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Old Jul 17, 2007, 07:11 PM
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Voyager

SS, Yes I have the Voyager. Check this thread from pages 27 to 50 for lots of discussion on building and flying. The fuselage is 3 inches across at the cockpit. NIce to have you here. Charles
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Old Jul 17, 2007, 08:42 PM
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Dress Rehearsal

Top surfaces were added to the canard. The motor was installed and the model was set up as on it's wheels for some photos. There will be a vee top on the fuselage which will flow into the rear of the canard wing. Charles
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Old Jul 18, 2007, 05:38 AM
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ARF Canard ??

For our Al Capp fan -- Mr. Skonkworks:

Take at look at this Rutan Defiant:

http://www.raidentech.com/rutandefiant74.html

It ain't electric, but it'd be real interesting to hear from someone who has one. Twin .40's in a push-pull configuration!


pjw
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Old Jul 18, 2007, 05:44 AM
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Delta Canard Question

Now that I see the pieces all coming beautifully together, I have one question, Charles: will the forward fuselage carry the stress of that large canard with the kind of power that Medusa will supply?
I looks to my untutored eye like there's just a couple of 1/4" stringers between the canard and disaster...perhaps a 3/32" sheet doubler for insurance?

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Old Jul 18, 2007, 06:40 AM
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Quote:
Originally Posted by pjwright
...will the forward fuselage carry the stress of that large canard with the kind of power that Medusa will supply?
I looks to my untutored eye like there's just a couple of 1/4" stringers between the canard and disaster...perhaps a 3/32" sheet doubler for insurance?...
Well, a closer look at the photo makes it appear to be a bit more than 1/4" square, but he raises a good point.

Look at the "beefiness" of the structure in the wing and canard, with sheeting in the leading and trailing edges, creating substantial fully sheeted D-tubes, vs. the simple open-frame fuselage with its light structure composed of open rectangles. If that much beef is needed for the flying surfaces, then it is also needed for the structure that connects them. Of course the opposite is possible, maybe the fuselage is adequate, in which case the wing and canard are much more substantial (and therefore heavier) than necessary. In any case, there should be a balance between all of the structural elements.

The stringers look adequate for the tension and compression components of the bending loads, but there's essentially nothing but the covering to handle the shear due to bending moments or due to torsion loads on the fuselage, particularly in that open bay between the leading edge of the wing and the trailing edge of the canard. Yes, covering can do that if done properly (we got away with that on the wings of the original version of our Chrysalis sailplanes, although the new Mk II version of the 2-meter has some added diagonal bracing to help the torsional stiffness). However, relying on the covering for this task depends on having covering that is stiff enough, and that it is kept tight with regular maintenance if needed.

Yes, a doubler would make the covering a non-structural item, but to fully deal with the issue, you need to sheet the top and bottom as well as the sides. It might not take all that much, 1/16" might be adequate.

Alternatively, some diagonal struts in each of those rectangular openings to turn all of them (including the top and bottom) into triangles would work nicely, and might be lighter and less work at this point than fitting a doubler. It is important to get nice tight joints at the ends of the braces, if they pull loose you lose the stiffening effect. Some gussets in the corners might be cheap insurance.

Ideally you need to brace all of the rectangular openings that are within the primary load paths between the engine, landing gear attachments (don't forget the nose wheel), and the spars of the wing and canard.
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Old Jul 18, 2007, 06:49 AM
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Fuselage Stress up Front

Thanks PJ for your observation. It reminds me of Andy Clancy's thoughts on his 40" Lazy Bee. He had four 1/8" sq. balsa longerons between the wing and tail. He advised spruce and that did the trick.Together with the film covering, there is lots of strength to hold the section together. The flying surfaces take all the load and the fuselage goes along for the ride.On my Delta,the four longerons weighed in at 7 and 8 grams each. If they were soft balsa, there might be a problem. Also, there will be a 1/4 by 1/8 spine piece along the top of the fuselage forming a triangular section from the canard to the spinner which should add strength. I am grateful for your thoughts and will welcome more from any of you. My main concern now is the ability of this design to perform. How do you feel Don S. and others about the stability of the layout? It now seems that it may weigh 25 ounces. Charles
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Old Jul 18, 2007, 09:12 AM
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Quote:
Originally Posted by canard addict
...Together with the film covering, there is lots of strength to hold the section together...
provided that the covering is strong and stiff enough, and that it's kept tight.

