zlin crash

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Cub flyer
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zlin crash

Postby Cub flyer » Tue May 06, 2008 5:40 am

http://ntsb.gov/ntsb/brief2.asp?ev_id=2 ... 136&akey=1

Sad and my regrets to the family. I hate hearing of these types of things.


Reading the above report some statements are a little odd.

rudder cable Hose clamps?

No ATSM standard for airspeed markings, wrong markings,

Another pilot says Stalls uncommanded while climbing at 58 mph in smooth air?

I wonder what type of aircraft the pilot was training for at flight safety international?



No condition inspection signoff except a sticky note from the mechanic that the owner lost?

It will probably go down as pilot error like others but there sounds like more to it than that.

I wonder where the CG was. The other pilots giving the description of flying characteristics are flight instructors, not students.

When will we get some true independent testing of these LSA designs before they hit the market? Especially stall characteristics.
Last edited by Cub flyer on Tue May 06, 2008 6:31 am, edited 1 time in total.

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Postby CTflyer » Tue May 06, 2008 6:15 am

Charlie - I join you, both in sympathy for those involved, and in wondering about the details.

Isn't there supposed to be some certification "standard" for that plane? Or was this an example of flying "naked" with no real safety and airworthiness inspection.

An experienced pilot having all those "airplane issues" - strange to me.

Edit: looks like more than one pilot reported surprises in the stall characteristic of that plane, according to the report.

I know zip about these things, but would appreciate your thoughts.

thanks.
Tom

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Postby Cub flyer » Tue May 06, 2008 6:55 am

back a while I read a pilot report on the savage when it was flown by John Mohr (stock stearman aerobatic pro)


They were comparing a savage with VG's installed and without.

Big differences in flying characteristics. With the VG's installed you could get the tail down to 3 point on landing.

The NTSB report leaves some info out.

Weight of occupants, estimated fuel to figure CG
Flap handle position. Big difference in stall speed depending on flap position
If VG's were installed
No interview with the condition inspection mechanic. only the importer
(importers are usually not mechanics or test pilots. they are salesmen.

Why no stall waring device or airspeed markings required for LSA. Just plain stupid.


The flight characteristics and uncommanded stall reports also leave this information out and it would be critical to determining what is happening.

The Savage is a November 2005 airplane. Like most early LSA imports the companies make changes then applied for the LAMA audit.

I would be very wary of any airplane built before the audit and also I'm not sure the whole thing will work. It's hard to believe anything when some members of the LAMA board have ties to LSA manufacturers. Especially when they are importers themselves and seeking LAMA approval for their products.


I am going to guess that this is plain stall spin pilot error. BUT...

How much aerodynamic stall warning was he provided, how low is the nose with flaps down and stalling angle of attack (no visual cues) how was the airplane rigged (trim tabs on controls instead of adjusting wings)
Any washout in the wings for gentler stall
how much testing was done at near gross weight or different CG locations
Doors/windows open during the accident flight?
Aileron spades installed?
how much force is needed to keep the airplane out of it's trim speed band (stick force when flying too fast or slow for trimmed speed)
how fast does it recover from a cross control stall.
how accurate is the airspeed indicator.
Static ports outside the airplane? if not airspeed will read higher depending on door position during flight. Door was probably open in August looking for a road location.

There are lots of questions that will probably never be answered.

only a true flight test program could.

I do know low and slow with the cub I trim for 55-60 mph and can easily maneuver with no flaps installed and never look at the airspeed. If it gets too slow there are instant cues in the stick and nose position. if I stall accidentally the J-3 recovers instantly by just pushing forward. Proper wing washout rigging is essential. The J-3 trim system is very fine adjustments and holds well so you can set exactly the speed you want and forget. Airplane pitches slightly down with power reduction and nose up with power application.

How do other new LSA designs compare? Who knows. the magazines never report on this stuff. Just "we went and flew around. It was bumpy so I made one less than perfect landing and the importer said I would be better with practice. He says it's easy to fly and the next batch of imported airplanes will be even easier. Sorry to whoever bough one already. We only built 850 of them and shipped them to Bangledesh and the're flying fine. You can sell yours and buy another. when yours is delivered. " Send us 100K plus taxes and shipping. Bull... but thats how most of the reports read to me.

Airplanes with large flaps slow fly flaps down with the nose in the same position as high cruise. Angle of attack is not a cue to the pilot. Nose position to the horizon is. This trap is what probably happened.

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CharlieTango
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Postby CharlieTango » Tue May 06, 2008 8:48 am

add some of this up

high density altitude
mountainous terrain
maneuvering close to the terrain
winds gusting to well over 20 kts
impact at 119 mph.
quirky stall characteristics.

maybe a stall close to the terrain, then recovery but failed to pull up in time. given the high speed on the ai he might have had trouble pulling up.

high time pilot but low time in the SLSA, but flying a mission as though he was high time

low and slow is fun and useful but you should build up to it, confidence in your skills, the aircraft, and use of good judgment are required

rsteele
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Postby rsteele » Tue May 06, 2008 9:03 am

Reading the report, the plane sounds like an accident waiting to happen: Questionable stall speed and slop in the rudder cable, Either condition could kill you. Imagine an unexpected stall, a wing drops and you try to use the rudder to correct, but the cable jams because it came off the pulley when you stomped on the rudder. Instant spin and no possible recovery.

