"Tail First Forever"

[Rktman]

Since Winter weather doesn’t present a lot of opportunities to fly, I’m using the time to make continued headway on my list of scratch builds.

I’m a fan of canard gliders even though they’re the most temperamental and unpredictable of critters. They’re more difficult to design then a “standard” planform and more prone to unexpected glide performance. But once sorted out and trimmed right, these “tail-first” gliders are a beautiful sight.
At the moment, all I have are some idea sketches.

Anyway, here’s the mind sim as a visual:




Here’s the simple canard control method that I’m thinking of:



I still have to figure out a way to dial in the right flap angle during trimming and test flights. Nothing fancy, just some kind of jig that allows testing different elevator angles by limiting how far it swings down.

Next step is to finalize scaling and refining things then print everything out on paper and lay it out to see how it looks and feels.

As usual, since I’m not a power-builder like @kuririn nor mega creative like @BABAR when it comes to imaginative mechanical solutions, the build pace will be more in the realm of “leisurely”.

Stay tuned…

 

[shockie]

Put your glider dimensions into this to see what it tells you

Canard Center of Gravity Calculator

Canard Center of Gravity Calculator. Helps you locate your Canard's Center of Gravity (CG).

rcplanes.online

As far as having an adjustable flap, take a look at the old Estes plans where they use a small nylon screw to adjust the flaps simple and lightweight. Great design!

 

[Rktman]

Put your glider dimensions into this to see what it tells you

Canard Center of Gravity Calculator

Canard Center of Gravity Calculator. Helps you locate your Canard's Center of Gravity (CG).

rcplanes.online

As far as having an adjustable flap, take a look at the old Estes plans where they use a small nylon screw to adjust the flaps simple and lightweight. Great design!

Thanks for the link.

 

[Crawf56]

I like it.

 

[Rktman]

Had a rare chance to do some flying yesterday so this is a bit delayed. Jumped back into focusing on my build today. Funny how different things look on-screen vs the object itself once it’s laid out IRL. I ended up rescaling things to get the proportions and component placements right.

 

[Rktman]

Decided to go with a 3.03mm square carbon tube for the fuselage. While I’d normally use hard balsa or spruce, this’ll be on the largish side so its “backbone” will need to support a lot of stress from its flying surfaces, especially when launched on a C-class motor. The spruce weighed in at 4.11g vs the carbon tube’s 3.12g, and the carbon tube is absolutely bulletproof when it comes to durability and strength.

 

[Rktman]

Made a little headway. Got the main wing outlines drawn in and cut apart. Progress is likely to be slower than my usual snail’s pace since I’m having to do some repair work from the recent test flights two days ago and some early Spring yard tending. I’m hoping to finish airfoiling the wings tomorrow. Maybe.

 

[Ez2cDave]

Eric,

I think the lack of dihedral may cause "issues" ( a "wobbling" glide, around the Roll Axis, for example ).

Dave F.

 

[Ez2cDave]

View attachment 564566


Here’s the simple canard control method that I’m thinking of:

View attachment 564563

I still have to figure out a way to dial in the right flap angle during trimming and test flights. Nothing fancy, just some kind of jig that allows testing different elevator angles by limiting how far it swings down.

Eric,

The Canard does not have a "common shaft" for both flaps, correct ?

That presents both a complication and a potential benefit.

COMPLICATION : Since each "flap" of the Canard can move independently, Glide trimming may be difficult, as each "flap" would need to be adjusted, individually. Getting everything trimmed out may be a bit tedious.

BENEFIT : Since each "flap" of the Canard can move independently, that might provide an opportunity to "fine tune" the Glide Circle, by using different Canard "flap" angles to induce a turn.

Dave F.

 

[Rktman]

Got the airfoiling done and glued the wings and rudders together, but not much else. Too many other things happening lately. Since I’m using 3/32” balsa I kept the shaping real conservative to avoid thinning the wings out too much and sacrificing strength. In retrospect, maybe I should’ve gone with 1/8” so I could have given it a better airfoil and ensure I could use a C class motor if I want to loft it that high.




