A bigger Depron Skyray

[Erfolg]

Simon

 

What is the wall thickness of your duct wall etc.?

 

With respect to flying speed, there are a lot (probably 8-15 or so) that fly incredibly well with a high turn of speed when required. Most hand launched, the rest have retractable undercarriages.

 

There is one, quite big, that when built looked like it may never fly or perhaps take to the air with confidence, even then just stagger around.  After many changes, it is now fast.

 

The times have changed with DF. Success is more often than not guaranteed.

[eflightray]

Speed isn't everything, (remember my EDP MIG, in my avatar), as long as it sits right, and looks right,- 'slow', (to some), show off jets at their best, as in the 'real world' air shows etc.

Nice one.

Now for a bigger, bigger one, ........ with EDP  ?

Ray.

 

 

[Simon Chaddock]

Ray

The current bigger Skyray is actually based on a 36" span Depron one (with an EDP) I built 13 years ago.

To accommodate the airflow from the trimmed 5x5 prop, not surprisingly, it had both oversize inlets and exhaust.

Nevertheless it was an easy hand launch and flew very well indeed.

It also had a respectable 10 minutes endurance from its modest 1500mAh 3s along with a slope soarer's glide performance!

[Simon Chaddock]

Erfolg

The duct is made up from single wall (0.4mm) vase printed sections all in LW-PLA. As it is entirely an inlet duct it relies heavily on the stiffness of the Depron formers that ar glued around it to resist any tendency to collapse under reduced pressure.

The motor mount and the short exhaust duct is also a printed structure but in normal PLA for strength The Emax quad motor drives a 3 blade 3x4.5 prop. The much reduced prop area compared to the 5" on the first 36" Skyray is why it will need 4s to achieve anything like a similar thrust to weight ratio.   

[Simon Chaddock]

To move on to 4s a Favourite 20A OPTO ESC was installed with of course a 5A SBEC.

 

These ESCs just do not get anything like as hot so the external fingered heatsink is not required. To save a bit move weight the motor wires were soldered directly to the ESC.

Initially I intend to use a 1000mAh 4s which fortunately is exactly the same size & weight as the 1500mAh 3s so no changes required to the battery box.

The 4s certainly give a substantial boost in thrust but the first flight did not go well.

https://www.youtube.com/watch?v=W7B-RcNuTrs

For some reason the 35meg Rx that performed faultlessly in the smaller Skyray had range issues. In the video the motor cut and all control was lost at least twice in the 15 second flight. More by luck than any input from me no damage was sustained. 

My concerns about range were confirmed by the fact that where it landed, about 150 ft away, the Skyray was unresponsive until I walked quite a bit closer. Not good!

The next task is to replace the 35meg with 2.4. 😉

So far the Bigger Skyray, despite its structural delicacy, has lead a charmed life as far as damage is concerned. I just have to hope I can get a good flight out of it before its "charm" runs out. 😲   

 

[Simon Chaddock]

The "charm" did not last. 😟

https://www.youtube.com/watch?v=kyZzbJSqb-o

Started out nicely but you can tell from the sound the motor cut out to a dead stop, followed by a "lawn dart" and a crushed nose right back to the inlets!

Despite the damage everything still worked. A testament to the Depron energy absorption qualities that the rest of the airframe was completely undamaged   

I wondered if something had over heated so I ran it where it lay and found that above 3/4 throttle the the motor cut out just at it had in the air.

Then it dawned on me what had happened. When I installed the 6s ESC I had not calibrated the throttle. Doh!

I calibrated it there and then and the throttle behaved normally. Just to convince myself I ran it a full power for a minute. Although not a recommended thing to do it nevertheless ran without issue.😊

 

All it needs is a new nose.

Not quite such a problem as it might sound as the nose was originally built as a separate item and stuck on.

I will just have to build another so I started straight away. 😉

The canopy was 'ejected' in the crash and was virtually undamaged.

A new set of Depron formers, a new printed nose cone and cockpit frames and all done on the day of the crash 

 

[Simon Chaddock]

A days work or "a load of pins".

The planked half shell ready to be lifted from the plan so the other half of the formers can be glued on. Then its do the same planking all over again. 😲

At the same time the fuselage has been cut back to the appropriate former and any local damage made good.

 

 

 

[Eric Robson]

Like me Simon you never give up.

 

[Simon Chaddock]

Another day and the nose is back on, again.

