Semroc Scissor Wing Transport Kit Build Thread

[Rktman]

So glad eRockets decided to do a repro of the Estes Scissor Wing Transport. I downloaded the plans for the original but what kept me from moving ahead with a clone was the pivot mechanism. Figured someday I’d get around to engineering one but eRockets took care of that with this kit. Truthfully, I was curious how they would reengineer that plastic piece, and I feel they did a really well thought out and improved clone with this kit. Heads up: this build will move at a glacial pace. Unlike @kuririn, I’m not a skilled speed builder, and I want to savor every step and not mess anything up.

That said, my kit arrived fairly quickly considering the shipping problems due to Covid-19 and the winter storms. Unfortunately, the box suffered some mishandling and got smooshed.



I was worried about the balsa parts, but they fared the best compared to the main body tube, which got somewhat tweaked. It was bent just enough to cause a concern that the motor tube wouldn’t eject at apogee. Even though it wasn’t eRocket’s fault, Randy sent a replacement gratis after I emailed him about it. Great guy and just one of the major reason I continue to patronize eRockets.




Here’s the kit unboxed.




And the components.



It’s a well done kit, and probably wouldn’t have been possible without the fine parts detail made possible by laser cutters.

 

[Rktman]

While I’m waiting for the replacement BT, I started on the sub-assemblies. Step 1 has you start on the recovery system by cementing 2 thrust blocks on one end of the 13mm stuffer tube. It’s listed as made out of craft paper, but the one in my kit appears to be made of some kind of plywood, though I can’t tell if it’s bass or hard balsa. It’s definitely an improvement over paper, since it’ll be exposed point-blank to the heat and force of the ejection charge.



I sanded the BT at the mounting points to get a good bond, but the fit was still tight, so I inserted an expended motor casing inside the stuffer tube to support it and prevent any squashing while I forced the rings into position. I’ll be coating the inside end of the tube and end ring with CA or epoxy to protect it from the ejection charge.

 

[Rktman]

Forgot to upload the exploded view of the glider. Makes it a lot easier than just trying to visualize how things fit together to form the whole.

 

[Rktman]

A nice, sturdy basswood centering ring is cemented to the opposite end of the stuffer tube. Although it’s totally not necessary, I added two additional CRs on either side of it to strengthen it. I have a tendency to over-engineer things —admittedly this would be better suited to an MPR or HPR build.






The next step involves marking the motor tube for fin, motor hook and dowel mount placement, and attaching the motor hook. The centering ring used to lock down the hook is a nice sturdy ply instead of the more common wound paper. The fit was too tight and took some sandpapering of the inside and notching it for the hook to get it to fit the motor tube.

The stuffer tube is then glued in place on the forward end of the motor tube. Something to watch out for here: I noticed the pre-punched opening for the motor hook is a hair over 1/16” too high. What that means is that the top thrust ring will stick out the top of the motor tube a little over 1/16” when you eventually glue it in. Personally I’d prefer a better and more solid connection by having that top ring sit flush with the top of the motor tube.

Not a big deal and easily corrected though. I ended up punching another slit for the motor hook a little lower so that the top thrust ring will sit flush with the motor tube.






Instructions note a good recommendation to assure everything is straight and aligned: roll it across a level surface. Did that, then slipped it inside the main body tube to dry and make sure everything is absolutely parallel and the assembly can slip in and out easily.

 

[Rktman]

Next come some of the small fiddly parts. Like the original, a small dowel is used to keep the wing locked in launch position. This is mounted on a basswood standoff.




Balsa sides are then glued on to reinforce and strengthen the unit.




Two curved brackets are attached to the sides (It appears that these will be used to hold the elevator flaps on the stab down in a neutral position during launch). The brackets aren’t made of hard balsa and seem fragile, especially with the grain running parallel like that, so I soaked them in thin CA (good insurance to keep my fat fingers from snapping them off at some point).

 

[Ez2cDave]

Eric,

Back in the late 70's or early 1980's there was a mod for the wing, to give it dihedral when deployed. DuBro hinges were used and elastic pulled the wings up, during deployment. The hinges were about 1.5" out from the central hub, as I recall. I never did it myself, but the 1 or 2 models I saw had much better roll stability.

Dave F.

 

[TheAviator]

I saw the product announcement either on the eRockets or NAR Facebook page and was super excited. Really looking forward to your "stop and smell the roses" build thread.

 

[Rktman]

Eric,

Back in the late 70's or early 1980's there was a mod for the wing, to give it dihedral when deployed. DuBro hinges were used and elastic pulled the wings up, during deployment. The hinges were about 1.5" out from the central hub, as I recall. I never did it myself, but the 1 or 2 models I saw had much better roll stability.

Dave F.

I always wondered how gliders like the Scissor Wing Transport, the Estes Tomcat, and Estes Crusader could have any roll stability without any dihedral. I always assumed it had something to do with low wing planes benefitting from the "pendulum effect" (CG below the wing), except I've seen arguments that the "pendulum effect" is a fallacy and therefore can't contribute to roll stability. I still have no convincing answer, and I'm curious to see just what its glide will be like.

