OTS/Classic question

I know that in OTS and Classic you can make structural changes as long as they don't change the aerodynamics of the airplane. So here is the question: An airplane I am interested in building has a center spar. I would like to strengthen the design by putting in a top and bottom spar instead. Would I get any grumblings if I took such an airplane to the Nationals?

My concern comes from the fact that the center spar allows for the full tightening of the covering between the ribs, where the top and bottom spar raise the covering to the highest spot on the rib for the length of the wing. Some people argue that this acts like a turbulator on the wing and makes the model fly better.

So if it was you trying to decide and you truly didn't want to do the center spar, would you modify or pick a different airplane?

Ed Culver

Brodak has already made those modifications on several designs. Personally, I think while it should be allowable, it will be looked down on.

There are ways to do a center spar, retaining the look of the original and still gain enormous strength. It's a little more complicated but very doable.

I'm looking at two different methods to achieve this with Jerry Worth's Mirage. 72 ribs, a center spar and only the trailing edge sheeted. It can be done.

Bill

I believe the top and bottom spars are what disqualifies the later Ringmasters so the only conclusion one could come to is you can't do it......

>I believe the top and bottom
>spars are what disqualifies the
>later Ringmasters so the only
>conclusion one could come to
>is you can't do it......
>

The above statement is true for OT. Classic is another animal though.

You have much more latitude making changes in Classic. what would suffer are the fidelity points should your changes sustantially modify the design.

>>I believe the top and bottom
>>spars are what disqualifies the
>>later Ringmasters so the only
>>conclusion one could come to
>>is you can't do it......
>>
>
>
>The above statement is true for
>OT.

Conditionally true. Depends on whether the CD thinks it represents a deviation to the aerodynamics as opposed to/in addition to a structural improvement. I would allow it, others would not. It's a matter of opinion.

Hi Ed. The rules state that you cannot change the airfoil. If the spars do in fact change the airfoil, then it would be grounds for DQ. Internal changes to the structure to make it stronger or allow for a larger fuel tank, etc are allowable. Same for the landing gear, it must exit very close to the original spot and the wheels must be in the same position as on the plans. The intent was to suffer like in the "olden days". Lets face it, most of them did not fly worth a darn (read do the pattern well) and so they evolved into what we have today. If a major change is made to the wing or outline of the airplane, then it is no longer the OTS plane that flew bad in the 50's. Changes to make it fly better put you into the classic era. Frustratin ain't it?? Ty

I agree with Brett. This is especially true if a "cottage industry" guy has labored to cut kits with a band saw in his garage.

Deviations that preserve airfoil while having cap strips (thus allowing only one rib template on a constant chord wing) comply with the essence of the event.

There are some that believe that OTS should be a "scale" type deal, which rains on the parades of those that seek to have a bunch of fun.

It has always perplexed me why the "scale/purist" types don't think that the S-1-A (?) Ringmaster should be allowed, while allowing various similar permutations of the Barnstormer?

Preserve the dimensions and airfoil while allowing 'most any constructiom.

See Ya

Out of curiosity, what airplane are we talking about? In general I don't think I would make that kind of change. I would find it very noticable, and it would bother me. I've seen a classic era airplane (Mackey Profile) with exactly that done to it, and it just didn't look right.

I'd suggest things like laminating the center spar with spruce top and bottom, or carbon fiber, rather than obviously redesigning the wing structure. Another question; why do you think the wing is too weak?

>I'd suggest things like laminating the
>center spar with spruce top
>and bottom, or carbon fiber,
>rather than obviously redesigning the
>wing structure. Another question;
>why do you think the
>wing is too weak?

I would be strongly tempted to replace the center-spar with a center spar made from a graphite kite tube, or a combination of several. Maybe 3 right on top of each other to about 1/4 span then one continues to the tip. It's also dead easy to cut the hole!

The center-spar thing (like on the Ringmaster)is pretty wimpy. It'll only work if you use Sterling-quality wood and silkspan or silk. David's Ringmaster/Veco19 was lightened up drastcally with contest wood and Polyspan. And the outboard wing just broke off one day, in an outside loop.

Bob,

While it's true that the "later" Ringmasters (Sterling S-1A and Estes Stuntin' series) have spars on the top and bottom of the airfoil near the high point, isn't it really the fact that the leading edges are sheeted back to those spars that really is the fly in the ointment?

The latest Ringmaster 35 from Estes does not have a sheeted leading edge but it would get DQ'd in 99% of the OTS meets around the country.

>Out of curiosity, what airplane are
>we talking about?

I was thinking of a Super Duper Zilch (ugly I know but I like it)

>In general I don't think I
>would make that kind of
>change. I would find it
>very noticable, and it would
>bother me.

Me too

>Another question;
>why do you think the
>wing is too weak?
>
>Jim Thomerson

A single spar in the middle doesn't give much strength in the way of twisting. With a top and bottom spar you get a triangle effect with the LE and TE. Maybe I am wrong...

Ed

A Super Duper Zilch with top and bottom spars would be considered illegal by anyone's rules in OT Stunt, regardless of Brett's comment about letting almost anything fly.
As far as the Barnstormer repro kits go, although they change the structure from the original, the airfoil is still the same, or close to it. I haven't really measured one to compare it eactly. at least the original had a "C" tube wing. Most repro just forget about the rear spar.
Actually, I found the wing in one of the retro Barnstormers to be a beautiful fit for a Still's Stuka!
Bare

I heard at VSC 13 that Still used a Barnstormer wing in his Stuka. Kinda like a lot of early models were modified Noblers.