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Author Topic: Mid engine canard  (Read 37652 times)

Offline Wolfgang Nieuwkamp

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Mid engine canard
« on: August 31, 2016, 03:00:45 PM »
Own design, electric mid motor.

As long as the motor runs, see video  [url]http://myalbum.com/album/pygoyWSQBOZ9/url]

But when gliding, the canard stalls.
Comments welcome,

Wolfgang

Offline Tim Wescott

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Re: Mid engine canard
« Reply #1 on: August 31, 2016, 04:24:58 PM »
Picture?  Show the glide?

What leads you to believe that the canard stalls rather than believing that the thing doesn't just have a normal pitch-down on loss of power?
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Air Ministry .

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Re: Mid engine canard
« Reply #2 on: August 31, 2016, 06:49:46 PM »
But Canards CANT stall .  ;D

Offline Brett Buck

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Re: Mid engine canard
« Reply #3 on: August 31, 2016, 08:28:00 PM »
But Canards CANT stall .  ;D

   Huh?  Magic relieves you of the laws of physics when the smaller wing goes first?

   Brett

Offline Brett Buck

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Re: Mid engine canard
« Reply #4 on: August 31, 2016, 08:32:44 PM »
Own design, electric mid motor.

As long as the motor runs, see video  [url]http://myalbum.com/album/pygoyWSQBOZ9/url]

But when gliding, the canard stalls.
Comments welcome,

  I really couldn't make much useful out of the video, aside from you needing to do something about the engine, it sounds rather dire!

     Brett

Offline Wolfgang Nieuwkamp

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Re: Mid engine canard
« Reply #5 on: September 01, 2016, 07:08:11 AM »
The gliding angle is about 15°, even with full up (elevator 45" down). That convinces me that the canard is stalled (not the wing!).
As long as the canard is in the propeller slipstream, it is effective.

The strange motor sound during level flight is caused by ny motor speed regulating system. The accelleration sensor based system tries to keep the line tension (more corruptly: the centripetal acceleration) at around 3g. If too low, the speed is increased a little. Next measured after 8 ms, If too high, the speed is decreased with the same amount. Tim, this is an integrating regulation, correct?

The video was taken using a 2 blade propeller, with a 3 blade one the sound is much more pleasant.

Hope the picture will show:
[img]http://myalbum.com/photo/FfAQjYtkqi9v/1k0.jpg/img]

Thanks for the comments,

Wolfgang



 

Offline Tim Wescott

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Re: Mid engine canard
« Reply #6 on: September 01, 2016, 09:34:25 AM »
   Huh?  Magic relieves you of the laws of physics when the smaller wing goes first?

   Brett

Section IV, subsection 37, paragraph (A), Unusual Planforms, of International Standards for Model Aviation Aerodynamic Analysis clearly states:

"Aircraft that do not conform to the usual monoplane layout, with a single main lifting surface ahead of a single, smaller stabilizing surface, may be analyzed using magical thinking, as long as you can make it sound convincing. This rule specifically applies in the case of biplanes and other multiplane lifting surfaces, flying wings, 'flying lawnmowers', asymmetrical aircraft, and canards." (my emphasis)

There.  Now you know.

The gliding angle is about 15°, even with full up (elevator 45" down). That convinces me that the canard is stalled (not the wing!).
As long as the canard is in the propeller slipstream, it is effective.

So the prop is ahead of the stabilizer.  Could you please post some pictures?

Just because the shallowest glide angle is steep doesn't mean the canard is stalled -- it just means that it's generating insufficient lift for the conditions.  Have you tried moving the CG back?  I assume this is going to be an interesting balancing act, as having the elevator so close behind the prop is going to really crank up the sensitivity when the motor is running.

The strange motor sound during level flight is caused by ny motor speed regulating system. The accelleration sensor based system tries to keep the line tension (more corruptly: the centripetal acceleration) at around 3g. If too low, the speed is increased a little. Next measured after 8 ms, If too high, the speed is decreased with the same amount. Tim, this is an integrating regulation, correct?


