SMALLnet post453

Yesterday evening after the rain quit, I went out to the club field about three miles from my house. It was calm and cool and very pleasant. A friend had called and said he was going to the field for some testing, and since my Kloud King was charged up I took it out to join him. It would be the third flight on the KK, and I wanted him to appreciate how fine it was, as it is one of those rare models that fly just right, "off the board".

The KK is a 66-inch-span OT ship from 1938; boxy but simple and light. It's powered with an R/C car/truck motor (the Magnetic Mayhem), geared, turning an 11/7 and powered with 8 X NiMH 3300 mAH Sanyo cells.

Bob Kopski years ago wrote that he had tested many car motors for aircraft use, and this was the best, and came very close to an Astro Flite Cobalt 05 in power (and probably better efficiency). This is true in my experience, and I am flying two of them direct drive, with happy results.

Anyway, just to show off I took off, let the KK climb in a left hand spiral just like a free flight; got to good thermal hunting altitude and just let it glide, which it does very well indeed. No thermals in the damp cool air, with 10/10 cloud.

When it got low, I set up a landing pattern and did a touch and go, then repeated the climbout. I repeated this basic flight pattern three times, enjoyed the touch and goes just rolling the wheels, no big bounce. Lovely and satisfying.

I like for models to fly on the wing. I don't care for guided missiles, or trying to fly a model on the prop like a helicopter. But that makes me old, odd and out of step with the times. But happy.

I need to take my KK to the post office to find out what it weighs. Here's a few more details: The gearbox is a MAS 3/1; the prop is a Windsor electric-only 11/7. I don't know what the current is, but the motor and the battery are not hot after a flight, so the current is not high.

My Kloud King was built from a Holman partial kit, but the plan was just a copy of the original, with no changes. So I made a lot of changes to make this model practical: some beefing up here and there, like spruce spars and shear webs, doubling of the uprights in the front cabin area, a simple sheet aluminum landing gear with the axle under the leading edge (the original position is ground loop city)...

The aluminum landing gear is bolted to a plywood plate which glues to the longerons. No reinforcement. On a bad landing I believe the plywood will peel away with minimal damage to the structure; easy to glue back on. I am using what Hobby Lobby calls "low temperature Polycover," which is thinner and lighter than most iron-ons.

Pat Tritle < > answered questions from [JW] about today's iron-on covering materials:

For small lightweight models I would suggest "Microlite" from Great Planes, or Nelson "Litefilm". It's the stuff we used to call SolarFilm. If you haven't used this film before, follow the temperature recommendations closely. It goes on at very low temps, but in spite of that its adhesion is the best I've ever seen.

It shrinks a little warmer, and there's not a wrinkle you can put in that you can't shrink out. Yet it won't twist the airframe into a giant pretzel like Monokote will, and it only weighs .6 oz./sq. yard. Best of luck on the project !

For the trim you asked about, none of the films hold paint at all well, and as a result will chip and peel if not handled very carefully. My solution has been to use "sign vinyl", available from our local hobby shop.

For simple trim, I will cut the required shapes from Litefilm, and spray Windex to the area to be applied. I then lay the trim in place, squeegee out the excess Windex, and allow the rest to air dry. The adhesion will be terrific, with no heat applied.

I think the ammonia in the Windex activates the adhesive some- how, and coupled with the suction created by the evaporation process pulls the film down so tight it couldn't possibly come off.

I talked with Steve Staples today, and he's all set to go with this year's SMALL. He was kind enough to extend an invitation, so I'll be bunking up with him this year; should be a real good time. And that is the kind of thing that makes SMALL such a terrific event!

This will be the 8th SMALL I've attended, and by the second year it was already beginning to feel like a "family reunion". Now, it's my annual outing with "good friends"!

...I e-mailed Callie right after receiving Pat's message, asking whether she could provide the markings for my "Spirit of Randy Randolph" models in time for the Little Rock meet.

Callie replied to me IMMEDIATELY, and in three exchanges of e-mail information over the next hour, provided an "on-line sample" of the markings I asked for. And her prices are indeed EXCELLENT. [JW]

I can accept JW's tests that moisture absorbed from the air doesn't make glow fuel go bad. So, what does? I have had fuel turn a darker color and still run fine. I've also had fuel go bad so that .40 and smaller-size engines won't idle. Usually this is accompanied by a noticeable lack of top end power, but not necessarily the darker color. New fuel has always fixed the problem.

...Ken, Glow fuel is peculiar stuff. I did plentiful research on that years ago, when I was writing lots of articles for Model Airplane News. (Now Model Advertisers' News.)

