Vladimir's ELF DLG Build Log - Assembling and Trimming a V-Tail Discus Launch Glider

Santa was exceptionally good to my family this year. A nice new ELF Discus Launch Glider appeared under the tree. I had never flown a glider before, but they looked like a lot of fun.

My first impression on opening the box was amazement on how light everything is.

If you aren't familiar with this glider, it is a 39 inch mosquito class. Fully outfitted, it should weigh just shy of 100 grams - which is pretty good for its pod and boom construction! It is launched into the air with a discus-like spin and it can reach altitudes of about 60 feet without too much effort. The REALLY good ones have been reported at over 100 feet.

It is a two channel plane, only needing controls for the elevator and rudder. There is no motor (obviously) or ailerons (thankfully!). The simplicity of design and control makes this a great choice for beginners.

Here's a V-Tail in Motion

Which is your favorite? V-Tail or X-Tail?

  • V-Tail
  • X-Tail
See results without voting

V Tail or X Tail

The first choice you need to make when ordering is the tail configuration.

I chose the V-Tail thinking that it would be safer when landing. The X-Tail has part of the rudder that hangs below the carbon fiber tube of the body. Owners of the X-Tail say it isn't a problem for them, but I thought I would be extra-safe, just in case.

The drawback with the V-Tail is that the servos that control the elevator and the rudder must be mixed in order have the glider move where you want it to. Check out the video to the right to see what I mean.

With the X-Tail, one servo is dedicated to controlling the rudder and one servo controls the elevator.

I'll discuss the configuration of the V-Tail and the radio later.

With a quality transmitter like the Spektrum DX6i, this shouldn't be a problem though.

The completed ELF from Vladimir's Models.  A great kit for F3K
The completed ELF from Vladimir's Models. A great kit for F3K | Source

ELF DLG in Flight

I know of two distributers for the ELF.

In the USA, you may order from Kennedy Composites.

In Europe, you may order from Hyperflight.

Opening the Package

First of all, I was shocked at how light the package was. I don't know why, because the whole point of the glider is to be light, right?

The wing was carefully packaged in bubble wrap and I was very impressed at how securely the Aerolite covering adhered to the wing. I have had mixed results with the product when I tried to install it on planes myself so I can appreciate the skill it takes to make this so crisp!

The two part pod is a translucent yellow and easily dry-fit into the wing. The two push-rods were tucked nicely inside the boom.

A small bag of parts including some screws and the teflon tubing to keep the pushrods aligned was also included.

Glue the pod to the boom in the three locations noted.  Again, don't use an accelerant. Click on the picture to get the Full-Sized image
Glue the pod to the boom in the three locations noted. Again, don't use an accelerant. Click on the picture to get the Full-Sized image

Glue the Pod to the Boom

The first step is to dry fit the pod to the boom. I tested the fit of all of the electronics first just to make sure there were no major issues.

The front of the fixed pod section should be aligned near the spot on the boom where it starts to slope. Set the wings on the mounting pegs and then make sure the removable nose pod fits fine. You don't want to mount the fixed pod section so far back that nose pod won't fit.

Once you are satisfied with the location on the assembly, take it apart and sand the boom with 150 grit sandpaper where the fixed pod section will attach.

Put the fixed pod section back on the boom and glue at the three attachment points using medium CA glue. Again, don't use a kicker! Make sure that the two predrilled holes for the pushrods remain clear of the glue.

Installing the Control Horns

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The control horn should be installed 13.5 - 14 mm from the outside of the bevel.  Make sure that you cut ALL the way through the foam.  A helpful tip is to cut the slit about 6 or 7mm.  Then, insert the control horn from the OUTSIDE.  As you pull it through the foam, it will gently cut the foam and guarantee a perfect fit.Make sure the control horn is flush with the outside of the tail surface.  You will add a drop of foam safe CA to each, and the horn will wick the glue all the way through.
The control horn should be installed 13.5 - 14 mm from the outside of the bevel.
The control horn should be installed 13.5 - 14 mm from the outside of the bevel.
Make sure that you cut ALL the way through the foam.  A helpful tip is to cut the slit about 6 or 7mm.  Then, insert the control horn from the OUTSIDE.  As you pull it through the foam, it will gently cut the foam and guarantee a perfect fit.
Make sure that you cut ALL the way through the foam. A helpful tip is to cut the slit about 6 or 7mm. Then, insert the control horn from the OUTSIDE. As you pull it through the foam, it will gently cut the foam and guarantee a perfect fit.
Make sure the control horn is flush with the outside of the tail surface.  You will add a drop of foam safe CA to each, and the horn will wick the glue all the way through.
Make sure the control horn is flush with the outside of the tail surface. You will add a drop of foam safe CA to each, and the horn will wick the glue all the way through.