If the increment is constant then it's sorta-kinda integrating control.  True integrating control would have you calculate the throttle as:

<throttle now> = <last throttle> + <integrator  gain>(<target accelerometer> - <accelerometer reading>)

If you have what I think you have it'll adjust slower than it could for large speed errors, and it'll always oscillate around the correct value instead of settling in to a constant value.  For a large enough increment the constant seeking of the throttle will cause the system to consume more power than if it settled out to a fairly constant value, but that effect may be washed out by the necessary throttle changes in response to maneuvering.

Given the various lags in the system, I expect that you could get snappier control with a proportional-integral controller, but if you do that then tuning will almost certainly be harder than with integrator-only control (and based on the tuning parameters that Igor exposes on his system, I suspect that's not what he does).
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline john e. holliday

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Re: Mid engine canard
« Reply #7 on: September 01, 2016, 11:28:46 AM »
Several years ago I built Richard Sarpolous Blue Goose canard to prove to some individuals that they were not thinking straight.   First flights took some getting used to with tail out front.  It was also sensitive to the controls as he showed them.   I putt longer control horns on and added nose weight.   I have a witness that has seen me put it through several AMA patterns when the air and engine run were right.   It landed like a dream.   

So I thought I could improve on it by building a Ringmaster variant.  I left off the trailing moving surfaces on the main wing.   Only the forward elevators move.  Draw back is there is no air going over the surface to keep the nose up.  Will correct that with a skid as it is still a little sensitive.  I have witnesses to this as it will go okay if hand launched.  It lands okay also if you keep the speed up on landing.   So far it has not stalled like I think a plane stalls by dropping the nose.   It will not glide like a normal stunt plane, but is a lot of fun to fly.
John E. "DOC" Holliday
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AMA 23530  Have fun as I have and I am still breaking a record.

Offline Wolfgang Nieuwkamp

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Re: Mid engine canard
« Reply #8 on: September 01, 2016, 12:14:16 PM »
John,

many years ago I also built a similar canard, and it did fly well, powered by a Fox 45.
Built a similar one, with electric power, but could not get it stable. So I tried an original layout, with a mid engine.

Tim,

a nice article on aircraft with 2 lifting surfaces can be found in    http://soartech-aero.com/SoarTech-6.pdf   on page 100 ff. I used Fraserīs reasoning for my layout. The pdf of Fraserīs article was too large to upload…..
The algorithm you suggested is somewhat difficult to implement in my old microprocessor, Microchip 12f675, but thanks anyway.

Hope the attached picture now shows.

Regards,

Wolfgang

Offline Tim Wescott

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Re: Mid engine canard
« Reply #9 on: September 01, 2016, 12:40:23 PM »
Tim,

a nice article on aircraft with 2 lifting surfaces can be found in    http://soartech-aero.com/SoarTech-6.pdf   on page 100 ff. I used Fraserīs reasoning for my layout. The pdf of Fraserīs article was too large to upload…..
The algorithm you suggested is somewhat difficult to implement in my old microprocessor, Microchip 12f675, but thanks anyway.

Hope the attached picture now shows.

Regards,

Wolfgang

Aw c'mon.  It's got 35 easy-to-use instructions.  And doing math in assembly is fun.  If you're sampling at 125Hz there should be plenty of time to do the calculation.  I'd implement the integrator gain with a shift -- trying to do multiplies on that chip would be a bear, and changing gains by factors of two usually gets you in the ball park.  If you want to get more precise, you can multiply by any factor of 2 times 1, 1.25, 1.5 or 1.785 with just shifts and either one add or subtract.

I'm not arguing with the layout -- just saying you should try moving the CG back and see how it glides.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Wolfgang Nieuwkamp

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Re: Mid engine canard
« Reply #10 on: September 01, 2016, 01:24:25 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.

Regarding the CG, I will make a new firewall as far back as possible, around 7 cm back-
I am also considering to use a slotted flap elevator, but that will be a winter project.

Offline Wolfgang Nieuwkamp

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Re: Mid engine canard
« Reply #11 on: September 01, 2016, 01:25:57 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.

Regarding the CG, I will make a new firewall as far back as possible, around 7 cm back-
I am also considering to use a slotted flap elevator, but that will be a winter project.

Offline Tim Wescott

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Re: Mid engine canard
« Reply #12 on: September 01, 2016, 02:06:03 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.

