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Old Jul 21, 2004, 01:16 PM
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SoarNeck's Avatar
Calgary, Alberta
Joined Nov 2001
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Marske Pioneer IID

Hi folks,

I've come to the conclusion that I don't "design, build, and fly" model airplanes...I only design them! Haven't been able to get out in a few weeks now, and I'm getting the shakes Maybe this weekend.

Anyway, in my neverending quest for a decent winter project (the stability analysis on the Baby Albatross was a little scary), I came across the Marske Pioneer IID. The structure is simple, and its uniqueness appeals to me, since as far as I can tell only one model was ever built (Kuhlman, 1/4 scale).

That's both good and bad, since it means that I don't have a lot to go on. I've also never designed a flying wing before, so I have a few questions for those that might know.

First, the photos:
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Old Jul 21, 2004, 01:34 PM
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Now, the questions:

1) Apparently, the full size model uses a bridle on tow. I couldn't quite figure out what type of tow was being referred to...does it use a bridle on aerotow as well? Why wouldn't a traditional nose release work?

Knowing first-hand what can go wrong with a single release point, I don't fancy having to use two release points

2) Aerodynamics. From what I read on the B2Streamlines site, the 1/4 scale version used the full-scale airfoils. This was successful for a slope model, but tended to cause trouble with tipstalling/spinning on the thermal field from all reports.

Thinking that there are better choices for the reduced reynold's numbers of a model, I started some research. I wanted to stay with a section that was close to the overall dimensions and thickness of the scale airfoil, lest the model look odd.

The first step was to nail down a size, and I arbitrarily chose 4m. I like big sailplanes, and 4m seems to be the point where they really start to shine, but don't overload a medium-sized tug.

So, root chord is 21", tip chord is 7", and wing area is around 2200sq". I'm guessing at 16 lbs to be pessimistic, since there's lots of area, but not much fuse or tail.

The Re# at thermal speeds is likely the limiting case, so I'm dealing with 360,000 at the root and 120,000 at the tip (25mph). To support that mass, the local Cl at the root is about 0.6625, and 0.3267 at the tip (my spreadsheet).

I looked at the full-size airfoil first, out of curiousity. Not a polar that inspires confidence. Strangely, the curve seems smoother at lower RE...but there have to be better choices. First, the graph:
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Old Jul 21, 2004, 01:42 PM
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So, armed with just enough knowledge to be dangerous, I started looking for alternatives. The best choices I have so far are the MH60 and MH45.

After messing about a bit, I determined that the MH60 could be thickened a little without messing up the polar too much. A thicker section would be closer to the scale look, and would make the spar a lot stiffer as well:
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Old Jul 21, 2004, 01:47 PM
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The tip polar at 120,000. I decided to stick with the stock thickness, since it gave a nice aerodynamic washout twist over the total wing:
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Old Jul 21, 2004, 02:11 PM
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By playing with the transition point between the 12% MH60 to the MH45 (ie where the airfoil is halfway between the root MH60 and the tip MH45), I think I was able to take care of the tipstall issue. With the transition point at 0.25 span (closer to root), and just a hair of washout at that point, I get the following graph. Looks good to me, since the max cl location is nicely inboard.

The sum of aerodynamic and geometric washout has the following progression from root to tip, in increments of 19" (over the 2m panel):
0.0, 0.0, -0.3, -0.4, -0.9

This is accomplished with only 0.2 degrees of washout at the transition point. The root and tip airfoils are both set at the same angle of attack.

The only thing I'm still worried about is c/g and longitudinal stability. How to I calculate the former, and analyze the latter?

Regarding pitch stability, most flying wing designers talk about the "Cm" of the airfoil. Is this referenced to a particular angle or attack, or lift coefficient? The reason I ask is that it changes over the range of these parameters, so I don't know what I'm looking for regarding "needing" a postive Cm for a plank wing".

Any suggestions would be welcome - I feel a bit out of my league with this design.

The full size aircraft can be seen here, BTW:
http://www.continuo.com/marske/pioneer.htm

Nice scheme:
http://www.continuo.com/marske/pione...31,%202001.jpg
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Old Jul 21, 2004, 02:17 PM
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Bridles for tow releases are usually used to avoid having to make a 'hard point' (with its attendant structure, and added weight) some where else, like on the nose.
It is more weight efficient to do this.
Quite a few years ago I used to fly a full size Fauvel flying wing which used a bridle, and I always wondered what would happen if one side refused to play ball at the critical moment........one day of course it happened (but not to me!) and apparently apart from causing about 15 degrees of yaw and almost stopping the tug from climbing all was just about controllable. The tow pilot guessed what had happened and let the glider pilot have the other end of the rope aswell. All landed happily...but quite a few people stopped wanting to fly the Fauvel.
As a matter of interest (or not) the early L13 Blaniks had bridle release for winch launching.
Best of luck with your project.