Installing the Control Horns

The first step to properly assembling the V-Tail is to install the control horns.

Measure precisely per the instructions (13.5 - 14 mm from the outside edge of the bevel) and cut a slit through the control surface. The instructions call for an 8 - 9 mm slit, but I cut mine about 6 or 7 mm. Then, from the OPPOSITE side, I inserted the control horn. The slit was too small, but as I gently pulled it through, it lengthened the opening to create a perfect fit. The edge of the control horn should be flush with the outside of the tail foam and secure it with foam-safe CA glue.

Note: Make sure the control horn is fully seated. The horn should go all the way through to the other side of the tail as it will need the entire thickness of the foam to get the best adhesion. One of the most common failures of this piece is due to it not being installed with the entire depth of the tail.

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Set the angle to 106 degrees using a protractor and tape it in place.  Then, use some foam safe CA glue secure the two sides together.  Do not use an accelerator.The first step is to align the two tail pieces and tape them together temporarily.
Set the angle to 106 degrees using a protractor and tape it in place.  Then, use some foam safe CA glue secure the two sides together.  Do not use an accelerator.
Set the angle to 106 degrees using a protractor and tape it in place. Then, use some foam safe CA glue secure the two sides together. Do not use an accelerator.
The first step is to align the two tail pieces and tape them together temporarily.
The first step is to align the two tail pieces and tape them together temporarily.

Assembling the V-Tail

I didn't have a protractor handy, so I downloaded a picture of one from the internet and used that as a template.

Temporarily tape the two tail pieces together on the back side. This is used to ensure properly alignment on the next step.

Bend the tail pieces to exactly 106 degrees and tape it to the protractor. Then glue them together, but do not use a CA accelerator.

I put a piece of plastic under the joint to catch any glue that dripped down - it saves cleaning up a mess later.

Now, use a protractor and glue the two tail pieces at 106 degrees. I did not have a protractor, so I downloaded a picture of one from the internet and printed it. I used that as the gauge. Do not use accelerant during this step. Instead, use some low-tack tape like painters tape to keep the tail assembly at the correct angle until the glue sets up on its own. Just to be safe, I kept it taped over night.

Click thumbnail to view full-size
This is a great trick for aligning the tail PERFECTLY!  Temporarily add the wing and turn the glider upside down on the table.  Add the tail in place so the tips of the tail and the wing all touch.  Voilà! The tail is aligned!After the glue has set up, it is easy to see how the tail bisects the angle of the wing.
This is a great trick for aligning the tail PERFECTLY!  Temporarily add the wing and turn the glider upside down on the table.  Add the tail in place so the tips of the tail and the wing all touch.  Voilà! The tail is aligned!
This is a great trick for aligning the tail PERFECTLY! Temporarily add the wing and turn the glider upside down on the table. Add the tail in place so the tips of the tail and the wing all touch. Voilà! The tail is aligned!
After the glue has set up, it is easy to see how the tail bisects the angle of the wing.
After the glue has set up, it is easy to see how the tail bisects the angle of the wing.

A Cool Trick to Align the Tail with the Wings

Temporarily bolt the main wing in place. Turn the glide upside down and gently rest the wings on a flat surface like the kitchen counter. The V-Tail will automatically align with the wings as shown in the picture to the right. Cool trick, right?

A thin line of CA glue on the boom will tack the the tail in place and secure it well enough to turn the glider right side up. Once the CA has set up, turn the glider right-side-up and run the CA glue along the entire boom where it touches the tail. We don't want THAT falling off mid flight!

