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Old May 14, 2007, 12:11 PM
Rhinebeck CD-99,00,01,02
Tom Smith's Avatar
New Bern, NC
Joined Mar 2001
3,022 Posts
Tommy, my CG is at 15 3/4" from the leading edge of the canard. I changed two things for the next flight, which goes against my princibles. I added up canard and reflex in the ailerons. Now if it flies ok I will have no idea which change fixed it. Maybe I will remove one of those and try it that way. Heck, I know it flies the way it is.

RL, I will be at Morriston. Going to bring up some stuff to sell that I don't fly much anymore. Have you been to the last events up there? I was wondering if it would be worth while dragging that stuff there to sell. Tom
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Old May 14, 2007, 04:32 PM
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Airboatflyingshp's Avatar
B'ham UK
Joined Oct 2005
2,990 Posts
Tom sounds like You need a few fleets of these working............. or a Skycat
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Old May 15, 2007, 02:09 AM
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G_eronimo's Avatar
Near Koblenz
Joined Oct 2006
284 Posts
Voyager First Flight

F I N A L L Y !!

I did the real first flight with my Voyager. CG is too much in front, so I have to put it 1/2" or so back until it flies straight without elevator deflection.

I changed the batteries to LiPo 3S 2000 mAh, because in this plane died 3 packs of NiMh in a row and it didn't even fly. I'm running out of NiMh-packs.

My Plettenberg-motor has enough power but gets too hot, even with the improved cooling. I think, i should build in a brushless. Bigger brushed motors (600-size) are a little heavy. With an additional servo in front for nosewheel steering already and some lead in the nose, the battery can't be moved more forward. So any more weight in the back adds lead to the nose.

Landing gear is a bit "jumpy". Any idea how to change that? I can't move the CoG forward.

Uli
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Old May 15, 2007, 07:30 AM
Rhinebeck CD-99,00,01,02
Tom Smith's Avatar
New Bern, NC
Joined Mar 2001
3,022 Posts
We fly from a mowed cow pasture, and mine was jumpy too. Hold full down till she gets going and then let up on the stick. That should help to plant the nose wheel till she is flyable. Just where was your CG set at, and describe the rest of the flight. Did you have to hold full up like I did? My Mega was cool to the touch after my one and only flight, and I too am using a 3s 2400 lipo. .Tom
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Old May 15, 2007, 09:39 AM
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Joined Jun 2005
2,453 Posts
Uli, It seems that the UP reflex in the ailerons did the trick to kill some of the lift of the main wing. I believe that mine is set at 3/16" midway and it flies so great and hands off with neutral elevator. I shimed 1/16" at the canard front.My CG is at 15.75. This model is a joy to fly and each landing is a grease job. Some guys may get bored with it but I get a big charge of just watching it as a piece of art in the sky. Charles
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Old May 15, 2007, 07:14 PM
That motor isn't hot...
rosco's Avatar
Brisbane, Australia
Joined Aug 2005
425 Posts
Help with Canard prototype

Here is the a test bed that I had cobbled together. I have made it , so that I can get a feel for this...
http://www.rcgroups.com/forums/showthread.php?t=677858

This is a 'destroyable' prototype, of the prototype in the above link. Its an old flying wing of mine with a fuse and canard. The canard will do the work of the elevator and the wing part will only be ailerons.

I have a couple of questions for anyone who would be nice enough to chime in.

1.On a canard, does the elevator work opposite to a conventional plane?

2.The main wing is a meter wide (about 3 feet)...How much throw on the elevator should I have?

3.What types of reactions should I expect the plane to do, like porposing etc?

Thanks for any knowledge.
cheers
rosco
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Old May 15, 2007, 07:18 PM
That motor isn't hot...
rosco's Avatar
Brisbane, Australia
Joined Aug 2005
425 Posts
Woops, here's the picture...lest try again

Here is the a test bed that I had cobbled together. I have made it , so that I can get a feel for this...
http://www.rcgroups.com/forums/showthread.php?t=677858

This is a 'destroyable' prototype, of the prototype in the above link. Its an old flying wing of mine with a fuse and canard. The canard will do the work of the elevator and the wing part will only be ailerons.

