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Dec 13, 2010, 08:41 AM
An itch?. Scratch build.
eflightray's Avatar
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Discussion

My Winter Project, Update #5. She's flown.


I seem to get a bit carried away at times, ........this time it might be in a straight jacket .

It started some time ago when I was thinking, 'how about a jet', but not an EDF or a pusher, ....but an EDP. I had asked some time ago in the EDF forum about a 'largish' F-86 Sabre, ....... powered by a ducted prop, (the P in EDP). Yes, I got a similar reaction there as well.

Give up ?, me ?.

Well yes on a Sabre, it was a problem with holes. The one at the front and the one at the back, compared to the possible thrust from a low powered system, (I hate lots of amps when it often isn't necessary).

So, two EDP's sound better, (short delay while I scan through some pictures of planes to find a candidate).......a Mig 1.44 ?, mmmmmmmm!.

A bit of sketching and a, 'what if I used two 6" props' later. And I am either committed, (in more ways than one ), to building a 'something like a Mig 1.44', or some industrial size air conditioning trunking

Anyway, here's some pictures of just some of the bits so far, no glue involved, yet, just a mock up, (Yes and some of you may read that 'mock up' starting with a 'c').

You have to guess the rest of the sizes, (just like me), but the props will be slightly cut down 6" diameter, (around 5.8" dia, I really should put my glasses on when measuring things).

And yes it will fly, and probably on a ridiculously low watts for a jet.

The saga begins -------
Last edited by eflightray; Mar 03, 2011 at 02:55 PM.
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Dec 13, 2010, 09:36 AM
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larryross's Avatar
Looks like it's going to be big so I'm in.
I had often thought about trying to apply an EDP to something. Interested in how you do on this project.
Dec 13, 2010, 10:17 AM
An itch?. Scratch build.
eflightray's Avatar
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Hi Larry.

My 'concept' is based on a few models that I have flown using 6" props, and when you put two of them together and a fairly big wing, (low wing loading as well), it works very well.

I have a scratch built A-10 at 59" span using two 6" props on the front of the nacelles, (not EDF), and drawing about 200 watts total. It take-off grass and flies very scale like.

Also I resurrected my Vulcan, 48" span, with a couple of pusher 6" props and it too flies quite scale like from a hand launch.

Some of the EDF fliers tend to look for speed, (a lot of amps needed), where I'm quite happy to fly at a slower, more scale like speed, so don't need the extra power.

It works for me.


The picture of the assembled 'stack', only comes up to the wing leading edge so far , so you're right, it is going to be big. Though I think the span is still only about 62".
Dec 13, 2010, 10:27 AM
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larryross's Avatar
Will the motor/props be inside the tube and near the inlet or closer to the outlet of the tube? Do you taper the outlet to a smaller diameter like they suggest for EDF piping?

Did you do a thread on your A-10? If so, do you have a link to it? Sorry for all the questions.
Dec 13, 2010, 01:31 PM
An itch?. Scratch build.
eflightray's Avatar
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Quote:
Originally Posted by larryross
Will the motor/props be inside the tube and near the inlet or closer to the outlet of the tube? Do you taper the outlet to a smaller diameter like they suggest for EDF piping?

Did you do a thread on your A-10? If so, do you have a link to it? Sorry for all the questions.
The ply cross beam is where the motors will sit with the props about 1" inside the tubes. There will probably be some blending between the front fully open ducting and the change to two tubes, just to help the air flow. The motors will also probably get spinners and some rear nacelles to.
The design is all in my head at the moment. (Boy, it makes my brain hurt, I must vac some of the Depron out of there soon )

I decided to try a 10% reduction in the tail pipes, based on the prop swept area, similar to an EDF.


Here's a link to the A-10 - Oh not another A-10
Dec 13, 2010, 01:58 PM
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larryross's Avatar
Have you thought about whether you will have the motors behind of the prop in tractor config or in front of the prop in pusher configuration. For air flow I would put the motor behind the prop tractor config and as You said use a spinner. A thought... if you put a slight reduction in exhaust tube and 1" area between the prop and the tube wall, you might get a lot of by pass around the prop ends.
Dec 21, 2010, 06:21 AM
An itch?. Scratch build.
eflightray's Avatar
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Here's some latest pictures. This is going to be a fairly long project, so please don't expect too many updates.

I'm already having trouble taking pictures in my 'work shop', (the small bedroom/box room, 7' 5" x 10'), the lens on my web cam is not exactly wide angle.
Also I 'share' the room with a single bed turned on its side, (my 'work bench'), the Sunderland, (no more room in the garage for planes), my desk and computer, TV, DVD player, etc etc. So those of you who like to show their workshop pictures, showing caverns with wood working machines dotted around, enormous benches etc.............(sigh!), I can still make scratch builts in a matchbox .

