DaveP

This isn't really a build log, because I've already got it all framed up and it'll still take me months to finish, but I think Vern Clements' little 28" Bi-Gone is so pretty I just had to share it. This is actually my second Bi-Gone. I built my first as a free-flight as soon as I saw the magazine article, back in May, 1955, MAN. Pretty sure I had my Atwood .049 on that one, but can't remember either flying it or what happened to it. The local flying field was very marginal for free-flight.

Now, 55 years later, RC equipment will fit a little feller like this, so I've started my second Bi-Gone. I'm trying an OK Cub .049 this time since my Atwood is very tired and harder to replace. I'll hand-launch it, control just rudder and elevator, and let the engine run till it empties the tank. This is a step up from my 1955 Trixter Beam, which had only bang-bang rudder.

I worry a bit about power since the also-tired Cub, with an exhaust collector, is turning a 6x3 only 12K rpm on 25% fuel. I guess I'll find out the first time I launch it. If it can't get higher than 10' by the time it's gone 500' or so, it won't clear the bushes alongside the grass strip and I'll have to dump it and rethink power. I tried to leave room for a Cub .074, but it'd be very tight. Ideally, power will be enough to maintain altitude during lazy figure-8s.

I plan to cover the wings with Litespan and the rest with tissue and water-based polyurethane. I'll dope the wings and stab silver and leave the rest natural - the same colors as my first Bi-Gone.

-Dave

soarrich

My Feedback: (98)

Looks nice. How about a close up of that fairing on the tail?

build light

Dave, thank you for sharing this.
A very stylish plane with very classy lines. Good choice!

You don't often see a nice old Cub powered model anymore. I would like a closer view of the exhaust collector. Home made?

I look forward to each installment as it becomes available.

Robert

mylamo

My Feedback: (1)

Nice work,educated hands.
Ralph

BMatthews

Ya know..... it occurs to me that some spatted wheels on the lower wing would sure give the Bi-Gone a Beech like look.

Jaspur_x

My Feedback: (1)

Tha is an example of classic beauty to be certain and the construction looks to be flawless fron the pics( wish I could build like that)
Keep us posted will you?
I may have to try my hand at building one.

DaveP

Thanks a bunch, guys!

It's a bit hard with a 2-dimensional photo to show the 3-D way the fuselage fairs into the fin, but maybe a look at the plan will help, especially the top view and former F5. I took some liberty with the formers and widened the top of F5 for 3 reasons:
1 - I used stiffer (and heavier) 1/16" sheet balsa for the fuselage sides than I should have.
2 - I wanted to use .060 carbon fiber rod for pushrods and they fit better if F5 is wider.
3 - I think it fairs better with wider F5 top.

Also, since I've not yet planked the fuselage, you can still see the flat-topped F5 in photos.

-Dave

DaveP

Here's the exhaust collector.

I hate cleaning airplanes, especially the gobs of castor oil that seems to drip all over previously-flown 1/2-A models. Noise is also an issue, even though the closest neighbors to our grass strip are the 100,000 or so chickens on the farm next door (on a hot summer day, when the breeze is just right......well, you can imagine). I like engine sounds, but want to take the edge off the .049's sharp exhaust note.

There's top & bottom plates and a sleeve, all sandwiched between the Cub's crankcase and the first regular thin fin above the exhaust ports. The sleeve length is sufficient to squeeze tightly (.010" interference?) between the top & bottom plates. The exit is through a 7/32"D aluminum tube squashed a bit to fit into the sleeve and soldered with Dura-Fix rods. Those are the rods the hucksters on TV use to repair soda cans, though I can't fathom why one would want to repair a soda can. I use these same rods to make mufflers for my larger engines.

Be aware that of the 3 OK Cub .049Bs I own, all are sufficiently different that this collector will fit only one. Dimensions of the others are each subtly different. The problem is mostly the fin diameters, so I'd need new top plates to fit this on the other engines.

I don't expect it to keep the plane clean - just cut down the scum and hopefully localize it somewhat. It does cut the edge off the scream and leaves a very pleasant engine sound which should let me know when the engine's quit and I should start wishing I had more altitude.

I don't plan to use this feature, but closing off the exhaust with my finger very effectively controls the engine speed. This would make a nice throttle except for having to have your finger along for the ride. This is similar to the rotating exhaust sleeves sometimes used on 1/2A engines, but not as critical of tolerances.