I can't remember the name of the method*, but it's based on the fact that when you subtract a number you generate a string of ones:

In C-ish pseudocode:

0.75 = 1 - 0.25 (y = x - (x >> 2));
0.875 = 1 - 0.125 (y = x - (x >> 3));
1 = 1
1.125 = 1 + 0.125 (y = x + (x >> 3));
1.25 = 1 + 0.25 (y = x + (x >> 2));

Then you repeat, shifted up one:

1.5 = 2 - 0.5
1.75 = 2 - 0.25
2 = 2
2.25 = 2 + 0.25
2.5 = 2 + 0.5

Then

3, 3.5, 4, 5

Then

6, 7, 8, 10

Etc.

Multiplying by a fixed number is easy; if you want to have a user-configurable gain then you probably want to have some sort of a mantissa + shift arrangement (8-bit floating point!  Wow!) with the assembler equivalent of a switch statement for the four possible mantissas.

You could also stick to just 2 or 3 for the mantissa -- going in steps of 1, 1.5, 2, etc. is really good enough for most practical work.

* edit: Booth's Algorithm.  Here's the Wikipedia page
« Last Edit: September 01, 2016, 02:28:39 PM by Tim Wescott »
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Wolfgang Nieuwkamp

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Re: Mid engine canard
« Reply #13 on: September 03, 2016, 09:49:57 AM »
Thanks for the algorithm. It would take a lot of space of the limited memory (and a lot of programming time), so I will stick to shift right/left…..

Offline john e. holliday

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Re: Mid engine canard
« Reply #14 on: September 03, 2016, 07:43:47 PM »
Now I remember why started skipping over some of the stuff the late-great Wild Bill Netzband used to write. 
John E. "DOC" Holliday
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Shawnee, KANSAS  66203
AMA 23530  Have fun as I have and I am still breaking a record.

Offline Igor Burger

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Re: Mid engine canard
« Reply #15 on: September 06, 2016, 01:30:53 PM »

Given the various lags in the system, I expect that you could get snappier control with a proportional-integral controller, but if you do that then tuning will almost certainly be harder than with integrator-only control (and based on the tuning parameters that Igor exposes on his system, I suspect that's not what he does).

No, it is really not what I do :-) ... mine timer is feed forward, not feed back, so it is not PIDsomething at all :- )) ... simply it adds nose up and that is all :- ))

The biggest problem of such stuff is good tuning of proper filters, otherwise it reacts to improper things, for example if you try pull handle during flight, my algorithums calculationg "nose up" is confused and model will react by pulsing. But it will certainly not add power over head and so accelerate before descending - that is reason why it is not feedback system. It (PID) is not tunable if you do not have enough power (so it tends to wind up) and enough power will be too heavy. So it works only "somehow" - and that "somehow" is question of proper tuning :- )) so well working regulation is more about proper coefficients = hard work, not programming skill :- ))) ... I am programmer, so I did not have probles with it, anyway I spend 4 years testing until I tol myself "done".

I have here around 2 other friends trying do similar timers, but they still did not not get reliable feedback system fo far. I told them what they do wrong, but hard heads are hard heads :- ))))))))) 

Offline Tim Wescott

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Re: Mid engine canard
« Reply #16 on: September 06, 2016, 02:20:57 PM »
No, it is really not what I do :-) ... mine timer is feed forward, not feed back, so it is not PIDsomething at all :- )) ... simply it adds nose up and that is all :- ))

The biggest problem of such stuff is good tuning of proper filters, otherwise it reacts to improper things, for example if you try pull handle during flight, my algorithums calculationg "nose up" is confused and model will react by pulsing. But it will certainly not add power over head and so accelerate before descending - that is reason why it is not feedback system. It (PID) is not tunable if you do not have enough power (so it tends to wind up) and enough power will be too heavy. So it works only "somehow" - and that "somehow" is question of proper tuning :- )) so well working regulation is more about proper coefficients = hard work, not programming skill :- ))) ... I am programmer, so I did not have probles with it, anyway I spend 4 years testing until I tol myself "done".

