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cookwithgas(at)HOTMAIL.CO
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 Posted: Sun May 13, 2007 6:07 am Post subject: Wing Sweep |
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Guys:
I've been reading the speculation posted here for the past few days about
the 601 crashes. I know many of you have stayed in a Holiday Inn Express,
but how many of the guys with opinions here have actually installed the
wings on a 601XL and measured the wing sweep?
Last weekend when I was installing my wings, I was confused over this idea,
then a very smart guy helped me figure this out - Dave Miller. Dave is one
of the founding members of our local EAA and is building a 601XL in the
early stages from plans just like I did. In the final stages of building my
601XL, Dave has been a great help. Here's what he helped me understand
about the wings of the XL concerning wing sweep:
As was mentioned earlier, the spar is not vertical when the airplane is
level. If you place a string from wingtip to wingtip across the fuselage
with the canopy open, it will APPEAR that the two rivet lines are sweeping
forward. In other words if you put the string on the end rivet for the spar
cap drop a plumb bob from the center of the string, it will not drop down to
the top of the spar cap on the center spar. Why? Because with the airplane
sitting level, the spar leans forward. You have to either tilt the airplane
backwards so the spar is vertical and use a plum line, or project a line
from the spar along the angle. If you do this, you will see that the wings
don't sweep forward. There is a caveat here:
I had to trim my rear spar tabs on the fuselage to bring the wings back -
this is because the spar tabs were hitting the first rib, causing the wings
to sweep forward a little. I test-fit the flaps before trimming the tabs
and they were crazy-far away from the fuselage so it was a no-brainer to
trim them and move the rear of the wings closer to the fuselage which takes
away the forward-sweep. I cut about 1/4" off the tabs.
I won't speculate about the latest crash. I saw a bit of misconception
being spread here on the internet (imagine that) and wanted to bring back
some reality.
Scott Laughlin
N5SL, Wahoo, Nebraska
Getting Close
www.cooknwithgas.com
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dbrown(at)avecc.com
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| Posted: Mon May 14, 2007 6:52 am Post subject: Wing Sweep |
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When I drew the string from spar tip to spar tip I had to make the same
adjustment described below. It still looks swept forward when the
fuselage is level, when you project the plane of the spar upward it
intersects the string.
Future N601EX
David W. Brown
Email: dbrown(at)avecc.com
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ashontz
Joined: 27 Dec 2006
Posts: 723
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| Posted: Mon May 14, 2007 7:22 am Post subject: Re: Wing Sweep |
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When the plane is level (which means the wings are level), the wings are in fact swept forward. If there was no dyhedral (even with the inclined spar), the wings regardless of whether it was tilted back or forward 9 degrees would would have no sweep. It's the dihedral in conjunction with the inclined main spar that causes a slight sweep forward when the plane is level.
At what angle of attack does the plane fly at at cruise speed? 9 degrees. In that case, the wings would have no sweep while in flight.
Even so, I don't think the sweep is too much of a problem now that I think about it. I think the bigger issue is that personally, now that I think about it and compare the XL to other planes, it doesn't have enough ribs in the wing. A RV has ribs every 9 inches, even a Grumman Traveler has them every 15 inches where as the XL has them at 21+ inches. Push on the skin on either of those wings and they feel solid where as the XL feels a little anemic. A fellow builder has remarked that a lot of guys go ahead and put false ribs in the eliminate oil-canning in the wings because there's just such a large space between ribs that it's almost a give you're going to get some oil-canning, particularly on the lower skin. I think thats a major indication that it doesn't just need false ribs, but actual ribs in those locations. It's showing an inherent weakness in those areas. Slightly oil-canning or depression when pushed by hand is much more significant distortion under flight loads. An oil can effect just with hand pressure probably distorts the wing by half a millimeter. In flight conditions that could have up to a lot more shifting of the structure. I think extra ribs in there would be a good idea. The strength of the wing is reliant on the ability of the skins to distribute the force. Allow that skin to move too much and you have problems. Not enough ribs is as bad as oversized sloppy wholes on a plane that has enough ribs.
