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Kevin,

Thanks for the link. Dan has done an amazing amount of work the past few years, dealing with all the bugs and Excel versions. His spreadsheet is clearly more sophisticated than Suter’s for sure but lacks the simplicity of input for fairly common configurations such as the Orion.

In other words, Dan’s spreadsheet will design and analyze anything… detailed input – detailed output. Suter’s will quickly analyze an existing design, which is the subject here, and suggest a CG location safe for first flight and areas for future experimentation. It will also aid in design for fairly simple configuration. Both tools have their place.

In terms of AVL, Drela is a hoot and his work is solid. Having said that, most people in this hobby have no desire to dedicate the significant time required to learn its use. They want to just fly!

Did you have a chance to look at Suter’s work?

Thanks again,

Dick

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Kevin,

I totally agree with your comments. I would love to stuff the Orion into Dan's spreadsheet for a comparison. Now if I just just had a Windows machine! My iMAC doesn't like VB macros!!!!!

This is fun stuff all the same.

Dick

Wow, I've read the last few posts over a few times and need to re read a few more. What cool info to learn with, thanks!

Dick, maybe we can hook up some day and fly Orion's. I'm in Santa clarita which isn't too far away. Where do you normally fly at?

Thanks all
Doug

Kevin,

I looked further at Dan’s spreadsheet after canning the VB macros. It is clearly excellent for complex geometries and may prove more accurate than Suter’s work, but the input format reminds me of Blaine Rawdon’s Plane Geomentry… a very thorough design and analysis tool. Both excellent for results I suspect. I know Blaine’s work is as I have used it many times.

Suter’s GUI is so easy. Just fill-in the yellow cells on the graphical representation of the subject surfaces, select a static margin and out comes the distance from the root LE of the wing. I am not diminishing Dan’s work but only seeking a simple solution for non-aero savvy folks looking for guidance on common sailplane designs.

To be honest, I miss the tools we had at the airplane factory where I configured Blended Wing Bodies in collaboration with Blaine, Talk about a hoot!

I guess I need to parse my hard disc and run Windows, as a comparison is called for. I bet the results will be within spitting distance.

Best regards,

Dick

Doug,

Decades ago I flew with Joe Wurts at the Santa Clarita Soaring Association site. Their web site suggests they no longer exist. So… where do you fly?

I fly at Fairview Park in Costa Mesa, just 5 minutes from my home. Goggle Waldorf School on Canyon Drive in Costa Mesa and you will find it. Was there today and the whole sky was going up! It is the flying site for the Harbor Soaring Society, a very active club offering lots of training for the kids. Ah, the miracle of flight!

Cheers,

Dick

I put the elevator to zero with an incidence meter for center of the servo, but on the NAN site they show: (78 mm measured from bottom of fuselage to trailing edge) That isn't anywhere close to what I have with a meter. What's up?

Monster,

Just my two cents. Was that from the bottom of the fuselage or fin (where the stab TE occurs)?

I never trust that stuff. I block up the fuselage to where the wing is zero-zero on the bench. On the Orion I wanted about 2 degrees "up" stab (the stab/wing decalage) for first toss with the CG at 105mm behind the wing root LE.

The SIN (or TAN if you want, makes no difference) of 2 degrees times the stab chord of ~4.7" is about 0.16", thus I wanted the stab TE ABOVE the LE by that amount. Worked for a first toss and have trimmed that down a bit now.

Hope this helps.

Dick

Wow man, you lost me.

Block-up the fuselage on the workbench so the distance from the wing LE is the same distance to the workbench as the wing TE. That is zero incidence for the wing.

Now measure the distance from the stab TE (at the TE kink where the rudder operates) to the bench, Distance 1 and measure the distance from the stab LE to the bench, Distance 2.

Distance 1 should be ~0.16" more than Distance 2. That will provide about 2 degrees "up elevator."

Dick

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Kevin,

That is so true. Now let's help a non-aero guy go fly his airplane. If one does as I suggested success could ensue.

Do you know what the camber is on the Orion. I do because I measured this proprietary airfoil that lacks published polars. Everything will be okay we if simply help folks go fly their birds without the need to study aerodynamics.

