Rolling G formula?

[plattsburgher]

I was speaking with someone the other day about aircraft G limits and we recalled the rolling/asymmetric g limits from the tweets and T-38s. The tanker doesn't have anything like that listed as an ops limit. Maybe it should.

I was wondering if anyone knew of a general formula where the rolling g limit might be derived from the standard g limit. I suspect it is different for each airplane and comes from the manufacturer; however, I thought I'd ask here.

Thanks in advamce for any info.

 

[JungleJett]

Why would the KC-135 need a rolling G limit?

 

[plattsburgher]

Because they put some items in the continuation training syllabus that require us to be other than straight and level. The normal load limit isn't much (2 or 2.5 depending on fuel load) and if we are exceeding a rolling limit, I'd like to know what that is.

 

[Andy]

Because they put some items in the continuation training syllabus that require us to be other than straight and level. The normal load limit isn't much (2 or 2.5 depending on fuel load) and if we are exceeding a rolling limit, I'd like to know what that is.

I don't know the definitive answer, but suspect that the G limitation is lower than max rolling Gs for the 135. IIRC, the G limitation was due to generators coming off line; probably more restrictive than any rolling G limitations.

 

[Benhuntn]

Good grief the jet is 50 yrs old and you think you need to learn a rolling G limit. If it was an issue they would have come up with one by now. By the way if you fly a jet that I have flown take .5 off the limit. I flew my jets like I stole them

 

[JFReservist]

Limits

Ummm,

I think the limit is when two engines depart from the same wing. Oh, right... that was wake turbulence, not "rolling" limits. Sorry Mike - I owe you another beer...

 

[Eagleflip]

There is no generic forumula for determining maximum rolling g for all airframes. At risk is the acual maximum allowable g for the most restrictive structure involved in the asymetric g situation, specifically either the wing load carrying structure or the most significant mass item, the engine.

That maximum rolling g would be calculated by using the distance from the mass item (or wing structural element) to the center of roll axis, times the acceleration experienced by the centroid mass of the aircraft, times either the roll rate or rate of acceleration.

Thus, if the a/c was pulling 4 gz symmetrically, the engine would also be pulling 4 gz. If rolling, however, the outside engine (on the outside of the roll circle, for lack of a better term) would have to pull more gz just to stay "with" the rest of the wing. That total g would depend on just how far out on the wing that engine is located, e.g. the total x distance from the longitudinal axis.

 

[Benhuntn]

The guy that shed two engines might have made it if he was a full time -135 pilot. In real life he was an IBM exec that flew on the weekends.

 

[GasPasser]

Now my memory is not what it used to be, but I was flying -135's at the time of this incedent. If I recall correctly, it was an ANG or AFR crew and E model airplane. I don't know if any outside of the board or his unit knew what his 'other job' was. Anyway, I recall he credited the SIM training he recieved at AA for his successful 2-eng out, same side, approach and landing. We used to fly them (in the AA SIM) as well as HW 2-eng out, same side missed approaches with and w/o rudder power. Not too bad if you followed the proceedure, which was proved out in real life by that crew. It was later duplicated by another crew who lost 2 on the same side to birds.

 

[JFReservist]

No doubt those guys did a good job getting it back down. I don't know if its in the r model sim syllabus or not, but I seem to remember doing a two-engine out RPO go-around at some time in my short career. I didn't much enjoy it in the sim. Pretty high suck factor.

On an unrelated note - I heard a story once about a space A in the jumpseat of an A model (probably an old retired flight crew member) who seemingly tried to "help out" the crew by raising the flaps prior to T/O roll. They finally made it off and got out of ground effect. The A/C called for gear, then flaps at the required speed only to find they were already up. There are a few things that I question about the story, but an R model is different from an A - so, anyone hear about this one?

Thanks