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-   -   Underwing engines and mounting (http://www.Wattflyer.com/forums/showthread.php?t=73588)

solentlife 04-19-2014 06:58 AM

Underwing engines and mounting
 
I'm always intrigued as to how some mount their engines underslung wing style. Propellor motors replacing Jet is easy to see and devise ... but EDF ? That's not so easy.
a) EDF is proportionally much larger than a Turbo-jet in relation to the aircraft
b) EDF has either no mount or has the two flat plate lugs

Whatever - they do not lend themselves easily to this concept. I'm talking in terns of ie 737, 747, 320 etc.

Interested in ideas ...

Nigel

fhhuber 04-19-2014 07:20 AM

Well... I could devise the mounting. Just a mod to single pylon instead of dual pylon I used for the nacelle I put on my big EDF.

Cylinder of foam cut in half.

Carve out for EDF lip and mount lugs if any. If there are lugs then inset appropriate wood plates to accept the screws.

Pylon core is 1/8 aircraft ply for my big EDF. 1/4 inch balsa laminated both sides (below the foam of the nacelle) for something to sand into a symmetrical airfoil. Smaller load I'd use thinner ply maybe... aiming for just stiff enough for the job.

For the dual pylons I have them slotted in and epoxied to the lug mounting plates. For single, depending on EDF size, I might just slot the pylon into the foam and epoxy it or I might arrange to have it BE one of the bolt plates and then add other reinforcement.

Simple and effective.

Note that many EDF foamies just have the EDF nested in the foam.

solentlife 04-19-2014 07:29 AM

Trying to picture this ...

As to the RTF ... I know they just slide the EDF in and lock it with Chinese GOOP.

What I'm aiming for is to realise a way to mount without increasing the size of the motor unit overall ... an EDF is already oversize compared to the real thing ... adding a tube and mount adds to that ...

I have so many models in mind that I have wanted to build - but shy away from because of this.

Nigel

fhhuber 04-19-2014 07:32 AM

Just make a relatively thin foam nacelle.. a little thicker than a styro coffee cup is enough. You want the better intake ring and the cone at the back to squeeze the efflux.

I flew one of the same "bobcat" clones with a bare fan... it was much slower. Just putting a wild guess nacelle around it is a HUGE difference.

solentlife 04-19-2014 08:01 AM

1 Attachment(s)
One of the cheap Haoye EDF units ... think it's the 51mm has both intake and efflux addition rings ... I know they work well having used them.

My Concorde improved when I 'tubed' the efflux after trying with the square bare nacelle units. I haven't 'tubed' the intake as she now flies ok on 4S ...
I used 3mm Depron rolled round and then just simple taped in place .. rough but works.

I have to admit that I am looking at this as a project :

http://www.luft46.com/fw/fw1000a.html

FW 1000x1000x1000 Bomber.

An interesting and sleek looking machine.

Nigel

fhhuber 04-19-2014 08:53 AM

For that fw1000... look at the Dynam Me262's solution. Exactly the same problem of getting an adequate EDF mounted under the wing in a nacelle that isn't on a pylon...

They made the Nacelles a bit fat, but decently scale looking.

Just mod a set of the Dynam nacelles... they are available as spares. Inside tube is very good for their 70mm EDfs which are cheap. Scale the plane to fit.

solentlife 04-19-2014 09:54 AM

I looked at 262 gear .. as you say it is similar and works. But what I'm after is a scratchbuild solution so that we can do it for whatever size EDF we have.

I want to do the FW with twin 50's ... or 51's ... so looking for a scratch solution.

I have a 262 plan .. Outerzone and Hippocket are really good ! ... in balsa / ply .. but transposed to foam is iffy ...

Nigel

Abuelo 04-19-2014 03:20 PM

Intriguing, and subscribed.

fhhuber 04-19-2014 04:07 PM

The point is... look for the best overall solution.

A bare fan won't be it.

solentlife 04-19-2014 05:13 PM

Quote:

Originally Posted by fhhuber (Post 945896)
The point is... look for the best overall solution.

A bare fan won't be it.

The 50 could be as it has front and rear add-on cones ... but it still needs fixing in place.

http://www.hobbyking.com/hobbyking/s...inch_50mm.html

Prev. post I thought it was the 51mm with cones ... - I've had so many of these 50 and 51mm's - its hard to remember which !!

Nigel

fhhuber 04-19-2014 06:08 PM

Get that fan and measure the outlet dia.. do the calc of FSA vs Efflux exit area... if Eflux area is more than 85% of FSA its wrong (and that is obviously wrong just from a glance at the picture)

solentlife 04-19-2014 06:20 PM

Quote:

Originally Posted by fhhuber (Post 945921)
Get that fan and measure the outlet dia.. do the calc of FSA vs Efflux exit area... if Eflux area is more than 85% of FSA its wrong (and that is obviously wrong just from a glance at the picture)

It has a definite taper and it DOES work well ... I've used them ... it may not be optimum but it is less diameter than the 50mm Mini jets exhaust ...

The efflux cone actually is a reasonable match for the Mad Thrust 50mm alloy ... If I had 2 of them - they would have been fitted to my Concorde - but unfortunately I only have one left ...

I'm just putting my lips to Eggs - sucking them ... ;);););)

Nigel


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