Thread: Prop pitch

Hi Ed,

Took out another 1/2 degree on prop pitch. I'm up to 5580 rpm. Much better on performance all around (take off distance, climb, cruise/speed). It performs better too in the higher density altitudes. Fuel barley got tagged. Now I'm more appropriately pitched for the altitude a would normally fly. 5200rpm from factory is way too course. You absolutely need 5500 or slightly more to develope good plane and engine combination performance. The Rotax 912uls really likes 5500rpm and comes on strong at even slightly higher rpm's. On the power curve the best engine torque is between 4800-5200 rpm, but that is not its best HP rating. The higher the rpm the higher the horse power gain, but there is a trade off point and 5500-5600 rpm WOT works very well for the altitudes the majority of us fly. Your prop/rpm need to be set at the altitude you most often cruise at, like your's. Most of us don't fly at ground level at our airports. If you cruise between 4K-8K most of the time then set up the prop pitch to perform at those altitudes. 5200 rpm factory becomes lower and performs even worse the higher we fly and the HP takes an even worse hit if you can't develope any rpm.
5200 rpm hurts horse power too severely especially if you normally fly at 4K and above most of the time. I know of a dozen or more people who have repitched and all like the performance better. I get faster rpm and speed recovery too if it is needed on a bad landing if you have to nail the throttle to save your bacon.
I've got the prop repitch down to a science now.

Prop pitch is everything when it comes to the performance of our plane.
Maybe I can keep up with you now!

there is a 5 minute limitation on rpms > 5,500 to 5,800. is this 5 minutes available only at take off or any time in the flight?

when the autopilot has the altitude and puts the nose down with the throttle wide open it will exceed my level flight max by about 75 rpms. wonder if it is even worth thinking about?

Hi Ed,

Max rpm's are for anytime. 5 min. limit. If you set the max rpm for 5500 WOT then you never have to worry, but if you set it for higher then you need to watch it when you are over the 5500. Not a big deal just something to keep in the back of your mind. To me it strickley depends on the type of flying and the type of flyer you are.

There has to be something wrong with my plane somewhere. The faster it goes the rougher it gets. Doesn't seem to be the engine but the whole airframe. I see alot of people talking about cruising at 5500 RPM but when I do that (I can only get 5400 WOT and level as I have not repitched) and get 120 plus it is constant commotion. Don't know if it's wheel shake, a blade out of pitch, carb sync or a combination of it all. Can't find anything loose on the airframe. I find I am most comfortable at 4800-5000 RPM.

Any thoughts?

if you have not re-pitched then maybe you haven't confirmed the blades all have the same pitch. i don't know of anyone who has had their props dynamically balanced on their ctsw but i would be real interested to see the result.

if the wheel is spinning/vibrating the brake will stop it ( avoid using the parking brake )

if the wheel pant is buffeting you or your passenger can see it

has this roughness always existed? what about in a static run up to wot? if rough on static i would look at carb sync, prop balance, engine balance ... etc.

rough ride is not unusual at speeds > 120kts IAS but on good days i can descend 130+kts IAS and have it real smooth. i'm never real smooth at 145 and i always think there is gradient at work when descending to see 145 ias.

flutter?

have your ridden in other ctsw's? are they different?

my ct is a pleasure to fly so i think if your's isn't it can be addressed.

Hi John,

The carb sync if out usually has a slight vibration at a certain rpm that you can feel.
The wheelpants can cause a vibration, just look out the window and see if they are shaking. Mine shook pretty bad and you could feel it throughout the plane. Tightening them helped. I put a big fender washer between the rubber sleeve and the wheelpant and tightened my wheelpants up and that took care of the shake. That means there is a large washer on each side of the plastic wheelpant (sandwhiched) so you won't crack the plastic when it is tightened. That being said I have also trimmed my wheelpants up from the bottom outside edge about 1" or more all the way across. This makes for easy access to my valve stems. I don't see my wheelpants shake any more. The prop blades may be out of pitch to each other. Only takes one and only takes a little out.

Orrr it could be a combination of these things.

I am reasonably certain it is not the wheels spinning. I an feel it a little on take off and then it stops. Sometimes I use the brake. When I have had the pants off the wheels are not moving in cruise.

When in cruise I can see the left pant shaking, alot. Passengers say the right one does the same. When I took the pants off the feeling in cruise seemed about the same. Loose gear maybe? I'm going to look into that this afternoon. I have had no hard landings. Most are squeakers, especially since I started using 2200 RPM until touchdown. I assume the washer you use on the outside, Roger, is large enough that it has more diameter than the depressed area on the outside of the pant where the bolt goes thru? Or is it small enough that it fits into the depression?

The problem has been there since day one so maybe I'm just used to a smoother ride of a C-182. I have not been in anyone elses CT since May so can't really compare. Saw Roger H. the other day and we are going to get together for a comparison.

I don't think it is flutter as I have always associated that with a high frequency vibration. I have not tried a WOT static but can easily do that.

I may have a carb sync problem that is recent. When I pull the throttle back to about 4200 I am felling a slight vibration that wasn't always there. At that RPM I can put the carb heat on and it goes away. Take it off and it comes back. Whe I changed plugs I noticed the plugs for the front two cylinders (1 & 3 ??) were dry but black. Rear cylinders were tan. I saw last night fron a previous posting to a link that this can be a sign of carbs out of sync. I'm not sure this has anything to do with my high speed cruise felling.

the wheel pant buffet can be pretty annoying. we used a steel band to stiffen and i noticed this week this same fix is still being used. of course this buffet would have been absent when your wheel pants were off

Hi john,

First the slight vibration at 4200 is most likely the carb sync. Easy to fix. Black sooty plugs do happen in a lot of Rotax 912's. Mine is that way on cyl. 1&3 and light tan on 2&4. Change plugs at 75 hrs.
A washer is used on the outside and the inside of the wheelpant against the plastic. It gives it a little surface area and keeps it from cracking under vibration and from tightening. My wobble went away when I tightened them down.

John,
Where do you live?

I live just outside of Salem, OR. Real close to Roger H.