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Old Dec 22, 2008, 04:30 PM
Jets are for kids-of all ages
Florida, USA
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See my Blog for a DWF version of the 44" Velocity plans, they are still rough but useable.
Roger
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Old Dec 22, 2008, 05:11 PM
Canard Driver
R.A.P.'s Avatar
san diego, ca.
Joined Nov 2002
428 Posts
Long Ez

MULLINSPAN--- Thanks for your input very helpfull..... I just ran into this
web site "www.rcpowers.com" they have a Long Ez that flys really great
and they sell the plans. The Ez I built was exact scale from the Rutan
plans, and was a balsa built up model. I have quite a few flights on it,
and have moved the c/g so far back it entered a flat stall and came down
like a parachute, and nothing I could do would get it to start flying again! it
landed in a big bush and nothing was broken!!!!The Ez has working rudders
and retractable nose wheel, it is a little on the heavy side so in the future
I am going to lighten it up and continue my testing.So I guess you could
say I'm hooked on canards. I notice that the rcpowers L.E. has a full floating
elevator,and elevons in their video, they have it working great.
Dick
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Old Dec 22, 2008, 05:24 PM
Canard Driver
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san diego, ca.
Joined Nov 2002
428 Posts
long ez

on the rcpowers site you have to go to the pdf files.......
Dick
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Old Dec 22, 2008, 05:38 PM
Jets are for kids-of all ages
Florida, USA
Joined Jun 2008
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Thanks R.A.P. that foamy is definantly light, I wouldn't want to fly it in much wind. Mine are a horse of another color. I am running a 35-48-1000 on mine but only proped to about 30 amps, on a 25c 2250 3s1p. I don't even have a power system for the RC Powers canard. But it is COOL, I like to see any canard flying. It seem like a lot of canard flyers are using elevons, this intriques me as it seems they are flying with a very rear c.g., more like a Delta Winged Aircraft only with canard assist.
Roger
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Old Dec 22, 2008, 05:41 PM
Jets are for kids-of all ages
Florida, USA
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I know that according to Velocity Aircraft, that fully 1/3 of the flying weight is usually supported by the canard. Models can get away with murder, we have so much more power to weight available.
Roger
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Old Dec 22, 2008, 06:58 PM
Jets are for kids-of all ages
Florida, USA
Joined Jun 2008
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Here is my latest 44" span Velocity I am about ready to install the radio gear and motor. The red is paint and the black is Sharpie marker.
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Old Dec 22, 2008, 07:09 PM
Canard Driver
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san diego, ca.
Joined Nov 2002
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Ez

Nice plane Roger
That should look great in the air!good luck on the maiden flight.......
Dick
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Old Dec 22, 2008, 09:45 PM
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Quote:
Originally Posted by tedrobphoto
...I am currently flying a "Rogallo" wing (R/C hang glider type)...
Yup, very familiar with the type. Used to instruct in them. Got one (18 ft. span) rolled up out in the barn. Declared it no longer airworthy due to the age of its "landing gear" (me). Didn't get much flying time after I graduated from college anyway. Thanks to the last ice age, everything around here that's north of the Ohio River is pretty much flat, at least compared to what one of those needs. My initial impression the first time I saw a standard Rogallo hang glider fly was just how horrendously bad the L/D was! The one I own is better than usual, a bit over 4:1, but most of them aren't much better than 3:1. They have a number of nice qualities, but efficiency isn't one of them!

Quote:
...delta wing machine for aerial photography which is great until I want to penetrate some wind when power just causes height gain...
The natural result of strongly positive static pitch stability (i.e.: the tendency of the plane to return to its original angle of attack if the angle of attack is disturbed) combined with a very low thrust line. Any increase in airspeed makes the plane want to pitch up. Any increase in thrust also makes the plane want to pitch up. This turns any increase in power into a climb, if everything is set up properly.

Quote:
...and stalling...
The natural result of carrying the above concepts a little too far. The plane pitches up too much, loses airspeed, and stalls.

Quote:
...as at present there is no elevator control as such.
It's using throttle to act as the elevator. Power increase raises the nose, power decrease pitches the nose down.

Moving the C/G aft would reduce pitch stability, and you might be able to change the pitch-change-with-throttle by playing with the location of the prop and the angle of the thrust line.

However, there are some funny interactions that may occur between the propwash and the aft portions of the wing that could counteract some of the basic effects of changing the thrust angle.