I have here around 2 other friends trying do similar timers, but they still did not not get reliable feedback system fo far. I told them what they do wrong, but hard heads are hard heads :- ))))))))) 

The problem for the rest of us is that you're a programmer and a better pilot than almost any of us can hope to be.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Gerald Arana

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Re: Mid engine canard
« Reply #17 on: September 06, 2016, 03:00:06 PM »
John,

many years ago I also built a similar canard, and it did fly well, powered by a Fox 45.
Built a similar one, with electric power, but could not get it stable. So I tried an original layout, with a mid engine.

Tim,

a nice article on aircraft with 2 lifting surfaces can be found in    http://soartech-aero.com/SoarTech-6.pdf   on page 100 ff. I used Fraserīs reasoning for my layout. The pdf of Fraserīs article was too large to upload…..
The algorithm you suggested is somewhat difficult to implement in my old microprocessor, Microchip 12f675, but thanks anyway.

Hope the attached picture now shows.

Regards,

Wolfgang


Boy! You sure had me confused with that "Mid" motor comment! Now this post is starting to make sense!

Hey Doc, shouldn't your LO's be just behind the CG like a "normal" plane? Or actually in front of the LE?
Just asking, Jerry

Offline john e. holliday

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Re: Mid engine canard
« Reply #18 on: September 06, 2016, 04:26:18 PM »
The CG seems best if ahead of the main wing. 
John E. "DOC" Holliday
10421 West 56th Terrace
Shawnee, KANSAS  66203
AMA 23530  Have fun as I have and I am still breaking a record.

Offline Tim Wescott

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Re: Mid engine canard
« Reply #19 on: September 06, 2016, 05:17:27 PM »
The CG seems best if ahead of the main wing. 

Yup.  There's complicated math to figure out where the CG goes.  Then, there's Depron foam or 1/16" balsa with which to make gliders.  Wherever the CG goes to make it fly nice, it needs to be about 1/10 of a wing chord forward of that for a starting point, and then experiment and experiment some more.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Wolfgang Nieuwkamp

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Re: Mid engine canard
« Reply #20 on: September 07, 2016, 11:33:10 AM »
If you read the link,  http://soartech-aero.com/SoarTech-6.pdf  after page 100, you will find that it is easy to calculate  where the CG should be: Just 8% of the distance between the MACīs ahead of the NP of both surfaces…..

Offline Wolfgang Nieuwkamp

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Re: Mid engine canard
« Reply #21 on: September 07, 2016, 12:24:45 PM »
igor,

maybe the attached Castle log convinces you that my feedback system works. I agree with Tim that the integrating algorithm could be faster, but until now it works for me.

Offline Brett Buck

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Re: Mid engine canard
« Reply #22 on: September 07, 2016, 12:47:56 PM »
I can't remember the name of the method*, but it's based on the fact that when you subtract a number you generate a string of ones:

   That's also how many floating-point units work, even the oddball IEEE 754 types. MIL-STD-1750 floating point was designed to be able to implement it directly as the fastest method (although not th emost precise). Effectively all A/D convertors use something nearly identical implemented in analog and TTL logic. In fact, the design of A/D almost certainly greatly predated Booth working out the general principle.

    Brett

Offline jim gilmore

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Re: Mid engine canard
« Reply #23 on: September 07, 2016, 04:07:35 PM »
I am Not an aircraft engineer but here is what I thought I kew about canards,s an aircraft.
The canard being the aircraft itself Not the elevator connected to the front of the aircraft, weather it have an elevator and horizontal stabalizer or just a fully rotating elevereon <sp>.
That the wing itself will not stall because the smaller elevator is meant to stall first .
So yes, The elevator may  well stall on a canard.
That is my understanding of the inherent stability of a canard aircraft.
Bear in mind that diheadral works in a similar way to make an aircraft stable.

Offline Tim Wescott

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Re: Mid engine canard
« Reply #24 on: September 07, 2016, 05:06:26 PM »
   That's also how many floating-point units work, even the oddball IEEE 754 types. MIL-STD-1750 floating point was designed to be able to implement it directly as the fastest method (although not th emost precise). Effectively all A/D convertors use something nearly identical implemented in analog and TTL logic. In fact, the design of A/D almost certainly greatly predated Booth working out the general principle.

For the most part, in order to retain my sanity, I view digital logic as a black box with lines coming in from the outside and magic inside.

