Bob Wright's HM18 Flying Flea.

[David Davis]

On 11th September 2002 my best friend and former lead guitarist, Michael Harker, died of leukaemia. He was fifty-two years old. He was fairly active until the last few weeks and in his last year he asked me to recommend a model aeroplane which he could build. I suggested all of the usual suspects but he had a private pilot's licence and for him it had to be a scale model and just to make things more interesting he chose to build Bob Wright's HM18 Flying Flea as  modified by  Abbott-Baynes. https://outerzone.co.uk/plan_details.asp?ID=12222. This aircraft has a fixed tailplane, or more correctly a fixed rear wing and pitch control is achieved by pivoting the mainplane. He had never built a model aeroplane before but he was very handy and a better woodworker than I will ever be. After he had died his widow gave me a box containing all of the parts which he had cut out.

 

After over twenty years it's high time that the model was built and flown so this evening I opened the box and as far as I can see most of the parts are there, beautifully cut out too. So after I've finished the Guidato https://forums.modelflying.co.uk/index.php?/topic/50866-ill-bet-youve-never-seenone-of-these-before-brian-sichis-guidato/#comments I'm going to have a go at steaming the spars to a curved template he made up stuck to a piece of oak.

 

One question for the aerodynamicists amongst you. On the plan it states that the leading edges of the wings should not be rounded off.  I have always thought that sharp leading edges were more likely to provoke a sudden stall while rounded leading edges made the stall more gentle.

 

Is this true and if you were me would you leave the leading edges sharp or round them off?

[J D 8]

  Usually a sharp leading edge will lead to a sudden stall as you say, however there are some special wing section's  Thin [ish] with flat or near flat bottom that can have a sharp leading edge but the edge will be more or less in line with the bottom of the wing. 

The F104 Starfighter had a sharp leading edge that lead to an early nickname of "flying razor" but this was for high speed reasons. If you saw one on the ground the leading edge would be fitted with a guard.

  The early HM14 did have a wing leading edge as described above the idea being to try and reduce drag for the limited power available. Pic's of the later HM18 appear to show a more rounded edge but it is still in line with the lower side of the section.

    I think steaming is the way the full size flea spars were made.

[David Davis]

Thanks for the reply JD8. The model features a reflex wing section, i.e, from the rear spar the wing rib slopes upwards. It's also an undercambered wing section. That'll be fun to cover! Michael had cut out all of the wing ribs. I'll post pictures once construction starts in earnest.

[J D 8]

     Hi David, Out of interest do both wings have a reflex section?  Some pics of early Fleas do have reflex on the front wing. This may well be to improve fore/aft stability. On later and modern one's the wing section is normal. Tandem wing types are still seen mostly in France both ultralight aircraft and microlight types, the main difference [ build/aerodynamic ] you see is in a greater distance between front and rear wing. Abbot-Baynes fleas had a bit more distance between the wings, the problem of aerodynamic interference between the two wings in some situations had already been noted. 

  The use of stuff like Deluxe materials Cover Grip on the under camber ribs will keep covering secure.

  Anyway good luck with the model. Will be following with interest.  John.

    My old Bleriot XI wing when I was giving it a clean.