Zenair Zodiac CH601 XL (microlight) banned
You're dragging a pretty old thread back up to the top of the forum.... did you have a look at the FAA information on the type? See https://www.faa.gov/sites/faa.gov/fi...ort/Zodiac.pdf and https://www.faa.gov/sites/faa.gov/fi...c_Appendix.pdf
Join Date: Mar 2001
Posts: 317
Likes: 0
Received 0 Likes
on
0 Posts
Apologies, I only came across the thread because I was looking at one of these for sale, and was somewhat surprised by the wing storage and then saw this thread.
Thanks for the FAA info ...
Thanks for the FAA info ...
The main structural members in a metal wing are the spars (forward and aft of the baggage bay by the looks of it) and the skin, with the ribs mostly there to keep the airfoil shape as close to ideal as possible. That baggage bay should not weaken the structure in any way. A handy feature though!
Moderator
That baggage bay should not weaken the structure in any way.
I am guessing (I know, I should use better information) that the whole leading edge is a D-section box-spar. If you add a rear spar to that, you should be able to get away with a baggage hatch like this. Having just looked at some photos and images here: ZODIAC XL Design & Construction - WINGS - Kit Plane it looks like my guess is pretty close. The wing lockers are optional items, so you would have to look at the individual aircraft that crashed to find out whether they had these baggage bays installed.
Moderator
the whole leading edge is a D-section box-spar. If you add a rear spar to that, you should be able to get away with a baggage hatch like this.
You've got a good point... I have had another look at the documents I linked to in post #22. Flutter was definitively a factor in the accidents mentioned, but to me the most damning statement is:
and:
I cannot find out from those documents whether the baggage bays were installed on the airframes that crashed, or whether this option played a part in the accidents. To me it sounds like the wing problems were bigger than that baggage hatch.
I would like to revise my statement to: "you should be able to get away with a baggage hatch like this in a properly designed wing".
FAA analysis of the aircraft showed that the loads used by the
manufacturer to design the wing structure did not meet the ASTM standard for a
1,320 lb aircraft. FAA analysis estimated that the wing design loads were 20 to 25
percent too low. Static structural tests completed in the Czech Republic, and testing
done as part of an investigation by German authorities support this conclusion. Those
tests revealed that the wing structure could not sustain the original design loads
developed by the manufacturer for compliance to the ASTM standards for a 1,320 lb
airplane.
manufacturer to design the wing structure did not meet the ASTM standard for a
1,320 lb aircraft. FAA analysis estimated that the wing design loads were 20 to 25
percent too low. Static structural tests completed in the Czech Republic, and testing
done as part of an investigation by German authorities support this conclusion. Those
tests revealed that the wing structure could not sustain the original design loads
developed by the manufacturer for compliance to the ASTM standards for a 1,320 lb
airplane.
However, it is clear from the evidence from aircraft involved in structural failure
accidents that flutter was a causal factor. It is not possible to determine whether
flutter was the primary root cause of the structural failure or a secondary cause after
some initial structural deformation of the wing. Because of the concerns with the
wing structure, it is likely structural stiffness may have influenced the flutter
characteristics of the wing. The FAA is aware that some reports of flutter or vibration
in the airframe have been traced to improperly rigged aileron cable tensions, and
improperly installed flap stops.
accidents that flutter was a causal factor. It is not possible to determine whether
flutter was the primary root cause of the structural failure or a secondary cause after
some initial structural deformation of the wing. Because of the concerns with the
wing structure, it is likely structural stiffness may have influenced the flutter
characteristics of the wing. The FAA is aware that some reports of flutter or vibration
in the airframe have been traced to improperly rigged aileron cable tensions, and
improperly installed flap stops.
I would like to revise my statement to: "you should be able to get away with a baggage hatch like this in a properly designed wing".
Join Date: Jan 2002
Location: Niort
Posts: 1,235
Likes: 0
Received 0 Likes
on
0 Posts
As ever little research and some comment. The photo looks to be a CH601HD or UL. This has a deep centre section and then a choice of two types of wing, the short tapered and the 'full fat'.
The CH601xl also has wing lockers, but the wings have a dihedral from the fuselage outboard. The wings are substantially thinner. The flutter problem with the xl model was fixed in a number of ways, the most important being to mass balance the ailerons. There are other modifications depending upon the regulator authority, In the UK the maximum weight in the fuselage was limited, pretty much necessitating the fitment of the wing lockers if not already there.
Either way since the aileron balancing there have been no common cause accidents to the xl. The size of the xl lockers is smaller and shallower than the HD/UL but with a couple of purpose made bags they were very useful.
The CH601xl also has wing lockers, but the wings have a dihedral from the fuselage outboard. The wings are substantially thinner. The flutter problem with the xl model was fixed in a number of ways, the most important being to mass balance the ailerons. There are other modifications depending upon the regulator authority, In the UK the maximum weight in the fuselage was limited, pretty much necessitating the fitment of the wing lockers if not already there.
Either way since the aileron balancing there have been no common cause accidents to the xl. The size of the xl lockers is smaller and shallower than the HD/UL but with a couple of purpose made bags they were very useful.
