Flight Times

jander14indoor
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Re: Flight Times

Postby jander14indoor » January 25th, 2010, 12:28 pm

IF you have a stock of good, light balsa and light covering, yes hitting 7 gm or below is easy. WS planes are actually fairly heavy for their size.

BUT, without a plan or experience it is pure random chance. I think a good BOM is even MORE important for those flyers moving beyond the very basics. Its the fastest way to get experience and reinforce it.

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Re: Flight Times

Postby 3slh9 » January 26th, 2010, 11:01 am

I am the coach of the 11g plane and we got our design and wood from a wonderful gentleman in our community who builds planes as a hobby. It has been very frustrating since we are building it exactly to plan and his plane was 7 grams and ours is 11. I have watched my student build these planes and he is so careful about how he is building them that I can only think that the wood is the problem. We got the 1 min 23 seconds using the plane from last year which is right at 7 grams.

I finally broke down and bought a Leading Edge 2010 kit which is very similar to the design we have been using. Do you think this would be a good one to create a BOM from? I just got it yesterday so it is still in pieces. I have a scale that can measure to 0.005 grams so I feel that we can get a fairly good measurement on the weights.

We really have a competitive region and state as even at our invitationals, winning times have been over 2 min 30 seconds and we have seen over 3 minutes during practice flights and this is in a gym with a 28 foot ceiling.

Thank you for your recommendations.

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Re: Flight Times

Postby jander14indoor » January 26th, 2010, 1:52 pm

Note, I'm making an assumption your students building skills are good and glue isn't excessive, but this can add weight FAST. Do you have any data on how much glue you use?

The Leading Edge is a perfectly fine design to work from.

But you don't build the Bill of Materials from the kit. You build it from the plan. Calculate the ideal piece part weight from volume (length, width, thickness on the plan) and density (look up, measure or estimate) to target 6.5 to 6.8 gm (leave a few tenths for clay ballast to adjust center of gravity). Adjust the woods estimated density to hit the total weight target. Note, I do cheat and weigh the prop due to its complicated geometry, but that's the only part I do that for.

As a starting point, see the table below from one of last years designs.

THEN you start selecting parts (either from the kit or from scratch) and weighing to find the correct parts to build to your target density.

With the scale you mentioned, that's plenty of resolution for all but the smallest parts. I tend to select sets of ribs (they are so light individual ones are at the limit of the scales usefulness) and weigh them, reselecting till I find a bunch that weigh the target amount.

Note, when I'm really serious, I record the weight of wood used, and calculate weight added by glue as I go. Lets me adjust the BOM if I find one part breaking too often. That's how I arrived at that 0.5 gm estimate on the below BOM, it used to be 1.0 gm.

The following table is cut from my Excel spreadsheet where its MUCH easier to play with the numbers and adjust. Its for a particular design, so don't use it blindly as a guide.
Not, I don't weigh parts to thousandths, only hundredths. And I only measure to thousands of an inch. And I mix units TERRIBLY, sorry, I grew up with the english system and engineer in metric, deal with it.

Code: Select all

Finny 09   by Bill Gowen                     
PLANNING DATA                        
Part Name                                 qty   length   width   thickness   volume (in3)    rec density (lb/ft3)   wt (grams)   
wing spars                                   2   15.5   0.0938   0.0625   0.182                   8                0.382   
wing ribs                                   7   4   0.0625   0.0625   0.109                   8                0.230   
stab spars                    2   7.75   0.0312   0.0313   0.0151         5                0.020   
stab ribs                       5   2.25   0.0312   0.0313   0.0110         5                0.014   
wing fins                                   2   7   0.0625   0.0625   0.0547                   6                0.086   
stab fins                                   2   4.5   0.313   0.188   0.527           6                0.831   
motor stick                   1   10   0.375   0.25   0.938                   8                1.970   
tail boom                                   1   12   0.188   0.125   0.281                   5                0.369   
wire prop hook                   1   1.5   0.02      0.000471      489.6                0.061   
rubber hook,wire                   1   0.75   0.02      0.000236      489.6                0.030   
wing posts                                   2   4   0.0625   0.0625   0.0313                   10                0.082   
prop                                                                                  1.750   
groc bag covering, wing   1   15.5   4      62                   8                0.320   gm/m2
groc bag covering, horz stab   1   7.75   2.31      17.9                   8                0.092   gm/m2
groc bag covering, wing fin   2   4   2      16                   8                 0.083   gm/m2
groc bag covering, stab fin   2   2.25   1.5      6.75                   8                0.035   gm/m2
glue, tissue tubes, etc(est)                                                  0.500   
total wt estimate                                                                  6.856   


