Spin testing – Spin chutes and rockets

spin_recovery_system

Spin testing is definitely a hazardous flight test, but is an essential part of a FAR-23 certification process. For cases of unrecoverable spins encountered during the tests, a Spin Recovery System (SRS) deploying a spin chute is used to stop rotation and reduce the AoA for the airplane to regain control. The SRS is usually composed from three main parts: i) a supportive structure attached to the fuselage ii) a spin chute and iii) a rocket that deploys the chute. Various secondary supportive systems come with those, all of which have to be tested for sound operation by themselves. Current work includes a review of a spin Test Plan and supervision/management of a SRS dealing with both technical as well as non-technical challenges like shipping of explosives. This project is fun, but is not a game…

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Testing for Oswald factor

total_oswald

As long as you are involved in airplane aerodynamics, either by design or by testing or by any other means, you are surely aware of the span efficiency or Oswald factor “e”. This factor accounts for the difference of a wing’s lift distribution to the elliptical lift distribution. Literature suggests usually values of 0.8-09 or sometimes even 0.65 upwards. Various methods for estimating “e” from wing geometry parameters have been published. But what happens when coming into testing? A proposed method of deriving the “e” for prop aircraft is found in D.T. Ward’s book “Introduction to Flight Test Engineering” based on a generalized power curve. An application of the testing method resulted in really unexpected outcomes. At least for 3 different light airplanes the “e” has received values below 0.5, while in an aerobatic airplane case which was tested with various wing tips gave some values even below 0.3! Some error maybe? Values seem extraordinary, but I wouldn’t rush in such conclusion. There has been one reference before in literature of a general aviation airplane being tested for “e” with a result of 0.45, but that outcome was not commented at all. At the momentĀ I am tending towards the effect of the tail plane produced lift contributing to a reduced overall “e”. It needs to be investigated more and maybe the analytic tests results will be interesting for a paper (time permitting…).

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SETP Symposium, Anaheim CA, 24-27 Sept 2014

anaheim_2014

Attended the Annual Society of Experimental Test Pilots (SETP) Symposium at Anaheim California as an exhibitor this time with the ITPS booth. We had the chance to meet some distinguished flight testers, attend some really good presentations and enjoy some great banquets. Constructive experience and some time spent in nearby Disneyland. Amazing place..

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Frequency sweeps and Bode plots

The Advanced FCS course was repeated for the second time these year. Course material was further expanded in accordance to DM recommendations including this time frequency sweep training in all axes. Data were gathered (managed to get a sample rate of 20Hz out of the flight sim which was just enough for our training purposes) and further processes. (The sweep shown below wouldn’t be the most comfortable in real conditions, but student will improve with training.)

pitch_sweep

Various FCS response types were examined and through system identification Bode plots were eventually created and analysed in class.

bode_plot

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T-6 Harvard flight

A short flight took place in one historical training aircraft. T-6 has served many Air Forces including the Hellenic one. What is certain is that flying with these airplanes you built huge respect for theĀ aviators of that era.

T6_Harvard_Vitsas

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Director at SFTE BoD

Great great honor to be nominated and elected as a Director in the SFTE International Board of Directors together with some exceptional individuals.

The period of duties is 2 years where each board member serves different responsibilities and all together working towards the benefit of the society, flight testing an science. Regular meetings take place mostly through teleconferencing but also during the international symposiums.

SFTE_BoD

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Time Space Position Information (TSPI) notes

tspi_overview

Time Space Position information is all about accurate referencing. Especially nowadays that high precision is critical for various air operations, either manner, unmanned, or testing of systems, TSPI is of paramount importance. Sensors employed in TSPI include theodolites, radars, GPS, IMU, RF sensors, optical techniques and others. Through sensor fusion multiple sensors can be combined for accuracy that comes down to few cm’s of position uncertainty. One of the basic problems associated with this process is that the aircraft coordinate system is different than the TSPI coordinate system. Transformation and post processing is not as simple as it might initially seem when looking for higher order accuracy where earth model concepts of world geodetic system (WGS-84) and geoidal separation have to be taken into consideration. Working with JM at the moment to develop some complete notes on the subject.

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