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Feb 24, 2008, 01:50 PM
Thread OP
Discussion

Molded BS-1 scratch build


I'm just beginning to undertake a build of a fully molded BS-1. I just love the looks of the plane and want a challenge. I've done only a few small molded parts and had plenty of trouble with them but I want to learn to do it right with this plane.

I've done my research. There are a fair number of pictures on the web. I've even found a BS-1 owner in Wichita who will help out when I have questions.

It turns out there's a guy in Germany who's done this already. I was a little disappointed at first but he's not producing them commercially and I like the looks of his model so I'm going to go ahead anyway. His site's at www.cb-roter-baron.de-index.htm.

Also, and don't flame me for this, I fly electric scale and I do it the "ugly" way. I cut off the nose and fit folding props and a spinner. I paint the props white so they blend with the fuse and I think they look pretty darned nice in the air. I don't have to mess with aerotow and I don't have to spend thousands of dollars on the fancy retracting systems. I just hand launch them and they are spectacular to see. I've found that the Neu 1509/1.5d motor has worked beautifully for this. With a 3S lipo it'll handle up to about 150 oz. planes. With 4S it handles my 4 meter Salto spectacularly at about 215 oz. It climbs out very steepy and is at 800 feet in less than 15 seconds. I think the Neu with the 4S pack would handle a 300 + oz. plane very nicely.

But that's really an aside. Back to the build. I considered doing 1/3 scale but that's a lot of plane for a first molded project. And, though I like a big plane as much as the rest of us, there's something pretty comfortable about a 4.5 meter plane as compared with a 6 meter plane. I actually fly from my local school yard a lot. It's a big field and plenty of room to fly and land but there does get to be a point where you feel a plane is just to big for that kind of environment.

At this point, I've done a 3D model of the plane. I'm an animator by trade so it's a natural to do it this way. I started with Martin Simons' drawings, imported them along with some others I found on the German builder's site and started drawing the fuse. With that built, I took cross sections and exported them into Adobe Illustrator for printing. My idea is to cut a vertical longitudingal section and then do cross sections about every 4 inches. Then I'll bend strips of either balsa or maybe pine over the forms, sand to shape, fiberglass, bondo and paint to get everything smooth.

I've attached a few pictures from my computer model. I even put in a figure scaled to my height so I could get a feel for scale.

I'm starting with building the fuse and will probably also mold the stab before even thinking about the wing. I'm nervous about the molding process since the few molds I have done on little hand launch fuselages were pretty traumatic. My first set of molds, the plug stuck in the mold and they were a total loss. The second set came out okay but the plug still wound up getting destroyed. I would have to destroy this fuse plug after all the work that will go into it.

I'd welcome comments and help here as I go along. I've got a lot to learn about this process and maybe you all can help me avoid some disasters.
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Feb 24, 2008, 03:36 PM
Registered User

Bs-1


Hi -- Curtis ........ If you want I have much bettre drawing of BS-1 than the one you are talking about , PM me . The fuselage sections are wrong in the book , yes I do have the book and original plan of SB-1 from Germany .

Mirek J.
Last edited by Mirek J.; Feb 24, 2008 at 04:44 PM. Reason: Changing info.
Feb 25, 2008, 04:03 PM
Thread OP
One of the early decisions I need to make is the choice of airfoils for the wing. I have only a fair drawing of the E348 airfoil. If I use it, it will be an approximation at best and I have no idea how I would make decisions about thickness or twist at the tips of the wings.

The other alternative is to use one of the ubiquitous HQ series of airfoils or some such. I've attached a small drawing I received from Martin Simons which comes from a German source close to Eppler. The airfoil ordinates have not been published to my knowledge.

My goal for the sailplane would to be for it to behave similar to the original.

I'd welcome opinions on the airfoil choice.
Feb 26, 2008, 08:21 AM
Registered User
Curtis,

I am far away from giving you airfoil expertise, but I have been in this model sailplane hobby long enough to tell you that all these thick Eppler and Worthmann airfoils were used here in Germany in the 70ies and 80ies "of the last century" but at the end of the day, they were no match at all compared to HQ, NH, RG a.s.o.
I would not push the scale idea that far.

Herbert
Feb 26, 2008, 10:59 AM
SoarScale
Curtis, I concur with Herbert. For the BS-1 I would choose a 2.5% or 3% chambered HQW or the newer 2.5% HQ/DS airfoils (http://www.hq-modellflug.de/). Thickness should be about 11 to 12% in general with perhaps 12 to 13% thick at the root.

