An RC Depron Douglas X3 Stiletto

[Bill Southwell]

Looks awesome!! 

[Simon Chaddock]

Yesterday was just about calm enough to try the Bluff nose Stiletto again.

A bit better this time. The gyro managed to keep thing under control for nearly a circuit but it is still a bit tail heavy.

Flight time nearly 15 seconds!

Eventually it did stall despite my best efforts and as it was going a bit faster the impact was a bit harder.

 

A seriously crushed nose. The battery actually broke free forward and disconnected itself!

However on the positive side the Depron structure did its usual "crimple zone" thing so the rest of the airframe is completely undamaged 

 

It just needs a new nose ahead of the intakes to be built and to move the battery a bit further forward then try again.

  

[Murat Kece 1]

You are one determined and patient builder Simon.. I admire you. Well done.. Keep going. I am sure it will eventually fly well.

[Simon Chaddock]

The broken nose cut back to the inlets.

Although important to have a good surface to work from it is always a concern as you are cutting away a lot of damaged but original airframe.

Having cut out the L&R formers the new nose is built in exactly the same way as the original fuselage a half shell over the plan.

When the planking is complete the half shell can be lifted and the other half of the formers added.

Then the planking starts all over again but ensuring each plank is as accurately preformed as possible to avoid stressing the half shell and ending up with a twist.

Although rather tedious it does mean the new nose will weigh exactly the same as the original/ 

[Mike Chantler]

16 hours ago, Simon Chaddock said:

 ensuring each plank is as accurately preformed as possible to avoid stressing the half shell and ending up with a twist.

Although rather tedious it does mean the new nose will weigh exactly the same as the original/ 

 

Have always wondered - do you chamfer the edges of the planks to fit. (Its looks as if you have yours nicely butting)

 

And if so, what's the best way with delicate 3mm foam?

Edited April 3 by Mike Chantler

[Simon Chaddock]

I do chamfer the edges of each plank preferably on both sides so the plank to plank joint is normal to the surface.

I use a sanding block with surprisingly coarse (60 grit) paper on it. New paper cuts the foam very easily with low pressure.

I hold the plank in my figures and then locally sand the joint surface and when done work along the full length of the plank. It really only requires the block to "kiss" the foam.

It does take a bit of practise to be able to judge how much chamfer is required as it changes depending on the radius of the surface the plank is covering.

In general I have found it better to slightly under chafer. It does leave a small gap at the surface but that can be easily filled/painted. Acrylic paint is itself quite a good glue for small gaps!

Over chamfering leaves a gap on the inside which you may not even see. Such a plank joint is rather susceptible to splitting from handling pressure.

It is worth reebering that much of the strength of a planked structure comes from the plank and it joint with its supporting structure. It is twisting that puts load directly on the joint and than only in shear. Glue is good in shear and a plank joint is very long. 

 

The new hose glued on with the new printed "short" nose cone.

 

It just needs the glue to fully harden before light sanding, filling and white acrylic paint.

The battery box has been extended to allow the battery to more forward.

  

 

[Mike Chantler]

4 hours ago, Simon Chaddock said:

I do chamfer the edges of each plank preferably on both sides so the plank to plank joint is normal to the surface.

I use a sanding block with surprisingly coarse (60 grit) paper on it. New paper cuts the foam very easily with low pressure.

I especially like the idea of the fresh 60 grit - and think I'll also try this on some XPS shaping that i am doing at the moment.

[Simon Chaddock]

The weather has effectively stopped any more testing until a) the field has dried out a bit and b) the wind is less than 5knots!

Going through the plans I noted that my long printed nose is about 50 mm to short and even worse the front part of the fuselage is not quite the right shape. 😟

Given that the next flight(s?) will always use the short nose cone I will leave the current fuselage nose shape as is for the moment, particularly as there is a fair chance it will have to be rebuilt anyway.

I did however print the new longer nose and it also matches the correct fuselage nose profile, as and when it gets done.

Not noticeable but at the base it is also a bit taller and wider than the original nose.

Of course it is still impossibly fragile so unlikely to ever actually fly more than once!

[Simon Chaddock]

With the high pressure on Saturday I did managed to fly the Stiletto a bit. It actually flew passably well and got reasonably high but the roll control sensitivity is a nightmare to the extent it flew into a tree 35 ft up!. I just manged to get it down with my 7m roach pole but with virtually no leaves on the tree the drop was quite a long way.

The tail plane suffered most and with a big hole in the side but fortunately none of the ducting was damaged so fairly easy to fix.

It is still a bit tail heavy so next will be simple nose weight rather than the structural mods necessary to get the battery any further forward.

Not quite sure what to do about the roll control. Reduce the aileron deflection or simply cut them short  leaving the tip section fixed.

Getting there slowly.  

  

[GrumpyGnome]

I admire your tenacity....

[Zflyer]

Surely filling the nose or even printing part of it a little thicker the chu k rhe nose weight in there. May give a luttle more strength and help c of g! Or am i being a bit naive

[Trevor]

Sounds like a promising step forward. Time to fit a stabiliser perhaps? At least on the roll axis.

[Simon Chaddock]

I already has a Lemon 3 axis stabiliser Rx fitted although with no rudder the yaw is not connected.

It was the rapid rolling from side to side which is a classic symptom of an over sensitive roll gyro. However the roll sensitivity "pot" is set to the mid point which suggests the ailerons themselves are far to powerful. My favoured solution is not to limit their travel but make them a good bit smaller in area.

The replacement nose cone will be printed in PLA rather than LW-PLA which will add 3g. No much but it is along way forward.

As I surmised the long fuselage area ahead of the centre of pressure means the CofG has to go much further forward than "normal".  

[Chris Freeman 3]

Well done Simon. Glad you are making progress. A long nose does affect the stability, when the Airbus 340 600 was introduced to South African Airways 25 years ago it had bunks for the cockpit crew to sleep in on the long haul flights and many complained of air sickness due to the oscillations and Airbus had to tweak the software to reduce this.  

[GrumpyGnome]

I now have visions of Airbus engineers buying AS3X receivers......

[Shaun Walsh]

12 minutes ago, GrumpyGnome said:

I now have visions of Airbus engineers buying AS3X receivers......

Surely that should be Boeing? 

And each plane would have just one.

And they wouldn't tell the pilots where it is, what it does or how to turn it off.

[Simon Chaddock]

Now all back together.

Hole? What hole.

A new "heavy" nose cone printed in double wall PLA rather than a single wall in LW-PLA. 

It also has 5g of lead in it so 13g rather than2.

The CofG is now still further forward.

It looks crazy but it flew impossibly tail heavy at the left hand mark (25% mean chord). Still flew tail heavy at the middle mark (18%). The right hand mark is at about 12%.

I just have to accept that the long relatively bulky forward fuselage compared to the tiny wing creates a substantial nose up pitch at the normal angle of attack for such a light weight low powered plane.

The final modification will be to cut down the full span ailerons as the roll sensitivity is much too great. Even the gyro can't control it at the moment.