How to reduce plane weight

[freed2003]

Right now my planes are averaging around 11 grams and are getting around 30 seconds. I think that if I can reduce the weight to around 7.6 grams the time will hopefully increase.
Also on a side note should a 0.65 rubber normally get to 1800 winds?

[bernard]

Use less glue. You hardly need any 3M Super 77 to attach mylar, just a mist a foot above the wing frame is enough. Less glue for joints, enough to be rigid but not covered in glue. Sand the motor stick and tail boom if they contribute significant weight.

[freed2003]

If the hole the glue comes out of is a considerable size(like duco cement) How should I apply the glue

[JasperKota]

.65 rubber should be able to wind beyond 1800.

Don't apply glue directly from the bottle, whether the bottle has a large opening or small. Put it in like a petri dish or just put a small blob on a tissue, and then use a toothpick and dab it onto where you need the glue. Here's a detailed document on minimizing weight gain while maximizing glue strength that I suggest you read: https://www.soinc.org/sites/default/fil ... weight.pdf

[kevin_vs_the_world]

Sanding might seem to be the obvious choice, but don't do too much of it. With mylar, the light stuff that seems very breakable can work if you crinkle it and stretch it back, which will make it much more resistant and it will not lose its shape once air gets under it, unlike a traditional lay over and glue, where the mylar will cause bad things to happen if a single flaw comes about. Other ways to reduce weight are to cut off excess, because you can care about your CG later if you have an adjustable wing, find or build a lighter propeller and if all else fails, use a lighter rubber motor, because that numbs the weight that is added with the motor, but this should only be done if the aerodynamics are good enough to work with the lower amount of power you put into it. 1800 turns on a motor of that size is adequate, but if I were in competition, I would kick it up to 2100, or somewhere in that range. On my planes, I usually go up to 1650, but that is because the height and size of my school's gymnasium is fairly low in height. I hope this helped!

[freed2003]

.65 rubber should be able to wind beyond 1800.

Don't apply glue directly from the bottle, whether the bottle has a large opening or small. Put it in like a petri dish or just put a small blob on a tissue, and then use a toothpick and dab it onto where you need the glue. Here's a detailed document on minimizing weight gain while maximizing glue strength that I suggest you read: https://www.soinc.org/sites/default/fil ... weight.pdf

How to I think the glue? Should I just pour it into the dish and add acetone everytime I'm using it?

[JasperKota]

How to I think the glue? Should I just pour it into the dish and add acetone everytime I'm using it?

I personally never thinned the model cement I was using (duco cement), but I believe you might want to get a different bottle and then thin the glue and store it in the bottle so you don't have to keep adding acetone.

[jander14indoor]

Weight is CRITICAL in the flying events. If you are flying an 11 gram plane 30 seconds you pick up TONS of time with a 7.5 gram plane.

BUT, it's VERY difficult to lose significant weight on an already built airplane. The best solution is to build light to start with. How do you do that? Build with a plan called a Bill of Materials.

- List EVERY part in your plane in a spreadsheet.
-- Describe the quantity, size (length, thickness, width) to figure volume and an estimated density.
-- Figure out the weight of each part.
-- Make an allowance for glue and hard to calculate stuff like tissue reinforcement. How much depends a little on experience and skill, but you should be shooting for less than 0.5 gm.
-- Don't forget the covering and the prop assembly. You'll need to weight your prop assembly. Probably need to weight covering samples to get weight per unit area info.
- Now, add them all up, if you aren't under the max by say .25 to .5 gm, adjust density/sizes until you are.
-- You don't need to be consistent density in the wood, in fact it isn't wise. Wing spars and posts need strength so should be higher density. Ribs and tail components don't need the strength, use lower density there.

With this, you can start to build. Weigh the wood parts, or at least ensure you start with stock at the target density you used. If you aren't building with a scale next to you, you will have difficulty consistently building to a target weight.

Here are some real killer's I'm seeing often this year for weight.
- those red molded props with the attached plastic prop hangers are HEAVY AS SIN! A couple of grams alone, 25 to 50% of your weight budget.
-- This used to be common knowledge, but if you are using molded props you HAVE to scrap them thinner to lose weight
-- Ditch the plastic prop hanger and that WAY oversize prop wire. I saw some today that were probably 0.032 inch diameter or thicker, you don't need more than 0.020 thick wire for your prop. Sleeve the prop hole to that size so it doesn't flop on the wire.
-- Look around the web to see how to make your own prop hanger.
- Coverings.
--You should only be covering on one side! Saw a many double covered wings, top and bottom the last couple of weeks.
-- Watch the covering weight, you can't use just any material! Anything that isn't easy to tear is too heavy! Saran wrap is too heavy! Any decorative wrapping paper is too heavy. Try produce bags from your local grocery store. Dry cleaning bags tend to be light. SOME grocery bags are light. I've found the local Home Depot bags to be fairly light, some pet store bags. Look around, weigh samples. Your weight budget for cover TOTAL should be less than a 0.5 gram with a fairly heavy covering. 0.3 is a better target.
- Stick sizes
-- Except for the motor stick, you should have no sticks over 1/16 square, and for many parts you can go thinner! Control strength by managing density.
-- Again, I saw planes with huge sticks. 1/18 for wing and tail spars.
-- Motor sticks are the most stressed part of the plane and they have to be stiff/strong enough not to bend significantly for consistent flight. However, you shouldn't get there by using dense strong wood. You have a weight budget for your motorstick, all up, including any prop hangers, motor hooks, etc of about 1 to 1.5 gm, 2.0 at the VERY most. If you use dense wood, it will have to be thin in cross section and be very bendy. Instead, use very LOW density wood and increase the size up to what your weight budget will allow. OR, learn how to make hollow motor sticks (discussed in previous threads if you look).

I hope those are some helpful suggestions, again, weight is CRITICAL in the flying events.

Jeff Anderson
Livonia, MI