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Why not an upside down rudder?

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Michealvalentinsmith

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Also if I recall the Gossamer Condor used reverse warp much like a PG for roll/yaw.

I do remember something about the 2fl concept being adopted in a powered ultralight - I forget the name now. Later the high wing concept was abandon and it morphed into the Goldwing.

The concept of the high wing was to eliminate canard wake over the mainwing and to suspend the pilot low enough that weight shift was viable for pitch control. The diagrams show the pilot supine but the limited commercial version had the pilot rotate prone on a sliding board.

The idea was to reduce the inherent inefficiency of a canard in that the Cl max of the main wing is limited to a value below the canard - as the canard must stall first. (MaCCready avoided this by simply having the canard stall last - no big deal with such low wing loading and low altitude).

The idea was that with weight shift for pitch the canard could be set at a fixed value only slightly below the mainwing and remain constant since it wasn't required to move for pitch control.

There are some pilots who remain interested in the design who are continuing to research the concept.

The 2fl was recalled by the distributer - Butcher - and reincarnated as an ultralight. The canard was used for pitch and if I recall one version used a slotted canard. This would seem counter intuitive as it would really delay canard stall - but the canard was loaded such that it still stalled first.
 

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HumanPoweredDesigner

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That makes perfect sense. I would not have thought of that. The glider looks very fun to fly though. I saw some pictures of it before, but did not realize how small it is. I'll definitely use twin rudders and ailerons. I don't know if I should use a canard for higher wing loading and less drag, or if I should use a rear elevator to simplify the structure and have even greater front visibility.

A rear elevator in the shaddow of the main wing would lose most of its control, whereas the main wing in the shaddow of a canard would be just fine, especially with the ailerons so far outboard. I think the canard would be safer, but the rear elevator would be more fun to fly.
 

HumanPoweredDesigner

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Wow. You posted another great piece of info while I was posting.

If I shift my weight forwards, the nose goes down. If I shift my weight back, the nose goes up. I don't have to build candard flaps or rotate the canard. Very nice. Now You solved one of my problems. I still have to design the ailerons though. I don't think leaning left and right will be good enough on a high wing. It may work on a low wing.
 

Dan Thomas

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Dan I think what you alude to with the Sirroco is blanketing of the wing ROOT which is the same as extending a spoiler on the inside of the turn initiated by yawing. Spoilerons work similarly but I've yet to see them used as a sole means of roll control on any enduring design that has neither dihedral nor generous amounts of pendular stability, fly-by-wire excepted.
Nope. I was referring to the spanwise flow (toward the fuselage in the top, and away on the bottom) being altered in a skid or slip. In a skid, the flow will be disrupted so that the vortex on the outside will be diminished and lift will increase on that tip.

Dan
 

Culleningus

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Hi Dan
I think you'll find that to expect this effect to work nearing the deck would be a millisecond, and a centimeter too long.

Jurcas huge fins in the normal upright erection work well with the wing upper surface blanketing I described to you above. If the rudder was inverted at low power settings and therefore less propwash the a/c would almost certainly spin without aileron input.
 

Culleningus

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Nope. I was referring to the spanwise flow (toward the fuselage in the top, and away on the bottom) being altered in a skid or slip. In a skid, the flow will be disrupted so that the vortex on the outside will be diminished and lift will increase on that tip.

Dan
Dan T.
Ive put some thought into what you've just said above and I'm afraid I really dont buy that explanation.
Yes swept wings tend to have better Yaw stability for the reason you cite (the lagging wing tip has a relatively smaller tip vortex).
But this type of drag (induced drag) acts perpendicular to the rolling plane.
Therefore I stick to my guns that its a slab-sided fusalage coupled to a low wing configuaration which is responsible for a rudder induced roll, where there are no ailerons, dihedral, or pendulum stability present.
 

Dana

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Wow. You posted another great piece of info while I was posting.

If I shift my weight forwards, the nose goes down. If I shift my weight back, the nose goes up. I don't have to build candard flaps or rotate the canard. Very nice. Now You solved one of my problems. I still have to design the ailerons though. I don't think leaning left and right will be good enough on a high wing. It may work on a low wing.
No. There's a reason why people don't build weight shift powered aircraft like that any more. Shifting just your body weight is not suffiient for safe control. I learned this the hard way after restoring an old weightshift Quicksilver a few years ago. The only weight shift aircraft still being made today are the trikes, where everything but the wing is shifted.

-Dana

Politicians are those who deal with the problems which would not exist if they didn't exist.
 