 

[Rktman]

I saw the product announcement either on the eRockets or NAR Facebook page and was super excited. Really looking forward to your "stop and smell the roses" build thread.

It might be a bit more "leisurely" for a while than I anticipated after my rotary blade got a bit too close and took a bite out of two of my fingers...

 

[K'Tesh]

What I find interesting was that the original Scissor Wing Transport from Estes used die cut plywood for the pivot. I'm sure that Semroc's laser cut parts will be far superior to the originals, but it's neat to see them go back to wood.

 

[Ez2cDave]

I always wondered how gliders like the Scissor Wing Transport, the Estes Tomcat, and Estes Crusader could have any roll stability without any dihedral. I always assumed it had something to do with low wing planes benefitting from the "pendulum effect" (CG below the wing), except I've seen arguments that the "pendulum effect" is a fallacy and therefore can't contribute to roll stability. I still have no convincing answer, and I'm curious to see just what its glide will be like.

The "SWT" is prone to going into a sprial dive and not recovering, under "bumpy" conditions. As for glide, remember that there is no Wing airfoil, the wing loding is high, and it has a lot of drag. In my opinion, it's more of a "stabilized horizontal descent", than a "true glide", with a high rate of descent.

Dave

 

[Rktman]

The "SWT" is prone to going into a sprial dive and not recovering, under "bumpy" conditions. As for glide, remember that there is no Wing airfoil, the wing loding is high, and it has a lot of drag. In my opinion, it's more of a "stabilized horizontal descent", than a "true glide", with a high rate of descent.

Dave

I was considering sanding in an airfoil if it didn't weaken the wing too much. It may be more trouble than it's worth though, since I'll put in at least one flight (in single-digit wind conditions) then probably retire it as a "classic" sport design to keep the paint job and decals unscathed.

 

[Ez2cDave]

This, of course, is not a high-performance design.

Dave F.

 

[dvdsnyd]

Nice Build! Hope you recover quickly from the rotary tool accident!

Here's some video of a prototype Semroc SWT from 2020.
Looks to enter into a nice glide. Video cuts out kind of quick though, almost as it it's starting more of a "falling with style" descent.

I wonder if the conditions that these are flown in affect the glide the most? Kind of like Dave was saying, "bump" conditions affect it.

Dave

 

[Rktman]

Nice Build! Hope you recover quickly from the rotary tool accident!
Here's some video of a prototype Semroc SWT from 2020.
Looks to enter into a nice glide. Video cuts out kind of quick though, almost as it it's starting more of a "falling with style".
I wonder if the conditions that these are flown in affect the glide the most? Kind of like Dave was saying, "bump" conditions affect it.

Dave

Actually that's a pretty decent glide for a sport model up to the point where the video cuts off. I've seen much worse roll and stability problems with flying wings even when they've got dihedral. Probably not a good idea to fly a SWT in turbulent or gusty wind conditions though.

 

[Ez2cDave]

I was considering sanding in an airfoil if it didn't weaken the wing too much. It may be more trouble than it's worth though, since I'll put in at least one flight (in single-digit wind conditions) then probably retire it as a "classic" sport design to keep the paint job and decals unscathed.

Eric,

As high as the wing loading is, and given the relatively small wing area and thinness of the wing, I doubt that any meaningful benefit would come from sanding a lifting airfoil into the wing.

Deployable "flaps", to create an undercambered wing, might increase performance, but it would also decrease glide speed. If the decrease is sufficient, the glider might be prone to stall. If it stalls, the lack of dihedral could cause it not to recover.

It might be interesting to build a "hotrod" version, at some point in the future, perhaps with a thicker or built-up, airfoiled, wing and the "dihedral mod".

Good luck on your test flights !

Dave F.

 

[Ez2cDave]

Actually that's a pretty decent glide for a sport model up to the point where the video cuts off.

Right before the video ended, it looked to me like it was "mushing".

https://forums.ubisoft.com/showthread.php/378730-mushing-vs-stalling

https://aviation.stackexchange.com/questions/26932/what-is-a-mushing-glide

Dave F.

 

[Aeronerd]

Subscribed

 

[Aeronerd]

What I find interesting was that the original Scissor Wing Transport from Estes used die cut plywood for the hinge material. I'm sure that Semroc's laser cut parts will be far superior to the originals, but it's neat to see them go back to wood.

View attachment 503992

"Hinge material?"

 

[K'Tesh]

"Hinge material?"

Ok... I used the word "hinge" where the kit referred to it as a "pivot" (part N). I've changed the previous post.

 

[Alan15578]

I was considering sanding in an airfoil if it didn't weaken the wing too much. It may be more trouble than it's worth though, since I'll put in at least one flight (in single-digit wind conditions) then probably retire it as a "classic" sport design to keep the paint job and decals unscathed.