Note: The instructions do not call for it, but I went ahead and sanded to portion of the boom that abuts to the tail surface. I then glued to the sanded surface. I can't imagine that there would be a glue failure on an unsanded surface, but I figured it was better to be safe than sorry.

Aligning the Teflon Tubes

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Slip the five pieces of teflon tubing over the pushrods and tape the pushrods in place, ensuring as straight of a line as possible.Spread the cut tubing along the length of the boom and gingerly tack it in place with CA glue.  I used a pin to apply the glue to the tubing, making sure not to have any slip into the ends of the tubes.
Slip the five pieces of teflon tubing over the pushrods and tape the pushrods in place, ensuring as straight of a line as possible.
Slip the five pieces of teflon tubing over the pushrods and tape the pushrods in place, ensuring as straight of a line as possible.
Spread the cut tubing along the length of the boom and gingerly tack it in place with CA glue.  I used a pin to apply the glue to the tubing, making sure not to have any slip into the ends of the tubes.
Spread the cut tubing along the length of the boom and gingerly tack it in place with CA glue. I used a pin to apply the glue to the tubing, making sure not to have any slip into the ends of the tubes.

Install Teflon Tubing for Pushrods

The next step is to install teflon tubing guides. These tubes guide the carbon pushrods and will route along the upper side of the boom.

Cut the tubing into ten 3/8" pieces. Slip five on each pushrod and lay the pushrod from the control horn on the tail into the rear of the fuselage. Spread the five pieces fairly evenly along the boom and then tape the carbon rods to the boom. This will secure them in place and serve as clamps for the teflon tubes.

Now its time to glue. I was a little bit nervous about applying the CA. I decided to dip a pin in CA glue and then touch it to the joint where the teflon touches the boom. It was a lot easier to control the amount of glue using the sewing pin and you really don't need much sticking power.

After the glue has set up, flip the boom over and repeat the process on the other side.

Once the glue has cured, remove the tape.

Click thumbnail to view full-size
Step One:  Bend the pushrod tip to 90 degrees using a pair of pliers.Step Two:  Slip the pushrod tip over the pushrod and crimp it tightly with a crimper (pliers work well too).Step Three.  Add a drop of Thin CA glue as an added protection.  Let dry.I had to sand the tips a bit to get them to insert into the control horns.  It took a bit, but they are very snug and aren't going anywhere.
Step One:  Bend the pushrod tip to 90 degrees using a pair of pliers.
Step One: Bend the pushrod tip to 90 degrees using a pair of pliers.
Step Two:  Slip the pushrod tip over the pushrod and crimp it tightly with a crimper (pliers work well too).
Step Two: Slip the pushrod tip over the pushrod and crimp it tightly with a crimper (pliers work well too).
Step Three.  Add a drop of Thin CA glue as an added protection.  Let dry.
Step Three. Add a drop of Thin CA glue as an added protection. Let dry.
I had to sand the tips a bit to get them to insert into the control horns.  It took a bit, but they are very snug and aren't going anywhere.
I had to sand the tips a bit to get them to insert into the control horns. It took a bit, but they are very snug and aren't going anywhere.

Install the Pushrod Tips

Extend the pushrods beyond the tail to give yourself some working room. Take two of the pushrod tips and bend them to 90 degrees using a pair of pliers.

Note: one end of the pushrod tip is tubular, and one end is a thin piece of metal. Don't bend the tubular section.

Slip the opening of the pushrod tip over the end of the pushrod until it is well-seated.

Crimp the pliable metal over the carbon pushrod. Be careful! You don't want to accidentally bend or snap the carbon pushrods.

Lastly, add a drop of thin CA glue to the connection. The crimping alone should be enough, but it is better to be safe than sorry!

When the glue is dry, insert the pushrod tips into the control horn.

An Alternative Technique

As an alternative to adding a drop of CA glue, add an inch or so of heat shrink tubing on to the pushrod before installing and crimping the tip. Afterwards, slide the heat shrink over the joint and shrink it per the manufacturer's instructions.