I don't have a picture of the BS-1 but the taper ratio on the wings does not look that high and therefore you could more than likely safely use the same airfoil across the span with a minor variation in thickness from root to tip.

Ideally, however, you would be better off increasing the chamber towards the tip, starting at the aileron root, by about 0.5% over the length of the aileron and then adding washout equivalent to the zero lift angle differential between the lower and higher chambered airfoils. Fairly easy to determine - let me know if you need help here.

Tony Elliott
www.laserflight.com
Feb 26, 2008, 12:55 PM
Thread OP
Thanks guys. I guess I had been coming to the same conclusion on the airfoils. Particularly as I looked at the section with its radical pressure gradient on the latter half of the top surface.

Tony, I've read another post of yours on the topic of camber and twist. I am familiar with the concepts from having read Martin Simons' Model Aircraft Aerodynamics but I'm not confident as to how I would apply them here. You're correct that the BS-1 does not have a lot of taper in planform. It's a fairly deep wing in chord. I'll attach a top view so you can see.

Could you clarify for me how I would determine the zero lift angle and why the increase in camber? I do have Profili and could probably figure it out but would appreciate the help.

Tony, I followed your link to Lightflight.com and I see you do CNC stuff. Have you ever done CNC wing molds or plugs?
Feb 26, 2008, 01:06 PM
Thread OP
I went to check out the Quabeck airfoils site. Wow! What a lot of spectacular sailplane photos. How would I go about dealing with translation? Does the HQ/DS refer to Dynamic Soaring?
Feb 26, 2008, 02:05 PM
Registered User
I had the privilage of meeting Helmut Quabeck at Hahnenmoos. He speaks excellent English and is a very gracious person and very generous with his knowledge. You might write to him with your questions.

Regards,

Steve
Feb 26, 2008, 04:13 PM
Thread OP
For the moment, I'm waiting to connect with Mirek to see if his drawing is good enough and/or sufficiently different that I should re-work my fuselage design before building the plug. I'll attach here the drawing I had prepared which contains the fuselage profile and the cross sections. The cross sections are in position for where they occur on the profile. There are two odd ones that correcspond to the angled planes defiining the leading and trailing edges of the cockpit.
Feb 26, 2008, 08:07 PM
Registered User
Quote:
Originally Posted by Curtis Miller
One of the early decisions I need to make is the choice of airfoils for the wing. I have only a fair drawing of the E348 airfoil. If I use it, it will be an approximation at best and I have no idea how I would make decisions about thickness or twist at the tips of the wings.

The other alternative is to use one of the ubiquitous HQ series of airfoils or some such. I've attached a small drawing I received from Martin Simons which comes from a German source close to Eppler. The airfoil ordinates have not been published to my knowledge.

My goal for the sailplane would to be for it to behave similar to the original.

I'd welcome opinions on the airfoil choice.
I woukld definately not use the full size section. A shape like that would not work well at our scale and speeds (renolds number) Go with a HQ section at 2.5 to 3 % camber and a root thickness of 15% tapering to 12% at the tip.
Don't worry about washout or, if you must, then just a wisker like say 1.5 degrees.
Have a look at the drag polars in Profilli 2 if you are in doubt. RE of 100000 will tell the story.

Allan.
Feb 26, 2008, 08:28 PM
Registered User

Washout


I had a quick look at the lift distribution and I think a little washout is needed to suppress the tip stall. 1.5 degress from the midspan break out to the tip looks good.
I'll try and attach the spread sheet to show this. You basically want a decrease in lift coeft as you approach the tip to give good handling. This assumes a few things like similar sections along the span in terms of camber and efficiency but is a pretty good guide that I have tested practically many times over the years.
I can take a look at the handling behaviour and recommend C of G too in Plane Geometry if you need this.
Looks like a very suitable model though and should look beautiful. I hope it goes well for you.
Allan

PS. It won't let me upload an Excel S Sht. You it is Lift Roll by John Hartzel as I recall. I can send it off line if you wish.
Feb 27, 2008, 12:22 AM
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SZD16's Avatar
Quote:
Originally Posted by AllanK1
PS. It won't let me upload an Excel S Sht. You it is Lift Roll by John Hartzel as I recall. I can send it off line if you wish.

