« Reply #11 on: Jul 21, 2019, 8:22 pm »
Who is wouter please?
Memories are BETTER than Dreams---"Capn" FLINT

« Reply #10 on: Jul 21, 2019, 7:55 pm »
If you want to see some how skirt design have a look at the front of Wouters craft..

« Reply #9 on: Jul 21, 2019, 4:41 pm »
What's actually needed is a properly designed solution rather than hacks to production hovercraft ( the hacks do work but are not very user-friendly!). 

Ideally, the part of the cushion in front of the divider thingy should run at a slightly lower pressure than the rear - that gives the system reserve lift power to "pump" the nose up (the current hack relies on the higher feed plenum pressure to do this - costing power).  It's actually really easy to do this - simply block most or all the plenum feed holes in the front compartment!  The partition flap (which can be ligtweight material) will then naturally be  forced forward into a curved shape by  the differential pressure - air leakage from under the divider feeds air into the front compartment.  However, the snag is that the craft we are talking about have poor CofG - in other words you'd need to move the CofG rearwards to compensate for the lower cushion pressure at the front (i.e the centre of pressure has moved rearward).  Maybe not possible with a heavy lift engine up front.  Our Hovercraft Designer will do all the work if you know the weights and position of stuff on the craft..

The lack of stability of a segment skirt is definitelly a contributor to the plough in issue (it's not the primary cause but it definitely makes it much worse than it should be).  Loop skirts (Griffon and every other commercial hovercraft on the planet!) are inherently stable not, as most peopled think, due to the skirt pressure but because when the bag is squashed it automatically and instantly moves the contact point outwards thus shifting the cushion centre towards the lowering side (and pushing the craft back up level again).  Even better is that on the opposite side the loop gets larger,. moving the contact point inwards helping shift  the cushion centre to the low side even more.   Segment skirts have very poor stability due to the shape of the skirt at the ground  (high contact angles means it doesn't move very far out when crumpled.  Of course, for racing this lack of pitch and roll stability (and the high drag from crumpled segments) is an asset when you need to turn quickly - for cruising it's really not a good thing at all purely on safety grounds.  I don't understand why recreational cruising craft are still being built with segmented skirts (and we haven't even talked about  the power-wasting plenum feed system  - no-one seems to know what it's for)!

As to the Griffon thing. AFAIK most of their smaller craft don't have partitioned cushions - they rely instead on the shape of the bow part of a loop skirt to shift the centre of pressure forward in response to a nose-down (this is a very old solution originally used on the SRN5 initially back in the '60s).

« Reply #8 on: Jul 21, 2019, 3:44 pm »

Does Griffon partition the air cushion under their larger craft?  If so, I’m wondering if there is anything to be learned from their effort?

I’ve installed the British designed anti-plow flap, posted in the Hoverclub of America publication, HoverNews, several years ago, and it resolved the plow in issue on a Scat 2 and a Scat 12.  I used baler belt, from Tractor Supply, for the flap, which is pretty close to indestructible on a hovercraft.  However, it’s also heavy.  I don’t know that the relative weight caused any issues because the craft flew fine with the flap installed.  Just have it in my head that it shouldn’t weigh so much. 

Dan Heidel, from Cincinnati, installed a flap made from baler belt on his HA5 which, I understand, is an Osprey.  Rather than use heat to bend the flap material at the hull attachment point, so that the flap would tend to favor “bending forward” and maintain a near vertical position in flight, Dan chose to hang his flap from the hull using baler belt splices.  So, basically, he hung his flap from a hing and he didn’t use anything like a bungee cord to pull the flap forward in flight.  I have a lingering doubt about a flap hanging from the hull this way because, in my mind at least, it seems like in order to be effective it needs to remain vertical or near vertical in flight.  If the flap readily folds backwards when conditions favor a plow in, I’m not understanding how it works to prevent a plow in.

