Engine Alignment

[Rogerck]

We are having some work done on our 06 CTSW and it will be good time to check for proper engine alignment. The specified downward angle is 5 degrees and is easily determined using a digital angle meter. ( BTW, the LS down angle is 3.4 degrees.) My first question relates to setting up the 2.5 degree right thrust. Not sure what people have used as refenence points or tools to establish this angle. .

 

 

IF the front of the cowling is perpendicular to the centeline of the aifrcraft, then a 2.5 degree offset would require the back of the spinner plate to be approximately 5/16 "closer to the cowling on the right side than the left (front to back). That's a fairly large difference and I'm not sure that most SW's have this kind of offset. A 2.5 degrees side angle is fairly significant (think of a 3d glideslope.)

 

On the other hand, perpaps the cowl is fabricated to include the right hand and downward angles. Refer to section 3.3.7 of the attachment, Note . This would seem to suggest that the cowling has these offsets built in if its used to line up the engine.

 

In summary, I have two questions:

 

- what process have people used to set up the right thrust?

- Does the cowling shape include both the right and downward angles?

 

BTW, our CT has always required a fair amount of right trim for straight and level flight. If power is reduced the nose falls to the left, power increase nose turns right. See section 3.3.8 of the attachment for proper flight verification. We'd like to get this right.

 

Roger Kuhn

Firewall repair Engine Angle CTLS.pdf

[Jim]

My 2006 CTSW requires a lot of right rudder trim as well. Aileron alignment has been verified correct. I look forward to more discussion.

[chanik]

Huh. I don't know, but I can think of a fairly accurate and simple way to check with a piece of string. Tape one end to a prop tip, align it perpendicular to ground and measure straight back to the leading edge of the horizontal stabilizer. rotate 180deg and do the same on the other side. It should be 2.835" longer on the left side.

[FredG]

My 2006 CTsw used to require a lot of right rudder trim (so much that I would run out rudder trim authority at cruise speed). My mechanic removed the (tundra) nose gear fairing and that tendency went away completely.

 

When asked, FD USA recommended installing a CTls nose gear fairing and we did so. Since that modification, the problem has not returned. Apparently, for some airplanes, the CTsw tundra nose gear fairing has enough surface area ahead of the centerline of the steering axis that it would push the rudder. Obviously, I have no idea if my experience applies to your airplane.

[mocfly]

Roger,

Having done this on a few aircraft I can tell you how we did it.

1. Establish 0,0 to the aircraft datum

2. Create a template that gives you the required offset in both directions.

4. Mount the template so it's offset does not move independent of the aircraft. We used a laser pointer mounted to the engine ref point so it pointed at 0,0 on the template.

3. Adjust the engine mount according to the Flight Design procedure to give you the proper thrust angle.

 

This outline is for informational purposes only.

 

 

 

I believe that the cowl has the offset built in.

 

Chris

[Rogerck]

Kurt,

 

Thanks for your suggestion. Easy and straight forward.

 

Roger

[CT4ME]

I had a similar problem... 'turned out the the nose gear was rotated a bit, which also required minor adjustments on the ground as I taxied. It apparently was acting as a "front rudder", enough to cause me to have to compensate. It was fixed, and "most" of the problems went away. As short as the CTsw is, I'm pretty sure it will always require a good deal of rudder work.

tim

[Rogerck]

It seems to me that checking the 5 degree down (SW) and 2.5 degree right thrust angles is easy enough to do and it should be verified. Engine alignment and nose wheel pant rudder effect are two different things that can cause similar problems. I have heard from several sources that the CT tundra nose wheel pant can cause directional problems. Since we are having our front pant replaced, we're going with the LS model which is reportly much better. This is an option for those who want to spend the bucks. I'll provide performance feedback one we're flying again.

 

Roger Kuhn

[Znurtdog]

Re Tundra Tires..On a CTLS with tundra tires, is the nose wheel and pant larger, or just the mains? thanks

[coppercity]

Nose pant is the same, just the mains increase size.

[chanik]

It is supposed to be bigger. The nose changes from a 4.00-4 to a 4.00-6 tire with the standard tundra setup. It means a new nose fork and pant which is why I left the 4.00-4 nosewheel on mine when I went to the larger 6.00-6 (tundra) mains and Matcos

 

Edit. My bad, mine is the CTSW'; you asked about the CTLS. I think the nose is the same 4.00-6 tire for the LS

[N89WD]

My experience has been the same as Tim's if it will track straight on the ground it will take less right rudder. If it is tracking straight chances are the pant is straight. Also pay attention on roll out, when your nose wheel touches down, the CT may want to dart o pull. It's possible once again your alignment may be out which would cause it to "lean" to that side while in cruise. I have the LS nose pant, but had no problems with maxed out trim, etc.