One side of the servo mounting tab is cut off.  Removing both sides will make it that much easier to position them next to each other on the boom.
One side of the servo mounting tab is cut off. Removing both sides will make it that much easier to position them next to each other on the boom.

Servos and Battery

The distributors recommend using the following servos: Dymond D47, Ripmax SD100 or the LSX110. I chose the Dymond D47 because that is what they had in stock. I can't vouch that one model performs better than the next.

I did cut off the mounting horns from the servo body. These were just extra weight and got in the way in the tight confine of the pod. A quick dremel tool cut will take care of it. There is no need to worry about being too neat. (Plus, I will do just about anything to get the opportunity to use a dremel tool!)

The Shread Smart Lipo 240 is the battery to beat. This has an onboard charging circuit, voltage regulator and gives warning beeps when it is running low. It is pretty slick and can be recharged straight from another Lipo. It is a lot more expensive than a regular battery, but I like the features. You certainly could go with a less expensive battery.

The Servos are glued in place.
The Servos are glued in place.

Locating the Servos

Lay out the assembly before trying to glue it in place. The battery goes in the very front and the servos behind. I made an ink mark on the boom where the battery would be installed, making sure to leave enough room for the speaker in front.

The servos are installed immediately behind the battery. Make sure you know which servo controls the rudder and which one controls the elevator (or elevator and aileron if you choose to use elevons). The pushrods will be cut to different lengths, so now is the time to plan it out.

Once you are satisfied, gently sand the bottom of the servo and the top of the boom. Then use a bit of CA glue to secure the servos in place.

Shread LIPO Instructions

If you have never used a Shread LIPO, here are the instructions on how to use and recharge it.

Install the Battery

The battery is installed in the very front of the fuselage. Simply add a drop or two of CA glue to keep it in place.

Again, route the wires to the receiver box. You will need to remove the plastic connector and insert the wires under the bridge before reinstalling the connector.

I used a toothpick dipped in thin CA glue to hold the battery wires in place along the boom, just to keep them out of the way and neat.

Install Pushrod Tips to Servos

The pushrod tip bent into a Z-Bend.
The pushrod tip bent into a Z-Bend.

Attach Pushrod Tips to the Servos

Using pliers, make a Z-Bend into the pushrod tips that will connect the servo lever arm to the pushrod.

Slip the Z-bend into the lever arm. Make certain that the servo is centered by temporarily connecting the receiver and battery, binding the equipment and testing to make sure the servos are centered.

You will need to trim the pushrods to length.

Tip: Use the good practice of measuring twice and cutting once. Cut the pushrod too short, and you are guaranteed a trip back to the hobby shop for new pushrod tips and carbon pushrods. Not fun!

As you read above, I secured the servos in place with CA glue BEFORE I cut the the pushrods to length. This caused a bit of a problem as the Z-bend tips had to be inserted into the lever arm before the pushrods were set in place.

To solve this dilemma, I unscrewed the lever arm from the servo, installed the tip onto the pushrod and screwed the lever back in again. I am not sure that was any easier than installing the pushrod tips to the servo and then glueing the servo in place - but it worked! Another option is to remove the pushrod tips from the control horns on the tail and sliding the pushrods back far enough to insert them into the Z-bend tips. I did not choose that option as the pushrod tips fit extremely tightly into the control horn and I did not want to try to remove them.

Make sure everything is at the correct length and the control surfaces are in line with rest of the tail. Once satisfied, crimp the tips and put a small drop of CA glue over the joint.

Just in case you need to replace the servo at some point, you can unscrew the lever arm from the servo. That keeps the pushrod, pushrod tip and lever arm together. Simply replace the servo with an identical one and everything should fit right back together without having to reassemble the pushrod mechanism.

Now is a Good Opportunity to Try it Out

With the servos attached and the pushrod tips secured in place, go ahead and power up the receiver. Sure, neither the receiver nor the battery are permanently affixed, but now is a good time to make sure the servo/control horn mechanism is working fine.

There is a bit of extra space now to work out any kinks. Install the remaining equipment and it will be tighter.

