Zenith Load Testing Analysis

[Thruster87]

A Video has been created from the Analysis of the FAA Report and its comments on the Zenair 601XL / 650 load test. �You can see the video at�[media=vimeo]10340573[/media]� �Please pass the URL along to anyone who would be interested. �� [thread copied from matromics]

 

 

[sleemanj]

A Video has been created from the Analysis of the FAA Report and its comments on the Zenair 601XL / 650 load test. �You can see the video at�

I thought the failures had been largely attributed to flutter (hence the requirements to check and adjust the cables), and so.. wouldn't static load testing not actually be of a huge amount of relevance here?

 

I'm sure the wings can support many G static loads, but if you setup a rapid harmonic resonance in those same strong joints, fatigue is going to set in quickly to cause a failure.

 

Not saying the guys analysis is wrong, or not independent (although have to say, it sounds a bit "pro zenith" to be truly independent), just that maybe it's not looking at the right stuff?

 

 

[ianrat]

Below is an insert from the FAA report.

 

A POTENTIAL FOR FLUTTER

 

Although the FAA found the available flutter data results were inconclusive, they stated that it's clear from the evidence (from aircraft involved in structural failure accidents) that flutter was a "causal factor." Further stating that it's not possible to determine whether flutter was the root cause of the structural failure or a secondary cause after some initial structural deformation of the wing, the FAA is looking at the seemingly diminished structural stiffness influencing flutter while also noting that improperly rigged aileron cable tensions, and improperly installed flap stops have certainly been the culprit in non-catastrophic flutter incidents

 

The above post is in response to the FAA stating that the data should be re tested.

 

As you can plainly see the results are within the limits required.

 

I do not believe that the author is any way involved with Zenith other than a plane owner.

 

I would suggest that the whole FAA report would have to be read in conjunction with the above report to get the full picture.

 

Ianrat

 

CH601XL Brisbane

 

 

[country kid]

hmmm still not really conclusive reluslts and it dose seem a bit pro zenith. but im sure the problem will be resolved then they will need to re-establish their sales and reputation. so i think it will be a few years before there back to bring a reputable company

 

 

[Thruster87]

4. Flutter results for the CH601XL

 

 

 

 

 

 

 

 

Flutter calculations have been performed for the CH601XL based on the results of complete

 

 

 

 

 



ground vibration tests up to Eigen frequencies of 80 Hz. All results, the input and output files

 

 

 

 

 



for the software package ZAERO, as well as all pre- and post processing MATLAB program

 

 

 

 

 



codes are stored on the corresponding project DVD CH601XL. The files on the DVD CH601XL

 

 

 

 

 



allow complete analysis and reproduction all computed results:

 

 

 

 

 

 

• minimum and maximum take off mass

 

 

 

 

 

 

 

 

• controls fixed and free

 

 

 

 

 

 

 

 

• cable tensions of aileron control system from 5 lbs to 45 lbs

 

 

 

 

 

 

 

 

• low altitude flight (MSL) and high altitude flight (5000 m)

 

 

 

 

 



No tendency to flutter or divergence was found within the flight envelope. The analysis does

 

 

 

 

 

not show any reason to install mass balancing weights nor the need for spades.

 

 

5. Summary

 

 

 

 

 

 

 

 

JAR-23 guidelines require testing to ensure that “the airplane is free from flutter, control

 

 

 

 

 



reversal and divergence for any condition of operation within the limit V~n envelope”. With the

 

 

 

 

 



classical linear approach for flutter analysis with ground vibration test and up to date flutter

 

 

 

 

 



calculations using the software package ZAERO, no aeroelastic instability was found within

 

 

 

 

 



the flight envelope of the CH601XL.

 

 

 

 

 



When the flap stops are installed according to the manufacturer's specifications is mounted

 

 

 

 

 



and the cable tensions are within the specified tolerances set by the manufacturer, the

 

 

 

 

 



occurrence of flutter with the CH601XL is improbable within the well defined flight envelope.

 

 

 

 

 



The analysis in this report is based on linear methodology. The analysis of possible nonlinear

 

 

 

 

 

vibrations due to structural instabilities was not the subject of this investigation

 

 

 

[djpacro]

I could be wrong but my understanding of JAR 23 (and FAR 23) was that a ground vibration test plus analysis was only acceptable for comparison with a dynamically similar aircraft which had previously been demonstrated to be free from flutter.

 

Generally, to demonstrate freedom from flutter requires a flight flutter test plus analysis.

 

 

[Thruster87]

JAR 23.629 Flutter

 

(a) It must be shown by the methods of (b) and either © or (d) of this paragraph, that the aeroplane is free from flutter, control reversal and divergence for any condition of operation within the limit V~n envelope and at all speeds up to the speed specified for the selected method. In addition -

 

(1) Adequate tolerances must be established for quantities which affect flutter; including speed, damping, mass balance and control system stiffness; and

 

(2) The natural frequencies of main structural components must be determined by vibration tests or other approved methods.

