News

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Issue No. 10, August 2001

European Transonic Windtunnel GmbH

Ernst -Mach -Strasse D -51147 Köln

The European Transonic Windtunnel,ETW, after some five years of operation,continues to prove that low temperature(cryogenic) flow conditions resulting intrue flight Reynolds numbers cansuccessfully be combined with high flowquality and productivity as good or betterthan modern conventional wind tunnels.

ETW provides an additional advantagein that flow velocity, pressure andtemperature can be very accuratelycontrolled individually, thereby allowingthe Mach number or the Reynoldsnumber or the dynamic pressure to bevaried while keeping the other twoparameters constant. Thus, theaerodynamic effects of these essentialparameters can be clearly separated anddistinguished (e.g. Re number effectsand model deformation effects) which isnot possible in other wind tunnels.

Airbus A380 in Test at ETW

Also an absolutely accurate repeatabilityof test conditions is possible regardlessof the time between tests.

ETW is being used by major aircraftcompanies as a development and/orcheck-out facility for their currentprojects (e.g. Airbus, Fairchild Dornier,Dassault).

Being open for clients world-wide, ETWis in the position to still accommodatefurther test entries by extendingestablished shift work schemes.

The extraordinary features of ETW haveinduced the Airbus partners to issue thestatement quoted on the next page.

If clients wish, ETW is able to offer thecomplete package of model design, model

manufacture and wind tunnel testing inthe form of well co-ordinated contracts.

By this means, the lead time for testsmaking use of the outstandingperformance and quality of ETW can beconsiderably shortened.

For this purpose, ETW has establishedclose links with E2CM, a co-operativeorganisation of some major Europeanaerospace research establishments forcryogenic model design and manu-facture, as well as with two Germanmanufacturing companies, DEHARDEGmbH in Bremen, Northern Germany,and EUBEL GmbH in Troisdorf, closeto the ETW site.

Both have very successfully beeninvolved in preparation of various testassemblies for cryogenic environment.

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The Airbus Partners Praise ETW, the World's Most Advanced Wind Tunnel.

• The ability to measure near flightReynolds number flight loads, allowingthe early right sizing of key structuresand the avoidance of expensivecomponent retrofits.

• The only tool to allow the investigationof the effect of wing twist uponaerodynamic characteristics, indepen-dently of all other flow parameters.

• The ability to test at high speeds, undermoderate cryogenic conditions(–30°C), with a conventional 4 bar wingat a Reynolds number of about 15Millions (based upon AMC).

Overall Comments

of the Facility:

A User’s View

• Customers: All of the Airbus Industriepartners who have tested at ETW havefound the customer focus of the ETWstaff to be exemplary. ETW's attentionto detail, plans & time scales meant thatas users of the facility we always felt inthe driving seat.

• Performance: The modern, purposemade facility proves to be veryproductive in comparison withcomparable existing facilities.

Drawing on their experiences gained withtesting in ETW the Airbus Partners,Airbus UK and EADS Airbus (formerlyBAE SYSTEMS Airbus, AerospatialeMatra Airbus and DaimlerChryslerAirbus) last year have released thefollowing statement:

ETW, A Unique

European Facility:

An Industrial View

The Union of four key European aero-space research institutes has, in the viewof industry, produced the best wind tunnelfacility in the world; a facility that providesthe following unique capabilities:

• The potential to capture aerodynamicdata for flight performance of newaircraft without the need to refer back toa reference aircraft possibly allowingthe underwriting of flight performanceguarantees for new, innovative designs.

• The provisions to undertake completebalance calibration, within one workcycle, to an incredibly high standard.

• The only tunnel in the world that allowsthe user to always get an exact tunnelsetting, irrespective of time betweentests and external factors.

Issue No. 10, August 2001

• Quality: In terms of both force andsurface pressures, we have found therepeatability and quality of the data tobe excellent. Similarly, the quality offlow, both in terms of stability andhomogeneity, has proven to be veryimpressive. In addition, the facility'sexisting quality control procedures andpost-test reviews underline the commit-ment to the customer in delivering aquality service.

• Innovation & Technology: Much of theproductivity is derived from modernworking practises and technology. Ofparticular note is the on-line dataanalysis suite, providing the user withimmediate access to corrected data asthe test is progressing. All partnersfound this a very powerful tool inassisting the reactive management ofthe various test programmes.

• People: Our experience is that problems,when they occur, are quickly andeffectively addressed, reflecting theunderstanding and knowledge base ofthe facility's staff. The knowledge baseof the ETW staff is seen as a key strengthof the facility and in our experienceunderwrites the quality andproductivity of the service provided.

ETW’s Quality Management System Appreciated.

After the first certification of ETW'sQuality Management Systemfollowing the thorough audit and therespective recommendation byLloyd's Register Quality AssuranceLtd. (LRQA) in March 1997, thetriannual reassessment by LRQA in

March 2000 again resulted in theunqualified award of the approvalcertificates of the official QAaccreditation bodies of France,Germany, Great Britain and TheNetherlands.