Regarding the cross bag/sausage, the collective wisdom here in the states is to use relatively high pressure air from the tips of the fan blades (lift or thrust) and to protect the cross bag with a sacrificial flap.  I’m assuming the same approach is employed on that side of the pond.  I’ve thought about using baler belt to protect the cross bag because of it’s relative toughness.  And, I think, hinging the protective flap would be ok in this configuration.

Chris Barzynski Sr. commented on Facebook that for his racing craft, he installs skid buttons forward of his cross bags to protect from pinching the bag during the transitions from water to land in a race.  Where I fly in Texas, I frequently transition from water to sand bars so Chris’ idea has drive up appeal for me.

Getting relatively high pressure air from the lift or thrust fan tips on the CP2 may be problematic.  The underside of the lift fan on the CP2 is not exposed below the hull and the thrust duct doesn’t have a splitter plate.  Dave Reyburn and I will look at it on the way to HoveRally here in a few weeks. In the mean time, I have thought about using a 70mm brushless DC fan, like is used to power remote control model aircraft, to feed the relatively high pressure air into the cross bag rather than trying to figure out how to capture air off the blade tips and duct it to the cross bag.  At least on the CP2, and the TS3 for that matter, the hood area in front appears to have ample room for mounting one of these brushless fans, would have a relatively short duct run to feed a cross bag and would be fairly well protected from spray. 

I just don’t know what the performance output of one of these brushless fans would need to be to feed a cross bag properly.  It just dawned on me one day that 70mm was about the size of the duct that is used to feed air from the blade tips on other craft.

« Reply #7 on: Jul 21, 2019, 12:19 pm »
Where is the best place to buy the conveyor belt material?  I seem to remember I bought it from Cornwall for the last one, but no idea what I ordered and where I bought it  :-\ :-[  It must be an age thing  :-X

I need to check the millibar readings in the plenum and under the skirt to see what they are and see if they change in different locations and lift RPM etc. 

« Reply #6 on: Jul 21, 2019, 12:02 pm »
I'm assuming the skirt is for the TS3 as I had it made by John Scriven the same chap that made Bryan White's TS3 skirt.  I tend to run the lift at around 2400 rpm on the water which keeps spray to a minimum and noise down.  On the beach I increase the lift RPM to allow for losses through the pebbles and sand etc.   Thrust engine was propelling me to 26 + mph at 2500 rpm.  with two on board we were doing 21 mph at 2500 rpm.

The thrust engine tops out at 3400 RPM static and the lift engine tops out at 3360 RPM   

I could of course increase my lift RPM as I did when travelling down wind which gave the front a wee bit more stability.  At the moment its a learning curve finding out where the craft limits are and also finding the best way to fly it. 

« Reply #5 on: Jul 21, 2019, 12:00 pm »

Great to see the craft out there  :D

Regarding the plough-in, when the craft first comes into view the bow is already down ('nibbling') which suggests the plough in has already started. Later in the video, the nose is further up showing better trim. It's hydrodynamic drag on the skirt material that pulls the nose down and once started its pretty much inevitable that it'll proceed to full plough in. There's a full explanation on the site somewhere.

The inflatable sausage is likely to be vulnerable in the cruising environment. The anti plough flap works, is fairly robust and continues to do its job even when it's looking a bit ragged. It seems likely that it could be a bit shorter and still work, I think we cut them to 2" shorter than the main skirt. You could experiment with that. The other thing you could experiment with is inclining the divider backwards, a bit likes SEV skirt in an effort to make it a bit more likely to fold up neatly when landing. There's a guide on making and fitting them on this site, it's about an afternoon s work.

The other development that would be useful would be SEV like skirt vents,these would allow you to often the front compartment for braking and slow manoeuvres.

