scissor wing transport upscale but no scissors, ie running without scissors?

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burkefj

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So, I don't know why, I've thought about doing a SWT upscale for a long time, but could never rationalize getting the mechnanism to work and be solid enough with my preferred foam medium, and I like to pilot the boost anyway and don't like to chase pop pods. I also question the theoretical extra boost altitude with a fast burning motor and with extra fins and a swing wing having more wetted area than un unfolded wing without extra fins boosting on a slow burn motor. In any case yesterday I saw a posting by Richard Boyette on a 2.25x upscale SWT on FB he did that got me to thinking.

His glider version was 46" long, 34" wingspan and used G motors for a 46 ounce boost weight and 41 ounce glide weight. The original was around 2 oz glide weight I think so with the scaling of factors, it means a 2.25x gives you 5x wing area and 5x weight for similar wing load, but we know larger can carry more weight typically than a direct scale. His glide weight is around 20x for a bit more wing loading than I like of around 25-29 oz/sq foot. I thought a 2x upscale would give me 4x wing area, so if I could get around 9-10 oz glide weight for a scaled wing it might not be too bad.

So I looked at my components, a 9.5" long psII 2" cone, two 13.5" 2" diameter tubes and a coupler. I used a 5 3/8" long bt-60 tube for the tail and proceeded to scale some depron tail and wing surfaces that looked approximately correct. I used a 3mm spar in the horizontal stab and a 3.2mm spar in the wing.

The scale 2x length should be around 42" long ignoring the pop pod, and wingspan around 31.5". My length I had available with cone was 36.5 and the cone is longer than scale so for looks I shortened the wingspan to 28" and widened the chord a bit to give me a similar scale area. I'll use just split elevons on the tail for roll/pitch. I did some openrocket modeling to move components around to give me a boost CG of around 30% chord, since it's an eleptical wing, the % root chord is same as % MAC. I moved the wing back just a bit to reduce nose weight and came out with this. RTF should be 10.75 oz with 9.75 oz glide weight and 12.5 oz wing loading. Mark at stickershock is working his magic on markings. I like the look of it in glide mode, I put a fake black pivot circle and a dummy front wing hold down just to keep the asthetic.

Maybe I'll call it a an oblique wing transport where I've chosen 90 degrees....I was considering angling the wing for fun but then found this quote: ". Although the oblique wing is still considered a viable concept for large transports, the unpleasant flying characteristics of the AD-1 at extreme wing-sweep angles may have discouraged aircraft designers from adopting this configuration."

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burkefj

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Got the radio installed and all put together and did two flights tonight. Using 31% cord for Boost CG was perfect I just needed a very minor bit of down trim for straight boost and the Glide trim was nearly perfect. I needed about a half an ounce more nose weight than I originally planned but it actually flew pretty darn well even with that small wing.
 

burkefj

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So did two simulations just for fun, one with a simulation of the wings folded and with pop pod and fins with reduced nose weight to give proper glide when motor/fins were removed, and one with the standard design as I flew it. I added a bit of weight for the swing pivot that would be needed for my design for the folded version. I set the pop pod fin size to give me a reasonable boost CG/CP margin. The rail exit speed required for stability needed an E-18 at least for the folded version, and an E-6 for my version since static stability isn't required. So boost weight is about half an ounce lighter for swing wing with this design, but interestingly the boost altitude wasn't vastly different, 714 for folded and 663 for the fixed wing. The E-18 has a few extra NS as well. This is with a purely vertical boost which isn't required on the unfolded wing, so you can trade off some of the thrust for speed instead of pure lift and get a higher boost potentially that I did not calculate but is probably on the order of equal boost altitude. For me personally at this size, much over 700' starts to get hard to tell orientation for glide control, so I'm ok with these altitudes. I believe the altitude difference is primarily the weight difference.

Of course the glide weight is around 9.2 oz for the pop pod version and 10.7 for the fixed wing which is significant. So, if I count the time required to find and prep the pop pod versus extra glide time(with this small wing and the ratio I'm estimating an extra 15 seconds of glide time), I probably still win with fixed wing:) Plus at my RC field we can't eject anything with hot components attached that might go into the crop field that surrounds us.
 