5 extra ribs adds maybe 3 pouns to each wing. That's practically nothing. Considering a the fact that the top spar cap angle is 90 degrees, I don't thinks its a bad idea if that was made out of 1.5" x 3/4" x 1/8" extrusion. Maybe another 5 pound overall to each wing. I also think the wing locker takes away from the strength of the wing in a critical area and should be avoided. I also think I'm going to scrap the 15 gallon tank idea and 3 skins (new kit design), and go back to the 12 gallon tank and one continuous noseskin.
| dbrown(at)avecc.com wrote: | When I drew the string from spar tip to spar tip I had to make the same
adjustment described below. It still looks swept forward when the
fuselage is level, when you project the plane of the spar upward it
intersects the string.
Future N601EX
David W. Brown
Email: dbrown(at)avecc.com
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bryanmmartin
Joined: 10 Jan 2006
Posts: 1018
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| Posted: Mon May 14, 2007 7:38 pm Post subject: Wing Sweep |
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Most RV's are 200 mph airplanes that weigh over 1600 lbs and can take a
180 hp engine. The Grumman Traveler is a four place 150 mph airplane
with a gross weight of 2200 lbs and an O-320 engine. Do you think that
might explain why they have more wing ribs than a 1320 lb, 130 mph
airplane designed to handle no more than 130 hp?
As far as wing sweep is concerned, take a good look at a Cessna Skyhawk.
Notice the straight leading edge and the tapered trailing edge? Would
anyone call the Cessna wing a forward swept wing? Many aircraft have
been built over the years with a similar planform and none of them are
considered forward swept wings. From a practical standpoint, a wing is
not considered swept unless both the leading edge and the mean chord
line are swept back or forward. Even if there is a small amount of sweep
to the CH601XL wing, it isn't enough to have a significant effect in the
flight envelope the plane operates in. The aerodynamic problems
associated with forward swept wings only show up when there is a
substantial amount of sweep and, usually, speeds well beyond the safe
limits of the CH601.
We're not building F-15s here, we're building lightweight sport
airplanes. I could build an airplane that would never break up under any
conceivable flight conditions, you could fly it through thunder storms,
hurricanes and even tornadoes. The only problem is, it would be so
damned heavy, you would need a GE-90 to get the thing off the ground.
| Quote: |
When the plane is level (which means the wings are level), the wings are in fact swept forward. If there was no dyhedral (even with the inclined spar), the wings regardless of whether it was tilted back or forward 9 degrees would would have no sweep. It's the dihedral in conjunction with the inclined main spar that causes a slight sweep forward when the plane is level.
At what angle of attack does the plane fly at at cruise speed? 9 degrees. In that case, the wings would have no sweep while in flight.
Even so, I don't think the sweep is too much of a problem no that I think about it. I think the bigger issue is that personally, now that I think about it and compare the XL to other planes, it doesn't have enough ribs in the wing. A RV has ribs every 9 inches, even a Grumman Traveler has them every 15 inches where as the XL has them at 21+ inches. Push on the skin on either of those wings and they feel solid where as the XL feels a little anemic. A fellow builder has remarked that a lot of guys go ahead and put false ribs in the eliminate oil-canning in the wings because there's just such a large space between ribs that it's almost a give you're going to get some oil-canning, particularly on the lower skin. I think thats a major indication that it doesn't just need false ribs, but actual ribs in those locations. It's showing an inherent weakness in those areas. Slightly oil-canning or depression when pushed by hand is much more significant distortion under flight loads. A
n !
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| Quote: | oil can effect just with hand pressure probably distorts the wing by half a millimeter. In flight conditions that could have up to a lot more shifting of the structure. I think extra ribs in there would be a good idea. The strength of the wing is reliant on the ability of the skins to distribute the force. Allow that skin to move too much and you have problems. Not enough ribs is as bad as oversized sloppy wholes on a plane that has enough ribs.
|
--
Bryan Martin
Zenith 601XL N61BM
Ram Subaru, Stratus redrive
Do Not Archive
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_________________
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Bryan Martin
N61BM, CH 601 XL, Stratus Subaru.
do not archive. |
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ashontz
Joined: 27 Dec 2006
Posts: 723
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| Posted: Tue May 15, 2007 3:48 am Post subject: Re: Wing Sweep |
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I'm well aware of the differences. I also have a 601XL wing sitting on my workbench and as careful as I've been constructing it, I'm not happy with the oil-canning potential of the widely spaced ribs.
