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2015 Design Contest - Airrow Two

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2015 Design Contest - Airrow Two

Old 08-24-2015, 08:32 AM
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Okay - so I asked trusted source to refresh my memory about what was so great about the 23012 and confirmed that it has the good balance of low and high speed performance as well as what I couldn't remember - a low induced drag and low pitching moment. Never knew or even cared what that meant in the past so I asked and got an explanation of what pitching moment is. I'm still learnin' stuff so that's cool and fun too.

Many years ago I struck the #2 pylon with my GLH; it had the original built-up wing. The fuse survived so I built another wing - same planform and root rib but now I thinned the wing out to the tip to about half thickness. In other words the wing is still a swept constant chord wing but it has a tapering airfoil thickness. Since it worked and didn't show any nasty tendencies, I perhaps foolishly thought from then on that airfoil design was of little concern. It was faster than other GLH's but still couldn't keep up with the Undertakers and Hunton Taperwings so I was humbled in that regard...
Old 08-24-2015, 01:14 PM
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Originally Posted by H5606
Okay - so I asked trusted source to refresh my memory about what was so great about the 23012 and confirmed that it has the good balance of low and high speed performance as well as what I couldn't remember .......................... Since it worked and didn't show any nasty tendencies, I perhaps foolishly thought from then on that airfoil design was of little concern. It was faster than other GLH's but still couldn't keep up with the Undertakers and Hunton Taperwings so I was humbled in that regard...
These relatively heavy pylon racers don't fall within my qualifying statement about the importance of airfoil design VS wing loading.
That said, the course record at a local club that has been racing 16 to 20 ounce 1/2 A since before I got into this hobby is still held by a GLH that has the allowed thickness reduction from mid span to the tips.

Last edited by combatpigg; 08-24-2015 at 01:19 PM.
Old 08-25-2015, 06:34 AM
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And they're still racing to this day? Gee, you guys know how to have fun. I'm encountering club members now who act like they've never heard of or seen .049s.
Old 08-25-2015, 06:51 AM
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Originally Posted by combatpigg
I built and flew dozens of 1/2 A RC combat wings that were all identical except for the airfoils.
36" x 7" and 12 ozs or so when new.
We flew hundreds of "combat hours" over a period of several years using identical power [AP .061s].
Flying side by side, rubbing wing tips, chasing through the maneuvers....
None of the airfoils we used were thin [for strength reasons they were about 14% or more] but we tried flat bottom, semi sym, full sym and variations of each type. We finally settled on flat bottom, since they were the easiest to build and keep trimmed after repairs.
Flying combat gave us a unique opportunity to do side by side comparisons during the dozens of all day sessions we had when there was a small group involved with this. There just weren't any clear cut advantages noted in performance other than the model's weight, or how many times it had been repaired.
In the case of the Contest Plane we're talking about here, I think you could build a few different symmetrical or semi-sym airfoil sections with the same thickness and I would challenge you to tell me which NACA number you were flying with this 10 - 12 oz plane.
I don't disagree or challenge this. But you are talking about 7oz/sq ft wing loadings where a radiused flat plate would almost do the job - this is the extreme end of the (outdoor) RC wing loading spectrum, where there will not be dramatic difference between many examples. But.. I have experienced, first hand, remarkable differences in the performance of similar scratch built models using different airfoils - specifically huge improvements by using suitably chosen, computer plotted airfoils. These are at more conventional wing loadings where the properties and efficiency of the airfoil selection are more significant. I recall the most dramatic change was a small glider design, 5.5x36 wing IIRC, I went from a flat bottom with rounded nose Gentle Lady/generic glider airfoil to a plotted good old Clark Y (a real Clark Y not what people tend to call Clark Y). The difference in penetration, energy retention, glide slope, everything, was huge. Never forgot that lesson.
Old 08-30-2015, 09:07 AM
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Yesterday, I threw everything I could think of that would go into the airplane on the scale and became highly distraught that I was already at 12 oz and that's w/o wing, some more sheeting, pushrods, hardware, covering, etc. So, I weighed the original's foam wing (1st pic) to see where I'm headed. I'll shoot for 18 oz in the hopes I'll be pleasantly surprised to hit 16? Maybe I won't even break 20 at this point but I figure I've got to at least be able to beat the prototype weight (unknown). Just holding the fuse with all the stuff in it felt hefty and gave me cold feet on wing area so I upped it a couple inches each side to bring the wing area back above 200 sq" (2nd pic).

