An RC Depron Douglas X3 Stiletto

[Bill Southwell]

The lamp is the back up light....lol. 

[Simon Chaddock]

Bill

Thanks for all those pictures.

They do seem to show a "one piece" tail plane yet some of the 3 views show a long narrow trim tabs? as well.

If the elevator was purely manually operated this would make sense but I would expect for a plane meant to go supersonic the elevator would have been fully powered with artificial feel making a trim tab unnecessary.

The all moving tail plane on the Starfighter was definitely a single piece structure with no trim tabs so I guess that is what I will use on the Stiletto when the time comes.

 

I love the picture of a pilot getting into the drop down seat. I bet that was a nightmare to do with a full pressure suit on!

I wonder if it was this layout that led to the downward ejection seat on the initial F104A Starfighter. 

 

[Bill Southwell]

Hi Simon,

 

You are most welcome. I worried I overdid it, but it seems like every picture had a tidbit. When I saw the picture of the instrument package and that it was said there was 1200 lbs. worth of it, the inertial coupling issue started to make sense.

I agree with you on the stabilator and the trim tabs...the only way they would be of any use would be in a manual control system. The photos of the horizontal stab looks solid without any sign of tabs or actuators. Artist interpretation affects most 3 views in some way. I like the one piece stab. 

 

   That must have been a sobering moment sitting in that elevator seat and knowing how long it would take to bail out. Then add the high g gyrations that seem to go with experimental flight testing....low probability of survival.

 

The F104 really benefited from the X-3. I wonder how many engineers from the X-3 project were later involved in the Lockheed efforts.

 

Best Regards,

Bill

[Erfolg]

Bill

 

Those pictures are spot on IMO. The X3 has been of interest  for a long time.

 

I have seen the Doulas 558 (Crimson Test Tube) at Pensacola, where it is fastened to a wall in the foyer.  One of your collective images. It is tiny.

 

A long with the (Gut less) Cutlass (also in Pensacola), engines and the lack of power was a major issue, many engine programmes failed or were cancelled.

 

 

[J D 8 - Moderator]

    Early US jet engine power was an issue, most of the successful ones had their origins in designs from the likes of Rolls Royce, De havilland, Armstrong siddeley.

[Simon Chaddock]

The 1300mAh 4s and the Lemon stab Rx fitted in the battery bay.

I have run into a significant problem.

The HK Orange TX6i that I am using has a neat pre programmed dual aileron and combined flaperon feature. It is easy to set up and works well BUT it uses channel 5 for the LH aileron. Unfortunately the Lemon stab Rx reserves channel 5 to switch the stab on and off in flight so the channel is unavailable for any other purpose.

At the moment I can have rate stability on the control surfaces but no flaperon.

I rather suspect some flaperon is going to be as important as the gyro at the launch so a quick work around is to mechanically set the ailerons with a modest but permanent 10 degree droop.

 

The other alternative is to explore flaperons on my Spektrum DX6i. Spektrum uses channel 6 for dual ailerons so if flaperons can be programmed it should not effect channel 5. On the downside the DX6i is now a very old design so has limited programme capability as well as only having 2 position switches.

 

[Andy Stephenson]

Can you mix channel 5 to itself -100% to nullify the effect of the switch then mix the desired channel on the tx to ch5. This approach has worked on other brands of radio.

[Simon Chaddock]

Andy

The Lemon stab receiver is set internally to expect a 100 to -100 signal on channel 5 to switch the stab on and off. On my version of the receiver an "always on" option is not available. Seems strange as a dipswitch combination does give an always off! 

The pre programmed dual aileron and flaperon feature on the Tx only uses channels 1 and 5. The output channels are not selectable in any way.

The other six mix option on the Tx are rather limited and cannot be assigned to switches. As a result I cannot see a way of emulating the dual ail and flaperon feature using the available mixes.

 

The initial flights will be made with the ailerons set with a modest fixed droop. I shall be very happy if it can achieve just one flight without destroying itself. 

You never know it it launches at all well I may be able to do away with aileron droop but I doubt it will be controllable without the stab gyro.  

[Andy Stephenson]

There might be an on-board mixer that would do the job.

[Simon Chaddock]

Not much to show as I have given the X-3 a light coat of white acrylic.

It is amazing how it shows up small defects and dents you didn't know were there. Some filling and sanding next.

Then the three finger holes on the underside followed by a final white "wash" coat.

Until I know it can launch and fly limiting weight is a top priority.

I am rather looking forward to the possibility of building the crazy "Stiletto" nose!  

 

Edited March 8, 2024 by Simon Chaddock

[Simon Chaddock]

The figures hole tubes are printed in LW-PLA.

They are inserted through the skin and are glued to the underside of the wing. There are two sizes, a slightly bigger one for my thumb. 

It does mean this Stiletto is a left hand launcher!

Note the permanent 10 degree flap. Rather than make new slightly longer links and as the aileron servo horns and screws are readily accessible the droop was made by rotating the servo horn one spline. This has the advantage it will be just as easy to reset the flaps back again if and when I find a way of using adjustable flaperons.

Now more or less complete just waiting for the weather.

In the meantime I will build but not fit the full length nose. 😉

     

[Tom Gaskin 1]

On a lot of flat-plate wings used by Chris Golds he would also droop the leading edge to give a higher lift section. His 29" span Sea Vixen is one that springs to mind, with 32mm fans.

