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Author Topic: SO Wright Stuff 2022  (Read 585 times)
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Little-Acorn
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« on: September 11, 2021, 05:40:36 PM »

2022 rules just came out a few days ago, here's a fairly generic design built to conform to them. Flies OK, though I'm sure it can do better.

Adapted the big wing tip fins from an earlier design to avoid going around in ever-tightening circles, they seem to work. The T pin in the nose is to bring the plane (without rubber motor) up to 8 grams. Might substitute a square-aluminum motor mount so we can bend in some right thrust, downthrust etc., that proved handy a few years ago.

Got a 50-second flight out of it outdoors this morning, better than nothing. When the motor runs down, though, it glides like a brick, maybe because of those huge prop blades (24cm Ikara) hanging out in the breeze. Smaller propellers tend to be less efficient, but I wonder if a longer climb and slower, flatter glide would make up for it. In 2018 my students (Div. B) were breaking 2 minutes with a 15cm Ikara with slightly clipped tips. Lots of experimenting still to be done.
Attached files Thumbnail(s):
SO Wright Stuff 2022
SO Wright Stuff 2022
SO Wright Stuff 2022
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Olbill
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« Reply #1 on: September 11, 2021, 06:37:11 PM »

They're not supposed to glide.
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ceandra
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« Reply #2 on: September 18, 2021, 12:51:05 PM »

My teams built yesterday. High school completed "Harold", which came in at 4.135g. This is less than ideal, as nearly 4g of ballast does no good. I may have them remake the MS/TB assembly with larger cross sections for robustness. MS is stiff enough, but TB is probably a bit thin at 1/16" 8# wood, 3/8 tall tapering to 3/16". Fine for lighter classes, but too weak for the rough handling of SO.

EWS got about halfway done, same design, lighter MS, so it too will likely be under weight.

Hoping to get a gym in October for a test session.

Chuck
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Little-Acorn
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« Reply #3 on: September 18, 2021, 09:02:29 PM »

Great, Chuck. What size motor and prop are you using for the Wright Stuff plane? And same question for the Electric Wright Stuff plane.

Got any pictures?

Our school district is getting sticky about SO using ANY classrooms or gyms for students to gather outside actual school hours, due to Covid. So I cancelled the scheduled Fun Fly with the students, went to the gym alone last night. No meetings or build sessions with students so far.  Angry

https://youtu.be/2-qt2zCyfas - Electric Wright Stuff canard

https://youtu.be/mnJZTXzz0uI - Wright Stuff tractor, 15cm prop

https://youtu.be/UaJnoCXbhIc - Wright Stuff tractor, 24cm prop

Pretty low flying times so far. But the season is young. Lots of work  and learning needed - and not just by the students. Undecided


« Last Edit: September 18, 2021, 09:26:30 PM by Little-Acorn » Logged
ceandra
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« Reply #4 on: September 19, 2021, 06:42:21 PM »

I probably won't be showing the student's design, but it is similar to prior years, sort of like a Gowen Carbon Penny. Prop is 24cm flaring wood prop formed on a printed prop block. We always use the max sized prop (except in 2019, there was no max, had to optimize). Motor will be 1.5g, though since we have not flown yet i do not know the length. Probably in the range of 0.050g/in (Oops, cannot use those units this year), +/- 0.010 g/in (That is a Wag).

For EWS we have several 6mm-class motors from micronwings, and a plethora of props to try. All pre-cast nylon props also from micronwings, ranging from 30mm to 60mm diameter. Will have to make a very small pitch gage to adjust pitch to optimize flight times. Later in the season we may try making some props, but at this point that is not on the table.

Div B has one experienced kid (flies F1D and LPP), and two completely new kids, so it is a juggling act to keep all engaged. Made the mistake of having all 6 (3 in each div) at once, it was too much with the rank beginners. Building is in my house, with homeschooled kids, so no restrictions. Looks like we may be able to fly starting Oct 1 in a church gym that we rent. But with Worlds on for December, we will probably have to take a break until after Worlds, after we get 1-2 flying sessions.

Chuck
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Little-Acorn
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« Reply #5 on: September 21, 2021, 01:37:36 PM »

Looks good, Chuck. Are you making the flaring prop yourself? I hadn't heard of any commercially available wooden ones. Haven't had much luck with making my own props myself, except maybe for those helicopter rotors last summer. Let us know some flying times when ready, OK?