I’m hoping to get two coats of lacquer onto the balsa surfaces to strengthen and humidity-proof things.

 

[Rktman]

Made a little more progress; most of the main components are together, with only the more involved and time-consuming canard retention and trimming system to be devised and fabricated.

 

[Crawf56]

Looking very nice!

 

[Rktman]

Looking very nice!

Appreciate that, and thanks for visiting the build.

 

[Rktman]

I decided to try something a little different this time around with the canard hinge assembly. Since I’ve yet to find a self-adhesive tape that doesn’t eventually come loose after several flights, I sandwiched a strip of Tyvek between two pieces of 1/32” balsa laminated together to form an interior hinge. I’ll still attach a Blenderm or Mylar strip to the outside of the joint as usual, but the interior strip of Tyvek should make for a hinge that lasts longer than the glider. If this works well, I’ll use the same method for all my future hinges.

 

[BABAR]

I decided to try something a little different this time around with the canard hinge assembly. Since I’ve yet to find a self-adhesive tape that doesn’t eventually come loose after several flights, I sandwiched a strip of Tyvek between two pieces of 1/32” balsa laminated together to form an interior hinge. I’ll still attach a Blenderm or Mylar strip to the outside of the joint as usual, but the interior strip of Tyvek should make for a hinge that lasts longer than the glider. If this works well, I’ll use the same method for all my future hinges.

View attachment 566586


View attachment 566587

Use sewing thread or dental floss to "sew" the inboard and outboard edges of the tape hinge to the balsa. I prefer floss as it is stronger. Wick in thin CA once you are done to lock it in. You're balsa will break before the hinge does. I prefer a double tape hinge with this technique, but it will work with a single tape hinge. See "Au Naturale" thread under Scratch Builds for details. I used to sew the full width of the hinge, until I realized that only the inboard and outboard portions really see any stress. In fact, to reduce weight, you can actually REMOVE the middle part of the tape hinge, leaving only 5-10 mm on the inboard and outboard edges, sew those in, and the hinge will work just as well.

 

[shockie]

Hey Rktman:

When you get the chance before you test fly it, put it's dimensions into that cg calculator and let's see how close it comes out to versus real life.

Like to see where the boost and glide cg is located

 

[Rktman]

Use sewing thread or dental floss to "sew" the inboard and outboard edges of the tape hinge to the balsa. I prefer floss as it is stronger. Wick in thin CA once you are done to lock it in. You're balsa will break before the hinge does. I prefer a double tape hinge with this technique, but it will work with a single tape hinge. See "Au Naturale" thread under Scratch Builds for details. I used to sew the full width of the hinge, until I realized that only the inboard and outboard portions really see any stress. In fact, to reduce weight, you can actually REMOVE the middle part of the tape hinge, leaving only 5-10 mm on the inboard and outboard edges, sew those in, and the hinge will work just as well.

I can see where this would really work well on a larger glider like my Ecee Thunder. I probably wouldn't have had to resort to Dubro hinges had I used your method. I have some larger glider scratch builts swirling around in my mind sim vault that I want to get to, and will definitely consider it as a better (and lighter) alternative.

 

[Rktman]

Hey Rktman:

When you get the chance before you test fly it, put it's dimensions into that cg calculator and let's see how close it comes out to versus real life.

Like to see where the boost and glide cg is located

I ran it earlier out of curiosity. The app put the CG about 1.4" from the apex of the main wing's leading edge. The final placement of the canard will probably change so I'll definitely run it again before trimming and a test flight to see how it compares.

 

[Rktman]

After experimenting with different methods of devising an adjustable elevator-stop using a malleable piece of wire, I realized that it was a dead end. The music wire I had on hand was either too stiff or too thin and soft, and the closest I came was a paper clip; stiff enough to stop the flap’s travel but still bendable. Unfortunately bending both stops at exactly the same angles in both the X and Y axes in a consistent way proved impossible.




So change of plans. I decided to adopt the method used by the designer(s) of the Estes Spaceplane: tiny nylon adjustment screws.

To position the screws so that they’d be in the most effective area possible (on the midline of the motor tube) I had to relocate the canard wing to the tube’s top.




