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psm(at)att.net
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 Posted: Mon Mar 16, 2009 7:04 pm Post subject: Fwd: Re: Is Your CH601XL/650 a 1320 lb Airplane or a 1041 |
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Hi Sabrina,
What is your normal cruise speed? I have heard of XL's with normal
cruise considerably higher than 112 MPH. If I remember correctly,
the standard with Jabiru engine is 138.
Paul
do not archive
At 07:15 PM 3/16/2009, you wrote:
| Quote: | my airplane has completed its speed tests and I can't imagine having
it fly faster than 112 MPH for the foreseeable future.
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psm(at)att.net
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| Posted: Mon Mar 16, 2009 7:34 pm Post subject: Fwd: Re: Is Your CH601XL/650 a 1320 lb Airplane or a 1041 |
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Actually, that is not even close to a true statement.
The LSA definition calls for a maximum indicated (actually
calibrated) airspeed of 138 mph at sea level and maximum continuous
power. From a simplistic point of view this might be considered
level cruise speed. It would be quite reasonable for a legal LSA to
go considerably faster than this if extra power is applied or if not
in level flight.
The issue of maximum continuous power is really slippery. For E-AB
airplanes this is specified by the aircraft manufacturer - not the
engine maker. There is no rule that says you must operate your plane
at or below this number. For example, you might decide your engine
should be limited to 2800 rpm if the outside air temperature is above
90 degrees F but you could still reasonably run it at 3200 rpm for
long periods of time if the OAT is lower. Given these numbers is
the RPM for maximum continuous power 2800 or 3200? The practical
answer is to use whatever number makes your plane qualify as LSA.
The other obvious issue is how you choose to measure your speed. The
LSA limit is calibrated airspeed, but for most purposes TAS is more
useful. True airspeed is almost always higher than indicated - often
15 to 20 percent higher.
I know I am not being totally reasonable here. My point is that 112
mph might be a very restrictive speed for an XL. I have recently
seen even lower maximum speeds called for by European governments (97 mph?).
The good news - there are no cops with radar guns checking up on
us. Therefore, there is no practical speed limit.
Paul
do not archive
At 08:15 PM 3/16/2009, you wrote:
| Quote: | the LSA speed limit is 138... (120 knots)
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psm(at)att.net
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| Posted: Mon Mar 16, 2009 8:02 pm Post subject: Fwd: Re: Is Your CH601XL/650 a 1320 lb Airplane or a 1041 |
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That only counts if the ATC guy remembers to bring his slide rule to
work and gets permission from his union steward to calculate your
indicated airspeed . . .
At 08:50 PM 3/16/2009, you wrote:
| Quote: | I guess radar and mode S don't count...
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tonyplane(at)bellsouth.ne
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| Posted: Mon Mar 16, 2009 8:47 pm Post subject: Fwd: Re: Is Your CH601XL/650 a 1320 lb Airplane or a 1041 |
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For what its worth:
I consider my cruising speed for cross country to be 105 kts IAS (about
120mph). If I wish to conserve fuel for just enjoying the sky then I
usually cruise between 90 - 100 kts IAS. If I push it up to my max
cruising RPM it is 115 kts, but fuel usage goes up too much. It will do 120
kts IAS WOT. It does not have wheel fairings, but has 600x6 tires/wheels
with an 801 nose fork, so it is a little more "draggy" than a standard XL
The Max IAS I have taken it to has been 195 MPH IAS in a shallow dive at
3300 RPM on my Jab at about 1150 lbs weight. This was in calm air with
gradual approach to that IAS which is 8% above my Vne of 180 MPH at 1300 lbs
during my Phase I testing. My Vne at 1320 # is 160 MPH
I have flown it at Va in turbulence such that my headset would not remain on
my head unless I held it on.
My airplane has wing lockers and the hingeless ailerons. My LH aileron has
a trim tab.
My airplane is also equipped with a wing removal device (it may also remove
the horiz stab first), AKA a stick (actually two of them - one on each side)
Tony Graziano
601XL/Jab3300A, kit built in my barn, Ser 6-5342; N493TG; 474 enjoyable hrs;
1041 landings, with over 150 rough field landings.
