BAC One-Eleven doing a Churchill dog

[DavidK]

I've really been enjoying getting to grips with the BAC 1-11 (in FSX). One thing I've noticed, though, is a tendency for it to nod like the Churchill dog once cruising along on autopilot (i.e. continuously pivot slightly up then down). Does anyone else recognise this?

I'm wondering whether (1) that's how it was back in the 1-11's halcyon days; (2) that's how it was back in the 1-11's halcyon days when flying into a headwind/crosswind; (3) I need to change how the payload is distributed; (4) it's because I'm using the model in FSX and/or I'm not flying it correctly and should do X, Y and/or Z; or (5) something else..?

David

[Garry Russell]

I've not flown for a long time but I think the One-Eleven and VC 10 will do this if flown too fast. ...maybe too high as well??


Someone else might have a better clue

[DaveB]

I've never noticed it happen in FS9.. can't really say I've ever flown it in FSX. The real one would fly like this if your airspeed A/T wasn't set to 'throttle' if that's any consolation Been a while since I've flown it but I think the 'other' alternative is IAS in which the AP maintains the airspeed by descending to gain speed if the aircraft slows or climbs to scrub it off. A/T to 'throttle' negates this I honestly don't know if DM programmed this level of accuracy into the AP or if indeed it CAN be programmed thus

ATB
DaveB

[cstorey]

What you describe is known as a phugoid and is a well recognised tendency in many aeroplanes. What is causing it in your case I do not know, but as someone else has suggested if you have the AP in IAS mode it will tend to perpetuate a phugoid as the a/c overcorrects in pitching up and down to maintain IAS . Is there a Mach hold? You probably would be better using this . There is in fact a Mach Trimmer on the real 1-11 but I don't know whether it works in FS - this is to alter pitch trim to compensate for the aerodynamic changes , most notably to the position of the centre of pressure, which occur at higher mach numbers

[WhisperJet]

One thing I've noticed, though, is a tendency for it to nod like the Churchill dog once cruising along on autopilot (i.e. continuously pivot slightly up then down).

Hi David,

do you recognise that on very 1-11 model?
Or just the 510ED series model?

Best,

Nick

[NigelC]

Sorry Dave but IAS mode for climb/descent only and throttle mode for approaches, rest of time (including IAS) should be manual power setting.

I recall in the depths of time one of the BIA aircraft had a tendency to phugoid but I can't remember if it was autopilot or tailplane related. Remember one of them going into BCALs hangar to use their taildock, but think that one was to do with water ingress into the tailplane screwjacks that was freezing at altitude and causing a jam.

Nigel

PS Throttle mode is a nice cheat for going and making the tea though

[DavidK]

Thanks everyone for all your suggestions and explanations:

What you describe is known as a phugoid......

I think I've seen that word before, in connection with that heavily-loaded Japanese 747 that crashed into mountainous terrain during an internal flight sometime in the 1980s -- the accident where the tail broke off the fuselage, making it near-impossible for the pilots to control the aircraft (if I remember correctly).

Meanwhile, here's some more information:

• I almost always cruise along at FL280 in all the models, around Mach 0.74 (maybe a little fast? -- although it's to keep up with the VA schedule. Fly slightly slower at say FL300 instead?)
• The phugoiding (if that's the word) may be less/absent when flying the 510ED, i.e. with the autopilot that includes the IAS vs Throttle speed-control options. But it certainly tends to be there in the other 1-11 versions.

David

[NigelC]

Speed/Flight Level shouldn't be a problem, though your a bit on the low side for longer flights. Rule of thumb is distance in miles + Flight Level up to a max of FL350, so a 330 mile flight would be FL330, a 140 mile flight FL140 etc as the optimum and fly the nearest available semicircular level.

Climb at 280kt indicated until that = Mach .74 then maintain ,74 for the rest of the climb. I tend to use .72 which was more typical of 1980s operations.

Nigel

[DaveB]

Phugoid.. what a great word

Tks for the explanation Chris/Nige

ATB
DaveB

[DavidK]

Speed/Flight Level shouldn't be a problem, though your a bit on the low side for longer flights. Rule of thumb is distance in miles + Flight Level up to a max of FL350, so a 330 mile flight would be FL330, a 140 mile flight FL140 etc as the optimum and fly the nearest available semicircular level.

Do you mean nautical miles? Though I guess it probably doesn't matter which -- my most recent lengthy 1-11 flight was Nice to Birmingham (639 nm) so I suppose that should've meant the max FL350 and a Mach 0.74 (0.72?) cruise speed..?

Phugoid.. what a great word

Sounds like something looking for Doctor Who -- or, if it's rock'n'roll, a good name for a band?..!

David