I have a couple of questions for anyone who would be nice enough to chime in.

1.On a canard, does the elevator work opposite to a conventional plane?

2.The main wing is a meter wide (about 3 feet)...How much throw on the elevator should I have?

3.What types of reactions should I expect the plane to do, like porposing etc?

Thanks for any knowledge.
cheers
rosco
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Old May 15, 2007, 08:33 PM
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Joined Jun 2005
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Rosco, Down elevator is nose UP. !/2" elevator throw should be plenty. Get the CG correct with 10% static margin and it should fly. The winglets look a bit small. I would add some area to them. Charles
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Old May 15, 2007, 08:49 PM
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G_eronimo's Avatar
Near Koblenz
Joined Oct 2006
284 Posts
@Canard addict
Hello Charles,

What is an UP reflex? I am sure I know it in German, but I couldn't find a translation. My ailerons are straight with the profile, so no up or down like flaps (unless I have to roll). Is it that?

My CoG was at 16" from LE elevator. Maybe I can try the shimming too. I still have to correct the elevator, because it is not horizontal.

I measured the Voyager and put all the data into my ENTEX-Program and it gave me a CoG of around 18" from LE elevator.

Nitroplanes has a correction for the CoG for 270-280mm (~10.75") from the front end of the canard. That is way too much up front.

Lot of different CoGs to choose from.

So I'll stay with mine + 0.5" and maybe a little shimming at the elevator.
The problem with the shimming is, that the cover on the elevator will be higher than the fuselage.

But first I have to find another motor.

Uli
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Old May 15, 2007, 09:52 PM
Rhinebeck CD-99,00,01,02
Tom Smith's Avatar
New Bern, NC
Joined Mar 2001
3,022 Posts
I believe the CG should be measured back from the leading edge of the canard wing, not the elevator, which is the trailing edge of the canard. Mine CG is at 15 3/4". Reflex on this particular model refers to having both ailerons up a little when the stick is in neutral. Mine Long EZ is loaded in the car already and going to the field with me tomorrow. Tom
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Old May 16, 2007, 05:57 AM
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pjwright's Avatar
Chattanooga
Joined Nov 2004
149 Posts
LEZ Voyager Power

I worked with Medusa Research on a power system for the Voyager, based on reports here that the model was coming in around 40-44 oz. complete. I asked them what they had in a 400-size (28mm) brushless that would develop around 250-275 watts. This was based on a "rule of thumb" I'd read that 100 watts per pound was a good place to shoot for when designing a power system. They recommended a 1700Kv motor with 3S3200 lipos, drawing about 27 amps on a 8x4E prop. I added a Jeti 40-amp ESC. Total weight for this system is about 14 oz. This looks like about 3+ ounces more than a 3S2000 system, with at least 100 more watts of developed power.
I followed Canard Addict's advice on locating the receiver beneath a cockpit hatch ... turns out it's the only reasonable place to run all the wires. Will get the wings epoxied in place this week ... and then tackle setting the incidence of the canard relative to the main wing. No question but a shim is required. The kit design is roughly a zero-zero decalage which is apparently causing the need for up-elevator trim. Every 1/16" on the canard is about 1 degree positive incidence, by my calculation.

pjw
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Old May 16, 2007, 07:17 AM
Rhinebeck CD-99,00,01,02
Tom Smith's Avatar
New Bern, NC
Joined Mar 2001
3,022 Posts
Wow, 100 watts per pound. Mine is around 60 wpp and it flies great. Let's hear about the maiden. Tom
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Old May 16, 2007, 07:19 AM
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Don Stackhouse's Avatar
United States, OH, Bradford
Joined Jun 2005
3,988 Posts
Quote:
Originally Posted by pjwright
... This was based on a "rule of thumb" I'd read that 100 watts per pound was a good place to shoot for when designing a power system...
There are a number of rules of thumb, most of them questionable. The old rule of thumb (back before brushless and Li-polies became as common) was 60 watts per pound for a typical sport model. 100 watts per pound was considered appropriate for things like racers. I found that for slowfliers, indoor models and lightly loaded park fliers, 30 watts per pound was about equivalent to 60 watts per pound in a larger, heavier model.