I don't know what you can do about the stall speed other than flight test the plane. But there is no excuse for slop in the rudder cable, A plane shouldn't fly in that condition. Even if the cable stays on the pulleys, you could get flutter, even at these slow speeds.

Beats me you could can have a production plane with a questionable stall speed.

Ron (shaking head in dismay and disbelief)

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CharlieTango
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Postby CharlieTango » Tue May 06, 2008 10:58 am

rsteele wrote:...Beats me you could can have a production plane with a questionable stall speed...


realize that there is not such thing as a stall speed, but yet the concept is useful

your aircraft can stall at any speed, exceeding the crtical angle of attack causes the wing to stall.

the concept is still usefull because on a landing approach, the closer you get to the runway the fewer options the prevailing wind has so your airspeed becomes a good metric.

when climbing ( in percieved calm air ) at 58 kts stalling a lsa can be done. if there is a smooth flow of rising air you could exceed the coa and stall.

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Postby Cub flyer » Tue May 06, 2008 12:45 pm

a lot of tailwheel airplanes have sloppy rudder pedals when nobody is pushing on them . There are very weak springs and no cable tension except for natural foot weight. Aeroncas, citabrias, cubs, vagabonds, taylorcrafts, and others are all this way. no flutter problems. the surfaces are naturally resistant to this.

But the cables should not jump the pulleys. That's what cottor pins and cable guides are for.


The old Beech 18 elevator cable will jump out if taxing on rough ground with the yoke full forward. I know you shouldn't do that but sometimes you want weight off the tail.

the cable pops around and falls between the pulley and its mounting bracket. Then it wears and eventually breaks. A little tightening up of this area prevents that from ever happening. cable tensions are ok but it's a long run back there.

rsteele
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Postby rsteele » Tue May 06, 2008 1:55 pm

Cubflyer, I don't doubt you for a minute - you've been doing this a long time, But why would you have loose cabling? It seems like it would give you sloppy maneuvering in addition to other problems. I can see that with a long run of unsupported cable you could have problems even with relatively high tensions. Seems like you would want intermediate supports in a case like that. Otherwise rough air could move your rudder around.

Was the loose condition of the cables in the planes you mentioned "standard" or an indication of a maintenance problem?

My curiosity is has been tweaked about the ASTM S-LSA standard - I just might have to start taking at them. I like the idea of simpler/cheaper system of regulation than traditional certification, but I'm not sure the fox isn't watching the hen house with the S-LSA rules.

Sure stall is entirely based on angle of attack. I inferred from the report that stall characteristics for this plane may not be consistent from plane to plane. These characteristics would manifest themselves as different stall speeds for similar loads/CG etc. Gives me shivers to thinking about it.

Ron

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Postby Cub flyer » Wed May 07, 2008 6:32 am

I don't notice any real problems with loose rudder cables. When I say loose I mean when pulling left or right rudder the opposite cable is the one with no tension.

Most Cessna singles are this way also.

The steerable nose wheel pushrods can be adjusted on a Cherokee or Tripacer to eliminate this.

Most taildragger light airplanes have light springs just to keep the pedals from falling aft under the cable weight. when you place your feet on the rudders that gives a little tension. The cables don't stretch much so the controls feel direct. Also on the ground the tailwheel springs give some artificial feel which is replaced by airload after takeoff.

My favorite system is the Stinson Gullwing, Beech 18 and Stearman type of system where you have a short cable linking the rudder pedals in the forward fuselage. This forms a loop out of the rudder cable system and you can set exactly what tension you want. These airplanes have all ball bearing pulleys, needle bearing hinges, and real nice controls. Very light forces for the size of the airplane.

Also the above airplanes have very little adverse yaw. all three were designed before World war II.

But back to stall characteristics. If most of the LSA designs were being produced in other countries before the LSA rule why are they finding these problems out now? It should have been corrected with the first prototypes before any production in any country.

We can make a nice stalling airplane which performs well. It has been done many times.

just sloppy designing.
"Perfection is finally attained not when there is no longer anything to add but when there is no longer anything to take away." Antoine de Saint Exupery

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Postby Cub flyer » Wed May 07, 2008 12:41 pm

Another example of flutter resistance with proper control surface shape.

My 1961 Piper Apache has a very large rudder with rudder trim tab and actuator.

No aerodynamic balance, centering springs or balance weights. Just a straight hinge line. cable controls.

Redline is 227 MPH. fastest I have gone is 190 mph in a dive. steady as a rock.


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