Author Topic: 600 sq's, what's your model weigh? (Read 674 times)
Avaiojet
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« on: December 30, 2013, 10:55:14 AM » Reply with quoteQuote
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I'm trying to determine the average weight of a 600 sq' model.
Tad over or under will do.
Without IC engine or "E" motor.
Just built, finished, painted and empty of any power equipment.
Thanks in advance.
Charles
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« Reply #1 on: December 30, 2013, 11:31:20 AM » Reply with quoteQuote
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Hi Charles....
I would imagine around 45 ounces....
Happy New Year!
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« Reply #2 on: December 30, 2013, 12:12:37 PM » Reply with quoteQuote
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Hey Charles,
There is no simple direct answer. Today, I do not think there is any way to determine an "average weight" of a 600 in2. I assume you are asking about a CL stunt model (after all, this is a CL stunt forum).
If you are looking to have a top performing stunt ship that has a wing area of around 600 in2, the desired total weight sort of depends on the power train you choose. A good 35 or 40 can pull a 600 in2 competently through the pattern if the total weight is in the 50 oz range plus or minus a few ounces. If you choose to use a piped system matched to that design with larger flaps and elevators than what was used on the classic 35 size stunt ships, (a piped 40 or even larger on a 600 in2, then a higher total weight could be tolerated where 55-56 oz, plus or minus would still provide good performance. Heavier planes than this can still fly the pattern, but these weights will allow a good design to fly acceptable corners and be able to perform in turbulent conditions.
I will defer the electric gurus to respond about their power plants.
So, once you decide on the power plant, you will have to calculate on your own the allowances needed for the power plant, tank or batteries, prop, spinner, and whatever else you do not have on your "finished" model to get it ready for flight to answer your question.
Now, if you are just looking for a model that flies without much consideration to how well it can fly a stunt pattern, there really is no answer to your question.
Keith
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« Reply #3 on: December 30, 2013, 12:34:13 PM » Reply with quoteQuote
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Quote from: Avaiojet on December 30, 2013, 10:55:14 AM
I'm trying to determine the average weight of a 600 sq' model.
Charles
With what airfoil!!
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« Reply #4 on: December 30, 2013, 12:53:41 PM » Reply with quoteQuote
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well my 600 inch airplanes are usually at their best below 50 ounces ready to fly,,, with motor,, so if you subtract the engine,, typicaly 9 ounces or so, tank,, a couple ounces, you would end up around 40 ounces orr less depending upon airfoil you can get performance higher than that,, say another 5 or 6 ounces with a good airfoil,, and good power,,
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« Reply #5 on: December 30, 2013, 03:02:53 PM » Reply with quoteQuote
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A world class stunter at 600 sqs per your definition will weigh between 28 and 33ozs.
These are hard figures and if your plane is either side of these numbers it is just
another everyday practice model. RJ
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« Reply #6 on: December 30, 2013, 03:20:17 PM » Reply with quoteQuote
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Quote from: Avaiojet on December 30, 2013, 10:55:14 AM
I'm trying to determine the average weight of a 600 sq' model.
A while ago there was a discussion on wing loading as the means to determine appropriate weight for stunt model. Wing loading between 11 and 13 pounds per square foot was the ideal range.
Based on the formula( wing loading = (weight of the model in oz)/(model in wing area in sq in * 0.00694444444)) the weight range of the model in the flying ready condition would be between 46 and 54 oz.
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« Reply #7 on: December 30, 2013, 04:18:40 PM » Reply with quoteQuote
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After building many planes I have found it works out close on the average size wing to one ounce per inch of span. Its not scientific its just a SWAG. Smaller planes with less span work out to weigh less per inch of span.
I am sure this is due to the compounding of area verse's paint. Most 60 inch span models of today weigh 60 ounces plus. Modern day power trains are much heavier than the days of a 6 ounce Fox. My 54 ounce Viper is carrying 27 ounces of fixed weight. So it would be hard to get it any lighter (but I am trying) its 670 squares.