Unless I need to convince some digital guy that I have an approach that is, too, possible -- then I suddenly find enough competence to convince his manager that I could do it given time.  That usually sparks a territorial response that results in him doing all the skut work to make it happen.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Brett Buck

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Re: Mid engine canard
« Reply #25 on: September 07, 2016, 08:36:36 PM »
For the most part, in order to retain my sanity, I view digital logic as a black box with lines coming in from the outside and magic inside.

Unless I need to convince some digital guy that I have an approach that is, too, possible -- then I suddenly find enough competence to convince his manager that I could do it given time.  That usually sparks a territorial response that results in him doing all the skut work to make it happen.

  I needed to know how the guts worked for several of my past assignments, including programming processors down to the machine code level, not assembly, literally directly setting the ones and zeros, and generating self-modifying code (which generally unwise but invaluable when you have very tight space constraints). I had the advantage/opportunity to be around for the end of TTL logic as the primary method of operating to very simple flight computers, and also endless free time and lots of paid time to kill with literally nothing else to do.

    You would be surprised at how many "quirks" and errors some processors have in the microcode and similar levels. I know of one processor (Teledyne 1750A) that has about two fullpages of one-line descriptions of instructions that don't work exactly as expected in some conditions. Many of them were discovered by either me or some of my compatriots.

      Brett

Offline Brett Buck

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Re: Mid engine canard
« Reply #26 on: September 07, 2016, 10:21:48 PM »
The CG seems best if ahead of the main wing. 

     But his point was that you need the leadouts to be about 3/4" to 1" behind the CG, which means they need to be in front of the wing. You certainly cannot put the CG near the CP of the wing, that's why canards don't fly all that well. Hunt's wing had lots of forward sweep so the leadouts could be in the wingtip.

      Brett

Offline Brett Buck

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Re: Mid engine canard
« Reply #27 on: September 07, 2016, 10:33:59 PM »
No, it is really not what I do :-) ... mine timer is feed forward, not feed back, so it is not PIDsomething at all :- )) ... simply it adds nose up and that is all :- ))

   Do you only use one axis of the accelerometer (X/fore and aft)?  I had assumed that you used the X (fore/aft acceleration) and Z (load factor) axes as feedforwards, and the Y just like you used the swing-weight on the mechanical system to control the gross lateral acceleration/speed. The latter would indeed need a very slow filter.

       Brett

Offline Igor Burger

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Re: Mid engine canard
« Reply #28 on: September 10, 2016, 03:26:45 PM »
The problem for the rest of us is that you're a programmer and a better pilot than almost any of us can hope to be.

And that means lot of flying and less time for testing and programing :- )))))))))))))

Offline Igor Burger

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Re: Mid engine canard
« Reply #29 on: September 10, 2016, 03:46:53 PM »
igor,

maybe the attached Castle log convinces you that my feedback system works. I agree with Tim that the integrating algorithm could be faster, but until now it works for me.

Well ... I believe it does "something" as I wrote. I also tried to see such chards but it did not show correlation to maneuver, so I decided to install full set of sensors, including pitot tube, altimeter etc ... and it still did not tell me more then real tests. I was able to see lagg, I saw speed lose, but it did not tell too much. The point is ability to say what it really have to do, it is much less obviouse then one can think :- ))) ... constant speed is not the answer (btw constant to what?) as well as constant line tension etc. It needs simply tuning, testing, tuning, testing, tuning, testing :- )))

Offline Tim Wescott

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Re: Mid engine canard
« Reply #30 on: September 10, 2016, 03:58:02 PM »
(btw constant to what?)

If you have perfect inertial sensors you could make the speed constant in inertial space.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Igor Burger

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Re: Mid engine canard
« Reply #31 on: September 10, 2016, 03:59:36 PM »
   Do you only use one axis of the accelerometer (X/fore and aft)?  I had assumed that you used the X (fore/aft acceleration) and Z (load factor) axes as feedforwards, and the Y just like you used the swing-weight on the mechanical system to control the gross lateral acceleration/speed. The latter would indeed need a very slow filter.

       Brett

I use only X (lines) and Y (thrust), means no Z (the lift). From X and Y is calculated fuselage angle to horizont (in 3d). I was surprised, but in math, Z was eleminated :- )) .