Last pic shows Ace foam wing tracing at top, oh and BTW, I exaggerated in a previous post - found templates for my GLH - airfoil thickness was only reduced by about a third at the tip. Bottom is current airfoil templates prior to fabricating ribs.
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Last edited by H5606; 08-30-2015 at 02:58 PM.
Old 08-30-2015, 10:15 AM
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1st pic - fixture of root and tip templates with 1/16" balsa blanks screwed between prior to shaping. 2nd pic - shaped ribs in fixture. 3rd pic - half done with rib fabrication. Last pic is layout prior to wing fabrication.

Just for my info and for future ref: span is 38"; avg chord is 5.5" Aspect ratio = span/avg chord so in this case 38"/5.5 = 6.9
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Old 08-30-2015, 11:37 AM
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Looking great and stats are always a good idea you will have all the data on tap should anyone or yourself want to build another.
Airfoil looks good and should reduce stress on engines at cruising speed. Are you going to exhaust throttle one of the engines or both
Old 08-30-2015, 03:00 PM
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My intention was to make the airplane 2 channel - 2 ail servos and 1 elev servo; no plans to do so but I'd be interested to hear other benefits to throttle than what I'm thinking. Hoping it will track well w/o rudder and judicious use of differential throw on ail if it flies... As of now, the airplane will be incapable of ROG's due to the short landing gear - i.e. prop arcs don't clear ground.

Last edited by H5606; 08-31-2015 at 03:03 AM.
Old 08-30-2015, 04:00 PM
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Originally Posted by H5606
Yesterday, I threw everything I could think of that would go into the airplane on the scale and became highly distraught that I was already at 12 oz and that's w/o wing, some more sheeting, pushrods, hardware, covering, etc. So, I weighed the original's foam wing (1st pic) to see where I'm headed. I'll shoot for 18 oz in the hopes I'll be pleasantly surprised to hit 16? Maybe I won't even break 20 at this point but I figure I've got to at least be able to beat the prototype weight (unknown). Just holding the fuse with all the stuff in it felt hefty and gave me cold feet on wing area so I upped it a couple inches each side to bring the wing area back above 200 sq" (2nd pic).

Last pic shows Ace foam wing tracing at top, oh and BTW, I exaggerated in a previous post - found templates for my GLH - airfoil thickness was only reduced by about a third at the tip. Bottom is current airfoil templates prior to fabricating ribs.
Well, if you think of it as 9-10 oz per engine it doesn't sound so bad. I'm real curious about how potential top speed would compare between a tandem and conventional twin. I figure you have the fuselage frontal area of a single engine with ~ twice the available thrust, Kinda like an inline twin .098 with a 4 blade prop without the inefficiencies of the extra blades. Or whatever.. anyway, I think there must be a performance advantage at least in theory.
Old 09-07-2015, 04:30 PM
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Was lazy and resorted to traditional and familiar methods of wing construction except that wing is built upside down; didn't pay close attention to leading edge contact while I was partially into gluing and got sloppy a ways into it - had to pull ribs off TE and reposition to maintain desired chord length... Don't know how to tackle shear webbing at this point - wondering if I can fit between ribs, leave proud and sand off before installing bottom caps.
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Old 09-07-2015, 08:04 PM
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Looking great H5606,
For spar webs, I would fit 1/8th inner third, 1/16th to 2/3d the span, and none outer third. Making spars into I-beams works great.
Glue in before/while adding the top, err, I mean bottom spar in your case !

I was thinking about starting the thing up... then launching...
Start the rear engine first, so it runs out of fuel before the front one?

Wonderful Project !

Thanks for sharing with us...

