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

cluttonfred

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A 7' center section with, say, 5' outer panels works perfectly for Mignet-style upward-folding wings *if* you are talking about a two-axis machine with pitch by variable front wing incidence, in other words a true Pou-du-Ciel. It could also work well on a two-axis machine with a fixed incidence front wing and a large elevator on only the front wing center section, perhaps even extending beyond the normal trailing edge to get more area for control, sort of a hybrid between a Pou-du-Ciel and an Lacroix Autoplan. Ditto if you move the pitch control to the rear wing with either variable incidence or a center section elevator. Once you introduce ailerons or any other control surfaces outboard of the hinges, however, things get more complicated.

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’
That works if you have a long narrow storage space and/or a long trailer but you run into problems if you are limited to a specific length like a 20' container or a single-car garage (typically 12/14/16' wide and 22/24' long in the 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.
 

cluttonfred

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Just for fun, here is what I get when I mess around with the idea of an 65 hp VW-powered equal-area tandem using the proven NACA 23112 airfoil. That gives a max CL of about 1.5 but due to the 150% front wing loading bias I dropped the CL to 1.25 to reflect the rear wing never getting to make more than about 1.0. Keeping the span limited to 18' to build and store one-piece wing panels in a 20' container works well for a single-seater but for a two-seater the low-aspect ratio and high span loading result in a low climb rate and high power-off sink rate. Even the single-seater comes down pretty fast power off. Note that I have increaded parasitic drag by 50% over the spreadsheet directions as I think the indicated figure is exceptionally slippery and not reflective of a simple homebuilt. This spreadsheet also treats everything as a simple monoplane, so it thinks I have a single 18' span and 8' chord wing, hopefully a tandem with two 18' span wings of 4' chord would do a little better.

PRELIMINARY PERFORMANCE ESTIMATE FOR PROPELLER DRIVEN AIRCRAFT
Crew weight200lbs
Fuel + baggage weight100lbs
A/C empty weight400lbs
Total weight700lbs
Stall speed (flaps up) Vs138.98mph
Climb airspeed50.674mph(climb speed = 1.3 x stall speed)
Climb airspeed74.3ft/sec
CLmax1.25(flaps up)
CL at 1.3 Vs0.74(at 1.3 Vs, CL = CLmax x (1/1.3²))
Wing area required144.0ft²(L=1/2 rho V² S CL)
Propeller efficiency at take-off7070%
Propeller efficiency in the climb7575%
Propeller efficiency in the cruise8585%
Cd (profile)0.010.01
Cd (parasite)0.02250.015(Speeds between 1.1 Vs and 2.7 Vs)
Aspect ratio2.25
Induced drag factor K1.2(Cd (induced) = K CL²/π A)
(K = 1.0 elliptical wing, 1.1 moderately tapered, 1.2 rectangular)
Wing span18.0feet
Mean wing chord8.00feet
ESTIMATED PERFORMANCE WITH AN ENGINE OF YOUR PROPOSED RATED POWER
Selected rated shaft power65.0BHP
Effective flat plate area5.40ft²
Take off run218feet
Rate of climb at 1.3 Vs1542feet per minute
Max level speed114mph
Cruise speed at 75% power103mph
Flaps up stall speed38.98mph
Glide descent rate at 1.3 Vs756feet per minute
 
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cluttonfred

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And here's what I get for a 80 hp (Aerovee, Revmaster) VW-powered two-seater with the span pushed out to 24', not bad at all for a fun flier with decent climb two-up on a VW. This gross weight is on par with an Evans VP-2, for example, and it should perform quite a bit better. This cold be for a low-wing forward design like the Mauboussin Hémiptère or for a clean and neat Pou-du-Ceil or Autoplan type. Obviously you could reduce the wing area to get more speed, but I prefer favoring climb rate and power-off descent and for that you need lots of wing area.

PRELIMINARY PERFORMANCE ESTIMATE FOR PROPELLER DRIVEN AIRCRAFT
Crew weight400lbs
Fuel + baggage weight50lbs
A/C empty weight600lbs
Total weight1050lbs
Stall speed (flaps up) Vs141.34mph
Climb airspeed53.742mph(climb speed = 1.3 x stall speed)
Climb airspeed78.8ft/sec
CLmax1.25(flaps up)
CL at 1.3 Vs0.74(at 1.3 Vs, CL = CLmax x (1/1.3²))
Wing area required192.0ft²(L=1/2 rho V² S CL)
Propeller efficiency at take-off7070%
Propeller efficiency in the climb7575%
Propeller efficiency in the cruise8585%
Cd (profile)0.010.01
Cd (parasite)0.02250.015(Speeds between 1.1 Vs and 2.7 Vs)
Aspect ratio3
Induced drag factor K1.2(Cd (induced) = K CL²/π A)
(K = 1.0 elliptical wing, 1.1 moderately tapered, 1.2 rectangular)
Wing span24.0feet
Mean wing chord8.00feet
ESTIMATED PERFORMANCE WITH AN ENGINE OF YOUR PROPOSED RATED POWER
Selected rated shaft power80.0BHP
Effective flat plate area6.96ft²
Take off run298feet
Rate of climb at 1.3 Vs1232feet per minute
Max level speed112mph
Cruise speed at 75% power102mph
Flaps up stall speed41.34mph
Glide descent rate at 1.3 Vs653feet per minute
 

cluttonfred

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On second thought, I may have dropped the stall speed too low for that last one. Keeping the same 24' span but dropping the wing chords to 3' would raise the "stall" speed to 48 mph but increase cruise by more than 10%. I think I like that balance better.