Click thumbnail to view full-size
With a small screwdriver, gently release the tab holding the wires in place.One servo lead is fed under the bridge and the plastic connector is reassembled.The second set of servo wires is routed under the other side of the bridge and fed back into the connector.Ah!  OCD is back under control and both sets of servo wires are in place, under the servos and through the bridge.  No loose mess here!And on the backside, all the wires are tacked into place out of the way of the pushrods.
With a small screwdriver, gently release the tab holding the wires in place.
With a small screwdriver, gently release the tab holding the wires in place.
One servo lead is fed under the bridge and the plastic connector is reassembled.
One servo lead is fed under the bridge and the plastic connector is reassembled.
The second set of servo wires is routed under the other side of the bridge and fed back into the connector.
The second set of servo wires is routed under the other side of the bridge and fed back into the connector.
Ah!  OCD is back under control and both sets of servo wires are in place, under the servos and through the bridge.  No loose mess here!
Ah! OCD is back under control and both sets of servo wires are in place, under the servos and through the bridge. No loose mess here!
And on the backside, all the wires are tacked into place out of the way of the pushrods.
And on the backside, all the wires are tacked into place out of the way of the pushrods.

Route the Wires Neatly

You really don't need to do this step, but I like to have a nice, clean interior. I took the lead wires from the servos and gently pulled back the three plastic tabs and removed the red, white and black wires from the plastic connector.

The three wires were fed under the plastic bridge to the area where the receiver will be located.

Once the wires are through and are free from obstructions (like the Z-bent pushrod tips) reinstall the plastic connector. Make sure the three wires are installed in the exact same location from where they were removed. I took a picture with my camera phone, just to be sure.

Once the wires are securely seated in the connector, press the plastic tabs back into place. On my servos, I heard a little *snap* when they were secured in place.

To make sure the wires stayed out the way, I added a small drop of hot glue to keep the neat, clean and orderly. Look at the pictures to the right to see the process.

Ah!  Everything in place.  I just need to tack the servo wires out of the way.  Note how the wires all are routed UNDER the bridge.  A small dab of CA glue applied with the tip of a pin is just enough to hold the wires in place.
Ah! Everything in place. I just need to tack the servo wires out of the way. Note how the wires all are routed UNDER the bridge. A small dab of CA glue applied with the tip of a pin is just enough to hold the wires in place.
Finally!  The receiver, smart LIPO battery and two tiny servos arrived and are ready to be installed.  The AR6255 receiver was recommended due to the carbon fiber in the boom.  Carbon may interfere with the reception from the transmitter.
Finally! The receiver, smart LIPO battery and two tiny servos arrived and are ready to be installed. The AR6255 receiver was recommended due to the carbon fiber in the boom. Carbon may interfere with the reception from the transmitter.

The Receiver

Both Hyperflight and Kennedy Composites list receivers that work with this model. I was particularly concerned with issues some folks reported that some of the receivers were having problems when used with the carbon fiber boom.

The AR6255, however, is designed to be used with a carbon airframe. It is a 6 channel DSMX receiver, but you'll only use two of the six channels for the stock setup.

The receiver is compatible with Spektrum's Telemetry and Flight Log modules.

Kit Review of the ELF

Here is an article from RC Model Aeroplane that reviews the ELF Kit.

Antenna Placement

One option is to route the antenna under the receiver and through the plastic bridge.
One option is to route the antenna under the receiver and through the plastic bridge.

Installing the Receiver

Fitting the electronics inside the pod can be a challenge. I used the AR6255 receiver and it was a bit too wide for the pod. I could have removed the plastic covering of the receiver and shrink-wrap it, but I decided to gently bend the pod outward to squeeze the receiver in place. It was a very - VERY tight fit, but it did finally set in place.

I have seen two different setups with the antenna. One routed the antenna out the back of the pod which leaves two small "whiskers" unobstructed. The other was to route them underneath the receiver and forward towards the servos inside the pod. Because the pod is made of plastic and not carbon fiber, there should not be any degradation in the performance of reception, but you can bet I will range testing it before hand. I am also tempted use the Spektrum Flight Log to make sure that the receiver was operating up to par.

