Revisiting paper airplanes - like we probably all started out with...

You could always print an extension to slip over the arm, i have lengthened some of mine with carbon arms bolted on 

A bit more background....  the design of the printed paper airplane fuse requires an arm extension and one was included in the kit of parts to be printed as well as a specific control horn. I assume that the designed arm and horn are matched.  So if the replacement yields the same length then hopefully the designers intent.  Whether a 5g servo will be up to it is something to discover later.

I do think that they were being a bit optimistic assuming that Nylon and PLA could be glued flat robustly.  And better if there were some alternative arm extensions included.

Splines might be something to do some experiments on later....

In parallel with getting to grips with new Tx and Rx I returned to the printed paper plane.  One of my concerns is the low position of the motor and the mechanism on which it sits.  There are so many return-to-earth scenarios where that mechanism and the motor is likely to 'eat earth' or 'eat mud' or 'eat sand'.  I had in mind creating a somewhat aerodynamic skid to elevate it somewhat.  

In the past I have created an 'ellipsoid shape' in FreeCAD.  For the printed paper plane I wanted the skid to nestle int4o the lower bit of the Fuse. Since the Fuse is made up of an STL file it makes sense to 'subtract' the Fuse shape from the skid so the attachment would fit nicely.  If anyone wants the details find but here is the workflow:
a) take the STL mesh describing the front-most part of the Fuse and convert it into a shape and then into a solid.
b) I wanted the skid to extend a bit back from this known section of the Fuse so I created two sketches representing the X-section just aft and 'lofted' it into a shape.
c) I joined together the two Fuse bodies.
d) I created an ellipsoid body in FreeCad, shifted and rotated it into position. It was 180 degrees of rotation so as to represent the lower half.
e) I subtracted the Fuse body from the ellipsoid skid.

Here are a few images:

The Fuse sections and the ellipsoid.

 

Front view with skid in place:

 

View of skid after the Fuse was cut away:

 

Inside of printed skid:

 

I made two variants - one that was 50mm tall (1 perimeter, 6percent infil 9g) and on that was 36mm tall (2 perimeters, 6 percent infil 7g).

 

 

If I was doing it again I would create sketches at several sections of the Fuse body and loft them to have a less complex solid to cut away.

The point of the exercise is that if you can USE some of the STL files used to print the model to form additional components that fit nicely.

 

jpn
Is there not a danger that the very "rounded" skid will cause a "nose over" and positively put the motor in the mud?
I think you may find the skid has to be quite close to the nose.
A prefer to belly land and with a cowling around the motor.

Putting out the images and idea for comment before the CA goes on allows me to go back a tweak the CAD to move the skid forward.  Thanks for the feedback.  

In addition to my recent post on the "Radios" chat I decided to finish setting up the Printed Paper Airplane.  With the transmitter setup with new values I was able to check the servo action and could then glue in the servo mountings and adjust the rods. I then glued on the skid just behind the prop.

I had added in a mix on the 'rudder' servo linkage of the motor housing at 10% of the aileron stick and tried that out. Just a tiny side-to-side. Figured out battery position for a slight nose-heavy COG. Tomorrow is supposed to be sunny with light winds so I will take the beastie out to a fair-sized open area in Singleton Park with is a 5m walk away.  

I have action cam rig sorted so hopefully will record it for review.

 

jon
Ideally the tips of those Rx aerials (the bit beyond beyond the black insulation)  should be at 90 degrees to each other to give the best protection from 2.4 directional weak directions.
Probably unlikely to be a problem unless your paper plane gets really far away.
Look forward to the video.. . 

I will send you the skid STL file.  Also (see the next post) I found that the arm of the motor mount to the control rod is not nearly strong enough and I have designed and printed a replacement.  Ditto the control horn - broke the horn and I designed one that is way more robust.

So the initial flight of the Printed Paper Plane..

Only a gentle breeze so out to the park, waited for the dog walkers to wander somewhere else and did a couple of test glides.  First impression of that is that it needs a serious toss to get sufficient speed to get more than 10m.

I launched it and found it climbing more than I wanted (even with rates there is quite a bit of control surface area).  But I didn't have sufficient throttle and it didn't get all that far and landed with what I thought was minimal stress.

I thought I checked all the linkages for 2nd flight. It stayed level but drifted to the right, would not climb.  It is possible that one of the elevons horns had sheared, or perhaps it did that on landing. One working elevon on a Delta is rather useless at low altitude.  Thunk.
 

I noticed that the motor support had sheared off, one servo holder was loose as well as one of the elevon horns. The point of failure for the motor arm was at a screw hole and the point where it change of angle.  They must not have had their coffee when they designed that. I decided to take the original STL file and bulk up that arm.

 

 

 

 

And the control horn - the base was seriously thin and sheared off.  So again I imported the STL into FreeCAD and added some additional bodies to get the thickness up and more surface area for gluing and made sure that had a nice fillet as well to limit stress.

 

 

If anyone has this PlanePrint model save yourself some time and send me a message asking for these replacement parts. 

 

After I beefed up the motor mount and elevon horns and after setting up rates and expo on the Tx I took it out to the local park for a test.
Which was brief, however I recorded it in order to begin to assess its flight characteristics and foibles.

Classic user error from not having flow a delta wing in a long time and begin late on the sticks to properly finish a turn. And one error short on altitude...

Takes more throttle than I expected. Less wobble. Might be fun once I get my delta skills back. I have reprinted 25mm of the nose.  Will look for a larger field to learn on....


 

Thanks for the preflight check comments. I take your point about being behind and the unplug during COG check.. And yes, I had trimmed the aileron checks out of the video.

Interesting - before heading out to the test site I had spent some time checking out the control surfaces and had found one of the servo linkages was overly tight and it was bowing the CF rod so that the control surface travel was not quite the same on the left and right.  The rods only have one intermediate support so there was more bending than I expected. In the past I had only used piano wire rather than CF for control rods.

Interested in the observation that it was a "stall into a spiral dive".  So a lack of speed for that turn. Useful (but painful) way to get an early indication of where stall kicks in.
Visually I thought the test site I had found was sufficient and it was almost calm so air speed and ground speed would match. But models cover distance so quickly...

I am certainly planning to find a different field to test the model on. Somewhat farther away there is a collection of playing fields so perhaps 3-4x the size. One thing I would like to ask....  Just beyond the park is Swansea Bay with a seriously massive extent of sandy beach. Serious wind there but when it is calm and there is a gap in the dog walkers there should be lots of space with smooth packed sand.  I have never seen anyone flying there other than hang gliders and land yachts. Should I try that or stay well away?

Anyway, I will start with some short straight flights to check trim and what it is like landing first.  Then some super-lazy turns at altitude before trying some figure 8s.

Using the prop and motor suggested by the designers. Perhaps once it is up high enough it will be possible to back off that throttle a bit.  I wonder what the glide path of this kind of Delta is?