Of course all of that refers to the power we can measure easily, the watts being pulled from the battery. That ignores the effect of motor efficiency, prop efficiency, aircraft efficiency, etc., so in the end it becomes a pretty inaccurate rule of thumb. The fact that we're now upping the requirement to 100 watts per pound for general applications, WITH a brushless motor on top of that, suggests to me that there is a bit of an epidemic of Tim-Allen-itis (MORE POWER! UGH! UGH!) going on these days.

Yes, it's nice to have the power (and with brushless motors and the new batteries it's easier to get without too many weight penalties), but remember that power is just one parameter, and more of it inevitably means less of the other parameters. The Gee Bee R1 was great in the power department, but was not particularly known for low speed performance, nor for stellar handling.

Quote:
... and then tackle setting the incidence of the canard relative to the main wing. No question but a shim is required. The kit design is roughly a zero-zero decalage which is apparently causing the need for up-elevator trim...
Way too much sleep is being lost over these incidence issues and the amount of elevator trim needed.

You all need to ask yourselves: "Do I only fly at one airspeed?" If so, then exactly what airspeed?

There are a bunch of forces and moments that result in nose-down effects, and a bunch of others that result in nose-up effects. Some of these are related to angle of attack ("alpha") and airspeed, others are relatively independent of them. The net result is some airspeed and angle of attack that results in all of these forces and moments being in equilibrium. This is the "trimmed airspeed".

If you change the elevator deflection a little, that alters the effective camber and incidence of the surface (stabilizer or canard) it's attached to, and therefore alters the trimmed airspeed. Other than perhaps in very extreme cases, it does not make the drag go through the roof, or the plane fall out of the sky, or the earth to rotate backwards, or the re-unleashing of the plagues of Egypt. Relax!

So, assuming a "zero" elevator deflection, a zero-zero incidence setup results in one trimmed airspeed.

Adding a 1/16" shim under the leading edge of the canard results in a slightly lower trimmed airspeed. Deflecting the elevator downwards by a similar amount will result in that same new, lower trimmed airspeed. Moving the C/G back a small amount will also result in that same new trimmed airspeed. Deflecting the ailerons up a small amount, increasing washout and in effect lowering the incidence of the main wing, will also result in that same new, lower trimmed airspeed. There are many ways to skin this particular cat!

So which way to reduce the trimmed airspeed is better? That depends entirely on your priorities. What airspeed do you want to fly at? Unless you have something very specific in mind for that, the whole issue becomes pretty pointless to begin with.

A better question is which approach results in the greatest versatility for the aircraft?

Yes, slightly increasing the canard incidence will probably reduce the trimmed airspeed with an infinitesimally smaller increase in drag than the same change made by deflecting the elevator.

Moving the C/G back will do it with even less drag, but at the expense of less static pitch stability (how much surplus do you have to begin with, so how much can you afford to lose?).

However, now what happens when you want to fly faster? You have to deflect the elevator to trim the nose down. If you did the initial retrim using an incidence change, then you will now have more drag at the higher speeds than if you had made the initial change with elevator trim.

If your main priority was maximum endurance at minimum flying speed, the incidence change might be better (although you will find it almost impossible to actually measure the vanishingly small improvement!). OTOH, if you want better top speed, you might be better off to leave the incidence alone and use elevator deflection for reduction in trimmed airspeed.

The other thing to bear in mind is that for trimmed airspeed, the "decalage" (the angle between the wing and the horizontal tail or canard) is what matters. However, the angles between each of those and the fuselage determines what angle of attack the fuselage will fly at. Carrying a lot of angle of attack on the fuselage at higher speeds will definitely increase drag! It also increases it at lower speeds, but is less of a factor there than at high speeds.