Quote:
The machine is 92" wingspan and I wondered whether fitting an elevator in the "canard" configuration would allow me to bring down the machine and allow some penetration (in your opinion)
Cheers Ted (UK)
This aircraft is fundamentally designed to be a "one speed airplane". There are things you can do, but they involve reducing the plane's pitch response to throttle and airspeed changes. Since the plane uses throttle and airspeed changes as its sole means of pitch control and stability, getting rid of that (without adding it back in by some other method) means giving up your stability and control in pitch. This also means giving up your ability to flair for touchdown on landing, as you have apparently noticed.

Your idea of adding an elevator is therefore right on the mark. However, adding it to the front, as a canard, is probably trickier and filled with more potential pitfalls than adding one behind.

The factor that determines static pitch stability is called "static margin". It's the distance (expressed as a percent of the wing's Mean Aerodynamic Chord, or "MAC") between the C/G and the Aerodynamic Center ("AC").

The key here is that it's the AC of the entire plane that matters, NOT just the AC of the wing alone. Remember those old "rules of thumb" that set the C/G location based on wing chord alone? They're wrong, or at least grossly incomplete. You have to find the AC of the complete airplane, including the tail (and/or canard). In this regard there is no difference between a canard and an aft-tail layout; both are two-surface aircraft, with differences in the ratios of the areas of the forward and aft flying surfaces. A canard is just an aft-tailed airplane with an unusually small wing and an unusually large horizontal tail. The equations that describe the behavior of both are the same.

If the fuselage has any significant influences on pitch (for example, if you were building a model of one of those "Super Guppy" airplanes that NASA used for transporting rocket parts, or Airbus uses for carting airframe parts from various sites around Europe to the assembly plant in Toulouse), then you have to include the fuselage in the calculations as well.

If you add area to the front of the plane (such as a canard), the AC of the aircraft is pulled forward. If you don't want your static margin (and your static pitch stability) to be reduced, you have to move the C/G forward to compensate.

If you add area behind (such as an elevator, or a horizontal tail assembly), the AC of the plane moves aft, and therefore you can move the C/G aft by that same amount and still have the same amount of static pitch stability.

Placing the elevator aft means it will probably be sitting in the propwash, enhancing the elevator authority, but slightly reducing its stabilizing effect. This could be an advantage or disadvantage, depending on how you apply it. A canard will most likely not see this effect, which, again, could be an advantage or disadvantage depending on how you apply it. It's possible to make a truly awful airplane via just about any approach. It all depends on how you do (or don't do) your homework.

Moment arm is very important on all of this. So far we've just talked about "static" stability, and about control authority. Both of these are linear with increases in tail (or canard) area, and also linear with increases in tail or canard moment arm. Double the area, or double the moment arm, and you get double the static stability and control authority.

However, "dynamic" stability (i.e.: the ability to damp out oscillations) is linear with increases in area, but proportional to the square of the moment arm. Double the area and you get double the dynamic stability. However, double the moment arm and you get FOUR TIMES the dynamic stability.

Likewise, if you double the area, but cut the moment arm in half, you end up with the same static stability and control authority as before, but only half as much dynamic stability.

The same is true for vertical surfaces and yaw stability. This is why we typically have so much trouble getting decent yaw stability on canard models; the moment arm for the vertical tail surfaces tends to be so unusually short that even with enormous vertical tails, it's almost impossible to get good dynamic yaw stability. Meanwhile, the canard and all its supporting structure are typically so far ahead of the C/G that they add a significant amount of destabilizing effect in yaw. Even a slender boom or space frame that far in front can have a significant effect, as well as the side forces of even a zero-dihedral canard. None of these problems are insurmountable, but you do need to acknowledge and deal with them. If you decide to go with a canard, better plan on enlarging your vertical surfaces to compensate for the additional lateral area up front.

The other option is to resort to "weight-shift" control for trimming in pitch. Mount the wing on a pivot at the C/G, then raise (to slow down) or lower (to speed up) the nose of the wing relative to the fuselage pod to alter the trimmed airspeed. In flight, what actually happens is the fuselage pod swings forward and aft, altering the C/G location. As long as it doesn't move so far aft that the plane becomes unstable in pitch and/or yaw, it will work. Make sure you use a very beefy servo to control the wing incidence, the forces on it could be very large.

Of course the dynamic stability of a Rogallo is pretty terrible (some studies indicate dynamic instability, in other words the oscillations get bigger and bigger, instead of damping out), so be careful to avoid getting any oscillations started. Adding a tail of some sort on a decent moment arm could be a big help in that regard.

