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Author Topic: Flat Wing P-30  (Read 3277 times)
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calgoddard
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« on: June 07, 2020, 02:52:11 PM »

I am a member of the San Diego Orbiteers free flight club.  That club was responsible for originating the P-30 event in the late 1970’s. I have seven (7) built P-30 models and two (2) un-built P-30 kits.  My P-30 models range from John Oldenkamp’s low-tech HOT BOX P-30 to Burdov’s high-tech Pirate P-30. Obviously, I like the P-30 class.

Tomorrow marks the beginning of my fourth month of stay-at-home. I have started to build a different P-30 wing just for fun.  I want it to incorporate a design that looks different, is relatively easy to build, resists warping, and hopefully provides good performance. My plan is to use it as a substitute for the existing wing of my Air Shark P-30.  The wing of that model has a large 5-inch chord and a difficult geodetic rib construction.  It has dihedral wing tip sections.  The ribs of my Air Shark wing have under camber.  I am attaching a picture of my Air Shark P-30 which is an excellent flier, particularly in the glide.  I fly it with a 10 x 1/16-inch rubber motor that weighs 9.8 grams prior to lubing.

The Air Shark P-30 was designed by Stan Buddenbohm and has been around since at least the early 1990’s. Most people know Stan as a world class designer and flier of HLG and CLG models.  However, he has flown rubber powered models for many years and is pretty much unbeatable in any class of rubber powered models that he flies.  However, I have not seen him fly F1B models.

I have never seen a P-30 wing that is flat with vertical tip plates.  DerekMc please confirm that you are not aware of a P-30 with such a wing configuration. As pretty much everyone in our hobby knows, tip plates provide effective dihedral that gives roll stability.  I have used them with great success in my indoor LLP and A-6 models where they greatly simplify wing construction. My plan is to use the NACA 6409 airfoil in my P-30 “flat wing” to hopefully get a floaty glide.  This airfoil has a slight under camber.  My outdoor flat wing will have a 5-inch chord and will use carbon fiber (CF) composite tube for the wing spar as is common practice in modern F1G models and some P-30 models like Berdov’s Pirate.  I plan to cover my P-30 flat wing with ¼-mil Mylar film or MicroLite film.  The ribs, leading edge, and trailing edge of the flat wing will be made of balsa wood. I am just planning to use my Air Shark fuselage, prop assembly and tail feathers as a convenient test bed for my P-30 flat wing.

I understand that the use of a carbon fiber spar will provide torsional stability and resist wing warping. Therefore, I can use simple parallel ribs made of 1/16-inch sheet balsa wood and avoid the complex geodetic rib wing construction of my Air Shark wing.  I plan to include false ribs, i.e. short “partial” ribs that extend in parallel fashion from the leading edge to the spar, between the full-size ribs.  During construction I will shim the rear wing tips to provide about 1/8-inch of wash-out to improve roll stability and impede any tendency for the model to spiral into the ground if upset by turbulence. The tip plates will be made of light 1/16-inch sheet balsa wood.

The current wing on my Air Shark P-30 weighs 16.97 grams.  The wing of my Pirate P-30 weighs only 11.52 grams, but it has a much narrower chord yielding a much higher aspect ratio than my current Air Shark wing.  I’d like my P-30 flat wing to weigh somewhere between these two sample weights. I want my modified Air Shark P-30 to have a weight near the 40-gram minimum allowed under the P-30 rules followed in the United States.
 
I am wondering if I should cap the tops of the full-size balsa wood ribs with CF material?  If so, what CF material?  With this capped construction the ribs could be made of 6# density balsa wood.  More specifically, what CF material should I purchase from www.cstsales.com? I assume it should be very lightweight unidirectional CF material.  Do I just cut it to length and width and glue it to the top edges of the full-size ribs with CA? How do I keep the un-woven fibers together when cutting and prior to gluing?

I don’t know how to build a D-box wing such as that used in Don DeLoach’s Polecat MK. X P-30. That’s a challenge for some future P-30 project.

There are some who post on HPA that feel very strongly that since P-30 is a beginner’s class, that construction of P-30s should be kept simple to stay true to the spirit of the rules.  But I sometimes compete against world class fliers like Stan Buddenbohm, Don DeLoach and Clint Brooks. You need a strong P-30 with a good design that is well-trimmed and near minimum weight in order to have any chance of getting into a fly-off with these fliers.  They are masters at picking good air.  In addition, I know that Stan winds to very high torque. Don and Clint probably do the same.  I am not yet to the point of including VIT into a P-30 as these world class fliers don’t do that.  However, Tapio Linkosalo has indicated that I may gain an advantage by keeping the stab at zero degrees incidence for the first four seconds after launch. Maybe someday I will experiment with VIT on a P-30 but I would need a good, lightweight timer that can activate both the VIT and the DT in a consistent and reliable manner.

