Own design single Ducted Fan Foamie

[davereap]

After a lot of reading on here I thought I would give it a go and try to make a craft using the materials I already have.
Using photos from here as the basis.
http://rc-hovercrafts.com/
check out the photos of speedy by Guillaume

I fist did a sketchup model then started the construction of the real thing.
I thought to use this type of skirt setup..see pic1..

[davereap]

so far ive got to here...As I know nothing of hovercraft any sugestions will be taken on board, with thanks

[davereap]

here is the sketchup file if any body wants it...If you havnt seen google sketchup you are missing a great free 3D construction program

[metroidrc]

looks really cool! I think there is a trend starting here, maybe next year there will be an r/c hovercraft racing league!

[Ryan Archer]

awesome dude,
how do you plan to make it hover?
ryan

[Kelownan]

Sketchup is superb, But Im lucky enough to own 3d Studio Max :cool:
So i use that :p

[metroidrc]

i use max also. :)
the axon racer was designed in max!

[davereap]

For achieving the hover I am splitting the flow from the ducted fan, using some thin ply..
The air flowing under the split should inflate the bag skirt and provide the lift... the air flowing over the split should provide the thrust..

At least this is what I hope will happen... for goodness sake please put me right if I am going haywire here.. Is this correct
I have looked at the construction photos I mentioned earlier..His bag skirt ( see the very first picture..post1 ) gets inflated by the split airflow, you can just see the bottom of his duct , then the air goes into the area under the craft through a series of holes in the skirt, the air then escapes under the inflated skirt to provide the low friction cushion/hover effect...

[davereap]

here are a couple of views under the craft to show the lower split .... weight at the moment 6 1/2oz

[davereap]

Now to add some rudders for control and to find some skirt material....

any sugestions for the skirt?

[metroidrc]

I'd say nylon or that tarp material. I used the tarp material for my full size hovercraft and it resists rips pretty well.

[davereap]

wouldnt tarp material be a bit thick for this one? its only a smallish model..I was thinking along the lines of using material from an old umbrella, or kids play tent

[metroidrc]

yeah maybe too thick depending on the size. some kite rip stop nylon would probably work.

[Stef]

I've used plastic trash bags. take a strip about twice as tall as you want the finished skirt. Glue it around the edge of the craft glue the seam. Fold the free edge of the strip into the center of the plenum and glue it forming a sort of doughnut. Take a hot soldering iron and melt small holes in inner edge of the doughnut. The lift fan fills up the "doughnut" and excess air flows from the inner edge holes to form the cushion. Adjust number and size of holes for best effect.

[davereap]

thanks ..stef
I was going down that route and then..
Ive found an old waterproof Regatta overjacket that used to belong to my son ( it is far too small now) and cut that up..Its a pvc coated nylon material and should be stronger than the trash bag material that I was trying... I made a rough up out of the polybag, rough fitted it to make sure I was correct in my cutting..etc.. then cut out the sections from the jacket..
I will try making the holes with a soldering gun on that material, it should work..

I am still not sure if I should have started with a two fan craft...with this design I have to have forward thrust on to get lift, so how can I get slow speed manouvering?

[Stef]

That's the problem with single fan craft. The only fix I ever found was to control foward speed not by fan speed but by diverting thrust from the fan. Power setting needs to stay high enough to give good lift.

[Kelownan]

mmmmm i get what you men..... I decided to use 2 edfs for that reason, iff you check my WIP

http://www.rcgroups.com/forums/showthread.php?t=947846

[metroidrc]

another thing to note: if you use a lift fan on a seperate channel with on or off, its nearly uncontrollable.

[davereap]

Oh well if it dont work it wont be the first time ive made some mods...I can always add another motor and prop for lift..
what do you use to control the second motor? would the flaps channel be ok

[bigbadbob2003]

Because i am using a DX7 i have it setup as a heli that way i can have my lift fan set on the pitch channel giving me a pitch curve to fine tune the lift. It also has the 2 idle up positions (stunt/flap switch) which i can have preset values on the curves for constant lift.

[Kelownan]

Because i am using a DX7 i have it setup as a heli that way i can have my lift fan set on the pitch channel giving me a pitch curve to fine tune the lift. It also has the 2 idle up positions (stunt/flap switch) which i can have preset values on the curves for constant lift.

Thats a great idea, I still dont know much about my DX6 so some setup iinfo would be cool.

What i noticed when i tested mine - solid skirt, It woudnt stay still, If i attached a bag skirt would that be solved?

[metroidrc]

you want to have the lift fan and thrust fan on the same channel. you don't want them on seperate channels otherwise it drifts around by itself and there isn't enough hover control.

[Kelownan]

Mmm i figgured that from my 1st test but would a bag skirt minimalise this effect so i could plug the thrust EDF into the elevator channel

[Stef]

The two fans on seperate channels will not cause instability. It will give better control set lift fan at "X" value with throttle and put drive fan on a controlable channel for speed. On third channel either thrust vectoring, rudders or both for directional control.

[metroidrc]

Its better to have control over the lift fan as you are driving. otherwise its impossible to slow down. Then again I'm making skirtless hovercrafts. Maybe hovercrafts that have skirts don't have the problem of drifting because they aren't hovering that much.

[davereap]

from the look of your replacement parts I seems you are using the solid foam skirt as a partial friction brake for when you drive.. obviously this works very well on the harder smoother surfaces, how does it go on the rougher ground. will the more solid foam go over grass?

I glued my skirt sections together and now Ive also fitted my skirt,
Now I have to cut some holes for the flow through to the central area...any thoughts on how many and their placement

[Stef]

Just start slow it's easy to add holes tougher to seal them up. Holes closer to source should be smaller than ones further away to insure skirt inflation.

[davereap]

OK Ive had first tests... it does hover and it does move....but its rubbish...

The ducted fan, whilst a good idea for size , produces poor static thrust and only just sufficient an airflow through the bag skirt for lift
..I should have known because ducted fans are designed for going at high speed rather than 3D hovering..the current draw was also very high at 29A..

So ive ripped it off and will go for a normal aero prop in a duct.. this poses some problems because the normal setup I use has a 8-9" prop and this is going to be out of proportion/too large for this size machine.

my normal motor/prop setup that produces 20+oz static thrust at 15A, whilst shifting a larger volume of air should be more efficient..but I might have to widen and lengthen the whole craft...oh well its not too difficult a job..

[Stef]

I've been through my hovercraft stage.....long ago. I built a craft with good performance completely out of card stock except for motors, batteries and RC gear..... lift fan included. I drew in turbocad a centrifugal fan on 110lb stock cut it out glued it together and it worked great. A lot of full size craft use them for lift because they provide decent volume at good pressure. I'm sure you could find or build a fan that would do the job it really isn't that difficult. What size motor are you going to use for lift?

[Kelownan]

Great progress, What kind of foam is that you using? EPP?

[davereap]

the foam is 6mm depron....

I think I will try with one prop to start and split the airflow, similar to before..I can then stick on a lift fan if that doesnt work....its easy to chop and change with the depron