That meant scrapping the two existing side-mounted canard/flap assemblies and modifying a new one that was in one piece. Since I was out of 1/32” balsa I had to sandwich 2 pieces of 1/16” to form the canard wing and flaps.

Since it would sit on a curved 24mm motor tube, there wouldn’t be much contact area to glue it securely in place so I decided to use balsa “fillets” – two balsa strips sanded down to match the tube’s curvature.









I can see that this will take a bit of trial and error to get right, so fair warning that updates may be delayed.



…to be continued.

 

[Ez2cDave]

Eric,

I think the lack of dihedral may cause "issues" ( a "wobbling" glide, around the Roll Axis, for example ).

Dave F.

Eric,

The Canard does not have a "common shaft" for both flaps, correct ?

That presents both a complication and a potential benefit.

COMPLICATION : Since each "flap" of the Canard can move independently, Glide trimming may be difficult, as each "flap" would need to be adjusted, individually. Getting everything trimmed out may be a bit tedious.

BENEFIT : Since each "flap" of the Canard can move independently, that might provide an opportunity to "fine tune" the Glide Circle, by using different Canard "flap" angles to induce a turn.

Dave F.

Eric,

You may have missed my earlier posts ( quoted above ).

Dave F.

 

[Rktman]

Eric,

You may have missed my earlier posts ( quoted above ).

Dave F.

Your concern is acknowledged, but as we’ve discussed at length before in one of my other build threads, it won’t present a problem.

 

[Rktman]

Finally able to make additional progress on this build.

0° flap locks (1/8” dowels) were glued in. I had to use standoffs since the flaps now need to clear the tube sides, something I didn’t anticipate when relocating the canard wing to the top of the booster tube. With the flap locks in place, the elevator flaps are kept at a neutral 0° angle until the motor unit is ejected, releasing them.

 

[Crawf56]

Good stuff. I think many times, there are different solutions to an issue.

A lot of the time, the solution is inspired by what building techniques are comfortable to us. Personally, I am used to sanding balsa or plywood. Foam and 3D printing aren't really my specialty (though I have built foam RC models).

 

[gsitexas]

Finally able to make additional progress on this build.

0° flap locks (1/8” dowels) were glued in. I had to use standoffs since the flaps now need to clear the tube sides, something I didn’t anticipate when relocating the canard wing to the top of the booster tube.

View attachment 569169

Awesome job Eric, really liking this design and following your build process closely.

Best regards,

Keith

 

[Rktman]

Awesome job Eric, really liking this design and following your build process closely.

Best regards,

Keith

Much thanks for the kind words!

 

[Ez2cDave]

I'm looking forward to the trimming and test flights !

Dave F.

 

[Rktman]

Installed the adjustment tab and screws. Tiny fiddly pieces that initially required tweezers in lieu of fat fumbly fingers. I ended up having to hold them in place and aligned for 20 minutes until the wood glue set enough for me to put in a CA fillet to reinforce the attachment area.

Just a tip: if you ever use this method on a scratch build or an Estes Spaceplane repro, you might want to consider drilling the screw hole through your piece of balsa before cutting the tab out and drilling it later. Why? I used 3/32” hard balsa and when using a pin vise to drill the hole, the wood still split along the grain. Tried again after coating the tab with thin CA, and this time the wood split again while I was putting the nylon screw through.

I guess the tab is small and relatively fragile once cut out. Drilling the hole through the balsa sheet first should present far less problems since you’re not trying to manipulate a tiny piece. Hindsight is a great thing isn’t it? Wish I’d realized that at the time. Anyway I ended up laminating a 1/64” piece of ply onto the tab. Did the trick, no more splitting problems, and being harder than balsa, it keeps the nylon screw snugly in place so it won’t tend to back out.




I put reference marks on the screws and tabs so I could track how many adjustment turns I made to keep it even for both sides, ensuring each elevator flap would have the same angle of deflection. What’s nice is that I can also use these to correct for a too-tight circling radius (usually the result of one wing or side being heavier).




The finished flap lock/motor unit in launch position.