I'm using a standard 24cm Ikara prop so far, also got some 24cm flaring ones from Dave at FFM. They're plastic, look a lot like the standard 24cm ones, maybe made by Ikara too. Haven't tried the flaring ones yet, might do it soon.
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ceandra
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« Reply #6 on: September 21, 2021, 02:08:26 PM »

We have always made out own props since 2016. While Ikara props are a good starting point, we have found that the "fine tuning" to optimize flying usually entails making props. The kids usually make at least 25 props each year. Some don't work well, others are refined and improved multiple times. Log book becomes crucial to understanding what worked and what did not.

NFFS has a video (from me) on prop making at https://youtu.be/SWyspuWi6Tw. This video is making a smaller prop for Scraps living room flyer, but the techniques are pretty much the same at 24 cm.

The flare stiffness of the Ikara can be adjusted by sanding, and is an important parameter to maximize altitude without girdering the plane.

Coach Chuck
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Little-Acorn
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« Reply #7 on: September 24, 2021, 01:37:56 AM »

Three Wright Stuff planes so far. A simple, generic tractor with 24cm Ikara prop and .093" motor, simple generic tractor with 15cm Ikara prop and looong motor stick (for .058" motor), and a canard pusher with 15cm prop and similar looong motor stick. .058" motor didn't seem enough for the 15cm tractor, but 1 .065" motor put it into the gym ceiling, I'll probably shorten both 15cm motor sticks and try 0.62" motors.

1 min 29 second flight for the 15cm tractor so far, needs more adjustments. Haven't put the wing tip plates on yet, maybe don't need to. But probably will anyway to see if it affects aspect ratio and of course flight time.

0 min 54 seconds for the 24cm tractor, ditto.

Canard pusher with 15cm prop was just built today and had no rudders on its fins (yet), flew straight ahead into a wall several times. Time to take the hint.
Attached files Thumbnail(s):
Re: SO Wright Stuff 2022
Re: SO Wright Stuff 2022
Re: SO Wright Stuff 2022
Re: SO Wright Stuff 2022
Re: SO Wright Stuff 2022
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Olbill
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« Reply #8 on: September 28, 2021, 04:24:26 PM »

I posted a pdf of my 2022 WS design in the plan gallery. It hasn't been built or tested as of now. All weights shown are approximate. My next flying opportunity is Oct. 23. I hope to have one built for testing by then.
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Little-Acorn
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« Reply #9 on: September 28, 2021, 08:49:03 PM »

I've been convinced for years that a plane had to be able to glide before it can fly, certainly before winning a contest. Hence the long noses and nose ballast on all my (tractor) planes so far, and CGs at or near the middle of the wing chord.

But have also notice for a few years, a few tractor planes whose wing were place up at the very front, like less than an inch from the propeller. No way could those balance out near the middle of the chord. One contestant let me handle such a plane, it balanced slightly behind the trailing edge. I gave it a gentle toss (not wound up), it immediately reared up, stalled, and flopped to the floor in maybe two feet. I thought there was no way that plane could ever fly... except I had just seen it fly with a fully wound motor, smoothly for more than a minute.

Finally got it through my thick skull that maybe I shouldn't worry about whether it can glide. Instead build one with the wing all the way up front, and figure out a way to keep the prop turning a really long time.

This morning I took the plane shown in the first post of this thread, scooted the wing all the way forward (CG was 1/2" behind the TE), and glided it. It flopped to the grass as expected. Then wound it up and, a few stabilizer adjustments later, it flew beautifully for 1 min 31 seconds with a .093" motor.

https://youtu.be/2ez_5nn5Wrs

I'm still baffled by how it does that. But I'm a convert. I guess I don't **need* to understand, just need to do it.

Now building a new plane with a CG about half an inch behind the wing's trailing edge, a lifting stab, a wing that isn't warped (old one has a lot of flights and collisions under its belt), an adjustable thrust line, and some other bells and whistles. And of course a 24cm Ikara prop. That flight length is still very short compared to some other planes (and videos of planes) with wings all the way forward that I've seen.

Still a LOT of work and learning to do.
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bjt4888
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« Reply #10 on: September 28, 2021, 09:15:00 PM »

LA,

I use a static stability margin calculator to determine a logical starting point for CG and corresponding decalage. And yes, with a reasonably long tail moment arm, a typical CG for this year’s Wright stuff rules would be about an inch behind the wing TE.