Fix weight to include Motor,esc,timer,battery.prop,spinner,wheels,bellcrank,horns,pushrods,ball links,hinges and lead outs. Then there is 6.5 ounces in paint and covering. That means the wood airframe is 20.5 ounces but heck it's easy to build them light.
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« Reply #8 on: December 30, 2013, 04:31:02 PM » Reply with quoteQuote
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Quote from: Bob Whitely on December 30, 2013, 03:02:53 PM
A world class stunter at 600 sqs per your definition will weigh between 28 and 33ozs.
These are hard figures and if your plane is either side of these numbers it is just
another everyday practice model. RJ
LOL!
Chris...
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« Reply #9 on: December 30, 2013, 05:05:24 PM » Reply with quoteQuote
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Hypothetical airplanes, which one flies better?:
Airplane A: 585 square inches, piped PA65, moderately thick wing (18%), 54 oz
Airplane B: 585 square inches, piped PA65, very thin wing (~12-13%), 66 oz.
Airplane C: 595 square inches, electric w/fixed speed governor, very thin wing (~12%), 69 oz
Both are built by skilled builders, both have front-row finishes.
Brett
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« Reply #10 on: December 30, 2013, 05:11:06 PM » Reply with quoteQuote
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Quote from: Brett Buck on December 30, 2013, 05:05:24 PM
Hypothetical airplanes, which one flies better?:
Airplane A: 585 square inches, piped PA65, moderately thick wing (18%), 54 oz
Airplane B: 585 square inches, piped PA65, very thin wing (~12-13%), 66 oz.
Airplane C: 595 square inches, electric w/fixed speed governor, very thin wing (~12%), 69 oz
Both are built by skilled builders, both have front-row finishes.
Brett
If you can tell me how long a piece of string is I could answer. The correct answer is not as long as you make it.
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« Reply #11 on: December 30, 2013, 05:49:18 PM » Reply with quoteQuote
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Quote from: Robert Storick on December 30, 2013, 05:11:06 PM
If you can tell me how long a piece of string is I could answer. The correct answer is not as long as you make it.
That's about the right answer - basically, you can't tell how it will fly by looking at the wing loading or the power/weight, so not enough information.
And I lied above, these are actual real airplanes. Airplane A was hopelessly out of trim and needed a much smaller prop, and ultimately could have flown just as well, or better, with an Aero Tiger or 40VF. Airplane B is Jim Aron's 20-pointer, pre-NATS-crash, and it flew very well, better than most of the airplanes in expert. The last is the same airplane after the rebuild and after conversion to electric, except instead of a PA65 on a pipe, it has an electric with a fixed-speed governor (vice a accelerometer feedback system). It flies substantially better than it did before, now better than many in the Top 20.
Note that I am not claiming that knocking 8 oz off Jim's airplane would hurt it, but it does show that even at a wing loading of 16.7 oz/square foot, if you get the airfoil and power right, it's not a significant impediment to performance.
As an aside, Jim's airplane uses a Phil Granderson style airfoil that is much, much thinner than what most people are using, with a very far forward high point. Just goes to show that if you don't do something silly (like the ARF Strega) the thickness doesn't matter very much.
Brett
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« Reply #12 on: December 30, 2013, 05:55:05 PM » Reply with quoteQuote
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I prefer to equate weight in ounces to engine displacement in cu.in. If a model is 46 oz dry, it's perfect for a .46, etc. This is not to say that more displacement is bad, but less probably is, or that all .46's are created equal, because they are certainly not.
The "standard" for stunt wing loading has been 10 to 13 oz per square foot for about 50 years. If you hit 50 oz dry weight with engine, tank, tipweight, CG correct, you're at 12 oz/sq.ft. But that still doesn't mean it will fly worth a darn. Coffee Steve
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« Reply #13 on: December 31, 2013, 08:14:48 AM » Reply with quoteQuote
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Is this like the question my Dad used to ask me, "Which weighs more, a ton of wet sand or a ton of dry sand". I just try to build straight and light. Then let the finish fall where it does. Takes a lot of sandpaper and elbow grease to keep it light.