GeeW
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Old Jul 21, 2004, 02:35 PM
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Quote:
Originally Posted by GeeW
Bridles for tow releases are usually used to avoid having to make a 'hard point' (with its attendant structure, and added weight) some where else, like on the nose.
It is more weight efficient to do this.
Quite a few years ago I used to fly a full size Fauvel flying wing which used a bridle, and I always wondered what would happen if one side refused to play ball at the critical moment........one day of course it happened (but not to me!) and apparently apart from causing about 15 degrees of yaw and almost stopping the tug from climbing all was just about controllable. The tow pilot guessed what had happened and let the glider pilot have the other end of the rope aswell. All landed happily...but quite a few people stopped wanting to fly the Fauvel.
As a matter of interest (or not) the early L13 Blaniks had bridle release for winch launching.
Best of luck with your project.

GeeW
That's very interesting, thanks very much! I was hoping that a bridle on aerotow wasn't something that was particular to the aerodynamics of flying wings.
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Old Jul 21, 2004, 03:21 PM
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Contact B2 and talk to them about it. They are very helpful and giving with knowledge gained from their vast experience with flying wings.

Have you seen the latest mods to the full scale Pioneer 2 on the Marske site. Wow! it is very nice.
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Old Jul 21, 2004, 03:54 PM
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Do the numbers on a blend fom root to tip E205 root 8.0% and E214 tip 7.0%
this is the section I use on my planks
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Old Jul 21, 2004, 04:04 PM
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Quote:
Originally Posted by MikeC
Contact B2 and talk to them about it. They are very helpful and giving with knowledge gained from their vast experience with flying wings.

Have you seen the latest mods to the full scale Pioneer 2 on the Marske site. Wow! it is very nice.
Already done, though I couldn't find an active email address for them. I posted to RCSE in the hopes that they were monitoring. Might also be my email server...I'll check that out later.

I did see the newest version (impressive), but I was looking for something simple The new version would be a much more complex project.
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Old Jul 21, 2004, 04:05 PM
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Quote:
Originally Posted by steve wenban
Do the numbers on a blend fom root to tip E205 root 8.0% and E214 tip 7.0%
this is the section I use on my planks
Okay, I'll check that out. What chord lengths are you used to dealing with?
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Old Jul 21, 2004, 04:08 PM
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This graph shows why I'm confused about the "Cm of an airfoil". Where should I be looking?

Best as I can understand, I think that people mean the Cm for level flight. My spreadsheet is telling me that level flight @ 16lbs and root Cl of 0.6625 means that the root is at an angle of attack of 5.4 degrees (relative to the zero-lift angle). Do I look there for a positive Cm value? That would be -0.7 degrees (zero lift) + 5.4 degrees, or +4.7 degrees.

Help please
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Old Jul 21, 2004, 05:51 PM
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Mt Annan Sydney Australia
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chord and span

Quote:
Originally Posted by SoarNeck
Okay, I'll check that out. What chord lengths are you used to dealing with?
chords I have used are vary greatly from 312mm to 500mm spans are also wide and varied from 500mm to 4.0 metres my homepage has photo's if your interested I have used numerous foils in my search for the right plank at our slope and have found what is to me anyway the right combo which is my evolution 50 and 60 as well as the Spade 52 and the Marley 60 but you will see some of mine and other guys stuff on the site
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Old Jul 21, 2004, 06:02 PM
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United States, CA, Novato
Joined Sep 2003
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Interesting build.. As I recall Barnaby Wayfin (sorry about the bad spelling) was involved in that project. I also recall him being a big fan of testing air craft designs in the R/C world before building full scale. He also built the facet-mobile etc. An intersting guy.

I'd imagine you should be able to connect to those guys online and they would probably do all they can to lend you a hand. I think Barnaby writes for one of the Experiment Aviation Associations magazines..?

It is a good looking plane.

-Wayne
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Old Jul 21, 2004, 06:29 PM
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Go look at their website http://www.b2streamlines.com/ and send e-mail to them at bsquared@b2streamlines.com ... You might also be able to contact them over the Nurflugel mailing list http://groups.yahoo.com/group/nurflugel/ ... Best of luck with this one. I too like the Marske planforms, tailless with slight forward sweep.

J.P.
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