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Terry Phillips
Joined: 11 Jan 2006
Posts: 346
Location: Corvallis, MT
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| Posted: Wed Mar 18, 2009 10:41 am Post subject: Fwd: Re: Is Your CH601XL/650 a 1320 lb Airplane or a 1041 |
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At 07:15 PM 3/16/2009 -0700, Sabrina wrote:
| Quote: | Terry,
I am approaching this from a different perspective than you. It was suggested at AirVenture 2005 that I build an airplane as a learning experience. I looked at the RV, the Midget Mustang and the Zenith. At the time I committed to the XL kit, there had been no wing failures. Whereas I learned a lot during the build, including budgeting and time management, I never imagined that I would be sending a test pilot up in an aircraft I built after someone had just died in a similar design, time and time again. I have grown up a lot in the past 14 months. I am now 44 months into this process. (6 to decide which aircraft, 22 to build, 2 to certify, 14 planning flights.) I am only 188+ months old.
Flutter will occur in any aircraft with unbalanced control surfaces if you go fast enough.
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I think that is probably true. What I do know is that the FAA rules required flutter testing for certificated airplanes, so, obviously, flutter is a problem that must be dealt with.
| Quote: | I like the French number of 112 MPH released last week. I had heard a similar number given for a potential onset of flutter in the XL design without more. Maybe your 3D program was the source of the number, I don't know, it sounds reasonable.
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My understanding is the 180 km/hr (112 mph) comes from the German rules which require GVT for planes that fly faster than 180 km/hr. Since the 601XL had not been vibration tested, the German response to the accidents was to mandate reducing Vne to the 180 km/hr limit for untested aircraft. The French decided to copy the Germans.
| Quote: | To go faster than 112 MPH, what do we need to do? Either balance the control surfaces or maintain cable tension. Just because cable tension is not an “acceptable” means of preventing flutter in certified aircraft, does not mean that it does not work.
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Actually, cable tension is acceptable and valuable. What is not acceptable to the FAA for certificated airplanes is relying solely on cable tension. Their view is that flutter is so dangerous that a multilayered defense is required. I.e., cable tension, counterbalances, wing stiffness, etc. I think that it works out that counterbalances are one of the most weight efficient countermeasures.
| Quote: | We clearly have to train XL pilots on how to properly slow down to 112 when flutter starts. Personally, I like my idea of adding AS5 rivets on the inboard aileron attach points, it may give you that extra second or two to slow down. So too, I would not advise anyone to get into any experimental aircraft without an emergency parachute, BRS or not.
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Isn't it interesting that German microlight rules require both GVT and a BRS? Regarding maneuvers, be sure to read the account "601XL Flutter_Hinge-less_No_1.pdf" in the ZBAG files section. Good idea for everyone to learn and practice such maneuvers. I like your AS-5 rivets. I'll use those or solid rivets. And on the control horn too.
| Quote: | I don't think the currently designed rear spar and piano hinge aileron can handle the extra stress of mounting counter balance weights. I would rather slow my aircraft down than counter-balance the ailerons at this point in time. Your 3D models should help us with that.
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Take a look at the photos of the Sonex-Waiex counterbalance that is posted on the ZBAG file section. A similar setup would probably be effective in the 601XL. Bear in mind that there is not a lot of stress on the rear spar way out on the wing. If analysis indicated a problem, one could always install a doubler around the rear spar aperture.
| Quote: | I am so used to flying in a C150L that 112 does not sound that bad to me.
If it would save a single life, I would offer my airplane up for destructive testing but I have incorporated so many modifications that I don't know what good it would do.
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That's a generous offer. I'm still hopeful that Zenair will change their mind and agree to do the testing. They are already destroying the airframe to do the DAeC tests. It would be so cheap and simple to combine the tests. But there are other things to do besides destroying your XL.
| Quote: | I strongly believe in 3D modeling and encourage you to spend your money that way rather than requesting further testing of a European version of our XL. Ground vibration testing of an airplane with its wing spars set at a different angle than mine, gives me no useful data. NONE.
