Some thoughts on building light ...
Building light requires knowing the stiffness required for every single component of the model. One good news is that the lighter the model is, the less stiff its components need to be.
It requires a "pursuit", possibly a pathological one! One must know exactly how much every component needs to weigh. Before I build a model, I specify the dimensions and weight of every single component of the model. One must make sure every component, when cut and built, actually weighs the specified amount. When preparing a motor stick, for example, I weigh it after a first cut. Rarely does it meet the weight requirement, so I cut or sand it again, then weigh again. I only stop when the weight requirement is met. I may be a little crazy, but I keep a spreadsheet for every model and component I have built -- the specified thickness and weight, and the actual thickness and weight.
It requires good wood but not necessarily the best or the lightest. For example, the wing spars of my best EZBs come from 5.4# to 6.0# sheets. I dimension the spars so that they are a little thinner than a 4.3# spar. My 5.4# spars may not be as stiff as comparable 4.3# ones, but they weigh the same and are stiff enough. Some components, though, require light wood -- motor stick and prop -- because they take up about 1/2 of the weight of the whole model.
It requires a lot of test flights. Without a lot of flying, one cannot determine if the lighter model flies better than the heavier one. What does the stopwatch say? Are the wing tips deflecting too much? Is the motor stick stiff enough to withstand .10 in-oz of torque -- how about .08 in-oz? Careful record keeping of test flight times is a must. A keen eye on how the model flies helps.
It requires building a lot of models. By building a good flying EZB that's 800 mg, you begin to see "why it works." You then begin to have an idea of the stiffness requirements for a 700 mg EZB. From there, you gain knowledge for the next lighter one, and so on. By building lighter in incremental steps, the next step can be done with more certainty. On the other hand, yyou also learn a lot by building and flying a model that's too light and too weak. This knowledge will point out where the next model need to be stronger. My 5th EZB wing was too flimsy, and I've made sure that future ones are heavier and stouter.
One thing is for sure, though. If you follow Larry Coslick's directions for the Hobby Shopper or the MicroEZB, you WILL build a light model that is stiff enough. Larry has put in all the work to dimension and specify the weight and stiffness of every component. In my experience, building to his deflection requirements will result in a very sturdy model. However, you still must do a lot of flying of your model. Without lots of flying, you won't learn why the model works.
Hope that help!
-Kang
--- In Indoor_Construction_at_yahoogroups.com, themaxout@... wrote:
>
> OK...you haven't seen my fingers either...I might as well use clubs to
> build with. If I drop a pin I have to get a magnet. The first real EZB I
> built was the Hobby Shopper under Tim's pushing. He gave me everything I
> needed...the directions...and I built jigs, forms, tools and everything. I did
> all the right things with the bending gages, you name it. I made a feeble
> attempt to document it in the Max-Out. To me building an indoor ship was
> building a model that flew inside and not outside.
>
> The first time I flew it I thought I did rather
> well..considering....considering I probably doubled it's weight with glue from fixing by the time it
> had made 10 flights. Watching Kang fly in Colo Springs made me a true
> believer that there are some people who can do this...I believe I can again
> too..given another bunch of free time! I did figure out that after being an
> outdoor builder for 55 some odd years...indoor is a special animal if you do
> it right. You have to re-think things. But it will improve your skills.
>
> The steps to start with a P-24..then to a penny...then A6 and then EZB is
> logical. I built the EZB first, then the penny and then the A6. I'm not
> sure that was logical, but I did learn a lot. My next step is to not try to
> prepare 2 weeks before a contest! And, I have had some great folks to
> watch and ask questions of...Don D, Bill Leppard, Kang, John Kagan, Bill
> Gowen...it's good to see what the state of the art can do. Doing it? I defer
> to the club fingers.
>
> It's magic......and pretty magic it is!
>
> Rick Pangell
> Editor of "The Max-Out" Newsletter of
> The Magnificent Mountain Men FF Club of Colorado
>
>
> In a message dated 10/3/2011 1:19:35 P.M. Mountain Daylight Time,
> brucemccrory_at_... writes:
>
>
>
>
> Rick P. wrote: "And, how do you guys build that light? I am impressed."
>
>
>
>
>
> Rick,
> Didn't you process some of Tim Goldstein's Tru-Weight balsa that he cut,
> 6, 7 years ago? The rage was to find balsa that would bend and snap back to
> original shape, and hold hammers without bending. Once you have this
> outrageously strong wood with an MOE to match, you can start building really
> light. (Yes, some indoorists will disagree with this pre-requisite.)
>
> I built an under 260mg A-ROG, using reject cuts from under 500mg EZB
> building efforts. Building light required a mind set, on my part, to do the
> task. The target weight was 300mg. Plus same for motor. It was not to be braced.
>
> My weighing scale was limited to 0.01g, so I weighed mulitple copies of
> each part and averaged. Never new the total weight until it was finished.
> Even then, there was a substantial +/-, due to humidity and scale accuracy. I
> tested parts for about a dozen models, to get the stiffest and strongest
> (and lighest) parts. Once covered with y2k2, I could not breathe directly
> onto those parts; and many of the bones, prior to covering.
>
> There were two "go-by" models I used for material sizing guides. Both were
> braced models: Jim Richmond's difficult to trim model, and Louka's, which
> I copeid. However, I sized parts based on final support of 600mg. I stabbed
> built wing frames into the weighing scale to make sure each half resisted
> 0.3g with reasonable deflection. One of the last things I did was crack the
> wing spars for a 3rd set of polyhedral. It strengthened the spars and
> reduced fatigue bending during flight. The motor tube collapsed at more than
> .1in-oz during the first competitive attempt, so that was a limit. The
> highest time was 20+ minutes at Kibbie.
>
> It survived about a dozen launches, until stress fractures crippled
> flights.
>
>
>
>
> From: "themaxout_at_..." <themaxout@...>
>
>
>
>
> MARKETPLACE
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Received on Tue Oct 04 2011 - 21:01:21 CEST