ukengineman

I recently heard that Doug Spreng passed away on 19 April 2010. Doug was a true pioneer of digital proportional and along with Don Mathes developed the first commercial digital system called Digicon in the early 1960's. The key to the digital systems was the concept of controlling the servo position by varying the width of a pulse. This method, still in use today, was invented by Doug and even the variation in pulse length from 1ms to 2ms remains the standard. He did not patent the idea so made no money from it, the idea was copied by every other R/C manufacturer and this led to the rapid developement of these systems. Later in the 1960's he came over to the UK and developed digital R/C systems here, namely Sprengbrook and Stavely.

It should also be remembered that he was a top international R/C aerobatic pilot and designed some of the best models of that period. The Stormer, Thunderstormer and Twister come to mind. He was a real character and I remember meeting him shortly after he came to the UK, when someone asked him about the demise of an earlier model he replied "I tried a vertical nine", typical of his humour.

More information about Doug can be found on the AMA web site here:-

https://www.modelaircraft.org/files/SprengDoug.pdf

Alan in the UK

RFJ

What a shame. I'm very sorry to learn of Doug's death. He was certainly a hero of mine and I admired all his published models. I think his design philosophy was to look at current fashions and do the opposite. His writings were most entertaining to read and usually had very little to do with the subject

I had e-mail contact with him some years ago about his Thunderstormer design and he was most patient and helpful in answering all my silly questions. I asked him why he left the hobby and he he told me it was to concentrate on ballroom dancing - no, I didn't believe him either [X(]

There are many, mostly unrepeatable, stories about his time in the UK and I think Alan's description of him as a real character just about sums it up.

Ray

pchristy

Very sad to hear this. I've still got my Sprengbrook "red box" radio - probably one of the most reliable of the era.

The pulse tracking servo amp was pure genius - so simple that it took and extra-ordinary mind to conceive it! The fact that we are still using his original parameters nearly 50 years later is a huge tribute to the man.

Fly with the Angels, Doug!


Pete

NM2K

My Feedback: (14)

I am very sad to learn of Mr. Spreng's passing. There goes another great that I have read about many, many times, but will never get to meet. My condolences to his family. Doug will be missed.


Ed Cregger

ukengineman

As I mentioned above, when Doug was in the UK he designed a digital R/C system for Staveley Industries to replace their analogue system. I have been in touch with Cliff Nancarrow who was a director of Staveley at the time Doug was there. Cliff has given me these memories to post here:-

"Thanks for the news. I remember Doug very well from my Staveley Industries days when he came in to design a replacement for the analogue system, but also to show the Engineering Development Division that development did not have to take years. Doug was quite light hearted and livened the place up quite a bit.

He flew for Staveley and also Sailplanes/Powerplanes International in the early days. He was a great character and had a great sense of humour, even after a "few" drinks. I remember at one of the shows, Doug was flying for Staveley, when his model suddenly started some wild gyrations. Some of us near him shouted a warning and the model was brought under control again. Doug exclaimed "Jeeze, I was flying the wrong model".

Quite a character and a nice guy who contributed a lot to the development of model flying!!"

Thanks to Cliff for those additional memories, Alan in the UK

TFF

His Kraft Signature Series design was always one of the tops of radios, and still one of my favorites. He literally designed modern RC and gave it to RCers.

heggen

There are so many "old timers" who haave passed on that I would have liked to meet, Doug ranking high among them. I loved reading the construction articles he wrote and the unique models he built and flew. Oh, how I miss the construction articles in the current models mags.
My favorite is the Thunderstormer which is on my list of models to build. Has anyone out there built the one and if so where was the CG. It does not show on the plans and the wing does not have a typical airfoil with the maximum thickness way back on the chord. I am thinking the CG may be further back as well. Anyone?
It would be fun to keep his efforts in modeling alive with the building and flying of his designs.

pimmnz

In his own inimitable style, Doug says that the 'whole mess balances about 50% chord'. Just forward of the mainwheels, then, in proper fashion. I too have the plan, a NIB K&B series 73 .61, with vented muffler, the RCM plans and a bit of time. The instructions are in Septembers' RC Modeller magazine, 1966. I would prefer to start about 33% chord for the first flights, and slowly move the balance back as you trim. It has a long moment and a big stabiliser, so the more rearward balance should not be too much of a problem, but you know what they say about tail heavy models...
Evan, WB #12.

RFJ

My favourite Spreng design would be the Twister- a sort of miniature taper wing Thunderstormer. Was very popular in these parts for it's ability to fly in strong winds. Strangely, another good design for windy weather was Phil Kraft's Bar Fli.

Doug told me that the Thunderstormer shown in the RCM article was the second version (hence the large number 2 on the fin) On the first one he tried an all moving tail which fluttered off in the air []

Ray

ukengineman

When Doug first came to the UK he was flying a Thunderstormer. I was impressed and built the airframe but it got put to one side for a while. Eventually a friend finished it off and we both flew it. The wing section is a sort of laminar flow section and is very slippery, you need to use the throttle a fair bit through the flight. Also when landing it just goes on and on like a glider. Overall a nice model with no nasty tendancies. In the end the fuel soaked airframe fell apart and it was scrapped. I've got a photo somewhere, I will post it if I can find it. I can't remember where the CG was but it was not as far back as 50%, maybe was about 40%
Alan

jaymen

He did not patent the idea because this type of pulse width modulation, or what is sometimes called pulse position modulation was already well know and being used for control and guidance of missles, drones, and spacecraft. Do not forget that Doug met Jerry Pullen who had an analog proportional, and found Jerry had acess to then hard to obtain NPN transistors, as Jerry worked at Jet Propulsion Labs in Pasadena. Thus Spreng applied for and got a job there to gain acess to new technology solid state devices and remote control technology, which JPL was developing and using at the time. Once there, he was able to "borrow" the designs of more complex guidance systems and adapt them to the hobby of flying model planes in a miniature and simplified form.

Thus, although Mathis, Spreng, Pullen, and many others are often cited as inventors, they were actually adapters who took existing technology and applied for their own use in a different field. Additionally, they would have run afoulf of the law had they tried to patent technology developed for and by the US government, and most of it was highly classified as secret back then, so one can understand why they could not try and sell it, as it was not theirs to sell!

This does not diminish their contributions to the R/C hobby, but we must appreciate what they did in proper perspective: They introduced us to a new technology that had previously been only used for top secret and space exploration projects, and made it practical for commercial production of low cost hobby R/C guidance systems.

ukengineman

PWM was a well established technology in military and professional data comms at that time. Where Doug must be given credit is to realise that by making a simple circuit that enabled a model servo to track the width of a pulse he was able to apply this system at relatively low cost to R/C. As with all innovations it is always about being in the right place at the right time and then having that lateral thinking moment that others failed to have.
Alan