PRELIMINARY PERFORMANCE ESTIMATE FOR PROPELLER DRIVEN AIRCRAFT
Crew weight400lbs
Fuel + baggage weight50lbs
A/C empty weight600lbs
Total weight1050lbs
Stall speed (flaps up) Vs147.74mph
Climb airspeed62.062mph(climb speed = 1.3 x stall speed)
Climb airspeed91.0ft/sec
CLmax1.25(flaps up)
CL at 1.3 Vs0.74(at 1.3 Vs, CL = CLmax x (1/1.3²))
Wing area required144.0ft²(L=1/2 rho V² S CL)
Propeller efficiency at take-off7070%
Propeller efficiency in the climb7575%
Propeller efficiency in the cruise8585%
Cd (profile)0.010.01
Cd (parasite)0.02250.015(Speeds between 1.1 Vs and 2.7 Vs)
Aspect ratio4
Induced drag factor K1.2(Cd (induced) = K CL²/π A)
(K = 1.0 elliptical wing, 1.1 moderately tapered, 1.2 rectangular)
Wing span24.0feet
Mean wing chord6.00feet
ESTIMATED PERFORMANCE WITH AN ENGINE OF YOUR PROPOSED RATED POWER
Selected rated shaft power80.0BHP
Effective flat plate area5.08ft²
Take off run398feet
Rate of climb at 1.3 Vs1260feet per minute
Max level speed124mph
Cruise speed at 75% power113mph
Flaps up stall speed47.74mph
Glide descent rate at 1.3 Vs626feet per minute
 

cluttonfred

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That’s very cool, Mike! When I have sketched that sort of layout I have always concluded that there would be visibility issues, especially in the flare. Why didn’t you pursue that design?
 

rotax618

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Mike W’s tandem would be better if you lowered the front wing, merged the two wings into one plank of say 18’ span, 10’ chord with 5’ outboard sections folding up. Makes everything simpler.
 

Sockmonkey

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Mike W’s tandem would be better if you lowered the front wing, merged the two wings into one plank of say 18’ span, 10’ chord with 5’ outboard sections folding up. Makes everything simpler.
That would be the Arup S2.

Or the Hatfield Little Bird.
 
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Groundhog Gravy

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A 7' center section with, say, 5' outer panels works perfectly for Mignet-style upward-folding wings *if* you are talking about a two-axis machine with pitch by variable front wing incidence, in other words a true Pou-du-Ciel. It could also work well on a two-axis machine with a fixed incidence front wing and a large elevator on only the front wing center section, perhaps ...
If you used Daniel Dalby's approach to three-axis control and had separately-rotating halves of the front wing, it seems to me you could still make use of the Mignet style folding wings, because there's no cables or hinges running through that part of the wing.
 

cluttonfred

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That’s an interesting idea, but if used on the front wing I’d be worried about stall behavior when the stick is to the left or right and on the rear wing I don’t know if there would be enough control authority due to the reduced wing loading.

If you used Daniel Dalby's approach to three-axis control and had separately-rotating halves of the front wing, it seems to me you could still make use of the Mignet style folding wings, because there's no cables or hinges running through that part of the wing.
 

Groundhog Gravy

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... I’d be worried about stall behavior when the stick is to the left or right ....
That strikes me as equally true of any three-axis Flea. Stalled left front wing, unstalled right front, unstalled rear wing is a combination I'd have to think through carefully. I'd be more concerned about having too much travel in the same idea applied to the rear wing, though; flying front wing with half-stalled rear wing sounds like a bad time.
 

Sockmonkey

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With separately rotating halves, If you're willing to go with two-axis (pitch and roll) the tail section can be a completely passive structure with no control runs that could be unplugged from the front section of the fuselage for storage.

The disconnect point is just ahead of the seat. The tip fins are non-moving and only for yaw stability.
 

cluttonfred

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That's an interesting concept, Sockmonkey, and not unlike what I was describing with elevons on the front wing (though I was still going to have a conventional rudder). The question is what happens if you stall the front wing in a turn so only one half stalls? That seems like a possible stall-spin scenario.

Groundhog Gravy, I agree to a point, but then the most successful three-axis Flying Flea-like planes were the Lacroix Autoplan series with pitch control from the rear wing and roll from the front. If using roll control from the rear there is definitely something to worry about in terms of a hard roll input at low speed stalling half of the rear wing, but I think that could be prevented through limits to the degree of movement. I believe Daniel Dalby's designs actually have just a few degrees of travel, you don't need much when the whole wing half is serving as an aileron.
 
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Mike W

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Hot Flea.

About this time I left home and went to work at Westland Helicopters and indulged in other pursuits that a young lad gets up to. So building an aircraft went on the back burner for several years.

The design was influenced by the sexy formula 1 racers about such as the Cassutt.

The forward view is probably no worse than many other taildraggers and could be improved.

I did wonder about using the front wings differentially as ailerons, but as you say stall spin problems could occur. A test model would be advisable.

The Aviasud Mistral aircraft used the lower wings differentially for roll control, They were fitted with anti balance tabs. I once had a flight in the Mistral and from memory the stick moved sideways without much roll effect, then suddenly grabbed and rolled. It felt a bit odd initially.

Mike

mistral.jpg
 

rtfm

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Hi,
So far you have all talked about 3-axis Fleas in terms of stalling one half of the wing because of either ailerons or from pivoting the wings differentially. A neat solution would be to use Junkers ailerons.

The Fleabike will have (eventually, once full testing in "standard" form has been completed) Junkers ailerons on the inner section of the rear wing (for ease of building). Deploying the Junkers ailerons does not affect the wing to which it is attached. No stalls.

Duncan
 
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