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The devil is in the details, my friend. There is nothing cut and dried about pitot-static system design, as it can get damn close to FM (F_ _king Magic). At best they're dart game compromises between accuracy, durability, and complexity. The biggest issue is coming up with a static air reference value that is unaffected by airspeed, angle of attack, sideslip angle, propwash, disturbed air flow, etc, etc. The surfaces of an airframe are a patchwork of constantly varying "static" air pressures as all of these variables change, and without an accurate static pressure your pitot system has no meaningful reference to compare its sampled dynamic pressure to. The charted calibration factors are approximations at best. Even changing the position or location of the pitot tube (for durability's sake, maybe - ever hear the term "hangar rash"?), will cause a different airspeed indication, even if all other conditions remain equal. Matching Chance Vought's pitot mounting installation might have been Grumman's attempt at an apples to apples comparison, not necessarily with fraudulent intent.Claims from Grumman stated that the F6F-3 & F6F-5, despite reading a difference in 10-15 miles an hour, were actually much closer in top speed due to a repositioning of the pitot-static system so it would be closer to the F4U-1. It seems an odd thing to lying about admitting to (as it seems to be confessing to fraud).
I kind of figured that to an extent: That's kind of why I posted it under technical.The devil is in the details, my friend.
It's kind of amazing that they can make the device read accurately with AoA factored in.There is nothing cut and dried about pitot-static system design . . . . The biggest issue is coming up with a static air reference value that is unaffected by airspeed, angle of attack, sideslip angle, propwash, disturbed air flow, etc, etc.
Actually, I'm not sure I have. I have heard of road-rash though, but they're almost certainly different things. Regardless, I don't think either can be fixed with latex...ever hear the term "hangar rash"?
Did they use the same pitot-static systems on both?People can invest a hour or two looking at speed graphs produced by independent entities (is this case - US Navy, testers in the UK) and see that F4U was faster on same horsepower and altitude.
...
Did they use the same pitot-static systems on both?
That's true, but the real issue is the static port(s). They have a way greater effect on accuracy than pitot tubes do, and are so much harder to get right. Getting a reliable and accurate static pressure in the midst of a virtual hurricane of moving air is a real challenge.As for slipstream, I figured that's why most propeller aircraft have the tubes mounted on the wings.
Where are they located on the F6F-3 and F4U-1?That's true, but the real issue is the static port(s).
What I was basically curious about had to do with the fact that...Have to agree with Tomo on this one. I have exhaustively examined test data from many sources and it's glaringly obvious that the F4U had a distinct speed advantage over the F6F at all altitudes and power settings.
Why would the British have any trouble -- the US and UK both used miles per hour or knots at that point in time.And although there may have been some errors induced by pilot inability to accurately read US instruments (concerning the British tests) this probably occurred with both airplane types equally.
Do you have information on the F6F-3 & F6F-5 regarding position/compressibility/both errors? Also, do you have anything on the F4U-1?Grumman relocated the pitot static port from the wing tip and placed it on the starboard side mid-fuselage of the F6F-5 which obviously changed the position error and charts reflect this in pilot manuals.
The F6F's propeller might have been more efficient: I remember reading that they started swapping the F4U's normal 13'4" propeller with the 13'1" or 13'2" propeller used on the F6F. They showed a difference in top speed and climb-rates.Given the larger wing area and fatter fuselage of the Hellcat it would be logical to assume that it would be slower than the Corsair.
This had been discused in British tests concerning the P-47C (see item 14):Why would the British have any trouble -- the US and UK both used miles per hour or knots at that point in time.
Where are they located on the F6F-3 and F4U-1?
Do you have information on the F6F-3 & F6F-5 regarding position/compressibility/both errors? Also, do you have anything on the F4U-1?
The F6F's propeller might have been more efficient:
How did they generally determine the latter item? I assume they either had another plane with properly calibrated instruments, or towed some kind of probe behind them.
This doesn't seem to have to do with units of measurement, so much as the technique of reducing the data. This actually came up on another post, regarding discrepancies in climb performance. I have no idea how they were reducing the data, and I got some discrepancies in the rate of climb.
Right around the same spot where the static port is...The static port is located near the wing tip on the F6F-3.
That's an odd spot to put them, you'd be in the slipstream. At least the pitot tube was located on the wing-tip.I believe that the F4U series had them located on the fuselage but someone here may know for sure.
I'll see if there's any on this site...DarrenW said:Check with pilot manuals for the type in question.
Yeah, I don't have a clue on that either...This is way above my knowledge level.
That's an odd spot to put them, you'd be in the slipstream. At least the pitot tube was located on the wing-tip.
What I was basically curious about had to do with the fact that...
- They calculated based on the plane's IAS
- Then corrected for altitude and temperature
- Then they corrected for position and compressibility errors
Back in the day, Cessna 150s had a single static port, located on the starboard side just forward of the doorpost. One of the things you had to make sure students understood before getting in to slips and crosswind landings was how much that affected IAS. In level cruise flight you could yaw the plane with rudder enough to indicate any speed between Vstall and Vne. Better be sure your student is past the "white knuckle" stage before you try this.Grumman engineers had no previous experience with such an installation, so they put a port on the left side only. But Navy test pilots discovered indicated airspeed would drop to zero in a left sideslip in landing configuration.
(In the book Meyer admits he laid a tremendous egg in the relocation of the static port from its co-location on a boom with the pitot port to the fuselage. Grumman engineers had no previous experience with such an installation, so they put a port on the left side only. But Navy test pilots discovered indicated airspeed would drop to zero in a left sideslip in landing configuration. As senior engineering test pilot, Meyer should have caught that. The fix was to use a static port on both sides of the fuselage.)
IAS F6F-3 F6F-5
100 +12 -5
120 +12 -6.5
140 +13 -7
160 +13 -10
180 +14 -11
200 +14 -13
220 +15 -15
This would have been in the 1970's to 1980's right?Back in the day, Cessna 150s had a single static port, located on the starboard side just forward of the doorpost.
Then how did you know how fast you were going at? I was reading a NATOPS manual on the F-8J and they mentioned that there was a discrepancy in airspeed reading (I think it was 3.5 knots) at high AoA, though in that case, the way one would carry out an approach almost certainly revolved around simply focusing on alpha and glide-path to determine this.One of the things you had to make sure students understood before getting in to slips and crosswind landings was how much that affected IAS. In level cruise flight you could yaw the plane with rudder enough to indicate any speed between Vstall and Vne.