As far as structural concepts for adding a tail (or a canard for that matter), you might take a look at the horizontal tail added to the "Easy Riser" biplane in the movie "Fly Away Home". The other ultralight in that movie is a good example of using weight-shift to control pitch (and in that particular case, roll control as well). Some of the pre-WW I classics, such as the planes in the movie "Those Magnificent Men In Their Flying Machines" might be another good source of ideas.
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Old Dec 23, 2008, 01:59 AM
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Joined Jun 2006
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Quote:
Originally Posted by Don Stackhouse
Yup, very familiar with the type. Used to instruct in them. Got one (18 ft. span) rolled up out in the barn. Declared it no longer airworthy due to the age of its "landing gear" (me). Didn't get much flying time after I graduated from college anyway. Thanks to the last ice age, everything around here that's north of the Ohio River is pretty much flat, at least compared to what one of those needs. My initial impression the first time I saw a standard Rogallo hang glider fly was just how horrendously bad the L/D was! The one I own is better than usual, a bit over 4:1, but most of them aren't much better than 3:1. They have a number of nice qualities, but efficiency isn't one of them!



The natural result of strongly positive static pitch stability (i.e.: the tendency of the plane to return to its original angle of attack if the angle of attack is disturbed) combined with a very low thrust line. Any increase in airspeed makes the plane want to pitch up. Any increase in thrust also makes the plane want to pitch up. This turns any increase in power into a climb, if everything is set up properly.



The natural result of carrying the above concepts a little too far. The plane pitches up too much, loses airspeed, and stalls.



It's using throttle to act as the elevator. Power increase raises the nose, power decrease pitches the nose down.

Moving the C/G aft would reduce pitch stability, and you might be able to change the pitch-change-with-throttle by playing with the location of the prop and the angle of the thrust line.

However, there are some funny interactions that may occur between the propwash and the aft portions of the wing that could counteract some of the basic effects of changing the thrust angle.



This aircraft is fundamentally designed to be a "one speed airplane". There are things you can do, but they involve reducing the plane's pitch response to throttle and airspeed changes. Since the plane uses throttle and airspeed changes as its sole means of pitch control and stability, getting rid of that (without adding it back in by some other method) means giving up your stability and control in pitch. This also means giving up your ability to flair for touchdown on landing, as you have apparently noticed.

Your idea of adding an elevator is therefore right on the mark. However, adding it to the front, as a canard, is probably trickier and filled with more potential pitfalls than adding one behind.

The factor that determines static pitch stability is called "static margin". It's the distance (expressed as a percent of the wing's Mean Aerodynamic Chord, or "MAC") between the C/G and the Aerodynamic Center ("AC").

The key here is that it's the AC of the entire plane that matters, NOT just the AC of the wing alone. Remember those old "rules of thumb" that set the C/G location based on wing chord alone? They're wrong, or at least grossly incomplete. You have to find the AC of the complete airplane, including the tail (and/or canard). In this regard there is no difference between a canard and an aft-tail layout; both are two-surface aircraft, with differences in the ratios of the areas of the forward and aft flying surfaces. A canard is just an aft-tailed airplane with an unusually small wing and an unusually large horizontal tail. The equations that describe the behavior of both are the same.

If the fuselage has any significant influences on pitch (for example, if you were building a model of one of those "Super Guppy" airplanes that NASA used for transporting rocket parts, or Airbus uses for carting airframe parts from various sites around Europe to the assembly plant in Toulouse), then you have to include the fuselage in the calculations as well.

If you add area to the front of the plane (such as a canard), the AC of the aircraft is pulled forward. If you don't want your static margin (and your static pitch stability) to be reduced, you have to move the C/G forward to compensate.

If you add area behind (such as an elevator, or a horizontal tail assembly), the AC of the plane moves aft, and therefore you can move the C/G aft by that same amount and still have the same amount of static pitch stability.

Placing the elevator aft means it will probably be sitting in the propwash, enhancing the elevator authority, but slightly reducing its stabilizing effect. This could be an advantage or disadvantage, depending on how you apply it. A canard will most likely not see this effect, which, again, could be an advantage or disadvantage depending on how you apply it. It's possible to make a truly awful airplane via just about any approach. It all depends on how you do (or don't do) your homework.

Moment arm is very important on all of this. So far we've just talked about "static" stability, and about control authority. Both of these are linear with increases in tail (or canard) area, and also linear with increases in tail or canard moment arm. Double the area, or double the moment arm, and you get double the static stability and control authority.

