Jeremy_H

Pushers have arrived, and here's the results of a thrust test using the first of a few sizes to try:

Front engine only 9x4 Graupner prop = 2 pounds and 1/8th oz of thrust
Rear engine only with a 9x7 Graupner pusher = 2 pounds 6 and 7/8th oz of thrust
Front, and rear engine together = 4 pounds and 13 oz of thrust

Which is great news, but do you see the oddity?

Jeremy_H

First run:

http://www.youtube.com/watch?v=_zZaksV_AwI&feature=youtu.be

St.Marek

Hello.
AirBoat interesting floats, quickly enter into drifty, but I thought that the two engines will be faster. Well, unless it was not maksymalka speed. Could you tell the weight of the model with all the equipment? ? ?
We look forward to more films from spitting.

Good luck

Greetings from Poland
Marek&Wojtek

Jeremy_H

Hi Marek,

The test boat is very heavy, around 6kg. These engines are working very well to be able to move that boat, the final boat will be much lighter.

yellowufo

Lighter boat will b???????? Your handiling is great the lighter or less mass will go faster but that great handiling will sfuffer do a slow diet for us so we can view the weight ver handling delima.. ya may need a wing if ya get to light....

*delete M i k e u p delete*

Jeremy H, your airboat runs great for its size!!!!

Jeremy_H

An interesting thought. The original single engined version of the target boat had a wing, but only set neutrally. I'm figuring it can be made light, at what I dunno, maybe 4kg? I can always add weight I suppose, grey area. The original was superlight, more like an RC aeroplane in construction, including solartex top surfaces, and the handling on that was only effected by a tad too high a CoG (handling changed as the tank emptied) and the torque issue. In conversation with my local model shop we are starting to think it might be fun to use gyro's, so I'm planning to add control surfaces which can be activated later if there's value in it. Touching back on the torque problem I will say that the test boat does indeed seem to be very consistent in turning behavior left or right, but this flat hull won't be showing it as much I'm guessing.

For now though some sorting to do. After two runs the throttle servo gave in due to water getting into it, It's fine now after a drying session but there's no point putting it back there. So, I've started on a bellcrank mech. A vertical shaft on the centreline of the boat is moved via a sleeved pushrod, the shaft operates a bellcrank horizontally which is to be sat where the servo was. The bellcrank can be adjusted through a central slot to help with matching the two different throttle lever strokes, and better adjustent on each link arm to the throttle should give be a chance to balance the throttle ranges better. I'm still dwelling on having seperate throttle servos for the final boat, dunno yet. I have to swap out the control rods, they are Gold'n'rods and really bad for friction leaving me unable to get a decent return to neutral (making trimming pointless), need better ones. All being well I'll have this stuff in place for next weekend's trip to the pond.



The bad news is that the Irvine is leaking on the crankshaft, and that junk carburettor is living up to its predecessors. I'm going to see if one my my other Irvine engines can donate the later and much better metal bodied carb for a while.

Side issue:
I've been thinking of having water rudders as an option, that's always been there, but rather than swapping out parts, how could I deploy a water rudder via radio?

yellowufo

I have seen gryos work well for snow drifting or on grass when used on the rudders. For me a gyro on my bow may b cool to try. My rig goes about your speed but weighs (29.5 oz)

asmithnc

Jeremy.... QUIT!! You have a very successful great handling boat on your hands. No water rudder or gyro wing needed.. Not to be mean but your boat is just too slow for the aero forces to work correctly. If the speed was double from what I've seen then yes. There is just not enough air flow. We add water rudder to a flatty for control and to add drag. The drag allows us to correctly trim out the boat whilst in motion. Yours is running perfect and no need to over engineer anything. The only thing I would suggest is adding a three blade prop to the rear engine. The first engine is blowing disturbed air and you need extra surface area on the rear to prop to somewhat counter this. A++ on your build...You should be proud!

Jeremy_H

I'm guessing that you've missed a bit. This is a rough hull to act as a stable platform to test engine setups, it's speed, handling, and indeed it's looks are almost immaterial. The aim is to sort problems, or unknowns, before finalising the design of a much faster craft. This is a process to iron out any problems on an unusual, but fun, way of running twins. But I'm happy to recap.
To date the following has come to light:
Contrary to what was considered as a lesser way to mount two engines this is in fact developing more power than anticipated.
Problems with keeping fuel mass centrally and at low height are close to being solved.
I'm learning a lot about rudder design.
Twin engine controls are shaping up.
Methods to stabilise the operation of the final boat are under way.

So, to me, this is what modelling is all about. Once I've finished the hybrid hyrdo/flatty the actual boat is I'll run it a few times and move on to the next project. I'm a builder more than a user, it's what I get from this hobby. This test hull is going to have a petrol motor fitted later for another development idea, hence its size, call it future proofing. I don't give a hoot about how this one handles, it has nothing to do with the final design, come the end it's probably going to be made into a highly controllable low speed rescue boat to bring in the various hotty boats that reside on our local spot, or the bin.

The focus of everything I am doing here remains on this, where aerodynamics will matter:



I have considred three blade props, but there simply are not available in the UK, so I achieved that same effect by over pitching the rear prop.

