Semroc Scissor Wing Transport Kit Build Thread

[Rktman]

Well it's been awhile but I finally found a dry, low-wind day to see how effective the "Gurney Flap" is. It doesn't seem to be. I'll keep futzing with it but I don't want to go too much larger and have it affect the launch trajectory negatively.

The SWT still seems too nose-heavy for comfort even after increasing the elevator angle, so I'm going to add a gram or so of tail weight and see if that improves things. July is the wettest month here so my next window of opportunity may be a slim one.

 

[Ez2cDave]

Well it's been awhile but I finally found a dry, low-wind day to see how effective the "Gurney Flap" is. It doesn't seem to be. I'll keep futzing with it but I don't want to go too much larger and have it affect the launch trajectory negatively.

Hi, Eric !

I have some thoughts about the "Gurney Flap" . . .

I think its effectiveness is relative to airspeed and the faster the Glide Speed, the more effective it becomes. Conversely, the slower the Glide Speed, the larger it would need to be, in order to be effective.

Thoughts ?

Dave F.

 

[Amsterdam]

Any way you could shim in even a degree of positive incidence under the main wing? You could do it in such a way that the incline would represent a tilt at boost, then when the wing swivels it will give you positive incidence on the wing.

 

[Rktman]

Any way you could shim in even a degree of positive incidence under the main wing? You could do it in such a way that the incline would represent a tilt at boost, then when the wing swivels it will give you positive incidence on the wing.

View attachment 527803

That's a great alternate idea to induce a nice, safe, wide turn. It's actually even better than angling the rudder, since doing so won't affect the boost trajectory.

Unfortunately I already shimmed the forward end (post #52) to even it up because the pivot post was 2 degrees off vertical.

 

[Amsterdam]

Unfortunately I already shimmed the forward end (post #52) to even it up because the pivot post was 2 degrees off vertical.

I believe were referring to the the same spot . I was thinking if you shimmed the main wing to have positive incidence in glide, (the sketch is the wing in boost position) then you wouldnt need to add weight to the tail, . I could be off on my trimming game tho

 

[Rktman]

I believe were referring to the the same spot . I was thinking if you shimmed the main wing to have positive incidence in glide, (the sketch is the wing in boost position) then you wouldnt need to add weight to the tail, . I could be off on my trimming game tho

I didn't know the glider would end up being so nose-heavy, otherwise I would have shimmed it to have a positive incidence instead of just leveling the wing. Your idea is a good one and if I were ever to build the SWT again I would definitely consider sanding the entire pivot box assembly so that its forward end was angled upward two or three degrees if possible.

There's a limit to how much it can be angled though because the dowel that anchors the wing in launch position has to be able to slide into the launch lug in the wing tip.

 

[Ronz Rocketz]

It glided.

 

[Rktman]

It glided.

MUCH improved glide after adding that tail weight! Still a tiny bit nose down, but at least that improves odds that it won't leave the park.

 

[Ronz Rocketz]

MUCH improved glide after adding that tail weight! Still a tiny bit nose down, but at least that improves odds that it won't leave the park.

I think the nose down was the perspective of the cam. It circled around us and had to spin to keep it in view. I tried it again yesterday and crashed because the wing caught in the front tab. Minor damage. Just need to pay more attention to the tip.

 

[Rktman]

"Takes a lickin but keeps on tickin".

 

[Ronz Rocketz]

Rapid Expected Disassembly

 

[Rktman]

Finally had a chance to do some follow-up trimming. I added just a bit more tail weight to the SWT so that now it doesn't pitch nose down at all anywhere along its glide path.

Interestingly the glide CG falls at exactly 8.75" from the rear of the main BT, the position specified in the original Estes instruction sheet. That's encouraging.

Boost CG with a B6-2 falls at 5.75" from the rear of the main BT as also specified by Estes in the original instruction sheet. That means if I want to move up to a C6-3 I'll have to add additional weight to the front of the motor pod.

 

[Rktman]

Painting completed. Just waiting for a low-wind day to put it up on a test flight. If all goes well, it earns its decals.

 

[Rktman]

Maidened a few weeks ago. Despite prolonged multiple hand-trimming sessions to get a decent glide, it was still extremely nose-heavy and put in a really short duration flight. Not sure you can see it, but as you can see from the time stamp from launch to when I start walking over to retrieve it, it was only about 15 seconds.

I'll need to do some serious retrimming, to the point that it glides with a slightly nose-up posture.

 

[Ez2cDave]

Maidened a few weeks ago. Despite prolonged multiple hand-trimming sessions to get a decent glide, it was still extremely nose-heavy and put in a really short duration flight. Not sure you can see it, but as you can see from the time stamp from launch to when I start walking over to retrieve it, it was only about 15 seconds.

I'll need to do some serious retrimming, to the point that it glides with a slightly nose-up posture.

Eric,

I think several factors are in play here.

