I have a weight problem.

[WindyParticipant @windy30762]

I have a weight problem before anyone says it we know we have seen you.

It’s not me it’s the hydro having spent a long time removing fractions of an ounce off various parts of the model.

Then painting it for Harrogate to try to make it more presentable it’s weight is now at the limit for competition.

A plastcote type of spray paint was used and wondered from a 400ml can what is the weight of it when it has dried.

I used more than that.

This paint weight problem has happened in various other forms when the object is painted, model aircraft come to mind.

Are there any formulas to work out the dried or cured weights of paint finishes I think there are instruments to measure thickness.

It might be back to bare wood if I cannot find another ounce to remove without weakening it?

Paul

[WindyParticipant @windy30762]

[Gordon WParticipant @gordonw]

paint is heavy stuff, full size aircraft were often left bare to reduce weight and carry more people. Actual weight depends on the bases used, eg. lead oxide versus titanium oxide. Best way is to measure a quantity of the paint, let it dry and then weigh it. Bare wood with a single coat of varnish maybe best for you.

[Michael GilliganParticipant @michaelgilligan61133]

For a particularly good example; look at the Space Shuttle.

They saved about 600 pounds of weight, by not painting the external tanks.

MichaelG.

Edited By Michael Gilligan on 24/05/2013 14:29:14

[Old SchoolParticipant @oldschool]

Paul

I have no idea on the weight of paints, when I built my B class steamer (8lbs) I could not afford the weight of paint the wood was sealed with model aircraft sanding sealer and then a two pack varnish called areokote. The hull was built from 1/32 " plywood to save weight my other big saving was the boiler casing was 4 thou stainless shim in and out with a thin ceramic blanket sandwiched between to keep the heat in.

Regards

Olly

[Ed DuffnerParticipant @edduffner79357]

I remember seeing a model making tv program where they increased the structural integrity of model aircraft balsa wood many times by applying a super glue(cyano type glue) to it. I suppose it's a bit like case hardening for wood.

In my teens I did some training at British Aerospace, learning to fabricate aircraft parts. In particular using the fly press to make formed holes to remove material but retain strength. Could you possibly add structural holes to any frame work of your Hydro?There are some images of this on Google but I'm not sure if I'm allowed to post a link here without permission from the web site or ME forums.

[WindyParticipant @windy30762]

Hi Olly my model is built similar to yours it does not help with the aerobatics and submarine impressions it has done at 100mph plus.

The repairs make it look like a patchwork quilt with no paint on it.

I am about at my limit of lightening the hull without weakening it.

A bit more cogitating on the weight job then might decide to rub the paint off.

Olly are you at the first Kingsbury hydro regatta would like to know more about your cars you might have a convert if they would allow steamers.

Paul

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Ed Duffner on 24/05/2013 15:31:20:

I remember seeing a model making tv program where they increased the structural integrity of model aircraft balsa wood many times by applying a super glue(cyano type glue) to it. I suppose it's a bit like case hardening for wood.

.

A great concept, Ed … but unfortunately, I believe that CyanoAcrylates degrade/de-bond in water.

MichaelG.

[Ian S CParticipant @iansc]

Thought I might be able to weigh a sample, took a bit of sheet metal, and weighed it 38.8g, spray painted it, two coats, wt 38.8g. The area of metal 30 mm x 100 mm, perhaps I should have got a set of scales that read to another decimal point. Perhaps I should paint the other side too. Ian S C

[WindyParticipant @windy30762]

I decided to rub the hydro hull down but not to bare wood apart from one small part it is still covered with paint.

It is about 1Metre long I weighed it before and after there was a reduction of 3/4 ounce will rub a bit more to make it one ounce.

That should make me legal for competition at a guess paint on the hull weighs about 2 1/2 ounces.

Paul

[jason udallParticipant @jasonudall57142]

Paul I guess you have replaced all fasteners possible with titanium?
Saved about
2kg on a motor bike.

[jason udallParticipant @jasonudall57142]

Another wrinkel “observed”…part fill boiler with wax..reduced cc for first race and scrutiny…clears out for futher runs…well seen it done in motorcycles anyway. .

