Semroc Scissor Wing Transport Kit Build Thread

[Rktman]

There was an earlier issue with the wing not swinging out exactly perpendicular to the main body tube when in glide mode. This isn’t just an isolated problem with my build, as it was pointed out by another builder in one of the SWT reviews on eRockets’ website. I should have mentioned it earlier, but was trying out different solutions in the interim and it slipped my mind as I moved on to other things I could post.




Since it was off by a few degrees as you can see from the image above, I tried driving in a small piece of music wire into the slot that limits how far the wing can rotate, in an effort to stop it from over-rotating. (See post #30 to get a clear idea of how the mechanism works). It didn’t work out too well, as it started to dent the small raised piece (Pivot Stop) that rides in the slot each time the wing snapped open into glide position.




In the end, I just inserted a piece of music wire on the underside of the wing to limit how far the wing could rotate. It’s the simple method commonly used for WSMC S4A-type swing-flop gliders and is uncomplicated enough to just plain work — and very effectively.

 

[Rktman]

I think I've figured out a better solution to the above wing alignment problem for anyone building the kit, an easier fix and potentially less problematic one than what I did. I'll need to take some photos to best explain it, so stay tuned.

 

[Rktman]

Okay, here’s what I came up with. But first, a little visual clarification of the problem. (You might want to refer to the illustration of the parts in post #3).

The following photo of the Wing Pivot Plate (left) and the Wing Pivot Top (right) shows how the holes for the Pivot Stops (the kidney bean-shaped inserts) are rotated by about 6° (reddish lines) compared to the corresponding slots on the left. I believe this is what’s responsible for the wing not being perpendicular to the glider’s main body when in glide mode. This was probably a mistake that happened when the laser cutting template was being laid out in the software. (Note: for orientation purposes, the top of the photo shows the part of the Wing Pivot Top that faces the back of the glider).




The following photo shows how the Pivot Stops (the kidney bean-shaped inserts) on my build are consequently skewed 6° clockwise (reddish line) instead of being directly across from each other as they should be (blue line).




Notice that the Wing Pivot Plate has a small hole in it. There’s a matching hole in the wing. Per instructions, a small piece of 1/8” dowel is glued into the hole in both pieces to lock the wing into a preset position on the Wing Pivot Plate (in this case incorrectly). I suggest NOT doing this, or your wing will end up being skewed like mine was.





Instead, I feel a better solution to the problem is to:

1. Place the Wing Pivot Plate over the Binding Post and onto the Wing Pivot Top in the deployed position as shown. Tack it down temporarily with double-sided tape so it can't move.




2. Coat either the area of the wing to be attached to the Pivot Plate or the top of the Wing Pivot Plate with glue. Since the wing is no longer locked onto the Wing Pivot Plate with the dowel, you’re now free to fine-tune its position. Slide the wing over the Binding Post and down onto the Wing Pivot Plate and adjust so that it is exactly perpendicular to the glider's main body tube. Check to make sure no glue has oozed out onto the Wing Pivot Top. Let dry. The wing should now be attached to the Pivot Plate in the correct position to ensure it will be perpendicular to the main body tube when deployed. Carefully remove the wing/Pivot Plate unit and peel off the double-sided tape or whatever you used to tack it down with.

I hope the images help make things easier to understand. Feel free to ask if you need anything clarified.

 

[Ez2cDave]

Eric,

I wonder if that was just a "bad run" of kits or if they are all like that ?

Dave F.

 

[dvdsnyd]

Eric,

I wonder if that was just a "bad run" of kits or if they are all like that ?

Dave F.

Not sure, but I'm a little nervous about starting my kit. I have a very early production kit.

 

[Rktman]

Not sure, but I'm a little nervous about starting my kit. I have a very early production kit.

Just be cognizant of the pitfalls I've mentioned and the workarounds I've used to deal with them. I'd be interested to know if you run across the same issues, and if you found a better way to address them than I did. If so, please post them to this thread, it may help others building the kit. BTW, I had kit #29. You may have zero problems building your SWT if you have a kit later than that.

 

[Tobor]

I wonder if eRockets is even aware of the issue...

 

[Rktman]

I wonder if eRockets is even aware of the issue...

A reviewer on the eRockets site mentioned the problem of the wing not swinging out exactly perpendicular to the main body tube. Hopefully they pay attention to what reviewers are saying.