I apologize in advance if I have offended any of the P-30 purists.  In their defense, I admit that flying a simple P-30 model, I did win the very first P-30 contest I entered.  In that contest I flew my rudimentary Square Eagle P-30 against very experienced P-30 competitors.  It seems to me that there is room for both types of P-30 enthusiasts in our hobby - those who like simple models and those who want to take advantage of high-tech materials and more advanced mechanisms.  A P-30 constructed with carbon fiber and plastic film is stronger and less prone to warping than a stick and tissue P-30.  I do like the appearance and nostalgia of the latter type of P-30 which can still be very competitive in the right hands.

Your thoughts and comments would be appreciated.
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Flat Wing P-30
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TimWescott
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« Reply #1 on: June 07, 2020, 03:18:12 PM »

... As pretty much everyone in our hobby knows, tip plates provide effective dihedral that gives roll stability.  I have used them with great success in my indoor LLP and A-6 models where they greatly simplify wing construction.

Not me, and I've been flying for about 40 years.  But my rank in FF is "piker".  Are you sure this isn't just something that only applies to super-low Reynolds numbers, like indoor?

... My outdoor flat wing will have a 5-inch chord and will use carbon fiber (CF) composite tube for the wing spar as is common practice in modern F1G models and some P-30 models like Berdov’s Pirate. ... I plan to cover my P-30 flat wing with ¼-mil Mylar film or MicroLite film.

That sounds like a lot more added complication than anything you're subtracting by having a dead flat wing, particularly because you're signing up to those big tip plates.

I'll be interested in seeing how it all works out, particularly if your tip plates = dihedral notion works at P-30 Reynolds numbers.
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RalphS
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« Reply #2 on: June 07, 2020, 03:58:46 PM »

Geat class, like Coupes.  Simple and easy to experiment.  I would be worried that the large upright tip plates would easily break off in bad/windy landings but, on the other hand, easy to try.

Just one more thing - why P30?  I understand the 30, being the dimensions, but what is the meaning of the "P"? 
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flydean1
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« Reply #3 on: June 07, 2020, 04:13:50 PM »

Ralph, the "P" stands for the plastic prop.

Someone on this Forum has built an end plate flat wing P30.  Hopefully he will chime in.

Darcy Whyte's beginner model called "Squirrel" has a flat wing with end plates.  I think his web site is called "Endless Lift" or something like that.
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flydean1
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« Reply #4 on: June 07, 2020, 04:38:13 PM »

I knew I had it somewhere.  The builder was Ding Zuarte from somewhere on the West Coast.  We corresponded briefly via PM on the Forum.  At the time (2012) he was actively flying it in his club's monthly meets.  It flew OK, but could not recover from a death spiral which occurred after a major upset.  The wing was flat except for some washin on the left tip.
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DerekMc
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« Reply #5 on: June 07, 2020, 05:16:08 PM »

Calgoddard, I haven't seen a plan for a P30 wing like what you are describing. I look forward to flight reports! 
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Derek
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« Reply #6 on: June 07, 2020, 06:34:18 PM »

Went back to the correspondence.  Ding was flying with a club in the Sacramento area.  Searched the Endless Lift site.  No picture of the P30.
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randoloid
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« Reply #7 on: June 07, 2020, 08:42:03 PM »

I too will be following and hope to hear progress reports. 


I'm fairly new the the hobby and have only built three P-30's. The first two were Majestyk's by Thom Greenhalge. My first flew OOS due to a fuse malfunction on a test flight before my first planned competition. The second actually made it there... I dearly love that plane.

My second build is the above mentioned Don DeLoach Polecat X.  I chose it because I was attracted by the wing construction and the use of carbon caps. 

Quote
I am wondering if I should cap the tops of the full-size balsa wood ribs with CF material?  If so, what CF material?


The carbon is 1/16 strips 36"L. I purchased mine from Mike Woodhouse also the short kit of the Polecat as well as Mylar.  Don's wing construction is super rigid and the carbon caps add a lot of strength and rigidity with very little weight. While I could have built it lighter, I'm very pleased with the all up weight of around 51g.  I have just finished the build and only glided the model but hope to log powered flights very soon.

