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Old Jan 22, 2013, 11:48 AM
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Build Log

F-15 (Jetset44 ) 70mm EDF Conversion


Hi All,

I’m 43 and a year ago I started flying again after a break of 25 years - haven’t things moved on!

I have been flying electric RTF’s in the local park and have been inspired build again after reading a couple of Steve Shumate’s (jetset44) blogs on RCG.

My youngest son Corey, aged 9, is becoming a keen modeller, which is great as that’s about the age I started with free flight & control line models.

I have always fancied building a ducted fan jet and Steve’s Supper Banded really got me excited. That was until I saw his F-15, which from what I have read would be the EDF to start with.

I’m a freelance design engineer and Steve has kindly given me the go-ahead to adapt his F-15 design to suit a 68mm EDF unit.

I will be designing in 3D CAD (SolidWorks) and in a spirit of the RCG blog environment, where everyone could participate and contribute firstly to developing the design and then the build.

The basic plane –
  • Based on Steve advice and the complexities of designing for EDF I’ve started by just Blocking out a 34” version in 6mm Depron (see pics 1).
  • I will then model the all the equipment (fan(s), batteries etc.) and add them to the model to give me a good indication of packaging space, wing load, CG, overall weight etc.
  • Once the driveline has been resolved I intend to design the ducting and then design the rest of the air frame to suit.

I expect the learning curve for me to be really steep as I have had no experience in EDF model building or flying. But as Steve said “that's part of the challenge of EDFs that make them fun.”

My first question for you all –

When calculating the wing area do you base the calculation on pic 2 or pic 3?

Thanks again Jetset44 for the encouragement and support.

SteveJ
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Old Jan 22, 2013, 12:05 PM
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This may be of use. https://www.rcgroups.com/forums/show...2#post22430764

Look at posts 2117 and 2130
Old Jan 22, 2013, 01:31 PM
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Thank CoolerByTheLake,

In this configuration, a 34" Span, gives me a wing area of 431sqin.
Old Jan 22, 2013, 11:22 PM
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Glad to see you're giving this a go, Steve! I look forward to seeing how this progresses.

For wing area, go with picture 2. But don't include the strake--just draw a line straight across the fuselage at the wing root leading edge. That's close enough for our purposes. Note the fuselage on a jet fighter design also contributes quite a bit to lift, but you can generally ignore that for model airplane designs like this (it just adds a margin of safety in terms of lifting area).

Steve
Old Jan 23, 2013, 06:23 AM
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Cheers Steve,

Gdimonte has joined me on the project and is keen on a 6C version. Priority at the moment is to tie down a target weight range for a couple of set-ups. It’s very early days but this is where we are at (pics).

Learning loads… loving it!

SteveJ
Old Jan 28, 2013, 02:35 PM
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Design Update


We had a great week on the design front with some exciting new build techniques (for me anyway) to explore.

Quite early on in the week Gery (Gdimonte) & I made the decision to really try and push the design and staying as close as possible to scale. The design is evolving daily, far quicker than I thought due to the fantastic input from Gery.

So far out combined wish list for the model is –
  • Fan : 70mm 700-800W – 4C or 6C – flight time 5min (approx.)
  • Materials : Blue Foam, Carbon Rod, Light Ply, ľ”oz glass cove & WBPU.
  • Build Method : Fuselage Hot Wire sections 2” – 4”. Wings – Hot Wire with aerofoil.
  • Ducting : Bifurcated duct design – Fiberglass : Inlet @110% FSA, Exhaust @85% FSA
  • Retracts : Electrical.
  • Fun to Fly with a good balance between scale flight characteristic’s.
  • Documented well enough to share the design with others.

So with all this in mind we went back to the drawing board concentrating primarily on the ducting design as this seems to be critical to the success of the project…. I never really appreciated how much engineering goes into ducted fan models.

I have modelled the front section & fitted Gery EDF unit in my first stab of the ducting assembly– see pics.

If you would like to download the 3D eDrawing model (imbedded in a webpage) click the link below. You will need to open it in Internet Explorer 5.5 or higher. Once opened you can rotate, hide &show components, do cross sections, animate the assembly etc… have fun.

Duct GA (eDrawing) 2013_01_28

Cheers, SteveJ
Old Jan 28, 2013, 02:50 PM
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I think that the 110% FSA intakes are a little much. 100% should be a great plenty!
Too small is no good, and too large is just as bad. Depending on the make of fan, see what is suggested.

Why 110%?
Old Jan 28, 2013, 04:47 PM
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I changed Jetset44 plans a little to make it more scale i could give you the plans.
Heres the link to my build https://www.rcgroups.com/forums/show....php?t=1783803
Old Jan 30, 2013, 06:40 PM
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Quote:
Originally Posted by CoolerByTheLake View Post
I think that the 110% FSA intakes are a little much. 100% should be a great plenty!
Too small is no good, and too large is just as bad. Depending on the make of fan, see what is suggested.

Why 110%?
Hi CoolerByLake,

Sorry I'm showing my lack of experience, you are totally right. For some reason I go 110% in my head when writing the post.

The XL calculator sheet that Gery used actually states it needs to be 100%. I have done a lot more reading since and revised most of the ducting... Hopefully post some pictures later in the week.

Thanks very much for the feedback.

Stevej
Last edited by meerkat13; Jan 30, 2013 at 06:46 PM. Reason: Spelling
Old Jan 30, 2013, 06:45 PM
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Quote:
Originally Posted by chester2240 View Post
I changed Jetset44 plans a little to make it more scale i could give you the plans.
Heres the link to my build https://www.rcgroups.com/forums/show....php?t=1783803
Wow, It's a shame you didn't get a chance to shoot some video. I would have loved to see it in the air. A copy of you plans would be great.

Cheers, Steve
Old Jan 30, 2013, 06:47 PM
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Enjoy the build Meerkat. I just transformed it into a 3-55mm one off I call the TF-12 RONIN. LOTS of redesigning !!Steve has some great planes.
Old Jan 30, 2013, 06:52 PM
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Quote:
Originally Posted by RogueAce View Post
Enjoy the build Meerkat. I just transformed it into a 3-55mm one off I call the TF-12 RONIN. LOTS of redesigning !!Steve has some great planes.
Yeah, I have been following your build... Mental, super cool . Looking forward to the flight reports.
Old Jan 31, 2013, 12:19 AM
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Ive started building another one and the build is going much faster that i know what im doing.

I have the plans only on the simple paint system and i dont know how to transfer it to adobe
You can do what ever you want with the plans!
If you need any help let me know im more them happy to help!
Old Jan 31, 2013, 06:36 AM
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Design update


Thanks Chester,

The duct work is getting there... really interesting stuff!

Main changes -
  • Total Inlet now 100% FSA
  • Fan moved as far to the rear as possible (long Inlet / short exhaust). This should give a bit more flexibility with the COG.
  • Trying to keep the wetted surface area as small & smooth as possible.

It still needs tweaking as the inlet cross section area grows as it sweeps between sections B-B & E-E (see pic / PDF)

As always I would appreciate any words of wisdom & observations. Hoping to get the ducting resolved this week to start the fun stuff next week.

Cheers, SteveJ
Old Jan 31, 2013, 09:11 PM
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You should read this on how AIR SALLY does his ducts. Start at post 605

https://www.rcgroups.com/forums/show...672388&page=41


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