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« Reply #14 on: December 31, 2013, 05:09:42 PM » Reply with quoteQuote
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Brett, did you say Uncle Jimby's pretty plane has Phil's wing in it? Or at least Phil's airfoil?
Happy New Year, John
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« Reply #15 on: January 02, 2014, 11:17:18 AM » Reply with quoteQuote
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I’ll chime in here with a little history re. the airfoil Brett is referring to. If you have the Diva article published in Feb. 2005 Model Aviation you will see it referred to as a ‘dynamic airfoil’ which is just a name I came up with. Way back in 1969 when I was young and better looking I began experimenting with airfoils for both combat and stunt planes. My Tyantula which was designed in ’68 and flown in competition was the inspiration for several other West Coast thin airfoil high aspect ratio designs including the Winder. Incidentally the airfoil for the Winder was actually the #7 rib from Larry Scarinzi’s Super Satan. My original Tyrantula used a standard NACA 0018 airfoil.
In ’69 I began experiment with moving the high point of the airfoil forward on my combat planes and settled on an airfoil that had its high point at 18% if the cord. The Tyrantual II published in July 1971 Model Airplane News was a derivation of that airfoil which I used on constant cord combat planes and ultimately won one of the last single elimination Nats in ’78. At the same time in ’69 I began experimenting with stunt airfoils that featured a fairly laminar foil at the root (30 – 40%) graduating to a tip where the airfoil moved forward to around 20%. Those stunt wings used the standard plan form with LE taper and straight TE. The wings seemed to generate considerably more lift with no ill effects. The only problem is it was difficult to carve a consistent set of ribs using the blank stack root/tip method of the day.
Fast forward to 1999 and Bob Hunt’s very innovative ‘Lost Foam’ building system. Suddenly here was a way to get very accurate ribs at each location and produce an airfoil that changed gradually progressing from the root to the tip. Now I could fine tune the wing to work better in the variety of flying conditions (wind, turbulence etc.). The Diva wing published in ’05 works very well in a variety of windy and turbulent conditions especially if you are using IC engines for power. Although it performed admirably better in turbulent conditions than other designs I always thought it could be improved.
Electric power was just the thing to refine the wing even farther to handle turbulence. Without getting into the great electric vs IC power debate I’ll just say there is no valid reason for me to ever power another stunt ship with an IC engine. E-power let me concentrate on designing a plane that would handle noticeably better in turbulence and wind. Starting with Elroy aspect ratios began to get lower and flying in turbulence was easier. Since Elroy there have been three airplanes. Each has the same airfoil as the ’05 Diva but with different plan forms and decreased thickness at both the root and tip. My current model TLD (the last Diva) or Miss Attitude is better in wind and turbulence by a noticeable margin. It has a low aspect ratio nominal 4.8 and a very thin airfoil nominal 15% root and 9% tip.
Finally, 2013 I rediscovered RC (yeah I know) and there will be an E-powered RC Diva in the near future.
Happy New Year
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« Reply #16 on: January 02, 2014, 01:23:01 PM » Reply with quoteQuote
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"just goes to show that if you don't do something silly (like the ARF Strega) the thickness doesn't matter very much"
Snicker.. Haha
Totally.....
It's only five inches but it's thick....
Pfffffftttt..... Haha
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« Reply #17 on: January 02, 2014, 02:22:03 PM » Reply with quoteQuote
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Quote from: ptg on January 02, 2014, 11:17:18 AM
Each has the same airfoil as the ’05 Diva but with different plan forms and decreased thickness at both the root and tip. My current model TLD (the last Diva) or Miss Attitude is better in wind and turbulence by a noticeable margin. It has a low aspect ratio nominal 4.8 and a very thin airfoil nominal 15% root and 9% tip.
It's's remarkable how much more effective it is than the Pattermaster-style Nobler airfoil blowups like the ARF Strega, even at something like 3" thick at the root, and it seems to be a match for Trivial Pursuit and Infinity wings that were designed for intentional large amounts of parasitic drag. Mine looks like a cross-section of a blimp.
