kingaltair

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FB

I wish I would have known about your interest...I would have taken a picture of it. When I visited, I briefly saw it, but was not really paying attention to Nimbus. I can tell you for sure there is NO LIGHT BLUE or dark blue on Nimbus...it is a totally different color combination.

I also would like to be contacted .....about the plans and some questions I've asked, but Mrs Brett hasn't responded; I don't exactly know why.

I am about 75% sure the colors of Nimbus are either an off-white, or tan, and maroon, or dark red. Maybe Evan can verify that.

Duane

pimmnz

Don't know if I can...the only photos I have of Nimbus 1 and 2 are b&w from the mags of the time. I can tell you the 1 had open structure wing, and looks to be basically white with a dark colour trim lines, same as the 2, Neither scheme is in any way similar to the 'Nimbus twins' scheme. Not much help I know, but knowing this thread someone will step in with a kodachrome and the definative answer.
Evan.

pimmnz

Nimbus 2 plans and photos, 'American Modeler' June 1962. Not one that I have, but I bet someone has it, RFJ?
Evan.

RFJ

Sure do Here are a few shots from the June 1962 Nimbus 2 article - no mention of the color scheme used.

Ray

kingaltair

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It might also be white and brown. I'll ask a couple of the club members who might know.

Duane

UStik

Duane, after just looking over the stab drawings I think it has a substantial amount of anhedral. All pictures you posted give that impression, especially the attached one. There seems to be substantial decalage, too, and a very decent down thrust corresponding to it.

The horns or bellcranks drawn under the stab seem to be bent wires with a pice of sheet metal (brass?) bent around the wire and soldered to it (the part with the holes for clevises). The three small drawings on the left side could be three-view of the linkage that has to be in the fin.

The symbol in the right half of the stab is commonly used for c/g. I don't think it's "center of pressure" or MAC but I don't really know.

Just don't remember if someone said the root rib is semi-symmetrical, but in this case I think it's symmetrical and just distorted (lens distortion of the photo).

Michaelj2k

Tom's work is a classic method of providing lofted parts on an assembly drawing. The top view of the structure is viewed looking down. Each rib is rotated 90 degrees to its vertical plane as it would be placed in the stab. It looks like the stab is a double taper with each rib a different thickness. The leading edge is placed at a 45 degree angle referenced to the center rib number 1. Ribs #1 and #2 form the basis for the stab mounting to the vetical fin. What is interesting is that Tom did not loft rib #1 and the leading edge at that rib is a shaped block. This leads me to believe that ribs #1 and #2 are the same. The elevator control horn in the top left is a three view assembly layout. The control horn at the bottom of the drawing is an alternate layout using two pushrods in a "Y" configuration, probably to allow for the changes in the bend angles as the surface is moved. A visual inspection of which scheme Tom used to actuate the elevators is required to determine what Tom used. It also appears that the stabilizer is fully sheeted and has a few degrees of dihedral. The building tabs you see on each rib is actually a height above base where the bottom of each tab would be placed on the building board. This is a model sail boat builders method of placing each bulkhead in its proper position in the hull as most model yachts are built upside down on a board.

Actually from the looks of the drawing, the stab as Tom designed it is very easy to build. He took the time to loft and design the stab in a way so that the majority of the time spent building is in the "tooling" or set up of the building board to insure proper alignment.

Show us more!

UStik

Good analogy to building model yachts! But the center rib is lofted (has two tabs), it's just drawn outside the plan view as is the tip block. I think the plan view is a bottom view and the stab is built upside down because it has anhedral. Rib #1 and #2 are different, and each rib is correctly shaped for its position diagonal in the swept and (single) tapered stab. Notice the thickness at leading and trailing edge! There are three helper lines between lE and TE to construct the rib outlines. (I think someone said that before.)

Notice also the horizontal line on top meaning the building board and the stab lower (actually upper) edge with the shape of the supporting block under the tip, which is also shown in the top view.

Now I had the enlightenment about the control horn. The three-view on the top left is just that - a three-view of the horn (both horns, that is) aligned to a rectangular coordinate system (see my sketch). It shows how the horns have to be bent from straight wire. The horn at the bottom is not an alternative but just both horns as they are positioned on the complete stab (see the next three sketches), not rectangularly aligned but swept back 10 degrees and with maybe 4 degrees anhedral, aligned to the TE/hinge bar.

Free Bird

UStik,

Very nice renderings of the control horns. The perspective views make easier to understand how it all fits together. I hadn't thought about building the stab upside down, but it does make sense after looking at the drawing again. Perhaps you could do the same with the stab drawing?