 

[Rktman]

Adding some visibility with my usual permanent marker color palette (orange, best for contrast against the tan of crop stubble or green planted farm fields that I fly in).

 

[Rktman]

Now that everything is in place, I went to the online canard CG calculator recommended by @shockie (Canard Calculator https://rcplanes.online/cg_canard.htm) and got the following:




At a 10% static margin, the CG would fall 8.93” from the canard root LE. With a static margin of 15% it would fall 8.76” from the canard root LE. At 20% it would be at 8.6” from the canard root LE. All of these CG locations seem excessively far back, as they generally are located somewhat ahead of or near a canard glider’s main wing leading edge, even in the case of a swept-wing design like this.

Any suggestions on what static margin to go with from the group?

Since the canard wing will have adjustable flaps and that’s what I was going to trim it with, I was going to go either with the more *conservative 10% or a middle-of-the-road 15%.

*The website notes that: “Low Static Margin gives less static stability but greater elevator authority, whereas a higher Static Margin results in greater static stability but reduces elevator authority. However, too much Static Margin makes the aircraft nose-heavy, which may result in elevator stall at take-off and/or landing, whereas a tail-heavy aircraft will also be unstable and susceptible to stall at low speed, as during the landing approach.”

 

[shockie]

Installed the adjustment tab and screws. Tiny fiddly pieces that initially required tweezers in lieu of fat fumbly fingers. I ended up having to hold them in place and aligned for 20 minutes until the wood glue set enough for me to put in a CA fillet to reinforce the attachment area.

Just a tip: if you ever use this method on a scratch build or an Estes Spaceplane repro, you might want to consider drilling the screw hole through your piece of balsa before cutting the tab out and drilling it later. Why? I used 3/32” hard balsa and when using a pin vise to drill the hole, the wood still split along the grain. Tried again after coating the tab with thin CA, and this time the wood split again while I was putting the nylon screw through.

I guess the tab is small and relatively fragile once cut out. Drilling the hole through the balsa sheet first should present far less problems since you’re not trying to manipulate a tiny piece. Hindsight is a great thing isn’t it? Wish I’d realized that at the time. Anyway I ended up laminating a 1/64” piece of ply onto the tab. Did the trick, no more splitting problems, and being harder than balsa, it keeps the nylon screw snugly in place so it won’t tend to back out.

View attachment 570496


I put reference marks on the screws and tabs so I could track how many adjustment turns I made to keep it even for both sides, ensuring each elevator flap would have the same angle of deflection. What’s nice is that I can also use these to correct for a too-tight circling radius (usually the result of one wing or side being heavier).

View attachment 570497


The finished flap lock/motor unit in launch position.

View attachment 570498

Now that everything is in place, I went to the online canard CG calculator recommended by @shockie (Canard Calculator https://rcplanes.online/cg_canard.htm) and got the following:

View attachment 570763


At a 10% static margin, the CG would fall 8.93” from the canard root LE. With a static margin of 15% it would fall 8.76” from the canard root LE. At 20% it would be at 8.6” from the canard root LE. All of these CG locations seem excessively far back, as they generally are located somewhat ahead of or near a canard glider’s main wing leading edge, even in the case of a swept-wing design like this.

Any suggestions on what static margin to go with from the group?

Since the canard wing will have adjustable flaps and that’s what I was going to trim it with, I was going to go either with the more *conservative 10% or a middle-of-the-road 15%.

*The website notes that: “Low Static Margin gives less static stability but greater elevator authority, whereas a higher Static Margin results in greater static stability but reduces elevator authority. However, too much Static Margin makes the aircraft nose-heavy, which may result in elevator stall at take-off and/or landing, whereas a tail-heavy aircraft will also be unstable and susceptible to stall at low speed, as during the landing approach.”

I'd start at 10% and try a few canard elevator angle adjustments. I think you will want more elevator authority Then repeat it with 15%.

You could add a small angled hook towards the nose and catapult launch it for trimming, before launching it.

What motors do you plan to use

Where will the boost CG be located ?.
It will obviously change as you go up from A to C.

View attachment 570499