Cheers,
Dave'crosscheck'Fallowfield
Maac 6437
Unabashed Combat Team
Old 09-23-2015, 05:13 PM
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Aileron detail, sanding with tape to protect ribs, added TE sheeting to bottom, filing a piece of 3/16" brass tubing to make a hole saw to create hole for LE dowel pin, added false rib doublers to center rib. Made some really dumb mistakes; I've been told I tend to do things the hard way and true to form, that's what I did - I could have brought the fwd sheeting over the LE but I decided to butt it and hence had no support between ribs depending only on a 1/16" butt glue joint. Should have had a "false" LE and added the LE after sheeting... It was painful but I fit small pieces of wood to the LE between ribs to try to get some support back for the sheeting since I already had the sheeting cut to width. Another dumb one is cutting the ailerons out chordwise rather than normal to the TE - I don't know yet if there will be an interference problem with aileron operation. Also forgot hard points in TE for mounting hardware. Also kind o' forgot or was too lazy to install a carry thru spar/dihedral brace - hoping glassing center section will take care of it. Dreaded task: sheeting LE is next.
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Last edited by H5606; 09-23-2015 at 05:24 PM.
Old 09-30-2015, 05:04 PM
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Sheeting of bottom and top. Had a couple beers to take the edge off and decided [after all] to finagle a 1/16" ply carry-through piece in the center section. This event turned into a crisis with lots of cursing and cracking of adjacent ribs with more of an edge put on. Poor wife didn't know why I was in a bad mood when I came upstairs for dinner. Shaped some end-grain balsa block pieces and fit them into the TE to back up wing mounting screws. Added wing tips (tri-stock).
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Old 09-30-2015, 06:15 PM
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Scratch building is 10% inspiration and 90% perspiration.
Old 10-04-2015, 05:16 PM
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Center section, tip detail - including addition of sheeting fwd of ail area, and shaping LE. Cap stripping, aileron servo installation, and sanding up next. Its a shame I didn't weigh or check wood closely for construction and have a heavier left side - you can see L&R LE grains/densities are different...
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Last edited by H5606; 10-04-2015 at 05:29 PM.
Old 10-04-2015, 06:37 PM
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Nice work really clean assembly so far and great effort getting it all down with photos.
Old 10-05-2015, 07:59 AM
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Originally Posted by Pond Skipper
Nice work really clean assembly so far and great effort getting it all down with photos.
In another thread, you posted a picture of what I believe was a Tee Dee that was modified to a marine powerplant. Did you fabricate the additions? If so, how did you make the muffler and water jacket?
Old 10-11-2015, 06:28 PM
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Finished cap stripping, servo bay sheeting, and shaping LE - called the wing construction complete at this point and moved on to more interesting stuff for me... Weighed the wing and servos but am not impressed by wing build weight at this point compared to the Ace wing shown previously - of course it does have two servos in it though.

Started at the nose to begin integrating tank and a removable 1/16" balsa subfloor with longitudinal stiffeners on the side not visible for the Rx batt. Fwd belly cut out for radio/tank access hatch as well. (I think I had the batt below the tank on the original which may not have been optimal.)
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Last edited by H5606; 10-11-2015 at 06:41 PM.
Old 10-11-2015, 06:32 PM
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The wing saddle was originally cut to accept the Ace wing, so I had to add back material to the fwd portion; 3M77 was used to adhere 80 grit paper to the bottom cntr section and the wing was used as a sanding block in a span-wise motion to make a nice wing to fuse union. Progress is checked with a leveled fuse and surface gauge comparing LE to TE.
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Old 10-11-2015, 06:51 PM
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Using the wing as your sanding block did a real nice job..!
Old 10-13-2015, 04:57 PM
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Piled lots of components into fuse and checked rough CG and was pleased to see that the diet aft seems to be doing some good. Thanks to all for the weight saving tank feature. One pic shows the heavy hub and a .45 Caliber lead slug I had on the nose of the original foam-wing equipped prototype to offset a heavy tail; hoping I can omit these on this one. Detail shots of the interior nose compartment and an assembled shot. FWIW, airplane as equipped in last pic with nose down on scale reads 11 and 7/8 oz...
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Last edited by H5606; 10-13-2015 at 05:18 PM.
Old 10-13-2015, 05:13 PM
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Nice workmanship!
Old 10-13-2015, 06:02 PM
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Lovely craftsmanship and design execution.

Look forward to seeing it flying in the blue skies. The landing skids are a nice touch,
what sort of landing zone are you working with cut grass or pavement?
Old 10-14-2015, 03:32 AM
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The local club I belong to is a grass field; original in video stills (post #31) seemed to do alright landing on a grass runway in FL.
Old 10-17-2015, 03:13 PM
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Paranoia with personal info and the internet in generating an account was painful but my wife helped me out - bless her heart. I couldn't come up with an easy way to convert VHS to digital vid so I used a low tech solution... Set up video camera in front of TV screen and recorded VHS tape playing through player/TV; not sure if the narration helps or hinders this 6.5 min video of the original from last century.

https://youtu.be/VWuf7r3-uyc

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