That was the thing we missed in 1990 when the TP and Infinity were designed. We knew you didn't need it to be that thick to get the requisite lift as long as you didn't screw up around the leading edge. It's thick for airspeed stability/parasitic drag, not for lift. But what we hadn't figured on was the degree to which you can control the airspeed with engine adjustments. Early on, we didn't know very much about it and we might have been in trouble for a few years with other airplanes, but as soon as we figured out how to control the airspeed with the engine, the thick airfoils were not necessary.
You're a generation ahead of Ted and I on that one. Add electric with essentially infinite control, then all you need to do is design the wing for enough lift again, without the downsides of extra drag for drag's sake.
But, what's this stuff about R/C? Can't you just get a simulator and fly that? Then you never have to leave the house, it's like nirvana. Split screen with re-runs of McHale's Navy and you are all set.
Hey, now I want to fly R/C...
Brett
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« Reply #18 on: January 02, 2014, 03:30:40 PM » Reply with quoteQuote
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Ptg,
Wow!
You just described a wing like the one I recently designed at 600 sq's, aspect ratio and all. Well, close enough. I'm at 4.848 to be exact.
Root and tip thickness is so close it's scary.
Only difference is my wing is elliptical. Grin
Thanks for the info and reply!
Charles
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« Reply #19 on: January 02, 2014, 04:56:23 PM » Reply with quoteQuote
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Phil
Very interesting story. Thanks for sharing it. Smiley
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« Reply #20 on: January 03, 2014, 12:49:50 PM » Reply with quoteQuote
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I have been designing planes lately with an airfoil using the ACAD ellipse function for the front end. The high point of the ellipse is set at 20% of the total wing chord (including flaps). The back section of the wing is a straight line from the hinge line tangent to the ellipse. Both my Mako Jet and my current Bearcat 617E (Yes, it is electric) airfoils have an 18% thick wing at the root and a 16% thick section at the tip. This makes the tips resonably thin for the purpose (in theory) of behaving better in the wind.
My conjecture about the ellipse front end is that as a mathematical shape, it allows the air to flow over it with a constant rate of change in the pressure gradient. I don't know if this makes any sense to some (Please Brett, PTG, Ted), but it seems to work well. It is not dissimilar to PTG's approach on earlier combat models.
The one thing beautiful is that it is very easy to make various wing ribs with high points and thickness percentages which vary from the root to the tip.
I would love to hear what you all have to say.
BTW, in the 600 inch range my Mustang 626 is 57 ounces, and the Bearcat 617 target is 55 ounces.
Pat Johnston
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« Reply #21 on: January 03, 2014, 01:18:52 PM » Reply with quoteQuote
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Pat,
Thanks for the reply! Great info.
I'd like to know what you're using for setups on those models?
I don't have a CAD airfoil program for ribs. I get it done other ways with my drawing programs, but I do get it done.
I like the look of ellyptical wings.
My root cord length is 12.375", and is 1.875" thick @ 33%. The outermost rib, actually 3.5" from the tip is .875" @ 50%.
Charles
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« Reply #22 on: January 03, 2014, 01:28:45 PM » Reply with quoteQuote
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Charles,
The frontal view of the wing is drawn showing the ribs in position. This gives you the exact thickness for each rib. The little section of line at each rib station is used as the minor chord of the ellipse. The wing planform will establish the length for each rib. I place the line for the minor chord on the 20% of the chord point, obviously with it's center on the chord line. Then the ellipse function is used to draw the front portion of the rib. A person could set the highpoint of the root at 25% of the chord and the tip could be at 16% for example. Whatever you want. I just do 20% for all. The straight line for the trailing edge is drawn tangent to the ellipse. Some more nuances in the complete process, but this is a good start.
Pat Johnston
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« Reply #23 on: January 03, 2014, 02:11:02 PM » Reply with quoteQuote
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Quote from: Pat Johnston on January 03, 2014, 12:49:50 PM
My conjecture about the ellipse front end is that as a mathematical shape, it allows the air to flow over it with a constant rate of change in the pressure gradient. I don't know if this makes any sense to some (Please Brett, PTG, Ted), but it seems to work well.
