1/2 scale Dragon - a Baby Dragon

[Simon Chaddock]

It was suggested that the Giant was big enough to carry a small plane aloft.

 

Not that easy with a high wing pusher layout but it set me thinking, just how small would be practical?

 

To keep the same sort of wing loading (6oz/sqft) at half size (20" span) it would need to weigh only 1/4 as much or just 2.5oz. This would be almost impossible using a conventional radio/ESC/servos set up.

Increasing the wing chord a bit would permit the weight to rise to 4oz,

So a Baby Dragon.

This wing is actually based on the outer 10" of the 40" wing but with smaller ailerons.

It uses a central aileron servo with a closed loop 'external' system (as on my Depron Pup)

The complete wing including servo will weigh less than an ounce.

With an 11g 60w outrunner and an 800mAh 3s the target is 4oz all up.

I must be mad but at least a 20" plane will be hardly noticeable.

Of course at 4oz the Giant Dragon could easily carry two, one under each wing, a bit like this!

[Simon Chaddock]

Part of the external closed loop aileron system.

Like the 24" Depron Pup it uses a one piece line from servo horn to servo horn. This allows the aileron neutral positions to be fixed after the whole system has been tensioned.

The wing is quite a bit lighter than I anticipated at just 0.71oz (22.1g)

The first test of the ailerons.

I bet this will ever so "twitchy" to fly!

Edited By Simon Chaddock on 10/10/2010 19:06:27

[Simon Chaddock]

The 1404 micro motor on its test stand with a 5x3 prop.

On a 3s LiPo it draws just over 2.5A and gives almost 4oz thrust..

The 420mAh 3s LiPo.

It weighs 35g.

A flying weight of 100g (3.5oz) looks achievable.

 

[Simon Chaddock]

The power train is made up of about the smallest individual components I could find.

As it only draws 2.5 amps (6c) this should give a full power duration of 10 minutes.

Edited By Simon Chaddock on 15/10/2010 21:05:57

[Simon Chaddock]

A short video of the Baby Dragon motor on test.

It is worth noting that the RX went haywire sitting on the motor mount as in the picture above. It did not seem to like the high frequency vibration of the motor. Hanging free, as in the video, it gave no trouble. 

[Simon Chaddock]

On such a small plane the weight of even a 3.9g servo is quite significant so it was no longer realistic to mount the elevator servo in the fin as I had done on the bigger ones.

The result is quite a short compact fuselage.

The 3.9g micro servo and a Corona 4ch just fit in.

The external elevator servo horn.

To clear the prop the cables will run though an eye fixed to the tail boom and then up to the mid fin tailplane.

[Simon Chaddock]

All glued together with everything installed.

The CofG is at 1/3 chord which is just about ok for a Clark Y but if necessary I will extend the nose by 1/4" and move the battery forward accordingly.

It weighs 3.4oz

 

[Simon Chaddock]

The final picture.

Now I just have to see how (or even if!) it flies.
 

[Simon Chaddock]

Weather not good enough to fly so a short test video of it sliding up a 45 degree slope!

And not at full throttle either.

Edited By Simon Chaddock on 23/10/2010 22:59:24

[Simon Chaddock]

It appears that YouTube are taking their time to process this video so it comes up as "unavailable".

If you click on the logo in the top left corner it will display directly from You Tube.

[Simon Chaddock]

Two very short flights

Each time it climbed away easily responding nicely to the elevator,

CofG feels about right but boy! is it sensitive on the ailerons. Put in a correction and its on its back. So different from the Giant!

I think I will put in longer aileron horns to reduce the deflection and improve the definition.

 

Seems to tighten readily in a turn despite no aileron differential, so maybe the fin is just a bit too big.

 

Second "arrival" (actually a cartwheel!) broke the nose but easily fixed.

Never expected it to be easy with such a small plane outdoors.

[Simon Chaddock]

As the conditions were so calm (see Giant Dragon post) I gave the Baby another go.

 

The longer aileron horns have indeed reduce roll sensitivity to manageable proportions and a 5x3 prop gives a bit more usable thrust so it now flies quite well.

Still pretty twitchy but then it is only 20" span.

 

The thick wing does mean it can fly quite slowly with an interesting rapid left/right "wobble" at the stall but at speed it it a real handful with completely unpredictable pitch changes.

More tailplane area might help although I understand that a conventional wing section a very low Reynolds numbers can behave rather differently. A new "thin" wing maybe.

 

I am now sure it will be able to lift a Key Fob cam so next flight...... 

 

[Simon Chaddock]

I made a mistake when I built the Baby Dragon, the aileron servo works in the opposite sense to all my other planes.

The TX does have reverse switches but it was only a matter of time before I flew one with ailerons the wrong way round!

So a bit of surgery to extract the aileron servo and turn it round to face the other way.

The top line eyes also have to be repositioned further forward.

Re-rig the aileron lines and the jobs done.

A larger elevator is being fitted at the same time.

Edited By Simon Chaddock on 01/11/2010 15:59:30

[Simon Chaddock]

Further flying confirmed the CofG was really too far back so a fuselage "plug" added allow the battery to be moved forward.

