Tandem-wing LSA/microlight concept and poll

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Which tandem-wing configuration would interest you the most (pick one in each of four categories).

  • A1 - High wing forward, low wing aft (Flying Flea) OR

    Votes: 18 37.5%
  • A2 - Low wing forward, high wing aft (Quickie);

    Votes: 26 54.2%
  • B1 - Two-axis controls (no rudder pedals like an Ercoupe) OR

    Votes: 9 18.8%
  • B2 - Three-axis controls (with rudder pedals like a Cessna);

    Votes: 34 70.8%
  • C1 - Conventional (taildragger) gear OR

    Votes: 23 47.9%
  • C2 - Tricycle (nosewheel) gear;

    Votes: 20 41.7%
  • D1 - Tractor engine (engine and propeller at front) OR

    Votes: 32 66.7%
  • D2 - Pusher engine (engine and propeller at rear);

    Votes: 13 27.1%

  • Total voters
    48

erkki67

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The Dodo-V is meant to bring tall luxury bodys like mine safely into the air, while being sturdy and simple to build, and safe to fly.

The powerplant foreseen is around 40hp but would also fly on 23hp reducted, but not as good as with 40.

The design is being calculated by an german aeronautical engineer, so Ill have the required numbers for our authorities.

Only drawback today is the fact, that the american and chinese housbuilding is requiring million tons of wood, so our sawmills are doubling their prices now, without any end in sight of the price increase.

But ill pay whats required to get local aircraft grade spruce similar wood.

.
 

Victor Bravo

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Here in Switzreland, you can't just build a craft and going aloft, without stress numbers no way to get the permission.
Unfortunatly we don't have a similar class like the FAR103. SSDR or 120kg german class.
But in Switzerland you have the ETH and probably several other universities with engineering students. You can approach one of these engineering programs and offer them the chance to train their students on an actual flying aircraft project that is not theoretical. You will pay the materials cost of building the aircraft, and the school engineering program will perform the engineering calculations and/or physical load tests sufficient to receive government authorization to fly. The students get a better education, you get a properly engineered aircraft, and the homebuilt airplane community gets another viable, safe design.
 

rtfm

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Brisbane, Australia
While I wait for epoxy to cure in the shed, I'm stuck here behind my laptop, and drawing planes. This is my concept for a fast X-country side-by-side Flea. Yes, I said fast.

As of now, I plan to have a single mast (well, two of them - one on either side) acting as both the wing anchor and the single pivot (like the Croses Flea). The rear wing will pivot also (subject to this modification proving to be successful on the Fleabike once I have accumulated sufficient time on it to warrant being able to experiment with it. The rear wing will be completely cantilever, rotating on bearings. I strongly suspect that pivoting both wings will allow this Flea to travel much faster than fixed rear-wing Fleas. And land slower.

Very clean, 100hp, optional (removable) canopy. Wood construction.

Well, that's the dream, anyway.

1620890459248.png
 

Victor Bravo

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The airfoils that are known to work well on the Flea (Cl not moving around with AoA changes, etc) may be inadequate for a fast aircraft.

The front edge will stay where it is, but the lower rear edge of the red strut in your drawing is actually going to be underneath the front of the windscreen, in order to be rigid enough for the increased drag loads of higher speed.

The landing gear will have to fold into the fuselage F-16 style or Grumman F3F style. The space that this takes up will force you to leave your ankles back on the ground. So b ring zip-ties to reduce blood loss, and count on developing hand controls :)

Sorry Duncan, I am not happy about puncturing your dream, but I'd rather rip the SpeedFlea apart in order for you to finish and develop the Amazing FleaBike !
 

rtfm

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Hi VB,
No worries mate. This is an initial sketch. Took all of two hours. Pull it apart with gusto...

Airfoil: NACA747A415 It has better (i.e. lower) CM than either the NACA 23112 or the Fraser airfoil. And it is laminar flow to 40% of chord on top, and 70% on the bottom surface.

Sorry - I don't understand the concern with the red strut.

Landing gear: I haven't even thought of that yet. 2 hours isn't a big chunk of time...