The cad program I use (LibreCAD -- what can I say, it's free) regularly spits up when I try to use ellipses. You can make a rib that's frighteningly close to an NACA 0018 section with just four splines -- one from LE center to spar, one from spar to TE, then mirror that for the bottom.
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« Reply #24 on: January 03, 2014, 02:34:28 PM » Reply with quoteQuote
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Quote from: Tim Wescott on January 03, 2014, 02:11:02 PM
The cad program I use (LibreCAD -- what can I say, it's free) regularly spits up when I try to use ellipses. You can make a rib that's frighteningly close to an NACA 0018 section with just four splines -- one from LE center to spar, one from spar to TE, then mirror that for the bottom.
Better yet, just use the NACA polynomial and fiddle with the parameters. You can match most anything. At least one world champ stunt plane had ribs done this way. Then use the formulae to generate polylines for AutoCAD. Works a treat.
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« Reply #25 on: January 03, 2014, 02:57:01 PM » Reply with quoteQuote
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Quote from: Pat Johnston on January 03, 2014, 12:49:50 PM
My conjecture about the ellipse front end is that as a mathematical shape, it allows the air to flow over it with a constant rate of change in the pressure gradient. I don't know if this makes any sense to some (Please Brett, PTG, Ted), but it seems to work well.
I don't know if the conjecture may make sense to those guys, but I don't think it would, nor can I imagine why that would be a virtue. Use JavaFoil or XFoil and look at the pressure distribution. I regret that I'm busy assembling your fine components, or I'd do it. I'm not saying your airfoils don't work well, though.
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« Reply #26 on: January 03, 2014, 02:58:39 PM » Reply with quoteQuote
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Howard,
Just to show my complete ignorance, what is a NASA 0018 airfoil. The numbers don't mean squat to me. Not like arrow shaft numbers like a 2117 is a 21/64th diameter with a .017" wall thickness. Does the NASA number have any correlation to something real that a person can wrap his mind around?
Also as a side issue, the EAA has an aerobatic plane event which uses an airfoil which is 16% thick, 20% back to the high point and straight line to the trailing edge tangent to the ellipse. Very good performer. I think you can google EAA aerobatic airfoil for more poop.
Pat Johnston
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« Reply #27 on: January 03, 2014, 03:01:15 PM » Reply with quoteQuote
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Quote from: ptg on January 02, 2014, 11:17:18 AM
I’ll chime in here with a little history re. the airfoil Brett is referring to. If you have the Diva article published in Feb. 2005 Model Aviation you will see it referred to as a ‘dynamic airfoil’ which is just a name I came up with. Way back in 1969 when I was young and better looking I began experimenting with airfoils for both combat and stunt planes. My Tyantula which was designed in ’68 and flown in competition was the inspiration for several other West Coast thin airfoil high aspect ratio designs including the Winder. Incidentally the airfoil for the Winder was actually the #7 rib from Larry Scarinzi’s Super Satan. My original Tyrantula used a standard NACA 0018 airfoil.
In ’69 I began experiment with moving the high point of the airfoil forward on my combat planes and settled on an airfoil that had its high point at 18% if the cord. The Tyrantual II published in July 1971 Model Airplane News was a derivation of that airfoil which I used on constant cord combat planes and ultimately won one of the last single elimination Nats in ’78. At the same time in ’69 I began experimenting with stunt airfoils that featured a fairly laminar foil at the root (30 – 40%) graduating to a tip where the airfoil moved forward to around 20%. Those stunt wings used the standard plan form with LE taper and straight TE. The wings seemed to generate considerably more lift with no ill effects. The only problem is it was difficult to carve a consistent set of ribs using the blank stack root/tip method of the day.
Fast forward to 1999 and Bob Hunt’s very innovative ‘Lost Foam’ building system. Suddenly here was a way to get very accurate ribs at each location and produce an airfoil that changed gradually progressing from the root to the tip. Now I could fine tune the wing to work better in the variety of flying conditions (wind, turbulence etc.). The Diva wing published in ’05 works very well in a variety of windy and turbulent conditions especially if you are using IC engines for power. Although it performed admirably better in turbulent conditions than other designs I always thought it could be improved.