Quote:
...The flying surfaces take all the load and the fuselage goes along for the ride.
The canard generates forces and moments. The wing generates forces and moments. The sum of all of those forces and moments determine the motions of the airplane. Something (the fuselage) has to connect those two and do that "summing" of the foces and moments. The fuselage definitely is not just "along for the ride".

Quote:
On my Delta,the four longerons weighed in at 7 and 8 grams each. If they were soft balsa, there might be a problem. Also, there will be a 1/4 by 1/8 spine piece along the top of the fuselage forming a triangular section from the canard to the spinner which should add strength.
Not the same "triangle", and doesn't accomplish the same thing. The shapes formed by the top stringer and the cross members and longerons are still going to be rectangles, and in any case still involves only the top, not the sides and bottom.

In a truss structure, you have long, slender struts that (theoretically) are each carrying pure tension or compression loads, and in combination absorb all of the forces and moments applied to the structure. In order for that to happen, there has to be a complete load path through the structure for each and every force and moment.

Generally speaking, that means that the shapes formed by the struts in the truss need to be triangles. Any polygon with more than three sides is not rigid, it can be distorted without changing the length of any of the sides.

In the case of your fuselage structure, your truss is formed from rectangles. Theoretically, the structure can be twisted and distorted without changing the tension or compression loads in any of the struts in the truss.

In traditional methods of stress analysis of trusses, the joints at the ends of each strut are assumed to be "pin" joints, in other words, hinges that can only transmit tension or comression into the individual strut, not bending. In the "real world", the (more or less) rigid connections at the ends of the struts (such as in your fuselage truss) can carry some bending loads, and the struts themselves do have some bending stiffness and strength. The torsional stiffness, and the carrying of shear loads due to bending loads in your fuselage structure comes from this reliance on the bending stiffness of the struts in your truss.

So, yes, your present structure does have stiffness in torsion and bending that is more than zero, even without the help of the covering. However, using the struts in the truss in this manner is very inefficient, and a poor use of their natural characteristics. Long, slender struts are much better suited to carrying pure tension and compression loads than bending, and trying to use them in bending also sets them up to fail from compressive buckling at a much lower load. Converting each of the individual rectangles in the truss into a rigid triangle by adding a diagonal member is a much more efficient approach. And yes, your covering can serve this same purpose, but only if it is tight, and sufficiently strong. If it's slack, or too thin, then the truss reverts to trying to apply bending loads to the individual struts.

Yes, you might get away with it, but the result will not be as strong, and for a given amount of strength and stiffness will not be as light, as a structure that uses the natural characteristics of its parts more efficiently.

Quote:
...My main concern now is the ability of this design to perform. How do you feel Don S. and others about the stability of the layout?...
To quote Harrison Ford, "You want it sugar-coated, or "right between the eyes"?"

Well, you've just heard some of my comments about structural stability. My guess is that your fuselage truss will hold together in the short term, but will be a maintenance headache in the long term. It's going to see a lot of flexing in directions that the individual parts are not well equiped to handle, so it's going to tend to get loose in the joints. This will be an especially nagging problem since the only way to get to some of those joints to re-glue them is likely to require stripping off the covering.

Besides from the canard, the fuselage is likely to see some substantial torsion loads from the nosewheel, assuming you're going to have landing gear. These will keep torquing the fuselage along its length, causing the joints and covering to loosen up, resulting in a loss of torsional stiffness. One possible problem that could result from this is flutter between the canard and the wing.

