Digging into an old issue ( June 1939) of Model Airplane News, lamenting as always, "They just don't make them like this any more," an article by Charles Hampson Grant caught my interest: "How to Make Your Model Behave." Having been exposed to numerous trimming articles and theories in the past, all of them of some merit (But I'm still wondering about the one that advises giving the model a good push while it's on the ground, unpowered, and watching it either zoom up and stall or rise in a smooth, gentle way.), I read on.. The author in this case has a prominent place in the history of our hobby and deserves special attention.

I was startled to learn that in this article on flight trimming, he makes no mention of thrust line adjustment. His discussion is centered on models with movable wings, a common sight in endurance models those days. Moving the wing forward or backward made the CG changes we now make with ballast. The practice seems to have been abandoned in recent years, possibly because it might affect stability as the tail moment arm is lengthened or shortened; it did save weight though. Thus if the model was tail heavy, you moved the wing backward; for nose heavy it moved forward. Obviously this is not possible with scale models.

Mr. Grant advises that if the model does not seem to climb adequately under power, "the wing should be moved slightly forward....if the wing is of the fixed type, a little weight may be added to the tail of the model." But if the model stalls under power, moving the wing to the rear should correct this condition." Presumably it follows that in the case of a fixed wing, adding weight to the nose is remedial. Now for trimming the glide: If the model dives, "the setting of the wing and tail is not correct." In the case of a dive in the glide, "the difference in the setting," (i.e.,the decalage), is too great and must be reduced. So the incidence setting of the stabilizer should be increased "about one half of a degree." This assumes, of course, that the stabilizer has been set with negative incidence, so the intent is to move it one-half degree toward neutral. But at the same time "the wing should be moved forward slightly." And you guessed it, now it's necessary to return to the trim under power. If it becomes necessary to again move the wing in powered flight, return to the glide may again result in a dive, but this time it will not be as steep. To fix the glide, the stab incidence is again moved toward neutral, but this time by a tiny amount. Then back to the power trim, and so forth; each time, the correction (hopefully) will be by smaller and smaller amounts.
I am only speaking for myself and the modelers I know but common practice today calls for trimming the glide as necessary and then using thrust line adjustments to trim the powered flight, down thrust and right thrust most often. In my own case, I sometimes end up with so much down thrust that it looks ridiculous so I resort to reducing the decalage if it's not too much trouble. If I don't feel like doing the ungluing, regluing, and generally tearing things up, I let the guys laugh. Of course, the logical policy is to simply not glue the tail down solidly, using an easily softened glue (white glue can be easily softened with rubbing alcohol) and omitting the final tissue covering of the tail area.

Since I work with fixed wings almost exclusively, I will try Mr. Grant's approach substituting tail ballast (usually considered a no-no) instead of moving the wing forward and nose ballast instead of moving the wing backward. The complete absence of thrust line adjustment in Mr. Grant's article at first might make it appear that such was unknown at the time. But strangely enough, the same issue of MAN, of which he was editor at the time, carries an article and plan by Frank Zaic that calls for "slight down and right adjustment" in a note next to the prop. The model is the "Stout Outdoor Record Holder," a 39-inch beauty that set a record with a flight of over 17 minutes. He used a 17" prop with P/D equal to 2 and 18 strands of 1/4" rubber. which, he says "....in determined hands has quite a kick in it." You said it, Mr. Zaic, wherever you are these days!

Incidentally, Grant also points out that too large a vertical tail "may be the loss of lateral balance. Then , when the model circles and banks the nose will drop and the model will dive in. This is due to the fact that the large fin acts as an elevator when the plane is banking." He recommends a tail area of 12% for rubber-powered models and 7% for gas. Many model designs show increased areas for both stabilizer and fin. Even with scale tail surfaces, it sometimes happens that the "real" airplane had an enlarged rudder to facilitate control at low landing speeds. When a pilot is at the controls, the rudder can be managed adequately in a bank so we sometimes see excessively large fin areas in model designs even when the tail area has not been enlarged. His recommendation for dihedral is 8 to 8-1/2 degrees.

Food for thought. Comments?

NEW "CONTEST GRADE" BALSA?

Word is making the rounds that our suppliers of contest grade balsa have been cut off by the new owners of the plantations or whatever that produce the stuff. The use of balsa in composite construction has created a demand far greater than we poor free-flight customers (RC, too) buy. Balsa is light in weight but fairly strong when compressed across the end grain. Of course, we modelers rarely use it in such a way as to compress the end grain. Longerons, parts cut out of balsa sheets and carved items such as nose blocks and props are our main applications. While there are modelers who seem to do very well with 1/20" square, 4-6 lb balsa, others, like ye editor, have a miserable time with the stuff. That light grade saves weight initially but the repairs after a few hours of handling soon add up to something substantially heavier - plus much aggravation. The only way balsa can be lighter is to be more porous, resulting in poorly-defined grain and a certain amount of sponginess. It is better to use good medium-weight stock and size it to a smaller dimension, which is already being done by some suppliers. Thus a 6-8 lb. sheet can be sized slightly thinner to equal 4-6 lbs. Of course, this practice can't be carried too far because the decrease in dimensions means less strength regardless of the nature of the material. But not to worry....recall the demise of Tan II rubber. Has anyone noticed much change in flight times? Sure, there have been the occasional defective batches of Super Sport but that was also true of Tan II. The scarcity of "contest grade" bal might lead us to reconsider bamboo and basswood and (perish the thought) even plastic.

NOT MODELERS, BUT...

