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Post by mrcapitalism on Apr 29, 2020 18:46:49 GMT -5
Finally managed to take Jens B. Kristensen's nice Douglas C-124 for a real flight. Flew from Groom Lake AFB (Area 51) back to McCarran Las Vegas. Even with a light fuel load she lumbers up to 14,000ft to clear Mt. Charleston! I noticed the following remarks from the operating notes  Is there something special about the design of the C-124's cowls (or operating choices by the USAF) that allows the R-4360 to produce TOGA from brakes released to 130KIAS with the flaps closed, and not melt the engines? Is this a FDE issue? I tried using 30% instead and had a very anemic takeoff and climb... but I suspect that's normal for this big lumbering bird. Thanks for the discussion! |
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Post by Tom/CalClassic on Apr 29, 2020 22:03:36 GMT -5
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Post by Dan on Apr 30, 2020 1:59:54 GMT -5
Hi,
Sad, but I have not any C-124 Flight Manual, so will refer to the "Flight Handbook KB-50 Aircraft (1958)" (T.O. 1B-50(K)-1)
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Section II
page 2-27
Before Take-off
Engineer
15. Cowl flap switches - CLOSE untill 15 degress cowl flap setting if reached.
18. Report to pilot - "Check list complete, request cowl flap check ready for take-off."
page 2-28
Engineer
1. Cowl flap switches - As required.
Six to eight degress flap setting for OAT up to 20C (68F), for OAT above 20C, start take-off with flaps at 15 degrees and gradually reduce to eight degrees at approximately 75 knots.
page 2-29
After Take-off
Engineer
4. Cowl flap switches - As required.
Do not open cowl flaps in excess of 15 degrees in flight.
Section VII
page 7-16
Cowl Flap Operation
Take-off
Cylinder head temperature at start of take-off 160C to 170C. For OAT up to 20C use 6 to 8 degrees cowl flap opening, for OAT above 20C, start take-off run with cowl flaps at 15 degrees, reducing to 8 degrees at approximately 75 knots. Do not exceed 12 degrees cowl flap opening at take-off point.
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Of course, despite the same 4360s, C-124 may had some own particularities in the cowl flaps take-off settings.
Also this reminds me what I was read in the "Bringing the Thunder. The Missions of a World War II B-29 Pilot in the Pacific (2006)" by Gordon Bennett Robertson, Jr. (although B-29 had 3350s of course):
"... One might think that increasing the ram air over the engine by opening the cowl flaps more would help. But that was a self-defeating procedure. As cowl flaps were deployed, there was more drag created, which had a decaying effect on airspeed, which in turn required more throttle, which then created more heat. It was a "damned if you do, damned if you don't" situation. In the spring of 1944, a crew started a takeoff run with the cowl flaps full open in an attempt to keep the engines cool. This was in a light airplane-bomb bays empty and probably less than a full fuel load. Witnesses became alerted to a troubled aircraft. It used nearly all of a 1.5-mile runway and then staggered into the air wallowing like a sick whale; unable to gain more than 50 feet in altitude, it slid to one side to let a barn go by. Those listening and watching expected to see the dreaded black cloud of smoke, but in a few minutes, it came back over the field flying normally. The lesson? A B-29 cannot take off' with full open cowl flaps... "
"... We accomplished the preflight, and after the engine run-up, the tower cleared me for takeoff. I responded with "Roger, tower, rolling," as I turned on to the runway and advanced the throttles to full power. Bud started calling out the airspeed as he always did through acceleration and rotation: 90, 110, 130, but we were not about to fly. I knew immediately and instinctively what the problem was and veiled, "Flaps!" Bud calmly and nonchalantly turned around in his seat and said to the flight engineer, "Hey, Pic, close your cowl flaps." I yelled, "Wing flaps, goddammit!" Bud uttered it surprised "oh" as he hit the wing flap switch. By then we were going 150 mph or so, and the airplane literally jumped into the air as the fence and a cornfield at the end of the runway streaked by under the wings. Bud was so chagrined about his mistake that he could hardly sleep after that, but it was really my fault-I had inadvertently failed to match the command with the action when the word "flaps" came up on the checklist. Or maybe Bud failed to read it-I'm not sure... "
Regards,
Dan
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Post by mrcapitalism on Apr 30, 2020 13:34:10 GMT -5
It was 30C at about 2,000ft. I'll try 10% next time and see how it likes that. The remark about 15-12 degrees max for start of takeoff, and 15 degrees max in flight coincides with my experience with other propliners, in that the taekoff setting usually coincides with the maximum open setting for flight (not full open, as stated that can be fatal). I had not considered the effect of closing them as the aircraft accelerates, but that seems to relate to having an actual human FE that can perform that duty.
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Post by Erik on May 1, 2020 4:38:45 GMT -5
It seems clear at least that take-off with cowls nearly closed is very realistic. It could be the choice was made to have them fully closed for t/o in the FDE, in order to achieve the best overall performance within FS9 constraints. Just my $ 0.02.
Erik
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Post by Defender on May 1, 2020 5:20:14 GMT -5
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Post by Erik on May 1, 2020 5:56:24 GMT -5
The 5th photo there clearly shows how the cowl flaps were impressive spoilers just ahead of the wing...
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Post by Herman on May 1, 2020 7:19:12 GMT -5
Interesting account of cowl flap use and operation/miss operation. I have always used fully open on TO's because I felt maximum cooling was required for full power take offs. Will now have to use the recommended procedure. Interesting.
Herman
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Post by mrcapitalism on May 1, 2020 18:35:20 GMT -5
I have always used fully open on TO's because I felt maximum cooling was required for full power take offs. Do you suffer severely degraded takeoff performance? I was under the impression that all of the CC propliners modeled cowl flaps drag. |
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Post by Tom/CalClassic on May 1, 2020 19:05:11 GMT -5
We do, but only realistically in the flying range. I doubt that we increase the drag enough when full open; that was never discussed.
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Post by mrcapitalism on May 1, 2020 21:46:33 GMT -5
A couple more takeoff tests (and I just brushed some trees while trying to accelerate  ). Looks like no performance difference with the JBK C-124A with the cowl flaps either closed or at 30% open. Also my statement of the field elevation was incorrect. Groom Lake is actually at about 4,500ft MSL, and with this evening's 25C that's about 6,600ft Density Altitude! |
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Post by Herman on May 2, 2020 7:07:28 GMT -5
My most recent flights using the B377 did not show any problems for take offs, as these were mostly at or near SL and standard temperatures. As Tom mentioned, there was some performance improvement during the climb to cruise altitude when reducing the cowl flap settings incrementally.
Herman
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). Looks like no performance difference with the JBK C-124A with the cowl flaps either closed or at 30% open. Also my statement of the field elevation was incorrect. Groom Lake is actually at about 4,500ft MSL, and with this evening's 25C that's about 6,600ft Density Altitude!