Optimum CG • discussion on 'Pilots of America' forum

[RFguy]

Putting aside CG location, recovery is usually about two things. Elevator authority that situation, throttle position. Certain combinations will be unrecoverable.  But I think you know that , and that's not quite the question you are after. Recovery may not be possible if the CG is aft of the COL and  the elevator gets locked into an aerodynamic  situation where it (continues) to have no authority (IE no ability to pitch the aircraft so to  reduce the AoA of the main wing below stall angle) . Take a look at some of the aircraft with specified NORMAL, UTILITY and AEROBATIC category weights and CG limits.  Aero cat takes into account the higher likelihood of getting the aircraft into a more difficult to recover situation/configuration. So, its possible but unlikely to get NORMAL aircraft into difficult (recovery)  situations, but highly likely with AEROBATIC. That and limits of airframe G force limits (weight).

 

Nev (since you flew them)  I was reading about 727s years ago  in one of 'Jobs books where the recovery of the T tail in some attitudes was problematic, and this was new to many.... 

Edited April 23, 2023 by RFguy

[facthunter]

Deep stall It's called. The tail is not in good air when that happens. We were trained for it.   Nev

[RFguy]

26 minutes ago, facthunter said:

Deep stall It's called. The tail is not in good air when that happens. We were trained for it.   Nev

What was recovery ? move all the drinks trolleys to the front of the aircraft ?  

[facthunter]

Mainly AVOID it. It's probably coming down at about 40 degrees AoA. Other high rate of descent situations ON APPROACH with full flaps nearly resulted in it's Cert Of Airworthiness' being cancelled but further investigation showed extra training could cover it and it went on to be pretty popular with a lengthened version. It was a plane you didn't put inexperienced Pilot's on and considered by most Pilots to be a plane that could "bite" if you didn't treat it with respect. The flaps were very   effective at providing lift but with a lot of DRAG as well. A lot of approaches were at quite high engine Power. which meant time had to be allowed for them to cool before shutting them down if you'd used more than 80% power I think is the figure on approach..  Nev

[facthunter]

The general concensus is IF you're tail heavy it will spin easier and be less easy to  recover from. If you are very nose heavy the plane may hard land and be hard to stall at all.  Nev

[Bruce Tuncks]

There is a true story that agrees with your comments nev, but I must admit to not really understanding just what was happening. On my Mosquitp glider, the tailplane was fixed with a bolt at the front, and a slight amount of wear could be felt as a "clunk"  when the tailplane went from lifting to pushing down.

I could make the clunk happen just by flying slow enough, say 45 knots. At this speed, the tailplane transitioned to lifting I think.

In the olden days, wings had a "center of pressure" which moved back as speed increased. This was changed to a moment, since it was embarrassing to have a wing where the center of pressure was behind the trailing edge.

Getting back to the Mosquito, I finished up putting some foam rubber near the bolt and this stopped the clunk completely.

[Bruce Tuncks]

A mate of mine was captain of a Fokker Friendship which was flying back from the N of SA with a bunch of miners who had been loaded evenly through the half-full plane.

When it had become quite nasty to fly, my mate found that all the miners had congregated to the back of the plane to play 2 up.

When he told them to resume their allocated seats, they said to get f#cked.

OK, he replied, then we are all going to die. Well this worked.

[facthunter]

I borrowed a mates DH 82 at Kyneton one day and the control column developed about 4" of loose travel and made pitch control extremely uncertain as the elevator would flop to  the other  limit position and back again at will.. A ball races cage at the control column fulcrum had failed and all the balls dropped out but I only found THAT out after I'd landed it with some considerable consternation and difficulty. The trim is only a spring that works through the same mechanism so no help there. Pitch is the ONE control you MUST have and should have redundancy.  Nev

[Bruce Tuncks]

There was once an instructor who used to show his confidence in a student by throwing the control stick away .

One day a student got a spare stick and pretended to throw his away too. I dunno if the instrutor died of a heart attack or not.

[facthunter]

That story was around Newcastle Aero club when it operated from District Park. The student was "worded up" supposedly  that this particular instructor did this. about 1958-9. I think It's probably true. They were operating Tiger moths and 2 Avros 2 Miles Geminis and  a couple of Dragons and a few Ryan STs. and more. It was a very small airfield  and where I started fly training in earnest. (like  having a SPL and all. (gosport tubes and cloth helmet of my own which I made the metal parts of). I still have that helmet but it is a bit sad with the rubber bits NO radio or brakes in the tiger Moths. There were so many DH 82s the spare ones were stacked on their Noses tail up.  Nev