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Aug 19, 2019, 07:19 PM
XFM
XFM
eXperimental Flying Machines
Meanwhile, relax with a ready to run skirtless hovercraft........

E016F (2 min 39 sec)
Last edited by XFM; Aug 19, 2019 at 07:39 PM.
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Dec 05, 2019, 08:04 PM
Registered User
Skirtless Hovercraft Projects - past experiments (6 min 19 sec)


Not much activity in this place recently (well, any activity)....but I've seen my other thread steadily racking up views so it seems we have a fair number of people reading. I'm still working on a few different skirtless hovercraft, I've had a bit more time for building and some better weather for testing. I've got a lot of 'data' to report, not so much hard numbers but a bunch of observations on different designs for stability ports, flaps, rudders etc. It'll probably be a while before I can collate it all into a post, truth is my job involves sitting at a computer all day so I'm not much in the mood to spend hours writing stuff up and putting videos together in my 'free time' now

I was thinking of drawing up a proper model plan for a single motor split flap design, complete with dimensions, details of the linkages, list of suggested motors/props etc. Something to allow a reasonably working model to be built from scratch like the foamy planes are. Maybe something I can take a look at over the Christmas break.

Anyway I was going back over some old videos and realised there's some stuff I've never published. A lot of that is because it was very crude or didn't work so well, nevertheless I thought some more footage might be appreciated.
Feb 08, 2020, 06:00 PM
Rapidly aging user
raw89's Avatar
Quote:
Originally Posted by FiftySlicks
https://www.youtube.com/watch?v=NcgQFk3N3kU

Not much activity in this place recently (well, any activity)..../....I was thinking of drawing up a proper model plan for a single motor split flap design, complete with dimensions, details of the linkages, list of suggested motors/props etc. Something to allow a reasonably working model to be built from scratch like the foamy planes are.
Thanks for your recent posts & info. Encouraged by that, I finally decided to try building one of these critters for my winter project. I wanted to try using $tree foam board & some of the build ideas from the airplane guys while shamelessly using the design info you & the other guys have provided.
I was able to try my craft this AM, so I figured I'd post some pics and info on the build. Hopefully, this will generate some more interest here......
The craft ended up at 38 x 66cm at the lift slot, 44 x 70cm OA (Longer than I wanted). AuWeight is 680g (24 oz) with a 2200, 3S lipo using a 2836-9, 950kv and either 9x4.5 tri blade or 9x4.5 reg.
As a proof of concept and test bed, I'm very happy with how the build came out but wouldn't recommend using the $tree board like I did as I think it's going to be fragile. The foam is too soft for this application ( I removed 70+g of paper cover where I thought I could).
IT FLIES!!......
THE GOOD: The “maiden" was just in my little Apt but I was surprised that it hovered @ less than half power & seemed stable. It will really jump up @ about 2/3.
THE BAD: My design of the port stators to counteract the prop rotation/left turn deal needs work. I can get it going straight or right but not like I want.
It's supposed to get above 40F tomorrow so I hope to get it outside......stay tuned..........
Last edited by raw89; Feb 10, 2020 at 08:16 AM. Reason: 70cm
Feb 09, 2020, 06:42 PM
Registered User
We have lost a lot of people and discussion if you look back over the older threads. Very much appreciate your interest

The hull section on the bottom left looks very good, in theory it's a much nicer turn for the airflow than just a flat plate to the bevel. Though I've found that things which are 'supposed' to be better for airflow don't seem to have much if any of an effect on these models. My older builds were full of sharp corners and obstructions to the airflow, in comparison my recent builds are much cleaner and - they work exactly the same. Haven't seen any gains in hover height from making rounded corners and streamlined sections inside the hull. Maybe the flat walls are too restrictive for any other gains to be apparent, might need a whole hull made with the rounded section to be noticeable.

The stators at the rear - I found I needed a pretty substantial curve to get the anti-torque effect. See the attached picture for what I used. That may be a little too much but the model turns pretty well against the prop. Makes me wonder what a set of servo driven vanes linked to a gyro would do.

I don't think your current flap setup will work very well, I tried the same thing previously, check the 4 minute mark on my past experiments video. If the flaps close completely to vertical when they open you'll likely have too much nose down moment and not enough forward thrust. Then again maybe it'll work and it was my setup that was wrong. My current models all use a flap angle of 60 degrees from horizontal when closed and they work well.

I started off with servos mounted on top of the hull right at the flaps and a short push linkage to close them. I tried out the internal servo with a pull rod and got it working alright but never great. It's difficult to get enough force to close the flap completely and enough travel to get them opened out. It worked acceptably on a smaller model but not on a larger one so I went back to the external servo mount. It's less neat for sure but much easier to adjust and get working.

If it's not too much hassle, try building in an adjustable front jet on a servo control. Being able to open and close it remotely is really handy for pitch trim.

---

I have drawn up a build plan for a 40x60cm craft, I started going into step-by-step instructions but I'm not sure if so much detail is necessary and I don't really have the focus to write out a whole guide like that. I can look at finishing off the basic plan at least as it covers the most important design points.

---

As it happens I got my larger single motor build onto a beach for the first time recently:

Single motor skirtless hovercraft - beach test (4 min 18 sec)


I've also got another triple motor build just completed and tested, hover height seems a little poor for the size of it but there are many refinements still to be made. Will get it out for a proper test once the storms clear off.
Feb 11, 2020, 11:27 AM
Rapidly aging user
raw89's Avatar
Slick; thanks for your reply. Basically, I fully agree w/ your observations and comments.
My maiden test went pretty good Sunday, it even survived it's first 2 crashes!

My replies to some of your comments:
The inside scoring required to form the rounded test hull from the foam board makes it surprisingly less sturdy than the flat sided versions so I decided to keep things simple for my 1st attempt. I want to try some wool tuft airflow studies to, hopefully, get a better idea of what goes on inside there.....

Most of my design choices are good old TLAR engineering and I got a little optimistic with the needed offset on the stators. Actually, it didn't steer too bad when I got it moving and I have room to make some easy improvements.

Trying to limit the number of sheets used kind of limited the incline on the flap setup to 80deg and I do have some down pitch problems. It was less pronounced when I opened-up the center duct for more lift but that hurts the thrust. After I try some mods to the current set-up, I may redo the rear to get near your 60deg figure. At that time I'll also take another look at mounting the servos externally.

If I haven't destroyed the craft by then, I'm thinking that a front lift flap could be controlled by a mini KK2 board running a servo like the Super Simple camera Gimble firmware on my quad. (The fewer controls my 70+ year old pilot skills(?) have to deal with, the better!)

I'm looking forward to your plan while I play with getting this one working better as the weather permits. Your larger craft in the beach test video looks like it works great....congratulations!
Ralph


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