 

[dvdsnyd]

Just be cognizant of the pitfalls I've mentioned and the workarounds I've used to deal with them. I'd be interested to know if you run across the same issues, and if you found a better way to address them than I did. If so, please post them to this thread, it may help others building the kit. BTW, I had kit #29. You may have zero problems building your SWT if you have a kit later than that.

Will definitely post back here for what I find and how I deal with the issues if I have them. Assuming I will. Kit #18 here
Dave

 

[Rktman]

Elevator clearance problems

Just when I thought there couldn’t possibly be another hiccup, I ran into yet another problem: not enough space for the elevator flap to fit between the end of the stab and the dowel standoff.

I've repeatedly gone over the instruction sheet and double-checked all my alignment measurements, but the only logical answer seems to point at the very real likelihood that the fin slots (which serve as an engine block and limit how far the engine pod/stuffer tube assembly can travel up into the main body tube) is too long by 1/8".

If you look at the first photo below, you can see how the fin’s slots serve as a block to prevent the assembly from moving forward once the end of the main body tube bottoms out in the slot.




As a double check, I scaled everything out precisely in Illustrator and the fin slots end up being too long, decreasing the space between the dowel support and the end of the stabilizer so that there is insufficient space for the elevator flap.




While there could be another reason for the clearance problem (including something I did) I sure can’t think of what that would be. As previously mentioned, I’ve repeatedly checked all the alignment measurements, and the kit is a fairly straightforward build. So if anyone else has a clue, please share, I’d be glad to hear it.

 

[kuririn]

There was an earlier issue with the wing not swinging out exactly perpendicular to the main body tube when in glide mode.

So it's an oblique scissor wing plane? Wonder if that was intentional or not?


My experience with first production run kits is that there will invariably be "gotchas".
More so the more complex a kit is.
Hopefully erockets will iron those out in later runs.
Great build thread by the way.

 

[Rktman]

So it's an oblique scissor wing plane? Wonder if that was intentional or not?
View attachment 511735

My experience with first production run kits is that there will invariably be "gotchas".
More so the more complex a kit is.
Hopefully erockets will iron those out in later runs.
Great build thread by the way.

Thanks @kuririn. Definitely a challenging one.

Wonder if eRockets (or any other large kit vendors) use beta testers? Would've helped catch the current crop of problems.

 

[Ronz Rocketz]

Just be cognizant of the pitfalls I've mentioned and the workarounds I've used to deal with them. I'd be interested to know if you run across the same issues, and if you found a better way to address them than I did. If so, please post them to this thread, it may help others building the kit. BTW, I had kit #29. You may have zero problems building your SWT if you have a kit later than that.

I've already glued the pivot plate to the wing and glued in the dowel, only to discover that the wing won't line up with the dowel and is over rotating like you show. Gary told me about this thread yesterday. I guess the fix is to Dremel out one end of the pivot groove and block the other. If I get it to work properly, I'll be flying this before I paint to see if I'll get it back.

I sent an email to Randy two days ago but no reply. I imagine they're tearing into the kits now trying to figure out which kits are misaligned.

 

[Ronz Rocketz]

.

 

[Ez2cDave]

My experience with first production run kits is that there will invariably be "gotchas".

Apparently, they didn't do a "test build" before putting the SWT kits on the market.

Dave

 

[dvdsnyd]

Wonder if eRockets (or any other large kit vendors) use beta testers? Would've helped catch the current crop of problems.

As I understand, there were several beta testers for this kit, and quite a bit of engineering to get everything "right"?

 

[Rktman]

As I understand, there were several beta testers for this kit, and quite a bit of engineering to get everything "right"?

Apparently I'm not the only one having glitches. Possibly more than 1 kit version is going out, with corrections being made along the way?

 

[Rktman]

Been thinking about some solutions. I first thought of notching the elevator flap so it clears the dowel support, but abandoned it as being somewhat risky. Not only would It would obviously weaken the flap, and it could very well break at the notch or cause a split along the grain line when it snaps up against the angled portion of the Nacelle Support (which serves as an elevator stop to limit the angle).

Or I could try to shorten the length of the fin slot by 1/8”. Options are to glue in a tiny 3/32” slice of basswood (difficult) or try to fill that same space with epoxy (messy and inexact at best).

I don’t like the idea of filing away 1/8” from the base of the dowel support either, possibly weakening the structure.

