Restart on an old bird

[Steve P]

If you are needing new, you may want to consider carbon fiber over fiberglass. You can get 25 mm carbon fiber rod from a number of sources. Mr. Google can help you.

Here's one GRP example in the UK -- https://www.carbonfibreprofiles.com/...sf713626mu3br4

Antenna suppliers can sell you 25mm fiberglass rod. Again here, you'll probably have to look to Europe for millimeter sizes.

[LRFitch]

Steve,
Thanks for the post and info.
Larry

[Mark9]

Grainger says they have 1" dia.fiberglass rod. That would be about .016" oversize. Would require one to sand it to fit though.

https://www.grainger.com/category/fiberglass-rod-stock/fiberglass/raw-materials/ecatalog/N-c18Z1yzbae0?okey=Fiberglass+Rod&mkey=Fiberglass+Rod+Stock+Isophthlic+Polyester+Resin+%28ISO%29+Fiberglass+Material+&NLSCM=4&EndecaKeyword=Fiberglass+Rod+Stock&searchRedirect=Fiberglass+Rod#nav=%2Fcategory%2Ffiberglass-rod-stock%2Ffiberglass%2Fraw-materials%2Fecatalog%2FN-c18Z1z0nwtbZ1z0nyqiZ1yzbae0%3FEndecaKeyword%3DFiberglass%2BRod%2BStock%26NLSCM%3D4%26searchRedirect%3DFiberglass%2BRod

Mark

[LRFitch]

Mark,
Thanks for the info. Would it be possible to sand the 1" rod down to 25mm? If that is possible, it would be a bunch cheaper. The source in England will sell one at 25mm for about $30, but shipping is over $80. Don't think that is a responsible option for me. Is anyone knowledgeable about sanding a round fiberglass rod and keeping it round, but smaller in diameter?

Help,
Larry

[ARUP]

Can you chuck it in a drill press and wet sand it? (better than scattering all of that fiberglass dust!) Better yet if you have a wood worker friend then the rod could get chucked into a lathe and sanded/ turned. A cheap Harbor Freight dial indicator will help. Or... get a honing stone, dress it to size then hone your wing tube? 25.4mm is an inch so you wouldn't need to remove much from either.

[ARUP]

Maybe a gunsmith could help with the wing tube!

[LRFitch]

ARUP, Thanks for the ideas. Likely could use my drill press. You hit on the real issue--fiberglass sanding dust.

Larry

[LRFitch]

New saga on this old bird. Last weekend I tried to calculate a starting CoG for this bird. As you likely know, "wing sweep" is a big variable for getting the calculation correct. The Nimbus 4D is a two place glider, and most two place gliders have a forward swept wing to aid in getting the balance point to a place where you can fly the glider with one or two people in the plane. So, to measure the sweep, I assembled the glider in the back yard, got some measuring tools, tape, and string. I must say, to my old eyes, I couldn't see much sweep, in either direction, and couldn't measure anything reliably. So for my initial calculation, assumed no sweep

Steve P. just happened to buy a 1: 3.75 version of the glider, and the instruction sheet says the CG should be at 45 mm. My calculation for a slightly larger scale (1/3) and no sweep (an invalid assumption) yields 99 mm. So, my guess is the real value for this 1/3 scale glider is somewhere between these two values. My question is, how can I accurately determine the real sweep for my glider?

Looking at Martin Simons' three-view of the Nimbus 4DM (self-powered version), I can see a bit of forward sweep out to about mid span, and rearward sweep for the last 1/4 of the span toward the tips. In fact, it looks like the rear sweep of the tips looks to be more than the forward sweep along the first 1/2 span--way,-- confusing. How can I measure this sweep well enough to calculate a safe starting point for balance?

Thanks,
Larry

[Mark9]

Larry,
Do you have Excel on a PC? If so Curtis Suter has a spreadsheet that can do that, as well as calculate other factors for a sailplane configuration. I have used it and was pleased with the output from the formulas. It is described in an article in the RCSD link below and is available from his web site listed below as well.

http://www.rcsoaringdigest.com/pdfs/...SD-2008-04.pdf

http://tailwindgliders.com/Files.html

[LRFitch]

Mark, I do have the spreadsheets form Curtis. What I don't have are the several accurate measurements it takes to calculate the needed info.

Thanks for the links.

Larry

[Steve P]

To Larry's point in post #23... Here is the Paritech 7 meter Nimbus 4D I brought home from Etienne at ICARE. It has a somewhat more Arcus-like appearance in the transitions. I'm in love.

BTW, it has amazing build quality and appears incredibly strong.

[Steve P]

FWIW... Here are two full scale 4D photos I had saved off on my iPad. You can see the sweep in the main panel section.

[LRFitch]

Steve, Thanks for sharing. Now I just need a technique for measuring mine. Nobody said it would be easy?

Larry

[LRFitch]

Just an update on CoG. I was able to contact Bruce DeVisser in the California Bay Area. As you folks may know, Bruce had been importing Rosenthal, until they stopped make gliders again. Dang! He states that the 7 meter version has the CoG recommended at 35mm, and the 8.83 meter version starts at 70mm. I will start there.

Larry

[ARUP]

Get one of those inexpensive laser bubble levels cum 'chalk lines'. I have a small hand held one. It has a spot laser point and when you click the on/off/position button it cycles from 'spot' to 'chalk line' to off. It isn't really a chalk line but a red laser light line. Lay out your assembled model then use the laser 'chalk line' to see if there is any sweep by laying the line from a point tangent to each LE tip. If you get someone to help you or affix the laser light to a stand you can then measure what, if any, sweep you have. Hope this makes sense