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lincoln
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« Reply #8 on: June 07, 2020, 11:38:38 PM »

I think pre cured, unidirectional carbon fiber laminates would be the right thing for reinforcing the ribs. I suspect that the .005" thickness that CST sells is overkill. This stuff is easily stripped with a knife, but watch out for splinters any time you are handling it.

A carbon tube is far from the lightest way to add torsional stiffness to a wing. Fiber orientation is important. If all the fibers run parallel to the axis, it won't be very stiff. The lightest way may be carbon capped diagonal ribs. However, there may be some kind of covering that will also do a good job, assuming it doesn't shrink so hard it bends the leading and trailing edges or crush the ribs.
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Tapio Linkosalo
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« Reply #9 on: June 08, 2020, 12:31:42 AM »


I do my carbon capped ribs (for larger FAI model tailplanes and E-36) by carving a rib block from balsa, laminating uni-directional carbon over it and then cutting the individual ribs out of the block with a miniature tabletop circular saw and a diamond cutting disk. Not for P-30 though, for that I use conventional ribs and only a short length of carbon capping at the trailing edge, to strengthen that thin and weak part, and to solidly glue the carbon strip trailing edge to the wing (too little surface area to glue to balsa rib only).

For spars, the russian thin-walled non-tapering carbon tubes (if I understand correctly made by Burdov, I buy then from Mike Woodouse in the UK) make superior spars. 5.5mm diameter for the center sections and 3.5mm for the tips. No more weight than balsa spars, and super solid and stiff wings. Much recommended.

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lincoln
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« Reply #10 on: June 08, 2020, 01:52:13 AM »

BTW, the 6409 isn't so great for small, light models. If we can trust Profili, which uses Xfoil, you can do slightly better with a Neelmeyer airfoil, which is also about 9 percent thick, but flat bottomed, which would make it easier to build. This is based on a Reynods number of 30,000/sqrrtCl and a turbulator at 40 percent. If you want to get fancy, there are free flight airfoils which will perform somewhat better, with higher maximum lift and lower profile drag. They'll be a little harder to build, though. The Archer A-18 doesn't look too bad. However, with an open structure wing, you will only get the nominal Cl at the ribs, with an infinite number of other airfoils in between. A moderate Jedelsky airfoil doesn't have this problem, though I don't know if one could be made light enough unless you used foam, and in that case you could just hot wire a suitable section. At least Profili likes it. An advantage of the 6409 and the Jedelsky is that they develop a lot of drag at low lift coefficients. Maybe, particularly in P-30, they could be dethermalized with down elevator? I suppose with a lot of down elevator, the model would try to fly inverted, which might come down even faster, though it would probably flop around. Anyone ever experiment with this?
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lincoln
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« Reply #11 on: June 08, 2020, 01:58:12 AM »

Here's a rough picture of the Jedelsky airfoil I analyzed, plus a picture of the Neelmeyer, if I can find it.
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Re: Flat Wing P-30
Re: Flat Wing P-30
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TimWescott
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« Reply #12 on: June 08, 2020, 11:03:55 AM »

... However, with an open structure wing, you will only get the nominal Cl at the ribs, with an infinite number of other airfoils in between. ...

There's a couple of Selig airfoils that are designed for this -- i.e., the published airfoil is a rib pattern, with sag expected between ribs.  The calculations and measurements are then done taking this into account. 

But I think they're for RC gliders; this would mean that the design Reynolds number would be at least 10 times greater.
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cvasecuk
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« Reply #13 on: June 08, 2020, 11:40:09 AM »

  But I sometimes compete against world class fliers like Stan Buddenbohm, Don DeLoach and Clint Brooks. ......  They are masters at picking good air. 
Surely that is the most important part of flying P30's!
Ron
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lincoln
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« Reply #14 on: June 08, 2020, 02:42:05 PM »

... However, with an open structure wing, you will only get the nominal airfoil at the ribs, with an infinite number of other airfoils in between. ...

There's a couple of Selig airfoils that are designed for this -- i.e., the published airfoil is a rib pattern, with sag expected between ribs.  The calculations and measurements are then done taking this into account. 

But I think they're for RC gliders; this would mean that the design Reynolds number would be at least 10 times greater.
I knew that there had been a couple of Drela airfoils that had flat segments behind the d-tube, but I hadn't heard of Selig airfoils that take sag into account. Do you remember,the names or a link? DJ Aerotech designs are supposed to account for sag, but they're proprietary and probably don't have enough camber for a P-30.