I built the original Estes kit with an airfoiled wing and full "Contest finish". Mine is very light and glides great. I would not fly it in a contest because it could thermal away. I usually use an Astron Invader for a second contest flight.

 

[Ez2cDave]

I built the original Estes kit with an airfoiled wing and full "Contest finish". Mine is very light and glides great. I would not fly it in a contest because it could thermal away. I usually use an Astron Invader for a second contest flight.

I find it hard to visualize an Estes Scissor Wing Transport "thermalling away".

However, THIS would, definitely.

https://www.nar.org/wp-content/uploads/2018/12/Spanish-S4A-Design-2018-1.pdf

Dave F.

 

[Rktman]

Congrats on the Invader. I built one as a kid and never could get it to launch right. It would put in a squirrely all-over-the-sky ascent before doing some loops and then sorta pancaking down. I just called it my "acrobat" glider, and hilariously the other kids thought it was supposed to fly like that and loved it.

 

[Rocketclar]

I have an old Estes SW that's been repaired/rebuilt several times. A long time ago, the plastic pivot and stop pin broke. I replace the plastic piece with a screw and nut and the stop pin with a 4X40 nylon (shear pin) screw. It's trimmed and flies fairly well....certainly not a competition flyer.

 

[Rocketclar]

BTW....I am finishing a Semroc Blue Jay and it seems like a very nice kit.

 

[Rktman]

BTW....I am finishing a Semroc Blue Jay and it seems like a very nice kit. View attachment 504487

Like the Edmonds Deltie that it's based on, it's not only unique and unusual looking, it's a fast easy build and flies great. You're really going to enjoy it.

 

[Rktman]

Something I should have mentioned earlier: the motor tube marking template didn’t quite reach all the way around the motor tube. It was short by about 1/8”, so the spacing for the fins, dowel mount and engine hook were a bit off. I’d suggest you make your own if you find yourself in the same situation. (Easily done. Go here: https://www.apogeerockets.com/Advanced_Construction_Videos/Rocketry_Video_75
for an Apogee Rockets video on how to do so using Inkscape, Illustrator, or a similar vector program).
EDIT: SEE NEXT POST (#26) FOR CORRECTED TEMPLATES I MADE IF YOU'D RATHER NOT MAKE YOUR OWN.

Moving on. One of the nice changes in the Semroc/eRockets kit is that fragile components or ones that are tiny or that are at risk of breakage during deployment or landing are laser cut out of sturdier basswood.




Instructions have you next attach the basswood fin stiffeners to the fins that will be glued to the motor tube. In my case, the fit of the tabs into the slots was too tight and I had to do some sanding with a small file to make them fit. The stiffeners are tiny and would easily be broken during handling if they were made of balsa. Take your time here and sand carefully if you find you have the same problem.




Since these two fins will be attached to the motor tube (which will be ejected at apogee) a rough landing could easily damage them, so I appreciate that the kit provides basswood ones.




One thing to keep in mind: the stiffeners should be attached so that the fins are mirror images of each other. There’s a reason for that. They’re like the wings on a glider — you don’t want to end up with two right or two left wings. Once glued on to the motor tube, the stiffeners will both have to be on the same side of the fins, facing each other.



To be continued…

 

[Rktman]

Next step has you use the main body tube marking guide to mark the locations of the launch lug and tube centerline. Like the motor tube guide, it’s short by about 1/8” and won’t wrap completely around the tube, so the positions of both components is off (they’re not 180° apart from each other like they should be). It’s because the templates were based on a BT-50 sized body tube, but the kit uses a Semroc ST-9180 which is not only thicker but has a slightly larger outside diameter.

This is why the marking guide for the motor tube was off as well. Semroc’s motor tube is larger in diameter than an Estes-type 18mm tube by 0.023”. No big deal, I let Randy know. In the meantime, if you’re building a SWT kit, you can use the templates below that are based on the actual OD of the Semroc tubes used.

 

[Rktman]

The stab is glued on to the body tube next. In case it’s not abundantly clear, remove the elevator flap first! (I mistakenly thought the entire unit was to be glued to the body tube at first. That would’ve been a disaster). The elevator flap actually needs to hang off the rear of the body tube.

 

[Rktman]

There are some minuscule parts like the pivot base that are a challenge to assemble if you have Fat Finger Syndrome like me. Tab and slot joints were too tight for me to get them to fit, so to avoid breaking anything, cautious, conservative sanding with something like an emery board or small diamond file will enable the parts to fit together snug and square. Remove just a little more than the char and you should be good.




The wing pivot assembly gets mounted to the support base in the previous photo. There are some tiny bits here that need special attention fitting and cementing together too. Be careful not to let any glue ooze out around the colored area shown. The reason is obvious in the next photo following this one.




I think I’m getting an idea of how this new pivot mount unit all comes together and works. Really a clever reimagining and reengineering of the original design IMO. Definitely an improvement in strength and durability.