[Jeff DaymanParticipant @jeffdayman43397]

Fasteners are a good target for weight reduction if you haven't already done so. The link below shows bolts for aircraft with heads drilled through the flats and also up the centre. The drillings can be used for safety wiring of course, but also reduce weight.

**LINK**

Flanged head bolts with a small hex or torx drive raised in the centre are usually lighter than plain hex bolts and just as strong, if forged or cold-headed.

Going down a size in fasteners (say going from #10-32 to #8-32 in the UN system) will also reduce weight significantly.

Pushrods can often be ground from a round to a triangular or cross-profile section to reduce weight while maintaining most of the stiffness. Shafts can be drilled for same effect.

If accessible for wrenching, nuts can have two corners ground off and still be removeable. All but a small land beside each corner of the hex can be filed or ground away for further reductions. Even better, snap rings can replace nuts on some shafts and are far lighter than nuts.

Washers can be drilled with mutiple holes, or thinned in some cases, or a thinner washer substituted to save weight.

If fasteners can be removed entirely (ie use 3 bolts instead of 4 etc) weight obviously can be saved. Loctite is lighter than lockwashers. To secure shafts in clevises or between brackets, tack welds by TIG process are lighter than nuts or snap rings! (although the welds must be ground off for disassembly)

O-rings are usually lighter than gaskets, but form-in-place gel gasket when dry is lighter than either flat gaskets or o-rings.

If thinner sheetmetal can be used it will reduce weight significantly due to large area multiplied by mass saved per cubic unit. If edge strength is important but panel centre strength is not, the sheetmetal can be etched away in the centre of panels "picture frame" style by chemical etching or careful tedious noisy grinding…

If there are thick plastic or fibreglass sections in key areas requiring strength, often a small aluminum or titanium thin sheetmetal part will be as strong and much lighter.

On piping, o-ring joints with telescoping thin sleeves retained by a wire or sheetmetal clip are lighter than flanges/screws or olive and compression nut fittings and are just as strong and fluid tight.

Control cables on fast machines briefly used do not need fancy chromed ferrules or PVC rain-proofing jackets. Soldered nipples on control cable ends can be drilled from either end or made from tubing to save weight.

Nylon cable ties are much lighter than screws and brackets for holding and assembling many things.

All tricks from my fast bike building days.

(more just for bikes – chain guards, full fenders, and hand straps are for sissies!)

Good luck, JD

Edited By Jeff Dayman on 25/05/2013 16:33:41

Edited By Jeff Dayman on 25/05/2013 16:35:10

[WindyParticipant @windy30762]

Thank you for the suggestions to save weight the steam generator is heavy with 12metres of 321 tubing and inner and outer cases with insulation between.

The cases are stainless, inner 0.010" have tried thinner but the heat destroys it.

It is not cheap and to use more exotic heat resisting materials are behond my financial means.

The outer case is 0.004" stainless.

Nearly all fasteners are 3 and 4 mm 12.9 Allen screws and Titanium would be nice but what grade to be equal to the 12.9 allen screws as they have a very hard life.

Paul

[Ian S CParticipant @iansc]

The weight of the bit of sheet metal is 13.8g (not 38.8g), and I painted the other side, it now weighs 14g, thats on 60 sq cm, so thats about .2g. The paint was Catapillar Tractor black touch up aerosol paint, 2 coats each side. Ian S C

Edited By Ian S C on 26/05/2013 02:06:57

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

(1) Weigh the spray can before , weigh it afterwards . Bit of loss to account for but reasonable estimate .

(2) Bare wood wiped with linseed oil . Oil weighs almost nothing and gives a renewable sealcoat that will in any case last several runs .

(3) You probably have something like a plane-ing hull with surface skimmer propellor but for wetted hulls the quality and finnish of paint coating can affect hull drag by a surprising amount .

Depends on several things including wetability of surface ( ie does water stick to it ) , bubble nucleation and simple roughness .

(4) Drag on wetted hulls is also affected greatly by the shape as such but more subtly by the shape ' quality ' and the length of hull relative to the running speed .

