rccrazedman

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Hello guys I know this has probably has been asked many times before But I'm looking for some good tips on how to build light without compromising strenth. I've seen things like replace heavier wood with lighter wood, and Use balsa in places instead of using plywood, build stick built tail sections. Some of these (like using balsa instead of plywood) sounds to me like your loosing strenth. how do you know where and when to use these woods . anybody with some good tips I would love to hear them. thanks.

Dr1Driver

Most of our R/C kits are drastically over-engineered. Use ply and hardwood where strength is needed, nowhere else. DO NOT use epoxy or other heavy adhesives. Use CA. I've used CA exclusively on planes as large as a giant Stinger with no structural failures. Cut lightening holes wherever possible. You can even change out sheeting to the next thinner size many times, with little strength loss.

Sometimes it's hard to tell just where to cut weight without cutting necessary strength. Only practical experience will tell you where you can trim.

I have a self-designed sport plane (The Piranha II) that's 48", is a rocket with a .32, uses 4 channels with 5 servos, and weighs less than 3.5#. The plans are a good manual on building light.

Build to fly, not to crash.

Dr.1

tashley

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All wise words from the Driver.

oscar2005

the only thing to add is that the strenth is needed in high stress areas.ie,firewall,wing hold down,gear mount,wing spars.good joints vs poor fitting joints add strentgh..balsa fuselage sides with a ply or balsa doubler at the wing saddle is lighter than plywood sides,etc

rccrazedman

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thanks for the replies guys. I also have built quite a few planes with Carpenters wood glue. What is the Weight differance between using this and Ca ?

Tired Old Man

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The CA is lighter, but a lot of moisture weight dissapears with the wood glues, so the Tite Bonds and such still work out better than epoxies where the high bonding strength of epoxy isn't needed.

Dr1Driver

Also, many "quick-set" epoxies don't really soak into the wood, leaving the builder with a false sense of strength. If epoxy is used, it sohuld be the slow-set type, at least 24 hours, and holes, grooves, or other types of channels must be cut into the wood to allow the epoxy to flow into the joint fully. Two smoothly-sanded pieces of wood simply clamped together with epoxy is NOT a strong joint.

Dr.1

kdheath

Some random notes in no special order:

CA glue is terrific, but you cn't control where it goes very well. Titebond can be well controlled, saving weight. Slobbering glue into all the corners adds a surprising amount of weight and no strength. The key to strength is tight fitting joints, not piles of glue. If it doesn't fit, re-do it 'til it does.
Use light weight hardware-esp wheels where you can. Substitute nylon screws for steel ones on hatch covers and such.
Read this for more about balsa:
http://www.mat.uc.pt/~pedro/ncientif...s/techbal.html
Go online to Lone Star Balsa http://www.lonestar-models.com/ and order a box of their 4-6 pound per cubic foot contest wood.Weigh each piece with a gram scale and figure the density. Here's a calculator for doing that.
http://www.nclra.org/Programs/BalsaDensity.php
Use this light wood to replace the oak/balsa hybrid found in so many kits.
Use good quality, but thin plywood. Lite ply really bites the big one. For fuselage doublers, 1/32nd birch ply is plenty for instance.
Look for light wood that is stiff.
Swear off of huge blobs of filler. It's heavy. If the part needs a lot of filler, replace it. Use the light spackle to fill nicks. Use light material like AeroPoxy Lite or West Systems light weight filler for fillets. Put a drop of water on small dents-the wood will swell and maybe not need any filler at all.
Weigh the finished parts. Like make a tail surface. Weigh it. Then try to build a lighter one. Build it lighter until it falls apart. Back off a notch and you're there.
Build to fly, not crash.
If you can make a part do two jobs, you save the weight of one part.
Don't take a part that is strong enough and slap carbon fiber on it. You get a part tht is now heavier and may not be any stronger. CF is not a panacea. You only ned it to be strong enough. Any stronger is just dead weight/.

That's a lot of stuff to throw at you... The point is that building light requires a committment to think and experiment and fail a few times. Ask yourself: Is this piece too strong or just strong enough? Can I make it thinner or smaller and do the job? Too many kits are made to be built by guys with axes. Think more in terms of surgical tools, not axes. Hope this is some help. Building well is a real challenge and can be very interesting and exciting. Go for it!

RITTMEISTER

DR 1 DRIVER DID YOU RECIEVE THE VIDEO OF THE RED BARON? INTERESTING CONCEPT
BUILD TO FLY NOT TO CRASH
IN LOUISIANA IS WAS NOT AN ISSUE WEIGHT... ONLY TO BALANCE IT... HERE IN COLORADO YOU HAVE TO BEG THE PLANES TO FLY AND STAY UP.. 5000 ALT[:-] DJCIII LACOONASSDJCIII

Dr1Driver

Video has not arrived yet.