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I may be wrong, but I do not believe the angle of the spar attachment is the critical variable. As I understand it, w.r.t. flutter, the critical data produced by the GVT are the spring constants and dampening coefficients. If the wing is oscillating, an unbalanced aileron will necessarily be pivoting about its hinge point. When the stiffness and spring constants of the aileron system (including the cables, linkages, etc., produce an aileron vibrational frequency that matches the wing's vibrational frequency, then the oscillations of the two components reinforce each other and bad things can happen. The upshot is, in my amateur opinion, a slight change in the wing attachment angle would not have much effect on what GVT are designed to measure.
| Quote: | At this point my airplane has completed its speed tests and I can't imagine having it fly faster than 112 MPH for the foreseeable future. I would appreciate you sharing your 3D model results as to Vne for optimally tensioned, unbalanced ailerons and what that optimal tension would be.
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This is the key! Our engineer's 3D model requires GVT data to fine tune and validate the model. Just as load tests are needed to prove the accuracy of the wing strength calculations, the GVT data are needed for the 3D flutter model.
| Quote: | Zenair's lawyers will never let them test beyond what is mandated no matter how much money you throw in. Your best bet is to persuade the FAA to have AMD GVT one of their 601XLs.
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I hope you are wrong. But time will tell the tale. I'm not optimistic about help from the FAA. If Zenair will not do the GVT and share the data, we need to look at the best way forward. Ideally, we could test an aircraft on ZBAG's nickel. But, then we'd have to pay for the entire setup rather than just piggybacking on the back of the DAeC test setup. That would double or triple the cost. We have bounced that around a bit, but haven't gone very far. One problem is that the testing resources are widely separated from our engineering resources.
A more promising way is to incorporate all the changes mandated by the LAA, and then adopt the LAA's operating limits. I would guess that would mean a reduced gross, possible limitations on flying at gross with reduced fuel loads, possibly reduced Vne, Vc, Va. But that's just a guess. We will have to wait to see what the LAA requires. But at least the LAA is committed to a flight test of the modified airplane. Hopefully it will include attempts to excite flutter.
| Quote: | Wishing you the best,
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Like wise. I'm sure that this has been an educational project in ways that you never anticipated. However, this is very much real world. You can do everything right, and still get the wrong result. And, as was recently told to me by an expert, an airplane can meet all the standards and still be unsafe. The standards are an attempt to enumerate and specify 100 years of aviation engineering knowledge and experience to produce safe airplanes. But nothing built by humans is likely to be perfect, including those regulations.
And when this is all done I'll buy you a soda at Oshkosh 
Terry Phillips ZBAGer
ttp44~at~rkymtn.net
Corvallis MT
601XL/Jab 3300 s .. l .. o .. o .. w build kit - Tail, flaps, & ailerons are done; waiting on the wings
http://www.mykitlog.com/N47TP/ [quote][b]
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_________________
Terry Phillips
Corvallis, MT
ttp44<at>rkymtn.net
Zenith 601XL/Jab 3300 slow build kit - Tail feathers done; working on the wings. |
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Gig Giacona
Joined: 10 Jan 2006
Posts: 1416
Location: El Dorado Arkansas USA
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| Posted: Tue Mar 24, 2009 8:02 am Post subject: Re: Fwd: Re: Is Your CH601XL/650 a 1320 lb Airplane or a 1 |
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| psm(at)att.net wrote: | Actually, that is not even close to a true statement.
The LSA definition calls for a maximum indicated (actually
calibrated) airspeed of 138 mph at sea level and maximum continuous
power. |
Actually that isn't even what the definition calls for 138 mph at sea level in level flight at maximum continuous power.
So let's say max power on a plane is 3200 rpm and at that speed I get 145 mph CAS at sea level. If I, as the builder, say that max continuous power is 2800 and that rpm gives me 138 mph at sea level, I'm LSA legal.
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_________________
W.R. "Gig" Giacona
601XL Under Construction
See my progress at www.peoamerica.net/N601WR |
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