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Manuals and service instructions

 

Following manuals are available in english:

 

Problem with the Engine Noise Level (enl) Sensor in the 302

An endless story - Finally now we found the solution!

The 302 is in production since 2002, total approx. 2 200 until now. The first lot was delivered without the enl sensor, since the approval procedure with the IGC was not finalized until Jan.13, 2003. The unlucky changeover of Cambridge Aero from David Ellis to a crook stopped development work and product quality. This has significantly improved since he is not involved any more.
The design of this enl sensor is equivalent to the one used in the proven GPS-NAV.
The small Microphone is sensitive to the low frequencies typical for a propeller, approx. 27 Hz, (20 to 80 Hz range). The audio at zero lift reads 440 Hz. It always worked super in the GPS-NAV (with its max 400 counts scale).
With time it came up, that quite a large number of enl 302’s showed too high enl levels (with its max 1000 counts scale acc. to new IGC rules) in the flight download files, and enl sparks in these logs only poorly match the real noise level in flight. The audio noise is reflected max. 10 counts in a 400 count scale, which means the audio noise error in total enl reading is negligible.

This malfunction can result in „engine ON“ enl levels, and therefore an „end of the flight“ scoring with the automatic OLC flight evaluation program.

The result was and still is mad phone calls and e-mails of the pilots involved, so the blame was mostly “downloaded” onto me. This ended in many board changes, tests, endless unpaid working hours, mail, and frustration by all and the the CAI guys involved. The boards often showed no enl problem at all on the test bench. Gary Kammerer did many new enl calibrations, but it did not solve the problem. Therefore I also had to swallow mockery.  Some frustrated customers gave their 302 back. The old Cambridge team could not help me.
After lot of detail work and questioning pilots, it came to me that this phenomenon only exists in the 302, but not in the 203A
(The 302A is a stripped down 302, used as Flight Recorder only). This 302A uses the same sensor technology and board hardware – but without the audio needed for the variometer.
Therefore the problem must come from the audio speaker. Against this solution stands the fact, that the audio frequency is at a much higher level as the 28 hz typical for a propeller, see above.
Finally we found out, that the problem is not really created by the noise of the audio, but the position of the Actuator potentiometer to change the audio noise in the main flying screen during flight.
After many tests, phone calls, and endless e-mails we (Dickie?) had an idea:
This unreal „noise“ has to come from the power supply voltage for the audio. The supply comes off the 5 Volt rail on the starboard. The same 5V supply drives the microphone.
Dickie Feakes eventually had the idea and did a test by using the 3,3 Volt rails to supply the mikrophone. This way enl and audio power is not coupled any more. – The success was our Christmas present!
I made tests with my enl bench setup, and a test flight with 3 systems on board: Two 302’s, and one 302A. Result: Brilliant readings, the noise reaction somewhat faster as in the GPS-NAV, but not nervous any more.
Now it is also clear:  The „Flight Recorder only“ boxes never had an audio parallel !!

Source of the problem: A turned up poti to change the audio noise with the actuator of the 302 creates spikes in the 5Volt rail, coming back with the audio cable, are fed into the flight trace. This way the enl level is recorded as a nervous, unrealistic enl curve of the flight log on many 302’s.

Therefore: All 302’s showing this problem have to be sent in for service.