LRQA continues to monitor the QAmanagement system through yearlysurveillance visits, the most recenttook place on 29th March 2001.

ETW is progressively amending itssystem to comply in due time with therecently issued revision of thestandard EN ISO 9001:2000.

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Issue No. 10, August 2001

Determination of the Wing Twist by

Comparison of Wing Pressure DataHigh Reynolds number testing of air-craft models at ETW requires, inaddition to cryogenic flow tempera-ture, an elevated tunnel pressure witha corresponding increase in the aero-dynamic loads. For distinguishingbetween true Reynolds number effectsand those caused by the elastic defor-mation of the wing, the determinationof the wing twist is very important.

ETW's unique ability to test models atthe same Mach and Reynolds number,but different combinations of tunnelpressure and temperature, allows thedetermination of the effective aerody-namic twist by comparing the pressurecoefficients measured at certain wingsections. The assumptions made are:

• At a given Mach and Reynoldsnumber, the variation of the pressurecoefficient versus the local angle ofattack is identical for each individual

measuring point, irrespective oftemperature and dynamic pressure.

• The local effective wing twist is a linearfunction of the lift coefficient and thedynamic pressure.

The computation of the effective aero-dynamic twist is accomplished by acomputer program which processes thepressure coefficients of one individualwing section that have been acquiredat different levels of tunnel pressureand temperature.

The software performs an extensiveselection and evaluation of the measureddata, including a correction algorithmfor scanner offset drifts.

Since the true (effective) angle of attackis the difference between the geometricand the induced angle of incidence, theobtained result does not represent the

geometric, but the effective local wingtwist, which is reduced by the differenceof the induced local downwash. Thegeometric twist of the examined wingsection can be esti-mated by computingthe induced downwash angle whichoriginates from the effective wing twistalone (see figure below).

The uncertainty in the determination ofthe effective aerodynamic twist, i.e. thechange of the local effective angle ofattack due to torsion and bending, isestimated to be less than ±0.1° at adynamic pressure of 100 kPa, gooddata quality provided. Concerning thegeometric twist, the additionaluncertainty in the computation of theinduced downwash angle has to beconsidered.

The main advantages of the describedmethod are the applicability over thefull operating range of ETW, lowsusceptibility to vibrations, tur-bulence, temperature gradients, etc.,and the independence from modelattitude and mounting.

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Personnel

Eric GERMAIN

Eric Germain from France joined ETW

as Test Engineer in Nov. 2000. His

prime responsibility is to co-ordinate

and supervise Client and ETW test

campa igns .

Eric graduated from the French

national engineering school ENSIMEV

in Valenciennes having been enrolled

at ENSMA in Poitiers for part of his

last year.

During the last six months of his study,

he prepared a diploma thesis on

evaluation of wind tunnel test data for

a wing with boundary layer suction at

EADS Airbus in Bremen, Germany.

In addition to his mother language,

Eric is fluent in English and German

and is familiar with a variety of

important computer software.

He enjoys travel l ing abroad, is

interested in astronomy and is in

advanced state of training for a

private pilot licence.

FAIRCHILD DORNIER 728JET TESTING

In April 2001, Fairchild Dornier hassuccessfully completed tests of severalwinglet configurations with a testassembly of the 728JET wing in the ETW.These tests were carried out in addition tothe first test series with the complete halfmodel of the 9.24 scaled 728JET aircraft,which covered the high Mach numberrange at low and medium Reynoldsnumbers. In the first test campaign inJanuary/ February 2001, Reynolds numbereffects were investigated in detail. In thesecond campaign, different winglets weretested at high Mach numbers and onefixed Reynolds number.

The incremental data comparison of thetest results for the different configurationswas used for aerodynamic performanceanalysis.

The test result was achieved due to theunique cababilities of ETW by alwaysproviding an excellent repeatability oftest conditions. Both tests also includedchecks to assess the influences of wingdeformation on the test results. Since it ispossible in ETW to control all tunnelparameters individually, this can beachieved by variation of the dynamic

pressure at constant Mach and Reynoldsnumbers. In both campaigns, the ETWmethod of using the measurements of thewing pressure ports for wing deformationanalysis was successfully applied. Theverification of the effectiveness of thedifferent transition tripping bands wasdone with thermographic images from theAGEMA infrared camera system atdifferent Reynolds numbers.

ETW News is issued byETW GmbH,Ernst-Mach-Strasse,D-51147 Cologne.http://www.etw.de

Editor: U. Walter,Tel.: +49 (0) 2203 609 115Fax: +49 (0) 2203 609 124uw@etw.de

Print: Druckerei Thierbach, Mülheim/Ruhr

Issue No. 10, August 2001