airboat steering

[ashley needhamParticipant @ashleyneedham69188]

Chaps. I am contemplating fiddling with an air boat and wondered if you need strakes on the underside to assist steering in a straight line, and if so at which end of the hull.

 

My previous experience from years ago, and this would have been as a mere BOY…is that they wander at speed due to the flatness of the bottom, and only having air rudders for direction.

 

I have a number of high speed motors and props from other projects and thought I might use at least one set up in this way. Don`t want something that doesn`t steer though!! any one out there who has built an air boat care to comment on this matter please ??? And also what are they like with any sort of breeze..as I know my various seaplanes become very wayward in a breeze.

 

Cheers, in advance,

 

Ashley

 

 

 

[ashley needhamParticipant @ashleyneedham69188]

[The Long BuildParticipant @thelongbuild]

I have wondered that as well , But at the moment we are staying true to the design chosen, here is a link to a test run of one built by a fellow member..

 

The battery was half rundown when I took this.

 

http://www.youtube.com/watch?v=4k44C2wtqBM

[Dave MilbournParticipant @davemilbourn48782]

Ashley

I built one of GG’s Skimmers from the free plan a few years ago. It didn’t have any strakes and I don’t remember having undue problems steering it, although response is sluggish compared with a water-rudder and it’s best to slow down a bit before taking corners – or it just slews a bit and carries on straight. You’ll soon get the hang of it, I’m sure.

Dave M

[Kimosubby ShipyardsParticipant @kimosubbyshipyards]

Hi Ashley,

 

I’ve built these too, its the hull shape below the water line that acts to keep it going straight – as I remember the hull is slightly bevelled towards the centre line – I’ll dig out my prototype (made it in ply but was too heavy for the power unit should have used polystyrene – which I did in later versions) and see if I can photo the hull shape for you.

 

They do “drift in the turn” but that’s the skill in running them. I remember also suffering from wire burn out do to high power drain. Still have the ESC’s purchased for them and the power units and pusher propellers!

 

Kimosubby.

[ashley needhamParticipant @ashleyneedham69188]

Thanks chaps. A quick surf on you-tube reveals some (most) faff around and spin when turning or running straight at speed, and then some hold a really good line.

 

Trouble is you dont know what was underneath the hull! The bottom REALLY needs to be flat or the boat will get caught in weeds and things which of course is just what they are designed NOT to do!

 

Kimo. I can see where you are coming from with the slight bevel, and wonder whether or not a couple of strakes at the edges would assist in not only keeping a line but trapping air and so lifting the hull?

 

They all sit on their bottoms when going along and so the contact area is only a small patch at the back, and likely as not side-to-side and not fore and aft which one wouldn’t have thought would help. I wonder how everglade`s full size boats are constructed?

 

Have you seen these RtR types that FLY as well as skim along the surface? truly amazing.

 

Gosh I see some experimentation coming along here!!

 

Ashley

 

 

[Kimosubby ShipyardsParticipant @kimosubbyshipyards]

Ashley,

 

I’ve put a couple images or 2 on albums.

 

I also have a pdf file with drawings and article re airboats and shapes etc. Can’t send as attachment till you contact me re pvte email address.

 

Yes, this is in pull format, but I did build with prop at rear of motor as a pusher too! I didn’t know the props were different, and yes, you get more power pushing.

 

Kimosubby

 

 

[Dave MilbournParticipant @davemilbourn48782]

I can confirm that the GG Skimmer has a flat bottom rather than bevelled like the one in Kim’s picture.

DM

[Len OchiltreeParticipant @lenochiltree67043]

Hi Ashley,

 

My one has a flat bottom and behaves perfectly.

Fit twin Air Rudders.

 

[ashley needhamParticipant @ashleyneedham69188]

Well.. it would seem that a flat bottom or one with only a small amount of `V` is the thing.

 

Thanks to Kimo for e-mailing me with an article on an airboat.