Join Date: Feb 2009
Location: Toronto, Canada
Posts: 37
Likes: 0
Received 0 Likes
on
0 Posts
I'll also chip in with similar comments, trying to be clear about what affected which aircraft:
TL;DR: XL design problems fixed long ago, 601's / 650's all ok now, wing lockers were never an issue
Details:
- The earlier 601UL, HD, HDS had wings that were completely different in design than the later XL.
- It was the XL that had all the problems, killing a number of pilots & passengers. (Roughly half a dozen crashes, just off the top of my head)
It took some time for detailed investigations to get going (eg, flutter analysis of the structure, ground vibration tests, re-evaluation of the expected aerodynamic loads used in the design).
Prior to the number of accidents piling up, accidents tended to have been blamed on the pilots simply overstressing the aircraft, based on lack of other evidence.
("Well he didn't seem like the type... but he must have been trying some aerobatics or throwing it around too hard.")
- The XL wings were designed a little too light and susceptible to torsion & thus flutter.
It was the biggest error of Chris Heintz' career I'd say.
- The flutter tendency could be exacerbated by slightly loose aileron cable tensions. Something that isn't a big deal on many slower light planes -- so owners weren't monitoring closely -- but was in this case where the design was marginal.
(I seem to recall that a proper tension meter is pricy, and something I only very occasionally borrowed for my dad's HDS, from an aviation repair shop. A place that homebuilts don't normally go to.)
- The XL problems were fixed with the substantial beefing up program, both to the wings and the fuselage structure around the wings (which anchors the wings ). A big mandatory rebuild for owners of already built XL's.
- The wing lockers were never implicated in any of the accidents. (An optional feature, but I think most people installed.)
I thought for light homebuilt aircraft, the torsional strength of the skin is assumed not to exist when designing the strength of the wing. Strength from the skin is just an extra bonus. (Not sure about leading edge D sections though, if that's ever considered in the design.)
After all, plenty of aircraft have been designed for fabric covering.
- Even the UL/HD/HDS had some pretty widely spaced ribs. But with the thick wing section there never has been any problem.
- I flew an HDS for years in Canada. Wing lockers were great for bulky storage if doing longer trips & camping etc. Sleeping bags, tie downs, etc. (Or for a wing tank on early 601's before leading edge tanks became an option) Especially true for the HD/HDS/UL with their very thick spar and wing section. Plenty of vertical depth. And each could hold 40 lbs max, to complement the 40 lbs that could go in the turtledeck (if one could stuff that much in).
- One danger of the wing lockers was forgetting to do up all the dzus fasterners. I know of one crash & burn accident where a pilot didn't come in fast enough with one locker unlocked & open, and stalled the aircraft over the runway. It would be a pretty big 'hole' in the top of the wing and loss of lift on one side, with a wing locker unfastened. A serious emergency situation.
TL;DR: XL design problems fixed long ago, 601's / 650's all ok now, wing lockers were never an issue
Details:
- The earlier 601UL, HD, HDS had wings that were completely different in design than the later XL.
- It was the XL that had all the problems, killing a number of pilots & passengers. (Roughly half a dozen crashes, just off the top of my head)
It took some time for detailed investigations to get going (eg, flutter analysis of the structure, ground vibration tests, re-evaluation of the expected aerodynamic loads used in the design).
Prior to the number of accidents piling up, accidents tended to have been blamed on the pilots simply overstressing the aircraft, based on lack of other evidence.
("Well he didn't seem like the type... but he must have been trying some aerobatics or throwing it around too hard.")
- The XL wings were designed a little too light and susceptible to torsion & thus flutter.
It was the biggest error of Chris Heintz' career I'd say.
- The flutter tendency could be exacerbated by slightly loose aileron cable tensions. Something that isn't a big deal on many slower light planes -- so owners weren't monitoring closely -- but was in this case where the design was marginal.
(I seem to recall that a proper tension meter is pricy, and something I only very occasionally borrowed for my dad's HDS, from an aviation repair shop. A place that homebuilts don't normally go to.)
- The XL problems were fixed with the substantial beefing up program, both to the wings and the fuselage structure around the wings (which anchors the wings ). A big mandatory rebuild for owners of already built XL's.
- The wing lockers were never implicated in any of the accidents. (An optional feature, but I think most people installed.)
I thought for light homebuilt aircraft, the torsional strength of the skin is assumed not to exist when designing the strength of the wing. Strength from the skin is just an extra bonus. (Not sure about leading edge D sections though, if that's ever considered in the design.)
After all, plenty of aircraft have been designed for fabric covering.
- Even the UL/HD/HDS had some pretty widely spaced ribs. But with the thick wing section there never has been any problem.
- I flew an HDS for years in Canada. Wing lockers were great for bulky storage if doing longer trips & camping etc. Sleeping bags, tie downs, etc. (Or for a wing tank on early 601's before leading edge tanks became an option) Especially true for the HD/HDS/UL with their very thick spar and wing section. Plenty of vertical depth. And each could hold 40 lbs max, to complement the 40 lbs that could go in the turtledeck (if one could stuff that much in).
- One danger of the wing lockers was forgetting to do up all the dzus fasterners. I know of one crash & burn accident where a pilot didn't come in fast enough with one locker unlocked & open, and stalled the aircraft over the runway. It would be a pretty big 'hole' in the top of the wing and loss of lift on one side, with a wing locker unfastened. A serious emergency situation.