Michealvalentinsmith

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Yeah - What Dana said. I forget the numbers now but the weight shifted must be a significant portion of the total weight to be effective in pitch, for roll the lever arm is usually too long to work without augmentation - HGs use billow shift.

Even if so there are also limitations on the static margin. I know of one designer at least that made a tailed, footlaunched HG controlled in pitch by weight shift and found the wing quite resistant to pitch input by weight shift with limitations on the acceleration and flare.

As such you need to keep the static margin below a typical amount - I can't give you actual numbers - I'm not sure there are any - it's found by trial and error. But it likely calls for short lever arms and reduced tail volumes. When you close couple a tail that much you may as well use a flying wing.

Given that it does seem the canard 2 fl was controlled adequately well in pitch by weight shift. But note the very low CG to increase pendulum effect. I have seen videos of tailed HPVs in Japanese competitions where the pilot is clearly weight shifting for pitch - but the responses are far from dynamic.

If you don't use an overhead hang point you also introduce the problem of control return. Say you use a sliding board and shift forward, the wing pitches down, let go and you fall forward pitching the wing down etc. You want pitch return to neutral hands off.

It's preliminary yet but I think this can be achieved with rollers in a curved track to simulate an overhead hang point.
 

Dana

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... have seen videos of tailed HPVs in Japanese competitions where the pilot is clearly weight shifting for pitch - but the responses are far from dynamic.
You might get away with it in something like that, but anything light enough to be an HPV will only be flown in dead calm conditions anyway. This is why ultralights used to be flown only in very light winds... and is why when FAR 103 was written, they allowed UL's to fly a half hour before sunrise and a half hour past sunnset.

The Quicksilver I restored used pure weightshift for pitch and weightshift and rudder (the rudder was controlled by the swinging of the seat) for roll/yaw. The breeze picked up while I was flying it, and on final approach i got into a situation where I needed full power (which with the high engine pushes the nose down) at the same time that I needed to get the nose up. It didn't end well:



Later, Eipper added a "trimavator" which was also linked to the swing seat, but it was a last desperate attempt to keep the weightshift control before they did the right thing and eliminated it completely.

Me, I sold the wreck for parts and bought a plane with proper controls.

-Dana

The dinosours died because they didn't have a space program!
 

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FlyGood

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My advice: don't use anything forward of the cg to provide directional control. It is destabilizing in yaw and will give you a hard to fly airplane. To make a forward rudder, or "banked" canard work, there will need to be an aft vertical fin for directional stability, adding to your designs complexity and weight.

Having the rudder attached to the (aft) vertical fin gives the most efficient structure for generating side force in a subsonic airplane.

The rolling moment due to rudder deflection is very small compared to the roll due to sideslip created by rudder deflection, so I would ignore the contribution and design the fin/rudder to best fit your needs. Don't forget you NEED an airplane that is easy to fly.

The discussion about airfoil pitching moment should not be ignored. Yes you can design the machine to have a high CL airfoil, but the attendant high pitching moment will result in a bigger canard (more drag) and a lot of trim change with speed change (less fun to fly). Work hard to find an airfoil with adequate CL, and a "flat" pitching moment variation with airspeed, and you'll come up with an overall package, wing and canard, that gives good efficiency and ease of pitch control.

I like the way you strive for innovative efficiency, but pay attention to stability and control: If it is bad, you won't enjoy flying your innovative design.
 

Michealvalentinsmith

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I think Paul MacCready got away with a forward "rudder" in a RC model simulation of a pterasaur where it was assumed the big bone on the head had the same function. I know it took quite a bit of fly by wire computer control to fly.

There was a guy who did quite a bit of work on rolling canards in hang gliders and seem to have got then to work.

The destabilizing effect is real and likely what happened in the 2 fl - it yaws, you roll the canard to correct and it now presents a negative AofA to the airflow so it yaws further in the opposite direction.

You'll note Gary's solution in allowing the canard to hinge and float freely in pitch was workable. Gary has a lot of experience in sailplane design - so I respect his opinion. He thinks he has a workable design based on the 2 fl that should be quite impressive - but he's reluctant to elaborate.
 

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Michealvalentinsmith

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You might get away with it in something like that, but anything light enough to be an HPV will only be flown in dead calm conditions anyway. This is why ultralights used to be flown only in very light winds... and is why when FAR 103 was written, they allowed UL's to fly a half hour before sunrise and a half hour past sunnset.

The Quicksilver I restored used pure weightshift for pitch and weightshift and rudder (the rudder was controlled by the swinging of the seat) for roll/yaw. The breeze picked up while I was flying it, and on final approach i got into a situation where I needed full power (which with the high engine pushes the nose down) at the same time that I needed to get the nose up. It didn't end well:

Later, Eipper added a "trimavator" which was also linked to the swing seat, but it was a last desperate attempt to keep the weightshift control before they did the right thing and eliminated it completely.