RC glider Reynolds numbers aren't all that much higher, except for slope soaring and dynamic,soaring. The latter can be so fast that the Mach number matters. The wing tip of a 1.5 meter glider in slow flight might have a Reynolds number of 60,000, but it would be much higher during a launch. I guess a big glider might have double that. Center sections will be somewhat higher.
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TimWescott
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« Reply #15 on: June 09, 2020, 12:14:14 PM »

... However, with an open structure wing, you will only get the nominal airfoil at the ribs, with an infinite number of other airfoils in between. ...

There's a couple of Selig airfoils that are designed for this -- i.e., the published airfoil is a rib pattern, with sag expected between ribs.  The calculations and measurements are then done taking this into account. 

But I think they're for RC gliders; this would mean that the design Reynolds number would be at least 10 times greater.
I knew that there had been a couple of Drela airfoils that had flat segments behind the d-tube, but I hadn't heard of Selig airfoils that take sag into account. Do you remember,the names or a link? DJ Aerotech designs are supposed to account for sag, but they're proprietary and probably don't have enough camber for a P-30.

RC glider Reynolds numbers aren't all that much higher, except for slope soaring and dynamic,soaring. The latter can be so fast that the Mach number matters. The wing tip of a 1.5 meter glider in slow flight might have a Reynolds number of 60,000, but it would be much higher during a launch. I guess a big glider might have double that. Center sections will be somewhat higher.


Gaa!  I just looked, and I think I was wrong -- Selig does mention sagging in a couple of articles, but only to the extent that "oh, it's not much".
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calgoddard
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« Reply #16 on: June 10, 2020, 08:44:50 PM »

Thanks everyone for your input.

In theory, tip plates on the wing should reduce wing tip vortices and drag. I am attaching a picture of a Science Olympiad Wright Stuff airplane with vertical tip plates (red in color) in case someone is not familiar with this type of wing configuration.

Tip plates of suitable size on the “flat wing” of a P-30 should effectively impart enough dihedral to yield sufficient lateral (roll) stability, during the climb, cruise and glide portions of its flight. Roll stability would be enhanced if 1/8-inch wash-out were incorporated into the wing tips.

The tip plates should extend from the LE to the TE of the wing, have a curved LE, and probably have a height of about ½ to ¾ of the wing chord.

It’s not likely that 1/16-inch sheet balsa wood tip plates on a P-30 wing would be damaged on landing, but they could be easily replaced if this happens.
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Re: Flat Wing P-30
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calgoddard
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« Reply #17 on: June 10, 2020, 08:46:13 PM »

In recently reviewing the 2010 P-30 Summary published by Free Flight Quarterly (FFQ), I have so far not come across a “flat wing” P-30, i.e. one with a having tip plates instead of angled wing sections. Someone on this thread questioned whether tip plates will work with outdoor models since the wings have higher Reynolds numbers than those of indoor duration models like Limited Penny Planes. 

The Big Cat Embryo that is sold in kit form by Volare Products has vertical tip plates and is an excellent flier. See the attached picture of the Big Cat Embryo. This Embryo model probably flies in a speed range comparable to that of a P-30. I guess I will eventually find out through experimentation whether tip plates work on a P-30 wing. 
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Re: Flat Wing P-30
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calgoddard
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« Reply #18 on: June 10, 2020, 08:47:50 PM »

After scanning through the 2010 P-30 Summary published by FFQ, I have come to the realization that it is very unlikely that any P-30 design I might conceive and perfect would give me any advantage in a contest over the best of the proven designs like the Air Shark,  Polecat MK X, Pirate, and Boomer  MK III. Therefore, I have decided to shift my focus and try to develop a simple P-30 design for the beginner.  

A tissue-covered flat wing with no under camber in the ribs, and with sheet balsa wood tip plates instead of angled wing sections might be the simplest wing to construct for a P-30. It could be married with a balsa wood sheet-sided box fuselage, a flat stick and tissue stab, and a sheet balsa wood fin. Much of the fuselage could have large oval-shaped laser cut-outs to reduce weight and it could be covered with tissue to impart increased torsional stiffness (and color).  The edges of the sheet balsa wood sides could have laser cut interlocking tabs for ease of assembly and to ensure squareness and straightness of the completed box fuselage.  The holes for the motor peg could be located to provide a 19-inch hook-to-peg distance, which is the length of an unbraided conventional 6 x 1/8-inch 9.8-gram rubber motor made of Tan Super Sport rubber.

