Readme for Bristol 170

T Goodrick

This was one of the tougher challenges in developing flight dynamics files that fit the aircraft. I am still not satisfied with the engine performance but it seems manageable if you use the Power Gauge. It seems to enable the proper performance including takeoff, climb cruise and landing with cargo loads from zero to 12,000 lbs. I also put a CARGO door button on the panel which makes it easy to open the front cargo doors when parked.

Among the obstacles presented were a thrust factor of 8, a backward interpretation of the x-dimension in loading and the inability to level off in cruise for the original air file. I replaced the original air file with the air file from the DC3. That helped control the the attitude in cruise and a few other things. See the included photo showing how level it flies in cruise.

This is being rushed a little bit because I suspect some will want to fly this in the GAAR. It should be a good airplane for that. If you do enter it, you'll do best to fly the test at about 50% power. You might also want to limit the cargo to about 6,000 lbs although that is a guess. I have flown it at zero cargo and at 12,000 lbs. But I have not flown a complete flight with the present complete configuration. All indications are it will work fine. (Power was added during the last climb to improve the rate with  full load. Before doing that I had to step climb to 5,000 ft!)

I do not understand the power problem. I was flying with a blade gauge that showed the angle of the propellers, They seldom moved off of 5 degrees. The propcontrol has no effect. The mixture control has no effect because, with a small amount of boost added as a simulation of the radial engine effect, I set the mixture control on auto. With this setting and the increased power, it should climb well to at least 8,000 ft. It should have no problem taking off from runways as high as Denver. There would be serious problems without the turbcharge effect.

You will see no sensible indication from the RPM gauges. I don't know why but I have seen this before on several aircraft with large radials. There is generally a separate function and lack of control of RPM versus throttle with any piston aircraft (for example, the Baron) when operating at very low speed as when taxiing. You start with the rpop lever at full rpm but the engine is idling so the rpm is at 1000 or less. Then as you taxi, the rpm goes up and down even though the prop lever stays at high rpm. Normally, though, when your forward airspeed builds up, the props do go to full rpm in the normal airplane like the Baron. They don't on this airplane.
They should do whatever the DC-3 does. The air file is the same and the aircraft.cfg file does not show any abnormality in this regard.

By watching the power gauge when setting the throttle, I was able to get performance that seemed reasonable. Full throttle gives about 80% for takeoff and climb. Cruise works fine at 70 to 75%. Slow level flight works fine at 50%. I would assume you can set first flaps at 100 KIAS and that gives good drag for descent. Full flaps will slow it down for landing. I made two landings - at light weight - at 73 KIAS and -110 fpm. 