I’d also suggest shorter winglets and a smaller fin on your design. Maybe you were heading this direction. Winglets for indoor model airplanes only need to be tall enough to provide roll control. Any taller than necessary just adds drag.

Have fun with the event this year.

Brian T
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calgoddard
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« Reply #11 on: September 28, 2021, 11:48:52 PM »

Little-Acorn -

It helps in our hobby to have a basic understanding of aerodynamics. I hope you find the following explanation to be useful.

A rubber powered free flight model airplane needs pitch stability so that it will automatically correct itself if the nose is too high (stall) or too low (dive).  In addition, it must maintain lateral (roll) stability, which generally requires adequate dihedral or tip plates (aka winglets). Yaw stability is provided by a vertical stabilizer (fin or fins) adjacent the stab.

Pitch stability is achieved by locating the center of gravity (CG) of the model (with the rubber motor installed) so that it is ahead of the neutral point (NP). The latter is the location where the model exhibits neutral longitudinal stability. How far the CG is ahead of the NP determines the so-called “static margin of stability" of a model airplane. Static margin calculators are available on the Internet.

The NP and the corresponding static margin of stability are generally based on: 1) the area of the wing; 2) the area of the stab; and 3) the distance between the wing and stab. The static margin of stability is usually expressed as a percentage of the mean aerodynamic chord (MAC). The further the CG is ahead of the NP the higher the static margin will be and the more stable the flight will be, but at a cost. The difference in the angle of attack between the wing and the stab (decalage) will have to be increased as the CG is moved forward and this makes the flight less efficient.  However, if the CG is too far rearward, the model will become more difficult to trim and may not recover from stalls and dives. 

Like everything else in rubber powered free flight, there are tradeoffs in deciding where to locate the CG.  If an indoor duration model has a very far rearward CG - aft of the TE of the wing for example - when it hits a beam or light fixture it may head straight for the floor.  Even if it recovers from a collision, it may lose so much height that it cannot achieve a good flight time.  When the model hits a beam or light fixture, the torque on the rubber motor is much lower than when the model was launched.  If the model drops 10 feet and then recovers, it may only climb 3-4 feet back up, by way of example.  In that case, the model will land with far too many unused turns and the flight duration will be severely compromised.

The holy grail in indoor flight competitions in low ceiling heights, like a HS gym, is a no-touch flight in which the model climbs to a height just 1-2 feet below the lowest obstruction, circles several times at the same max altitude, and then descends very slowly.  Consistent no-touch flights of this kind require use of a torque meter, max winding, and de-winding to an optimum launch torque. Much stripping of rubber is typically required to determine the optimum rubber motor size in terms of grams per inch. Then many practice flights must be undertaken accompanied by diligent use of a flight log.  Rather than trying different rubber motor sizes, one can experiment with different prop pitches, but this is typically a more difficult proposition. It either requires switching props on the same model or blades spars that can be easily and accurately twisted to new pitches as indicated on a suitable pitch gauge, and then fixed in their new positions.
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Little-Acorn
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« Reply #12 on: September 29, 2021, 12:33:12 AM »

Calgoddard, you are right every step of the way. My college professors couldn't have summarized better the basics of aerodynamics and design. Many people here will get a great benefit from what you wrote. Thank you!

Biggest thing I'm still wondering, is really two things. (1) if putting the CG somewhat behind the wing (especially with the large stab and long moment arm) is a good first pass at stability, why does my plane nose upward and stall literally within its own length when glided, with no impetus to correct its nose-up tendency (a clear sign of pitch instability)? and (2), When I wind up the motor and launch, why does the plane's behavior change so completely, and it flies normally and with good control of pitch for more than a minute?

The second question is the big one from me, of course. As I mentioned, I fully expected the plane to immediately stall and fall when gliding - all the calculations I ever learned in college, 100% predict the behavior I saw when gliding.

In summary, why does powering a big propeller in front, so completely change a grotesque stall, into a long and smooth flight? Clearly it does exactly that, I was watching closely as it happened. In my studies I had found that a front propeller **destabilizes** the plane in pitch (and yaw) when it is powered, to a point even worse than what happens when it glides. This plane (and several other aft-CG planes I have seen) behaves in the exact opposite way.