ARGGHH, the columns look right in edit, but bunches in preview, oh well, I'll post now and try to sort it out later.
Double ARGGHH..., even after I post, when I pull back up to reedit the spacing is right, is there a tab command I'm missing????

Jeff Anderson
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Last edited by gh on January 27th, 2010, 6:23 am, edited 1 time in total.
Reason: You can edit it in Notepad or something else with a monospaced font and then put the stuff into [code] tags to get spaces to show up. Sorry about messing with your post though.

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Re: Flight Times

Postby 3slh9 » January 26th, 2010, 6:44 pm

I understand now. I am new at this so thank you for your help. I will have my students start working on this first thing tomorrow. We are only a few weeks away from regionals and don't have a competitive plane yet so I am a little stressed.

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Re: Flight Times

Postby Draylon Fogg » January 30th, 2010, 9:09 am

ok so weighting them is working out very well, i never thought of doing that before. thank you
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Re: Flight Times

Postby Hamtown009 » February 1st, 2010, 6:42 am

Our plane flew a 1:46 in a gym that is about 24 feet tall. Hit the ceiling and continued... Are there any tricks to maximize times in a plane? Our weight is 7.6 grams. We used the Freedom Flight Models 2010 kit. Any suggestions?
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Re: Flight Times

Postby jander14indoor » February 1st, 2010, 7:16 am

Good progress so far. 1:46 is pretty good, your plane flys. Key to longer times becomes planned experimentaion and is where your flight log is critical to sort out what works, what doesn't.

No tricks though. Need to adjust trim to minimize drag vs lift (typically this means flying on edge of stall, with minimum difference between wing and tail angle of attack and rearward cg that's still stable). Need to match rubber to prop to maximize motor duration. Winding to torque vs turns is an advantage.

Of course losing that extra .6 grams will help, but there is more time in your current plane.

Give us some details of your current trim, prop and rubber and we can give some directional things to work on.

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Re: Flight Times

Postby Draylon Fogg » February 4th, 2010, 6:49 pm

YAY PLANES ARE WORKING NOW!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! :D :lol: :mrgreen: :!:
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Re: Flight Times

Postby Hamtown009 » February 5th, 2010, 6:09 am

Here are some specific details--- PROP: widest width - 3.5 cm length - 19.9 cm RUBBER: our best time was with a .095 rubber band at 80 winds after a dewind of two, trying to experiment with others too. What do you mean by asking us to measure the trim?
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Re: Flight Times

Postby jander14indoor » February 5th, 2010, 11:09 am

That sounds like one of those fat, high pitch, Ikara props. The true experts (trust me, there are folks who outfly me consistently, but not by a lot) like them. But I've found fat, high pitch props to require real expertise to get the best out of them, and I don't use them without lowering the pitch significantly. When coaching students I find much faster progress with a lower pitch prop and longer thinner rubber. You might try that.

What's the multiplication of your winder? I don't know if 90 cranks is a lot or under wound for a 0.095 motor. Do you measure torque? How close is that to breaking your motor? As I've said in the past, I often see otherwise very good planes underperform because the students don't WIND their motors. The motor is your fuel tank as well as your engine. This is a duration event, if you don't put every bit of energy in that it can store and then get it all back out, someone who does will beat you everytime.

Trim. Where's your cg with respect to your wing (either leading or trailing edge)? What angle of attack are your wing and tail at? Prop offsets? Wing offsets? Wing twist? Tail offset? Etc. In flight, is your plane on the edge of a stall, or over stabil? Dutch roll? Flight attitude (nose or tail high, wings level, rolled into or out of turn). Also, etc.