FB

Michaelj2k

Thanks UStik, I forgot about that view of the center rib. Does the airfoil section look somewhat flat on one side compared to the other ribs?

Good call on the control horns, I think you have it nailed. You did that with Solidworks?

I looked at the drawing again and I'll agree with you on the anhedral as the orientation of the views support that.

Tom took a lot of time to set up a fixture to insure a true surface and it is reflected in his drawing. I can't wait to see the rest of the drawings.

UStik

Yes it does, but I think that's simply lens distortion. Unfortunately there are no EXIF data in the picture so we can't undistort it. Maybe Duane can do it or otherwise provide an undistorted plan. I think the airfoil is symmetric and it isn't a real airfoil, just a nice curve (French curves like on the Perigee?) drawn through LE, the three intermediate (helper) points, and TE. The LE is remarkably round, even the TE which is actually the hinge bar.

Indeed very nice work by Tom Brett, could be a textbook example. Nice how even the rib center/chord lines and the building board lines below them are not parallel but follow the anhedral. I wonder if today's CAD work is simpler than this geometric construction on the drawing board. I start thinking that drawing new building plans (rib outlines, plan view for the building board) would be even better than using copies of the original plans.

I used the simulator model builder program (not used to Solidworks) because it's simple. Building the whole stab would be not less work than building and photographing it in reality. Just cut the ribs, pin them on the plan, glue the small bars on, sheet both sides, glue the bigger (outer) bars, and sand the radius. OK, I forgot the triangular center block and the tip block, but still simple.

I wonder what the linkage in the fin looks like.

BTW, could it be that the orientation of three views is different in American and German drawings?

Tango Juliet

Wow! What a treasure you've got. This is all a little before my time, but I'm enjoying it none the less. I love seeing these old sketches and technical drawings. It takes me back to my high school days when we still used T-Squares and Triangles in my drafting classes. Can't wait to see more from the Brett family.

Michaelj2k

Yes, Tom was a master at his craft. Imagine what he could do with CAD today.

Yes, very simple to build once it is properly jigged in a building fixture.

I think we'll find out real soon!

I don't think orientation is any different between American and German designs as it can be the designers choice according to what and how he wants to represent the view in question.

OK Duane, what other goodies are you going to show us?

kingaltair

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UStik...We can't afford NOT to have you contributing to this thread. You "engineer types" are going to really come in handy during the course of this thread. I said early on that the TBX-1 is drawn more like a plan Lookheed or Boeing would put together...it is not a simple little plan you find in a kit or even a model magazine construction article. I NEVER would have picked up on the idea of a "bottom view", and building the stab upside down, which I assume everybody here is now in agreement on. Does everybody agree with the "German guy"?

This sheds new light on a big question I had that I was going to "spring" on you later. When looking at the wing, I was perplexed when I studied the wing ribs. Here's just a hint of what is coming.... the wing is semi-symetrical, and the plan looks like each wing rib has the thickest portion on the BOTTOM. I have NEVER seen a semi-symmetrical wing configured that way..how could you get any lift? If the WING is ALSO built upside down, that would explain a lot. That's for a little later.

To get back to the stab. I have a few extra views of the completred TBX including one I haven't shown before because I didn't think it was important. To me it looks like the bottom of the stab is essentially flat, and the top tapers down somewhat...is that the "anhedral" you speak of? Take a look at these pictures and see if they throw more light on and confirm the orientation theories of the stab. After all, we don't want to glue the stab on upside down do we?

BTW..I have spent times these last few days photographing the 5 plan sheets in detail, and each section will be discussed as long as it takes to unravel the TBX's mysteries, (hopefully so that even I can understand them). This thread may go on for a while.

BTW-2 Burkhard...I've loaded the XTR-Ultimate on my new computer, and will start "playing" with it more. The planes seem to be underpowered compared to the real thing.

Duane

UStik

The first picture is excellent, the stab seen dead rear. Top and bottom side are drooping from root to tip, that is the anhedral (the reverse of dihedral). It seems to be 3 degrees (on each side), measured at the elevator TE. There's much optical illusion in the other pictures due to combined taper, sweep, and anhedral and non-square viewing angles.

As to the wing, the non-symmetrical airfoil is not visible but there might be a wash-in, I mean the wing tip has less angle-of-incidence than the root. AFAIK it's not uncommon to design highly swept wings with such a "belly" at root and decent twist/wash-in (airliner wings for example) but we'd need a real aero guy to explain the rationale behind that (especially for a pattern airplane). On the other hand, the attached picture doesn't look like "perverse" airfoil or wash-in. Maybe it's only the building method, upside down like the stab, what is shown in the drawings. After all the wing ribs with the tabs had to be constructed as well as the stab ribs to get the building fixture.

