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Old Mar 28, 2012, 07:24 PM
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TahoeDirk's Avatar
United States, CA
Joined Mar 2010
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How many grams should a cool paint job cost? and other stuff

After giving up on paint and switching to tint, I decided to try again.

I decided to try for a shinier finish by not blotting out so much extra resin; I messed up a spar groove , so I ran the second spar long.

I am delighted with my paint job and finish, but unhappy with the weight.

I have been pleased with my 130g, faced wings, they are stiff, and seem durable .

My newest is clearly stiffer, and looks way cool to me, but how much is too much?

What do you think? Dirk
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Old Mar 28, 2012, 09:33 PM
ground penetration specialist
Nathan Schmoekel's Avatar
USA, MI, Grand Rapids
Joined Apr 2007
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Pretty planes always fly better

130grams is well inside the ballpark for a bagged wingset. I think most guys bagged "production" wings are between 120 and 140, except for some extremists working with high aspect ratios...those folks are getting to110grams or lower.

You never said how heavy the painted set was...... ????
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Old Mar 28, 2012, 11:29 PM
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Joined Mar 2010
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The tinted set on the right weighs 131, the pretty , stiff one on the left is quite a bit heavier. My question is how much is too much?

I have nothing to compare my work to , no scene , no fellow fliers, I've never been to a contest. I wonder if I should finish building this wing up , there is still plenty of work left to make it functional. My suspicion is that , since people add up to four ounces of ballast at times , I should just lighten up and enjoy the colors. This design is far from high aspect, I think. 7 5/8 root 5" mid 3 5/8 tip . I originally decided that wider would be floatier for my 6300' home. Now I wonder , because I don't think they are high launchers.
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Old Mar 29, 2012, 08:34 AM
Aurora Builder
United States, MD, Lusby
Joined Nov 2003
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Immediately, those wings are not high launchers because the tips are very wide and hence draggy-it is possible to go too wide at the tips and it is possible to go too narrow at the tips, a happy medium is needed. Foil choice has a major effect as well, any of Gerald's foils will launch higher on a given planform than the AG series foils. Notice I said launch higher, not necessarily perform better, that is a different discussion. Then there is the layup schedule questions...

As far as paint weight, you still haven't said what "quite a bit heavier" is. I came into the shop when my wing builder was adding paint to Rohacell and had a heart attack-he had covered the foam in paint top to bottom (including areas that are not visible in the final layup), fortunately not super heavy on paint but heavy enough. Our math says we added 16g of weight in paint. It would be much, much better to paint the tips, that's 4-8g in paint weight max.
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Old Mar 29, 2012, 08:46 AM
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Overall and fundamentally, weight in airplanes is not good.

I started out of college on the design floor of Northrop (back when they were the small airplane company, making little airplanes). F-5E production was just kicking off, and I was responsible for identifying weight savings opportunities. The F-5E was almost exactly 10,000 pounds empty, coming off the production line. We were told that weight savings down to 1/10 of a pound was to be pursued. Ultimately, saving a pound of weight saved the user $10,000 in excess operating costs, per year.

You can tell yourself that your heavier airplanes will be for windy days, but believe me, it doesn't help like you think. When an airplane receives ballast, it shifts the performance curve. For a given trim setting, speed increases, but so does sink rate. A heavier airplane carries the burden, whether you desire to or not.

Build it light, and try it. I think you'll like it.

Yours, Greg
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Old Mar 29, 2012, 10:15 AM
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USA, OH, Worthington
Joined May 2002
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I know alot of folks are bagging very solid kevlar wings with normal planforms (think Taboo) at around 120g per set. Many are even lighter.

DLGs like to be light. Chase every tenth of a gram and it shows up directly on the scoresheet. I used to believe heavier was okay. I know better now.

You can add alot of color to an airplane, at a weight penalty of less than 5g.
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Old Mar 29, 2012, 11:27 AM
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Thanks for the answers guys , I was looking for some of your numbers, so I didn't post mine.

My heart filled with joy when I saw my new paint job and finish quality, then it sank deeper and deeper as I realized my target weight was not possible. I trimmed and trimmed, freed the flaps freer than previously possible with a hacksaw blade(hot tip) . Sadly I arrived at 155g.

I think I'll build the set on the right first. I guess I'm a tint man again! Dirk
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Old Mar 29, 2012, 11:50 AM
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Well that's not competition weight, BUT it's light enough to fly well. Many of us probably have repaired wings we still fly that would land in that weight category... I still get a lot of use out of my older planes, but they don't look nearly as nice as your painted wing would. In fact I would bet there is a market for a pretty wing like that even at that weight...a lot of DLGs are just carbon/foam and one or two stripes for a "paint job", which some people find rather boring.


Here are a couple ideas for you...
White foam....less paint is needed because you don't have to block the base color.

Shades of blue... work the base foam color into the color scheme so you don't need to fight it.

Just paint the bottom, or bottom and top in alternating areas so you end up with only half the surface covered with paint.
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Old Mar 29, 2012, 12:07 PM
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Tahoe:

If you must paint, here's a tip: black is always the lightest, dark blue is next. You can usually just mist-coat a surface with black or dark blue, and it will look good with the least penalty.