The designer of your kit had to make some decisions of their own in these regards when they first developed the model. Assuming they understood what was going on, and they went to the trouble to find some "optimum" setup (and I will admit there are some models out there where this was not done, or was not done properly, but natural market forces sooner or later will tend to weed those models out), they found some combination that resulted in what they felt was the best combination.

If your priorities are significantly different from theirs, you might benefit from a different setup. That does NOT make either your setup or their setup "right" or "wrong". It just means that you and the designer each have different priorities and mission profiles in mind.

In my own experience, the overall mission penalties for optimising for higher speeds and then using elevator deflection to achieve lower speeds are often better than the opposite approach. Carrying some elevator deflection is mainly a parasite drag issue, and parasite drag is more important at high speeds (induced drag dominates at low speeds, which is also why the fuselage alpha is less important at low speeds).

So, before you dive willy-nilly into redesigning the entire aerodynamic setup of your model, take a moment to figure out just exactly what it is that you're trying to accomplish. The key to success in airplane design is to understand the mission and to set good, clear goals based on it, then stick to what approach best achieves those goals.
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Last edited by Don Stackhouse; May 16, 2007 at 08:23 AM.
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Old May 16, 2007, 11:47 AM
Rhinebeck CD-99,00,01,02
Tom Smith's Avatar
New Bern, NC
Joined Mar 2001
3,022 Posts
Don

Don, I truly enjoy reading your analysis. On my maiden flight I had a little down elevator dialed in. Dumb move on my part. I thought I had set it level. The ailerons were straight, and the CG at 15 3/4". I needed full up to fly, but it flew pretty well. I hate to change two things at once, but I did it anyway.
WOW !
With 1/8" up elevator (down deflection) and 3/32" reflex (up) in the ailerons, it flew great. All that was needed was a few clicks of left aileron trim and she was flying hands off at a tad over 1/2 throttle.
I flew it around for about 10 minutes, doing a few rolls and a few loops. It handled very well. I set up for a landing and overshot the runway. This thing really is a floater. Went around and made a lower approach and greased it in. This is one really nice flyer. Just charged the 2400 mah pack and put back 700 mah. So two decent flights per charge are easily possible. She's a keeper. Thanks to all.
I must admit, I have flown just about everything in the book. I test fly models here for other guys on a regular basis, but this one had my knees knocking. Must be because it is such a different planform that I am not farmiliar with. Well, all that is behind me now, I really like this machine. Thanks again to all for their help and support. Tom Smith AMA 5953
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Old May 16, 2007, 05:08 PM
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Joined Jun 2005
2,453 Posts
Voyager Incidence

Don, I too, appreciate your discussions. Tom, You seem to have a sweetheart on your hands now!! I hope to see it fly some day. My Voyager has 67 watts per pound from the battery. The way I look at the Voyager's trim problems focusses on the angle of the main wing relative to the straight line of the fuselage bottom. You can easily see that the flat bottom of the wing is angled UP as it sits in the fuselage. For zero alpha or lift, this surface would have to be angled DOWN a bit relative to the fuselage bottom.. The wing is taking control and lifting more than it's share of the model. In order to correct this, leaving the wing as is, the canard wing has to be given more of the load by increasing it's alpha. I had this exact same problem with my original Goose as Andy Lennon Had with his. In filming the take off attempt, The rear of the model lifted first. This was corrected by adding 10% more area to the canard and dropping the main wing angle by one degree. The canard ended up with 3.5 degrees of positive and the main wing at zero. The angles were measured relative to the flat bottom of the surfaces and the alphas of the airfoils are not known. I figure that if the main airfoil is at zero alpha at flying speed,then it will get plenty of lift when the canard wing raises the nose. I use 3.5 degrees decalage. My Cango or Wingo canard had about -6 degrees of attack on the main wing when it was turned around relative to the fuselage so the canard wing had to be shimmed up 2.5 degrees at the TE to get the 3.5 degree difference. To kill some lift of the Voyager's main wing, the reflex had to be added thanks to the work of Ralph D. Charles
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