(1) No Airfoil on Wing.
(2) Glider is "Zero-Zero" ( no Angle of Incidence or Decalage ).
(3) No Dihedral.

All of that is making Trimming difficult and reducing flight performance,

Dave F.

 

[Rktman]

Eric,

I think several factors are in play here.

(1) No Airfoil on Wing.
(2) Glider is "Zero-Zero" ( no Angle of Incidence or Decalage ).
(3) No Dihedral.

All of that is making Trimming difficult and reducing flight performance,

Dave F.

> I sanded an airfoil on mine.
> The elevator flap at the rear takes the place of incidence to raise the glider's nose.
I've seen some exemplary SWT flights with original kit versions. Ron (Ronz Rocketz) had much better results with his eRockets clone. I'll retrim & retry.

 

[Ez2cDave]

> I sanded an airfoil on mine.
> The elevator flap at the rear takes the place of incidence to raise the glider's nose.
I've seen some exemplary SWT flights with original kit versions. Ron (Ronz Rocketz) had much better results with his eRockets clone. I'll retrim & retry.

Eric,

OK . . . Given all of that, it sounds, as you noted, like a CG problem.

The "side benefit" to removing Nose Weight is that the Wing Loading will also decrease, improving glide performance.

Dave F.

 

[Rktman]

Eric,

OK . . . Given all of that, it sounds, as you noted, like a CG problem.

The "side benefit" to removing Nose Weight is that the Wing Loading will also decrease, improving glide performance.

Dave F.

Didn't add nose weight, so I'll have to sand more angle into the elevator stop.

 

[Ez2cDave]

Didn't add nose weight, so I'll have to sand more angle into the elevator stop.

Eric,

Hmm . . . Was the Nose Cone unusually heavy ?

I think it's odd for the CG to be that far forward, otherwise.

Dave F.

 

[Rktman]

Eric,

Hmm . . . Was the Nose Cone unusually heavy ?

I think it's odd for the CG to be that far forward, otherwise.

Dave F.

Very ordinary balsa cone

 

[Ez2cDave]

Very ordinary balsa cone

Hmm . . . puzzling.

How much is the CG too far forward ? ( "estimate / guesstimate" )

Dave F.

 

[Rktman]

Hmm . . . puzzling.

How much is the CG too far forward ? ( "estimate / guesstimate" )

Dave F.

CG is 8.75" from rear of BT – exactly within range specified in the erockets instruction sheet. This was after having to add 2.12g of tail weight necessitated during trimming session. Will sand more angle into the elevator stop to avoid adding any more tail weight.

 

[Ez2cDave]

CG is 8.75" from rear of BT – exactly within range specified in the erockets instruction sheet. This was after having to add 2.12g of tail weight necessitated during trimming session. Will sand more angle into the elevator stop to avoid adding any more tail weight.

Eric,

I have been thinking . . .

Possible "typo" for CG location in the instructions or other possible error ?

How does it compare to the original Estes instructions ? ( attached below )

Dave F.

 

[Rktman]

Eric,

I have been thinking . . .

Possible "typo" for CG location in the instructions or other possible error ?

How does it compare to the original Estes instructions ? ( attached below )

Dave F.

CG exactly the same.

 

[Ez2cDave]

CG exactly the same.

Strange . . . I am at a loss for what could have shifted the CG forward.

Dave F.

 

[burkefj]

Can you hog out the balsa cone to reduce some nose weight?
Irrespective of the dimension from the rear of the tube, what is the chord of the wing at the center, and how far back from the leading edge at the center is the balance point, is it at 25%, 30%, of the chord or further forward than that?

Frank

 

[Rktman]

...how far back from the leading edge at the center is the balance point, is it at 25%, 30%, of the chord or further forward than that?

Frank

Frank, when you say "balance point", are you referring to the wing's balance point or the overall glider balance point?

 

[Ez2cDave]

Frank, when you say "balance point", are you referring to the wing's balance point or the overall glider balance point?

Eric,

I believe that Frank means the Balance Point of the Glider, relevant to its location on the Wing, when deployed ( distance back from the Leading Edge ).

Dave F.

 

[burkefj]

Eric,

I believe that Frank means the Balance Point of the Glider, relevant to its location on the Wing, when deployed ( distance back from the Leading Edge ).

Dave F.

Correct, measuring from the leading edge of the wing at the center, where does the model balance with respect to a point on the wing? And what is the chord at the center of the wing, ie distance from leading edge to trailing edge. Then you can figure out the % of the chord at the recommended balance point and we can see if it makes sense, compared to a normal 25-30% chord cg ...

 

[Cape Byron]

Correct, measuring from the leading edge of the wing at the center, where does the model balance with respect to a point on the wing? And what is the chord at the center of the wing, ie distance from leading edge to trailing edge. Then you can figure out the % of the chord at the recommended balance point and we can see if it makes sense, compared to a normal 25-30% chord cg ...

Nice, clear explanation.