis, climbed over & in it and got some detail photos, but this is a better overall shot than I could get in the crowded museum.

The Buhl is a sesquiplane, a biplane with a small lower wing. This one was used as a promo for Packard's diesel radial. Very sharp looking black fuselage & gold wings. I haven't decided on color scheme or dummy engine for my model.

[E-Challenged]

I have the General Aristocrat, Buker Jungmann, maybe another in my kit closet. I built the Aristocrat many years ago with Ace Pulse rudder only and TD.020 glow power. The lifting fuselage made it bouyant like a blimp. I think that the Medusa 12mm brushless in a DXA gearbox and 400mah 2S or 3S lipo would be fine for power with two micro servos and common sub micro receivers. The cheap Esskay 400XT outrunner from Hobby Lobby ( now on sale) would also work well in larger Flyline models. Lipo packs and gear would need to be located as far forward as possible (AFFAP) in short nosed models. Pull-pull linkage to tail feathers would be a good idea to help cg without added nose weight. Be careful with beefing up.

[JRuggiero]

Where are plans available for the (red) Farman 72 that Bowers is holding in one of the pics? It's a cool-looking low-wing, like its contemporary the Klemm L25. Any on-line info?

Jim R

[zbrubaker]

Nice thread Dave. It was Hurst's designs that got me back into modeling and lead me down the road to designing kits. My first kit was 100% inspired by his Monocoupe 90A design. I only wish I'd have had a chance to meet him. I'm also working on a L'Ouseiu Canari inspired by his design.

[DPlumpe]

E-Challanged -
Thanks for the motor input. I've heard the Aristocrat was one of Hurst's favorites. That and the Curtiss Robin.
See the attempt to send Hurst's Aristocrat off for a final flight at http://www.his.com/~tschmitt/010JUL0...PHOTOPAGE.html

Jim R -
About the Farman 72, I know noooothiiinnnggg. Pat posted the photo, maybe he knows something.

-Dave

[E-Challenged]

I have always been impressed by the Maxecuters models, do they know about our design and build-off contest? I think that a number of them fly "R/C assist"

[DPlumpe]

The Buhl fuselage now has formers and the tail is built and rough-sanded. I'll use sewn figure-8 hinges.

I can't plank the fuselage or build the wings until I decide how to mount the wings. The original model was FF and the wings were glued on, but I'll have RC stuff to get at and I'd like some structure flexibility to survive one of my less than ideal landings.

I'm leaning toward having the wing assembly (top wing, both bottom wings, struts, wires) removable as a unit. The bottom wing root ribs would register on 1/8" dowels protruding from the fuselage sides, and would be held against the fuse with spring wire clips across the fuselage bottom, grabbing wire loops extending from the bottom of the lower wing LE & TE. The flying wires would terminate at the lower wing roots and the landing wires at the top wing spars next to the fuselage sides. The top wing would have 4 balsa dowels protruding down into the cabin opening to keep the wing registered, but all lifting forces would be countered by the flying & landing wires and be transferred to the fuselage through the lower wing's dowels & clips. To remove the wing assembly, I'd just unhook the lower wing clips, pull the lower wings off the dowels, and lift it all off the fuselage.

In a nose-first "landing", the top wing balsa dowels will shear, hopefully saving the structure. Same for a wingtip "landing". With proper geometry on the lower wing clips, I think I can save it also.

Anyway, that's the theory. But it'll take a lot of thought to get all the clips, dowels & wires lined up, so while I'm thinking, I'm going to start the Kinner Sportster.

-Dave

[glue_sniffer]

Dave -

Your Macchi is an absolute piece of art - do you have any intention to publish the plans?

-Sky

[Kiwi]

Here is a shot of where my Buhl is at. I got it in a partly built state, the original builder was going to do it as a Pee Wee powered F/F, I am going to go down the electric 3 channel path.
Like Dave I haven't decided how I will arrange access to the gear, neither have I decided on a power plant.
Currently it sits at 3 on my "to finish off" list, as you can see it's basically all done except from a re-cover and wing struts. I also need to add one more cylinder to fill in where the pee wee was to go.
Nev

[DPlumpe]

Thanks much for the kind words about my Macchi, fellas, and yes, I have thought about publishing it. But I think about a lot more things than I have time to do. The plans are in fine shape and I have a few construction photos, but most magazines (Flying Models being my favorite) probably would want some accompanying words. And I'd have to do some redesign 'cause I can't believe anyone else would want to laminate all those formers. Then there's the matter of the motor being obsolete and unobtainable. Yes, it's on my list, but not at the top.