Ian Brooks
Gloucester, UK

« Reply #4 on: Jul 21, 2019, 10:34 am »
"Hugely susceptible" would be my humble opinion.
Not being able to actually monitor condition, followed by how do you repair it?
Your first operational video did show IMHO a "tendency to nose down".
All (as ever) IMHO---
Your bow skirt geometry appears to my eyes to be adding to the nose down tendency.
I am sure adjustment to the COGravity/COCushion could improve slow/static attitude, but will not solve the speed collapse of the plough in
but to my eyes the frwd fingers seem to fold back under with friction.
Either on shore or on water-at speed- the frictional grab comes into play.
Once the finger starts to fold back, it offers more surface area to this effect, aggravating this fold back tendency.
As the front skirt fingers deform back (under) the craft, the centre of cushion is altered - worsening the effect.
Are fingers AS per TS3 design or have they been altered,?
Is there any reason the craft HAS to have multiple BOW  fingers, and could it NOT have just one finger?---ie a a SEV front curtain?
The curtain could have the angulation copied from the Sevs? I WAS considering this for KingFisher
TS3s normally seem to hover well on static especially with a big engine sitting over the area in question.
As a frontal skirt "folds" the Centre of cushion should IMHO move  "forwards" i.e. a SEVs fold of the frontal curtain moves the point FORWARDS - thus proportionally increasing the tendency to lift the front.
IF the point moves rearwards (as it does in your film) it moves the centre of cushion the "wrong way" making ploughin inevitable

35 years ago---- I also added a cover over the liftal frontal zone of a Falcon with separate lift engine.
This made the lift noise decrease (as desired) but so did usable LIFT.
ONCE the lift engine was powered up to make allowance for this "strangulation to entry zone"
the noise was if anything - worse.
The craft was now heavier at the front, and just didn't seem to be able to deliver sufficient volume / pressure, especially when a large lump of lift was needed to replace lost air.
So OFF came my expensive cowling, lightening the front, delivering more usable air
just like Kip Mccollum said it would! ::)
After all that cost and effort, I NOW always pay SPECIAL attention to avoiding air flow constriction.

We have grown "So Used To" SEVs delivering their incredible skirt efficiency, that other skirt systems seem to be unable to deliver comparable performance.
IMHO "others" don't compare mainly because Barry Palmers designed Sevs are breathtakingly good.

Trying to improve "non sev type systems" will only ever tinker with systems designed MANY years ago.
IMHO they will never be as good.

Ive spent my early years with finger skirts, with their +ses,  -ses. (including my KingFisher)
Ive spent my last three years with the Otter (sev derivative) skirt, with pluses and minarses,,,
And I vote TOTALLY for
Sev / Otter bag divider and curtain with rear lift supply and C of Cushion set BACK to allow for its anti plough systems to operate..

WE are still modifying improving and thinking about our systems BUT the basics are THERE now.
We now only look how easiest to monitor, and service.

Just done year skirt service- good for a few hundred more miles.  8)

Memories are BETTER than Dreams---"Capn" FLINT

« Reply #3 on: Jul 21, 2019, 8:58 am »
I'm not sure what to fit on the TS3 yet, but I know it needs something.  I'm not used to having to think about the hover ploughing in as Sevtecs don't plough unless the divider skirt is missing or badly damaged.

My last TS3 I fitted a conveyor belt divider skirt, but it wasn't very good as it would get deformed under the hull from landing, and sitting on the trailer.  Even though the divider skirt was deformed that TS3 never ploughed in, so it was doing something.

If I fit an inflatable cross bag, then how susceptible to damage will it be?

« Reply #2 on: Jul 21, 2019, 2:32 am »
Sounds like the Coastal Pro 2.  I generally keep it below 28 MPH to avoid a plow in.  I’m hoping to get a cross bag/inflatable sausage on mine in a few weeks.

« Reply #1 on: Jul 20, 2019, 10:37 pm »
I learned a couple things about the TS3 today, firstly it needs either a partition skirt of an inflatable sausage, as it ploughed in a couple of times without warning.  Flying in to the wind it ploughed in at slightly over 26 mph, this can be seen at the beginning of the video.  Down wind two on board it ploughed in at 17 mph, but I only had the lift at 2300 rpm, after this plough I raised the lift rpm to 2800 and it was happy at 20 mph.

I need the seat cushions as my rear end had pins & needles ??? 

We were out for about an hour all but a few minutes.  Odometer says the craft has done 14 miles so far and thrust engine has done 1 hr 43 minutes.