MikeW

[Sub MandrelParticipant @submandrel]

I'm guessing Windy knows that – he briefly held the British record with his hydro (122.9 mph) although he probably too modest to say so!

Neil

[WindyParticipant @windy30762]

Hi Niel unless you know something I do not I still do but that might change in two weeks time when Bob and I run in competition at Kingsbury.

I know if Bobs flash steam hydro stops being a flying boat the record will be broken that is for sure.

If mine just sits right on the run it's speed will improve a mod I did on the piston looks promising after a static test but you can never take anything for granted with a competition flash steamer pops and breakages at times become common.

Close competition is great fun and the swapping of ideas between rivals helps the quest for speed no matter who gets the record.

Paul

 

Edited By Windy on 26/05/2013 22:07:10

[jason udallParticipant @jasonudall57142]

What mikew says ..reminds me ..teakoil or danish oil or maybe just wax , seal wood , repel water (reduce suface wetting)…might have some milage

[I.M. OUTAHEREParticipant @i-m-outahere]

For more accuracy i would try using a set of scales that measure in GRAINS and then convert it .
50 GRAMS = 771.9 GRAINS.

You can get a set of cheap( price – not quality ) scales like the ones made by MTM and paint a piece of the same material a the hull and measure the difference .

Have a look at a gun shop or places like Sinclairs in the USA – I don't think you will don't need a licence for these items but check anyhow and as usuall no relation or anything with this seller just a customer .

You can get a set of beam sales cheap too and also very accurate but will not convert the weight for you like a digital set .

I wonder how much difference changing between a gloss to a matt finish would make to the drag on the hull ?

Ian.

Edited By SLOTDRILLER on 27/05/2013 07:11:35

Edited By SLOTDRILLER on 27/05/2013 07:12:43

[Michael GilliganParticipant @michaelgilligan61133]

Paul,

Out of curiousity … How was your Hull originally finished [before you painted it] ?

MichaelG.

[WindyParticipant @windy30762]

For members of the forum who have not seen a propeller driven model tethered hydroplane or full size hydroplane at high speed.

For maximum speed the hull is completely out of the water with the very edge of the front sponsons at times just skimming the water surface.

At the rear the prop is a surface piercing type and only half of it is in the water it just about rides on the hub of it..

That’s one of the reasons they can take off and  somersault as an article on full size hydroplanes said 50 years and still flipping . **LINK**

Paul

Edited By Windy on 27/05/2013 08:53:02

Edited By Windy on 27/05/2013 09:01:04

[Chris123Participant @chris123]

I stripped the paint off a lightweight mounting bike frame once.

The weight difference before and after was 16 grams!

Edited By Chris Pocock on 03/06/2013 23:40:12

[richardandtracyParticipant @richardandtracy]

I was the weights engineer for a Jetstream 41 aircraft interior for a year. Great fun. If you like adding up the weight of everything to the last 0.001 lbf (equivalent to a 92mm square of photocopier paper).

With two coats of aircraft interior thickness paint, you are looking at 0.01 lb/ft^2. HOWEVER, one panel I followed through the entire manufacturing process to find out why the interior was too heavy, and measured a sidewall panel and window reveal before painting as 1.5 lbf, and after painting its weight had doubled. The panel was 4ft long and 3.5 ft high by 0.125" thick.

Regards,

Richard

[Sub MandrelParticipant @submandrel]

Hi Richard,

For a while my stepson did the similar but wholly different(!) task of assigning post containers to their positions when loading freight aircraft. Beleive it or not he only got 10-15 minutes and the supplied equipment was a biro and a sheet with pictures of the plane on it. There was a formula to follow but you had to start out by selecting the heaviest ones for either side of the c of g. The containmers were loaded using a semi-automatic system. He used to cheat and use the calculator on his phone. Apparently if you may a poor job of it the result was potentially a crash or an upset pilot – he claims never to have caused either. Apparently the pilot was meant to cross check the calculations but as an error would have meant unloading and reloading the plane…

Neil

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