That leaves me with possibly the best, but most difficult option: trying to remove the fins and regluing them 1/8” further forward.

 

[Ronz Rocketz]

Elevator clearance problems

Just when I thought there couldn’t possibly be another hiccup, I ran into yet another problem: not enough space for the elevator flap to fit between the end of the stab and the dowel standoff.

I've repeatedly gone over the instruction sheet and double-checked all my alignment measurements, but the only logical answer seems to point at the very real likelihood that the fin slots (which serve as an engine block and limit how far the engine pod/stuffer tube assembly can travel up into the main body tube) is too long by 1/8".

If you look at the first photo below, you can see how the fin’s slots serve as a block to prevent the assembly from moving forward once the end of the main body tube bottoms out in the slot.

View attachment 511724


As a double check, I scaled everything out precisely in Illustrator and the fin slots end up being too long, decreasing the space between the dowel support and the end of the stabilizer so that there is insufficient space for the elevator flap.

View attachment 511725


While there could be another reason for the clearance problem (including something I did) I sure can’t think of what that would be. As previously mentioned, I’ve repeatedly checked all the alignment measurements, and the kit is a fairly straightforward build. So if anyone else has a clue, please share, I’d be glad to hear it.

I see what you mean now. Yes, my fin slot is 13/16". The dowel goes into the fin tube about half way. My understanding is that the string pulls the elevator up after ejection. The MM mostly fits into the main body tube so not sure if more insertion is needed.

I did sand a little off the front of the fin slot so the stuffer tube can go in further. To fix the fin, Randy suggested sanding the kidney shaped knob so the dowel can insert into the fin. I added a spot of glue in the slot to prevent it from over rotating.

 

[Rktman]

Having problems removing the fins. Fortunately, I had a Plan B in case things didn’t go the way I hoped and had ordered replacement parts (stuffer tube, motor tube, CRs, fins, etc.) earlier. I’ll be reassembling the whole fin/stuffer tube/motor tube assembly with the fins mounted 1/8” further forward.

To be continued…

 

[Ronz Rocketz]

The completed glider seems to fly alright. Winds were moderate about 10mph. It needs to stay within the park so do I add more forward weight or less?

View attachment scissor.mp4

 

[5x7]

It needs to turn, so some clay on one wing.

 

[Rktman]

The completed glider seems to fly alright. Winds were moderate about 10mph. It needs to stay within the park so do I add more forward weight or less?

View attachment 512670

That's a pretty steep descent angle, I'd say a bit less nose weight or a little more up elevator so it has time to transition to glide from a vertical launch position.

 

[Ez2cDave]

That's a pretty steep descent angle, I'd say a bit less nose weight or a little more up elevator so it has time to transition to glide from a vertical launch position.

On the second toss, it looked to me like it stalled and went into a dive.

Dave F.

 

[Ronz Rocketz]

It did land flat and didn’t nose dive so I’m wondering. I don’t plan to paint and decal until it has successfully returned from flight. I don’t want to make the effort only to have it glide off into another zip code.

 

[kuririn]

Paint and decals will add more weight. Try trimming for glide after finishing. Consider using Sharpies or food dye to minimize weight and optimize glide. IIRC the reviews I've read say the Scissor Wing was not the best glider in the first place.
As 5 X 7 mentioned a little clay weight on one wingtip will produce a turning glide and a lazy downward circle, keeping it from gliding away. Not too much or you will have a death spiral.
I see you and Chris launched on Sunday in the windy conditions. You guys are nuts. Heh.

 

[Ronz Rocketz]

It needs to turn, so some clay on one wing.

I'm wondering if i remove the big of glue i added to keep the wing straight, would the canned wing cause it to circle more?

 

[Ez2cDave]

IIRC the reviews I've read say the Scissor Wing was not the best glider in the first place.

You have a talent for understatement . . . Draggy design, high wing-loading, no airfoil, 0-0 Wing Incidence, no Dihedral, etc, etc, etc.

Dave F.

 

[Ronz Rocketz]

You have a talent for understatement . . . Draggy design, high wing-loading, no airfoil, 0-0 Wing Incidence, no Dihedral, etc, etc, etc.

Dave F.

So B6-2 and hope for the best? This glider will have to earn its paint and decals. It’ll either lawndart or glide away.

 

[Rktman]

So B6-2 and hope for the best? This glider will have to earn its paint and decals. It’ll either lawndart or glide away.

Let us know how it goes!