Mercury cobra questions

[phil myers]

Hi, I'm in the middle of building a Mercury Cobra with extended wingspan 45" (original was 40). This is a kit that has been cut for me, but I don't have the plans. Can anyone tell me an ideal weight for this plane,its a profile, I'm guessing around 35oz. I plan to use an Enya ss30, will that be ok? Thanks for any replies... Phil

[PerttiMe]

This?

Sorry, don't know anything more about it. But maybe someone can guesstimate based on span and the picture.

[rustler]

I guess the suggested weight will be o.k.
I always think this Brit. Mercury design could be the Brit equivalent of the U.S. Foxberg event, with a Merco 35 engine. The "MercMerc" event. :-)

[Brett Buck]

Hi, I'm in the middle of building a Mercury Cobra with extended wingspan 45" (original was 40). This is a kit that has been cut for me, but I don't have the plans. Can anyone tell me an ideal weight for this plane,its a profile, I'm guessing around 35oz. I plan to use an Enya ss30, will that be ok? Thanks for any replies... Phil

  I don't know much about Enyas in general. If its the same as the Enya 30 I *do* know about, it will be adequate but not stellar for this airplane. I would sure try to get it under 35 by as much as practical. If it's a hand-cut kit I would expect the wood to be decent and if so, just eyeballing it, I would expect 30 is probably doable.

    Brett

[Bill Little]

I agree with Brett on the weight.  I would believe I would try to build it at 30 oz. and be happy if it was 28 oz.

I have no experience with the new Enyas.  I have heard the new 30SS is a pretty strong little engine.  My old Enya 5224 .35 is a pretty strong .35 for its vintage with the low compression head and the small venturi.  Back around 1993 I built a reduced size Impact profile.  That engine had no problems pulling the model and I think I must have used 12-15 lb wood for all the construction! (well over 40 oz.

BIG Bear
RNMM/AMM

[Steve Thomas]

The SS30 is plenty strong (and not all that heavy). 35 oz wouldn't be a problem for it. I'm planning to use one in a 'Miss BJ', which is 48" and originally used a Fox 35 (I think). I gather it's quite a popular combination in Brazil. (Martin?)

[Brett Buck]

The SS30 is plenty strong (and not all that heavy). 35 oz wouldn't be a problem for it. I'm planning to use one in a 'Miss BJ', which is 48" and originally used a Fox 35 (I think). I gather it's quite a popular combination in Brazil. (Martin?)

     I am not as concerned about the lack of power as the lack of wing for 35 oz. Particularly if it runs 6" of pitch.

    Brett

[PJ Rowland]

Thats right - Its not about the engines abilty to haul the weight - its about the wings ability to lift the plane at a given weight, in combination with the wee amounts of engine power avaliable to move it forward.


This is in part why a "heavy" 70 oz 600sq plane with a 75 can be competitive but with a ST.46 its not.

[phil myers]

Thankyou for all the replies, Its a big help, at this stage I don't really know what the finished weight will be but hoped the ss30 would do the job if it turned out at around 35oz. I will try for less..   Forgot to mention this plane will be flapped. I might surprise myself one day and build something light!!
Thanks  Phil

[Bill Little]

Thankyou for all the replies, Its a big help, at this stage I don't really know what the finished weight will be but hoped the ss30 would do the job if it turned out at around 35oz. I will try for less..   Forgot to mention this plane will be flapped. I might surprise myself one day and build something light!!
Thanks  Phil

Hi Paul,

Building light is simply a mind set.  Weighting balsa and using the lightest part that will work.

Also, learning to get finishes light by only applying enough paint to make it right.

BIG Bear
RNMM/AMM

[phil myers]

Bill, I'll be covering the entire plane with iron on film. The assembled frame (minus all hardware) weighs 16oz, I know the motor is 9oz that makes 25 so with covering, undercarriage, prop and tank, 30- 32oz should be possible.  Phil. ps i'm in for surgery today so will reply to any more in a few days time