But, there will be penalties.

Yours, Greg
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Old Mar 29, 2012, 12:14 PM
Jim C
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Also remember that some like to balance a wing to counter the blade install and reinforcements. Leave the reinforcements off the non throwing side and use color to counter balance. Paint the one wing for useful weight.
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Old Mar 29, 2012, 12:43 PM
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All great tips guys.

I only recently started paying attention to balancing the wings. I have been relying on luck to get the throwing side a couple grams lighter. Only now I realize I could simply soak up a little more resin on the throwing side. I struggled to discover some twist in one of my first wings which far outweighed any effects caused by unbalanced wings. Another current model has the throwing side 2 or 3 grams heavier , and it flies straight with even ailerons, I assume there is a little twist in that one too.

Black paint has been difficult for me, when I peel the mylars the black seems to stick in crazy patterns. I like the idea of balancing with stripes or highlights after the wing is built.

As far as wing design, I was wanting to try a higher aspect thinner tipped design next, but getting the correct dimension foils by scaling my printouts has been challenging. Also the edge foils that I downloaded are white on black instead of black on white which is hard to make a template from. Any tips?
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Old Mar 29, 2012, 01:19 PM
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United States, CA, San Jose
Joined Sep 2008
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http://www.rcgroups.com/forums/member.php?u=42881

Get your templates from JuzWuz. He has published designs already in his file and can cut you a copy very quickly, and better than anybody can do with paper. I used to make my own but use his now exclusively.

We are doing a local build like what you are doing. If you ever make it down to the bay area come have a look.

http://www.bayrc.com/boards/viewtopic.php?f=16&t=9040

+1 on dusting a fog of paint on the bottom mylar only. Light enough that there are still individual dots. It will light up nicely in the sun and differentiate your plane from others, also help with the annoying blue on blue problem.

Another option is Japanese tissue. I have not played with it myself but these guys have great luck with it.

http://wizard2525.blog41.fc2.com/

http://www.h4.dion.ne.jp/~kousaku/RC/RC_index.htm
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Old Mar 29, 2012, 03:19 PM
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Reno Nevada
Joined Oct 2007
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Dirk,

First, most everyone rarely flies at 6300 ft, let alone expereince the density altitude we get in our area in regard to our DLGs. I have found that flying thermals up here hones your skills and seems to make it easier to fly at normal sea level contests. Just my opinion.

I do have Compufoil, and most of the airfoil coordinates, so I can print you out whatver patterns you need.

I do have a very fast way to sand formica tempates, i. e. no hand sanding blocks. I also have quite a few templates made, so you might look to see if they are applicable to your needs.

I usually airbrush my cores with thinned water based paints and then let them dry for a day a or so (sometimes like 1 hour in our heat). Greg's comment on using tissue is really nice. I have done that. The tissue really does not add much weight and the amount of extra epoxy needed is low. It is also under the skin so you can sand the LEs and not leave a blank spot which can occur when you paint mylars. Besides, you can do some nice designs too, with sharp lines.

Most of my ships are alot heavier than most, so the comments made to count every gram is the right thing to do. Now that you have alot of wings under you belt, you should now concentrate on getting things light. Our average winds up here are quite a bit higher than those like at Poway, so I find that flying up here helps flying in winds down there easier.

I have not painted mylars. I once tried adding color to kevlar pods during a layup with really unlikeable results. So I would not do that with wings.

The big thing that I have found, because I like FG skins, is that you have to leave a bitmore epoxy in the weave to get better bonding to the cores. That's just my opinion because everyone who tries to bag to stabs can get the cloth just too dry. A real tradeoff. Kevlar skinned stabs etcs are OK. Since I also use nylon hinges, one has to be careful as the nylon can soak up resin also. I'll tell youa few good thngs to try in regard to hingelines with nylon when you visit.

Chris
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Old Mar 29, 2012, 03:38 PM
American Exile
Germany, BB, Nauen
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Grams of what, and what are you having painted? I got my El Camino painted in metallic purple gold flake, and it only cost me several grams of... wait, ENTRAPMENT, ENTRAPMENT!!!

Seriously though, the best paint job in my opinion is the one that doesn't weigh anything. And at high altitudes, the human eye loses the ability to discern colors, so the best scheme is dark on light or light on dark.
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Old Mar 29, 2012, 04:08 PM
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Quote:
Originally Posted by xbted View Post
Seriously though, the best paint job in my opinion is the one that doesn't weigh anything. And at high altitudes, the human eye loses the ability to discern colors, so the best scheme is dark on light or light on dark.

Up here in Reno , probably 20 miles as the crow flies fomr Dirk, I found that neither a light color or dark color works any better. I can't see oranges so that does not help. I have found that yellow Fluorescent watercolors over white spyder foam lights up well at altitude. However, I fly prescription polarized glasses and by tilting my head, I can change the sky from deep blue to very light blue. Nearly all my planes therefore have both dark and light patches which can be distingusihed by tilting my head. It might not be the best thing to do or use for glasses and normal full sized flying, but works great for me. And I fly very high.

Chris
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