SST yaw!

[Bluey]

Anyone with an SST wing have a yaw to the left at the moment of take off? Mine does and up till today it was quite pronounced. Yesterday I took off into a bit of a cross wind (about 10-14kts from 040) on runway 08 at ywol and was very strongly yawed to the left to the point where the trike base was now pointing around 40 to 50 degrees off track maybe even more. It quickly tracked off to the left before then beginning a strong roll to the right as it recovered from the yaw. After heading off to the coast to gather myself a bit before returning to land, I discovered a 2mm gap between the mast and the left inside of the bracket. Upon tightening the wing nut, I found that it was tight. Only to discover that there was a further gap between the washer and the thread on the hang bolt. After adding another couple of washers I found the wing nut now properly tightens and the gap is now closed. A test flight now reveals a fairly mild yaw to the left when taking off at full throttle one up as opposed to a more aggressive one before. Two up, the yaw is almost non existent now. I'm wondering whether I should bother taking it up to airborne for a further tune? The trike and wing has nearly 450 hrs. It otherwise flys very well otherwise. I had another experienced pilot go for a spin in it with me in the back today and also thought it flew nicely.

 

 

[Guest davidh10]

Does the trike have the correct mast fitted. The SST wing uses a thicker mast than all the other wings. When upgrading to an SST, part of the upgrade is replacing the mast. I assisted with such an upgrade with a friend's trike.

 

 

[alf jessup]

Bluey, As with most trikes the wing will want to yaw into the wind upon lift off'

 

Also as David said, is the mast the one for the SST it is supposed to be a bit thicker and stronger to allow for the extra weight of the strutted wing.

 

Wait till you get the wing to dutch roll (side slip) by rolling either way out of a s turn to fast, that will give you the most uncomfortable feeling and you may only do it once more after that (just to see if it does it again) "it does".

 

The airspeed indicator will momentarilary read zero while your sliding across the sky in the direction of your wing with this horrible feeling in your gut.

 

My advice, dont do fast S turns (bit off topic but i thought i would warn you).

 

Overall a better wing in turbulence and a direct feel input wing.

 

Cheers

 

Alf

 

 

[Bluey]

Thanks Alf, I haven't tried the Dutch roll yet and don't plan to either. The yaw into the wind was expected but the amount was unprecedented for me. Let me assure you that it was way more than expected for the moderate conditions at the time. Unless I experienced some kind of thermal near the runway which produced a strong crosswind component just off the ground then the amount of yaw was over the top. When it happened, the only thing I had control over was the throttle so I focussed on climbing as you would. Before I tightened up the gap between the mast (which is the right one for the wing), the trike would yaw strongly at full throttle when you first rotated if you pulled the bar in for a bit of speed. It now seems much better but a little yaw to the left is still present. What I want to know is: Is this normal behaviour for the SST? Many of the people I have spoken to about this say it is now ok but most of those are going on hearsay as they have never flown one.

 

Bluey.

 

 

[alf jessup]

Bluey,

 

I dont think its normal for the sst to yaw left, im trying to remember which way the pod swings once the wheels leave the ground, i think from memory the pod swings left and the trike goes to the right, its all automatic to me now at lift off the correction from the thrust of the prop.

 

Im pretty sure mine goes right the wing that is.

 

I do know any time i take off with a xwind component the trike will yaw into the direction of the wind and some times quite severe depending on the strength of the xwind.

 

cheers

 

Alf

 

 

[Bluey]

Well that does sound like what mine does. At the moment of lift off the pod starts swinging left. This causes the trike to start going left. As the yaw diminishes, the trike then tries to turn right as expected. Before I tightened up the hang point, the swing to the left was exacerbated considerably when you pulled in the bar a bit. The more it yawed left, the harder the roll right when it started to recover from the yaw. I'm not sure what causes the pod to yaw left at lift off. It also does it if you abort a landing just before touchdown. It however, does not do it in normal flight.

 

Alf, when you say it yaws strongly sometimes into a crosswind, how strong a crosswind are you talking about? And do you think the yaw is worse than on other trikes you have flown?

 

Thanks, Bluey.

 

 

[alf jessup]

Bluey,

 

No i dont think it does it any worse than any other trikes ive flown, all depending on the strength of the xwind component.

 

Ive have some rippers like taking off with say about a 12kt component she just wants to point into the wind and that has never worried me, sometimes it feels like you pointing say 30 deg off runway track while still tracking down the runway centerline.

 

No different than when im flying along a road with say a 20 kt xwind component, it feels quite normal to me, on takeoff its just different as your tracking down the centerline then bingo as soon as the wheels leave the ground she points her nose into the wind so to speak.

 

Cheers

 

Alf

 

 

[Bluey]

Thanks Alf, this has been really helpful. It does sound like mine is quite characteristic of what the SST seem to all do. I am however, going to go for a quick flight in another newer one to be sure it is the same. That way I should get a better idea of how mine compares and be more confident of what is normal and what is not.