Although neither member of this handsome couple is a modeler, they did give us Bruce Finley, who is a modeling champ. Pa Finley was a B-24 pilot in WWII, a champ of a veteran in his own right. With his crew depending on him, he had to bring the big Liberator to a safe forced landing in China. He and his crew found their way back to friendly territory after an arduous trek through perilous territory, aided all the way by the Chinese people as they helped them evade the enemy forces. He was the only member of his crew injured in the landing and appears in a photograph, displayed at Bruce's restaurant, with the rest of his crew and his Chinese benefactors. Lt. Finley is easy to spot because he has a large bandage wrapped around his head. Ma Finley was the third champ in this story, having to endure the uncertainty of her new husband's fate through the months that he was listed as Missing in Action. Great people for times that needed such as they.

MORE ON THE OLMSTEAD PROP

Very soon after he received the October issue of WS, a member of our Research and Development Department, Florent Baecke, carved up a sample of the Olmstead prop and put it on a reduced-size Old Timer, shown below. Florent used the plan from an old Air Trails magazine to build the "test vehicle" and attached the new prop to it. The results were not satisfactory, and Florent says the model did much better with a 7" Peck-Polymers plastic prop. In a way this is not surprising because the Olmstead prop, made from the complete data that appeared in WWI Aero, has a very pitch, and the model has only six strands of 1/16" rubber to power it, the equivalent of three strands of 1/8". This 24" model, in your editor's reckoning, would justify twice as much power, considering its structural weight of 34 grams, but at least four strands of 1/8." But if Florent can get it high enough to sniff out a thermal, the lighter model would have that much less dead weight to float around with. Florent says the original model was a trophy winner of the old days, possibly the Moffet, It is safe to assume that it was much larger, sported a much larger prop proportionately, and carried a hunk of rubber big enough to choke a small animal, if not a horse. And so on with the test flying.; more later, and keep us posted on any experimental effort going on in your area.

LEST WE FORGET

Old timers can look the other way but newcomers to scale modeling might not know: "WACO" is not a noun as in "Waco, Texas." It is an acronym, should be spelled with capital letters and stands for "Weaver Aircraft Co."

FLYING THE BRISTOL BOX KITE by Trevor Roche

(WS editor's note: This article is taken from WWI Aero and depicts the author's experience in flying this primitive machine on the occasion of the 100th anniversary of flight, December 17, 2003, at Old Warden Aerodrome, United Kingdom.)

"....Boxkite G-ASPP is not an original. She is one of 3 accurate reproductions built for the film THOSE MAGNIFICENT MEN IN THEIR FLYING MACHINES. In the film she was The Phoenix Flyer, and after filming was complete the aircraft was purchased by the Bristol Aircraft Company. She was presented to the Shuttleworth Collection in 1966 and has been displayed at Old Warden since then. The airframe is a faithful copy of the original, although our variant is powered by a modern 100hp Rolls-Royce Continental engine. This is twice as powerful as the original Gnome engine...Even with this engine installed, performance is fairly marginal. Furthermore, the pusher arrangement, with the engine in front of the propwash, means that overheating could be a problem (but possibly not with the original, smaller engine?...WS editor). This has been overcome by running the engine slightly rich, but this in turn can lead to problems with carburetor icing.....

"Before flying the Boxkite the pilot must remove all loose articles from his flying suit pockets. If this is not done, these objects might end up getting sucked through the propeller and causing significant damage. It is also important not to wear loose clothing that might end up entangled in the propeller behind the pilot. Entry to the aircraft is via a ladder, and once aboard one is aware of the extremely exposed flying position. It is hard to describe the pilot's accommodation as a cockpit. It is really a flat platform with a bench-type seat and a simple harness, with nothing at all to protect the (now slightly nervous) pilot from the elements. The control system is slightly unconventional. The large control stick (the top of which is almost level with the pilot's sight line) controls pitch through both the rear elevator (attached to the trailing edge of the upper of the two horizontal tail surfaces) and foreplane and roll through the four ailerons. However, the ailerons can only be pulled down and they hang limply until airflow aligns them with the wing in a more conventional position. Cables attached to the stick then pull down the appropriate aileron pair. This is slightly disconcerting when stationary on the ground, as lateral stick movement produces no control surface movement. Of course, they (ailerons) can be checked by asking the ground crew to align them and then ensuring the lateral stick movement pulls the appropriate surfaces down.

" The rudder bar is conventional and much wider than that found in the Avro Triplane. This makes it much easier to make small directional turn adjustments that are particularly important in this aircraft, where any tendency to be directionally out of balance can produce a severe drag penalty. The directional control surfaces themselves comprise three interconnected rudders between the horizontal stabilisers, and there is a centre fixed fin in front of the middle rudder. ‘Cockpit' controls and indicators comprise a throttle, carburetor heat control (very important), magnetos, fuel cock, airspeed indicator, RPM indicator, and cylinder head temperature gauge. There is also a glider-type string sideslip gauge attached to a bracing wire behind the foreplane. This is probably the most important instrument of all, since the aircraft's marginal performance means that it will only climb if the pilot accurately minimises any sideslip.

"Engine start is completely conventional for a modern power plant. Care is required to ensure that the engine is free of carburetor icing before take off as mentioned: the pusher layout makes this machine particularly prone to carburetor icing and it is vital to ensure that full power is available for the initial climb-out. Taxiing is easy albeit at relatively high power, although groundcrew are required to assist with turns as the tailskid is of the fixed variety. The seating position feels quite high off the ground and sitting ready for take-off I make a mental note of the picture to help with landing.

(to be continued in January 2008)

TIP: BUILDING WINGS

GADGETS