Rebuilding Merlin Wings - Can not figure out the Airfoil type

[[email protected]]

I am rebuilding the wings on my Merlin. My intent was to use the old
foam rib cores as templates but they differ from rib to rib, clearly
some have been replaced, not to mention some really shoddy
workmanship, warped ribs, broken ribs etc. So I search the web for
the airfoil type and find that it is supposed to be a Clark Y. Simple
enough I print out a Clark Y from Profili, not even close. So I
measure the thickness and find that a Clark Y15 has the right
thickness but still not even close to my ribs on the aft part of the
upper camber.
The upper part of my ribs are nearly straight from about 10% behind
the spar back. My suspicion is either remarkably careless building or
errors carried forward on the factory template. It is much easier to
make the upper cap strips this way ie straight, no camber.
So the question is, do I go with the Profili Clark Y, or perhaps the
NACA 4412 or ?
My only hesitation on the Clark Y is the affect of the trailing
suspended ailerons on the Clark Y. Most of the Clark Y applications
had the ailerons built into the wing. I called the Merlin Factory they
said just use the old ribs.

Thanks, Zac

[Capt. Geoffrey Thorpe]

> wrote in message
...
>I am rebuilding the wings on my Merlin. My intent was to use the old
> foam rib cores as templates but they differ from rib to rib, clearly
> some have been replaced, not to mention some really shoddy
> workmanship, warped ribs, broken ribs etc. So I search the web for
> the airfoil type and find that it is supposed to be a Clark Y. Simple
> enough I print out a Clark Y from Profili, not even close. So I
> measure the thickness and find that a Clark Y15 has the right
> thickness but still not even close to my ribs on the aft part of the
> upper camber.
> The upper part of my ribs are nearly straight from about 10% behind
> the spar back. My suspicion is either remarkably careless building or
> errors carried forward on the factory template. It is much easier to
> make the upper cap strips this way ie straight, no camber.
> So the question is, do I go with the Profili Clark Y, or perhaps the
> NACA 4412 or ?
> My only hesitation on the Clark Y is the affect of the trailing
> suspended ailerons on the Clark Y. Most of the Clark Y applications
> had the ailerons built into the wing. I called the Merlin Factory they
> said just use the old ribs.
>

Wouldn't be the first time that a designer straightened out part of an
airfoil to simplify construction.

If you want it to fly the same, use the same modified Clark Y that, from
your description, it seems to be.

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

[Stealth Pilot[_2_]]

On Sun, 16 Nov 2008 20:23:01 -0500, "Capt. Geoffrey Thorpe" <The Sea
Hawk @See My Sig.com> wrote:

> wrote in message
...
>>I am rebuilding the wings on my Merlin. My intent was to use the old
>> foam rib cores as templates but they differ from rib to rib, clearly
>> some have been replaced, not to mention some really shoddy
>> workmanship, warped ribs, broken ribs etc. So I search the web for
>> the airfoil type and find that it is supposed to be a Clark Y. Simple
>> enough I print out a Clark Y from Profili, not even close. So I
>> measure the thickness and find that a Clark Y15 has the right
>> thickness but still not even close to my ribs on the aft part of the
>> upper camber.
>> The upper part of my ribs are nearly straight from about 10% behind
>> the spar back. My suspicion is either remarkably careless building or
>> errors carried forward on the factory template. It is much easier to
>> make the upper cap strips this way ie straight, no camber.
>> So the question is, do I go with the Profili Clark Y, or perhaps the
>> NACA 4412 or ?
>> My only hesitation on the Clark Y is the affect of the trailing
>> suspended ailerons on the Clark Y. Most of the Clark Y applications
>> had the ailerons built into the wing. I called the Merlin Factory they
>> said just use the old ribs.
>>
>
>Wouldn't be the first time that a designer straightened out part of an
>airfoil to simplify construction.
>
>If you want it to fly the same, use the same modified Clark Y that, from
>your description, it seems to be.

the 4417 is the clark Y with the ordinates from the chordline instead
of the under surface.
the whole 44xx family is the same clark Y aerofoil just thickened up
or thinned down.

pick the one you are happiest with.

Stealth Pilot