 

Bluey

 

 

[Bluey]

One thing I don't think I made clear in my first post is, when the extreme yaw occurred I ended up tracking way off the runway centre line to the point where I was about 50m to the left of the runway at about 200 feet when control was re - established. The yaw itself was not the biggest problem, it was the fact that I ended up going in a direction that put me so far from the runway.

 

Bluey.

 

 

[Guest davidh10]

You should not be "losing control", even momentarily. I think you are correct to investigate it. The SST does yaw more than the S3, but each aircraft has its own flying characteristics and my S3 flies differently to the other S3 that the school had during my training. The CFI moved me around between the two S3 aircraft and the SST just so I didn't "get too comfortable" with the flying characteristics of just one. For this reason, it is good for you to fly another SST just for comparison, but you should expect that if you fly three of them, there will be some differences between each. While I'm mostly flying my S3, I still fly one of the school SST aircraft from time to time.

 

Also be aware that after the earlier SST wings were produced, there was an adjustment procedure issued to reduce the "heavy feeling" in roll that early SST wings had. It is an internal adjustment and also affects the susceptibility to turbulence. If adjusted in the wrong direction, you get a very rough ride. The instructions were of a nature that the direction of adjustment could be misunderstood.

 

Flying at an angle to the runway, as Alf describes is not at all unusual here, as there is often a much higher wind at circuit height than on the ground. I find that correcting for the consequent drift has become instinctive and I just observe it happening.

 

Keep in mind that once in the air, and a steady state has been achieved, wind is meaningless. The trike does not know if there is wind or not. It is only the transition from the ground roll to flying in which a cross wind seems to have a weathercocking effect. This is because while the wheels are on the ground, the cross wind component is cancelled by an opposing force between the tyres and the runway. When you lift off, that force suddenly disappears, resulting in an apparent yaw as the aircraft accelerates in the down wind direction. Your natural reaction is to bank toward the wind direction to compensate for the accelerating drift, until a steady state is achieved.

 

All the trikes here wear the left hand main gear tyre more than the right. We can only conclude it is the prevailing wind direction that is causing it, as the same is not necessarily true of trikes hangered at other aerodromes.

 

 

[Bluey]

Thanks David, I hope to get the chance to test fly another set tomorrow. The previous owner who is a friend of mine and an experienced instructor is at a total loss as to my experience. The day I took delivery of the trike, he observed me veer to the left as I took off. Up till that time he hadn't noticed any significant yaw on take off. Two up it behaves itself much better. I must add that I am at the lower end of the mass spectrum.

 

Bluey.

 

 

[Guest davidh10]

Mystifying. It was good you posted the photo of the gap between the mast and channel at the hang bolt (in another thread). I'll look at some SSTs this evening when I'm at the aerodrome and see how they compare.

 

 

[Bluey]

Sorry, I should have posted that on this site as well. Later, when I get to a computer, I will. When I spoke to Shane and Russell at airborne they were quite insistent about checking for a gap and closing it if there was one. To quite Shane, "the sst is horrible to fly if there is a gap between the mast and the hangpoint bracket". It amazes me that they rely on a washer between the wing nut and the hang bracket to ensure enough tension is present on the bracket to close the gap. $70000 and it doesn't fly right if you lose the washer?

 

Bluey.

 

 

[Tex]

It amazes me that they rely on a washer between the wing nut and the hang bracket to ensure enough tension is present on the bracket to close the gap. $70000 and it doesn't fly right if you lose the washer?Bluey.

That is flex wing for you

 

 

[Guest davidh10]

I checked two SSTs tonight and they both have a slight gap. From standing on the ground, I'd estimate about 0.5mm.

 

I'd have to say that you can see the pod twist from side to side a little as well as waving around underneath the wing in turbulence. It is really obvious when you are flying close formation.

 

 

[Bluey]

The gaps need to be closed. Mine was more than a millimeter and the wing nut was missing a washer so could not be tightened as it ran out of thread before it could reach the washers. This meant that when the wing or base moved around horizontally the gap would get even bigger and exaggerate the movement. Hence my wild crosswind take off the other day. I flew late yesterday with a crosswind from the same direction across the runway and it was really well behaved. I also noticed the directional stability in flight is much better. It now doesn't wander around as much in turbulence especiay when trying to line it up along the centre line of the runway for landing. Airborne have said that the wing nut needs to be finger tight. You can even nip it up slightly with a spanner but make sure you do not introduce any significant resistance in moving the bar in pitch. In other words when you let go of the control bar of an sst make sure it still swings forward to meet the downtube under it's own weight. If it doesn't then it is overtightned. I now make checking the gap a preflight check on the sst.

 

Bluey.

 

 

[Guest davidh10]

A good result, Bluey.

 

 

[eastmeg2]

Excellent Thread, Bluey.