It's called a hobby!

Dick

Well Kevin,

This was a good opportunity to finally upgrade to Office for MAC:2011 that runs VB macros. Having done that I entered the same Orion geometry into Dan’s CGCalc v.1.05_03 and Suter’s CG Calc. The results are NOT within spitting distance as follows. Note that column 1 is Dan’s result using the actual Z position of the stab, column 2 is Suter’s result using 0.6 stab efficiency as he suggests and column 3 is Suter’s result using 0.9 stab efficiency that is NOT recommended. Distance shown is from wing root LE measured aft.

Neutral Point (in) 5.32 4.62 5.33
% of MAC N/A 43.4 52.5
CG Location (in) 4.9 4.2 4.9
% of MAC N/A 38.4 47.0
Static Margin (%) 5.3 5.0 5.5

It is possible that I completely screwed-up the data entry but… I’ll let you and Dan check that.

My Orion as earlier stated balanced at 105mm (4.1”) for first flight and very slowly pulled up from a 45 degree dive… perfect for me. To suggest a first flight with the CG moved aft 0.7” (to ~125mm) would be spooky at best and likely demonstrate a severe tuck in the dive test when trimmed for thermal flying. I will let some brave pilot do that test.

This is long winded and really off-topic for an Orion forum so will conclude my review of Dan’s CGCalc as follows:

The instructions are way out of date… 10/23/09.

He starts off on sheet one with this: “The coordinate system is shown above. It's set up this way for formatting reasons. It's not a proper "right-hand rule" system, but who cares. Deal with it.” I care, having mentored new hires straight from universities we all care. As a configuration designer for many years on full-size aircraft I don’t want to deal with it. Fix it!

Is that why the vertical stab has forward to the right? The convention is forward to the left.

Clicking around the “take action cells” I get lots of run time errors. Could be my MAC, however.

Suter’s spreadsheet uses no VISABLE coordinates, just plug-in the numbers (all positive) in the yellow cells on the graphical representation of the surface in question. Scary simple! No remembering to enter negative X values needed as in Dan’s spreadsheet.

He does not offer %MAC values for the numbers… very handy. Suter does.

He uses a Static Margin Wizard which is okay, but why?. Suter has all of this stuff on one sheet allowing YOUR desired CG location, Static Margin OR %MAC to be iterated with simple data entry and output… no macros or solving required.

He requires dihedral to be entered in degrees. Hey, I have this airplane sitting on the bench and I have a tape measure. That is all Suter wants and no Trig needed to calculate degrees. Suter calculates the degrees for us. Cool.

He uses decimals out to 6 or 8 places. Why? It makes the data hard to read and means nothing in the real world of models.

He states this: “I should also give the disclaimer that the entire spreadsheet, including the fuselage contribution, can be thought of as a first-order approximation. There are many things it doesn't take into account -- things which are usually not incredibly important -- in order to make the calculations tractable and reduce the need for detailed user input. It's not meant to replace flight testing, but it should help getting the CG close on the first try so there are no big surprises. However, if you have a model with some unusual features you should be careful using the spreadsheet.” Amen.

I never recommend products but will suggest Suter’s spreadsheet is worth a try. To suggest Dan’s spreadsheet is “simpler and faster” to use is a real stretch. To each his own. If you want a very sophisticated MODEL design and analysis tool that conforms to industry standards look at Blaine Rawdon’s Plane Geometry.

Dick

Originally Posted by MonsterBFC

I put the elevator to zero with an incidence meter for center of the servo, but on the NAN site they show: (78 mm measured from bottom of fuselage to trailing edge) That isn't anywhere close to what I have with a meter. What's up?

All that calculation stuff is great, but I prefer to K.I.S.S.

I set up the stab so that the drive rod is just above the center of the fin slot, then visually check it from the front and side. It doesn't have to be perfect, just "close enough" to safely get the model in the air. Once you have it flying, you'll fine tune the stab neutral to suit you.

The stab neutral point will vary with your CG location, as Dick alludes to. With a 105mm CG location, I measured about 77mm to the stab trailing edges, with the fuse flat on the bench., so that is pretty close to the spec that you found.

Good luck,
Lenny