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burkefj

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Here are the sim pictures if anyone is interested, since the wing can't sit on top, I just broke the wing in half and put on either side of the body tube for the same effective frontal area...
My unfolded sim has a slightly longer wingspan to address the fact that the wing goes through the tube instead of on the top to give equal frontal area. Interestingly increasing span by an inch on either side even with a thick foam wing, 6mm, only changed altitude estimate by 12 feet, reducing it by 3" on both sides gained 30 feet, so at the low speed low thrust motor, the difference is not that significant due to frontal area. At least in this platform, the higher boost speed drag of this folded design does not give a significant altitude increase for a similar NS motor, even with lighter weight boost of the folded design, the primary gain is the lighter glide weight which in a non high performance design is not that compelling versus the complexity and recovery.

Of course in an another optimized design like JH does I'm sure it is a win.

sim2.PNG


sim1.PNG
 
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burkefj

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My conclusion is that this design in this size doesn't benefit greatly from the folded wing with added rear fins, but more from the saved weight of the drop pod, I think if you wanted to optimize you could use a drop pod without extra fins and still steer on the way up but have a lighter glide weight, but again, in a model that is just for fun it doesn't do a whole lot.
 

Crawf56

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Hmmm.......

What if you assumed that a mechanism (additional servo, or a pin attached to a servo) was onboard that released the scissor wing. Thus, a pop-pod would not be needed.

What do your sims say about that?
 

burkefj

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So that's an interesting one, for that you can set CG right at optimum glide CG, about 1/4" ahead of my tail heavy boost CG which saves about an ounce. This is because for boost the folded wing will have the CP further back. Now you have to carry some extra pivot, reinforcement and servo weight but that can be on the glide CG location not the nose. So, the boost and glide weight stays the same as for an unfolded wing. One thing I'm not sure of is how it would steer with RC with the wing folded, so I think you would still want to boost with a faster burning motor like an E-18 which is the closest motor in NS with sufficient rail speed, and maybe put in some slight roll into the tail surface deflection to counter the offset drag of the vertical stab and tube and folded wing which would have been offset by the pop pod fins. So, that will cost a bit of altitude that you gained by not having the drag of the pop pod fins.

Reducing the sim altitude by around 15% for roll drag, sim shows about 75' higher boost altitude, at the same boost/glide weight. However you aren't nose heavy so don't have up trim for glide which will mean less drag. That would probably get you around 10 seconds extra glide due to altitude gain and maybe another 10-15 due to less glide drag since that's at pretty slow speed, and you don't have to find anything in the weeds. Again, that's for this design if you can keep the pivot/release mechanism down to an ounce total weight.

Frank


Hmmm.......

What if you assumed that a mechanism (additional servo, or a pin attached to a servo) was onboard that released the scissor wing. Thus, a pop-pod would not be needed.

What do your sims say about that?
 
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Crawf56

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Thanks for working on my question, Frank.

I flew an Estes scissorwing, circa 1980. Only one flight, which was fantastic. It disappeared over some trees. :facepalm:

(About a week later, a storm blew it out of the trees, and it was returned to me. But it never flew again.)

Someday, I want to do an RC Scissorwing, for purely emotional reasons. :smile:
 

burkefj

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here is the video from yesterday with the nice markings from stickershock applied, I had a 8-10 mph wind and the model tends to baloon in a headwind so I had to keep some downstick on approach and just release it just before it lands on the grass so it didn't pop up and leave me stuck without any energy.

[video=youtube;zbZAQLebMIE]https://www.youtube.com/watch?v=zbZAQLebMIE&t=7s[/video]

IMG_20180611_160411368.jpg
 

Crawf56

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Regarding the old Estes Scissorwing.........

I have found the instructions, and pics of the wood components.

But are there actual plans somewhere?
 

burkefj

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Ok so I suckered Richard Boyette and Gary Crawford to try a kit of this, I've found that I can use ST-20 tubing from bms that is 34" long, use a coupler on the shoulder of the PS-II nose cone to adapt it to fit the tube and come out with a scale 2x length with the same overall weight. This allows me to move the wing forward and keep the same relative CG but would allow people to try to modify it to swing wing with an RC release if they wanted to and boost with some roll input on the tail to compensate for not having the extra pop pod fins. Stay tuned, I'm going to build another prototype tonight with a fixed wing just to check weight and CG.