Aerodynamically speaking, I haven't run any numbers on it, but my "gut feel" says the overall moments and areas look workable from a stability standpoint.

Aspect ratios are low, so induced drag in tight turns will be high. It's likely to lose energy pretty quickly in a tight high-G turn, unless you can brute-force your way out of that situation with enough watts from the motor.

The taper opens the possibility of tip stalls. However, the canard layout, that requires that the canard be designed to stall first, never allowing the wing to stall, should avoid that problem.

Generally high drag is a bad thing, but for certain extreme, very high angle of attack maneuvers this can be used to an advantage. I could do some interesting things with a "Pibros" delta-wing Depron foam glider by exploiting this, such as bringing the plane to a sudden dead-stop in midair by pitching up abruptly to about 80 degrees AOA, then letting it plop to the ground right at my feet. Of course that was with a 7 ounce foamy, I would NOT recommend doing that with your 25 ounce wooden airplane!

The airfoils of both the wing and canard are way too thick for this Reynolds number region, which will result in a loss of max lift and a big increase in drag. In all probability there will be some separated flow on the aft portions of the top and/or bottom surfaces at all angles of attack, which could result in rather "mushy" elevator and aileron authority until they reach moderately large deflections, but they might then suddenly increase when they reach the edge of the separated wake. Turbulators might help a little if you run into problems with this.

OTOH, the stall characteristics of each surface should be fairly benign, almost "fuzzy", with no well defined stall break. This could make for a very gentle stall, but it also could open the door to problems with the wing giving up before the canard. I'd recommend trying stalls up high first, with very gradual entries and only partial, gentle stalls at first, with a well-forward C/G. If you find problems, some stall strips on the canard leading edge might help.

The other issue will be yaw stability, and the side area of the nose and slab-sided fuselage will aggravate that problem. Make sure you have plenty of fin area and that it's as far aft as you can get it.
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Old Jul 18, 2007, 12:47 PM
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Quote:
Originally Posted by pjwright
For our Al Capp fan -- Mr. Skonkworks:

Take at look at this Rutan Defiant:

http://www.raidentech.com/rutandefiant74.html

It ain't electric, but it'd be real interesting to hear from someone who has one. Twin .40's in a push-pull configuration!


pjw
Yeah, these ARFS look the way to go!
I am a Kelly Johnson fan, which was an Al Capp fan-and got sued for using "Skonkworks" Had to rename it to "Lockheed Skunkworks".
Al Capp was cool though!
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Old Jul 18, 2007, 01:08 PM
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Quote:
Originally Posted by canard addict
SS, Yes I have the Voyager. Check this thread from pages 27 to 50 for lots of discussion on building and flying. The fuselage is 3 inches across at the cockpit. NIce to have you here. Charles
Thank you! Glad to be on board. I want a video transmitter on board, and it appears to have a roomy interior. For limited video piloting, I would feel it has a strong suit, as it is stable. Hope to try this soon!
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Old Jul 18, 2007, 02:12 PM
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Don and PJW, You really got me to thinking of my structure which is usually loaded with triangles. With the possibility of rough landings or catching the canard tip on landing, I figued that a little beef would be good so eight braces were added plus a small plate behind the canard. Don, I would not hesitate to fly in an airplane which you approved of and I appreciate all the thought you put into your posts. I guess the short coupled fuselage brought out my low attention to detail. Honestly though, I have never seen a fuselage break in flight but have seen lots of wings fold and lots of bodies show their weakness in hard landings and crashes. I figure this model will do about 50 mph and will probably stall at 15. I am counting on gentle landings with the 6" single coil nose gear and the torsion mains.The elevons on both wings should take some stress from the fuselage because when the front wing adds lift, the rear wing will lose lift. this will hopefully cause a gentle rotation at which time the battery's momentom will cause it to fly through the bottom surface. Seriously, the batteries in our models are hard to hold down. The ailerons on both wings should reduce fuselage twist. Charles
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Old Jul 18, 2007, 08:27 PM
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Can't resist joining in after seeing the Lazy Bee picture!

