Here is a list of all the postings N Pritchett has made in our forums. Click on a thread name to jump to the thread.
|Thread: Printed parts in strong sun.|
May be worth trying PETG. The nozzle temp for printing is about 230deg. So significantly higher than PLA.
It’s easier to print with than ABS as the thermal expansion is much less. I print with a bed temp of 60deg and it sticks.
Only issue is fine stringing. If you use a Bowden system then increase the retraction setting to reduce the problem.
|Thread: Anyone built a DIY hot wire bender for perspex|
I’ll run an experiment a bit later to check my hot wire foam cutter to see if the wire I use for that will be suitable. If so, I can send you some.
is this just for a temporary, or a ‘proper job’ where spending more than the basic may be worth it?
for a very basic solution you will need the following:
1/ some nichrome wire, could be salvaged from a bar heater element; like the ceramic rods with the coiled wire wrapped round in a spiral groove.
2/ some MDF/ply for a small table surface and vertical fence (12mm or more thickness would make for simple build).
3/ a length of aluminium U channel (12 or 15mm available from B&Q. Ideally matching the thickness of the MDF)
4/ a tension spring to provide pulling force of about 1kg. Only needs enough length to stretch about 20mm at that force).
5/ a few screws etc.
6/ some ‘hookup wire’
Following this, we need a bit of info about the nichrome wire you can lay your hands on in order to work out the voltage/ amps needed to achieve the temperature necessary. With the short length, the PSU is likely to need low voltage and high current. Do you have a multimeter to measure resistance?
The idea is to have about a 300mm x 400mm table with aluminium U channel along the 400mm edge so the open side is flush with the table surface.
Add a narrower table to the other side of the channel (so the plastic is supported both sides of the bend). Best way is to screw all three pieces down onto a couple of battens which act as support edges under the sides to the complete table. The heating wire will be fitted along the U channel, not touching it and about 2mm below the table surface.
The end fixings for the wire will depend on the actual wire you get.
More to follow when you have the wire info
Please answer the following questions:
How thick is the acrylic that you want to bend?
What is the maximum bend length?
Are you comfortable wiring up a project with some mains wiring involved?
Some experimentation will be required to get the best results. Are you up for that?
Do you have some spare acrylic to test the unit?
|Thread: Sabre build "Gotchas"|
May be in the forum posts but here it is anyway:
The rib spacing at the outer ends of the wings is typically 50mm except the end ones (R13), these are 49mm. Make sure you have the wing jig part J7 the correct way round or you will fine is impossible to line up the jig correctly with the plan. The giveaway is that the ends of J7 are slightly different as I noticed on closer inspection when I couldn’t get it to line up!
|Thread: Neil's attempt at a first scale model!|
Wow, that’s interesting. Appears to be counter-intuitive but can’t dismiss a live test result!
Makes me want to build a wind tunnel to experiment with tubular shapes.
Thanks for the advice, will keep it closed.
For interest, how can the drag from increased wetted area be compared to the blunt nose drag; where presumably the laminar flow along the fus’ will be seriously compromised?
Thoughts about the value of the air passage through the fus'?
Looks like it would trump trying to make cleaner servo exits, control horns etc. although I may try to keep the controls within the airframe but it's a lot of hassle, especially as my model isn't likely to rank highly in the scale ratings.
Me being a fully fledged 3D cad man, I wouldn't particularly vouch for the ease of use of DevFus Foam, but it does have some nice features. I don't find it as easy to use as led to believe from the publicity.
Anyway, it served a purpose here.
The thing I took note of most was the change in fairing line along the tailplane abutment face; the change in angle where a typical elevator hinge line would be. I also deduced that the fairings, for the most part, are virtually parallel so they merge into the fus' skin naturally at their leading edge.
Another part I'm pondering over is if it's worth having an air passage through the fus' to avoid the flat nose airbrake! Fairly easy to make way past the battery area with the use of suitable batteries as there are so many shapes to choose from these days.
I'm looking particularly at the 'Airsoft' batteries that are 10x21mm cross section per cell at 2000mAh. I'm using 2 of these in the nose of my own design sloper where the 20x21 combined cross section goes well into the nose area.
With modifications to the existing battery box (don't use solid front) the slim batteries would easily fit either side, leaving the middle clear for the airway.
BTW what's the idea of the 6mm holes in the sides of the battery box? Is it for some dowel arrangement to stop the battery sliding out in flight?
Progress has been slowed due to life’s unexpected turns intruding into model building time.
Anyway, continued research into the fairings led me to the basic thought that, aerodynamics and functionality of the actual plane, mixed with common sense manufacturing methods used way back then, determined the final shaping. I then knocked up the shape with DevFus Foam. To do this I used the shape of the formers in the short kit as a starting point.
I needed to add additional formers for DevFus to blend correctly. I then changed the F9 & F10 formers, along with the ones I added from F8 to the tail at 50mm intervals. These were tweaked to give fair lines to the fus’ skin.