Neither the RV or the Grumman have a large hole on the top of the wing (baggage compartment) in one of the most critical areas of the wing.
The additional support I believe the wing would benefit from (top spar cap angle extrusion and 5 additional ribs) would only add about 10 pounds to each wing. Hardly a difference in weight that would require a jet engine to get it off the ground. Take away the wing locker and whatever additional weight in hiking boots and toothbrushes to be transported would more than make up for it.
| bryanmmartin wrote: | Most RV's are 200 mph airplanes that weigh over 1600 lbs and can take a
180 hp engine. The Grumman Traveler is a four place 150 mph airplane
with a gross weight of 2200 lbs and an O-320 engine. Do you think that
might explain why they have more wing ribs than a 1320 lb, 130 mph
airplane designed to handle no more than 130 hp?
As far as wing sweep is concerned, take a good look at a Cessna Skyhawk.
Notice the straight leading edge and the tapered trailing edge? Would
anyone call the Cessna wing a forward swept wing? Many aircraft have
been built over the years with a similar planform and none of them are
considered forward swept wings. From a practical standpoint, a wing is
not considered swept unless both the leading edge and the mean chord
line are swept back or forward. Even if there is a small amount of sweep
to the CH601XL wing, it isn't enough to have a significant effect in the
flight envelope the plane operates in. The aerodynamic problems
associated with forward swept wings only show up when there is a
substantial amount of sweep and, usually, speeds well beyond the safe
limits of the CH601.
We're not building F-15s here, we're building lightweight sport
airplanes. I could build an airplane that would never break up under any
conceivable flight conditions, you could fly it through thunder storms,
hurricanes and even tornadoes. The only problem is, it would be so
damned heavy, you would need a GE-90 to get the thing off the ground.
| Quote: |
When the plane is level (which means the wings are level), the wings are in fact swept forward. If there was no dyhedral (even with the inclined spar), the wings regardless of whether it was tilted back or forward 9 degrees would would have no sweep. It's the dihedral in conjunction with the inclined main spar that causes a slight sweep forward when the plane is level.
At what angle of attack does the plane fly at at cruise speed? 9 degrees. In that case, the wings would have no sweep while in flight.
Even so, I don't think the sweep is too much of a problem no that I think about it. I think the bigger issue is that personally, now that I think about it and compare the XL to other planes, it doesn't have enough ribs in the wing. A RV has ribs every 9 inches, even a Grumman Traveler has them every 15 inches where as the XL has them at 21+ inches. Push on the skin on either of those wings and they feel solid where as the XL feels a little anemic. A fellow builder has remarked that a lot of guys go ahead and put false ribs in the eliminate oil-canning in the wings because there's just such a large space between ribs that it's almost a give you're going to get some oil-canning, particularly on the lower skin. I think thats a major indication that it doesn't just need false ribs, but actual ribs in those locations. It's showing an inherent weakness in those areas. Slightly oil-canning or depression when pushed by hand is much more significant distortion under flight loads. A
n !
|
| Quote: | oil can effect just with hand pressure probably distorts the wing by half a millimeter. In flight conditions that could have up to a lot more shifting of the structure. I think extra ribs in there would be a good idea. The strength of the wing is reliant on the ability of the skins to distribute the force. Allow that skin to move too much and you have problems. Not enough ribs is as bad as oversized sloppy wholes on a plane that has enough ribs.
|
--
Bryan Martin
Zenith 601XL N61BM
Ram Subaru, Stratus redrive
Do Not Archive |
| | - The Matronics Zenith-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Zenith-List |
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