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The 'Butterfly DLG' from Mick Page

Before the archetypal FF aeromodeller is allowed through the Pearly Gates, there are a few models that he has to have built to qualify for entry.

  1. Phantom
  2. Tomboy
  3. Caprice
  4. Senator
  5. Stinger CLG
  6. Butterfly DLG
  7. Junior 60
  8. Cloud Tramp
  9. A Spencer Willis P30

'Now is the time' , the Walrus said, to almost complete your task list and it came to pass that a Butterfly plan was acquired and work commenced to attempt to emulate one of, if not the most successful PMFC competition model of the past 35 years. Twenty hours later a Butterfly DLG emerged from the balsa dust and debris. The Master scrutineered my effort at the last Peakirk clubnight and apart from a few minor issues pronounced it mildly worthy.

I am not known for following a plan and it was ever so……..Some minor modifications and detail explanations follow.

1. Increased span from 27 to 30" retaining the asymmetric port wing (1" longer than the right) Or should this be 25mm?
2. The underfin is glued on the left side of the boom.
3. MP's moment arm is measured from wing TE to stab LE
4. Model uses a viscous micro DT device operating on a brake back fuselage with incidence setting on a 10BA setscrew.
5. Tail end stab/fin angles are 60/60/60. Wing panel angles to the horizontal are 4/18 degs approximately. This is not a change to MP's plan, just an advisory in case you want to build to angles rather than a linear dimension.
6. Plan says 45% CG root chord but MP's Butterfly was measured at 37%
7. Finish was talc/dope/beeswax.
8. No dihedral braces were used. Panels were sanded to angle on Proxxon disk sander, the end 'rib' pricked with a darning needle many times, glued with aliphatic and glassed with a 40mm strip of lightweight glass applied with dope. This is standard f3k practice on a blue foam vacuum bagged wing. Leads to a lighter wing (32gm) and easier to build….worth a try?
9. A stab incidence of -1.5degs is about 2mm difference between stab LE and TE using a steel rule from wing lower surface to stab.

Mistakes

1. Use of the thick end of a Skyshark 8gm 2PT carbon kite boom. Very stiff but not light.
2. Use of a fillet of epoxy/microballoons to attach the V-tail to the boom. Should have been CA/lightweight glass and sparingly applied.

The above errors gave me a heavy back end and a 55gm unbalanced model which needed 19gm !?***! of nose weight to get to a 40% CG…..74gm RTF and MP quotes 65gm. Moral is to use a decent DLG boom from Flitehook and try CA/ lightweight glass to attach stab.


Mick's Butterfly plan can be accessed here. - Left side - - - Right Side

Saturday March 1st sunshine beckoned and the Butterfly was glide tested on the local recreation ground. I had to shift the CG back to close to 50% and increase the decalage by a turn on the incidence screw to get a decent glide. Despite the right rudder offset the right glide was marginal. Throwing caution to the wind (well there wasn't any). I DL'd it into one of my best hooked launches. Model lawn darted into the ground …..minimal damage but viscous timer covered in mud and boom brackets broken. Following repair I will wait the wisdom of 'The Master' before attempting further shenanigans.

I now have only a Cloud Tramp to build to complete the mandatory aeromodelling set. Needless to say I am never ever going to build this and thus am very likely to live forever?

Ian Middlemiss
March 2014
contact@peterboroughmfc.org