 

Tom

Edited March 11, 2024 by Tom Gaskin 1
Added info

[Futura57]

T-minus not long now 🤪

 

I'm guessing you'll want a bit of a breeze to launch into. Wishing you every success 👍

 

[J D 8 - Moderator]

  Good luck, truly X3perimental.

[Bill Southwell]

Looks great! All the best on your maiden. May Lift be with you.

 

Best Regards,

Bill

[Simon Chaddock]

Thinking about the scale long nose I decided totry and 3d print it in LW-PLA.

More a technical exercise than a practical solution but this how it came out.

A CAD image of the 8 sections.

It is just over 800 mm long.

Each section is "lofted" between a 'start' and 'end' shape.

Just to see how it might work I actually printed it out although the first two are so small I printed then out as one. The remaining 6 section have 3mm formers to support the joints. Quite tedious to do but it significantly improved the strength of what it still a very weak structure.

The printed "test" nose in position alongside the Depron X-3.

. 

I fear that if such a nose is ever fitted It would definitely be a "one flight" structure! 

Edited March 16, 2024 by Simon Chaddock

[GrumpyGnome]

It's scarily pointed too - luckily, if it hits anyone it'll be travelling reallllllyyyyyyy slowly...

[Shaun Walsh]

1 hour ago, GrumpyGnome said:

It's scarily pointed too - luckily, if it hits anyone it'll be travelling reallllllyyyyyyy slowly...

"You'll take someones eye out with that" as my mother used to say.

[Simon Chaddock]

I fly alone so a scale nose is no problem for me but if is is ever taken to fly at a club site I suspect the whole nose would have to be replaced with something like its existing blunt one.

I can only hope it does indeed fly slowly but with a wing loading approaching 20 oz/sqft ( = light warbird?) I suspect major damage to the scale nose would be inevitable 

[J D 8 - Moderator]

  Just fold some light use once light paper cones over a former and slip on for flight.

   May be a daft idea but anyway good luck with test flight.   John.

[Bill Southwell]

The X-3 is looking good Simon. The picture you posted with the prosthetic proboscis and the X-3 together gave me a thought. If you have a set of small neodymium magnets grabbing each other embedded into the face of the fuselage and the rear of the nose cone and add a short indexing feature to keep it from moving around but not enough to prevent it from easily  dislodging at the hint of a side load or impact. It would not need to be more than a rounded nub with a corresponding small rounded divot to fit into. If you were to make the mating surface at an angle with it being leaned rearward at the top and forward at the bottom it would the slide up and off the model on landing or if it were to contact anything or anyone. It would slide or pop off rather than being stiff in compression on a straight on impact. 

[Simon Chaddock]

Bill

Snap!

No magnets yet (they are on order) but top and bottom pegs.

Not a problem for the bluff nose but the same will be used for the long one.

For the maiden I simply held the bluff nose in place with little bits of Blenderm tape.

Yes I have flown it, sort of, twice! 

It actually has sufficient thrust but proved to be tail heavy. The result is it went into a climb immediately after the launch. With no forced airflow the eelvator has virtually no effect so it stalled. First time little damage, second time even with full down elevator trim it still stalled with rather more damage.

As you can see it rather took out all the "sticky out" bits on the right hand side! I later discovered when the RH wing was ripped off the aileron link stripped a gear in the servo too. You can tell how muddy the grass actually was.

It will mend no problem. I will move the battery forward and a bit to the left to counter the weight of the ESC. 

As the thrust appears adequate I will reset the drooped ailerons to neutral as well which should reduce the nose up pitch. 

My fear is the huge fuselage area compared to the flying surface areas will require the CofG to be remarkably far forward for stable flight.

My late Bachem Natter was a bit less aerodynamically extreme and it was a pusher so had adequate thrust.

But it still needed the CoG to be at just 16%.

 

Until I set it that far forward every flight ended in an uncontrollable stall. I nearly gave up after 4 rebuilds but once right it flew remarkably well.

https://www.youtube.com/watch?v=cq6MzWCXn60&t=30s

I can only hope the X-3 gets "sorted" before it gets completely wrecked.

Edited March 22, 2024 by Simon Chaddock

[Bill Southwell]

    Sorry to see the test didn't go perfect but it proved your fan setup will work and you have a positive amount of lift. I think you are right that the longer nose sections are creating lift and is causing the cg to need a more forward position. You could think about it like the X-3 is a lifting body with just enough wing added to allow it to take off, well at 40% of mach one.....

 

Bill

[Simon Chaddock]

Now all repaired and ready to go.

The battery has been moved forward and to the left to counter the weight of the ESC. It was this imbalance that caused the right wing to drop a the stall.

 

The previous and new CofG position are shown. My trapezoidal calculations suggest the new position is at 21% of the mean effective chord.

With such limited elevator authority I am anxious not to move the CofG too far forward too quickly but I fear it might need to go still a bit further forward however it would not be difficult to adjust things too allow the battery to slide further forward.

We shall see once the weather calms down, although if the weather forecast is right it could be after Easter.    

[Simon Chaddock]

Still waiting for suitable weather but a picture of the X-3 with its long nose.

This nose is not flight worthy. It is only for show as apart from any safety considerations the retaining magnets are not strong enough to withstand the likely aerodynamic forces from any pitch or yaw.

If and when the X-3 does prove to fly well enough with the bluff nose I could in the privacy on my field tape the long one on just prove it will fly but landing with it undamaged is likely to be a different story.