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Author Topic: Mid engine canard  (Read 9840 times)

Offline jimmyy

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Re: Mid engine canard
« Reply #50 on: April 25, 2017, 01:31:36 AM »
design is good.

Offline jim gilmore

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Re: Mid engine canard
« Reply #51 on: April 25, 2017, 10:19:31 AM »
This in fact a funny topic for what the subject is...STUNT DESIGN.
The actual reason I say this is that stunt is basically something that require the airplane to be naturally unstable. An airplane that is designed to be rock streast stabe will by nature be hard to make unstable for stunts.
If you look at what a canard airplane itself does, and how stability is achieved you may notice why when power is cut it become difficult to do more than just land.
The design is such that the front control surface will stall long before the main wing so it will not as an airplane fall from the sky. when under power you might well be able to do stunts if the airplane has enough power to keep the speed up to prevent the front control surface from stalling and the airplane be pulled through the maneuver. When the engine cuts out as in our models there will not be additional power to pull the plane through maneuvers and the front surface will stall.
In a conventional setup remember that when the engine quits the tail plane does not need to provide lift in the same way. IT actually need to loose lift and provide a downward force to make the plane go up! To come in for a landing it would make a slight amount of life pointing the plane towards the ground and actually speed up the airplane doing so.
This may not all seem intuitive but it is the basic design of the canard.

Offline Chuck_Smith

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Re: Mid engine canard
« Reply #52 on: April 29, 2017, 05:42:16 AM »
This in fact a funny topic for what the subject is...STUNT DESIGN.
The actual reason I say this is that stunt is basically something that require the airplane to be naturally unstable. An airplane that is designed to be rock streast stabe will by nature be hard to make unstable for stunts.
If you look at what a canard airplane itself does, and how stability is achieved you may notice why when power is cut it become difficult to do more than just land.
The design is such that the front control surface will stall long before the main wing so it will not as an airplane fall from the sky. when under power you might well be able to do stunts if the airplane has enough power to keep the speed up to prevent the front control surface from stalling and the airplane be pulled through the maneuver. When the engine cuts out as in our models there will not be additional power to pull the plane through maneuvers and the front surface will stall.
In a conventional setup remember that when the engine quits the tail plane does not need to provide lift in the same way. IT actually need to loose lift and provide a downward force to make the plane go up! To come in for a landing it would make a slight amount of life pointing the plane towards the ground and actually speed up the airplane doing so.
This may not all seem intuitive but it is the basic design of the canard.


Well, an aircraft can be stable and maneuverable at the same time. In fact, if it's unstable it will be pretty darned hard to fly.

Second, the canard won't necessarily stall before the main wing. Unless the main wing and the canard have the same aspect ratio their effective angles-of-attack won't be the same. If the main wing has a higher aspect ratio than that of the canard, it will stall before the canard does. A stalled control surface can mean no stall recovery. A canard that stalls before the main wing would also make landings rather exciting, to say the least.

Lot's of the aero "lore" surrounding canards is, shall we say, "Popular Science" engineering.  Canards make terrible aircraft. If they were so safe, maneuverable and efficient as some people would like you to believe they would be ubiquitous, since aerospace engineering has lots to do with optimization and getting the most efficient use of available thrust specific fuel consumption.  Last time I was at the airport, I didn't see single canard.

Last time I saw a no-holds-barred Gen6 fighter design, the movable surfaces where in the back.

Canards *may* have some value in compressible flow regime "wave rider" designs, but the concept of a SST has been proven to be not viable and as stated, that's in compressible flow and only for going like a bat-out-of-Hell in a straight line.

Chuck
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Offline Serge_Krauss

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Re: Mid engine canard
« Reply #53 on: April 29, 2017, 09:27:15 AM »
The fore surface must stall first in order for an aircraft to be able to recover from a stall. This does not make a model into a "lawn dart." The only problem with the canard configuration is that it cannot be as efficient as a conventional configuration, and this relates to that first fact. Since it must stall after the canard surface, the "main" wing cannot be allowed to reach it's full lifting potential. On top of that, the wake from a canard surface generally reduces the main wing efficiency more. So one might expect the canard stunter nearing its stall ultimately to "understeer" or "push" like some ill-handling racing cars or what is encountered in over-driven front-drive cars, especially those engineered (so I'm told) for the American market. When the canard stalls, all that happens is that lift decreases greatly, and the AoA lessens until full lift is restored.

Stanford's Illan Kroo has written more about Canards, but this report about covers it: Excerpts from "Non-Planar Wing Concepts for Increased Aircraft Efficiency":  http://aero.stanford.edu/Reports/MultOp/multop.html  In it you will also see that, except when they are at neutral stability, canards are less aerodynamically efficient than aft-tailed planes.

