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Oct 22, 2015, 12:00 PM
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AA5BY's Avatar
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Build Log

90" Das Box Fly Bipe (scratch build)


Gentlemen.... This will open a build log for a sport biplane. The effort will be a scratch build of an OK models plan that was kitted as a .20 size 45" span by Pilot Kits of Japan back in the 1970's. Scale will be X2 and estimated to be fit with a 55cc engine.

The Das Box Fly Bipe was/is a sport flyer featuring
  • symmetrical airfoils
  • constant chord wings
  • light wing loading
  • WWI era looks
  • great flight manners
  • good ground handling manners

Construction
  • will be scratch built
  • from balsa and spruce
  • router cut ribs
  • sheet metal cowl

I'm just getting started for a winter build. The plans were scaled up last year. A flying friend recently donated several sections of balsa to the project. I've on order a 10" hollow ground planer blade to assist with milling the wood.

This build might interest several sport builders and in particular those who may wish for a reasonably straight forward build that results in a good sport aerobatic flyer with light loading and relatively slower flight manners.

Pictured is the Pilot kitted 45" Das Box Fly Bipe that I still have in my hanger.
Last edited by AA5BY; Nov 30, 2015 at 11:15 PM.
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Oct 22, 2015, 12:52 PM
CC (Certified Curmudgeon)
flyerinokc's Avatar
Count me in I have subscribed! So what color scheme are you planning? Transparent as shown or opaque? Or you could switch sides.
Mike
Oct 22, 2015, 01:00 PM
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flying_violin's Avatar
Interesting! A biplane with no struts or wires. That's the main reason I steer clear of them. Good luck, and yes, maybe the Allies need a few airplanes to ward off all those GWS slow sticks...
Oct 22, 2015, 01:01 PM
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Quote:
Originally Posted by flyerinokc
Count me in I have subscribed! So what color scheme are you planning? Transparent as shown or opaque? Or you could switch sides.
Mike
Mike... glad to have ya aboard. I'm thinking transparent as shown but there is lots of time to rethink.
Oct 22, 2015, 01:09 PM
CC (Certified Curmudgeon)
flyerinokc's Avatar
True, I did the same thing but in opaque red on a Sweet Stik (back in the late 70s), but instead of the Maltese crosses on white I did a black and white checkerboard Monokote trim sheet with a black pinstripe border.
Oct 22, 2015, 01:10 PM
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Quote:
Originally Posted by flying_violin
Interesting! A biplane with no struts or wires. That's the main reason I steer clear of them. Good luck, and yes, maybe the Allies need a few airplanes to ward off all those GWS slow sticks...
Yeah, the 45" version didn't need either.

I've not given a great deal of thought yet as how to configure a 90" version. Single, two piece or three piece wings will be thought through. The plan (45") for this plane may be available on line and if I can find it I'll reference it for those who wish a look.
Oct 22, 2015, 02:50 PM
AMA16634...Just Me
Would this be the plan??
Oct 22, 2015, 03:15 PM
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Quote:
Originally Posted by Brner
Would this be the plan??
Yep... that's it.
Oct 22, 2015, 03:29 PM
CC (Certified Curmudgeon)
flyerinokc's Avatar
Weird I keep getting a message the file can't be read.
Oct 22, 2015, 06:39 PM
ARFs Are Me
TomCrump's Avatar
I'm in.

What'd I miss ?
Oct 22, 2015, 09:09 PM
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AA5BY's Avatar
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Quote:
Originally Posted by TomCrump
I'm in.

What'd I miss ?
Ahh.. er... that wasn't it. Above was a kit build of a Pilot kit framed back in the early eighties that didn't get covered until after getting back in the hobby in 2001.

After the last build, I got to thinking what next. I wanted a sport plane and it had to be another scratch build and portray Golden Age or earlier. I got to thinking as good as the little plane flies, a larger version would likely be something special. More time was given and I couldn't imagine anything I wanted to build more.

