SaparotRob
Unter Gemeine Geschwader Murmeltier XIII
I'm trying to rebuild an RR Merlin XX in my garage. Tesco doesn't seem to have any parts in stock.
Picture of the day. (30 Viewers)
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That's the thing about Pilot Induced Oscillations (PIOs).The Dutch roll tendency was slight at worst, and was thought by the Army's Flight Research Section to likely be a "hunting" effect due to the engines being slightly out of synchronization with each other, rather than anything to do with the aerodynamics of the airframe. If testing had gone on a little longer, that would have been explored further.
"Bucking" at low speeds is a bit of an exaggeration (probably resulting from comments made by one of the 3 Army pilots who flew the airplane, Col W. F. Cooper, for a magazine article 30 YEARS after his only flight which lasted just 35 MINUTES) because what the 3 Army pilots who flew the plane in May 1944 said in their report was this: "...light buffeting starts around 140 MPH indicated and increases down to the stall. The stall itself is not violent; however, it is apparent that the wing is not completely stalled and that the tail is stalling out. The ailerons are effective at the stall and no tendency to spin was noted." This sounds like normal behavior for most aircraft, and certainly preferable to those that suddenly stall without warning.
Almost all of XP-67's flight time was done by MAC pilot Ed Elliott. His notes on the handling during the very first flight are interesting in this context: "...at the highest angle of attack on the landing approach, longitudinal oscillation was induced by slight pressure on the stick in an effort to stabilize the airplane in the desired angle of attack. The oscillation…was induced by the pilot and was of a very low frequency and amplitude and was not considered hazardous" except in extreme aft positions of center of gravity. And "throughout this condition... NO SIGNS OF BUFFETING [emphasis added] or directional instability were apparent."
My wife and I talked to the son of the MAC pilot who flew almost all of the XP-67's flights, and his exact words were "Dad always said he loved that airplane." I think Cooper's comments long after the fact have muddied the water significantly, which is a shame. Granted, the 3 Army pilots' conclusions were that the airplane had problems, but bucking at low speed didn't seem to be one of them.
Sorry to go on at such length about such a minor bit of wording, but XP-67 has absorbed most of my life over the past half-dozen years, and I'd like to share what I've learned when I can.
The pilots who do not have an immediate handle on it blame the aircraft. Your guy " This oscillation...was induced by the pilot" .
An example: The early 310 with the short fuselage and Tuna tanks could get a dutch roll-ey PIO on final in landing configuration. Just move the ailerons and the waggle gets started and the fuel mass at the wing tips exacerbates it. Just the gentlest tap on a rudder stops it, and I had to do it all the time with guys till they figured it out. Wiggle wiggle sweat swearing ,
tiny tap on rudder. Oops. Don't use the wheel thing without the foot-pedal thing please.
Everybody knows to use both for coordinated turns, but the 310 flies nicely above 170 with feet on the floor. pilots get lazy.
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Viking1066
Brigadier General
SAAF 6Sqn White E and M Durban South Africa April 1942 the net
Viking1066
Brigadier General
Fireflies landing on HMS Inplacable the net
Viking1066
Brigadier General
North American P-51D Mustang Iwoto 1945 the net
This "guy" was the pilot himself, speaking in the 3rd person as was common in those days, had decades of experience as a Navy flyer and then years more as a test pilot at Curtiss Wright, flying P-40s and the XP-60, so he had a wealth of experience to draw on. And of course the three Army pilots found the same things in their brief flights during May 1944 and recorded their comments in a report.
That report, and possibly a subsequent flight by the program's severest critic, Col Marshall Roth, led to a meeting between MAC and the Ames Flight Research Section at Moffett Field in late June 1944, where a lot of flying qualities issues were thrashed out. Remember that "flying qualities" as we know them today were poorly understood in the abstract then, and in fact weren't spelled out as specific requirements for new aircraft at that time, as was mentioned for one aspect of the reported issues in the meeting. I've typed out a copy of the meeting summary memo from a poor photocopy, and it makes interesting reading:
Ames Aeronautical Laboratory
Moffett Field, Calif.
Moffett Field, Calif.,
June 30, 1944
MEMORANDUM for the Engineer-in-Charge
Subject: Conference with McDonnell Aircraft Corporation representatives concerning the XP-67 airplane on June 27, 1944.
1. On the afternoon of June 27, 1944, Messrs. R. H. Miller and W. J. Blatz of the McDonnell Aircraft Corporation discussed certain XP-67 airplane handling qualities problems with Messrs. Lawrence A. Clousing and William M. Kauffman of the Flight Research Section. The following is a summary of this discussion.
2. Mr. Miller stated that the experimental model had been flying for a period of about six months, and that as modified at present, the airplane appeared to possess satisfactory flying qualities, except for low rates of roll and a long-period control-free lateral oscillation. The aileron effectiveness (as measured by maximum pb/2V for a given aileron angle) was approximately 50 percent lower than had been predicted, and in addition, large control forces limited the available aileron deflection to small values and high speeds. The ailerons are equipped with boost tabs which originally were rigged to give a large balancing boost-tab ratio. However, the pilots noted that with this rigging it was impossible to trim the airplane laterally, especially at low airspeeds. As soon as the controls were released, the airplane diverged rapidly and objectionably into a spiral. My. Clousing noted that the P-39 airplane also had this characteristic. As it appeared that this tendency had been due chiefly to aileron overbalance, aggravated at low airpeeds, the boost-tab ratio had been reduced (in fact, set to a deboost setting) in an attempt to overcome this difficulty. After this ratio was reduced, it was possible to trim the airplane laterally and there was no spiral divergence. However, the aileron control forces at high speeds are excessive, and the airplane (control-free) oscillates gently with a 30-second period in an S-type path. The bank builds up to 10 or 15° with little or no sideslip being present.
