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Jan 08, 2006, 05:57 PM
'Riders fan.
David Winter's Avatar
Build Log

EDF CF-105 Arrow: Scratch built foamy


I thought about where to put this thread for a while. It could have gone in in either Foamies or Scale but I figure it's an EDF model so this works.

Last year I attempted to build a CF-105 Arrow with traditional building techniques involving balsa. Original Arrow Build

This turned into a complete disaster. The airframe without power or RC gear and unfinished came in at a whopping 210grams! Ouch. the EDF50's were not going to move that around. The model sat around for about a year.

About 3 weeks ago I started looking at it again. Pulled out the original drawings (CAD files) and started thinking about building it in foam. I did not want one of those flate plate square Arrows. I wanted a scale model.

The first step was to build a foam cutter. I had read a lot of different ways to build one; google was a great assistant in that.

What I wound up with was the use of a very old model railroad power supply from my father (who does large scale model rail roads, check out his web page with great pictures and videos http://www.wvrr.ca/). For the wire I used steel guitar wire.
Last edited by David Winter; Jan 08, 2006 at 07:07 PM.
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Jan 08, 2006, 06:03 PM
'Riders fan.
David Winter's Avatar
For part creation I am using standard home insulation EPP foam. It cuts well and is strong enough. I plan on glassing the finished model anyway so strength should be okay.

The first task, after building the cutter, was to build templates of the major cross sections. The CAD drawings I have had these cross sections on it (it's a CAD version from the book 'The Avro Arrow'). Unfortunately, as noticed in the previous balsa build, the cross sections are not correct in height. Width they're fine, height wise, they needed adjustment. I worked them as best I could in CAD.

Once a couple of templates were cut, I began experimenting with cutting the parts from foam.

As you can see in the attachements below, the first part was less than spectacular. The power supply would shut down after a few moments and this meant I had to stop in mid cut and wait for it to cool down. This caused a lot of erratic cuts. Also, I had to learn the technique of moving the part around the wire (which was stationary). Overall, for a first attempt, and considering I was fighting the power supply, it turns out pretty good and I kept it.
Jan 08, 2006, 06:08 PM
'Riders fan.
David Winter's Avatar
Obviously the power supply was not going to cut it..punn intended.

So I puchased a MRC 'RailPower 1370' model rail road transformer. It's about $50CAD and it works exceptionally well. Set at between 45-50 (out of 100) it gets the guitar wire at exactly the right temp. Moving it up to about 60-65 heats the wire up to the point where I can make quick and dirty cuts but the foam pulls away from the wire due to the heat.. again, good for fast cuts that are not accurate.

With new power supply in hand and the hot wire cutter working very well I took another stab at the previously cut part. I also sanded the edges of the wooden template a bit more because on the previous attempts the hot wire would bind in little 'divets' in the template.

The second attempt worked much, much better.
Last edited by David Winter; Jan 08, 2006 at 06:36 PM.
Jan 08, 2006, 06:11 PM
'Riders fan.
David Winter's Avatar
Now that the cutter was proven and I knew I could cut a reasonably complex part (with inside cuts as well!) I moved on to the other parts of the models fuselage.
Last edited by David Winter; Jan 17, 2006 at 05:05 PM.
Jan 08, 2006, 06:18 PM
'Riders fan.
David Winter's Avatar
One of the challenges was making the engine inlets. The Arrows scale intake area was made slightly larger by changing, ever so slightly, their shape. The Arrows forward fuse has an Area Rule to it (like a Coke bottle) which I removed, this allowed the intakes to be more square and about 5% larger width wise and about 5% larger height wise. The profile section is scale.

The intake area is about 110% the size of the fan diameter so there should be no starvation for air to the fans.

The majority of the fuselage was done by glueing two blocks together along a centre line and cutting the whole part at once. Due to the contours of the intake area I chose to cut them out separately. The two parts are accurate to about .5mm and considering they're done by hand (using templates) I'm happy with that.
Jan 08, 2006, 06:24 PM
'Riders fan.
David Winter's Avatar
Building the nose area was a challenge if for nothing else than its shape. It was decided to build it in sections. The most difficult thing to deal with was getting the nose to fit over the forward section of the fuselage. As you can see in the previous photos, there is a square area inbetween the intakes, this is where the nose section joins up. A template pattern was created and the nose section, as a whole, was cut out. Then using the previously used intake profile templates, the joint area of the nose was cut out. It was then fitted, quite snuggly to my surprise, to the forward fuselage.
Jan 08, 2006, 06:29 PM
'Riders fan.
David Winter's Avatar
So this is what I have so far. 95% of the fuselage is complete. The only missing portion is the very forward nose cone section, which, depending on how the model balances, I may build from wood.