While I'm working out wing attachment for the Buhl Sport, I've moved to the top of my list Hurst Bowers' Kinner Sportster. A Golden Age plane if there ever was one, this plan was one of his Flyline models, done to 1:12, yielding a 39" span. I've been wanting to do this as a larger glow-powered model but couldn't decide on a scale, so this will be built as he designed it except electric instead of a Cox .049.

Here's a web photo of a fullscale Kinner and a shot of the start of my model. Gad, I love sticks!

-Dave

[Mike1484]

Is it just me or does that Buhl Sport look like a Curtiss Robin with an extra wing ???

Mike 1484

[DPlumpe]

Mike 1484 -
Or does the Curtiss Robin look like a Buhl Sport without the lower wing??? In the one hangar at the Golden Wings museum where I saw the Buhl, they also had a Cunningham-Hall PT-6, which looks like a Curtiss Robin Biplane with metal cabin sides and a Fairchild FC-2, which is like the Robin but with rounded tail and without the knee-level windows.

Neville - Can you shed any light on the origin of the Curtiss Robin "look"?

-Dave

[DPlumpe]

For those who aren't familiar with the designs, here's quickee views of the Buhl and Kinner plans.

Also, I've got the Kinner fuselage sides together. Next is to put on formers & stringers to flesh it out.

-Dave

[DPlumpe]

While I'm gluing stuff on the Kinner, I'm still trying to decide on a wing attachment scheme for the Buhl Sport. Hurst's original plan was for FF and everything was just glued together. I'd like to try having the top wing, bottom wings, struts and wires removable as a unit, with the whole abomination held by dowel pegs registering the bottom wings and wire clips holding them onto the pegs and against the fuselage.

The following force diagram looks at a 10G load on a 1 lb plane. I'm applying the entire load to the top wing and ignoring lift by the small bottom wing.

Each side has a lift of 5 lbs. The distance from the centerline to the midpoint between the top wing landing wire and strut is 6.1 inches. Splitting the 5 lb lift at this midpoint gives 1.85 lbs of lift loading the landing wire and 3.15 lb at the strut. The 1.85 lb vertical tension component on the wire is countered at its outer end by the strut, which must have 1.85 lb vertical compression. That 1.85 lb plus the 3.15 lbs lift located at the strut gives a total of 5 lbs vertical tensile force that must be provided by the flying wire (this is simply telling us that all the top wing lift is held by the flying wires). That 5 lbs vertical component is countered by the lower wing dowel pegs. Horizontal force trying to pull the lower wings from the fuselage is the sum of the horizontal components of the flying and landing wires, or 11.28-4.21=7.07 lbs. This is the force on the clips which hold the lower wings against the fuselage.

These are the forces per side and are split between two struts, pegs, clips and flying & landing wires per side. I'll have to separately calculate tensions with no flying loads to set tensions on the wires.

The idea is to be able to remove the whole mess by unhooking the wire clips with my fingernails, stretching the lower wings off the dowel pegs, and lifting it off. This'll give me an open cabin to reach my RC stuff. Also, it should give some flexibility to minimize damage during unplanned landings. All this just to avoid some rubber bands or nylon screws! No wonder I'm slow!

(Note added 3/29/07: Future posts about the Buhl Sport Airsedan will all go to a new thread, leaving the rest of this thread for the Kinner Sportster.)

-Dave

[DPlumpe]

The Kinner Sportster fuselage is fleshed out now and the tail group is framed. I've changed the wing mounting such that the wing leading edge is now continuous and not notched back at the fuselage. This allows the wing to break free in a wingtip "landing" without serious fuselage damage. Originally, the wing separates from the fuselage at F3A and F6A. Now, instead of at F3A, it'll separate at the red former I've added to the drawing below.

I shaved 1/32" off formers F5, F6 and F7 so the turtledeck stringers will stand proud. The bottom formers & stringers have to wait for the wing. BTW, I found that I forgot to get F1A, F2A, and the two F3A formers lasercut. I had them drawn but just forgot to transfer them to the laser cutting drawing. Oh well, they're simple shapes and, as it turned out, I didn't need the F3As anyway.

I've thickened the tail to give it some airfoil shape. Instead of the original flat 1/8" thick section, I've used 1/8" thick outlines, 3/16" spars and 1/4" ribs.

Right now I'm working on the wing. It'll have torque rod ailerons.

The more of the Kinner I get built, the prettier it looks and the more anxious I am to finish it!

-Dave