In a parallel universe, my pal Ian is putting together the same model, and has fed me with the modifications necessary to shoehorn two 70mm edf units into the frame. Nothing like belt and braces I always say...
Here are a set of card formers I produced for him to assess...
I must say, the more I look at it, the more I like the idea, oh well, I can always build another! :-D
Ian has kindly sent me some pictures of his progress so far, and I must say, it's looking extremely promising. I've been working with him over the past few weeks in modifying my original CAD rendition of the formers. As you can see from the pictures, his careful measurements and attention to detail has really paid off, and the twin 70mm edf units look perfectly balanced within the fuselage formers.
Here's all the bits (including 1.5mm ply rib templates)
Just to demonstrate the accuracy of the laser cutting, here's the waste material from the duct holes and the tube templates that were also cut from those waste holes..
Actually, of course the twin version is more in keeping with the real thing, which will enable him to create an even more 'scale' appearance than the original model design, as the F-4's twin exhaust ports can remain in position in the air.
Here we can see 'F6' which he has chosen to support the two 70mm units...
As I say, Ian's attention to detail coupled with the high accuracy of the CAD/laser cutting has enabled close tolerances to be usilised to maximise thrust. For those of you interested in edf units for future projects, Ian has discovered a very informative document concerning all aspects of ducted fan optimisation, which you can download and study here: FSA Calculator.xls
I can't get over the neatness of the installation, I want one!!!
If you've studied the plan, or my single edf build version, you'll see how he's opened up the 'nostrils' of 'F-3' to give a greater through-flow to the edf's. He tells me that he intends to 'cheat' a little by allowing extra air in behind the diffuser.
N.B I know it's a long way off, but I can almost see a couple of super bright red led's positioned somewhere in the ducts that would add some extra realism when viewed from behind in the air!
Well, a slight update; I plan to recreate the damaged canopy mould by making another from the original product I took off the mould. Ian has asked me if I can make another, plus it would be nice to be able to reproduce them in the future with minimal fuss. I have sourced some reasonably priced clear perspex from a local firm, but until I get back up to the vac former, I'm not sure if they are big enough to be clamped in the machine.
Darn & blast! I've just been up and checked out the dimensions of the vac former's material aperture, and it's larger than the length of an A3 sheet! The width is fine, but length is definitely about 2cm short. So, I have several choices,
A; Buy some more material the correct size
B; Cobble together an extender frame that brings the material to the correct size
C; Build my own A3 vac forming machine.
A is a little lacking in imagination (and wasteful!) B is possible, but knowing how temperamental the process is at best, may end up as a fail. So, although it's not an instant fix, C may actually be the best choice. It may seem a little crazy to embark on this seeing as I have at my disposal a c. £5000 vac machine, but in reality, I only get to use it when it's not in use, and usually have to rely on somebody to assist me, so not ideal. I've looked into making one some time ago on Youtube, and folk have some great success with them. My only question is if a home build will be up to moulding 1.5-2mm perspex, as the stuff I saw being formed appeared to be around 1mm or less. It does take quite a force to push the hot material down onto the mould, before the vacuum is applied (the commercial model employs a lever to raise the mould upward with some force) so we will have to see. Lets say I am cautiously optimistic!
I plan to build it from a sheet of 12mm plywood. I envisage that the base unit would be bolted down firmly onto a solid work bench, as it's helpful for it to be as steady as possible when hot plastic is being manipulated. I'll make it so that the material frame, or clamp will slide downwards easily into a sealed enclosure, to assist with the vacuum part of the operation. There is absolutely no reason why it shouldn't work on a £50 homespun vac former, any less good than on a 5k one, as the success in these things is mainly down to the experience of the user!
I like a challenge..
God managed without machinery, but most of us need a little help
We could always make a small modification( cheat) by reducing the length of the canopy by 20mm and build more wood into the fuselage. Just an idea
It's certainly an idea. I believe my canopy already has some built in 'waste', (it was easier to make the original former or plug for the mould that way).
I've found some surplus Formica lined shelves that will do nicely for the vac former's base unit. I need to have a good think about the best way to clamp the material, and seal it against the base plate. Now for the prototype...
God managed without machinery, but most of us need a little help
Six months later, Christmas out of the way and my 180 quad awaiting a good thrashing (technically speaking), I saw this offer from HK:
If you don’t like reading specs, just focus on the 51000 rpm!
Features: • High power/High thrust • Factory dynamically balanced • High-quality construction • 8-Bladed CNC Alloy rotor • Superior cooling • Easy to install • Fully serviceable • Pre-assembled • No housing distortion Specs: EDF Inner Diameter: 70mm Outer Diameter: 71.5mm Length: 146mm Construction: Alloy Weight: 315g (complete unit with 3.5mm connectors) Max RPM: 51000 Motor Type: B2970 3000kv in runner Max Power: 1300W (10sec) Continuous Power: 1400W Max Voltage: 14.8V (4S)
Features: High performance microprocessor brings out the best compatibility with all kinds of motors and the highest driving efficiency. Wide-open heatsink design to get the best heat dissipation effect. Improved Normal, Soft, Very-Soft start modes, compatible with aircraft and helicopter. Smooth, linear, quick and precise throttle response. Multiple protection features: Low-voltage cut-off protection / Over-heat protection / Throttle signal loss protection Programable via transmitter and Turnigy BESC programming card Programming features: Brake setting (we recommend using brake for only folding props applications) Battery type(Li-xx or Ni-xx) Low voltage cutoff setting Factory default setup restore Timing settings (to enhance ESC efficiency and smoothness) Soft acceleration start ups (for delicate gearbox applications) Low voltage cutoff type (power reduction orirnmediate shutdown) Governor mode Built-in BEC Output(5.25V or 6V)
Factory default settings: Brake: off Battery type: Li-xx (Li-ion or Li-Po) Low voltage cutoff threshold: Soft cut-off (2.6V) Timing setup: Low Soft Acceleration Start Up: Normal Low voltage cutoff type: Medium
It’s time I got this project back on track, especially as a rumour has it that Ian is rekindling his F4 as I write! I hope this edf unit can produce enough thrust to get me air-side! Fitting the edf unit will entail cutting the top longeron between two of the formers, but it should be a simple matter of reinforcing afterwards to allow removal of the unit for servicing.
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