Offline Igor Burger

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Re: Mid engine canard
« Reply #32 on: September 10, 2016, 04:08:50 PM »
If you have perfect inertial sensors you could make the speed constant in inertial space.

Well we spoke about it on compuserve many years ago, so some guys will remember ... you must count with wind, it makes problems and differences ... then ... flying high speed overhead when you have limited power for braking just before diving is also not the best situation for good pull-out in wingover (and not only) :- ))

But you are right, it will work well in gym indoors :- )) That is why I have different system for indoors and different outdoor.

Offline Brett Buck

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Re: Mid engine canard
« Reply #33 on: September 10, 2016, 09:31:12 PM »
I use only X (lines) and Y (thrust), means no Z (the lift). From X and Y is calculated fuselage angle to horizont (in 3d). I was surprised, but in math, Z was eleminated :- )) .

      I would think you could get even more lead on acceleration by using the Z axis to detect the load factor/lift/drag.

     Brett

Offline Igor Burger

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Re: Mid engine canard
« Reply #34 on: September 11, 2016, 03:02:29 AM »
Probably yes, but I was happy I can keep all in small PIC processor in 16bit math, so I was happy I not need Z :- ))

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Re: Mid engine canard
« Reply #35 on: September 11, 2016, 04:16:44 AM »
Dear Friends,

While I do respectfully adore, rather than really understand, how far you have gone in automatic power control nowadys, I begin to wonder where this will lead to. Will we, in order to remain competitive, frequently need to have (buy) latest generation power management systems consisting of black boxes being connected to various sensors? If so, how does such a perspective fit into the "keep it simple" paradigm of our sport?
 
Perhaps, instead of pushing automatic power control to the n'th degree, we may want to go one step back by giving the pilot in command throttle authority? After all, power management by the driver is part of the game in aerobatics of all kind and I do not really see a reason why this should not be so in c/l stunt. Possibly not only with electrics, but when using very quick responding modern r/c motors, too, further levelling the playfield.


 
Peter Germann

Offline Igor Burger

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Re: Mid engine canard
« Reply #36 on: September 11, 2016, 04:41:12 AM »
Well, Peter the timer which I use was done on very begin of electric power train. It simply imitates almost exactly what 4-2-4 or piped setup does (I can even show you relation in setup values in timer to physical parameters of piped setup). Since then I did not change it beside small changes allowing to use it with IC engines and carburator (and I told myself not to do it just for the reason you mentioned). So I do not know where your feeling comes from. I would say just opposite, that manual controll will push us to use new devices because it simply gives too much advantage in some maneuvers. That was reason why I always disagreed with remote controll of power train and the only thing which was acceptable for me was EMERGENCY cut off - not the cut off for proper landing approach relative to wind etc - something hard to do with IC. I personally do not see reason for redefining C/L stunt. But may be I am too conservative :- )))

BTW I cannot imagine how to disallow that thing with IC engines as it is its natural property developed during years :- ))

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Re: Mid engine canard
« Reply #37 on: September 11, 2016, 09:15:43 AM »
Dear Peter,
I think you lead the things in a wrong way.
Control line flying will never lose the old stunt masters which like to use piston engines. I guess you heard about Mr. Dave Fitzerald and since i know him in the top 5 fliers in the world he still use it and more over enjoy it. The problem if we consider as problem has never been electric motors and their power equipment. If we so regulary  base the problems like that i would than say - easy for transportation, especially over the other side of the globe for a contest, more clean, more silent and so on. Never the less at the end lets dont forget that all guys started up with piston engines in the begining. Mr. Bob Hunt changes the things in other direction as design and concept of cl models, and Mr. Igor Burger completed that changed becoming first world and european champion with electric system. Many articles were dedicated to both of them in stunt hanger, many explanation notes and great articles from Mr. Paul Walker....
The fact that something grown up and changed the old style (a little bit ) it doesnt make ot bad and it doesnt make the old un necessary. This is called evolution and exist in every sport, so far conected in industry and production.
The things on which we can stress in F2B are far away from that. Personally i like to see new motivated people, inventors, experimentors. Thats speaks only about that people in CL are not fallen asleep and goes together with the world of communication and technology.
Sincerely Tatyana

