Quote:
Originally Posted by IvanK
In the tests I have done (And just done in 4.09RC2) the very first signs of compressibility on the P38L Late at 10,000feet are occurring at 410mph (IAS) or Mach 0.65. By the first signs I mean an ever so slight tendency for the nose to drop from the trim state. As the dive increases the first signs of buffet are detected at Mach 0.72-0.74. As Mach increases both buffet and rate of nose drop increase.
that is not that far different from the POH values and the description given in Americas 100,000 Page 158 in the Dive and recovery paragraph.
What symptons and IAS/ALT values are you seeing Capt Stubbing that indicate it is happening at lower values ?
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Fair Question...
Did some flying and a little bit of testing with the J model last night. It could be the designers wanted to have the elevators be "stiff" much like the 109s at high speed and then have the compression problem start prior to the actual airspeed by a few MPH.
The onset of the problem starts at around 300MPH IAS and she becomes excessively stiff from then on. She does start to tuck under around the 410 MPH IAS mark. This plane suffers much more than any other plane in the series except the 109. Not sure why that is. Spits 51s Tempest 47s FWs LAs Yaks don't have this same problem at similar airspeeds. Was it modeled to show the bird was heavier or larger or some other quality? A 3 and half ton 47 doesn't have the problem with cement elevators why does the 38 have the issue? My guess is that this was meant to show compressibility was the problem. There certainly isn't a lack of surface area on that tail so that can't be it. That was the excuse given for the 109s cement problem.
Here are some bits and pieces taken from Wiki which mirror some of the texts I have. I think it's important to note the differences from what we have in the game.
"After months of pushing NACA to provide Mach 0.75 wind tunnel speeds (and finally succeeding), the compressibility problem was revealed to be the center of lift moving back toward the tail when in high-speed airflow. The compressibility problem was solved by changing the geometry of the wing's underside when diving so as to keep lift within bounds of the top of the wing. In February 1943, quick-acting dive flaps were tried and proven by Lockheed test pilots. The dive flaps were installed outboard of the engine nacelles and in action they extended downward 35° in 1½ seconds. The flaps did not act as a speed brake, they affected the center of pressure distribution so that the wing would not lose its lift."
The flaps we have in the game are nothing more than a Speed Brake which slows the plane down and causes some sort of lifting action.
Here is another dive Chart showing slightly different speeds in which it occurs.
Another interesting note...
The final 210 J models, designated P-38J-25-LO, alleviated the compressibility problem through the addition of a set of electrically-actuated dive recovery flaps just outboard of the engines on the bottom centerline of the wings. With these improvements, a USAAF pilot reported a dive speed of almost 600 mph (970 km/h), although the indicated air speed was later corrected for compressibility error, and the actual dive speed was lower.[66]
The P-38J-25-LO production block also introduced hydraulically-boosted ailerons, one of the first times such a system was fitted to a fighter. This significantly improved the Lightning's rate of roll and reduced control forces for the pilot. With a truly satisfactory Lightning in place, Lockheed ramped up production, working with subcontractors across the country to produce hundreds of Lightnings each month.