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Old May 17, 2015, 01:39 AM
romanxdsouza is offline
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some help on post 564 would be great
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Old May 17, 2015, 02:20 AM
jbarchuk is offline
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Quote:
Originally Posted by romanxdsouza View Post
some help on post 564 would be great
My answer at #555 and the 'I agree' at #556 are about all you're going to get as regards speed vs handling.

But to add a little more your original Q mentioned weight. Lighter is always-always better. Period. Using the auto racing analogy, that's why all classes of racers have minimum weight rules. The difference between ground vehicles vs air vehicles is that ground vehicles need both weight and aerodynamics to go though a turn, and air vehicles are purely hurt by any extra weight because they too can 'spin out' in a high speed turn, *BUT* they don't have the 'advantage' of ground traction to help make the turn.

The point is to not aim for an AUW. For the hardware you have, find a plan that is suitable for it. It's thrust/weight and not AUW that determines overall speed. But also decide whether you want 'speed with some reasonable handling,' (it can turn before it hits the wall ) Or 'handling/agility at lower speed.' Again, it's not possible to have 'high speed and super agile.' There's -always- compromise and tradeoff.

Another way to say it is to pick a plan/size that -should- fit, build it, and see what happens. That's a typical phrase at the field. I used to ask a *LOT* more questions. The answer was very often 'try it and see if it works.' And those were from advanced guru class builders/flyers. So over time with some experience that's what I've gotten to doing.

For something that I know will yield 'mostly unknown results' such as drastically changing the size of a given standard model I -generally- build a plane first, and find out what it weighs. Then I use ecalc.ch to figure out what power system it needs. Not the other way around by starting with the hardware and building the plane with a 'target' AUW. The reason that's difficult is that for a given standard plan, slightly different materials or building style/techniques could yield a result 20% heavier or lighter. Then after adding the power system the plane will handle either excellently or like a flying picnic table.

That's why for a long time I bought mostly ARFs because I knew they were designed and tested to fly reasonably well out of the box. It took a long time to learn what kind of -changes- caused what kind of -effects- as regards speed vs handling.

The given rule that 'lighter is always better' never changes. Gravity is always the opponent. Period. Lift is the tool that defies gravity, and airspeed/wing loading/wing style/thrust-weight create lift and flight.
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Old May 17, 2015, 04:28 AM
romanxdsouza is offline
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thanks jbarchuk i do understand what you mean ,i only wanted to know the size of mm carbon used in post#564
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Old May 17, 2015, 11:09 AM
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Quote:
Originally Posted by romanxdsouza View Post
thanks jbarchuk i do understand what you mean ,i only wanted to know the size of mm carbon used in post#564
Sorry! I Messed up! I saw 564 as 554. By -coincidence- 5 and 6 even look a little similar. By -coincidence- 554 happened to be a Q that almost no one else answered, so at the moment it made sense to *me* to try answering it further. A perfect storm of misunderstanding.

I looked at a similar PDF of a slightly different design at http://www.rcgroups.com/forums/showt...9#post20982385

What I thought would be the case turned out to be true. Think of a suspension bridge. The main curved catenary cable is huge-super-thick because it supports -all- the weight gathered by the smaller vertical cables that connect to the roadway structure.

That PDF says that the main outside frame structure are 1.0mm and all the internal pieces are 0,6mm.. That follows the suspension bridge idea that the outside airframe supports the forces and weight transferred and shifted around by the smaller internal pieces. The difference is that the suspension bridge operates in only 'one force-direction' supporting the vertical weight of the roadway, where an airframe must support forces in 3 dimensions as the plane yaws, pitches and rolls. (Yes I'm sure there are other 3-dimensional forces taken into account in the suspension bridge, but those are handled by the support towers and cable anchors at the ends, and it's not as if the bridge is in the frequent habit of doing snap rolls or inverted flat spins. )

In that PDF (or other similar styles) the one place I might think about changing the 0.6 to 1.0 is the LG mount area. The two pieces that make up part the trapezoid shape that connects the LG area at the bottom, up to the top-front of the cowl, and where the cowl meets the front of the canopy, will take a lot more stress on a hard landing. Changing those two pieces to 1.0mm would add a micro amount of weight while drastically decreasing the risk of damage on a harder landing. I wouldn't make the LG any stronger because that'll be the breakaway if it does hit really hard. If the trapezoid shape is strong -and- the LG is strong then on a hard impact the next weakest link would be the fuse or a wing snaps off, either of which would be tragedy. (I've ripped the motor mount off my foamie Byp Yak twice in the past month or so with little effort/time to repair it, vs the fuse repair I had to do a few months back. A -planned- weak point is a good thing.)
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Last edited by jbarchuk; May 17, 2015 at 11:16 AM.
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Old May 17, 2015, 11:43 AM
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thanks, thats some good info.
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Old May 19, 2015, 02:04 AM
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Originally Posted by Free View Post
That's pretty good for weight. I'm interested to see how the bamboo thing works out!

Free
I will finish construction on saturday. Wait for video, I'll post it on next Monday.
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