This gave me the visual 3d model that I could spin round and look from all angles matching the real life photos available. The formers were further modified so the model matched as closely as possible when compared to the “walkround’ photos available on line.
This may seem like a waste of valuable building time, but satisfied my tendency to be a perfectionist in intent (although rarely achieved).
I suppose it also gives me a possible foamy ducted fan build in the future!
Edited By N Pritchett on 03/02/2020 18:02:10
Thanks Chris for the photos and detail.
Gordon, no need for apologies. You’ve done a good job in bringing the plans to the state where the Sabre can be built with only fine ‘scale’ detail to be mulled over.
I’ve been looking at photos on a ‘walkround’ Set. These appear to show the tail faces are vertical and parallel to each other, only tapering in the rear quarter of their length.
The forward part, in front of the tailplane LE merges into the fus’ as it progresses straight forward. It also has a rounded top edge in this part, but sharp edge above the tailplane and to the rear above the tailpipe.
I would include the images if I could work out how to on my iPad
been reading some of the other build threads (it's great not to be first so to be able to learn from others!)
In Steve's thread 'Avon Sabre Spirit 78' I see he is well advanced on the planking of the fus', and notice he had a case of starvation between formers 8 and 9. it's probably a result of narrow planking with light balsa which is the way I will go too. Not sure if this is common, but got me thinking.
I want to include the barn door airbrakes so methinks I'll loft an additional former '8a' half way between. Hopefully this will avoid the wasting and give the airbrakes a positive edge to close against.
I'm keeping an eye on Adrian's progress with 3d printing of his airbrakes too!
I'm already really thankful for all who are posting in the various build threads. Very helpful for us newcomers.
Hi Mark, Yes the plans & kit from M & G.
Chris, any closeup photos?
Well, here we go with my first attempt at a scale model.
Looking on the web at the wide range of livery, it had to be the RCAF Golden Hawks colours (or should it be colors) as I was from Canada many years ago.
Anyway, got the short kit, good start.
Bought the balsa etc from Balsa Cabin (they usually supply good quality).
In the process of making a building board wide enough for the wing jig (my usual board is only 300mm wide).
While waiting for the cork surface bonding to dry I started looking carefully at the Fus' drawing. With the article in RCM&E and noting the former warnings I'm hoping it will not have any surprises!
Now here's my request for help from anyone who has mastered the tail fairings please:
The Tailplane shows the joiner wire slots to be perpendicular to the fus' mating edge. OK, so next looking at the small scale plan detail, it appears to show the balsa fillet's vertical surfaces tapering towards the tail of the fus'. How does that work out?
A tricky area that I'd like to look right as I don't want to bodge this on the first attempt at scale.
Looking forward to any input, thanks.
|Thread: PSSA Mass Build weekend attenders|
Very thoughtful offer of the buddy box help, thanks Martin. I’ll certainly look at the link and seek advice from Ade. I’m not one for reinventing wheels!
My only slope experience to date is a couple of times at Ivinghoe on mild days and a 3 day outing to a very blustery Mam Tor with 3 mates last spring (primarily flying a foam wing which was, fortunately, virtually indestructible).
|Thread: John A's Sabre build|
Don’t want to be a party pooper but: I believe you need to clear it with the CAA to have permission to drop anything from a flying object!
I know this used to be the case years ago when, in a previous existence, I ran a company manufacturing sports kites here in the UK. At the festivals some display teams needed to get this permission/license to drop small quantities of sweets from kites as they were covered by the same laws.
|Thread: PSSA Mass Build weekend attenders|
Hope to be there. Fairly new to slope soaring so may be a baptism of fire!
Got the short kit and starting the build. Will be doing the RCAF display team ‘Gold’ colour scheme all being well.
Looking forward to meeting and seeing the others
|Thread: Spektrum module for Taranis|
The only difference with my setup is that I 3D printed a carrying handle for the TX (replacing the metal one) and used the DX4 TX aerial embedded in it so the TX doesn't look like a porcupine!
This did mean drilling a hole for the aerial to pass through the module housing and another near one of the screw holes for the handle fixing. This allowed the aerial wire to go internally, up the handle and along inside the top horizontal portion for the business end (the handle is in two pieces with a front and back which screw together to allow the aerial to be fitted in it).
also added a small rectangular LED in the handle so it is visible from the front.
If anyone's interested, I can send them the handle design.
Yes, Internal off, External set to DSM2 - DSMX
Press Bind, = flashing + beeping
Receiver powered up with bind jumper
No sign of binding. The receiver does bind to my DX8 so the RX is good.
Just updated from 2.1.7 to 2.1.8 to see if changed things. Still no go!
Any other ideas?
Is there a way of checking that there is some RF output from the module?
There is a signal on the diode input to it and the 3.3v is Ok.
All suggestions gratefully received.
Got the same problem. Mine won't bind with any DMX receiver.
Have checked the receivers which will bind with a DX8. So the receivers are OK.
Trying an AR400 receiver using DSM2 - DSMX setting on the Taranis plus.
Anyone know if there has been a change in the TX firmware that could be causing this issue?
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