The build will start shortly with the first effort milling sticks from 3x4x60 inch balsa.
Oct 23, 2015, 08:13 AM
CC (Certified Curmudgeon)
flyerinokc's Avatar
Ah! The plans opened this morning!
Oct 23, 2015, 10:53 AM
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Quote:
Originally Posted by flyerinokc
Ah! The plans opened this morning!
Glad it opened so that you can see the project ahead.
Oct 23, 2015, 11:42 AM
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As noted, wood had recently been donated for this build. Three 3x4x63 inch sections of balsa, and one a bit shorter between 3-4 feet and one just under three feet. These will be milled into balsa sticks and sheets for the built.

Also note previously, I'd ordered a blade to assist with the milling process and it will be worth noting why a special blade was ordered. It arrived a few minutes ago.

The blade is a Hollow Ground Planer Blade. It differs from blades that are available at a home center. First, it is a steel blade rather than the typical carbide tipped blade of the last thirty years. The teeth have no set and are chisel toothed. That means that they are ground straight across to provide a full width cutting edge instead of the typical tooth which has set and is ground to a tip away from the blade center line.

Because there is no set in the teeth, the blade is ground with relief from the tip to avoid drag that would occur if the blade body thickness was the same as the teeth, as otherwise the kerf would be tight to the blade and it would bind, overheat, expand and wobble. The hollow ground is to a point near the hub center. In the case of this 10" blade, the hollow ground relief is three inches, which is close to the limits of my table saw height setting.

The teeth are also about half the width of a typical carbide blade so as to produce less waste by a cut.

The purpose of such a blade is that as named, it is a planer blade and produces a planed surface compared to a rough sawed texture. That means that planks can be ripped on the band saw from the balsa sections with minimal waste due to the thin blade, these then sent to the surface planer for sizing the thickness while producing planed surfaces on top and bottom and then last to the table saw with planer blade where the planks are cut into stalks such as square stock with all four sides having a planed surface.

When ripping the stalks, it is important to keep the stock tight to the fence to maintain dimension integrity... thus use of a feather board is advised. When milling the wood, pictures will be provided.

The greatest need for this build will be 1/2x1/2 square stalks. The stabs will be built from it as well as longerons and stick framing of the fuselage.

The last comment on the planer blade. Because it is a steal blade, it must not be exposed to hardwood or plywood glues that will dull it, though the teeth can be sharpened with a file. Cutting clean balsa, the teeth will hold their edge well.

Worth noting is that the blade is not overly expensive. This blade from Amazon was $14.
Nov 20, 2015, 09:00 AM
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What engine?


Gentlemen..... the project hasn't been dropped and I'm anticipating getting started after Thanksgiving.

Planning continues. Found in my parts larder are a pair of 5.5'' Dubro air wheels which will work ok.

The engine has been a question mark as I don't currently have one for it. I was leaning toward a 55 -65 cc two stroke gas but really wanted four stroke sound. Now on a retirement budget, the sky is not the limit when looking at the choice options.

Yesterday, we had a beautiful fall fly day with temps in the mid 70s and light winds and I chose my Phaeton 90 to fly. It is powered by a Zenoah G20 and flying it was a blast, but while doing so I realized how badly I wanted to avoid a higher revving two stroke on this upcoming build.

Torque is the name of the game for these kind of biplanes. They simply have too much drag to go fast and all those revs have diminishing returns and the noise of a revving two stroke fighting that drag is not what I want.

The idea all along was for a slower flying sport plane and while flying the Phaeton, i realized just how little power it needed to fly slow and close and yet still do a lot of aerobatics. Lift is just not a problem, so just how important is straight up vertical climb? Do I want this build to fly like an ultimate or a WWI era?

An engine choice that exist is an OS 40cc gas four stroke. I'm wondering if it would provide similar performance to the little Saito .30 that is powering the half size version of this plane that is in my hanger, a combo that I'm extremely pleased with.

I'm anticipating this build to weigh around 18 lbs but keep in mind it has 2400 inches of wing. What four stroke size would you choose? Is a 40cc 4 stroke a reasonable choice for this plane?


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