Some gluing has happened now I'm fairly sure I know what I am doing (). The front end, (the suck it in bit), is now sort of done, and I have added a bit of an air flow guide into the prop 'holes'.
I have even started some outer skinning to the front to see how ridged it make it, (very ).

The motor mounts are in place, plus a section of fiber tube for the wing spars. They will be fiber tubes as well, (ex-cheap fishing pole, so not carbon). It will all get blended inside the duct to give a reasonable airfoil for reduced drag, and minimum loss of duct area.

The front fuselage, (all that in front of the intake), is still in my head, and may need to be removable as it's getting a bit too long, (especially when the tail pipes go on). Yes I know I'm mad, don't rub it in.

So many questions, but they will all get solved one at a time.

She will fly.
Dec 21, 2010, 10:40 AM
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larryross's Avatar
I'm no expert, but from what I have read on builds with EDFs that the shape of the inlet rim is critical to the out put thrust. Afraid I can't be more specific than that as I say I am no expert on EDFs.

BTW a good place to buy inexpensive carbon arrow shafts (seconds)... I have used a lot of them.
http://canuckengineering.com/

A quote from your A-10 build "No, sorry no plans, I tend to rough out the outlines in some paper, then just built the thing. (A true scratch builder )".

Is that to say that someone that builds one out of his head and puts it neatly on paper and builds and post PDFs so others can build one too is some how not a true scratch builder?
Last edited by larryross; Dec 21, 2010 at 11:07 AM.
Dec 21, 2010, 01:25 PM
An itch?. Scratch build.
eflightray's Avatar
Thread OP
Ah!, but that's why I'm not building an EDF, too many, "you must do this, do not do that, and the area must be the square root of a thingamajig at the correct angle of dangle", or it wont work.

If I make up my own rules, I know it will work.

The definition of a 'scratch builder', .....is in a scratch builder's mind, ..like so many things about this hobby. Every one has their opinion.
Whether it's building from a kit, (laser cut or just a load of wood and a plan), building from a commercial plan, building from your own plan, or just building. Some may even see assembling an ARTF as scratch building, well only a RTF isn't, (could RTF be scratch buying ? ).

It's like another of my favorite words, efficiency. 'Most efficient motor/airfoil/model'.......

But that's another world, so I stay in mine and fly electric models that don't meet the 'rules'.
"Watts per pound", loverly expression, but does it still hold true for a left handed aerobatic pogo stick ?. So yes, I ignore that one as well.
Dec 21, 2010, 04:14 PM
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larryross's Avatar
OOOOK this one will be interesting to watch (I'll be glued to this one). Prop bypass ignored, intake air flow ignored. I too like to stretch the rules with my builds. You do realize that when you put the prop inside the tunnel it's a completely different world than having the prop outside and in front of the tunnel. Will watch with great interest to see if you get spanked for not following the rules.
Dec 31, 2010, 11:02 AM
An itch?. Scratch build.
eflightray's Avatar
Thread OP
Another update. It's progressing slowly.

I'm just picking off one problem at a time, if I look at the number of potential problems for the whole project, I just wouldn't have started.

For example, although I originally based the design on the Mig 1.42/1.44, mainly because it has a big mouth, if anything deviates from the original shape, (goes wrong ), then "it's all part of the design", is my logical reply, (Ok, excuse ).

So yes, the forward fuselage doesn't blend into the fuselage as per the Mig. But this is my version, currently 1.49 oblique stroke 7.03, version 15j dash 7r. Exactly to plan.
Jan 02, 2011, 10:51 PM
I crash planes
bbjsw10's Avatar
Looking good, and I do believe you on carried away with straight jacket, that thing is freaking huge. More balls than I have for sure.
Jan 06, 2011, 08:44 AM
An itch?. Scratch build.
eflightray's Avatar
Thread OP
A bit more done.

The 'power' section is now in place, also the tail pipes, and a few other bits and pieces.

Considering the wing span will only be 62", (not that big for a model), she is now 74" long, (taller than me).
Weight so far is 1lb - 10oz, (26oz), which feels like a ton, but probably isn't too bad.

She now has to be moved out of my 'workshop' for photographs.
Jan 06, 2011, 09:15 AM
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dstrout's Avatar
have you tried spinning up the motors yet? Any feel for amp draw or thrust?
Jan 06, 2011, 10:20 AM
An itch?. Scratch build.
eflightray's Avatar
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Quote:
Originally Posted by dstrout
have you tried spinning up the motors yet? Any feel for amp draw or thrust?
Nothing is connected in the model yet, but I have already used the motor in other models, see posts #3 and #5, so I have reasonable confidence that the model will fly how I wont.
But it wont be anything like the usual screaming EDF jets, I much prefer to see the model as it flies by, (count the rivets as it passes ), speed is for other modelers.


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