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If you are contemplating moving up a gear and building a canard-Flea, there are some caveats to be aware of.  PLEASE DO NOT PROCEED WITH YOUR CANARD-FLEA PROJECT WITHOUT READING THIS FIRST.

  1. A canard-Flea does not have its ideal CG at the usual 25% of the combined chord.  It is closer to 35%
  2. The NP (Neutral Point) is also much further aft (at about 41% of combined chord)

In Feb 2011, Axel Darling (Pou Renew #41) did pioneering work in his analysis of the Raymond Baudoin reverse wing Pou.  He wrote: “In the final analysis, I found that starting at 90cm/90cm [Ed: horisontal and vertical wing gaps] with any of the most used aerofoils on Pou’s that they remained in laminar flow all the way down to about 20cm/20cm”

In other words, so long as the vertical and horisontal wing gaps were identical, one could expect laminar flow over both wings.  This in itself is a huge breakthrough from an extremely well-respected aerodynamicist (and Pou advocate).

He then axamined the relationship between front and rear wing areas, and wrote: “One of the types of vortices on a typical wing is generated at about 89% of the semi-span as the flow from below swirls with that from the upper surface.”  He concluded: “A great deal of the interaction for an aftplane tip occurs here so the aftplane could be positioned at say 85-90% foreplane chord for good effect. ”

And building on this, he reasoned that it would be extremely beneficial to have a smaller wing up front.  Why?  Because “the smaller foreplane leaves lift bumps at about the vortex locations, which when the aeroplane yaws, allows a much greater yaw/roll force and much stronger dynamic lateral stability and much better and immediate pilotage in turns. This undoubtedly is the reason why Baudoin exclaimed that his backward Pou flew so much better than the reverse”

But he cautions designers/builders to consider the CG position in a canard-Pou:  “Consider the stability of such a planform… the N.P. is going to be much further back than in a standard Pou planform, even equal span, equal chord. For instance, with 4.4M forespan and 5.8M aft the N.P. is ~1.3M as apposed to .997M for the [standard Mignet] planform. That’s 41.3% as opposed to 31.65% of total chord”

Finally, David Isley (Pou Renew #48) hauled out his trusty sliderule, and using Axel’s analysis of the Baudoin canard-Pou, worked out a simple formula for estimating reverse-Poux CG positioning.

What I found difficult was that with the larger wing in the rear, it was extremely challenging to get things to line up.  My weights & balance estimates always placed the CG too far aft.  I had started off looking at one of the 35hp paramotors (both 4-stroke and 2-stroke) but they were simply too light.  Electric was only slightly better with similar weights, but batteries could be moved about to affect the CG.  And then there was the issue of required power.  I figure I’d need at least 35hp (continuous) to fly acceptability, even with 130ft^2 wing and 450lbs MAUW) So I looked at two smaller engines (fore & aft) in a push/pull config.  This would give me the power, but not the required CG.

Finally I ran out of options, and started plugging in numbers for a heavier engine.  I happen to have a Valley Engineering Big Twin (53kg with redrive, starter, full of oil and exhausts, 50hp).  That gets me very close.  But I keep glancing over at the Aeromarine v-twin (63kg, 60hp, EFI) but at a huge cost of over $10k USD.  I’m still not sure, but it sure looks attractive.