While I am a big fan of the Gizmo Geezer prop assembly, its installation, adjustment and clutch operation are probably a bit much for a novice.  I might include a simple thrust line adjustment mechanism similar to the single plastic screw design used by John McGrath in his Rocket Man P-20 kit. Perhaps laser cutting the front ends of the fuselage sides to provide 5 degrees of down thrust and 2 degrees of right thrust would be satisfactory, along with instructions to add shims for fine tuning.
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calgoddard
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« Reply #19 on: June 10, 2020, 08:48:54 PM »

My beginner’s P-30 could include a flat wing frame measuring 29 ¾-inches x 4 1/8-inches to yield a wing area within the 120 - 124 square inch wing area sweet spot recommended by P-30 legend John Oldenkamp. These dimensions result in an aspect ratio of 7.2 to 1. The 1/16-inch sheet balsa wood vertical tip plates would be glued to the outer sides of the outermost wing ribs.

I would test stability of my beginner’s P-30 without any wash-out because building in wash-out, or warping it in after construction, may be too much of a challenge for many beginners.  If necessary, I could try adding simple balsa wood wedges or Gurney flaps to simulate wash-out. I would recommend trimming my beginner’s P-30 to fly in a right-right flight pattern due to the forces generated by the free-wheeling plastic prop during the glide. A wedge glued to the underside of the TE of the right inner portion of the wing to simulate wash-in might therefore be beneficial.

A DT would not be included in my beginner’s P-30 design as it would be too complex for beginners to install and rig.  At a projected 45-50 grams (without the rubber motor), a DT would not be necessary for recovering the model unless it encountered a boomer thermal. If the model were to fly away in a boomer thermal, and not be recovered, a replacement could be quickly assembled.
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calgoddard
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« Reply #20 on: June 10, 2020, 08:49:46 PM »

If test flights validate the design of my beginner’s P-30, then I would offer the design free of charge to a friend who is in the business of making and selling laser-cut kits. Hopefully it would spur participation in the free flight hobby. I am thinking of calling my beginner’s model the THREE NITE P-30. This same suggests that a novice could construct my beginner’s P-30 in three evenings.

Thanks for reading my last five posts.  I am interested in your feedback.
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flydean1
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« Reply #21 on: June 10, 2020, 09:08:27 PM »

I agree with everything except the lack of a DT.  Nothing would turn off today's kids like putting in all the effort and seeing it fly away.  It doesn't take a boomer to grab even a 55 - 60 gram P30.  A simple viscous damper is easy to set up and operate.  An instructional video on a DVD included would be helpful.
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lincoln
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« Reply #22 on: June 10, 2020, 09:42:37 PM »

Sounds like it would work. I haven't seen stick fuselage P-30's, with the rubber outside, with the exception of a design called Lazybones, which also has sheet balsa flying surfaces. Is there a reason such fuselages won't work? I've been thinking of building an Easy Built Ritz for P-30.
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flydean1
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« Reply #23 on: June 10, 2020, 10:18:29 PM »

There's nothing in the rules outlawing an external rubber motor.  Probably torsional and possibly bending stiffness with a wound motor might be the issue.  It would greatly simplify the model. 

A "T" section fuselage would be simple to make, especially with interlocking tabs, and may address the torsion and bending stress.

The DT could be of the pop-up wing variety which would eliminate running a DT line back to the tail and routing it to avoid snags.

Another consideration on the flat wing concept:  Walt Mooney published a Ford Flivver peanut which was a low wing with zero dihedral.  He added a post forward of the cockpit which went vertically several inches and sported a large American Flag made of 1/16 sheet.  It flew very well according to Walt and several others outdoors as well as indoors.
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« Reply #24 on: June 10, 2020, 10:39:31 PM »

I have seen a paper bag and a P-30 wing get carried up from the ground by a dust devil. Once made 3 landing attempts witn an unpowered RC glider in a dust devil. Dust devils can be thought of as extreme thermals. If a DT were provided, some thought to make it as easy as possible to use.

Torsional stiffness might be enhanced by a spiral wrap of fiberglass or carbon tow. Just one or two tows, or maybe high tech fishing line. The latter wouldn't be stiff in compression, so at least one wrap in each direction would be required. An enclosd box would be much stiffer than a tee unless it was spiral wrapped with something.
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