-Dave

BMatthews

If I was doing one of these for RC I think I'd bump the wood for the sides up to 3/32 medium to medium light. That, along with either some water or ammonia, would allow the sides to pinch in nicely to the F5 former. I'd probably bump up the wood sizes for the wing's leading and trailing edges a little or add a vertical spruce "spar" to the backside of the leading edge. In checking the plan you showed above I noticed that the leading edge calls for 1/8 x 3/8 but it sure looks like it should be made from 3/8 square. For RC I'd probably go for 1/2 sq or 1/2 x 5/8 on the flat if it fits the airfoil better. The extra wood would definetly hold things together better.


Let's keep in mind that the original structure was intended for the fearful screaming power of the typical OK Cub, Anderson Spitzy, O&R .049 and similar. Although I remember that the article written by Vern described him using it at a free flight duration contest and beating out a lot of the hot power jobs of the day. Predictable flying, easy starting engine and lots of lucky thermals were in the recipe unless I miss my guess....

DaveP

BMatthews, thanks for the input. I originally cut an F5 like on the plan, but it didn't look right. If the sides are to join at the L.E. of the fin, then further forward and lower, at the top of F5, they should not yet meet, thus I redid F5 with a narrow flat top. I did moisten the sides some. The photo at the bottom of the article looks to me like his F5 was like mine, despite what the plan shows. The short section of the top from F5 back to the fin I've filled in with thicker wood so I can round it over aft of the 1/16" sheet top planking.

You're right about the wing leading edge. In fact, though the plan states 1/8"x3/8", it actually measures 1/4"x11/32", and that's what I cut mine to - about 12 lb stock. I scarf-jointed the dihedral breaks instead of using doublers. I used 8-10 lb for the T.E. and that seems about right. The wings in their present state are quite strong for the short 28" span, and of course very rigid in torsion due to the triangular rib layout.

-Dave

DaveP

Here's the fuel tank. At 0.554oz/cu.in., the 1"D x 1.5"L tank holds about 2/3 oz.

I was tempted to use a film can, but have no experience with them, have none of the recommended Fuji cans, and worried about leaks buried up in the fuselage nose, so I went with the old tried & true soldered tin can. It's made of the .008" thick bottom of a WalMart 16oz. peanut can (mat'l cost = $0.00), 1.25" of 5/32" brass tube (approx. $0.15), 4" of 1/8" brass tube ($0.30), 3/8" of med. silicone fuel tubing ($0.03) and an inch of solder ($0.01), for a total cost of 49 cents plus a couple hours of labor.

A couple of features might be worth mentioning. First, the fuel pickup is through a sump of 5/32" brass tube soldered over a hole in the bottom of the tank - there's nothing sticking up into the tank's inside, thus I can empty the tank completely. Another reason for the sump thingy: with the narrow fuselage nose and firewall-mounted OK .049, the fuel pickup has to go through the firewall below the actual tank. Second, the 1/8" brass vent tube slides up into a 5/32" tube fitting soldered through the bottom of the tank and the two tubes are sealed together with a piece of silicone fuel tubing. This lets me remove the vent to insert the tank in the fuselage and I can slide the vent in or out to adjust the tank capacity for shorter runs. An OK .049 with 2/3 oz. of fuel may exceed my attention span.

I bent the round end caps over a 1" dia. washer to form the flanges. I cut the body to 1" x 3.5", then formed a lip of about 3/32" at one end of the strip to form a smooth overlap and trimmed the 3.5" down so the body would fit into the end caps. I fussed a bit with the body's curvature so it'd fit smoothly in the caps, then spot soldered the body overlap. Then I cut holes for the 5/32" vent tube and sump and soldered in the 5/32" vent, end caps and sump, in that order. Finally, I soldered the 1/8" pickup tube into the 5/32" sump and assembled the vent tubes. To reinforce the vent tube fitting's solder joint, I placed a ring of #24 copper wire over the tube inside & outside the tank wall before soldering.

It fits well, I can get it in & out of the narrow fuselage nose easily, it doesn't leak, and IT'S SHINY!