With the LB's fuselage, Andy C came up with an incredibly simple gusset to strengthen the corner joints between longerons and uprights / cross members (are the latter 'shorterons' ? )

What he did at each longeron/upright/crossmember junction was to take a strip of 1/4 x 1/16" balsa strip, lay it across two of the above, CA glue it in place and trim it off to suit. He'd then brace the other one to the longeron at 90 deg. to the first gusset. It's easier to draw than explain, but I'm running a summer cold and can't cope with CAD right now The clever trick is that there's no complex cutting and sanding to fit of the gussets - lay them down, glue, trim off, wipe with sandpaper and now your three elements are nicely tied together.

Technically how good this is in engineering-speak, I have no idea.

But I had two Lazy Bees for a total of something like 7 Bee-years of flying and put those gussetted joints through some terrrible realworld testing. The oily Bee finally rotted away, the electric Bee was put into a situation that was basically un-survivable

Not bad performance for the price of a strip of 1/16" balsa, some CA glue and very little time.

Idle thought from one who scratch builds a lot of his toys - I don't even bother with balsa longerons and spars for my models, apart from the really small stuff. Spruce is hardly heavier than balsa that will do the same job. easier to find and much more reliable a material in strip form.

Cheers

Dereck
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Old Jul 18, 2007, 09:36 PM
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Charles, I am no expert, but based on other designs I have seen, I think it looks like it should work fine. The only question in my mind is about what will happen at full throttle. My thought is that you may have a bit too much lift for your power setup, which might make the pitch stability less predictable. To make use of full power, I am wondering if it may be necessary to try reflexing the ailerons on the main wing up slightly, and reduce the incidence of the canard. Anyway, I never mind to be proven wrong. I look forward to the flight tests.

By they way, have you seen the Gripen "Parkjet" thread. The recommended control setup is dual elevon control the same as your design. Looking at the videos it seems to give really good control at slow speeds and high angles of attack.
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Old Jul 18, 2007, 09:55 PM
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Lazy Bees

Good to hear from you, Dereck! My two Lazy Bees, an OS 10 powered 40" and an Electric powered 48" were built, I believe, in the mid nineties when they hit the market. The small one was flown for several years and was sold to a fellow in Americus, Ga. who flew it a few more years until the battery gave up and the nose was smashed. At SEFF this year, he said it was repaired and back in the air. The electric one was passed on to Tom Smith at Spring Hill, Fl. recently. Both models must be 12 years old. They were amazing light weight models built from tiny parts similar to Pat Tritle's models and seemed to depend on the film covering for strength. I have a 48" Tritle Stinson which weighs a whopping 15 ounces and shows what can be done with 1/8" balsa. I hope this post is still on subject since it follows canard structure integrity. Charles
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Old Jul 18, 2007, 10:55 PM
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John 235, Thank you for the encouragement and the Gripen thread. My chuck glider was the basis for the canard angle which is 3 degrees. I found that the nose just would not stay level at lesser angles. A hard nose UP toss only results in a gentle arc to level flight. I can only hope that the model,with full power at take off will climb to 200 feet where the power can be reduced for testing. I see no need for main elevon reflex with the high canard angle. The ugly chuck glider had the canard in the same plane as the main wing at first. I realize that the glider performance does not tell all. My first Goose required 10 square inches more canard area and a 1 degree reduction in the incidence of the main wing to give solid performance. It's glider flew well with the original set up. I hesitate to reduce the incidence of the canard because in my thinking, it should be loaded heavier to stall first. Charles
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Old Jul 19, 2007, 09:00 AM
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Charles, Have you ever built a canard that had the main wing stall earlier due to insufficient incidence on the canard?
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