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 36.7%
  • A2 - Low wing forward, high wing aft (Quickie);

    Votes: 27 55.1%
  • B1 - Two-axis controls (no rudder pedals like an Ercoupe) OR

    Votes: 9 18.4%
  • B2 - Three-axis controls (with rudder pedals like a Cessna);

    Votes: 35 71.4%
  • C1 - Conventional (taildragger) gear OR

    Votes: 23 46.9%
  • C2 - Tricycle (nosewheel) gear;

    Votes: 21 42.9%
  • D1 - Tractor engine (engine and propeller at front) OR

    Votes: 33 67.3%
  • D2 - Pusher engine (engine and propeller at rear);

    Votes: 13 26.5%

  • Total voters
    49

Victor Bravo

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I think the core question is how far from the wing can a Junkers flap be mounted before the air treats it as a separate airfoil rather than part of the wing.
YES, that is what I was trying to bring up.

I mentioned that I do accept the idea that a deflected control surface changes the load on the airflow, making more lift and everything that goes along with it. That is the core of my question, is there a difference between aerodynamically effective AoA and geometric AoA?

Is the wing chord line a line between the leading edge of the wing and the trailing edge of the elevator on a Cessna? Is the chord line a line between the leading edge of the front wing of a Flea and the trailing edge of the rear wing?
 

cluttonfred

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I see what you mean and I don't have any numbers, but given the (sometimes negative) interactions experienced with lifting surfaces in tandem as well as biplanes, my gut says that any control surface or high-lift device actually attached to a wing is going to have these effects. The rule of thumb for biplane gap is that about 1.0 chord (of the larger of the two wings) is good, 1.5 chord gap is better. I don't think I have ever seen a Junkers surface mounted more than about one control surface chord below the wing, and definitely not one wing chord below.
 

Sockmonkey

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I see what you mean and I don't have any numbers, but given the (sometimes negative) interactions experienced with lifting surfaces in tandem as well as biplanes, my gut says that any control surface or high-lift device actually attached to a wing is going to have these effects. The rule of thumb for biplane gap is that about 1.0 chord (of the larger of the two wings) is good, 1.5 chord gap is better. I don't think I have ever seen a Junkers surface mounted more than about one control surface chord below the wing, and definitely not one wing chord below.
I remember that rule.
Biplane wings at least partially overlap horizontally, which affects that interaction and how far apart they need to be.
In a flea the rear wing is supposedly right in the spot where it gets hit by most of the downwash coming off the fore wing. There was some debate in another thread about exactly what was going on with flea wings so that description may not be very good.
A junkers flap with a tall and wide gap would be in a weird place aerodynamically it seems.
Little to no overlap, and it's getting hit mostly be the air from the bottom of the wing.


And now I'm just being excessive.

Monowheel main gear on this with little wheels at the delta tips..
 
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cluttonfred

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Umm, while I would agree that there is continuum from conventional monoplanes with lifting tails (big in front, little in back), tandems (wings of roughly equal size), and canards (little in front, back in back) and some designs can be hard to categorize, I would definitely call the Lockspeiser a canard. That does underscore how much lift you give up if you design a canard according to the 3:2 front:rear wing loading rule of thumb with identical front and rear airfoils and chords. For a proper canard I would be tempted to break that rule by using other methods to keep the main wing flying (or force the canard to stall first).

 
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Martin R.

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Umm, while I would agree that there is continuum from conventional monoplanes with lifting tails (big in front, little in back), tandems (wings of roughly equal size), and canards (little in front, back in back) and some designs can be hard to categorize, I would definitely call the Lockspeiser a canard. That does underscore how much lift you give up if build a canard according to the 3:2 front:rear wing loading rule of thumb with identical front and rear airfoils and chords. For a proper canard I would be tempted to break that rule by using other methods to keep the main wing flying (or force the canard to stall first).

In my opinion the classification in Canard or Tandem is irrelevant in this case. (The developers called it a Tandem).

Just look at the countless very interesting details of Lockspeisers projects . Especially in terms of simplicity:

 

rtfm

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Hi guys,
I'm not sure where to ask this, but since the Croses Flea has both been mentioned and pictures of it posted, this is probably as good a thread as any.
Would anyone like to hazard a guess on the construction of the single struts as used on the Croses Flea?
1621592473998.png
And, of course, on how they are attached below the skin?

Duncan
 

TFF

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My guess is it’s 4130 welded to 4130 just like a traditional biplane or parasol. Very nicely faired in. There is some tube evidence looking through the side windows. How much is it a tub or full steel fuselage would need to be inspected.
 

Sockmonkey

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My guess is it’s 4130 welded to 4130 just like a traditional biplane or parasol. Very nicely faired in. There is some tube evidence looking through the side windows. How much is it a tub or full steel fuselage would need to be inspected.
I bet they go all the way to the bottom and form part of the firewall frame.
 

cluttonfred

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I can't help on the construction of the masts on the CLP as it's a much-modified prototype composite design by the son of Emilien Croses and I don't really know the details. I think I have always assumed that the father's designs with the cantilever masts were using built-up wooden spars, but I honestly don't know.

PS--Here's a Croses LC-6 under construction and you can clearly see that the masts are made of wood.

 

rtfm

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Hi guys,
Fascinating. So basically a wing spar? As far as I can see, the angle of the masts preclude it reaching the bottom of the airframe. However - another question: is there any essential reason (other than tradition) that the masts have to attach to the hinge point? Could they not also (for example) attach half way along the span of the inner panel?

And why not use large streamline tubing?

Regards,
Duncan
 

cluttonfred

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There may be some confusion in this thread between two types of hinge point: 1) the wing incidence pivot points at the ends of the masts; and 2) the hinges that allow the outer wing panels to fold upward carrier-style for storage.

As to the spanwise location of those pivot points, for a one-piece, constant-chord wing theory would ideally be at the 1/4 and 3/4 span points of the whole wing (the center of each half span) but other considerations can change that.

I suspect that the cost of streamline tubing is quite high in France and a wooden solution is more attractive to a builder tackling a wooden airframe.
 

rtfm

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You are a mine of information mate. I agree with you regarding the wooden masts. I didn't know about the 1/4 chord being the optimal position. So that's great. Now I just have to figure out how to anchor the masts so they don't go flying off into the blue...
 
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