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Re: Mid engine canard
« Reply #38 on: September 11, 2016, 11:05:32 AM »
Dear Peter,
I think you lead the things in a wrong way.
Control line flying will never lose the old stunt masters which like to use piston engines. I guess you heard about Mr. Dave Fitzerald and since i know him in the top 5 fliers in the world he still use it and more over enjoy it. The problem if we consider as problem has never been electric motors and their power equipment. If we so regulary  base the problems like that i would than say - easy for transportation, especially over the other side of the globe for a contest, more clean, more silent and so on. Never the less at the end lets dont forget that all guys started up with piston engines in the begining. Mr. Bob Hunt changes the things in other direction as design and concept of cl models, and Mr. Igor Burger completed that changed becoming first world and european champion with electric system. Many articles were dedicated to both of them in stunt hanger, many explanation notes and great articles from Mr. Paul Walker....
The fact that something grown up and changed the old style (a little bit ) it doesnt make ot bad and it doesnt make the old un necessary. This is called evolution and exist in every sport, so far conected in industry and production.
The things on which we can stress in F2B are far away from that. Personally i like to see new motivated people, inventors, experimentors. Thats speaks only about that people in CL are not fallen asleep and goes together with the world of communication and technology.
Sincerely Tatyana

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Re: Mid engine canard
« Reply #39 on: September 19, 2016, 08:35:17 PM »
 ;D


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Re: Mid engine canard
« Reply #40 on: September 21, 2016, 03:44:23 PM »
But Canards CANT stall .  ;D
Well, I do get your meaning beyond the wording Matt.

When the fore plane does stall it does so long before the main plane should do (loading and CG not withstanding).
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Re: Mid engine canard
« Reply #41 on: March 05, 2017, 10:04:31 AM »
Well, I do get your meaning beyond the wording Matt.

When the fore plane does stall it does so long before the main plane should do (loading and CG not withstanding).
.

I would say it depends on the aspect ratio of the canard WRT that of the wing. 

Canards are, for a preponderance of aerodynamic and mechanical reasons, inherently flawed aircraft, which explains why in the never ending search for speed and performance they have been pretty well kicked to the wayside.
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Re: Mid engine canard
« Reply #42 on: March 05, 2017, 10:31:37 AM »
I would say it depends on the aspect ratio of the canard WRT that of the wing.  

Canards are, for a preponderance of aerodynamic and mechanical reasons, inherently flawed aircraft, which explains why in the never ending search for speed and performance they have been pretty well kicked to the wayside.

Are you sure?



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Re: Mid engine canard
« Reply #43 on: March 05, 2017, 10:35:33 AM »
Are you really really sure?

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Re: Mid engine canard
« Reply #44 on: March 05, 2017, 12:34:18 PM »
Are you really really sure?



Yes, I'm very sure. 

Canards have some major drawbacks. First, why would you place your wing in wash of the stab? 

Second, and most importantly, aircraft store fuel and weapons in and under the wings. When you try to drop a bomb or fire a missile, or just burn fuel, the CG on a canard moves around too much.




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Re: Mid engine canard
« Reply #45 on: March 05, 2017, 12:54:23 PM »
Yes, I'm very sure. 

Canards have some major drawbacks. First, why would you place your wing in wash of the stab? 

You could say the same for a wing that's forward of the stab. Probably more so.

 

Quote
Second, and most importantly, aircraft store fuel and weapons in and under the wings. When you try to drop a bomb or fire a missile, or just burn fuel, the CG on a canard moves around too much.


On aircraft, the CG is a plus or minus measurement covering a designated area designed into the aircraft to allow for what you mentioned.

Controlled by "trim" input, as, what you're talking about, changes.

Simple decrease in RPM's will require a trim change.

I think the aircraft in the photos deserve some technical and design kudos.

Designed by people who certainly know a great deal about aircraft design.

The aircraft that circled the globe, I don't remember the name it was called, evidently the Conard design was realized for efficiency and usefulness for the purpose it was designed for.

They didn't go traditional and they easily could have.

CB 









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Offline Mark Scarborough

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Re: Mid engine canard
« Reply #46 on: March 05, 2017, 01:52:55 PM »
You could say the same for a wing that's forward of the stab. Probably more so.

