Primarily for general aviation discussion, but other aviation topics are also welcome.
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By BobDale
#1871047
Hi, I have a question regading weight and balance.

The T67M weight and balance chart has the usual envelope based on weight and CofG. The chart has vertical lines (sloping to the left) which are scaled 18% up 29% My question is regarding these percentages. Percentage of what?


Many thanks, Bob

Image
By PA28
#1871127
Most aeroplanes have their permissible CofG ranges between 20percent to 30percent Mean Aerodynamic Chord or in other words approx 1/4 chord back from the Leading Edge on a non tapered wing. It is imperative that the CofG is forward of the Centre of Pressure.
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By T67M
FLYER Club Member  FLYER Club Member
#1871165
As alluded to above, the numbers at the top of the graph are %MAC, while the numbers at the bottom give distance aft of the datum in millimetres. The slanted lines between them link direct equivalents.

For some reason, Slingsby decided to slant the lines so that changing the weight of a pilot/passenger would result in a vertical shift - fuel and baggage are varying angles of slanted lines. In my own Excel version, I decided that constant CofG position would be vertical, which seems more sensible to me and is the approach used by many other aircraft manufacturers. The results are identical, just (IMO) easier to understand.
#1871280
PA28 wrote:Most flight manuals give a forward and aft limit for the CofG range as distance (or arm) back from the datum point. This is usually inches aft of datum (AOD).
Yes, my copy of the T67M AFM states the CG limits as mm aft of the datum, as does the Type Certificate Data Sheet.

No mention of %MAC so disappointing that the AFM doesn't state what those numbers are.

However the AFM has that "Centre of Gravity Overlay" shown here. The interesting bit is the "Centre of Gravity Computer" on the next page where it is obvious why the lines are sloped as they are: the effect of crew weight is a true vertical line.
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By Dave W
FLYER Club Member  FLYER Club Member
#1871338
No, the sorry story of the T-3A did not have anything to do with calculating the CG position.

There were peripheral CG issues (due to the chosen engine, and knock-on effects on the fuel system, but I'd say not relevant to this.
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By T67M
FLYER Club Member  FLYER Club Member
#1871340
I think it is fair to say that like most accidents in aviation, the events occurring whilst the USAF operated the T3A (their name for the T67M260) had many factors, not a singular cause. Like any aircraft operated close to the edges of the aerodynamic envelope, there is more sensitivity to weight, balance, power management and pilot technique than one operated in the middle of the flight envelope. Suffice to say that I have been part of a syndicate operating a T67M Mk-II for 15 years, aerobating regularly and the aircraft also displays at airshows (although sadly my skygod skills are well below the standard required for me to be the pilot on these occasions) and I have never yet had the aeroplane take me anywhere I wasn't ready to go to, although I will admit to a couple (literally two) occasions where prompt action was required to remain within the envelope.
#1871385
It was a long time ago but, I seem to remember that the Americans were experiencing difficulty with spin recovery. I believe that the T67s were used in the role of primary trainer and there were a sufficient number of accidents that took one past the point of co-incidence and led ultimately to the withdrawal of the aircraft from operation.

I have myself a few hours on this machine and cannot recall a single instance of any discomfort. That said, a close friend - an instructor - was killed while teaching - it was believed - spin recovery to a student.
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By Human Factor
FLYER Club Member  FLYER Club Member
#1871390
Depending which flavour of T67 you fly, there are slight differences in the spin recovery technique. I fly the M MkII, M200 and M260 regularly and have found them all to be predictable in terms of recovery, provided the appropriate POH technique is used.
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By djpacro
#1871461
Loco parentis wrote:It was a long time ago but, I seem to remember that the Americans were experiencing difficulty with spin recovery. I believe that the T67s were used in the role of primary trainer and there were a sufficient number of accidents that took one past the point of co-incidence and led ultimately to the withdrawal of the aircraft from operation.

Yes, spinning as well as a separate issue with engine stoppages.

"A major factor driving the decision were three T-3 Class A mishaps in 1995, 1996 and 1997 that resulted in the deaths of three instructor pilots and three student pilots. The accidents were investigated, and the causes were attributed to spin recovery procedures and engine malfunctions."

https://www.af.mil/News/Article-Display ... sposition/

In 1995-97 I was working at the Pitts factory and an officer from the USAF contacted me as the identical engine was used in the Pitts S-2B. We weren't far from Colorado Springs and there were S-2Bs operating happily in the Denver area. I suggested they bring one to us to have a look and compare the engine installation with the Pitts. It didn't happen as they awarded a $10M contract to another company to find and fix the problem.
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By flyguy
#1871510
Wow. I think there is more rubbish written about the T3A (US T67M260 with aircon) than just about any other aeroplane.

The article earlier suggests that the larger engine put the CofG too far forward. Previous articles have suggested that addition of aircon put it too far aft. Perhaps it's both...

John Farley test flew the T3 and writes about it in 'A View from the Hover' (pp179-205). He described spin recovery at Colorado Springs pressure altitudes as 'classic textbook stuff'. He also tried the 'standard' fast jet recovery technique of letting go of the stick and said 'No joy'.

I understand that the USAF decided that teaching the T-37 Tweet recovery technique (the next aircraft in the training programme) was a good idea. As many with any modicum of aerobatic and UPRT experience will tell you, make sure you know the recovery technique for the specific aeroplane you are flying.

Am I biased? Hell yeah! I fly around 500 hours a year in T67M260s, and probably double that number of incipient and fully developed spins, and I want to make damn sure that they recover exactly as advertised, with the correct control inputs, every time.

And they do.
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