It was no small feat for the B-17, either. The best part of that (and I will emphasize that I had *nearly nothing* to do with this project aside from admiring it) was the panicked phone call from Howard, at my desk at work, trying to head off Paul's phone call
Howard calls - "you should hear what Paul wants to do with my engine mounts, he wants to cut them off to isolate the vibrations, isn't that awful!"
BB - "I don't know, that sounds like a pretty good idea to me, I can see that might be a problem"
HR - "No, it's a terrible idea, we made the spar and all 4 engine mounts together in one peice out of carbon fiber"
BB - "Yes, that makes sure that any and all vibration goes to all 4 of them. It was a good notion, but if it doesn't work...:
HR - etc.
5 minutes later, phone rings, it's Paul
PW - "Hey what do you think about cutting off the motor mounts and using fiberglass ones"
BB - "Howard just called me about that, trying to talk me into talking you out of it, but it sounds like a good idea to me"
PW - "I was going to do it anyway, I think the engines are talking to each other through the spar"
BB - "Yes, its 4 engines attached to a tuning fork"
PW - "Howard is really upset with me"
BB - "Yes, I got that..."
...
Awesome.
Brett
When I started the very first engine I immediately knew there was going to be an issue. There was a slight structural resonance with the engine running. I KNEW what the issue was, but found it hard to act on immediately. Howard had spent so much time building those mounts, and was very proud of them ,and I really appreciated his work, which also included the wing spar joint, the featherweight cowls (which has another funny story with them) and the glow power driver to start the plane. So I was not going to cut them off without a lot of consternation. However, I knew what had to be done. I spent the time to consult with a friend at work, a Dr. Lewin, whose specialty was aircraft structural dynamics. After an hour of discussion and a few calculations, it confirmed my worse fear. The carbon mounts had to go. Yes, I mentioned this to Howard, and you can only guess the response! They were his babies, and I knew his attachment to them. But they work perfectly on F2D planes was his response. However, they don't run 4 of them on an F2D plane!
Howard called Brett. Out of courtesy to Howard, I called Brett also. Very shortly after that the Dremel tool with the dangerous disc was fired up, and off came the first carbon mount. In its place went a cheapie RC radial mount, held on by four 4-40 bolts. Howard came down to my house, and we fired up the motor, and it was VERY OBVIOUS to me the problem had been solved. No hint of structural resonance at all. Still he pleaded to not cut the remainder of them off. The next on on that wing panel was cut, removed, and replaced with a radial mount. The two ran perfectly together. Shortly after, all four had been removed and replaced. After that, the motors ran perfectly, with respect to structural resonance, from that point on.
There were always issues with the slightest "junk" in the fuel plugging the regulators, and pressure cutoff switches. The pressure cutoff switches was an unexpected necessity. It turns out when the bladder ran out of fuel, the number one engine (inboard) would stop first as the head of fuel was pushing away from that position. The bladder pressure pushing against that head of fuel was enough to trigger the regulator to function, but when the bladder pressure stopped, the head of fuel in the fuel line was a negative gage pressure on the regulator, so it closed. Number 2 engine was "similar", but there was still a small head of fuel in the fuel line to number 1 engine pressing on the regulator. However, that was small enough to not allow the regulator to function. The problem came in engines 3 and 4. The head of fuel became high enough that the regulators would not shut down and it would run until all the fuel in the lines and been used buy these two, and the head pressure was low enough to shut the regulators down. Howard came up with the idea of making a pressure sensitive switch than when it reached the bladder off head pressure it would close, and stop all fuel flow. When it was working perfectly, it shut down almost instantly when the bladder was out of fuel. HOWEVER, this switch was extremely sensitive to any little bits of junk in the fuel, and the filters put in place were not fine enough to filter the problem crud. At the world champs, I flew seven official flights, and six shut down perfectly. There was one flight though that left the number 4 engine on for what seemed like an eternity. Then there was the Nat's the following year. It malfunctioned more often than not. However, with all this complexity, it made the starting sequence, a breeze, once the exact procedure was learned. At the world champs, on seven official flights, I flipped the props a total of only thirty times.
This required the fancy power panel Howard made. It had four separate circuits, one for each motor. Each had a meter to show the current draw, denoting a possible flooded motor. Each motor has a fuel cutoff switch mounted for easy access during starting. I also has a fuel mist atomizer for starting. The starting sequence with like this: Make sure all cutoff switches are in the off position. Load up the fuel bladder. Spray fuel mist in number one engine. Turn power on to that engine. Flip prop and fire motor. Repeat when it runs out of prime. Spray mist into venturi and check for a bump. Once bump established, turn off power to that motor. Repeat three more times on the other motors. When all checked out, signal for start, and turn on number one power. Flip prop, and when it fires open the cutoff switch. The exact timing of the switch opening is learned as too soon and it will flood the motor, and too late, is well, too late. Once running, turn power off to one, and power up on two. Flip, open cutoff switch, and on and on until they are all running. Once running the start up power panel is removed and it is ready for flight. It's just that simple!!!
With it running, the line tension was significant. It could go from that to next to no line tension when the number 4 engine would run on with a fault in the number 4 pressure switch. Lot's of backing up required. I guess that problem came at the World champs because Billy's P-47 had to turn back and I didn't have proper escort, and that problem was a result!
Then there is the story about how long it takes to get a flight once it comes out of the car. I has to go in the car in many pieces because it is so big. There was assembly time, and engine test run time, and that all added up to at least an hour. On one of the official flights, I was in the middle of that process when a significant rain storm came by. Some one from the US contingent produced a plastic tarp to cover us while we were working on it . All was going fine until I moved and a whole lot of the collected water from that tarp ran down the back of my pants!! Had to keep going as my flight time was coming. finally it was ready. It sat on the ready line, covered by the tarp. The supporters insisted that I get under a small tent to stay dry prior to my flight. I accepted, but never told them I was already quite wet on my backside!! But I stayed dry.
There are still plenty more of those B-17 stories, all seem funny now.....But then?
Topic: 2000 World Championships - Landres, France (Read 2505 times)