What else do you expect me to do while epoxy cures? Stare at the wall? I did manage to coat the almost cured outer ribs and their cap ribs with West System epoxy both sides and hang them up overnight, but that was in the last 30 minutes of so.

I LOVE your designation of the "SpeedFlea". Do you mind if I use it as a working name?

Regards,
Duncan
 

erkki67

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Romont / Fribourg / Switzerland
VB, indeed that would be a worthwhile approach, but the Dodo-V is designed and delivered with the required math for the Swiss authorities.
The math is always the Achilles to accept an aircraft in Switzerland
 

rtfm

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Brisbane, Australia
VB, indeed that would be a worthwhile approach, but the Dodo-V is designed and delivered with the required math for the Swiss authorities.
The math is always the Achilles to accept an aircraft in Switzerland
I am SO PLEASED I live in OZ. We can build what we like. It's our right.
 

Martin R.

Active Member
Joined
Mar 21, 2019
Messages
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.... The key is using identical or at least very similar airfoils and chords and respecting the "150% rule" for loading the front wing more than the rear so it always has to stall first. ...
Does 150% means that the front wing should carry one and a half times the weight of the rear wing? (e.g. MTOM = 450 lbs --> front wing = 270 lbs, rear wing = 180 lbs)

Or should we try to respect a one and a half relation with regard to the wing-loading? (e.g. front-wing 17.1 lbs/ft^2, rear-wing 11.4 lbs/ft^2)

And last question: does "similar chords" means the same mesures or one could also understand same AR?
 

cluttonfred

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My understanding is that you want 150% wing loading front vs rear, in other words if the front wing carries 6 lb/sq ft the rear wing would carry 4 lb/sq ft at the most rearward CG position.

It’s relative *wing loading* that remains constant, the relative total load would vary with the relative areas of the two wings.

That’s why the same principle would apply to a conventional monoplane with a lifting tail, a tandem wing, or a canard—load the front flying surface 50% more per unit area to ensure it’s working harder and will stall first.

This is just a quick rule of thumb for wings if similar profile and similar chord, very different front and rear airfoils or very different chords would require more careful study.

I say chords because of Reynolds number issues changing the behavior of the same airfoil at different sizes.

Does 150% means that the front wing should carry one and a half times the weight of the rear wing? (e.g. MTOM = 450 lbs --> front wing = 270 lbs, rear wing = 180 lbs)

Or should we try to respect a one and a half relation with regard to the wing-loading? (e.g. front-wing 17.1 lbs/ft^2, rear-wing 11.4 lbs/ft^2)

And last question: does "similar chords" means the same mesures or one could also understand same AR?
 

Victor Bravo

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I LOVE your designation of the "SpeedFlea". Do you mind if I use it as a working name?
I'll tell you what. I will TRADE you the millions in intellectual property licensing that I am owed for the use of that brilliant name..... for the millions in intellectual property licensing that is payable to you for sharing your ideas, sketches, and participation on this forum with all of us :)
 

cluttonfred

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True, unless your design wingspan is constrained by, say, workshop or hangar size, in which case an equal span tandem gives you the most area for a given span and equal chords. Over the years I have sketched out a lot of designs intended to be built and stored in a space no larger than a 20’ ISO container. In that scenario, two one-piece, removable 18’ span wings start to look pretty good.

The 150% loading is why I prefer the fore wing to be larger, because then you're getting the most out of the wing area you have.
 

rotax618

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Oct 31, 2005
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Location
Evans Head Australia
If you could keep the span of both wings slightly less than 16’ by increasing the chord, you could use the Mignet folding wing hinge which would make rigging a simple one man job. Using the same chord and airfoil on both wings is a ‘no brainer’
 

Sockmonkey

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Apr 24, 2014
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Flint, Mi, USA
I like the idea of the fore wing having a central mast that can rotate, so you can unhook the side struts and turn the wing 90 degrees for storage.
 

rtfm

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Location
Brisbane, Australia
I'll tell you what. I will TRADE you the millions in intellectual property licensing that I am owed for the use of that brilliant name..... for the millions in intellectual property licensing that is payable to you for sharing your ideas, sketches, and participation on this forum with all of us :)
Ha ha. Nice one...
 
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