The Throwing Peg installed - Epoxy and Micro Balloons do the Trick!
The Throwing Peg installed - Epoxy and Micro Balloons do the Trick!

Balancing and CG

The Center of Gravity should be 3" behind the leading edge of the wing. You may need to add ballast to balance it appropriately. This setting should be tweaked after you fly it for a while. You may find that the slightest adjustment to the CG will drastically change the flying profile of the glider.

Install the Throwing Peg

The instructions call for sanding the throwing peg to fit comfortable with your fingers and then supergluing the peg in place.

Some fliers have found that CA glue is not enough to hold the throwing peg in place. Instead, they used an epoxy with micro balloons. I opted to use this approach.

Another tip is to drill two or three small holes in the section of the throwing peg that inserts into the wing. This allows the epoxy to seep into the hole and bind to the other side of the peg. It offers a bit more strength, but is probably overkill.

Note: You don't have to install both throwing pegs. They are so light, it really won't affect the in-flight stability at all if you install the second one or not.

Review of the Building of the ELF

Here is a great review from Aviation Modeler International that discusses the building of this HLG.

Recommended Settings

 
Control Surface Movement
Differential
Rudder
3/8" Up
 
Elevator
3/8" Up
 
V-Tail Differential
 
20%
V-Tail Diff (up)
 
100%
V-Tail Diff (down)
 
80%

Programming the Spektrum DX6i

V-Tail vs. Elevon - There are two options for your DX6i to control this style of tail. I won't go into detail here, but read this article on how to use your programmable transmitter to control a V-Tail glider for more information. I chose to use the Elevon setting for this project.

The Differential function gives you the opportunity to fine tune the movement of the throws. The recommended amount is 20% (80% down and 100% up) - but play with it on your V-Tail glider to see what is most comfortable for you.

Deflection of the Tail Control Surfaces

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This is totally unscientific, but here is the tail at 0 inches.At full "up" elevator, the deflection is 3/8"At full "down" elevator, the deflection is 3/8" the other direction
This is totally unscientific, but here is the tail at 0 inches.
This is totally unscientific, but here is the tail at 0 inches.
At full "up" elevator, the deflection is 3/8"
At full "up" elevator, the deflection is 3/8"
At full "down" elevator, the deflection is 3/8" the other direction
At full "down" elevator, the deflection is 3/8" the other direction
A small hole was cut where the battery leads stick up.  This makes it easy to turn on and to recharge.  Be careful taking the nose cone off, as it may snag on the leads.
A small hole was cut where the battery leads stick up. This makes it easy to turn on and to recharge. Be careful taking the nose cone off, as it may snag on the leads.

Fuselage Modifications

We are almost done! There are two thing you may do to the removable front fuselage.

  1. If you used the Shread LIPO battery, you may want to use your utility knife (or a drill bit) to cut a hole where the on/off plug is located. This way, you never have to worry about removing the canopy as you will have access to the plug from the outside. It also minimizes the scratches on the inside of the canopy.
  2. Tape the fuselage in place using clear scotch tape. You don't want it falling off!

The finished ELF!
The finished ELF!

Finished

Simply screw the wing back on and test all of the control surfaces to make sure they are working properly.

Take the glider out to the flying field and gently toss it overhand to get a feel for the reaction and controls. When you are comfortable, try an easy discus launch.

This is a fun and easy build for a first time DLG and the two channel model will make it easy for the novice to control. Intermediate and expert fliers will enjoy the graceful gliding as well!

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I Would Love to Hear Your Thoughts! 1 comment

Geeze 4 months ago

Thanks for a good article. Too bad I didn't read it before I built mine. I just finished it today. I agonized over getting the best servo position and battery size for correct cg with no ballast needed. Don't bother. Just mount the servos and battery as far back as possible and select a battery size for correct CG. I am flying mine on one cell, 240 mah, and the hobby king/hitec clone 4 ch rx. A great full range rx small enough to easily fit under the wing or stacked with a thin battery at the nose.

I noted one error in your text. My instructions said to sand the entire boom. Tail area and guide locations are therefore ready to accept ca.

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