The graph below illustrates that maximum lift coefficient occurs when the aft wing is 20% to 40% of the span of the fore wing, making it a tail. The second illustration is my clarification of what this graph means, for anyone having trouble reading the graph. Incidentally these and more have been posted previously.

Offline jim gilmore

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Re: Mid engine canard
« Reply #54 on: April 29, 2017, 01:01:49 PM »
In regards to your comment (Chuck) I think about an unstable plane being hag to fly.
I guess it comes down the definiton of stable....
An aircraft meant to fly safely from point a to point b may well be stable flying upright with out flipping over or inverting and be considered to be stable......Give full up and the plane may resist going into a steep climb and looping....is that stable.....given a canard... doing the same thing the foreplane stalls and the plane flys straight ahead...Is it still stable.... ?
Now take a conventional plane give full up the the front main wing stalls and the plane falls and loses 1000 or more feet. Stability is questionable ....defined by what one expects the plane to be used for.
Yes in the context of stunt stability means something different than just flying safely and upright....
In regards to most control line models if you move the cg rearward you get a more unstable flight, and if you move it forward you get an over stable flight that will dive on loss of power and be hard to make go up with power.
A totally stable aircraft cannot actually stunt if we define stability as a airplane that resists being put into unsafe (maneuvers ).



Offline john e. holliday

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Re: Mid engine canard
« Reply #55 on: April 30, 2017, 07:48:52 PM »
Hey guys, I still have my Blue Goose and the Canard Ringmaster.  Once I get healed up , will have to get them out again and flying.   Same with a couple dozen other planes I have.
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Offline Serge_Krauss

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Re: Mid engine canard
« Reply #56 on: May 01, 2017, 07:35:39 AM »
As I understand it, stability is a measure of a planes tendency to return to it's previous flight direction when dislodged, in this case, pitched. You  need some of that tendency in order to control  the plane smoothly - unless you have a computer and appropriate sensors for it to react to divergent behavior instantaneously and proportionately. Neutral stability is still not good enough for us, since that would demand that we have incredible reflexes and placement of the handle. All pitch directions would be entirely our doing by simple hand placement, with no help from the plane. We really need a restoring force to work against. You're right, unreasonable stability would keep us from controlling the plane at all too.

The Wright brothers "Flyer" was deliberately "control configured" as a reaction to what happened to Lillienthal, when lack of control authority cost him his life. So they deliberately made it only marginally stable. The Flyer was a real hand-full to control, and the Wrights taught themselves not only to be the first pilots but to be expert pilots. From what I've read, Bob Baron must have excelled at flying closer to the edge too.

We all have our preferences in static "stability," how "lively" the plane is at the end of the lines. Canards and conventional aft-tail designs can each have the stability one desires. The problem with canards is that in order for them to have their best efficiencies and maximum lift coefficients, they must be about neutrally "stable," which just won't do in CL or anywhere else without computers. In fact, CL planes typically have significantly greater static margins (distance between c.g. and aerodynamic center) than R/C and full-sized planes. The FF guys have the furthest aft c.g.'s of all So we will have to stunt with canards that just cannot produce the maximum performance of the best conventional stunters.

Offline Avaiojet

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Re: Mid engine canard
« Reply #57 on: May 01, 2017, 07:46:41 AM »
Photos of the design?

CB
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Offline Brett Buck

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Re: Mid engine canard
« Reply #58 on: May 01, 2017, 02:06:01 PM »
Yes in the context of stunt stability means something different than just flying safely and upright...

  Correct. Until Paul Walker came along, people thought that maneuverability and stability were two mutually-exclusive  items. But modern stunt planes are extremely stable and highly maneuverable. In fact, Chuck is exactly correct that you have to have a very stable airplane to successfully fly stunt.

    The original purpose of large tails and tail volume coefficient was to permit far-forward CGs (by creating an unstoppable force (torque from the tail) to overcome an immovable object (tons of noseweight).) And this works fine, as long as your right forearm looks like Popeye. But you can also use the larger tail to permit further-aft CGs without losing stability, and as long as it is perfectly in trim, you can sit there with neutral elevator and watch it fly itself along like it was rolling on a pool table.

     Brett
« Last Edit: May 02, 2017, 08:00:42 PM by Brett Buck »

Offline Ted Fancher

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Re: Mid engine canard
« Reply #59 on: May 02, 2017, 05:56:25 PM »
  Correct. Until Paul Walker came along, people thought that maneuverability and stability were two independent items. But modern stunt planes are extremely stable and highly maneuverable. In fact, Chuck is exactly correct that you have to have a very stable airplane to successfully fly stunt.