I had full cooperation from several major fuel manufacturers, and one of them even "lent" me their chief chemist for a day, to try resolving some of the puzzling aspects of glow fuel's "variability".

The brands involved were Byron, Morgan, Sig, PowerMaster, Red Max, and Fox.

We didn't learn much that helped. Some makes of glow fuel were slightly acidic, and others a little alkaline. All were "electrolytic" -- that is, they all conducted electricity. All the fuels contained one or more additives -- but nobody was willing to state exactly what those were.

Anyway, what I did find out, combined with what I knew from previous experience, added up to:

Age itself has no detrimental effects on glow fuel.
Nitromethane cannot decompose into nitric acid.
Contact with any kind of metal alloy that contains zinc -- brass is one ! -- slowly catalyzes the methanol in glow fuel into acetic acid. That not only degrades the fuel's performance; it's a potent rust inducer. (Water alone is NOT.)
Exposure to air and sunlight will darken some glow fuels -- but not all. (The dye used in them may have something to do with that.)

But I never did solve the fundamental mystery: what makes glow fuel sometimes go bad? That's never happened to me. [JW]

Given that resources are slim, for my small engines, I order R/C car fuel at 20, 30 and 40% nitro content. Should I add more castor oil (was there any to start with?) to these fuels before using them?

Is there a better fuel available, and where? My only other source is to order fuel from major (R/C) catalog suppliers, usually 15% nitro for 2-stroke, and 10% for 4-stroke engines.

...Len, 30% nitro fuel is about as high as you'd ever need for sport-flying 1/2A engines. And at Hopewell's altitude, you could get by with the 20% blend.

I have no idea what the oil content of car glow fuel might be. You could query the manufacturer -- but as a guess I'd say that adding 2 ounces of castor oil to each pint of car fuel would provide more benefits than problems.

Doing that would boost the total oil content by about 11%, and will help cooling & engine life about equally. That would be especially true if you fly with 7-inch props. [JW]

I fly quite a few .049 (Cox) powered planes; mainly 1/2A size, 2 lbs or less, with about a 42-44 inch wingspan. Recently I changed props from the old 6x4 plastic to a 7x4 wood with a dramatic increase in run time combined with a better climb rate.

I actually had one run for about 4.5 minutes this weekend in the air. My question is, what is the largest size prop you can run on these engines, and how should the needle be adjusted to compensate the change?

...John, I've been flying Cox .049-powered R/C models like yours for decades, and 7-inch props are the way to go ! I've found that for the size airplane you mention, the Graupner "grey" 7-3 and the Cox 7-3 1/2 "competition prop" work equally well.

I've seen props as big as 9-inchers used on 1/2A Texaco models, using glow fuel with auto gasoline added (for extra endurance). But I believe SAM rules now set a maximum of 8 inch prop diameter for the 1/2A Texaco events.

As for needle adjustment, the important thing to remember is NOT to try leaning out the engine for "maximum shriek". Doing that will inevitably cause overheating and detonation.

With a big prop, rpm drops quite a lot. It's a temptation to make up for that by tweaking the needle for "ultimate go". But that's wrong. True, you DO lose engine power by reducing the rpm. But you more than make up for that by a great increase in propeller efficiency -- plus the extra duration that lower rpm brings. [JW]

The comments on what we used to call "solid models" brought back some interesting memories. I think it was Megow who used to put out a series of solid model kits where you cut the box open and used the outlines printed on the box to carve the plane.

Then there was a company I think was Strombecker or something like that who put out solid models with most of the rough carving already done. They did locomotives as well as airplanes.

Then in high school we were carving out solid models to be used for "recognition models" by the armed services. These were mainly just outline models painted black so they presented a silhouette at a distance to train gunners etc. The ones I made must have not been very good as I think I am the only G.I. who was pressed into being an "air guard" on a truck that took a flight of three FW-190s for P-47s. (Well they both had big round engines, and the wings were smaller at the tips than the roots.)

My "P-47s" then dived on us and with all those blinking red lights in the nose and along the leading edge I finally realized I made a mistake. Luckily we were in a narrow valley and the planes could not make a "fighter curve" attack. They just sprayed lengthwise on the trucks so not much damage was done on either side.

I could have been 1/5th of the way to an Ace (had visions of being the only Ace in the infantry) but my fifty caliber machine gun jammed after only one round.

