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Re: Improving the pilot's field of view 11 Dec 2013 01:05 #629

DAn,
A Very good topic! Yeah, the real problem is that the graphite is too strong for what is needed, In fact my buddy did a wing with two plies of glass ans said it was VERY robust. Using the thinner fiberglass with some type of core would likely be a good choice. The stickler is the core, NOMEX is expensive, and some times the foam has adhesion issues. Too bad they don't make some balsa wood plywood, or do they? You get lighter weight, and still get the separation of plies. Of course NOMEX would be deluxe, and I think Hexcel has a new prepreg for going directly onto the core without a layer of adhesive (which adds weight), but I'm not sure if the home-builder, sans the autoclave etc., would get the kind of product that is theoretically possible...


Some testing is obviously in order, but I think you are on to something; plus, if the carbon pultrusions in the spar caps the overall wing deflection should still be low even without the carbon leading edge.

--- On Fri, 10/14/11, Daniel Armstrong <This email address is being protected from spambots. You need JavaScript enabled to view it.> wrote:


From: Daniel Armstrong <This email address is being protected from spambots. You need JavaScript enabled to view it.>
Subject: Re: [Carbondragonbuildersandpilots] Re: Improving the pilot's field of view
To: This email address is being protected from spambots. You need JavaScript enabled to view it.
Date: Friday, October 14, 2011, 11:55 AM




When you are looking at your analysis of the D-tube and other shells, you might want to look at using a sandwich of +- 45 glass-0-90plywood-+-45 glass as one of your possibilities. Aircraft Spruce carries 1/32 (.8mm) Finnish Birch and 1.45 oz/square yard glass. This combo allows wider rib spacing to prevent buckling than a straight carbon shell and is slightly lighter than 2 plies of carbon 282. It is also cheaper and more damage tolerant and isn't as affected by moisture as the bare plywood of the prototype on the inside surfaces. I don't think there is much problem with torsional stiffness. The Carbon Dragon wings were very stiff in bending and torsion in flight. You can get allowables for wood and plywood from ANC-18, which is available on the web.

The carbon rod spar caps seem like the way to go for me as well. The Carbon tow that we used does not have even close to the same stiffness or strength allowables.

I did some layouts a long time ago with a low wing for the CD and if I recall correctly, the pilot's CG could move above 6" aft or slightly more due to the seat back angle. The visibility in thermals would be much better, because you could see across and back when you are banked up. You should be able to see all the gliders at the same level and above without difficulty. If you are in a notch in the D-tube, the visibility downward would be impaired, but since you would be climbing faster than the others, this is probably a better tradeoff.

The CD has a very low wing loading, since it was sized to allow foot launch. If foot launching is not important, you could reduce the area some and get better penetration. It appears that roll off launching is relatively easy in light winds with a wing loading up to around 3 or 4 pounds per square foot. There are videos on YouTube showing gliders roll off launching at 6+ pounds per square foot, but they have to roll a long ways before lift off. I think a reasonable wing loading for an ultralight sailplane that will be used for roll off or ground tow launch might be 3 lb/ft2. Gary Osoba has certainly shown that Microlift can be exploited in his Woodstock. A long wing with lots of area may make it difficult to stay under 155 pounds to meet the Part 103 requirements.




From: Kenny <This email address is being protected from spambots. You need JavaScript enabled to view it.>
To: This email address is being protected from spambots. You need JavaScript enabled to view it.
Sent: Fri, October 14, 2011 8:43:52 AM
Subject: [Carbondragonbuildersandpilots] Re: Improving the pilot's field of view


Dan,
Thanks so much for the input and taking time to share. One thing that has always bugged me a bit is that pilot weight limitation. What I'm looking at so far is keeping the wing pretty much as it is, but extending the wing inboard, or rather pushing the wing out, and the extrapolating the wing inboard. Currently the root rib is 60 inches. That would go up to 65. The increase in wing area is 15%. I think this would also be more tolerance of those trying to add some self-launching capability as well (as far as payload goes).You end up with a root rib of about 65 inches (rather than 60)the wing span is about 46 feet and you end up a rib spacing that goes up about 1 inch [is all]. The outer wing is exactly the same size as it was before, so the outboard sizing should track the same as what I call in my spread sheet the skinny dragon (as opposed to the Fat Dragon). Since Phil and I have been looking at using the carbon rods rather than the tape, it's surprising how little weight the extra wing can be done for.

Visibility is an issue now it appears, but I think it would be even bigger if the root rib grows a tad (it won't make it better for sure). Again, the closer you can stay to the proven design the better, so I don't thing it has to be super drastic, but say enough to where you can look around and slightly above the wings. It make total sense what you are saying.

I haven't sat down and compared the AE of wood vs. Composite (to compare expected deflection), but the E for the composite rods is around 20 E6 (aluminum is just over 10E6) and wood is 1.? E6 maybe (I'd have to look it up)? So, whether that leading edge is composite, or plywood, I think there is no doubt to make the spar out of composite (especially the caps).