    The original purpose of large tails and tail volume coefficient was to permit far-forward CGs (by creating an unstoppable force (torque from the tail) to overcome an immovable object (tons of noseweight).) And this works fine, as long as your right forearm looks like Popeye. But you can also use the larger tail to permit further-aft CGs without losing stability, and as long as it is perfectly in trim, you can sit there with neutral elevator and watch it fly itself along like it was rolling on a pool table.

     Brett

In addition:  The "Popeye" mode is wisely out of favor because a stunter with the CG well forward of where it needs to be for stability suffers greatly when flying in the wind.  As the aircraft is accelerated by the wind in maneuvers the forward CG (forward of the CP) attempts to open up the corner/loop and requires even greater pitch input to obtain/maintain the pitch change required to fly our tricks...every bit of which exacerbates the problem and demands even more control input. Thus the ever growing loops and the attempt by the plane to land firmly at 75 or 80MPH despite hanging on the up line!  With the larger tail allowing the CG to be located consistent with the CP that increased "pitching moment" is mostly mitigated and the airplane response rate is very modestly affected.  That's why guys like David, Paul, Derek,  Brett etc. etc. (you know, the guys that win the big trophies) do so all the time.

Ted

Offline Brett Buck

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Re: Mid engine canard
« Reply #60 on: May 02, 2017, 08:08:58 PM »
Thus the ever growing loops and the attempt by the plane to land firmly at 75 or 80MPH despite hanging on the up line! 


  Which also leads to the other issue with these era designs - you had to trim them to "manufacture" an immense amount of line tension, because otherwise, you will run into the Netzeband wall. So you end up with a bunch of goofy trim techniques that get the necessary line tension* that make it difficult to fly the rest of  the time. Also continually changing everything in the trim and engine to find the optimum "balance" between these various opposing forces for the conditions of the day/hour.

   Now, you just don't have to screw around with all this stuff continuously just to get it to work. You set it up properly once, then make very small changes from day to day, and don't really worry about line tension. Centrifugal force is plenty enough.

    Brett

*note that speed doesn't help this problem at all - going faster increases the line tension, but it also increases the loads, so you never get ahead. Hence the Tucker ballast experiment.

Offline Steve Thomas

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Re: Mid engine canard
« Reply #61 on: May 06, 2017, 06:01:35 AM »
It's all just too far canard.

Offline Serge_Krauss

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Re: Mid engine canard
« Reply #62 on: May 06, 2017, 10:36:40 AM »
Ha, ha, ha, ha, ha, ...!!!! That's just TOO good!

Offline Chris Wilson

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Re: Mid engine canard
« Reply #63 on: May 06, 2017, 11:37:57 PM »
Canardly wait for Steve's next reply!
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Offline Avaiojet

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Re: Mid engine canard
« Reply #64 on: May 15, 2017, 07:43:33 AM »
Nice colors.
Alpha Mike Foxtrot.

Owner of CFC Graphics. "Model Airplane Graphics from a Model Airplane Builder."

"No one has ever made a difference by being like everyone else."

Marcus Cordeiro, The "Mark of Excellence," you will not be forgotten.

I look at the Forum as a place to contribute and make friends, some view it as a Realm where they could be King.

"Ya gotta love it when a plane comes together."

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Offline Chris Wilson

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Re: Mid engine canard
« Reply #65 on: May 16, 2017, 12:03:48 AM »
On top of that, the wake from a canard surface generally reduces the main wing efficiency more.

Hi Serge,
                  If this is a mid engine canard would not the accelerated air stream from the prop that shares pretty much the same wake counter this nicely?
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Offline Serge_Krauss

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Re: Mid engine canard
« Reply #66 on: May 22, 2017, 10:12:45 PM »
'sorry, I haven't been by here recently. I think putting the main wing in the direct (close) prop wake would complicate matters, but the wing still needs to stall after the canard. The wakes from the prop and canard won't be nearly full-span anyway. So whatever is done to achieve that needed stall sequence should still compromise the main wing. There's still the Custer channel wing though...That (blown wing) would be sort of a "different animal" though.

SK

Offline john e. holliday

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Re: Mid engine canard
« Reply #67 on: May 23, 2017, 01:44:31 PM »
From experience with out the movable surface on the trailing edge of the main, the plane will go nose down even with the control deflection on the front moving surface.  That is why a skid is being added to front canard to keep nose up until air speed is arraigned for the moving surface to take effect.  I have plenty of witnesses to that and is why it has been hand launched like the old days with a running start.   The Sarpolous design has enough moving surface on main wing to counter act that.   Even then some times it get up on the nose until air speed is attained.
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Offline Howard Rush

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Re: Mid engine canard
« Reply #68 on: May 23, 2017, 02:14:03 PM »
I think Wolfgang's configuration with the prop ahead of the canard is good.  Blowing on the canard lets it get the lift it needs to pitch the wing with minimal area, which reduces the (statically destabilizing) pitching moment due to angle of attack of the canard.  I suspect that the air blowing on the canard also reduces the change in canard angle of attack with wing angle of attack, also helping static stability.  

