Aquabird - Electric Build - RC Groups
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Sep 23, 2012, 06:56 AM
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Trevorh's Avatar
Build Log

Aquabird - Electric Build

For those who don't know it, the Aquabird was designed by Laddie Mikulasko and was first published in 1992 in RCM magazine.

We have no retrieval arrangements at our water flying site so flipovers can be particularly embarrassing. Having experienced this predicament with both my Lazy Bee and Sealand, I was looking to extend my range of waterplanes with something that would be stable on the water. When I came across the Aquabird, I immediately felt I need look no further.

This 60in span model was designed for .40 - .46 two stroke power, had a balsa veneered, foam-cored wing and weighed in at 7lb. The Traplet plan ( ) which I purchased shows a built-up option for the wing but in all other respects is, as far as I know, faithful to the prototype.
Last edited by Trevorh; Jul 02, 2015 at 10:23 AM. Reason: Updated link to plan
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Sep 23, 2012, 07:19 AM
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Trevorh's Avatar

First Cut

So dire was the English 'summer' of 2012 that I started planning my 2012/13 Winter build early. Indeed, by July, not only had I chosen the subject and bought the plan, but I had all the wood in stock. The urge to relieve the tedium of the bad weather by starting the build early was becoming irresistible when my other half suddenly called to say that she had located four dining chairs which matched our existing 42-year old set of four.

Apparently, in spite of the family having left the nest some years ago, it transpires that we now have a need for eight chairs. So for an outlay of 32 I found myself with a project to restore all eight chairs, which kept the workshop full until the 2012 Olympics got underway - and then in mid August, at last, Summer arrived.

After a good late Summer's flying, the equinoctial gales now seem to have arrived, so the bench has been cleared, the plans rolled out and the Aquabird build is now formally underway.

Although I want to do a built-up wing, the version drawn on the plan does look as if it was drawn without the benefit of a prototype build. The combination of the forward sweep and gull wing dihedral does result in some awkward joining angles between the wing panels, but I can't help thinking that there must be a way to tackle this without resorting to the multiplicity of large, heavy 1/8in ply dihedral braces shown on the plan.

Also, because of the deep chord and symmetrical section, the wing ribs are huge. As a result, this wing seems to be a candidate for trying the Robin Fowler wing building method. I'm still working out the detail of how this is going to work so there's plenty of time to make your suggestions!

Meanwhile, just to prove that the project has really started, here's the first picture.
Last edited by Trevorh; Sep 23, 2012 at 07:26 AM.
Sep 23, 2012, 11:31 AM
eye4wings's Avatar
Hi Trevor,
Looks like this is going to be a fascinating subject.

What would be really neat would be if the inside line of the biggest rib section would be so kind as to coincide with the top of the next, but I suspect that might result in very skimpy ribs, which would not be a good idea with so much of the wing section being a straight line with no inherent strength from a curved surface. Maybe the first rib would happily lead to rib 3, 5, 7 etc. in that nesting manner with an intermediate cut for rib 2, 4, 6 etc?

For the joining of wings I suggest leaving the root of the top and bottom spar sections un-glued (with sheet only to one surface) so that they can be bent to a curve and fixed with a curved balsa doubler before the centre rib (or whatever structure there should be there) is added. Vertical spar webbing then can be added before the top skin is glued on.

Not sure your first mini-waste wing will necessarily save you a lot of work ('til you get used to it), but it'll certainly save you weight and waste!
Sep 23, 2012, 01:15 PM
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pentaxman's Avatar
Looks like an interesting model. I shall be watching this.

Are you able to fly glow machines at your water flying site?
Last edited by pentaxman; Sep 23, 2012 at 01:15 PM. Reason: Typo!
Sep 23, 2012, 03:52 PM
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Trevorh's Avatar
Originally Posted by pentaxman
Are you able to fly glow machines at your water flying site?
Nope! see thread title

I haven't thought about motor selection yet, until I get a better idea of likely all up weight. The prototype weighed in at 7lb but I really can't see why it needs to be more than about 5-6lb, in which case I envisage this as a 4 cell model , 4s x 3000mah being one of my 'standard' pack sizes.

Robin, the portion of the ribs aft of the main spar seems to be drawn with a ruler, so I haven't bothered trying to get the different sized ribs to nest neatly inside one another. I take your point about there not being a lot of time saved when using this method for the first time. I have cut out ribs 2 and 3 so far (i.e. eight rib halves). I'm in no rush though, so if it takes a week to cut out the rest of the ribs, so be it!
Sep 23, 2012, 06:34 PM
eye4wings's Avatar
Well at least you appear to have every rib drawn out full-size so it's a fairly easy tracing task.

Re retrieval a modestly sized model boat on 27meg and with a string attached would seem to be a useful accoutrement.
Sep 24, 2012, 04:39 PM
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pentaxman's Avatar
Sorry about that Trevor, I missed the heading.

I can't see why it couldn't be made much lighter, without that nasty big oiler on it and a nice smooth electric motor instead, you should be able to reduce a lot of the thicknessess of the wood sections.
Sep 24, 2012, 05:17 PM
eye4wings's Avatar
Mmm... Normally I would be saying exactly that, but I am not so sure for this model. Those floats are well down the wing which is taking all the landing shocks so the spars will need to be kept big enough to transfer them to the fus
Or to look at it from the other way, all the major weight is going to be suspended half way between the widely spaced floats which is about the worst case scenario. The original foam core wing would have had good stiffness... I'm just wondering how much torsion is going to be applied to the wing by those floats too.
Sep 24, 2012, 06:05 PM
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pentaxman's Avatar
Robin I am sure that view is valid but...
if the fuselage and float weights are reduced then the stress on the spars is considerably lowered whichever way you stress them.
Not only that, if the spar sections are carefully selected and cleverly used then the weight loss can be considerable without loosing strength.