Jeremy_H

Finished the engine end of the new throttle linkage today. I've made all the joints a close fit to try an eliminate backlash, it seems OK and free enough, but I've still got to fit the servo before I'll know for sure. Hoping to get that done before a trip to the pond tomorrow evening.



Whilst it was apart I took the other bit of advice and braced the front engine mount. Having removed the mount there were some small signs of chattering between it and the pylon. I added a thin polypropylene gasket between the brace and the mount, and the mount to the pylon, which will hopefully damp them down. I've also added an extra bolt front left to clamp it all down some more.

yellowufo

Looks good.. the gasket will soften the chatter.. a few posts back a 3blade was mentioned, might be an idea for the rear..... hope for another video, good running......

Jeremy_H

Yeah as I mentioned above JIm I can't get three Bladers in the UK right now, I'll have to source some from the USA it seems. A very costly exercise after shipping and import duties. I could shell out and buy them at what would be four times the price of a regular prop for me to get them in reasonable time, but I do like to keep the costs down so I'd might as well order them through the folk I got these pushers from, it's around a four week lead time. I'll see what happens because right now, considering this is just a .20 and a .25 on this heavy boat I'm getting results with enough potential.

yellowufo

My bad missed the hard to find part about the 3blade.. and i understand the keeping costs down thought.

Ps i ran my boat under a truck last night lol.. sure glad its all foam,
i snaped the pylon in half but alls well after some epoxy and drying time it good as new....

Jeremy_H

Oops! Glad it's still operational.
On the money front, I think it's easy to simply buy your way to better performance, no problem with that as if that's a person's bag so be it, but I do like to recycle parts and materials. On this boat costs have been a few control rods, some nuts and bolts, and propellors. Everything else bar the radio, which I needed to get for all my models anyway, is stuff I already had. Having a small machine shop for my other interests allows me to make stuff that helps to keep costs down a lot if you discount my time, but even my macihines had to pay for themselves. Even the radio was bought cheap off a club mate, so my wallet remains as firmly closed as it can be LoL!

Jeremy_H

Linkage worked well.

Nothing much more to say really, I've now tried bigger lower side of the rudders to stop the digging in but it's not eliminated it fully, it stops dead less and the chines only really dig in on sharp upwind turns. Foils added to the rudders I tried did the same thing in turns, but screwed the AoA on the straight so the next version will be moving foils. Simple links that alter the foils AoA as it turns. More fiddling LOL!
Engines ran reliably, though fuel consumption remains high on the rich setup. Engines are liking a safe mixture though, these are pretty much run in now so I may up the nitro to 16% from the 12% I've been using.

Couple of pics:




Edit: A mate just put up a short vid of the boat before adding rudder mods:

https://www.youtube.com/watch?feature=player_embedded&v=Asx0qbtB6HA#t=21

Altered1

Looking at the vid - at 17 seconds, when she digs in and noses forward (thrust pushing the dug in hull under water??) , I'm thinking angled sides will help the hull slide through the turns better.
\____/ instead of |______|

yellowufo

I was only able to view it once for some reason i cant replay it, but if i saw it right it dug in because the throttle was cut in the turn and weight transfer took over.. as i said i only saw it once.. guess i will restart my tablet and have another look.

Jeremy_H

Would a radius help? If I drop the height of the angled sides I'll get a steeper angle. I've got 13mm sides, and need to leave a 6mm glue join, so it could look something like this?

Jeremy_H

I'm seeing something very new to me when I throttle off in turns. So long as the boat doesn't dig in it just skims sideways for some distance, I had to stick my foot out at one point to stop it hitting the pontoon, I throttled off about 6 yards away whilst in a drift and it just kept coming at me lol.

yellowufo

Physics...........

Altered1

To a degree...... get it? lol !

but not as much as an angled side.

Jeremy_H

Hehe!

I've gone for what is the safest, fastest and reversable option, angled side plates. Safest because it keeps the strength in the chine, fastest because it's just a couple of strips of bent metal, and I can always take them off again.

Still don't really know why I'm bothering, but hey, why not? :-)

They may be too short looking at them on the boat now, but we'll see tomorrow. I screwed them to the hull bottom and covered them in sign vinyl to cover the screws and smooth the joins. I'll try and get a video if the weather holds up enough.

Altered1

See how it goes. in theory, this could be enough to encourage the hull not to dig in, but slide. they may catch, but you will not know until you try.

Jeremy_H

Dig ins probably reduced by half, if these were longer they would have worked. The boat was forced a tad more bow down by them so they must have been giving a bit of lift, so on a gentle turn pretty good results, less so on sharper stuff where the chine still dug in forward of these plates. Throttle caused differences too, at a smooth low planing speed really consistent, on full throttle the bow drops and those remaining exposed rails bite it.

No matter, engines...I've got to run a few trials to see if the Irvine is capable of behaving, and so some more work is needed to get it running sweet, or whether it's problem is as a result of the crank leak detected or fuel lifting problems. It runs fine, but the pickup speed from idle to full throttle is getriatric in comparison to the Thunder Tiger. Still to try other carbs, but I'll mount a temporary tank at carb height to see how it behaves first. If that seems to fix the problem, then there's a couple of things to have a look at, including using another Thunder Tiger lol!

We shot some vid so, I'll edit the interesting bits and pop it up asap.

In the mean time, a few pics from today: