Stab over/under

[Rich Holmes]

In case the following questions don't make it plain, my understanding of rocket glider design is pretty minimal, and my experience building them is zero, so please bear that in mind...

I'm building Geoffrey A. Landis's Nymph rocket glider. It was written up in the March 1974 Model Rocketeer, which I've downloaded from the NAR site. There also used to be a redrawn (in 2002 by Wolfram von Kiparski) plan on the NAR site; it's evidently not there any more but can be found on the Wayback Archive at http://wayback.archive.org/web/20131010013650/http://nar.org/competition/plans/pdf/nymph.pdf.

There are some slight differences between the two plans, the most significant being that the 1974 article shows the stab mounted on top of the fuselage boom while the 2002 plan has it underneath. I would assume on top was Landis's actual design even if it weren't for the photos accompanying the article, which are not the world's clearest but I think there's no question they show the stab on top.

But then that raises two questions: Why didn't von Kiparski draw it that way... and why did Landis write 'put one 1/8" long piece of launch lug under the wing, one over the stab, and it's built'? Maybe I'm reading too much into one preposition but to me that description of the launch lugs arrangement doesn't make any sense if the stab is on top of the fuselage.

Of course there's a third question (possibly related to the first): Regardless of how Landis designed it, is there a good argument for doing it differently?

[tbzep]

Ask Wolfram directly. His YORF username is astronwolf. :cool:

[astronwolf]

I don't know why I drew it that way. I remember building and flying one of these. I built it during a time when I was trying out many designs. My glider kind of sucked, and I lost interest in the design. If I had to, I'd just build it the way Landis originally did, and work it up from there. I favor slide wings and scissors-flop wings these days, and not gluing launch lugs to wings and stabs if I can help it.

[kevinj]

Could have been a typo, hard to tell from the photos where the lugs are.

Stab on top/on bottom depends on if the boom is tapered, and if the stab is airfoiled as it sets the incidence of the stab and affects the flight.

I'd build it to the plan, and not glue a lug on top of the stab.

kj

[Shreadvector]

Ask Geoff:

http://www.geoffreylandis.com/

https://webnews.sff.net/read?cmd=xover&group=sff.people.geoffrey-landis&from=-10

" I am now using my web address as my main e-mail: geoffmail (at) geoffreylandis (dot) com

--obviously replace the "at" with the symbol "@", and dot with a period."

[Shreadvector]

The Rocketeer drawing is wrong.

The airfoil on the Horizontal Stabilizer should be on the lower surface to generate lift downward AND the horizontal stabilizer should be glued to the lower tapered surface of the "boom" or fuselage. This gives you and angle of incidence to the wing so it will pull out of a "death dive" (unlike most of the Flat Cat gliders with no angle of incidence).

Gluing of the launch lugs should have them in a straight line along the top edge of the fuselage, so one would go directly under the wing and the other would go above the horizontal stabilizer but not glued directly to the angled upper surface of the horizontal stabilizer - it should be glued along the top edge of the fuselage. You can put something on top of the fuselage to easily locate the lug whilst gluing.

I built a large number of these back in the day. It was a good performer.

[Jerry Irvine]

As a practical matter you want under. You want tails out of rocket exhaust and you want negative incidence on elevators.

[astronwolf]

The Rocketeer drawing is wrong.

The airfoil on the Horizontal Stabilizer should be on the lower surface to generate lift downward AND the horizontal stabilizer should be glued to the lower tapered surface of the "boom" or fuselage.
That's the way I drew it. Maybe I knew something back then that I haven't thought about for a while. Thank-you.

[Ez2cDave]

In case the following questions don't make it plain, my understanding of rocket glider design is pretty minimal, and my experience building them is zero, so please bear that in mind...

I'm building Geoffrey A. Landis's Nymph rocket glider. It was written up in the March 1974 Model Rocketeer, which I've downloaded from the NAR site. There also used to be a redrawn (in 2002 by Wolfram von Kiparski) plan on the NAR site; it's evidently not there any more but can be found on the Wayback Archive at http://wayback.archive.org/web/20131010013650/http://nar.org/competition/plans/pdf/nymph.pdf.

There are some slight differences between the two plans, the most significant being that the 1974 article shows the stab mounted on top of the fuselage boom while the 2002 plan has it underneath. I would assume on top was Landis's actual design even if it weren't for the photos accompanying the article, which are not the world's clearest but I think there's no question they show the stab on top.

But then that raises two questions: Why didn't von Kiparski draw it that way... and why did Landis write 'put one 1/8" long piece of launch lug under the wing, one over the stab, and it's built'? Maybe I'm reading too much into one preposition but to me that description of the launch lugs arrangement doesn't make any sense if the stab is on top of the fuselage.

Of course there's a third question (possibly related to the first): Regardless of how Landis designed it, is there a good argument for doing it differently?

Here is the original Landis 1974 version.

Here is Wolf's version . . . PDF below.

Dave F.

[GuyNoir]

I built and flew mine with the stab on top and they flew fine. YMMV.

[BEC]

Thread necro:

I built one of these exactly as shown on in the Model Rocketeer, with the stab on top (while wondering about the line in the text about the aft launch lug being on top of the stab), with a lifting airfoil sanded in as best one can in 1/32 balsa.

It had its maiden flight yesterday and it didn't do well....nice straight high boost on a 1/2A3-2T. But then it came straight back down rather than transition to a glide. It was trimmed to glide rather nicely (I thought) from a hand toss.

I've replaced the crushed nose cone, but based on Fred Schecter's post (and what I saw) I think I will try to move the stab to the bottom of the tapered boom then re trim it for glide.

I'm not sure how Wolf's redraw works with the 1/8 square spruce fuselage, so no taper toward the tail...or is there a little?

The basic concept of a sliding pod is so simple that I'd love to fly something like this at NARAM this year, unless Jim Pommert can convince me to go the no moving parts route....

[GuyNoir]

Tunless Jim Pommert can convince me to go the no moving parts route....

If you're having trouble trimming a slide pod, which introduces a huge CG shift, I'm pretty certain that trimming a no moving parts glider is going to be a lot tougher, given that the CG shift there is substantially less.

My $0.02; YMMV.

[BEC]

If you're having trouble trimming a slide pod, which introduces a huge CG shift, I'm pretty certain that trimming a no moving parts glider is going to be a lot tougher, given that the CG shift there is substantially less.

My $0.02; YMMV.
Gee thanks, Bunny.....

I've not done rocket gliders before....I think this is my first that isn't one of Frank Burke's RC RGs, on which one does the trim change via the radio.

I can build to plans, but if the plans are not representing the actual working configuration of the aircraft, well...that's what this thread was originally about and where my questions still lie with exactly one flight's worth of free flight RG experience.

Jim Pommert has already shared some details about how NMP gliders are set up and I am likely going to give that a try as well.