-Dave

DaveP

Here it is May already and it's finally ready to fly! In fact, I took it out to the field last Monday but it was too windy to try even a test glide over tall grass. I regularly fly from 4 different fields, but the Monday field is the best for my Bi-Gone's first attempt. It's a long grass lightplane strip - there's hangars along one side of the runway, but only short bushes separating the other side from a large field of tall grass. My tired OK .049 will have a good 500ft to haul the little bipe from 5ft hand-launch height to the 8ft altitude needed to clear the bushes. If it can't do even that, I'll put it down on the grass strip under power (remember - no throttle control). The other 3 fields have either asphalt (hard & abrasive), rough grass (bumpy), or tall trees & thorns lining both sides (no explanation needed).

I think it turned out very nicely. The fuselage is covered with tissue and 6 coats of water-based polyurethane (I used Flecto's Varathane - it's completely fuelproof). That stuff is hard to sand between coats (not gummy, just hard), but ends up with a glass-like finish. The closeup shows the sewn figure-8 hinges and carbon-fiber rod linkage. The control horns are 1/8" dia nylon tube (inner Nyrod) tapped on the bottom for a 2-56 screw through the tail surface and with the top heated, flattened and drilled for the 1/32"D wire Z-bends wrapped and CA'd to the CF rods.

Wings are covered with Litespan and a light spray of Brodak silver dope. I've covered several small models with doped Litespan and really like the finish, but wish the dope adhered better. Next time I want to try an initial light "primer" coat of clear nitrate dope - it should stick better. Side stripes and wing lettering are cut from Ultracote and very gently ironed on.

Final weight without fuel is 11.9oz, which on its 238 sq.in. wing area gives a wing-cubed loading of just 5.6oz per cu.ft. (7.2oz/sq.ft. in more traditional terms).

I'll try again this Monday!

-Dave

foamdave

What a beautiful execution of a beautiful model.

Dave-

mylamo

My Feedback: (1)

Back in January I commented on the educated hands,now I must say
you also have an artistic bent. Very nice.
Ralph

BMatthews

If it flies half as good as it looks you've got a winner there.

DaveP

Thanks much, guys! But the beauty was built in by the designer, Vern Clements. I have 8 of his plans in old Air Trails and M.A.N. magazines. I also have a very nice 3-view of his of the Hall-Springfield Bulldog and apparently he did more good 3-views. I think he's no longer with us.

Weather's not promising for Monday - 12mph and thunderstorms. I should've taken it with me this morning to the rough grass field (a former landfill we're just whipping into shape), but I'd prefer to maiden it with the regular Monday group. I keep worrying about my OK Cub not being enough, but the little bipe came out pretty light, so I really think it'll be okay (it's hard to type that with my fingers crossed).

-Dave Plumpe

DaveP

Drat! I just now, over 4 years later, realized that I never mentioned that the little Bi-Gone flies! Well, maiden flight was on 26 July, 2010, and it flies great!

Power, with 25% SIG fuel and 6x3 MA prop, is enough to get it going from a hand launch and to loop from level flight, so no need to swap the OK Cub .049 for its .074 brother. End of flight is warned by the engine leaning out a tad, but that's not enough warning to gain altitude for the deadstick landing, so after the first few minutes I try to keep it above 50ft. The muffler/exhaustcollector holds the noise to a reasonable level and directs at least some of the goop away. I don't fly it often (only a dozen so far), but when I do, everybody watches!

If I had it to do over, I'd decrease the dihedral a bit, say to 1" from the 1-5/8" on the plan, to minimize tucking-in on sharp turns. Might also add a couple degrees of right thrust so power on/off trim doesn't change, but of course a couple washers would fix that.

Anyway, just wanted to complete this thread...
-Dave

Pond Skipper

Note this was a FF design there is no center spar be careful not to over power / over weight the wing loading and cabin frame.

Lovely plane post a vid when you can = )

Boomerang1

What a gorgeous little biplane!

Yes, it would look even better with wheel spats, everything looks better with wheel spats.

Will be downloading the plan from Outer-zone at the first opportunity, electric power for me.

John.

DaveP

John-
Be sure to use 1/4"x3/8" wing L.E., not the 1/8"x3/8" erroneously written on the plan. For electric power, I'd likely use pretty light 1/16" balsa for the fuselage sides, bottom, etc. - no vibration to absorb.
-Dave