Who cares which surface stalls first in a stunt plane?  You want to operate a stunt plane away from the regime where it's nonlinear and unpredictable.   Wolfgang's landing problem is worth the benefit he gets while the engine is running.  Landings aren't worth much in F2B anyhow.  

Electric power would be an advantage for both the prop-behind-the-canard configuration (you don't have to flip the prop to start the engine) and the prop-ahead-of-the-canard configuration (you can locate the battery to get the CG where you want it).  That Wolfgang did this with an IC engine is impressive.
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Offline Wolfgang Nieuwkamp

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Re: Mid engine canard
« Reply #69 on: May 24, 2017, 02:56:06 PM »
Howards comment is correct, the canard is very effective, as long as the (electric) motor runs. But the landing speed is too high, so I changed to a lighter motor. Hope to fly next week.


Offline Chris Wilson

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Re: Mid engine canard
« Reply #70 on: May 24, 2017, 05:15:17 PM »
I do not know much about electric motor controllers in stunt but if the canard responds better to an accelarated airflow would it be possible to have a low power 'idle' speed kick in after the schedule is finished  that is just enough to provide some assistance just like full size aircraft do?

Or is there some rule against that in F2B?
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Offline Wolfgang Nieuwkamp

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Re: Mid engine canard
« Reply #71 on: May 26, 2017, 05:25:13 AM »
Chris,
Thanks for the good idea. F2B requires that the judges can see when the landing maneuver begins. I will modify my timer so that after stopping, the motor will run again for 5 seconds. If it works, letīs see how the judges comment.

Regards,

Wolfgang

Offline Brett Buck

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Re: Mid engine canard
« Reply #72 on: May 26, 2017, 06:10:52 AM »
Thanks for the good idea. F2B requires that the judges can see when the landing maneuver begins. I will modify my timer so that after stopping, the motor will run again for 5 seconds. If it works, letīs see how the judges comment.

   Might want to check the rules on that one, and the general practice. I seem to recall that the rule is "prop turning slow enough to count the blades" = "stopped". I also think the start of the maneuver is defined as "when you cross 5 feet" on the way down in FAI, in an attempt to make you glide one full lap after cutoff, for reasons that no one can adequately explain.

    Brett

Offline Chris Wilson

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Re: Mid engine canard
« Reply #73 on: May 27, 2017, 02:52:28 AM »
Hmm, the law here is indeed an ass!

Well the idea is still good for proof of concept and I too have no idea why landings must be dead stick.

Time for a rule revision?
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Offline Brett Buck

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Re: Mid engine canard
« Reply #74 on: June 14, 2017, 07:17:14 PM »
Hmm, the law here is indeed an ass!

Well the idea is still good for proof of concept and I too have no idea why landings must be dead stick.

Time for a rule revision?

    Maybe. AMA is already more-or-less correct, we have had plenty of people landing with the engine running, even the eternally persecuted victim himself, and no one said a thing.

     If you want to try to fix FAI, you may soon get your chance, but don't get your hopes up. I have suggested getting rid of the 1-lap landing several times but no one has gone for it. The good folks in Peter Germann's rules forum are reasonable, but the byzantine/bizarre/opaque CIAM process that actually changes the rules is a complete crapshoot.
   
    Brett

Offline Preston Briggs

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Re: Mid engine canard
« Reply #75 on: October 01, 2017, 04:00:04 PM »
Tim, where can I find more assembler tricks? Multiply/divide by multiples of 2 is already used, but the other factors are new to me.

The best book for this sort of thing is "Hacker's Delight" by Henry Warren.

Note well that dividing a signed integer by a power of 2 via shifting gives surprising results for negative numbers.
E.g., -1 >> 1 yields -1, not 0 as you might hope.

For multiplication by a constant, I've got a program that finds good results, sometimes surprising.
To multiply by 21, it suggests the following sequence:
Code: [Select]
8x = x << 3
7x = 8x - x
28x = 7x << 2
21x = 28x - 7x
I can share copies (old C code) if folks are interested.

Preston


Offline Serge_Krauss

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Re: Mid engine canard
« Reply #76 on: October 02, 2017, 09:55:09 PM »


P.S. Well, I guess I did post this a long time ago. It's right up there. 'sorry.

Offline Wolfgang Nieuwkamp

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Re: Mid engine canard
« Reply #77 on: October 24, 2017, 06:54:58 AM »
Hello Preston,

Thanks for Hackers Delight, good book!


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