... The company that made partly-carved solid scale models was indeed what became known as "Strombecker". However, the actual/original name was Strombeck-Becker. [JW]

Bob Chiang < > shares with us his reply to Richard Tollner's mention of solid wood scale airplane models in the previous Posting:

Your solid models sound beautiful and I'd like to see a few photos. In case you haven't seen this web site, Ken Horne likes them too, and has some plans and information about them. I imagine he'd like to trade stories with you.

...Bob, solid scale models have never lost their "fun factor", though the advent of plastic model plane kits after WW2 reduced their popularity tremendously.

One big problem with the old solid model kits was in putting the parts together. I built LOTS of those: Megow, Hawk, Maircraft, Comet, Ideal, and Ace Whitman. Not one of those kits showed how to attach the wings to the fuselage ! Evidently we were expected to use plain old butt joints -- and when we did, our wings and fuselages parted company quite easily after the glue had a chance to get good and dry and brittle...

Around 1943, pioneer modeler (and long-time SMALLster) H. A. Thomas devised a unique way of building solid scale airplane models. A whole series of these were published in Air Trails. They started with warplanes (of course). I remember a Mustang, Thunderbolt, Lightning -- even a B-17. All were to the same scale, with full-size, exquisitely airbrushed plans in the magazine.

After V-J Day the series continued, with planes such as the Lockheed P-80 "Shooting Star" and various postwar lightplanes, such as the Navion and Stinson Station Wagon.

The neat innovation that H. A. devised was to join the wings to the fuselage with a central tip-to-tip "spar piece". I forget what H. A. called it, but it was a wooden structural member about 1/4" thick and shaped like the front view of the airplane, from the top of the wing downward.

This fit into a slot cut in the fuselage, and automatically insured a strong joint between the 4 wing pieces (two front sections and two rear) and the fuselage. And this clever arrangement also guaranteed correct alignment and dihedral -- plus the proper tapered wing thickness !

I can't understand why no kit manufacturer ever used this unique design for solid scale models. It worked beautifully, and writing about it right now fills me with the urge to build myself another few of those great little models of yesteryear. If I only had the time ! [JW]

A couple of months ago I asked if anyone on the list had built Early Models' Roaring 20 and Schoolboy with e-power.

I didn't get a response. I flew mine with motors from a CD-ROM drive. Both models are over powered. The Schoolboy has a 2-cell LiPo of 830 mAH. The motor has 22 turns, spins a 7-3 prop, and flies well at 1/2 throttle.

I made the Roaring 20 with a flat wing and ailerons. It's very twitchy. This CD-ROM motor has 17 turns and uses a 6-3 prop, 3-cell 830 mAH LiPo.

The Roaring 20 pulled 88 watts static. That comes out about 180 watts per lb. It's a little over-powered. (LOL)

The Schoolboy was my first R/C airplane, and the Roaring 20 was my second, in the early '60s

A few postings ago there was talk of the Mini Mambo -- a Sterling kit which was my first successful powered R/C. I built it in 1961 and it was powered by a Cox Thermal Hopper .049 with rudder-only control: one click of the transmitter for right and two for left.

It was a great little airplane and provided many great flights. I scratch-built a second Mini Mambo abut 20 years ago and powered it with a TD .049. It sported a servo-driven rudder. It was a bit heavy and didn't fly as well as the first. I remember wishing that I had elevator for trim.

I got the Mini Mambo bug again and scratch-built my third from Sterling Plans. The plans call for .049 to .074 power, which sounds like OK Cub to me. Fortunately both are available on eBay.

I modified the stabilizer to include a small elevator and installed motor mount beams so I could easily swap engines. The engine is bolted to 3/32" ply which in turn is screwed to the beams. The tank is made from hobby shop tin sheet and installed in the battery hatch just behind the engine compartment. The receiver is a GWS 4-channel with two HS-55 servos and a 6 inch coil antenna mounted in the fuselage.

Power is provided by 350 mAH x 4 NiMH cells. Covering is Lite- span with orange fuselage and yellow wings. I gave it a coat of Ultrakote clear to seal the seams. The Mini Mambo ready to fly weighs 13 oz., which I think is about the same as my original single-channel version.

The first flight was made with a Cub .074, which provides more power than needed. Since there is no throttle, I was glad that I could control the climb with elevator trim. Other than flying a bit too fast, all went well. The rudder and dihedral are in balance and turns are coordinated.

I'm very pleased with the Mini Mambo. I have both a Cub .049B and a PAW .03 diesel mounted and ready to try on future flights. The CG is correct with the PAW, which is heavier than either of the Cubs. Each of the Cubs is ballasted so that there is no change in CG when the engines are swapped.

SMALLnet Posting post453