Bob Wright's HM 18 Flying Flea as modified by Abbott Baynes. 53.5" wingspan.

[David Davis]

In 1997 my best friend and former lead guitarist Micheal Harker was diagnosed with leukaemia. We played our last gig together on New Year's Eve 1999 and within two years he was dead. Michael had had a private pilot's licence but had never built a model. As he became less and less fit he asked me to suggest a suitable radio controlled model which he could build and fly. I suggested the usual suspects but he wanted something more challenging and chose Bob Wright's 1/5 scale HM18 Flying Flea, as modified by Abbott Baynes. This aircraft is unusual in that instead of the elevator operating in the normal manner, the entire tailplane is fixed. The mainplane pivots to provide pitch control. I flew one at Cocklebarrow once and it flew very nicely but I handed it back to the owner for him to land it!

Searching through my stuff I discovered that Michael had kept the plan, a December 1992 Radio Modeller publication, and he had also cut out most of the components. He had even made up a template for the curved wing spars. Being a magazine free-plan, it's not that easy to follow; red ink is used for the starboard wing and blue ink for the port wing but maybe I'll build it in Michael's memory. I've got a few little four-strokes sculling about not doing anything.

However, on studying the plan, as we do, I spotted the following instruction, "NOTE: L.E'S ARE NOT ROUNDED." Then there is an arrow pointing to the leading edge of the tailplane.

I have a few questions for people with superior aerodynamic knowledge.

I learned at my mother's knee that if the leading edges are not rounded the model's propensity to stall is increased, so why is there this instruction on this plan?

Is it because it is a tandem wing aircraft?

Does this instruction apply only to the the tailplane or should the leading edges of the wing be left sharp too?

Anyone have a copy of the magazine? December 1992 Radio Modeller? I would willingly pay for a photocopy of the build article or for the complete magazine.

[Martian]

Hi David try to contact Ian Redshaw aka Reg Shaw on this forum he built a half scale flying flea the Bertie Bassett

[Doug Moss]

I have one which I admittedly haven't flown in years, not since the garage ceiling fell in on it.

It's about 1.6 meter span and flew very well on an O S 26 FS.

Both leading edges are definitely rounded. It didn't have any serious vices other than a tendency to pitch down with speed, I understand that the fullsize one did this with rather unpleasant consequences.

Perhaps it's time to dust it off.

[J D 8]

I have never heard or seen square leading edge's only trailing edge's being left square, something to do with better precision with aerobatic types.

[David Davis]

Posted by J D 8 on 03/01/2020 16:02:05:

I have never heard or seen square leading edge's only trailing edge's being left square, something to do with better precision with aerobatic types.

The leading edges are made from 1/4" square balsa turned on the side so that they present a sharp edge to the airflow. A diamond shape in cross section.

Martian, I was at Greenacres when Ian Redshaw flew the Bertie Bassett Flying Flea and I got to talk to him.

Edited By David Davis on 03/01/2020 16:14:04

[Bob Cotsford]

Let's see if this pdf link works, it says the early Fleas had a sharp LE which on later versions was changed to the rounder LE we would expect to see. Is the rear wing LE a square section set on edge to give the pointy LE? Is there any clue to the front wing section on the side elevation?

[David Davis]

Posted by Bob Cotsford on 03/01/2020 16:13:26:

Let's see if this pdf link works, it says the early Fleas had a sharp LE which on later versions was changed to the rounder LE we would expect to see. Is the rear wing LE a square section set on edge to give the pointy LE? Is there any clue to the front wing section on the side elevation?

All of the ribs on both wings feature a 1/4" square section leading edge set on the side to give a pointy leading edge.

[Bob Cotsford]

Overlapping posts earlier David! If I were building it I think I'd put a bit of a radius on both wings, I'm not sure you'd really want too abrupt a stall on the rear wing though the designer must have had a reason for adding that note!

[Max Z]

The HM18 is not an early model, and is not likely to have pointy LE's. I have built a HM16, and did some research although there is not a lot of reference material, but from what I could detect on the photographs the LE's are not sharp. Look HERE or HERE.

And THIS one of an actual vintage HM18. Looks definitely rounded...

The best known type is the HM14, Bertie Basset is one of those. As far as I know the Carden/Abbott-Baynes models were also modified versions of the HM14, not the HM18. If your model is one of those, it could have pointed LE's.....

Have a look at this article .

Edited By Max Z on 03/01/2020 18:27:20

[David Davis]

Thank you Max. I am only going on what is printed on the plan. I read elsewhere that the HM 18 had an enclosed cockpit as in your picture. My plan shows an open cockpit. I'm not sure how I'm going to finish it but one thing's for sure, I won't be entering it into any scale competitions!

 

PS. I've just bought a copy of the December 1992 Radio Modeller on eBay so maybe the build article will enlighten us.

Edited By David Davis on 03/01/2020 18:45:25

[Gary Manuel]

David.

Nothing to offer in terms of your question, but THIS might be of use / interest to you if you've not already seen it. Plenty of links to click on.

Edited By Gary Manuel on 04/01/2020 12:34:50

[Robin Colbourne]

Henri Mignet used his own wing section on the HM14. It along with several other features of the aircraft could lead to problems. This is what Darryl Stinton wrote in 'The Design of the Aeroplane':

The wings had a section invented by Mignet, with a sharp leading edge. Control in pitch was achieved by changing the angle of incidence of the foreplane by a direct linkage with the stick. Maximum incidence was limited to only about 4.8 deg on a specimen tested in the 24 ft (7.3 m) wind tunnel at the Royal Aircraft Establishment, Farnborough (ref 4.19). It is possible that the pitch control lacked authority, and that the lack would have been worsened by the tendency of a sharp leading edge to force premature separation and loss of lift at moderate angles of attack.

There is more of his article here: Nest of Dragons - Flying Flea Teething Problems

As a side note, the site of the Abbott's Factory, was next to the secondary school I attended. A 'Red Wheel' plaque was recently unveiled on the Co-op which now occupies the site. Abbott's also built the Scud series of pre-war gliders, hence the reason the Flying Flea pictured came from the nearby Gliding Heritage Centre at Lasham Airfield.