Me, I sold the wreck for parts and bought a plane with proper controls.

-Dana

The dinosours died because they didn't have a space program!

I had a fly of a friends Quicksilver many years back. He's meticulous and maintains it in immaculate condition but it was old even then. It's the one with rudder peddles to the rudder and the stick linked to spoilerons - and is still single surface.

I found it strange to fly, and got more roll with the rudder than the spoilerons, so I found myself flying much like a sailplane - where you put in a bootful of rudder with the stick. But high siding with the stick gives you nothing at first until it kicks in then it's full on. It a bit like skid turning a bobcat and I can see why they went with ailerons later.

I got bounced around a bit in light turbulence and couldn't imagine trying to fly it with weight shift. I can see why trikes have become so popular. The control is much better, they handle turbulence way better and they are much more portable with better performance than most tailed ultralights.

I see you can get an older Quicksilver now with every roll of film you get developed at the pharmacy. Many don't sell for much more than the motor and prop would cost second hand. Trikes seem to be holding their value though.

I note the 4 sets of upper and lower side wires - must have been a ton of drag - but it makes you wonder how some seem to think they can get away with none.
 

B52

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Working on a canard design with tween inverted rudders which also house the main wheels.. I am looking for a set of wheels 400mm (16") outer diameter, width under 100mm (4") including brake assembly, maximum takeoff weight 1 Tone.

any advise input appreciated.
 

BJC

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... it looks as if the wings had considerable washin. I don't think they really did.
It might be the combination of camera angle, the tapered planform, and the wing tip that make it look like it has washin. Lots of photos seem to indicate a wing without twist. cfm shadow aircraft


BJC
 
M

Manticore

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It might be the combination of camera angle, the tapered planform, and the wing tip that make it look like it has washin. Lots of photos seem to indicate a wing without twist. cfm shadow aircraft


BJC
Looking at the 3-view it seems to be mainly the wingtips that give the illusion. Also looks as if the ailerons might be set to a negative angle to give some effective washout.
Screenshot_2015-09-14_23-08-06.png
 

Aesquire

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Working on a canard design with tween inverted rudders which also house the main wheels.. I am looking for a set of wheels 400mm (16") outer diameter, width under 100mm (4") including brake assembly, maximum takeoff weight 1 Tone.

any advise input appreciated.
Bicycle wheels won't take the weight. Or the side loads.

Find a local Motorcycle shop that laces wheels custom. ( The guys at the closest shop will know who does the good work. ) Any top notch Bicycle mechanic who assembles wheels can advise as to the math on spoke lengths, offsets, etc. There are books on the subject.

Your problem is the side loads on a narrow hub. Are your twin inverted rudders going to be vertical on the ground or at an angle. If they are at an angle you offset the hub to take the side loads and use a disc brake. You may need to run drum brakes. to get adequate strength, as that maximizes hub width in the space available. Hope that helps, sorry if any is unclear.

Also, consider Honda "comstar" wheels used on 1970's-1980's Honda motorcycles. It's a riveted construction wheel and tougher on impacts than cast wheels.

Motorcycle wheels are going to be fairly heavy, that's a downside.
 

DangerZone

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Working on a canard design with tween inverted rudders which also house the main wheels.. I am looking for a set of wheels 400mm (16") outer diameter, width under 100mm (4") including brake assembly, maximum takeoff weight 1 Tone.

any advise input appreciated.
Will you be landing on paved runways or grass runways? Canards usually TO/land at higher speeds so a strong set of wheels would be needed for grass runways.

There are 50ccm/80ccm/100ccm motocross bikes which have the rear wheel of a similar diameter to what you seem to be looking for. They can take quite a lot of loads, hits and bumps, there are spoked wheel versions and full metal steel wheels. If you intend to land on a paved runway, maybe some of the larger scooter wheels could be good for you. The Mini and Fiat/Abarth also had some small diameter racing wheels which could withstand a ton, it is worth checking out at a local junkyard.

It might be wise to check everywheel before use cause a ton is quite a load. Some of those wheels are tested to 4 to 5 times the loads they usually endure during racing but some others might not be, some can even be pure junk like the cheap Chinese bikes from the early 2000s sold worldwide.
 

Hugh Lorimer

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Will you be landing on paved runways or grass runways? Canards usually TO/land at higher speeds so a strong set of wheels would be needed for grass runways. Using an all flying canard gave me a slower T/O and a nice flare on landing on my Iolaire. Hughie.
 
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