A recent thread talked about "stunt model numbers".  There have been several (numerous?) discussions/compilations about the "numbers" associated with these so called stunt models.  Here are three examples:  (I hope the tables shown are readable.)

Aeromodeller, January 1960: compiled 16 designs, all American (most are still familiar, including Nats winners) showing span, areas of the wing, stab, flaps, elevators, others and then listed a "Trend".  I used these trend numbers in the early 60's to design an elliptical wing/tail design (my airfoil/flap)  which for me flew well enough to gain experience in flying contests in Florida.  Those same numbers and airfoil went into a semi-scale design (FW Ta 152) that placed 5th twice at the Nats (66, 68) and then the Walker Cup in 70.  By today's standards, the flaps and elevators were too small and the tail too short.

Model Airplane News, August 1973:  Harry Higley (I think) did the Round and Round column in Model Airplane News and compiled a chart of 24 designs, most had been published and had placed well at the Nats over the years.  Chart presented engine and prop info and the dimensions and areas in enough detail that the any model could be duplicated except for the airfoils.  Interesting stuff.

Bill Netzeband had a web site that had a number of articles he wrote as well as material from others.  I do not know if that web site is still available.  Netzeband wrote a paper on "A Summary of Aerodynamic and Geometric Data for 101 C/L Precision Aerobatic or Stunt Designs active between 1946 and 1996".  Several charts are dated November 25, 1997.   He wrote nine pages explaining the basic measurements using more than 50 parameters.  There were 6 pages to show these parameters for all 101 models.  Then, he prepared 13 bar charts that compared these 101 designs in different ways including "Line Tension in Level Flight",  "Wing Area", "Airplane Dry Weight", "Dry wing Loading", "Level Flight Controllability Coefficient", "Static Pitch Moment Coefficient - defines ability to escape square corners, "Tail Volume Coefficient", "Minimum Turn Radius Path" measured in feet, "Geometric Tail Moment Arm" measured in inches between MACw to MACt, "Ratio of CG Distance from MAC wing to te MAC(X'/C), "ratio of Neutral Point to CB Dimenskion to MAC", "Tail Power Coefficient".  All interesting stuff for anyone who wants to take the time to digest all of this.

Netzeband may have included some or all of this in a series of articles that he prepared in the PAMPA Stunt News.  Great stuff until he got discouraged by the complaints that his material was too technical.  (He got similar complaints when he did the Round and Round column in Model Airplane News.)

Keith

(I have not been able to attach the Higley chart.)


 

We still get the same discouraging responses from people who seem to resent that technical questions most often call for technical answers, regardless of where they are posed, and seem not to want anyone to enjoy what they can't or choose not to enjoy. That these topic titles reference "numbers" is significant. Mathematics is still the language of science, simply because everyday language includes semantics that are often awkward and confusing in describing things they were not created to discuss. I am happy to see though that we have folks here who are curious.

   The problem with the idea is that everyone builds to a particular set of numbers, and they are not terribly different. A few of those models are very successful, and most of them are mediocre or awful. One thing I know for certain, "averaging out" all the successful designs will not guarantee success; at best it gets you in the ballpark.

     Successful airplanes are not designed "on paper" with reams of calculations, someone builds something, if they are qualified to evaluate the results (a very tricky issue), they then speculate as to the performance weaknesses, and then try to adjust based on their reasoning. It frequently takes many years/several decades, because random error is such a huge factor, piloting and trimming skills of the evaluator are a huge factor, the engine run is a huge factor. and there is little more than speculation as to why a particular quirk is present or absent. There is no engineering definition for the flying qualities, so you can't really calculate the answer.

   This has driven many people to distraction or annoyance over the years, Wild Bill being notable, because although he understood it as well or better than anyone, he also never got past the fact that on some level the demands of competition also require subjective evaluation, not just numbers. Don't let his "layman's" writing style fool you - he knew more about it from an engineering standpoint than anyone. He got a routinely negative reception for it. I just started to do it, got the same, quit. You see it here *all the time*.

   That's why I tried to suggest the Imitation article, that presents at least some of the reasoning behind the numbers (in addition to being the prototype/inspiration/starting point for some of the most successful models). It may not meet everyone's standards for engineering rigor, but at least a highly-competent, extremely successful, championship level modeler was able to explain his reasoning and, not for nothing, was qualified to evaluate its flying qualities.

  That apparently doesn't seem important and was quickly dismissed, so I have no idea what anyone wants for this topic.  I know who I can talk to about it, who is qualified to make valid observations, and who will at least listen and give wothwhile feedback, but it appears to be of no general interest.

     Brett

I liked your points Brett- when you're trying to get results in front of finicky judges you have to build planes that give what they are looking for.  There aren't fixed numbers for everybody that will work all the time.

The example of a larger plane and engine, besides everything else, needs a larger stab and elevator and a more rearward  center of gravity.  Once somebody says that one can sit back and think- well a bigger plane is gonna need more control.  The "standard" size stab and elevator, even if they are a bit larger are going to be harder to move.  that leads to making changes with more control authority- larger stab needs more leverage, make the tail moment longer.  That makes the plane too stable, move the balance back to mathch.

Nice work.  Thanks for posting it.