Fw-190 Dora-9 vs P-51D Mustang

[DerAdlerIstGelandet]

Thats why he is the forum tech guy...

[FLYBOYJ]

[Soren]

FLYBOYJ has got it exactly right.

[Sarge714]

Originally Posted by FLYBOYJ

I think you're confusing inertia coupling with torque roll. Inertial Coupling is a phenomena that occurs at higher mach numbers with aircraft with real heavy fuselages and light wings (F-100, X-1A, X-2 and F-102 all had inertia coupling problems). The 190D didn't come close to the speeds required to induce inertial coupling.

I don't think you understand what Inertia Coupling is. Calc the physics involved and I think you'll be surprised what you see with the Fw190D.

From High Speed Flight

A few of the experimental aircraft encountered a new type of behavior known as inertia coupling, a behavior that was not fully appreciated until the F-100 and F-102 also encountered it. Inertia coupling resulted from the tendency of the new generation of high-speed aircraft to concentrate most of the weight in a long thin fuselage, a departure from the distribution of subsonic fighters. The X-3 configuration is an excellent illustration. Even though its high-speed performance was disappointing, the X-3’s unanticipated susceptibility to loss of control from inertia coupling contributed to understanding the problem. With much less weight in the wing and tail, the dynamic motion in a maneuver could cause the inertia of the fuselage to overpower the aerodynamic stabilizing forces of the wing and tail. In the worst cases the pilot lost control and the resulting abnormal air loads caused airframe structural failure. The early F-100A models are remembered as a classic example of susceptibility to inertia coupling, although the initial F-102A models also encountered the problem.

From Cornell tam.cornell.edu/~tuhin/Aesi.prn

The prediction and analysis of airplane spin characteristics and design of recovery strategies has been of great interest to designers since the beginning of aviation. This problem has assumed more importance in recent years on account of significant losses that have occurred to military and general aviation aircraft because of out of control motions associated with spin. Modern day combat aircraft are required to perform maneuvers at high angles of attack. The aerodynamics at high angles of attack is nonlinear. In addition, there are nonlinearities due to inertia coupling during rapid roll. These nonlinear phenomena can cause stall and then spin departure.

From NASA Report NASA-TP-1538 1979-12

A real-time piloted simulations has been conducted to evaluate the high-angle-of-attack characteristics of a fighter configuration based on wind-tunnel testing of the F-16, with particular emphasis on the effects of various levels of relaxed longitudinal static stability. The aerodynamic data used in the simulation were based on low-speed wind-tunnel tests of subscale models. The simulation was conducted on the Langley differential maneuvering simulator, and the evaluation involved representative low-speed combat maneuvering. Results of the investigation showed that the airplane with the basic control system was resistant to the classical yaw departure; however, it was susceptible to pitch departures induced by inertia coupling during rapid, large-amplitude rolls at low airspeed. The airplane also exhibited a deep-stall trim which could be flown into and from which it was difficult to recover. Control-system modifications were developed which greatly decreased the airplane susceptibility to the inertia-coupling departure and which provided a reliable means for recovering from the deep stall.

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There are more tech reports out there in Inertia Coupling. It's a real interesting area and something that can be applied to WW2 aircraft in predicting their performance.

[FLYBOYJ]

I could assure you I know what Inertial Coupling is, I worked at a flight test facility for 3 years. Links are Interesting, but the point here is the -190D was never a subject of Inertial Coupling and your sources never discuss WW 2 aircraft. The low speeds spoke about in the article are still high mach numbers when compared to WW2 aircraft. The 190D was never reported to experience this is any form, even at altitude, and for that matter any WW2 aircraft. Here is a copy of the USAAF flight test report from Wright Patterson on this aircraft, not even a hint of anything related to Inertial Coupling is remotely mentioned.

http://www.wwiiaircraftperformance.o...d-fw190d-9.pdf

Again, Inertial Coupling came to the forefront during the development of early turbine aircraft where they had large heavy fuselages with large engines coupled with little or light wings...

Here....

