Author Topic: B-17 performance (Read 552 times)

Raubvogel · « **on:** November 14, 2001, 03:55:00 PM »

Was just checking out the TAS charts on the new help pages (btw nice work HTC). Noticed that the B17s TAS is a gradual continuous increase to a top speed of about 300mph at 30k. Is that accurate? Does it keep increasing to its ceiling?

Raubvogel · « **Reply #1 on:** November 15, 2001, 10:44:00 AM »

No one has good performance figures on the B17?

funkedup · « **Reply #2 on:** November 15, 2001, 01:34:00 PM »

Look at the climb chart. Service ceiling is altitude where climb rate is 100 fpm. The charts don't go that high.

Turbos on the B-17 engines enabled it to have constant power from sea level up to 33,000 feet. Speed increasing with altitude is normal if power is constant. P-47 and P-38 (turbos on both) have similar curves. I expect B-17 would do the same, losing speed as you get real close to the ceiling.

[ 11-15-2001: Message edited by: funkedup ]

Raubvogel · « **Reply #3 on:** November 15, 2001, 01:58:00 PM »

Right, I understand that. Just wondering if those Sputniks at 34k are up there doing 350mph. That would explain how they can outmaneuver anything I fly.

funkedup · « **Reply #4 on:** November 15, 2001, 02:10:00 PM »

I checked one source and it says 300 mph at 30,000 feet with WEP. So the curve probably goes left above 30k.

Maneuverability I think comes from MA fuel loads. A lot of guys fly a whole mission on what would have been reserve fuel in WWII. And check those climb charts. Even with a full load the climb rate (a good measure of excess power) is not far off many fighters above 30k. Take away the bombs and most of the fuel, and this plane has better wing loading and power loading than many fighters when you get to Sputnik altitudes. Remember that high altitude flight favors low wing loading.

EDIT Just did the calcs. Wingloading with 25% fuel and no bombs is 22.2 lb/ft^2. That's better than a Zeke with 100% fuel. Powerloading in the same condition at 26,700 feet is 5.70 lb/hp. I don't have exact figures handy but a lot of fighters are up near 7 to 8 lb/hp at that altitude.

[ 11-15-2001: Message edited by: funkedup ]

Raubvogel · « **Reply #5 on:** November 15, 2001, 02:14:00 PM »

You brought up an interesting point. In fighters there is a definitive difference with WEP. Is WEP modeled in bombers as full throttle? Or is WEP just not modeled? I'm totally guessing, but I would imagine that WEP on a B17 was just pushing the throttles past a gate to increase boost and it could only be maintained for a short period.

funkedup · « **Reply #6 on:** November 15, 2001, 02:21:00 PM »

I think AH B-17G is probably running WEP full time if you have the throttle maxed. However I don't know the manifold pressure / RPM for the WEP on this plane, only that it was 1380 hp at 26,700 feet. So the only "check" I can make is the WEP speed which seems to match AH speed charts.

BTW I don't have any good books on the Fort. Using this link here: http://home.att.net/~jbaugher2/b17_16.html