Simply achieved by cutting of the nose block an adding 8mm strips and then gluing the nose back on. Depron glues so well that simple butt joints are perfectly adequate.

Note also the external Depron "plates" to reinforce the fuselage just ahead of the pylon.

 

[Simon Chaddock]

I also made a new battery hatch cover incorporating a mount for the Key Fob cam.

Here is the result.

It is rather erratic as the Baby is extremely sensitive in roll and the radio was playing up.

With more than sufficient power it certainly lifts the extra weight ok but nice to fly it is not!

A bit more development is required.

 

[Simon Chaddock]

I think one problem with the Baby is that with a high set tailplane it is virtually all directly in the prop wash and to make matters worse it is less than 6 " from it.

This results in enormous elevator authority power on and precious little when gliding.

 

I always liked the V tail I tried on my original WD. It seemed to respond well to the 3 channel "bank & yank" layout. It was only abandoned when I wanted to put the elevator servo actually within the tail surfaces. Unless I used two servos (too heavy) the linkage would be very complicated.

 

The Baby of course has a cable operated elevator so a V tail with separate cables for each elevator half is quite easy.

The cables are very fine. The 1.7lb mono line is almost invisible.

A nightmare to thread but the beauty of this arrangement is that the whole thing is done with a single strand, starting & finishing at the bottom servo horn hole. The line is tensioned and secured first, then each elevator half is set to its neutral position and secured with a blob of glue.

Hopefully the V tail will be a little less sensitive to the effects of prop wash. 

[Simon Chaddock]

The V tail has certainly reduced the elevator variation between power on to power off.

Using the reduced aileron rate switch also makes flying at bit easier but it still exhibits a tendency to oscillate laterally after any aileron input despite the substantial tail volume. It is quite noticeable in this video.

Although it glides quite well with a reasonably low sink rate the relatively thick wing (12% root, 7% tip) seems to severely limit the maximum gliding speed achievable such that it will not loop power off.

So I am going to try a thinner wing (8.5% root , 5% tip) and with 25% less area..

The ailerons are also reduced by the same amount.

It will interesting to see what effect this wing has.

 

[Simon Chaddock]

The completed thin wing, same span but only half as thick. It has a balsa LE to better form the small nose radius.

To further reduce drag the aileron lines will be run along the leading edge rather than over the wing surface.

Edited By Simon Chaddock on 17/11/2010 00:18:10

[Simon Chaddock]

It also has a new thinner pylon.

The aileron servo will be mounted in the pylon rather than the wing itself.

From my research it appears that at low Reynolds numbers the airflow tends to be laminar over the complete surface so a thin wing and sharp leading edge gives the best L/D ratio  but at a certain angle of attack the flow completely detaches which results in a dramatic loss of lift and increase in drag.

This could be interesting!

[Simon Chaddock]

The original and 'thin wing' Baby.

Compared to the earlier version both the wing and tail have less chord giving it a rather more delicate appearance.

It has also lost 1/4 oz in weight. Not much but its still 8%.

A bit of decoration, re-rig the control runs and its ready to go.

 

 

[Simon Chaddock]

The thin wing Baby Dragon certainly flies faster despite having a smaller lower power prop but I am not sure it has really improved the flight characteristics.

The extra speed has made what was already a fairly twitchy plane even more so, as two hard contacts with an equally hard and frozen ground (requiring two nose rebuilds) has already demonstrated.

 

Hopefully more testing and adjustment will improve things and establish if the thin wing really does enable it to complete a power off loop.

Edited By Simon Chaddock on 03/12/2010 21:51:33

[Simon Chaddock]

With a little bit of tweaking (and another nose rebuild) the thin wing Baby Dragon now flies quite well.

 

This is an edited video, the full flight lasted just over 10 minutes and there was still plenty left in the battery. Not bad for only 420mAh.

 

Oh and by the way, it does glide faster but still not fast enough to complete a power off loop!

[Stephen Grigg]

Hi Simon you are obviously someone who likes to challenge himself and its great to see your experimentation and how successful you are with your mods to succeed congratulations,it must have looked small at that height

[Simon Chaddock]

Stephen

Thanks and yes indeed it was pretty small but as it was virtually still conditions that high pitch prop whine was quite easy to follow although its actual orientation was a bit more of a problem.

Of course no sound power off but I did keep it more or less overhead at altitude so with its limited glide performance it was never going to stray too far.

 

I flew the Giant Dragon at the same session and for the same size it is at least 3 times higher so I was very concious that if it chose to it could wander off for a great distance. 

[Simon Chaddock]

Ideal calm condition this week to fly the Baby Dragon.

I am amazed at how long it flies on its tiny battery. 8 minutes and you can pick it up and do it again.

It does have a problem. Although the single line 'closed loop' aileron circuit keeps the lines close to the leading edge does have a bit of friction so the ailerons tend not to return to exactly neutral.

To overcome this I replaced the servo arm so each aileron has its own pull/pull line.

A touch more drag with the lower line right in the airflow but the ailerons now centre accurately making it much nicer to fly.