[Runtoeat]

Wouldn't a good way to check "neutral" position of the nose gear in flight be to raise the nose while on the ground and see if the front wheel positions itself in-line with the airframe?

[Rogerck]

A new nose wheel fork and rear motor mount has been installed on our 2006 SW. I had checked the downward motor thrust angle on the old motor mount set up and it was 4.5 degrees. The spec is 5 degrees, so close enough.

 

As a starting point, our mechanic installed the new motor mount using the same number of spacer washers as the old. It turns out to have only 1 degree of down angle. In test flying at 1 degree, the plane flies and trims very well, hands off is improved and speed is the same as it used to be. The only perceived difference is that a small amount if increased down elevator trim is required. Since the plane is flying well, my mechanic suggests that I get 8 to 10 hours of flight time on the new motor mount rubber doughnuts before resetting the trim to 5 degrees.

 

Here's my question - the plane flies very well at the current 1 degree down engine angle. What is the adjustment to 5 degrees supposed to do and what are the issues of leaving it set where it is, at 1 degree? BTW, the plane now requires very little right rudder trim to keep the ball centered. In the past, a fair amount of right trim was required.

 

Roger Kuhn

[Roger Lee]

This question may be better for FD.

[Rogerck]

Roger, We have checked with FDUSA and get a mushy, non-definitive answer. Most of what we got was related to how the spinner spacing looks around the cowl, and if it's in a certain range it's ok. I did receive good input later this morning from at engineer/airplane designer at my field. His suggestion - fly the plane straight and level at normal cruise speed and adjust elevator trim to hands off. Leave that setting and land the plane. If the engine angle is correct, there should be very little elevator trim required. Roger Kuhn

[Roger Lee]

Hi Roger,

 

I had in my last post, but decided to remove it was a comment like this.

How does it line up with the cowling, does it fly straight , any adverse tendencies? Your post answered most of those questions and I also replied I see no reason to apply further degree changes since you already stated it flew better and trimmed better than before. It is possible FD had too much deflection to start. Point in case was when FD was shipping out all the CTSW's and some CTLS's with a prop pitch too course that it only achieved 5200 rpm at WOT in flat and level flight. I doubt you will see any changes in the ten hours you were going to fly and re-check unless the bolts aren't torqued to proper torque.

 

I had hoped FD would have jumped in with a more absolute answer.

[Znurtdog]

Roger, thread drift slightly. I have flown recently, an 06 SW and an 08 LS. Neither would turn more than 5200 straight and level and WO throttle. The manual states a static ground run up should net 4800 rpm IIRC and both a/c do reach this on the ground. I have been tempted to 'flatten' the blades a hair to raise the rpm a bit. Both a/c have the Neuform prop. Are they 'infinitely' adjustable or do they have 'stops' at certain angles? And do you suggest this change. Thanks!!

[Roger Lee]

Flatten the pitch? Absolutely positively. If you are only turning 5200 WOT flat and level then flatten about 2 degrees and shoot for 5600-5700 WOT at your average flight altitude. You'll climb better, cruise faster, use less fuel, have less streets on the engine and cooler engine temps. Even Rotax says that's over stressing the engine.

[FredG]

Znurtdog, the Neuform prop that came with my 2006 CTsw is continuously adjustable, no stops.

[Znurtdog]

OK thanks. What kind of static ground rpm will that give?

[Roger Lee]

Static is only good to get in the ballpark when dealing with an unknown. It should be around 4850-4900. Then you need to go fly at your average altitude and fly WOT flat and level for at last 45 seconds to 1 minute. You should be real close, but may need to make a small adjustment. You can't make it right on a certain rpm so shoot for 5600-5700. During the season changes and air density and altitude the WOT rpms will change slightly, but there should not be any need for adjustment.

[Jim Meade]

Roger,

 

I take it it goes without saying that when doing the WOT test, the plane should be trimmed as nearly perfect for straight and level cruise as you can get it. That if there is any doubt one would want to spend some time confirming trim is right to minimize drag in the desired configuration. Is this worth looking at?

[Roger Lee]

If you are only slightly out it won't make any difference on the WOT rpm. Maybe knock off a knot or two, but rpm should be the same. It's more important to be at your AVERAGE cruise altitude. The WOT rpms at 1000' msl will be greatly different than 10'000' msl.