 

I am wondering now if there is a standard sort of formula for the hull dimensions, you know, length should be 1 1/2 times the width or something? All the airboats look to be in the same ratio of length/width, or is this just because that`s what they should look like (as warships are long and thin, tugs short`n`fat etc)

 

Ashley

 

 

 

[Kimosubby ShipyardsParticipant @kimosubbyshipyards]

Ah Ashley,

 

by extrapolation then – do model boat builders look like their boats. (like dog owners resemble their pets!) or is that another “kettle of fish” [and what volume is that!] words words words words…………………….

 

Kimosubby

[ashley needhamParticipant @ashleyneedham69188]

Kimo, now there`s a thought!!

 

I would be a right mongrel then, as I have warships, floating cars,flying boats, a sub, a landing craft and several other motorised plastic toys..

 

Todays Sunday morning boating was very satisfactory, The Herald had an outing, and sailed well enough although the breeze was a bit fitful, and the motor stopped working for a bit (and I need it to tack properly !!!) which was a bit disconcerting.

 

Berengar had his three engined flying boat out which was working a treat, having had a propeller swap from the large fairly crude 3-blade fat paddled props to pukka thin two bladed types. The engines were revving so much more and the steering was better due to the increased prop wash from the centre prop.

 

This seasons secret project also had an outing after yet more modifications and was also performing well-ish. HMS Nelson battleship did not leave the dock (boot) as it was not needed for recovery work and the others were running without fault. Our little handies were getting all cold so after a couple of hours we headed back to harbour, or Grandma`s as its known for a cup of tea.

 

Ashley

[Peter FitnessParticipant @peterfitness34857]

Ashley, no one could ever accuse you of being boringly conventional in your choice of modelling subjects, one only has to glance through your photo albums to see why

 

I love ’em.

 

Peter.

[ashley needhamParticipant @ashleyneedham69188]

Peter , thanks for that., nice of you to say so.

 

I have a motto inspired by the SAS “he who dares, boats”.

 

I may have to offload some soon, as space is getting to be a premium, my little landing craft, the big and small rubber band boats and the converted RtR Severn are all languishing in dark recessess in the shed and to be honest i cant see myself using them much again.

 

The Severn is a nice little thing and goes really well on its 2×280 motors, but is a bit small and a bit fiddly, never mind. Perhaps I need to invent the collapsible boat?? If I ever get round to progressing the SRN4 hovercraft I prototyped, I may have to use it as a coffee table in order to store it !!

 

Ashley

[LARRY WHETTONParticipant @larrywhetton68737]

hi ASHLEY, mk 2 skimmer steered well ,but finding a prop to get more go is my challenged LARRY..

[ashley needhamParticipant @ashleyneedham69188]

Larry. Very nice, great driver !!!

 

I have found that the range of pitches in smaller size props is limited.

 

Full size aircraft with variable pitch have the prop set on “fine pitch” to take off , and switch to course when at speed. Pylon racer electrics use fairly course pitches (say, 6″ by 4.5 or something….fine would be 6×2, as an example) as they go very fast and accelerating to full speed is not an issue.

 

It may be that, in general, skimmers are over pitched, and they don`t go that fast (compared to the aircraft that such a prop would normally be put on) and could in fact benefit from a finer pitch prop. This would also let the engine rev out more, to the benefit of power consumption. See my last post regarding Berengar`s BFB3 flying boat. The difference was very noticeable.

 

Just a thought. No Doubt all those air-boaters have extensively trialled this sort of thing many times.

 

Ashley

[ashley needhamParticipant @ashleyneedham69188]

Well, the beastie has been partially built and goes ok, so far on tests

 

A fixed skeg has been fitted at the rear and has improved straight line steering no end.

 

A cheaty SRN1 hovercraft idea has fluttered past the brain cell….hmmmm

 

Ashley

[Richard J HuggettParticipant @richardjhuggett]

You chaps seen these?