Frank
 

burkefj

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Finished up the kit prototype using ST-20 tubing, 44" length, 28" wingspan, balanced for non swinging wing boost/glide it is at 11 3/8 oz rtf, and 10.2 oz glide weight.

It is designed so you can add ply disks on the top and bottom of the wing and make a swing mechanism/release via servo in whatever manner you want to and that will help support the center wing joint and spars.

So you can balance it at the spar with a loaded motor and wing fixed and it will boost/glide fine.

If you balance it 1/4" ahead of the spar for glide with an empty motor case, you will be set for glide trim and save 1 oz of nose weight, then boost with the wing folded and put in some roll trim to keep it going straight. You will have to add the swing and release mechanism, I've put the coupler right at the pivot point so the pivot mount will be supported with the coupler. The Swing/release mechanism will probably add an ounce or so so the overall boost/glide weight will probably be a wash but that's still pretty good for a glide weight.

I've included a ply front holddown, the holddown notch is uncut since that cut will depend on the height of your wing and pivot mount, and the rear will be held by the vertical stab tube.

These weights assume a 53 gram 24mm rocket motor, 15 gram 1s battery placed in the nose, 2 11 gram HS-65 servos, 1/2 ounce for two thin 24 in servo extensions, and a 7 gram ar-400 receiver. Any change to components will yield higher weight in most cases.

Frank

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burkefj

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My SWT got damaged in 2018 when my glider rack got blown off the table at NARAM, I decided I'd build a new one based on bt-60 tubing instead of ST-20, so an approx 1.7x upscale, keeping the 28" wing and using 40mm tubing for the tail tube, moving the mmt right under the top inside of the body so the thrustline will be higher and remove the down trim for boost. Tubing is .65 oz lighter and I won't need a coupler because I'm not cutting the tube to fit into a kit box, and I don't need the coupler to adapt the psII cone to the ST-20 tube and the cone is 3/8 ounce lighter as well. I'm also not using two spars since it isn't being intended for enabling swing wing pivot reinforcement as the kits were, and I can move the wing back an inch and still have it look correct reducing nose weight. It should come out about 2 ounces lighter.

Approx 28" wingspan, 1.65" body, 40" length....
 
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burkefj

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All framed up with test glides, ready to fly with motor 9.35 oz! 8.35 oz glide weight...
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burkefj

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Maiden this morning went well, gusty 7-10mpg but handled it well, I'm a bit nose heavy at 31%MAC with this version, will remove a bit of nose weight after I fly it in dead air just to confirm.

 

burkefj

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I did some more musings with this new design iteration, comparing altitude and weight versus doing a swing wing mechanism and adding that weight and release servo and having to move the wing forward an inch but moving glide CG back so reducing nose weight. I also canted the tail surfaces 5 degrees to model the roll input you would likely need to keep the boost vertical with the vertical stab drag. This assumes no pop pod. I assumed 1.25 ounces for ply plates to support the pivot top and bottom a ply stop plate mounted on the body, a rubber band mechansim to swing the wing and a 9 gram servo and an extra wing spar to go on either side of the pivot for support of the foam wing.

Boost weight for non folding wing is 9.35 and glide weight of 8.35 with altitude of 800'

Boost weight for folding wing with mechanism and wing moved forward but with better glide cg location is 10.2 ounces with glide weight of 9.2 ounces with an altitude of 700'.

Even with better glide cg 100' lower altitude and 1 ounce higher glide weight is probably going to yield a wash for overall performance.

This assumes the same E-6 motor to reduce stress on the airframe/tail surfaces.

Attached the original ORK file, one with the folding wing with added mass and adjusted CG with empty motor casing mass, and the folded version checking for CG/CP margin and the angled surfaces for launch simulation.

If you were to consider a true upscale but with RC and normal swing mechansim, your glide weight would be about 1.25 ounces lighter than my version but boost would be heavier due to the pod and the swing mechanism/support still needed, and you have to find a boost pod. Altitude will probably be lower, but glide longer, maybe a win, hard to tell. As I cannot drop things from the rocket glider as it will get lost in the high surrounding grass fields I did not simulate this and you risk the pod not ejecting/wing not opening.
 

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burkefj

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Boost with 35% MAC was great, nice hands off glide, about a 1:10 glide time, consistent for all three flights.
 
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