However, "dynamic" stability (i.e.: the ability to damp out oscillations) is linear with increases in area, but proportional to the square of the moment arm. Double the area and you get double the dynamic stability. However, double the moment arm and you get FOUR TIMES the dynamic stability.

Likewise, if you double the area, but cut the moment arm in half, you end up with the same static stability and control authority as before, but only half as much dynamic stability.

The same is true for vertical surfaces and yaw stability. This is why we typically have so much trouble getting decent yaw stability on canard models; the moment arm for the vertical tail surfaces tends to be so unusually short that even with enormous vertical tails, it's almost impossible to get good dynamic yaw stability. Meanwhile, the canard and all its supporting structure are typically so far ahead of the C/G that they add a significant amount of destabilizing effect in yaw. Even a slender boom or space frame that far in front can have a significant effect, as well as the side forces of even a zero-dihedral canard. None of these problems are insurmountable, but you do need to acknowledge and deal with them. If you decide to go with a canard, better plan on enlarging your vertical surfaces to compensate for the additional lateral area up front.

The other option is to resort to "weight-shift" control for trimming in pitch. Mount the wing on a pivot at the C/G, then raise (to slow down) or lower (to speed up) the nose of the wing relative to the fuselage pod to alter the trimmed airspeed. In flight, what actually happens is the fuselage pod swings forward and aft, altering the C/G location. As long as it doesn't move so far aft that the plane becomes unstable in pitch and/or yaw, it will work. Make sure you use a very beefy servo to control the wing incidence, the forces on it could be very large.

Of course the dynamic stability of a Rogallo is pretty terrible (some studies indicate dynamic instability, in other words the oscillations get bigger and bigger, instead of damping out), so be careful to avoid getting any oscillations started. Adding a tail of some sort on a decent moment arm could be a big help in that regard.

As far as structural concepts for adding a tail (or a canard for that matter), you might take a look at the horizontal tail added to the "Easy Riser" biplane in the movie "Fly Away Home". The other ultralight in that movie is a good example of using weight-shift to control pitch (and in that particular case, roll control as well). Some of the pre-WW I classics, such as the planes in the movie "Those Magnificent Men In Their Flying Machines" might be another good source of ideas.
Hi, Don
Well, you have certainly given me a lot of food for thought, it's just deciding where to start. I will study your detailed reply and let you know the outcome and perhaps when sorted I can let you have a more positive reply. Thank you SO much for the detailed reply and suggestions - at least I have something now to go on. Best Wishes to you and yours for the holiday.
Cheers Ted
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Old Dec 23, 2008, 06:46 AM
Crash Master
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As always, Don, thanks for the great explanation in terms we mere mortals can understand!
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Old Dec 23, 2008, 11:55 AM
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Roger, You have a great blog. Don, Thanks again! Your contributions to this thread would make a nice reference book on canards and other flying machines.
Charles
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Old Dec 24, 2008, 03:52 AM
What could possibly go wrong?
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Market Harborough
Joined Apr 2006
3,661 Posts
Quote:
Originally Posted by canard addict
Roger, You have a great blog. Don, Thanks again! Your contributions to this thread would make a nice reference book on canards and other flying machines.
Charles
I'll vote for that. Even I understood that one, mostly!

Merry Christmas to one and all

Nick
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Old Dec 24, 2008, 03:24 PM
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To all the Canard viewers and contributors: You have enriched my life with your participation in the thread. Best wishes to each of you for the holidays and the new year. Charles
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Old Dec 24, 2008, 05:43 PM
Jets are for kids-of all ages
Florida, USA
Joined Jun 2008
2,892 Posts
Merry Christmas Charles, Glad you started this thread. It is my favorite on RC Groups. Merry Christmas to all Canard-iacs. I went out this fternoon and flew the 52" Velocity again for three batteries, straight thru. It flies so good. Maybe Santa will bring me a real video camera, and I can get some good video of it flying.
Roger
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Old Dec 26, 2008, 08:51 AM
Jets are for kids-of all ages
Florida, USA
Joined Jun 2008
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Well went flying Christmas afternoon, and had set up the 52" Foamy Velocity for (2) 2250 batteries in parallel. I noticed a couple of times, a small glitch. But it was so fun to just keep flying, and after about 9-10 minutes, I was turning in towards the runway and from 75 feet up it went straight in. (Lost all control.) My wife did get a good video of it, and some post crash pictures. No damage to the hareware, so now it has all been transfered over to the 44" Velocity. I will post the video later.
Roger
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