 

(b) Flight flutter tests must be made to show that the aeroplane is free from flutter, control reversal and divergence and to show by these tests that -

 

(1) Proper and adequate attempts to induce flutter have been made within the speed range up to VD;

 

(2) The vibratory response of the structure during the test indicates freedom from flutter;

 

(3) A proper margin of damping exists at VD; and

 

(4) There is no large and rapid reduction in damping as VD is approached.

 

© Any rational analysis used to predict freedom from flutter, control reversal and divergence must cover all speeds up to 1·2 VD.

 

(d) Compliance with the rigidity and mass balance criteria (pages 4-12), in Airframe and Equipment Engineering Report No. 45 (as corrected) "Simplified Flutter Prevention Criteria" (published by the Federal Aviation Administration) may be accomplished to show that the aeroplane is free from flutter, control reversal, or divergence if -

 

(1) VD/MD for the aeroplane is less than 260 knots (EAS) and less than Mach 0·5;

 

(2) The wing and aileron flutter prevention criteria, as represented by the wing torsional stiffness and aileron balance criteria, are limited to use to aeroplanes without large mass concentrations (such as engines, floats, or fuel tanks in outer wing panels) along the wing span; and

 

(3) The aeroplane -

 

(i) Does not have a T-tail or other unconventional tail configurations;

 

(ii) Does not have unusual mass distributions or other unconventional design features that affect the applicability of the criteria; and

 

(iii) Has fixed-fin and fixed-stabiliser surfaces.

 

(e) For turbo-propeller powered aeroplanes, the dynamic evaluation must include -

 

(1) Whirl mode degree of freedom which takes into account the stability of the plane of rotation of the propeller and significant elastic, inertial and aerodynamic forces; and

 

(2) Propeller, engine, engine mount and aeroplane structure stiffness and damping variations appropriate to the particular configuration.

 

(f) Freedom from flutter, control reversal and divergence up to VD/MD must be shown as follows:

 

(1) For aeroplanes that meet the criteria of sub-paragraphs (d) (1) to (d) (3) of this paragraph, after the failure, malfunction, or disconnection of any single element in any tab control system.

 

(2) For aeroplanes other than those described in sub-paragraph (f) (1) of this paragraph, after the failure, malfunction, or disconnection of any single element in the primary flight control system, any tab control system, or any flutter damper.

 

(g) For aeroplanes showing compliance with the fail-safe criteria of JAR 23.571 and 23.572, the aeroplane must be shown by analysis to be free from flutter up to VD/MD after fatigue failure, or obvious partial failure of a principal structural element.

 

(h) For aeroplanes showing compliance with the damage-tolerance criteria of JAR 23.573, the aeroplane must be shown by analysis to be free from flutter up to VD/MD with the extent of damage for which residual strength is demonstrated.

 

(i) For modifications to the type design which could affect the flutter characteristics compliance with sub-paragraph (a) of this paragraph must be shown, except that analysis alone, which is based on previously approved data, may be used to show freedom from flutter, control reversal and divergence for all speeds up to the speed specified for the selected method.

 

Wings

 

 

[Captain]

A Video has been created from the Analysis of the FAA Report and its comments on the Zenair 601XL / 650 load test. �You can see the video at�[media=vimeo]10340573[/media]� �Please pass the URL along to anyone who would be interested. �� [thread copied from matromics]

So it looks like if another wing falls off it will all be the pilot's fault ..... again.

 

 

[Thruster87]

So it looks like if another wing falls off it will all be the pilot's fault ..... again.

The calculations/testing/analysis/reviews/flight tests etc all show the aircraft to exceed design requirements for 600kg LSA with the upgrade package installed.:thumb_up: So should one wait eagerly for another accident to say I told you so?????

[nong]

Lets cut to the chase. Engineering calculations and ground based tests must ultimately be put to the acid test. This takes place IN THE AIR. Reputable firms conduct these tests PRIOR to releasing aircraft for public consumption.

 

Why are we not seeing a member of the Heintz family donning a chute and then diving one of these crates to at least VD (with slack cables for good measure)? At speed the pilot could wiggle the stick with vigour.....trepidation?....to see what happens. On the next dive ( if he gets that far ) some stick force per G testing could take place.

 

If the crate folded up we would surely toast the bloke for his courage.

 

If it stayed together we would admire him for taking decisive action to prove his case.

 

 

[Ultralights]

Cessna Lost 2 prototypes during flight testing of their LSA, like mentioned above, there is no test better than real word airborne testing.

 

 

[winsor68]

I actually watched this whole presentation...

 

I could have misinterpreted but didn't they mention that the airframe tested was beefed up to meet Lsa standards and then tested? I thought the aircraft was already being sold as Lsa?

 

 

[Guest ozzie]

EAA - EAA Experimenter - FAA's Zodiac 601/650 Aircraft Report

 

A bit more from the EAA on the FAA report