3. Mr. Miller said that plans are being made to install a pre-loaded aileron spring-tab system, and that this should reduce the control forces at high speeds without giving overbalance at low speeds. This system will be arranged so that increase in control forces will result in a change in the aileron-to-tab linkages such that the boost ratio will be increased.
4. It was noted that the lateral oscillation, as described by Mr. Miller, was not covered in the Army requirements, and Mr. Clousing said that the motion described would not appear particularly objectionable to pilots in general, and appeared to be more desirable than the spiral tendency most airplanes possess, since the amplitude does not increase with time and the airplane continues on the average trim flight path indefinitely, and furthermore, since the motion is not apparent in normal flight with hands on the controls. However, Mr. Miler stated that the Army test pilot considered the oscillations undesirable, and that the company would like to correct them if possible. At his request for comments, Messrs. Clousing and Kauffman mentioned several items pertaining to possible causes, tests, and instrumentation. Mr. Miller was not sure if the rudder and/or aileron surfaces themselves oscillated slightly during the motion, since control surface positions were being measured only to within about 0.5°. It was suggested that the airplane motion be noted during runs made with rudder fixed, ailerons free, and also with ailerons fixed, rudder free. Motion pictures of the control surfaces could be made during control-free oscillation test runs and the surface motions (if any) could be studied. From a study of the results of tests of this nature, it might be possible to correct the difficulty by slight changes in the control system rigging, friction characteristics, etc. In this connection, Mr. Miller remarked that the original airplane had exhibited a snaking motion of about a 3-second period, and that this had been cured by the use of trailing-edge strips on the rudder. Messrs. Miller and Blatz agreed with the suggestion that there might be a "hunting" effect between the engines (equipped with Curtiss propeller synchronization) which might cause slight periodic power asymmetries, and said that this would be studied in future tests.
[signed] William F. Kauffman, Aeronautical Engineer
Thought about writing up a series of articles covering phases of the program, and seeing if AAHS would be interested. At the moment we're still gathering info, and in fact just yesterday I stumbled across a comment by someone who said they have 2 photos of XP-67 that are marked Top Secret. That would be a first for us, we've not seen anything with that high-level a security marking. There's more out there in private collections or boxes in attics or somewhere obscure.
For example, there are film clips of the XP-67 on fire after its final flight, but no still photos taken during the fire, even though several photographers with still cameras appear in the film. And there are photos after the fire was put out, but no film clips. Have all the other images been lost to time? Some of the photographers are in uniform, which isn't surprising considering that the Naval Reserve unit was based right beside the MAC buildings. Did their photos make it into the Navy archives? We haven't been able to find them in searches, but that doesn't mean they don't exist.
It's easy to spend years chasing faint leads like this, so in a sense I suppose The Big Book will never really be finished.
I like "Three of a Kind" - that's three 7s on the tail number, isn't it? Can't get much luckier than that!
special ed
1st Lieutenant
- 7,035
- May 13, 2018
I worked with a former USN photographer. He told me that part of his job was to sit in the fire station and was on the first truck out to the crash, taking as many pictures as possible. He told me he got to see the prints when developed but not keep any, "officially". He said they all were sent off with the accident files.Thought about writing up a series of articles covering phases of the program, and seeing if AAHS would be interested. At the moment we're still gathering info, and in fact just yesterday I stumbled across a comment by someone who said they have 2 photos of XP-67 that are marked Top Secret. That would be a first for us, we've not seen anything with that high-level a security marking. There's more out there in private collections or boxes in attics or somewhere obscure.
For example, there are film clips of the XP-67 on fire after its final flight, but no still photos taken during the fire, even though several photographers with still cameras appear in the film. And there are photos after the fire was put out, but no film clips. Have all the other images been lost to time? Some of the photographers are in uniform, which isn't surprising considering that the Naval Reserve unit was based right beside the MAC buildings. Did their photos make it into the Navy archives? We haven't been able to find them in searches, but that doesn't mean they don't exist.
It's easy to spend years chasing faint leads like this, so in a sense I suppose The Big Book will never really be finished.
I think you missed my point. The first pilot had a handle on it, addressed it as such and then, to quote you,
I was addressing that. Cooper was looking back through the dusty lens of time and projecting his faults onto the airframe.
Viking1066
Brigadier General
Three Westland Whirlwinds of 263 Squadron the net
Viking1066
Brigadier General
Short Sunderland (Flying Porcupine) on anti-submarine patrol the net
Viking1066
Brigadier General
VP-94 transfers their PBY-5A's to the Brazilian Navy in this ceremony held at Rio de Janeiro in October 1944 the net
Ah, I actually did misinterpret you. Sorry! The brain isn't what it used to be. One other thing that might not be clear in that extended quote about the meeting at Ames is that the objectionable weaving was under a very special condition. "Control-free oscillation" meant that the pilot had his hands off of the control yoke and just let the airplane do what it was naturally tending to do. Elliott made it clear that it didn't happen when he had his hands on the yoke. The Ritland/Cooper/Borsodi report comments don't say anything about whether it was hands-off or -on, and if it weren't for the Ames meeting memo we wouldn't realize that it only happened that way.