ZIP the file first....then you can attach it.
Feb 27, 2008, 02:03 AM
SoarScale
Curtis, regarding the machining of plugs and molds - yes, have done both - predominantly female molds directly into MDF with epoxy surface treatments and plugs using similar materials. I do the same when creating canopy plugs for my vacuum former - CNC the plugs directly from MDF, light glass and polyester resin coating.

Regarding the increased chamber at the tips - Read section 7.6 - stall control by chamber changes in Martin Simmons Model Aircraft Aerodynamics. This is a fundamental that designers of the full size have followed for years.

I follow this philosophy with all of my scratch built scale ships and have never had tip stall issues. Martin gives the fundamentals in his explanation but I can embellish if needed.

The zero lift angles can be found on the polars which are typically provided by Helmut Q on his website or via the UIUC site and publications. Since I don't use profili, I am not sure if the values are available from this software, but they are available for all airfoils from Compufoil. Eric Sanders has an algorithm that calculates the theoretical zero lift angle and I use this as the basis of the washout calculation with due regard to Martin Simmons comment "a little more"!

In all of my scale aircraft from the small 20 foot to the larger 35ft span aircraft, I typically start with a root chamber of 3% to about mid-flaperon or aileron root depending on taper ratio and then transition to 3.5% at the tip with the required washout defined by the difference in zero lift angle between the two. For HQ and HQW airfoils, the zero lift differential between 3% and 3.5% is about 0.9 degrees and I therefore, generally, add about 1.2 degrees of washout. The results are flawless - never had stall issues using this philosophy.

HQDS - well, the HQDS airfoils were designed essentially to increase the usable flight envelope over previous HQ airfoils. My understanding is that special attention was given to the profile form so that a wider, more usable flight envelope can be achieved with concise use of chamber changing flaps. Hence the term "dynamic". Dynamic in the sense that the envelope of flight can be increased by dynamically altering the wing shape during flight. Not to be confused with the US version of dynamic soaring - totally different beast!!

Tony
Feb 27, 2008, 04:31 AM
Registered User
Christian Baron's Avatar
Curtis,
the link to my BS 1 pages in your first thread is not working. Here are the right ones:

http://www.cb-roter-baron.de/framemodelle.html

with the page about the original (drawings and links at the very end):
http://www.cb-roter-baron.de/bs1seite.html

Where the 21 originals are today:
http://www.cb-roter-baron.de/bs1seite4.html

My model:
http://www.cb-roter-baron.de/bs1seite2.html

Here you see some lift distributions for my BS 1 wings:
http://www.cb-roter-baron.de/bs1seite3.html

Sorry that it's all written in german, but you can translate it with google.
I have the original fuse cross sections and better drawings that you are using so far. I can mail you dxf files if you can work with them!

I'm collecting everything about the BS 1 since 28 years and could write a book about.
The drawings in Martin Simons book are not correct, Mirek wrote it too.

I would recomment the use of a 2.5% profile at the root. I've used 13% thickness but would use 12% for a 1/3 ship. For the tip I've modified the 2.5% camber profil for low Re number by usind the bubble ramp at the upper surface. You are getting this in profili by shifting the point of max thickness from around 30% to 24%.

If you have questions concerning mold making and building fuselages and wings out of mold, don't hesitate to ask. I've introduced this technique with writting down my experience in two books in the 80ties in Germany.

Christian
Feb 27, 2008, 10:28 AM
Thread OP
Wow! Thanks everyone. I will need some time to respond to all of this. Thanks in particular to Christian as his web site has been invaluable in gathering drawings as well as photos of the BS-1.

Christian, what do you think about me doing the same scale as you? I've thought about the 1/3 scale mostly because it seems a shame to duplicate someone else's work. Do you ever sell your fuselage moldings anywhere?

I believe you used foam core wings rather than molding them. I expect that molding the wings will be the most challenging part of all. I'm glad to see that you speak english. I used the google translator on your site. It's pretty good but not entirely clear.

Thanks are also due to Mirek who sent me drawings. Unfortunately, they're the same drawings that are on Christian's site!

I will certainly welcome any help I can gather on the molding process. I'll ask more once I get closer to there. First, I want to make my plug for the fuse and the stab.

I can work with DXF files Christian if you have something more precise than the drawings on your site it would be fantastic. Best of all would just be a higher resolution image of the drawings you have on your site.
Last edited by Curtis Miller; Feb 27, 2008 at 10:52 AM.


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