Ted Fancher ???

[Allan Perret]

Just read about Paul Ferrell's Rhapsody In Blue in the latest Stunt News.  
Was curious why you recommended pairing the Imitation wing with the TP fuse vs just building the Trivial Pursuit.  
What are the differences between the Imitation and TP wings?  

[Ted Fancher]

Just read about Paul Ferrell's Rhapsody In Blue in the latest Stunt News.  
Was curious why you recommended pairing the Imitation wing with the TP fuse vs just building the Trivial Pursuit.  
What are the differences between the Imitation and TP wings?  

Just read about Paul Ferrell's Rhapsody In Blue in the latest Stunt News. 
Was curious why you recommended pairing the Imitation wing with the TP fuse vs just building the Trivial Pursuit. 
What are the differences between the Imitation and TP wings? 

Hi Allan,

It was primarily a time and experience balance.  Paul is an extremely talented young man who is probably the best guy I've ever coached at listening and implementing input...and I've worked with a lot of good pilots.  What he didn't have was a lot of experience building and a lot  of time to get something together for the '08 World Championships.  Paul and his family lived a fair distance  from those of us who mentored his flying so our ability to assist in the proper assembly of a competitive machine was quite limited.

Although his dad, Kevin, was helpful, he was also pretty low on the experience ladder and they had to do the lion's share of the work themselves and then drive down to the Bay Area for us to evaluate, advise and sometimes "cut" when necessary.  To get a more or less state of the art in Paul's hands required that we utilize alternative resources to make the project doable under the constraints he (and us) were face with.  As a result we helped Paul and Kevin make choices about the best way to get his "stuff" together without actually moving in with us...which wouldn't have been all that bad because he could have played my music so I could practice my "singing".  Paul is an amazing pianist!

The bottom line was that the fuselage is really nothing more than a tool to connect the wing to the tail and the powerplant.  Plus, it helps if it's kind of attractive.  It does, however, take a lot of time to build from scratch...especially in a take-a-part configuration..The TP fuse from RSM solved a lot of those problems nicely as it only had to be modified for the take-a-part hardware to do the job.  Having the parts essentially perfect and ready to assemble was a great time saver.

The Imitation wing is an excellent performing wing that was available as a sheeted foam core from a number of suppliers (and, as I recall, Paul got it from one of the the best...Bob Hunt).  IIRC, he also got the tail as a sheeted foam core unit.  This solved a lot of the time problems and the TP fuse gave it a modern, recognizable profile with all the parts laser cut and ready to put together.

The Imitation wing was sort of the grandfather of many of the wings that have been competitive in the last three decades or so.  Modest in area with small chord flaps, a well rounded leading edge and a forward high point to the airfoil make it a great choice for ideal to well heavier than ideal wing loadings.  I flew the original at as much as 64 oz on a 620 square inch, small flapped wing and could fly presentable "smaller than rule book" patterns with it using an Enya .46 four stroke.  It was/is not critical to trim or CG location and can be flown competitively with very little preparation.  David Fitzgerald used the basic Imitation wing and tail held together with Excitation fuselages for most of his early "Open" career and did extremely well with them.

IOW, Allan, the marriage of the two "designs" was not done for any performance "advantage" but was merely a recognition that time was of the essence and the foam core wings and tail of a proven design coupled with a compatible "connector" fuselage that wasn't going to make it look funny.

FWIW, although I loved to fly the Imitation I never liked the "look" of the wing with it's low taper ratio (.75%) and straight trailing edge (I've since learned to love straight flap hingelines, however, as forward swept ones gave me fits trying to trim them).  My competitive design built around the same numbers (the Excitation) looked prettier with a more tapered planform and a swept forward hingeline but it was a pain to trim well.  It was the last airplane I designed with that feature (swept forward hingeline).

The bottom line is...don't make to much about the marriage.  It was a matter of convenience!

Hope this answers your questions.

Ted

[Brett Buck]

FWIW, although I loved to fly the Imitation I never liked the "look" of the wing with it's low taper ratio (.75%) and straight trailing edge (I've since learned to love straight flap hingelines, however, as forward swept ones gave me fits trying to trim them).  My competitive design built around the same numbers (the Excitation) looked prettier with a more tapered planform and a swept forward hingeline but it was a pain to trim well.  It was the last airplane I designed with that feature (swept forward hingeline).

The bottom line is...don't make to much about the marriage.  It was a matter of convenience!

   But on the other hand, I think we pretty much came to the conclusion that we had overdone with the TP and Infinity airfoils well before this came up. When/if I build another 60-sized airplane, it will be the current planform with an Imitation airfoil, or something very close to it. Phil, Paul F. , and then David all tried something like this and it certainly seems to have worked out. Phil has is own airfoil ideas, Paul used the Imitation, and David used Billy's wing - but they all have the same basic characteristic, i.e. significantly thinner that the TP and Infinity "blimp" airfoils.  They have done well over the years, obviously, but have their weak points.