Hope that helps,

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Re: Flight Times

Postby germinator » February 5th, 2010, 7:10 pm

blue cobra wrote:What jander said is completely true, but I think that if you are significantly over weight, you are using way too much of something. I personally don't find the densities of my pieces (though I know I should) and my most recent plane, including bass for the wing posts and a few other components, came out to 6.93 grams (but do NOT use bass until you can build light, then you probably still don't want to). I think that if you use "regular" sizes of balsa; about 1/8x1/4 for MS, 1/8x1/8 for boom, and 1/16x1/16 for your wing and stabs, and don't go crazy on the glue, your plane should come out under 7 grams. I'm not trying to disregard what jander said, I just feel that it is very easy to build to 7g and making a bill of materials might be better when you are a bit more experienced and can start worrying about consistency.

I am using wood from a kit that is pre cut and came out to 7.4 grams. Does the fact that is is pre cut matter in the weight?
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Re: Flight Times

Postby WrightStuffMonster » February 5th, 2010, 8:44 pm

germinator wrote:I am using wood from a kit that is pre cut and came out to 7.4 grams. Does the fact that is is pre cut matter in the weight?
It depends on the kit. Sometimes kit wood is laser cut, which incurs a very slight weight penalty. (much less than .4 g)
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Re: Flight Times

Postby leetx » February 7th, 2010, 9:25 pm

I would like to share with others the flight times of our airplanes. I share them with the purpose of establishing an achievable benchmark based on the new 2010 rules and encouraging others to maximize their performance. These times have been made with the Freedom Flight kit and are achieved with dedication, hard work, and probably a bit of luck.

all times are no-touch

20': 3:15
25': 3:25
30': 3:40

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Re: Flight Times

Postby WrightStuffMonster » February 8th, 2010, 9:04 am

leetx wrote:
20': 3:15
25': 3:25
30': 3:40
Nice work! Those are very respectable times for a kit plane.
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Re: Flight Times

Postby leetx » February 18th, 2010, 9:47 am

Jeff,

I actually went through your table! I found a discrepancy in the weight of the stab fins:

wing fins 2 7 0.0625 0.0625 0.0547 6 0.086
stab fins 2 4.5 0.313 0.188 0.527 6 0.831

Your table was very helpful.


jander14indoor wrote:The following table is cut from my Excel spreadsheet where its MUCH easier to play with the numbers and adjust. Its for a particular design, so don't use it blindly as a guide.
Not, I don't weigh parts to thousandths, only hundredths. And I only measure to thousands of an inch. And I mix units TERRIBLY, sorry, I grew up with the english system and engineer in metric, deal with it.

Finny 09 by Bill Gowen
PLANNING DATA
Part Name qty length width thickness volume (in3) rec density (lb/ft3) wt (grams)
wing spars 2 15.5 0.0938 0.0625 0.182 8 0.382
wing ribs 7 4 0.0625 0.0625 0.109 8 0.230
stab spars 2 7.75 0.0312 0.0313 0.0151 5 0.020
stab ribs 5 2.25 0.0312 0.0313 0.0110 5 0.014
wing fins 2 7 0.0625 0.0625 0.0547 6 0.086
stab fins 2 4.5 0.313 0.188 0.527 6 0.831
motor stick 1 10 0.375 0.25 0.938 8 1.970
tail boom 1 12 0.188 0.125 0.281 5 0.369
wire prop hook 1 1.5 0.02 0.000471 489.6 0.061
rubber hook,wire 1 0.75 0.02 0.000236 489.6 0.030
wing posts 2 4 0.0625 0.0625 0.0313 10 0.082
prop 1.750
groc bag covering, wing 1 15.5 4 62 8 0.320 gm/m2
groc bag covering, horz stab 1 7.75 2.31 17.9 8 0.092 gm/m2
groc bag covering, wing fin 2 4 2 16 8 0.083 gm/m2
groc bag covering, stab fin 2 2.25 1.5 6.75 8 0.035 gm/m2
glue, tissue tubes, etc(est) 0.500
total wt estimate 6.856

ARGGHH, the columns look right in edit, but bunches in preview, oh well, I'll post now and try to sort it out later.
Double ARGGHH..., even after I post, when I pull back up to reedit the spacing is right, is there a tab command I'm missing????

Jeff Anderson
Livonia, MI


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