 
 

On aircraft, the CG is a plus or minus measurement covering a designated area designed into the aircraft to allow for what you mentioned.

Controlled by "trim" input, as, what you're talking about, changes.

Simple decrease in RPM's will require a trim change.

I think the aircraft in the photos deserve some technical and design kudos.

Designed by people who certainly know a great deal about aircraft design.

The aircraft that circled the globe, I don't remember the name it was called, evidently the Conard design was realized for efficiency and usefulness for the purpose it was designed for.

They didn't go traditional and they easily could have.

CB 

Charles, no you are wrong,
on a Canard, the CG is way ahead of the wing, hence if you have wing mounted stors, missles etc, or wing fuel tanks it will dramatically alter the CG, with a conventional setup, the CG is in the wing area, therefore releasing stores, burning fuel will have a significantly reduced affect on the CG.
please also note, we are in a STUNT sectionj of the forum, NOT in a sport section, therefore all answers are by default aimed at stunt airplanes and ther design, if a Canard was such agreat idea, I am pretty sure someone would have done it and we would have seen it at the Nats or at least a major contest.

The Voyager was a canard for different reasons that anything described here, it wa also designed by Rutan who had a thing for canards, the others had inherant problems in the design as well. Yes they were cool, and unique but if they were that great, pretty sure more would have followed in their footsteps,,
so Charles, sorry but you are wrong
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Re: Mid engine canard
« Reply #47 on: March 22, 2017, 08:07:07 PM »
Wolfgang,  I'd go back and check you earlier canard, and the plans for the Blue Goose.  I flew one of those a friend built.  With the flaps fixed and just the canard it flew pretty well, about like a Ringmaster.  Had similar behavior too.  It was easy to stall the canard if trying square corners, but it glided just fine.  I suspect you have a CG problem or the perhaps the swept forward wing puts the CG too far forward, putting too much load on canard when gliding.

The Canela is a pretty plane.  I hope you can get the problem fixed.

If I remember correctly, the Blue Goose had the CG just forward of the wing.  Unfortunately my friend died quite a few years ago and the plane got lost in the shuffle, so I can't check.

Phil C.
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Re: Mid engine canard
« Reply #48 on: March 22, 2017, 09:31:21 PM »
On aircraft, the CG is a plus or minus measurement covering a designated area designed into the aircraft to allow for what you mentioned.

   No. The CG is where the airplane balances, period, and it is a point, not a range. Sometimes an allowable range of CG positions is specified, and it moves around in flight, but at any instant in time, it is a single point.

    Brett

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Re: Mid engine canard
« Reply #49 on: March 22, 2017, 11:11:19 PM »

............ on a Canard, the CG is way ahead of the wing ............

Not always, on full size and non control line aircraft the center of gravity must be ahead that of the Neutral point by factor called static margin which should be between 5 to 15 % of the mean aerodynamic chord.
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Re: Mid engine canard
« Reply #50 on: April 25, 2017, 01:31:36 AM »
design is good.

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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.

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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 ).



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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

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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.
Trump Derangement Syndrome. TDS. 
Avaiojet Derangement Syndrome. ADS.
Amazing how ignorance can get in the way of the learning process.
If you're Trolled, you know you're doing something right.  Alpha Mike Foxtrot. "No one has ever made a difference by being like everyone else."  Marcus Cordeiro, The "Mark of Excellence," you will not be forgotten. "No amount of evidence will ever persuade an idiot."- Mark Twain. I look at the Forum as a place to contribute and make friends, some view it as a Realm where they could be King.   Proverb 11.9  "With his mouth the Godless destroys his neighbor..."  "Perhaps the greatest challenge in modeling is to build a competitive control line stunter that looks like a real airplane." David McCellan, 1980.

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?
MAAA AUS 73427

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 Nothing in life is so exhilarating as to be shot at without result.  It's not enough that we do our best; sometimes we have to do what's required

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?
MAAA AUS 73427

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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?
MAAA AUS 73427

You have enemies? Good. That means you've stood up for something, sometime in your life.
 Nothing in life is so exhilarating as to be shot at without result.  It's not enough that we do our best; sometimes we have to do what's required

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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