Paint and decoration still to do.

 

[J D 8]

 Cant beat a bit of long grass to prevent test flight whoopsy damage. First launch of Veron Cardinal.

[Simon Chaddock]

J D 8

Agreed but at my field the local council go to some trouble to keep the grass cut over the entire area, too short for any crash protection but too long for a wheel grass take off! 😟

Such is life. 

[Simon Chaddock]

Ready to go again.

As prior to the crash the motor cut but restarted followed by a complete loss of power I have to consider both the ESC and the separate BEC as suspect. Neither were new.

They will be replaced by a new ESC with a combined BEC so in effect replacing both suspect items however the problem could be with the Rx, the wiring or even the Tx. 😲

Just have to keep trying. 

[Simon Chaddock]

I replaced the ESC and BEC with a new 4s capable ESC with internal BEC.  I checked the max power amps even on 4s was only 11A well below the 20A rating of the ESC. Even waggling the sticks vigorously the 3.7g servo only drew 0.51A so well below the BED 2a rating.

So I tried again and exactly the same thing happened again! A few seconds of power (flew nicely) motor cut, after 1 second power returned only to cut again almost instantly but now with no control at all. This time the impact was rather harder with the nose completely crushed. 😒

The Depron did it usual energy absorbing thing so everything still worked where it lay! Beyond the crush damage non of the rest of the airframe was damaged in any way.

To prove a point I extracted the Rx and ESC from the bigger Skyray & put them in my "hack" Blue Dragon.

It has a bigger motor than the Skyray but on 3s still only draws 12A well within the ESC capability.

No real surprise but it flew faultlessly for 10 minutes so the "cutting out" fault must lie somewhere else in the bigger Skyray's 'electrics' but it is hard to imagine where.

Bizarrely the cutting out only happened when in flight. On the ground it ran at full power for over a minute, which is 20 times longer than it ever did when flying. As a result I will only rebuild the bigger Skyray nose section ,yet again, if I can find an actual fault.

We shall see. 

[Trevor]

Oh dear. Do I remember right that, in the pursuit of lightness you chose to rely on the enamelling of some wires for insulation? I’m just wondering whether this could be a source of some sort of short, maybe triggered by some sort of in-flight resonance?

[Simon Chaddock]

Trevor

Yes enamelled wire to save weight. The factory applied polyurethane enamelling is very hard to remove and with Depron formers all down the fuselage each wire is run individually keeping 10 mm apart. I suppose a short is possible but the difficulty cleaning off the enamel for soldering suggests the fault might be due to some sort of poor connection that is triggered only in flight.

I have used long enamelled motor wire on a number of planes and never had a problem with shorting but I have had the wires get warm, soften the Depron allowing the wires to move so they touched and soften a plastic snake thus jamming a control but the motor continued to run un effected!

 

I do suspect there may be some sort of radio interference. In the bigger Skyray a lack of space meant the 2.4 Rx's diversity aerials are not ideally placed, however as it has done the same sort of 'cutting out' with two different 2.4 Rxs and a 35 meg one I feel I may be 'clutching at straws'. 

 

[Ace]

Could it be a servo dragging down the power when under load deflected in the air which would not show up waggling static on the ground? 

[Simon Chaddock]

Ace

Thanks for the comment and whilst a possibility the bigger Skyray flies very slowly, for the short time when it does, and the 3.7g servos it uses have a stall current of 0.7A,so even with both its servo stalled it might crash but it would not drag down the voltage of a 2A BEC by much.

 

What might be possible is one of the servo intermittently goes onto a full short circuit which would likely bring down the voltage but doing so at the same point in a each flight seems rather unlikely.

Whatever it is it is most likely something odd or a combination of faults.

Still investigating.

.   

[Simon Chaddock]

Wow! its been hanging on the wall for 3 months looking like this.

To make a repair the problem is the crushed LH inlet duct. The whole duct is printed in LW-PLA, the parts glued together to make a single assembly and then it was used as a "spine" around which the fuselage was constructed. At the minimum this is going to require a substantial fuselage "cut back" to gain access to replace the bifurcated duct section assuming it can be joined effectively to rest of the duct. Reprinting the necessary parts of the bifurcated duct is no problem.

Well thats the plan along with a new Lemon 6 channel receiver. 😉

With the fuselage cut back it now looks like this.