I'm just a stress guy -- I wish I know a little more about aerodynamics, but I'm guessing you could probably push the leading edge forward a bit (not so that it was forward swept, but enough to shift the lift CG forward a few inches. My guess is that if you didn't get crazy, that is would not likely have a big effect on performance.

I got time, I'm not really in a position to build right now, but am willing to help run a few numbers and whatnot.
Kenny

--- In This email address is being protected from spambots. You need JavaScript enabled to view it., Daniel Armstrong wrote:
>
> Kenny,
>
> I helped build the prototype Carbon Dragon and flew it about 30 flights during
> development. I'm about 6'-2" and my eye line was just about even with the
> bottom surface of the wing with my head against the head rest. On several of
> the flights I flew with other gliders in thermals. The Carbon Dragon was pretty
> blind for me. In one thermal with 5 other gliders near my altitude, there were
> times that I could only see one other glider and couldn't keep track of the
> others. I flew away from the thermal because of the poor visibility and risk of
> collision.Â
>
>
> I talked with Jim Maupin about the configuration and why he chose a shoulder
> wing. He said that the flow over the wing would be better for climbing. The
> glider was designed originally as a prototype to set world records with a
> lightweight pilot (Rich Pfeiffer). The maximum pilot weight was planned to be
> 150 lbs and all of the structures were designed for this load. I weighed 210
> pounds when I flew the glider, which far exceeded gross weight and required an
> additional 12 pounds of weight to balance near the forward limit. I flew the
> glider very gingerly to keep the load to a safe level.
>
> I think that redesigning the Carbon Dragon with a mid-wing and strengthening the
> structures for heavier pilots is a great idea. The Carbon Dragon handled
> beautifully and climbed exceptionally well. A mid-wing would allow better
> visibility and moving the pilot aft several inches. Almost all the ultralight
> gliders that I have been around have been quite nose heavy. Eric Raymond's
> Edelweiss in its original configuration required a lot of tail weight. The
> Light Hawk had a little forward sweep to account for this problem, but is still
> requires tail weight for heavy pilots. In ultralight gliders, the pilot
> represents a far higher percentage of the gross weight than regular gliders, so
> the pilot needs a shorter moment arm from his CG to the CG of the system.Â
>
>
> Good luck with your interesting project.
>
> Dan Armstrong
>
>
>
>
> ________________________________
> From: Kenny <kennyrayandersen@...>
> To: This email address is being protected from spambots. You need JavaScript enabled to view it.
> Sent: Fri, October 14, 2011 3:26:53 AM
> Subject: [Carbondragonbuildersandpilots] Re: Improving the pilot's field of view
>
> Â
> Perusing some photos of S. Abbet's CD build and it's easy to see what the
> concern is about visibility. The wings would have to be spread a bit to be
> lowered, but looking at the other photos, that approach doesn't seem
> insurmountable. Moving the pilot down, not only puts the pilot CG forward, but
> adds to the overall frontal area (it seems), so does anyone see any obvious
> problems with moving the pilot up to the woodstock-type location? Seems like
> visibility would get much better. The moment at the wing root wouldn't change.
>
> www.carbondragon.ch/Book%20du%20Carbon%2...ier%20vols/index.htm
>
>
> --- In This email address is being protected from spambots. You need JavaScript enabled to view it., "Kenny"
> <kennyrayandersen@> wrote:
> >
> > so how about going the other direction like the pics of the woodstock that I
> >posted. You'd keep the CG more aft since less prone, and you'd improve the
> >visibility... I would think. Going more prone, as you say, would seem to take
> >the DC forward, and there is [apparently] already a problem with that.
> >
> > --- In This email address is being protected from spambots. You need JavaScript enabled to view it., Steve Adkins
> >wrote:
> > >
> > > I co-owned a Schweizer 1-35c which came either with a removable canopy or a
> >hinged canopy supported by gas springs. There is a large weight penalty for the
> >latter. The hinged option coupled with a heavy wing repair put me over the gross
> >weight limit for a period where I did not fly the aircraft.
> > > www.carbondragon.us/steve_redsailplane_sm.jpg ... me in N135EX
> > > members.goldengate.net/~tmrent/soar/docs...5_files/image002.jpg
> >... on final
> > >
> > > The mockup I built of the pilot pod included the huge wing root ribs (Steve
> >Arndt sat in it). The wing is really a view blocker. A more recumbent position
> >may help lower the eyes below the wing but that position moves the pilot's body
> >and feet forward; thus, moving the CG forward which in turn lowers the maximum
> >allowable speed when under tow according to the CG envelope. Also, extending the
> >forward length of the pilot pod results in more side area in front of the CG;
> >thus, impacting flight stability (for good or bad?). (The domino effect of
> >design changes.)
> > >
> > > S. Steve Adkins (Note: not Steve Arndt)
> > > carbondragon.us/ ... dormant website with New Photo

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