Also, the tail fin has been temporarily fixed in place. The tail fin is the only part rescued from the previously failed attempt.

The pictures below show the overall size of the model. The wings shown in one image are from the previous build attempt. They will not be used but are in the photo to show size. A 1:48 scale model of the Arrow is in frame to show scale.
Jan 08, 2006, 06:52 PM
Model Designer
keven64's Avatar
That looks excellent, David.
I particularly like the Avro Arrow...

What are those fan units in the pictures ?
To me they look like EDF-50's, though your posts above mention only EDF-55's...

Keven.
Jan 08, 2006, 06:57 PM
EDF rules... :)
AirX's Avatar
Yup looks like EDF50's to me too. Nice work on the Arrow though. I have a plan developed for the wattage fan, too manny planes and not enough time...

Eric B.
Jan 08, 2006, 07:07 PM
'Riders fan.
David Winter's Avatar
Quote:
Originally Posted by keven64
That looks excellent, David.
I particularly like the Avro Arrow...

What are those fan units in the pictures ?
To me they look like EDF-50's, though your posts above mention only EDF-55's...

Keven.
Umm eerrr... yeah.. they're EDF50's..not sure why I was thinking 55's when I was writing that.
Jan 08, 2006, 07:13 PM
Model Designer
keven64's Avatar

too many planes and not enough time...


...exactly - the same here - and with many other modellers, I am sure.

What motors are fitted into those EDF-50's, David ?

Keven.
Jan 08, 2006, 07:19 PM
'Riders fan.
David Winter's Avatar
The fans are stock GWS 50's I have plans to put in Fiego brushless but haven't been able to source them locally yet. Also, I want to see if I can make them work on a single speed controller. Brushless would work very well, but I think even the stock motors would work okay.
Jan 08, 2006, 07:28 PM
Model Designer
keven64's Avatar
I keep playing with the four I have here - wondering if I should bother trying them as they are before I 'bolt' the four Feigaos into place...!

If you can make that lovely Arrow to a weight of around 10oz, it will fly with the stock fan units...

What's the weight right now ?
What batteries are you planning on using ?

Keven.
Jan 08, 2006, 11:49 PM
'Riders fan.
David Winter's Avatar
Right now, the weight of what you see in the photos comes to ~98 grams. I think that's about 3.5 ounces.

That's empty.. no fans installed, no radio etc.

I figure the Wings should add another 25 to 30 grams.. then the running gear is about 165 grams.. so.. roughly estimated the total flying weight should be about 330 grams or about 11 ounces.

I'll be using 2S lipo's I'm sure.. unless I put in brushless.. then I'll go 3S.
Last edited by David Winter; Jan 09, 2006 at 12:51 AM.
Jan 09, 2006, 01:33 AM
Registered User
flyingwings's Avatar
David

I am presuming that the wingspan of the Arrow is 24".

My 18.5 inch Arrows have come out at 10 oz with all radio gear and pusher prop installed. My models are all foam with carbon fibre tissue or .7 oz glass.

Using depron I think I can knock off another ounze.

So if your flying at 24 inch wingspan my feeling is that you would be close to 13 oz all up weight.

As for the airfoil to use. Use semi symetrical. You need lots of lift if your flying with a 4 or 5 percent thick airfoil.

The more weight you can knock out of the rear of the airplane the better chance you will have of getting a light weight model.

Suggest you experiment with cheater holes.

Remember the wing, if extended to the start of the intakes can provide an opportunity for using the wing as part of your fuselage primary structure. That will allow you to reduce the weight of the model.

The Arrow wing is inherently strong so I would suggest that you use thin spar caps using carbon fibre or doubled up carbon tissue.

I have kept the area rule in all my fuselages and have never regretted it.

I wish you lots of success with your Arrow.

Paul


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