Bottom line is, though, that the plane DOES do exactly that: Powering the prop makes it more stable in pitch, not less. So the theories I was taught (and I proved many times over with models, wind tunnels, and manned aircraft) are clearly wrong on this point, at least as applied to this example. Have you ever taken an AeroEng class that predicted what I saw today on this plane? I can randomly guess that Reynolds number has something to do with it, but that's only the vaguest guess.

As i said, I clearly have a lot to learn, and a lot of work to do.

Dei sub numine viget 1976.
« Last Edit: September 29, 2021, 12:51:01 AM by Little-Acorn » Logged
Little-Acorn
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« Reply #13 on: September 29, 2021, 01:16:33 AM »

Brian, you're quite right about the wing tip plates. I put those huge ones on when a previous plane (EWS) developed a tendency to roar around in diminishing circles without letup. If you launched it in a left bank, it would roar around constantly to the left. If you launched it in a right bank (with no trim changes), it would roar around constantly to the right. I guessed it was lacking roll stability, and so put bigger tip plates on this one. Then it flew more normally.

But the fast-circle tendency might have been exacerbated by high speed. Subsequent flights have flown much slower (as they should), which might have done as much to cure the circling tendency as the tip plates did.

Next plane will have smaller tip plates, as most of my planes with tip plates do.
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Olbill
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« Reply #14 on: September 29, 2021, 11:47:27 AM »

Let me back up a bit. My statement about gliding was based on my thinking that you were trying to fly your models like an outdoor model where the motor would run out of turns while the model still had considerable altitude and then depend on the model gliding to add to the flight time. An indoor duration model using a fixed pitch prop should have power from the motor all the way to the end of the flight. There may be rare circumstances (such as indoor thermal) where you'll see a good flight dead stick in the air but in my flying experience that almost never happens.

As far as whether a WS model is CAPABLE of gliding then that is a different matter.

Every successful indoor flier will have their own method of setting up a new model. I use glide testing to arrive at a starting decalage. During this testing I'll replace the prop with a chunk of clay that is exactly the same weight as the prop, and also I'll replace the motor with another chunk of clay that is exactly the same weight as the motor and located at the midpoint between the front and rear hooks.

My models are designed using a design spreadsheet. Part of the resulting design is the location of the CG.  So when I'm doing glide testing my first step is to get the CG located per the design. This is where having a model that is initially underweight becomes important b/c you can place the ballast to get the CG where it's supposed to be. With the CG set I'll glide test the model and adjust the decalage to get a smooth glide.

The next step is to put the prop and motor on and fly the model at very low power - about the amount of power that will produce a level cruise. I typically will put in around 500-800 turns for this part of the testing. At this point I will increase the decalage in small steps until the model stalls under power. I'll back off the last increase in decalage and that will be my flight settings for that model. The turn circle can also be adjusted during this part of the process.

The final decalage might be a little different from the settings during glide testing but glide testing will get you very close to what you need. This will also help to avoid flying the model under power with initial settings that result in a crash and model damage.
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Olbill
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« Reply #15 on: September 29, 2021, 11:49:32 AM »

If you build my design please ignore the rubber recommendation on the plan. .060 rubber is going to be much too small for this model. I'll get the plan corrected when I make the next revision.
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bjt4888
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« Reply #16 on: September 29, 2021, 01:42:35 PM »

Bill,

Thanks very much for posting a plan. When I get SO teams that ask about designs, I definitely lean towards pointing them towards yours. Very helpful.

Brian T
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« Reply #17 on: September 29, 2021, 05:57:09 PM »

Little-Acorn -

Thanks very much for your complement about my Reply #11.

I hope Bill or Brian will correct anything I said that is erroneous.

Perhaps another aeronautical engineer could post an answer on whether thrust from a prop that pulls a tractor duration model through the air contributes to pitch stability.  

Bill - Thanks for posting your 2022 WS plan.  Many aspects of your latest design reflect your earlier designs for other classes, which of course were very successful.

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bjt4888
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« Reply #18 on: September 29, 2021, 06:09:41 PM »

Cal,

I like what you wrote on aerodynamics.