Electric power was just the thing to refine the wing even farther to handle turbulence. Without getting into the great electric vs IC power debate I’ll just say there is no valid reason for me to ever power another stunt ship with an IC engine. E-power let me concentrate on designing a plane that would handle noticeably better in turbulence and wind. Starting with Elroy aspect ratios began to get lower and flying in turbulence was easier. Since Elroy there have been three airplanes. Each has the same airfoil as the ’05 Diva but with different plan forms and decreased thickness at both the root and tip. My current model TLD (the last Diva) or Miss Attitude is better in wind and turbulence by a noticeable margin. It has a low aspect ratio nominal 4.8 and a very thin airfoil nominal 15% root and 9% tip.
Finally, 2013 I rediscovered RC (yeah I know) and there will be an E-powered RC Diva in the near future.
Happy New Year
I don't know which is more alarming, a Jive Combat Team member flying RC or admitting to being less good-looking than in the past.
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« Reply #28 on: January 03, 2014, 03:27:57 PM » Reply with quoteQuote
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Quote from: Pat Johnston on January 03, 2014, 02:58:39 PM
...what is a NASA 0018 airfoil.
It's actually NACA, the precursor to NASA. The first two digits pertain to camber, which we don't use, and the last two are max airfoil thickness in % chord.
The formula for the NACA 0018 is y = (.18/.20006)(.296x1/2 - .126x - .3516x2 + .2843x3 - .1015x4 . That gives the upper surface. The lower surface is y = - the same stuff. y = distance above the centerline and x is distance along the chord from 0 to 1. You can see where the .18 goes. There are formulas you can use to generate coefficients for the powers of x from desired TE angle, max thickness position along the chord, relative LE radius, and maybe some other stuff. That's where the ribs you cut for the current national stunt champ came from.
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« Reply #29 on: January 03, 2014, 03:30:45 PM » Reply with quoteQuote
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I make a combat plane once with a parabola for the front part of the airfoil and a straight line for the back. There was a kink where they met. That plane really sucked.
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« Reply #30 on: January 03, 2014, 04:26:03 PM » Reply with quoteQuote
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No point in not adding photos.
Taken off my monitor.
Top wing outline is for the Gee Bee R3.
I did some quick checking, no pun intended, I don't think it's 600 sq's. Close, more like 580.
What you see is 30 x 12.375.
Might as well drop in the second wing I'm designing. A tad different, but still the same measurements.
The second wing is for a stunt model. This is the wing with 600 sq's.
Charles
Edited: Made a mistake.
Bottom photo is the correct stunt wing, 30 x 12.375.
Center photo is my old design at 30 x 12.675.
Don't want to mislead, gotta get it right.
The center photo wing design is history, never removed it from my drawing program. I will.
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« Last Edit: January 03, 2014, 04:53:31 PM by Avaiojet » Logged
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« Reply #31 on: January 03, 2014, 04:51:29 PM » Reply with quoteQuote
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Quote from: Howard Rush on January 03, 2014, 03:30:45 PM
I make a combat plane once with a parabola for the front part of the airfoil and a straight line for the back. There was a kink where they met. That plane really sucked.
Sharp edges anywhere seem to be the kiss of death, Mr. Kline and Mr. Fogelman notwithstanding.
Brett
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« Reply #32 on: January 03, 2014, 04:57:55 PM » Reply with quoteQuote
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Quote from: Howard Rush on January 03, 2014, 02:34:28 PM
Better yet, just use the NACA polynomial and fiddle with the parameters. You can match most anything. At least one world champ stunt plane had ribs done this way. Then use the formulae to generate polylines for AutoCAD. Works a treat.
My CAD program doesn't do that well. The splines fit to within a few thou -- you'd change the airfoil more by painting the wing than by using splines.
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I put this thread back so people could use the info they said they missed, Please use it with that in mind, and not to start controversy Randy
Topic: The 600 thread (Read 1894 times)