 

http://www.sussex-model-centre.co.uk/shopexd.asp?id=35077

 

 

Rich

[ashley needhamParticipant @ashleyneedham69188]

Richard, yes, seen that one.

 

You can buy virtually anything nowadays !

 

I remember years ago when I was a lad fiddling about with a free-running airboat powered by some tiny little motor and made of balsa . I didnt have a clue then of course, and the performance was a bit , er, well..what performance??

BUT I HAD SOME FUN! (or was it frustration)

 

On a similar vein, Ibuilt a sub, nuclear shape, out of balsa (screwed down hatch on top, non-diving of course)..about 3″ square and 3 feet long, weighed down with tons of probably scrap metal bits from Dads basement pile , powered again by some tiny motor and “D” cell batteries..but that went rather well if I remember rightly, by luck, i suppose, but subs dont need an awful lot of power if they are mostly submerged .

 

Ashley Wallowing in nostalgia again.

 

[Richard J HuggettParticipant @richardjhuggett]

I guess we’ve all had a free running craft of some sort at some time in our lives, haven’t we? I had a free running air boat (ish) back then, but back then I was capable of running round the far side of the lake to retrieve it! And then there was free flight aircraft…but that’s another story!

 

I keep thinking about buying one of those airboats from SMC, but I’d have to swap the radio over to something better…having said that, 2.4Ghz outfits are as cheap as chips now, so I think I may just give one a try.

 

I keep telling myself all I want is something to throw in the car when I want to go sailing for half an hour…last time I told myself that I ended up buying an Engel Lafayette!

 

Rich (trying not to listen to myself again…)

[Richard J HuggettParticipant @richardjhuggett]

I’m afraid to report that I failed in not listening to myself, Ashley…my airboat is bought, paid for, and arrives tomorrow.

 

 

[ashley needhamParticipant @ashleyneedham69188]

Tut Tut. so naughty. No willpower etc etc

 

 

Pictures in due course??

 

Ashley

[Richard J HuggettParticipant @richardjhuggett]

Probably tomorrow Ashley…I’ve removed the awful stickers that the thing was plastered with, altered the rx aerial layout, and I’m in the process of finding a driver figure.

 

Once I’ve had a play with it in it’s ‘out of the box’ trim, plans are afoot to change the 380 motor for a brushless one, swap the 1600a/h nicad pack for a lipo pack, and change the radio to a proper 2.4Ghz one.

 

Total lack of willpower, I’m afraid…total lack of female in my life(at the moment…)allows my willpower to wander off.

[ashley needhamParticipant @ashleyneedham69188]

Richard. Just as a suggestion then, unless of course you have a replacement motor in view, I have used in the past a Park 370 brushless motor, an in-runner…so easy to mount, at 3700Kva, and this swings a 5.5 inch by 2 prop easily and within the motor current draw spec even at 9.6V..and it will run to a 3s Lipo (11V)

 

It is only 20mm diameter by 30 long and is billed as a 380 replacement..but in reality is about 100W worth of power so much stronger.

 

Or a simple speed 400 is a good booster instead of a 380 (although there are different 380`s about)

 

Ashley

[Richard J HuggettParticipant @richardjhuggett]

G’morning Ashley,

 

Another one who couldn’t sleep, huh? I may have to rethink the whole thing, due to the radio set up. I discovered last night that the rx/esc is a single unit, complete with a built in bec…very clever, but why does it have to be on 27Mhz?

 

So, if I go ahead with Plan A, that means changing the rx/esc/bec for separate units, then changing the motor and adding a lipo…and the r/c box is tiny. It may be possible, I’ll give it a good check out today.

 

And why do these boats come with those awful pistol grip tx’s ?????

 

Thanks for the info on the motors, I didn’t realise that the Speed 400 is the same sized motor as a 380. Interesting….

 

 

Rich

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