The Imitation (UPDATED - NOW TAKING ORDERS FOR KITS)

[Mike Bush]

Is this new kit going to have the original built up air foiled stab or a built up flat stab ?

[Ted Fancher]

Is this new kit going to have the original built up air foiled stab or a built up flat stab ?

Hi Mike, 
I see Mike Griffin hasn't responded yet so let me throw in my two cents.

The plans Eric sent me to critique did "not" include the unusually deep airfoiled stab of the original.   I felt it unnecessary to make a big deal out of it because I could see where for anyone other than an experienced craftsman would find it difficult to build and shape accurately.  In addition, the thick tail was an experiment on the original and on the Excitation that, while functional, gave no great performance increase worthy of exposing the less experienced/skilled builder to the potentially for a poorly shaped or installed one.

Two changes I did make to the plans.  The first was to increase the pre-airfoiling thickness to 3/8" vice 1/4' due to the comparatively large area and the fact that many will be covering it with heat shrink material which adds less rigidity to the structure.  The second was to alter the leading edge from rounded to "airfoiled" with a sharp leading edge which I personally find to result in improved level flight and corner exits...others disagree but I wanted the plan to reflect the opinions of the designer.

Quickly, I did think about suggesting alternative stab/elevators with either the full airfoil of the original or the essentially flat 3/8" version since it would be easy to laser cut an accurate fuse cut-out for a "perfectly" airfoiled stab to put in it.  Unfortunately, that word "perfectly" was a stumbling block I didn't think was worth the risk unless some sort of jig was included in which to shape the "tapered in four directions" tail plane that goes into it.

Hope that helps.

Ted

[Mike Griffin]

Thank you Ted.  I had not had the chance to get back to the thread and answer that. 

Mike

[Ted Fancher]

Thank you Ted.  I had not had the chance to get back to the thread and answer that. 

Mike

No sweat Mike.  It was a question I had anticipated as the tail on the original was pretty much unique.  It was an experiment triggered by Bob Gialdini's comment in one of his construction articles advising readers to "...remember that the tail is a lifting surface and must be thick enough to do the job."  Seemed sensible to me and actually started me on a series of experiments with, first, the Imi...and Exci...with the thick tails followed by a couple of very thin tailed mods to classic ships.  I noted nothing particularly dramatic in either case but--in part by visualizing how effective a surface would be if the airfoil was a 100% section (more or less circular) no amount of up or down would do much of anything as the camber would barely change no matter how far up or down the horn driving them had rotated I decided there was probably an aerodynamic limit in that direction while, as long as it could be kept rigid, even ultra thin sections would produce the lift necessary to steer the thing in the pitch axis.

PLus, the thick ones were a bummer to build accurately.  I still prefer airfoiled sections and, if I were to build another stunter, would do so again but with only modest upper and lower cambers meeting with a relatively sharp leading edge.

Worth noting, however, that my first Nats winner, the the 1991/92 Intimidation has a ~18% section that is a full inch deep at the root.

Ted

Ooops!  Make that 1981/82 Intimidation.  One's memory is a terrible thing to lose!

[Mike Bush]

Hi Mike, 
I see Mike Griffin hasn't responded yet so let me throw in my two cents.

The plans Eric sent me to critique did "not" include the unusually deep airfoiled stab of the original.   I felt it unnecessary to make a big deal out of it because I could see where for anyone other than an experienced craftsman would find it difficult to build and shape accurately.  In addition, the thick tail was an experiment on the original and on the Excitation that, while functional, gave no great performance increase worthy of exposing the less experienced/skilled builder to the potentially for a poorly shaped or installed one.

Two changes I did make to the plans.  The first was to increase the pre-airfoiling thickness to 3/8" vice 1/4' due to the comparatively large area and the fact that many will be covering it with heat shrink material which adds less rigidity to the structure.  The second was to alter the leading edge from rounded to "airfoiled" with a sharp leading edge which I personally find to result in improved level flight and corner exits...others disagree but I wanted the plan to reflect the opinions of the designer.

Quickly, I did think about suggesting alternative stab/elevators with either the full airfoil of the original or the essentially flat 3/8" version since it would be easy to laser cut an accurate fuse cut-out for a "perfectly" airfoiled stab to put in it.  Unfortunately, that word "perfectly" was a stumbling block I didn't think was worth the risk unless some sort of jig was included in which to shape the "tapered in four directions" tail plane that goes into it.

Hope that helps.

Ted

Ted
Thanks for the clarification

Mike

[Mike Griffin]

Is this new kit going to have the original built up air foiled stab or a built up flat stab ?

Mike I apologize for not getting back and answering your question quicker.  I have been buried with model duties and also some personal stuff that pertains to Christmas and I just had not gotten back to the thread and answered your question.  Ted jumped in there and did it for me in a much more eloquent and informed matter than I could have anyway.  I am usually a lot more prompt answering questions... Hope you have a great Christmas

Mike