Others have probably noticed this, but another resource for 2022 Wright Stuff design and trim ideas would be the thread in this forum from 2015 and the Scioly.org forum from 2015. The propeller diameter for this year is the same as 2015 and the wing loading is similar. Stabilizer for 2022 is bigger and rubber allowed is less (1.5 grams vs. 2015 2.0 grams).

Brian T
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calgoddard
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« Reply #19 on: September 29, 2021, 07:07:42 PM »

Brian -

Thank you for your reassuring comment on my Reply #11.

I am attaching a picture of a WS model built and flown by a team I coached in the 2015 WS competition. It won first place amongst a field of around 60 teams. The forward portion of the tail boom on this model is a carbon fiber composite rod.

The competition took place in a high school gym. The height to the lowest obstruction in that gym was about 23 feet.

My team's winning time was 189 seconds. This flight time was achieved on the team's first official flight. In 2015, just like in 2022, a team's score was based on the longer of two official flights.

The model in the picture had a CG well aft of the TE of the wing. With its relatively low decalage its ability to recover from a dive was very poor. The max altitude of the winning flight was probably around 18 feet. It was a no-touch flight.  

On the team's second official flight the students slightly increased the launch torque, as they had been coached for weeks before the event. This time the model climbed a little higher, collided with a beam, and dove down a significant amount until assuming a stable attitude. It then climbed back up about 2 feet, and ended up with a flight time of around 165 seconds.

Bottom line - competing with a WS model with a far aft CG is a gamble.  You must wind with a torque meter based on loads of data.  You cannot afford for the model to hit an obstruction.  You must achieve a no-touch flight that is reasonably high in the competition venue.

In my experience, an indoor duration model with more traditional CG location, e.g. 70 - 80%, will usually recover from a collision quite quickly, without losing very much altitude. Such a WS model is probably adequate to win most Wright Stuff competitions but the SO region where I was coaching was extremely competitive in WS.

Brian - you, Bill and Coach Chuck are well aware of the risk/reward proposition involved in competing with an indoor duration model with a far aft CG. I wrote this post for the benefit of others. I hope it is helpful. Thanks for all your insight and wisdom that you have posted on this website over the years. I always enjoy reading your posts.

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Re: SO Wright Stuff 2022
« Last Edit: September 29, 2021, 07:44:45 PM by calgoddard » Logged
bjt4888
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« Reply #20 on: September 29, 2021, 07:16:08 PM »

Cal,

Nice looking airplane.

Brian T
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ceandra
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« Reply #21 on: September 29, 2021, 08:12:58 PM »

Cal:

You are spot on concerning the aft CG.

We try to balance an efficient setup (low decalage, aft CG) with stability. We will move CG back, and then purposely skim the rafters and see how it recovers.

Our 2019 winning design (5:08 at Nationals) had a CG significantly behind the wing, but that year had a stabilizer as large as the wing (tandem). We touched the lamps in the facility multiple times and recovered with little loss (1-2 feet) of altitude. Last year, with a tiny stab, the CG was within the wing chord.

This year, with a generous but proportioned stab, I would expect the CG to be slightly behind the wing and still afford good recovery.

The air conditions, temperatures, and obstacles in a SO event are too unpredictable. We have done no-touch flights before, but even when planned they often do not occur, so we typically will take stability first. On most (reasonable) SO planes, like P-18, we have found about 5-6mm wing incidence and 0 tail a good starting point to balance stability and efficiency. Your mileage may vary!

Once we set this starting point, we adjust CG to get good initial letdown trim. Once the whole flight (high and low power) is trimmed, then we will start to deviate, using the stopwatch to judge effectiveness of the changes. But, we will always force a girder touch to check stability at some point after changing CG.

Chuck
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Olbill
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« Reply #22 on: September 30, 2021, 09:16:33 AM »

I don't remember helping any teams in 2015. My own model had a best time of 3:30 using 1/15 rubber in the St. Lukes gym - which hasn't been available for flying since the pandemic started.
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« Reply #23 on: October 06, 2021, 06:18:34 PM »

I've attempted to upload a revised plan for the Finny 2022. Changes are highlighted in yellow.
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calgoddard
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« Reply #24 on: October 14, 2021, 07:55:48 PM »

Little-Acorn - I sent you a PM.

Bill, your revised plan for the Finney 2022 showed up fine on the Plan Gallery. Thank you.

I am surprised that Freedom Flight Models is not yet offering a 2022 WS kit.
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