Dryden Online Education - Introduction to Flight Testing - Aileron Roll

"Fighter aircraft with high roll rate capability often experience another coupling phenomenon known as "inertial coupling". Inertial coupling may occur if there is a large difference between the roll moment of inertia and the yaw or pitch moments of inertia for the airplane. This is often the case for fighters which have short stubby wings (low roll inertia) and long fuselages with heavy engines, electronics, fuel, etc. (high pitch and yaw inertia). When such an airplane is exposed to high roll rates along the fuselage axis, the high mass concentration along the fuselage may cause it to behave like a "dumbbell". The centrifugal force due to the roll will cause the nose and tail to try to swing out perpendicular to the rotation axis. "

The X-3, one aircraft notorious for Inertial Coupling didn't experience the condition until mach .92

NACA X-3 supersonic research flight

My father in law is a retired test pilot and actually worked at Edwards AFB for a number of years - I'm going to get his take on this...

[FLYBOYJ]

OK - Just got off the phone with my father in law - just for the record he was a production test pilot on the F-15, F-5 and was the chief production test pilot on the B-1B. he also did other flight test work at Edwards...

"Dad" told me that Inertial Coupling usually happens at higher mach numbers on aircraft with wingspans matching or smaller than the fuselage length. Jet aircraft could experience this at lower speeds if an extremely high roll rate was induced at a very high angle of attack - he pointed out the F-16 and Mirage could be made to experience this, with the Mirage being a bit more unforgiving. He did state that in his experience with a recip or propeller driven aircraft, this condition would certainly have to be induced especially at lower speeds and high AoA as engine torque tends to prevent this from happening. With that said, one could INDUCE Inertial Coupling on a recip aircraft at lower speeds (He pointed out that aerobatic performers do this all the time in Pitts).

In the case of uncommanded Inertial Coupling on a recip aircraft, he stated he doubts it would be a factor unless the aircraft is at a high altitude and is configured to do so (small wings, long fuselage).

I brought up the 190D and his feelings is the aircraft would have to be close to a high mach number (high altitude). He did ask "didn't that thing have guns in the wings?" When I told him yes he went on to say that the weight in the wings would probably help in preventing Interial Coupling, even if induced. His feelings were that even though the 190D had a short wingspan when compared to its fuselage, uncommanded Inertial coupling would be unlikely.

BTW - he said he doesn't recall hearing about any recip, propeller driven or WW2 aircraft with any Inertial Coupling tendency, in fact he confirmed, in the test pilot community Inertial coupling is thought of as a "Post WW2" thing. The first theoretical publication addressing Inertial Coupling wasn't published until 1948 (William Phillips of NACA).

[DerAdlerIstGelandet]

You know what I think is funny. Someone who bases there whole knowledge on how an aircraft flies is telling a real pilot (FBJ) that he does not understand Inertial Coupling. Sim Pilots....

[twoeagles]

DerAdler you finally put into text what I, too, have been thinking...

[mkloby]

we've covered this already - sims are just as real as flying real planes. In fact, they are more realistic

[Soundbreaker Welch?]

You can feel the joy of flying without having to worry about bodily harm.

[mkloby]

Originally Posted by Soundbreaker Welch?

You can feel the joy of flying without having to worry about bodily harm.

Who worries about bodily harm? I am more scared when flying commercial than when I am at the controls. That's when I worry about getting hurt.

[DerAdlerIstGelandet]

Oh come on guys... when your flying a Sim you can feel the forces of the wind, you can feel the vibrations, you can feel the control, you are the king and master. Real Pilots suck!!!!!!!!!!!!

[FLYBOYJ]

[DerAdlerIstGelandet]

[mkloby]

Originally Posted by DerAdlerIstGelandet

Oh come on guys... when your flying a Sim you can feel the forces of the wind, you can feel the vibrations, you can feel the control, you are the king and master. Real Pilots suck!!!!!!!!!!!!

Chris - don't forget about the sweet smell of jet exhaust! You know - I can't even land a plane in microsoft flight simulator. I crash the F'ing thing EVERY SINGLE TIME.