Looking at the picture Trevor posted again, if enough weight is lost in the structure the floats could be reduced in size further reducing the weight and stresses.
Last edited by pentaxman; Sep 24, 2012 at 06:14 PM.
Sep 24, 2012, 06:25 PM
Registered User
To reduce possibility of the wing breaking in the middle when there is a hard landing, the plywood dihedral brace in the middle is needed. Use x spruce for the main top and bottom spars. I would cut out the ribs 1 and 2 from 1/8 lite plywood. Between ribs, glue the balsa sheer webbing as well.
Here is my electric Aquabird. I am using AXI 4120/18 motor on 6S 5000mA batteries. Actually, 4S would be enough, but that is what I have. The wing is foam, covered with craft paper. There is one full depth balsa spar.
Sep 25, 2012, 02:39 AM
eye4wings's Avatar
Congratulations are due on designing a very aesthetically pleasing model Laddie - I particularly like the three-quarter rear view.

'Hard landing' and 'TrevorH' are not seen in the same sentence without the negative!.. so he is redesigning to save a bit of weight - and therefore save some of the stress too.

As most woods come from your neck of the woods (haha!) I wonder why you still recommend spruce when Port Orford Cedar (Cyparis) is available?
Maybe only the rubbish is selected for export, because I have ceased trying to find good straight grained stock over here and have seen (and suffered) too many failures. Cyparis for me every time - straight grained, half the weight and far more resilient in the event of a mishap.
Only downside for the speed-builder is that it doesn't like superglue.
Sep 25, 2012, 04:20 AM
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Trevorh's Avatar
Wow, thanks for all the input guys. I'm still rib cutting so have time to change my ideas on the wing structure so this is all very timely. I didn't know you had done an electric version Laddie. Is it a complete new model or just another fuselage on the same wing used for i.c.? I would be interested to know what the electric version weighed.

The Pentaxman/Eye4Wings dialogue above takes place inside my head repeatedly. At the time I ordered the wood, my thoughts were as follows (this is all about the inboard panels - I haven't given the tip panels much thought yet:

Ribs: 3/32in medium weight quarter grain balsa, from R2 to R7, possibly reducing to a lighter grade (or, if I'm feeling brave, 1/16in) for R8 - R11. All cut in two parts as per post #2 above.

Main Spar: Full depth 1/8in medium balsa (sorry Robin!), joined to the top and bottom half ribs in 'egg box' fashion. 1/4in x 3/32in Basswood spar caps top and bottom out to R5. Balsa from R5 to R11.

Rear spar: 3/32in or 1/8in sheet fitted vertically between the top and bottom rib halves

False TE: 1/4in sq balsa as drawn.

Skins: 1/16in balsa sheeted back to main spar (to form closed D box), 1/16in cap strips for aft section of ribs. 1/2in x 1/16in strips along top and bottom of T.E.

Centre join: 1/16in ply brace on rear of L.E. Ditto across false T.E. (packed out with triangular balsa block). I'm still digesting the various ideas on the main spar joint!

I'll save the discussion on the sponson size for another posting but Robins' observation that the landing loads will put quite a bit of leverage on that central wing joint is definitely one that has been holding me back from lightening up the structure too much. It is a very deep wing though so, as long as the bottom spars are well tied together and the top spars are supported by the vertical web, I can't see the basswood top spars giving out under the compression load. So it all comes down to reinforcing that joint without creating any hard points at or around R2.
Sep 25, 2012, 12:38 PM
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pentaxman's Avatar
I like the look of that spec Trevor although I am confused by the terminology of spar caps.

I assume you will be fastening the 2 basswood spars behind the 1/8" main balsa spar at the top and the bottom of it, with the 1/4" side in the vertical position. Would that be correct?

I wonder if you could assist your strength dilema around the centre joint by using 2 x 1/16" main spars fixed either side of the basswood caps to provide a box section. This would help to give you somewhere to place your central wing join strengthener, the box spar is the way I have done my Mosquito, the Catalina outboard wing panels and my Basic 3D which was flown and doing aerobatics in the stiff winds on sunday morning.
There would be next to no weight penalty to do it this way either.

If you are fitting 1/16" rib caps then I can't see any issues in dropping to 1/16" ribs further along the wing.

Just a thought.
Sep 25, 2012, 02:27 PM
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Trevorh's Avatar
My idea was to place the spar cap strips horizontally to form an I section, a bit like the cap strips on the ribs. Placing them vertically as you suggest would give more bending strength, at the expense of deeper notches in the ribs which would in turn limit the scope for 'egg boxing' the rib/spar joint.

I like box sectioned spars but the spars are swept forward so I'm not sure how it would help with the centre joint?

I'll try to take a couple of pics tomorrow.
Sep 25, 2012, 04:15 PM
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pentaxman's Avatar
OK, I did not know about the forward sweep, but how about this for a wacky suggestion, why not laminate a wing joiner with a sweep built into it?

Some layers of nice thin ply cut to size and shape required, then lay up each layer at the correct sweep in a shallow V block jig until the thickness you require to fit in the box spar is achieved.
Then the laminated joiner can be fixed into the box spar.

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