       Brett

[Ted Fancher]

   But on the other hand, I think we pretty much came to the conclusion that we had overdone with the TP and Infinity airfoils well before this came up. When/if I build another 60-sized airplane, it will be the current planform with an Imitation airfoil, or something very close to it. Phil, Paul F. , and then David all tried something like this and it certainly seems to have worked out. Phil has is own airfoil ideas, Paul used the Imitation, and David used Billy's wing - but they all have the same basic characteristic, i.e. significantly thinner that the TP and Infinity "blimp" airfoils.  They have done well over the years, obviously, but have their weak points.

       Brett

Good points, Brett...and I don't disagree in general with them.  One comment I would make, however, is that David's wing is "not" Billy's wing.  As we both know, there is a lot more than an airfoil to a wing, a lot of which is more important than the shape.  After doing a little measuring of David's wing up in Eugene while discussing such things with somebody, it became quickly obvious that the defining difference had more to do with David's "changes" to Billy's wing than it did with the fact that he used his airfoil.

What he didn't use was Billy's very large flaps and tips and the aspect ratio is significantly higher than Billy's wing.  The reduced flap chord has a dramatic impact on pitching moment and (especially when coupled with the smaller flaps) the appx. 5.7 to one aspect ratio has a dramatic difference in induced drag.  I think these factor have a lot more influence than the thickness of the wing (although David's wing would be "thicker" than Billy's as a result of the smaller flap chord).

I think the .75 run the way David does make the higher aspect ratio more manageable because it is more resistant to acceleration when flying in winds and thus he can utilize the reduced drag throughout a wider range of conditions.

Having said that, I'm unlikely to use as thick a wing again (should I ever design a new ship) because I share your opinion that the original intent (carrying a higher wing loading without increasing the wing area to sizes that make them difficult to fly in the wind) hasn't proven to be necessary.  The power available from modern powertrains is such that they can overcome the drag of hauling higher wingloadings without reaching critical angles of attack...although the original T.P. under the right conditions might, in fact, require the assets available from the thicker wing.

Ted

[Brett Buck]

Good points, Brett...and I don't disagree in general with them.  One comment I would make, however, is that David's wing is "not" Billy's wing.  As we both know, there is a lot more than an airfoil to a wing, a lot of which is more important than the shape.  After doing a little measuring of David's wing up in Eugene while discussing such things with somebody, it became quickly obvious that the defining difference had more to do with David's "changes" to Billy's wing than it did with the fact that he used his airfoil.

What he didn't use was Billy's very large flaps and tips and the aspect ratio is significantly higher than Billy's wing.  The reduced flap chord has a dramatic impact on pitching moment and (especially when coupled with the smaller flaps) the appx. 5.7 to one aspect ratio has a dramatic difference in induced drag.  I think these factor have a lot more influence than the thickness of the wing (although David's wing would be "thicker" than Billy's as a result of the smaller flap chord).

   I was, uh, stating things in the way least likely to get me a lot of grief. I think we discussed the unvarnished reality on the way back from Eugene this year.

    I would say it was a bit of "convergent evolution" - Billy started out too thin and migrated to thicker, and we started out too thick and are migrating (or more accurately, giving sage advice to others to) to thinner. i also note that the Impact had it right to begin with.

I think the .75 run the way David does make the higher aspect ratio more manageable because it is more resistant to acceleration when flying in winds and thus he can utilize the reduced drag throughout a wider range of conditions.

Having said that, I'm unlikely to use as thick a wing again (should I ever design a new ship) because I share your opinion that the original intent (carrying a higher wing loading without increasing the wing area to sizes that make them difficult to fly in the wind) hasn't proven to be necessary.  The power available from modern powertrains is such that they can overcome the drag of hauling higher wingloadings without reaching critical angles of attack...although the original T.P. under the right conditions might, in fact, require the assets available from the thicker wing.

      I will be your "spray gun monitor" the next time.

      I think that the bit about the speed control for the high aspect ratio is also what we missed with the giant thick wing design. Stuff a large muffled engine in an 650 square inch airplane and you darn well need that thick a wing. What we didn't fully appreciate at the time was the ability of the low pitch/high rev tp. engine to control the speed - in both directions, both preventing whip-up and inhibiting speed loss. So you don't need a thick wing to inhibit whip-up, and you don't need it to keep it flying in the corners. Now that we have essentially mastered getting the engine to run the right way, there's no good reason to make the compromise.

      Brett

[John Sunderland]

I havent been active much in the past decade but surely concur with your findings guys. I used Billys foil and a smaller flap cord in my 2003 design (which sounds ancient) and it proved a step up from my fat wings of notably similar shape to the TP. This past winter I shortened the span three inches to better accomodate my 3 inch swept tips to get a little less high aspect as we were at 63 inch span with full length flaps. I wish it were finished but health and wealth did not allow me to participate much once again. Next year!