Westwind dutch roll and center of gravity

[Capt1124]

I have a lot of time in Westwinds, but most of it in I's. I recently started flying a II that has some Dutch roll.

At cruise, if you look out at the wingtips, you can see a slight, constant roll, it looks like the wings are moving around two inches with a frequency of one or two seconds. Hand flying has not been a problem, except for one I took it off autopilot on final and it started rolling quite a bit. It was windy but I don't think turbulence could explain it.

The CG on this airplane is somewhat forward, it gained some weight and the CG moved forward after paint and some interior work. It also has some ballast in the nose.

Now, can anybody with experience with II's tell me- does the location of the center of gravity contribute to this problem? We should probably take the ballast out of the nose anyway, since there is no need for it. Howver, if it's better to have a forward CG, I would like to know.

 

[sligo1]

IA1124A Westwind II

The dutch roll in the II from what I have been told is due to the winglets. I also had alot of time in the I with minimal in the II. If you disengage the auto pilot and yaw damper at altitude you can really experience the dutch roll.

Goodluck finding the answer and I hope you post your findings.

 

[SpaceBall 1]

Hey Capt,

Been a while since I have been in the pig, but I miss her. The majority of my time is in the I's but have some in the II. If I remember correctly, the II has dual yaw dampers and both must be operational for flight. Check your MEL for sure, but the I has a single yaw damper and it can be MEL'ed. The II (I think) needs both for dispatch. There is a reason for that. The dutch roll is caused by the winglets. Winglets reduce the stability and cause the issue. Some crews I know on the II keep the yaw damper on almost into the flare.

One of the training scenarios at FSI in ILG is the high altitude upset/unusual attitude. The instructor will configure the sim to a II (espically if you are there for WW I training). FSI gives a uncommanded Yaw Damper hardover and within 6 cycles of left to right rolls, most people will be inverted. If that happens to you PUT THE JET IN A SLIP AND HOLD IT! The cross-control will dampen out the dutch roll pretty quickly.

Will CG affect this......maybe. The dutch roll may be increased due to more mass forward of the point of rotation.

Either way, I would pull the balast out of the nose area. On one of my old birds we added balast under the aft baggage floor to help get the CG further aft to help out with the trim when landing with pax on the couch. With that forward balast and pax on the couch, I can about guarantee you will run out of nose up trim in the flare.

The WW II is a good bird. As you probably know, she'll carry about 1,000# more weight out the same runway for the given atmospherics over the WW I. There is nothing like a Flaps 0 takeoff in the Westwinds. It's like a go-kart on steroids!

 

[Rythm3]

Hey Capt,

Been a while since I have been in the pig, but I miss her. The majority of my time is in the I's but have some in the II. If I remember correctly, the II has dual yaw dampers and both must be operational for flight. Check your MEL for sure, but the I has a single yaw damper and it can be MEL'ed. The II (I think) needs both for dispatch. There is a reason for that.

The II, like the I has only one yaw damper, and for the WWII only, the yaw damper can be inop provided the autopilot is operational. Both the yaw damper and autopilot can be inop, but then your max altitude is 20,000 ft.

 

[WWDriver]

Good morning Capt1124,
I'm currently flying a 2. In our aircraft, I don't notice any difference in stability caused by CG. The "Westwind Waltz" seeems to be worse at higher altitudes and at higher speeds. With just a few legs in the aircraft, most pilots can get it under control in smooth air while hand flying. I have been told that if it does it to any extent with the A/P on in smooth air, that the A/P may need cleaning and adjustment (servos and cable tension?). If it's a problem for you, John Dunn down at Trimec (888 303 1124) can probably tell you more than most people about this.

 

[JumpJetter]

Before you pull the ballast out of the nose you need to run some CG calculations. We had a WWII that when loaded with 7 business men and no bags required significant aft ballast to remain within CG (sand bags, whatever was available). It really seems to depend on the configuration within the airplane (how much forward galley you have) Ultranav is great for making quick calculations to determine this.

 

[Falcon Jet 1]

It has been years, but we used to just kick in a little rudder trim with a/p and yaw dampner on