I can still recall my Rocket Scientist brother, as Blaine has always been known to me, recounting how he had to design both this airborne antenna but also the survivability test. This would ensure that it could withstand a bird impacting the plane at 250 kph. I found that story fascinating. Fortunately he has agreed to share that detail with me again. What I found particularly fascinating was that various products of Omnipless ‘shook the world.’
Sadly with transformation and BEE being the drivers of the ANC’s economic policies, factors such customer satisfaction or indeed world-class products have become a distant third or forth consideration rather than having primacy. Dean McCleland
Written by Blaine McCleland:
I came across this article below in fin24.com. I did the mechanical design of that antenna and all the mechanical and environmental qualifications. This was the aircraft HGA (High Gain Antenna) which provides radio telephony (and internet services nowadays) to the geosynchronous Inmarsat satellites.
Main picture: The HGA [High Gain Antenna] 7001 with its proud Production Manager
About this time we were dealing with Boeing on their 777 programme when their 787 boys got interested because we were so much smaller than the CMA antenna. But because they were striving for the ultimate aerodynamic aircraft with their composite design they would only accept the streamlined version. They were also interested in a common interface and our proposed streamlined version became the standard during the industry wide workgroup that they chaired in order to specify a ‘Standardised Antenna’. (Johan Gericke from Omnipless used to attend these meetings and an interesting fact came out about the CMA antenna – it was and had always been technically non-compliant with Inmarsat’s PIM specification but that is quite technical and needs a whole explanation on its own). This version of the HGA-7000 with the integrated streamlining became the HGA-7001 model and was the one that Airbus wanted tested to the hailstone spec.
Airbus were interested but wanted one that looked ‘right’, not all squared off and also to fit exactly where the CMA-2102 fitted with the same mounting points. I proposed a HGA-7000 with additional fairings and an adaptor plate.
Airbus’s requirements were rather stiff as they wanted an incredibly reliable antenna since any fault snagged on the antenna would ground a whole aircraft for the time that it took to get repaired or replaced. They wanted 150 000 hours MTBF (mean time between failure) for the system which included various electronic boxes such as the transmitter and receiver.
The environmental qualifications were exceptionally stringent as, apart from the standard mil spec levels of -56 to +80 deg C, vibration, lightning strike resistance tests, (standard with all aircraft antennas) they also wanted the ability to withstand hailstones. This was the first time that I had come across this specification for any aerospace product. They gave us a range of tests ranging from a 50mm diameter stone at about 250kph to a 10mm dia at about 940kph!
Firstly, we knew of no facility to do this and if we tracked one down in the States, it would be prohibitively expensive and, secondly, the boss always cajoled us and relied on us to conjure up a boer maak ‘n plan solution (which is why he’s a billionaire today). Also, we were not sure if we could make the antenna survive this test as it is not something that one can design for a priori. It’s better to have the test equipment in house so that one can test and then iterate quickly if there is a failure. In other words, we needed to play with it.
After a bit of thinking about it, I devised a solution that cost only about R10,000 and we used it in our underground parking lot. The things that gave me the most pleasure over the years of designing was coming up with simple, cheap and effective solutions to sometimes quite difficult problems. Believe it or not, this only involved a small DIY air compressor, a homegrown off centre butterfly valve and 2m of 75mm PVC drainpipe! The valve was welded directly onto the tank and the pipe attached to that. It worked on the sabot discarding shot anti tank gun principle. The ‘round’ was a polystyrene cylinder with a cup shaped front end that could accommodate the various hailstone sizes. On exiting the ‘barrel’, the polystyrene would essentially stop and the hailstone continue at a speed dependent on its weight and cylinder air pressure. I could go supersonic with the 10mm hailstones. Our biggest problem ended being casting the spherical hailstones without internal fractures.
Our original High Gain Antenna (HGA) was the HGA-7000. This was blunted fore and aft to give us even more physical size advantage over the only real opposition. This was the CMA-2102 (Canadian Marconi). I’ll be writing something about that development but we ended up being about 3x lighter and 2x smaller. The one picture with a lab tech standing on a test version of the HGA-7000 shows how strong it was. (The window had been cut in front to observe condensation inside during certain tests.) This version did not need to be hail tested.
The aircraft industry wanted a more streamlined antenna especially the Boeing 787 guys and also wanted us to be compatible with the rear electrical interface of the CMA-2102. This became the HGA-7001. This is the one that was tested. I’ve included the excerpt from the Airbus hail qualification test requirements.
HGA-7000 for Airbus
- Drag calculated to be 24N from CFD analysis.
- Mass of HGA-7000 is 8.6kg.
- estimated mass of Adaptor Plate is 2kg
- Drag reduction with fore and aft fairings is estimated to be 12N.