BTW, how about undistorting the photos? RCU seems to remove the EXIF data so only you could do that before uploading.

RFJ

UStik. That would be wash OUT - a very common way to prevent so called tip stall. A better way is to use a bi convex root section ( I refuse to use the meaningless term semi symmetrical ) and a symmetrical tip section with identical incidence angles.

Ray

kingaltair

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AFAIK....???????????

BTW, how about undistorting the photos? RCU seems to remove the EXIF data so only you could do that before uploading. ???????????

How???....I try to always tell the truth and not "distort" anything in the process.

kingaltair

My Feedback: (4)

Why use one word, (that means something to me), when you can say:

"... bi convex root section....and a symmetrical tip section with identical incidence angles..." Huh???

As I sometimes ask UStik ...........can you explain that in English?

Duane

Free Bird

As Far As I Know

FB

RFJ

I'll have a go

One way to build a well behaved tapered wing is to use an airfoil at the tip with less camber than that used at the root. On our sort of models this is usually done by choosing perhaps an NACA 2415 ( 2% camber) at the root and an NACA 0012 ( 0% camber) at the tip. This achieves what is sometimes called aerodynamic wash out as opposed to physical wash out obtained by building the wing with a twist where the trailing edge at the tip is "higher" than the trailing edge at the root.

I got this idea from Tom Prosser who used it on his 1970 Crescendo F3A design and have used it on all my models since.

Ray

kingaltair

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Further discussing the wing ribs I mentioned earlier, let me share with you the wing rib templates. The quality of this particular sheet isn't as good as some of the others...it is darker and more faded, but it is good enough to build from. As you can see, the "bi-convex" rib sections show the thickest portion on the bottom, which fits the idea of building the wing upside down.

There was a question as to whether of not "washout" was built into the wing. If I understand Ray correctly, (and please correct me if I didn't), in a "washout" situation the tip becomes more symmetrical, (or fully symmetrical), while the ribs toward the root are progressively more semi-symmetrical, (bi-convex). While I can't determine yet the DEGREE of "Bi-convexivity" change from root to tip(the amout of semi-symmetrical the airfoil is), and whether it becomes less as it reaches the tip, it appears to be uniform from root to tip to me.

What do you think?

Duane

AndyKunz

Duane,

Ray's using the correct terminology. A good model aircraft aerodynamics book will go a good deal toward explaining how these things work. Martin Simon's book will help tremendously. He discusses the proper terminology and you'll see immediately why.

An airfoil doesn't have to look like you normally expect in order to create lift and have good flying characteristics.

Check out the pictures here:

http://www.centennialofflight.gov/es...cal/Tech12.htm
http://www.nasa.gov/centers/dryden/n...-044-DFRC.html

Google for pictures of the "super-critical F-8 Crusader" to find more.

Now we aren't flying at those speeds, but the fact is, the DIFFERENCE is what makes your wing lift. The shape of the difference is what determines the lifting properties.

Andy

kingaltair

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Another question. If you look at the center detail on the drawing on the right...assuming the spars are also drawn to accept the wing ribs "upside down", does that mean the wing also has "anhedral", because the TOP of the spar is actually the bottom of the wing? On the right drawing you can see the angle formed by the two spars when they come together.

Looks like an anhedral wing with a semi-symmmetrical, (bi-convex) airfoil. Is that right?

kingaltair

My Feedback: (4)

It's obvious how the ribs fit the spars, but in the drawings of the wing ribs, is the wing bottom on top, or is the thicker section supposed to be on the bottom as it is drawn? Does the wing have anhedral, or dihedral? How can you tell if it's right side up, or upside down? If the wing ribs are right side up, it will be the first model I've ever seen to do that.

I hope we can all agree on this, as it obviously matters a great deal.

UStik

Ouch, that's me, I keep confusing left and right as well.

Duane, despite your strong and honorable efforts your camera distorts nearly all of your shots, and obviously you don't even know about it. Even though I know about it, my camera does the same to me [:@] and there's nothing I can do about it than undistorting the images ex-post. I even paid for a great little program called [link=http://epaperpress.com/ptlens/]PTLens[/link].

You might get this program as well or simply send those shots via e-mail where it's important to see them without lens distortion. See the T2 shot (Chuck's photo from fleabay) as an example for the impression.