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Old Mar 14, 2003, 12:12 PM
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Canada, ON, Caledon
Joined Aug 2002
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How do you design your scratch built jets?

Hello EZone,
I am new to jet airplanes.
I would like to know your ideas of designing a jet. I know that an electric jet, with a satisfied speed would have motor power 100W/lb, right?
But I need to know where to place the ducted fan in jet, where to place the main wings, from the fudelage...
There's a lot of stuff you can tell me. All the answers are going to help me a lot.
I just want to design my own electric jet too.
THanks, Florin777
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Old Mar 14, 2003, 01:41 PM
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Daren's Avatar
Los Alamos, NM, USofA
Joined Nov 2000
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Re: How do you design your scratch built jets?

Quote:
Originally posted by Florin777
I just want to design my own electric jet too.
If you're new to jets, edf, and designing it would probably be best to begin by building a few kits first. This will give you some experience to draw upon when you put pen to paper.

EJF's KC F-18 is a good one.
Haldor's HL MiG 29 is another.

Daren
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Old Mar 14, 2003, 11:57 PM
Bzulu
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Berlin
Joined May 2002
214 Posts
My first jet looked like this...
1.Take some thin styro plates and glue them together.
2. Cut them to the desired shape; delta preferable.
3. Hook the fan somewere at the aft.
4. Predict the CG.
5. Off to the flying field and loads of fun to be experienced, especially when you find out that the calculated CG is a matter of resin or should I say trail and error.

6. Brass spent: fiver or so...
IŽll send you a plan if youŽre interested.
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Old Mar 15, 2003, 10:57 AM
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Lilburn, Georgia, USA
Joined Nov 2000
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Designing

Hard work, attention to detail, scrutiny and lots of time
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Old Mar 15, 2003, 11:30 AM
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Joined Aug 2002
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Thanks FANMAN.
That's a wonderful airplane, did you build it yourself?
But what I meant was if you can tell me some formulas you must know when you want to design an electric foam jet(using 1 MiniFan 480). Like where the CG should be(in general, sport flyers, the CG is between 30%-70% of the fuselage, right?) ; how long should be the fuselage, if you know an exact wingspan and wing area ; what kind of tail wings you build for it, and depends on what. I want to know stuff like this, you know.
The design you attached for me has landing gear, so I suppose that you use a gas engine for it, or kind of 2 MiniFans or 1 MiniFan.
But what I want to use is a MiniFan 480 and a Graupner speed 480 race motor.
Therefore, what I reaally need to know is the basic ides, for a foam jet.
Thank you all.
Florin777
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Old Mar 15, 2003, 11:31 AM
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Joined Aug 2002
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Thanks FANMAN.
That's a wonderful airplane, did you build it yourself?
But what I meant was if you can tell me some formulas you must know when you want to design an electric foam jet(using 1 MiniFan 480). Like where the CG should be(in general, sport flyers, the CG is between 30%-70% of the fuselage, right?) ; how long should be the fuselage, if you know an exact wingspan and wing area ; what kind of tail wings you build for it, and depends on what. I want to know stuff like this, you know.
The design you attached for me has landing gear, so I suppose that you use a gas engine for it, or kind of 2 MiniFans or 1 MidiFan.
But what I want to use is a MiniFan 480 and a Graupner speed 480 race motor.
Therefore, what I reaally need to know is the basic ides, for a foam jet.
Thank you all.
Florin777
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Old Mar 15, 2003, 11:45 AM
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Lilburn, Georgia, USA
Joined Nov 2000
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Get the book

In the back of Model Airplane News there is a book entitled `Basics of RC Aircraft design' which I consider the book for anyone thats just beginning. It has percentage values and formulas on how to compute things like surface areas of ailerons, tail feathers, wing position, etc. After you get a good few designs under your belt, you may actually be able to pass the book on to someone else

For a mere $20 it will get you started in the right direction.........
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Old Mar 15, 2003, 11:51 AM
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Thx for the fast reply.
Where could I get that book from? Does someone has a copy that don't need?
I live in Canada, I am not sure if I can find it to the public library.
Florin777
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Old Mar 15, 2003, 12:17 PM
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Lilburn, Georgia, USA
Joined Nov 2000
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Book

Its a soft bound book, not available at the library, see if you can search for `Model Airplane News' on line. you should be able to get it from them......back to design, draw, build, fly
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Old Mar 15, 2003, 12:34 PM
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Actually I am not in hurry.
I am also working on a model, Sig Riser 78. It's a 2m sailplane, my first model. I also have a 3 channel for it, all I need is right here.
It was made for slow flight, 2 channel for rudder and elevator. But I am going to put a Fuji r/c .15 engine on it, and that's gonna be really nice I think. I will do some modifications, like do the wings stronger, modificate the nose for the engine.
The Fuji .15 is a very powerful, so I won't have problems with it. It can fly the 2m glider.
But still, I think ducted fans are the best, even if I did not fly any of them, I just saw some videos.
Florin777
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Old Mar 15, 2003, 12:55 PM
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St. Louis Intl, Missouri, United States
Joined Jan 1997
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A book will help as would a plan or a kit. The CG is based on mostly on wing plan form, but can also be influenced by portions of the fuselage.

It isn't hard to design and build something but getting it to fly well can require some tweeking even if you have a book or a "pro".

As far as basics, make sure the fan can breath and exhale easily.
Do a search on:
FSA (fan swept area)
Outlet area (tail pipe diameter)
CG calculation

You should come up with something.

The actual airframe depends on the mission. Fly fast? Maneuverable?
Scale? ROG (roll on ground) takeoff? Handlaunch? Bungee launch? Flight duration? These are just a few of the question that I ask myself before I start a project.

100watts/lb minimum is what I like but that again depends on your taste, flying skills, and the amount of space you have to fly.

Don't give up!
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Old Mar 15, 2003, 01:47 PM
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Canada, ON, Caledon
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Can someone help me with an electric motor? I would need a Graupner speed 480BB race or a Graupner speed 480 race ; even a cobalt 400.
I need for the MiniFan 480. I do not want a brushless setup for 2 good reasons... - brushless motors are very expensive
- if you put a brushless motor in MiniFan, that's gonna be for high speed jets, but me, as a beginner, I am looking to built the jet using the Graupner 480 race(or the BB version).
Florin777
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Old Mar 15, 2003, 02:07 PM
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Lilburn, Georgia, USA
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Quote:
Originally posted by Florin777
Can someone help me with an electric motor? I would need a Graupner speed 480BB race or a Graupner speed 480 race ; even a cobalt 400.
I need for the MiniFan 480. I do not want a brushless setup for 2 good reasons... - brushless motors are very expensive
- if you put a brushless motor in MiniFan, that's gonna be for high speed jets, but me, as a beginner, I am looking to built the jet using the Graupner 480 race(or the BB version).
Florin777
The Graupner 480BB with the Wemotec MF480 fan is a good combination, I think others will agree......
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Old Mar 15, 2003, 03:36 PM
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Have a look at pair of foam wings I have, and the measurements. Are they good for a small electric jet? What should I cover them with(balsa or monokote)?
Florin777
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Old Mar 15, 2003, 03:37 PM
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Another one.
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