 

A close up shows the problem of joining the bifurcated inlet to the remains of the duct without virtua;;y destroying the airframe to gain access.

On the otherhand this picture does rather show the simplicity of the "electrics".. 3 motor wires and two servo connections.

A shred of comfort is I might be able to salvage the RH inlet which would at least give me something to match to when rebuilding the LH one.

It will also require a special duct joining section to be printed.

 

Even when I have rebuilt the fuselage up to the inlets it will still require a complete new nose to be built and glued on.

I can now see why I left it hanfing on the wall for so long.

When finished it had better fly! 

Edited October 21, 2023 by Simon Chaddock

[Trevor]

Well done for facing up to this rather daunting repair project!

[Simon Chaddock]

The LW-PLA printed L&R ducts installed.

It required a short  "push on" joiner tube to be printed and glued on. Despite my concerns I all worked surprisingly well.This usually means there is some unexpected problem just around the corner. 😟

As I hoped the RH inlet has been fully salvaged. It has the advantage that it shows how the misisng skin is shaped and the necessary plank shapes to achieve it.

Before I go any further I will have to solder "extensions" to the motor wires as access is rather limited. In hindsight I have done it before I added the bifurcated duct.😉

 

With lots of drying time between each "addition" progress always seems pianfully slow for the results obtained.  

[Simon Chaddock]

The next big step is to replace the fuselage former that represents the joint between the fuselage and the separately built nose section. This former gives the point to complete the missing bits of Depron skin.

 

Still quite abit of of oddly shaped and in some cases 'formed' skin to add but it is getting there.

Note the ESC and BEC have been added. This ensures that both the air flow direction can be checked and the servos tested. I find it pays to re-test everything at each stage of such a 'rebuild' repair. 😉

[Mike Chantler]

Simon, nice build as always 🙂

 

Am curious, as I'm doing a mixed carbon/foam/pla build myself, what do you use to glue pla and lwpla to the foam? Do you use the foam glue you mentioned earlier in the thread? And is it CA for pla to pla?

[Simon Chaddock]

Mike

I use the same glue for foam to foam and foam to anything else. I also use it for LW-PLA to LW PLA as it is after all a foam.

PLA to PLA depends on the application. If the surface area is large I use the foam glue for convenience as it allows a fair degree of 'wiggle' room but it does take 24 hours to go truly hard which it does unlike POR. On 'delicate' PLA to PLA structures I use CA especially if the fuselage formers look like this.

Each half former is made up of 3 printed parts glued together with CA.

I tend not use carbon as compared to foam it is so stiff it takes virtually all of the load. The Depron thus becomes dead weight and is reduced to just "keeping the air out".

Where I need extra strength I use thin hard balsa fixed with the foam glue. 

My favoured solution is a balsa/Depron/balsa spar that is fully integrated into the Depron structure.

     

Just a sketch but it shows the principle.

With the right proportions although the 'spar' adds considerable stiffness but it will still bend to about the same degree as the rest of the Depron structure so at the point of failure much of the material in the wing is sharing the load.

On the other hand the proportions of the "Bigger Skyray" are such that no reinforcing is required anywhere. 😉

Edited October 25, 2023 by Simon Chaddock

[Mike Chantler]

Thanks Simon, enjoying your log and I especially like the wing construction above.

 

I'm building a 46" PSS spit, target 1kg plus so - so suspect I have a lot more weight that I can afford (and need) in the structure than you.

Front half of fuselage is 1mm PLA skin with some foam/carbon bulkheads to absorb hill landings in gales.  Rear likely XPS with some PLA bits (depends on overall weight!).

And it has an 18mm carbon ballast tube running 500mm from the spinner. I like that glue you recommended so will use this for  foam-to-foam and foam to carbon - thanks.

 

Suspect your weight will be a fraction of mine(!) and I don't even have a motor lol

 

Designing with Fusion 360, which I have to say is taking me quite a while to learn!

[Simon Chaddock]

The Bigger depron Sktray fuselage is now skinned up to the line of the inlets.

Top view.

Underside. Loads of ipns!

 

There is no point in filling and sanding until the nose is glued on which rather suggests I had better get on and build it.

In the Bigger Skyray's checkered past the nose was completley rebuilt so atleast I know it can be done. From this,note the inlets were undamaged.

To this

With a battery box and removable canopy it is quite a complex structure so it may take as long as the repairs did for the fuselage.