Dr.1

SamD

Capitalize on areas of the plane with higher lbs. per square inch- like metal. While working with contest grade balsa etc is certainly a way to save weight, there are plenty of other opportunities people tend to forget about. Anything made from metal rather than wood needs to be scrutinized. Fasteners are one area that deserve attention; drop the lock washers, over-length bolts/screws, don't use nuts if you don't need them. I see glass filled engine mounts with lock washers, flat washers, lock nuts and bolts 1/2-3/4" too long all the time- and for nothing! Take the mount, carve it down to size- anything hanging out past the front of the engine is worthless- it's just adding weight. Put it on the chop saw and clip off the excess. Drill big holes in it to further lighten it. Then, drill and tap for machine screws, use button head cap screws which have a larger head diameter- though shorter head than regular cap screws- , drop the washers and use blue loctite- job done.

From time to time, I see quick-links used to hook up push rods to servos. That's an arguable practice for another discussion but everyone seems to leave an inch of two of excess push rod hanging out- what for? More weight... Use set screws rather than cap screws on wheel collars or anywhere else a set screw is needed- the head isn't doing anything other than adding weight and looking ugly (okay, maybe they don't strip as easy since you use a larger allen wrench but that shouldn't be a problem with good tools). For that matter, drop the wheel collar althogether and simply solder a brass washer on in its place- especially on tail wheels. That extra 1/2" of axle hanging out catching the wind? Cut it off. Klett used to make some really nice axles that didn't use those clumsy, huge locknuts that Dubro & GP sells. Sure wish they were still available (maybe they are, anyone know?)Those big, out of proportion 2-56 & 4-40 locknuts people use; drop 'em and get some aluminum locknuts from Fastener express or RTL etc; smaller, look better and save weight. Most fasteners are used in shear and not tension so aluminum nuts won't be a problem (at least not for 2-56 or 4-40) Eliminate washers where a button head screw will do- they look better, too. Utilize existing structure for mounting things; I installed a remote glow using a lightening hole I previously drilled in the motor mount. Eliminated the extra mount and fasteners used to hold the mount. That fun-fly plane with no cowling around the engine; does it really need that aluminum spinner? Looks good but just adds weight.

Basically, scrutinize everything and ask if it really needs to be there- excess material, excess fasteners, etc, etc.

Dr1Driver

Hey SamD,

You don't do competition fun fly, do you? I've seen some of these guys remove the RX case to save a few grams. We used to weigh Monokote to pick the lightest colors. Can you say "triple-beam balance"?

Dr.1

RITTMEISTER

WEIGHING MONOKOTE PER COLOR LMAO!! WOW!!!! I DO HAVE A SMALL OZ. SCALE FROM ACE HARDWARE BUT DIGITAL SCALE OR TRIPLE BEAM MAN I,M NOT GOING TO MARS ALTHOUGH...... IF I STAY HERE IN COLORADO MUCH LONGER I GUESS I,LL BE LOOKIN INTO WEIGHING EVERTHING TO STAY UP[:-] DJCIII

tashley

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Klett Plastics is alive and well [link=http://www.klettplastics.com/pages/1/index.htm]here.[/link]

Triple Beam, boy that takes me back![8D]

SamD

Dr1,

Knew there was something I was missin'! Seriously, though, gettin' rid of metal is high on my list of priorities when looking at the relative densities of materials and amount removed vs. weight saved. Everything helps, though

Sure wish that Klett site had some better graphics and was bit more user friendly. They've got the axles I was thinking of but not in 5/32", curses! That's gotta' be one of the most popular, most used sizes and they don't have 'em!! Those big, old, clunky things DuBro sells are a joke; they look like something that should be on a lawn mower.

rccrazedman

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Hey guys thanks for all of the great infomation. I am reading this all and soaking up what I can. anyway I wouldn't personally go as far as weighing the monokote and taking the reciever apart. But lighter is always better. I also think I will try looking for the better quality ligher balsa from now on. Thanks for your comments also dr1 about epoxy. I personally haven't ever used anything less then the 30 min epoxy due to less strenth. I just never trust that 5 min and 15 min epoxy and you just confirmed my suspision.

tashley

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[link=http://www2.towerhobbies.com/cgi-bin/WTI0091P?&C=QDB&V=HIG]Here[/link] are the lightest steel axles that I know of and [link=http://www.centralhobbies.com/landing_gear/Axles.html]here[/link] are the absolute lightest of any.

SamD

The axles from Central I've been thinking about trying; I like the c-clip arrangement- much more elegant than regular collars and lighter, too. The Higley axles are better but still don't match the Klett, with its single lock nut, from the standpoint of simplicity (for a steel axle). I know, I know, I'm being fussy and hard to please. I'll give the Central axles a try...

tashley

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I know the Higleys come with two lock nuts but you can use a thin jam nut on the inside of the axle and use one lock nut on the outside. The ones from Central Hobbies are definately lighter but more spendy.

jaka

Hi!
One way of reducing weight is to carve away (with a Dremel and drum sander) unnecessary foam in foam wing.
Reduced this Q-500 pylon racer wing with 50g

Regards!
Jan K
Sweden

iaclmac

Lets not forget finishing. Coverings do vary some in their weight and strength. Also if you are painting, sealing balsa with filler paints gets heavy. When it comes to that I prefer to use CA on all the wood parts to be painted. Applying CA with a Q-Tip adds little or no weight and when sanded leaves the balsa with an extremely hard surface

kdheath

Happened to think about Micro Fasteners, the source for model hardware of all kinds. Here's their nylon selection. If you're paying 2 bucks for four bolts, you're getting sc****d.