1/8 scale F-104C

[F106DeltaDart]

For a while now I've wanted to not only do a scale plane but a jet. I love the f-104 and the f9f but I have a wingspan limit of 50", funny thing is there isn't a length limit so the f-104 came into favor. Actually, just recently was I introduced to scale flying and it's definitely different, but enjoyable, I can definitely say it's fun to be able to fly different aspects of the hobby.

If you are debating between the 104 and the Panther, the Panther would be much easier of an edf to start with. In fact, my first EDF was a Panther and it was an all around excellent flier. 104s fly well if you know exactly how to fly them. They can have a nasty stall, and extra care has to be taken to keep your AOA low. You also generally need a pretty good sized runway to land.

 

[Hai-Lee]

As for your request for ideas/help making the fuselage clean and scale like I would recommend that you plan the EDF installation and ducting first. Once the ducting is designed to fit inside the fuselage outline I would plan from the outer skin back to the Ducting/EDF.

A near perfectly smooth FB fuselage could be obtained buy planking strips of FB over formers. The planking would have the exterior paper removed and the formers would have facets or flat surfaces instead of the smooth curves you might use on a wooden model.

The strips are curved, glued, and edge shaped to fit and when all fitted and glued the whole, (paperless), exterior is sanded, sealed, filled, re-sanded and either painted or glassed. If you wish you could remove all foam after glassing and fit duct supports, battery supports Etc and finish the build as a basically empty to keep the weight down.

I am sure others may have their suggestions and some will possibly more suited to what you are imagining.

Just my thoughts!

Have fun!

P.S. Don't forget the flaps!

 

[Cj67]

 

[Cj67]

As you see I have the center section done, the formers places are marked. How should I tackle planning the edf ducting and etc?

 

[Cj67]

I do plan to have the whole "9 yds" edf retracts, flaps, and speed brakes but might have to leave them inopporative as I have a DX6i. Unless I can program them into the throttle.

 

[F106DeltaDart]

As you see I have the center section done, the formers places are marked. How should I tackle planning the edf ducting and etc?

The ducting is going to be dependent on what size EDF unit you use. Have you picked an EDF size/system yet? Good ducting can be critical for flight performance. Your intake area should be equal to the surface area that the fan blades cover when rotating (called Fan-squared-area or FSA). Remember that you need to subtract the area of the motor/spinner to get this value correct! In addition, try to ensure that the duct holds a constant or near constant cross sectional area. This will minimize intake losses.

The exhaust can be a bit smaller to squeeze more speed out of the plane and should be 90-95% FSA for a 12 blade, and around 80% FSA for a 5 blade. Typically, the exhaust ducts (thrust tubes) are made of a rolled acetate. This provides a light, rigid, and smooth duct for your fan.

 

[Cj67]

Is this a good basis? Ive never built An edf before.

 

[Cj67]

I plan on using a 90mm fan from hobbyking

 

[Cj67]

Oh and to answer to heli question, I'd love to build a scale one, but helis are just soo expensive, so I'll have to wait a little while.

 

[Cj67]

I thought about doing the gear similar to this f-16, also kinda like the freewing 70mm f-104, but 90 degree so they fit a little better in there

 

[F106DeltaDart]

I thought about doing the gear similar to this f-16, also kinda like the freewing 70mm f-104, but 90 degree so they fit a little better in there View attachment 91095

That's probably the best way to do it. Some wire struts on these retracts (https://hobbyking.com/en_us/servoless-retract-with-metal-trunion-44mm-x-41mm-mount-2pcs.html ) should do pretty well, and it would be easy to add a scale looking strut cover. Works great on the 70mm F-104, I did mod it so the gear stance was a bit more scale though.

I plan on using a 90mm fan from hobbyking

Personally, I would stay away from the Hobbyking Mad Thrust units. They are heavy, and inefficient compared to other units out there. The FMS 90mm is lighter and more powerful than most of the HK units: https://www.horizonhobby.com/12-blade-ducted-fan-w-motor-90mm-fmmdf002.

Oh and to answer to heli question, I'd love to build a scale one, but helis are just soo expensive, so I'll have to wait a little while.

Totally understand man, I'm in the midst of a few scale heli builds right now, but I have to space major parts purchases apart month by month to keep moving forward.

 

[Cj67]

I don't know if rotating the gear 90 degrees would help? Could you maybe post some pictures of your gear in your f-104? Lol that edf has a lot of power, although 120amp ESC aren't cheap.

 

[Cj67]

And also where is your cg? Thanks!

 

[Hai-Lee]

You question about the ducting is where I aim my suggestions:

Firstly determine you swept BLADE area and not the internal of the EDF unit. Once this is determined I would use this cross-sectional area to determine my duct area and shape the duct to run along the top of the fuselage as close to the outer skin, (upper hatch), as is possible.

As there is a difference between the centre line of the Duct and the fan unit I would make the upwards bend in the duct gradual or fit some flow directors in the duct to get the air travelling square on when it meets the fan blades.

Once the duct is running along the top of the fuselage I would split the duct into 2 separate ducts each of 50% of the cross-sectional area required and do a gradual bend down each side of the fuselage to the inlets which I would enlarge, (?), to maintain the same total cross-sectional area.

Where "Flow directors" are required, (They are used to change the airflow direction and limit "Slowing" of the air due to compression), They are little aerofoil shaped sections normally fitted or angled to force the airflow to change direction. They can also provide some structural support to allow for a thinner duct external wall and hence make the entire project lighter.

Also I would fit a pair of cones to allow the duct to match the blade area as close to exactly as is possible.

NOISE! I have seen many similar installations and the NOISE levels have varied widely. A lot of noise from the worst examples are due to airflow hitting the blades at an angle or the airflow into the fan being turbulent. Noise is a loss of energy, it consumes energy and means less thrust.

By doing the Fan unit and duct installation through a hatch in the top of the fuselage really aids changes and development as well as repairs and upgrades if required. With the ducts high in the fuselage it gives maximum room in the lower fuselage for tinkering with undercarriage, battery placement and allows for a solid wing spar build with possibly a simple underneath bolt on wing setup.

Just a few thoughts!

I will watch with interest!

Have fun!

 

[Cj67]

Ok, so I mostly get the flow director part, but the blade area? Is this the area of each blade added together? Maybe could you post pictures or drawings of what you mean, if it isn't too big of a hassle. Thanks!

 

[Cj67]

 

[Cj67]

Sorry the image is upside down

 

[Cj67]

Using the table as my friend. Lol! I'm getting the other side glued on.

 

[Hai-Lee]

The EDF blades have an external diameter so use that to determine the area of the circle the blade tips sweep.

Then determine the diameter of the circle that the blades sweep at the hub central portion driven by the motor.

Then just subtract the area of the centre, (NO blade section) from the area drawn by the blade tips and you have the blade swept area which is the cross-sectional area required for the duct.

Because the central section, (where the blade hub and the motor are has no airflow through it and so the air should be parted before the air reaches the blades, normally by fitting a streamlined cone shaped divider. the same cone shape is ideally used around the motor to smooth the exiting airflow and maintain diameter.

Some variations will be required to get cooling air to the motor and ESC of course.

Have fun!

 

[Cj67]

Ohhhh, that makes much more sense now. Thank you. I've been thinking, I'm gonna keep everything as planned except for right now put a prop on the back, but make it "edf ready" so everything is there to put an edf in when I can, this will give me a little more money to play with for now. I was thinking, like max an 8" prop, but what motor and ESC could I use to get good power to resemble flying it like a normal jet. I thinking it also might be better since it is my first jet. What is you guys' thougts?