It was a windy September morning when we arrived at Stadtlohn-Vreden airport. And with crosswinds gusting across the runway at 21 to 29 knots it was going to remain very, very quiet day in terms
of traffic. Needless to say, these conditions would also test our wind jamming equipment to their limits.
As we headed out to the hangar we met up with the good folks of Segelfluggruppe Wenningfeld that were helping us out. It turned out the DR400 in question was the DR400/180R variant and was used
as a glider tug. After dragging OE-DSE out of the hangar and into the daylight it was time for some pictures.
Once settled inside the cockpit we started by familiarizing ourselves with the aircraft, no two aircrafts are the same... especially true for aircraft that have been flying for a long time. The very first thing that grabbed our attention was the amazing visibility. And since the aircraft was also equipped with 3rd row windows, that visibility is also apparent when looking towards the rear of the aircraft. Furthermore, the cabin in general had plenty of space.
The aircraft in question was built in the 1970s and was very basic in terms of equipment and avionics. But then again, why bother with the fancy stuff if the aircraft's main role is being a glider tug. Apart from the ubiquitous stall buzzer, there was no electrical equipment noise to record. Still, there were plenty of switches and dials :)
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Fun fact, after switching on the master battery we were waiting for the typical screeching noise of running gyros. Little did we know, the gyros on the DR400 were vacuum powered. Hence
they are only audible when the engine is running. One of the few GA aircraft we've sat in where you can just carry on your conversation (or record sounds) in peace while the electrical system
is powered on.
Next it was time to record the interior engine noise. With the magnetos on and a push of the starter button the 4 cylinder Lycoming O-360 shook the airframe as it roared to life. The engine noise being reminiscent of your typical Cessna 172 but still unique because of the large interior space and differences in exhaust arrangement. Idle RPM was 800 with the top end between 2500 and 2700. Above 1500 RPM the engine (and prop) gets very noisy and above 2000 RPM the whole aircraft started shaking violently as it wanted to GO.
After a short and unexpected taxi run around the hangar area, we shut down the engine and started to make preparations for recording the exterior engine sound. Although the weather cleared up, the winds were still strong, so it was decided to position the aircraft close to it's hangar to eliminate as much wind noise as possible. This allowed us to put at least one microphone inside the hangar. In total 3 microphones were set up around the aircraft to capture the noise from multiple angles.
With the "outdoor recording studio" fully configured it was time for the star of the show. Since the engine was still warm, the O-360 started right up. Since the aircraft was equipped with exhaust mufflers, the engine was not nearly as loud as we expected. However, this meant the sounds of the fixed pitch 2 bladed propeller could be recorded in great detail.
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As this was the first time recording with a microphone placed behind the aircraft we quickly learned that everything even remotely near the path of the propeller wash is subject to being blasted by debris even if the ramp area appears clean. Our empty equipment bags were caught up as well and by the end of it, it looked like we went out to the beach instead of to our local airport.
In recording the exterior engine noise, the strong winds at the airport actually proved an added bonus. With the engine and propeller running at a steady low RPM setting, the winds were
significantly affecting the propeller noise. This makes for very dynamic and natural sounding recordings (as if the aircraft was moving). Our Sennheiser ME66 microphone tasked with recording
these effects was also heavily subjected to winds itself, but still performed flawlessly thanks to the RØDE wind jammer protecting it.
Once the engine run was completed we quickly packed up our gear and OE-DSE was moved into the hangar for a well-deserved rest.
Not 1 hour after completing our recordings the airport was caught in torrential downpour...
Und zur alle leute die mit uns daran gearbeitet haben; Vielen Dank für ihre hilfe, das hat alles wunderbar geklappt!
sources and links
- Flugplatz Stadtlohn-Vreden homepage (German language)
- Segelfluggruppe Wenningfeld's online club house (German language)
All photos in this article are by SimAcoustics unless stated otherwise.