propeller NR Propeller

[bcbushcaddy 27]

Hello, 

Just installed a new shiny and beautifully crafted NR Propeller on a Kitfox 4-1200 powered by a Rotax 912 UL. It replaced a 72” 3 blade tapered Warp Drive. There has always been even with the WDP a bit of vibration on full idle especially at short final with the engine completely unloaded and the “wind milling” Propeller apparently driving (leading?) the engine. Now this has been drastically aggravated with the 2 blade NR. 

Is anybody out there experiencing the same thing or a similar issue at final approach at full idle? The vibrations seem to increase proportionally with airspeed at full idle rpm. No issues once you add  a little power and load up the prop and engine. 

[flywise 169]

Hey Willy,

It is quite tricky to set the blade angles the same on both blades on the NRprop....here is why: the reference for setting the blade angles is the top surface of your half-hub using the simple angle tool to measure... and the problem I found is that if your two hub halves are not EXACTLY torqued to be parallel then your blades have quite a big difference in angles (I found up to 1,5deg). Make sure the gap on your hub halves is the same all way round (use a feeler gauge or vernier calliper). Last and not least after everything is torqued down make sure your prop tips are tracking within 1/16 th inch for best result. 

Hope that helps, regards, Laurent

Ps you can use an electronic inclinometer to set the blades more precisely ...make sure you measure angles with propeller hub in the same spot/location to prevent different/wrong readings

[1avidflyer 1983]

I made a laser tool that clamps onto the tip of the prop blade, and will project a line across the hangar.  You can see the laser spot move when the blades are tightened up.  I feel this is a very accurate way to get all blades at the same pitch.  JImChuk

[bcbushcaddy 27]

Thanks Laurent, Jim for your insights. We did double check the angle via digital inclinometer and both tips are 9deg. respectively. The gap all around can’t be the same as the outboard 2 (4) bolts are torqued to 164 and the main hub bolts at 214 if I recall correctly here. So there is a minor visual gap difference but I’d expect that with the difference in torque spec. 

The tips are running an extremely fine line, so we don’t think it’s on the install, but we can/will double check. I still think it’s related to the wind milling on descent at full idle, especially since it runs very smooth under all other power settings, climb, cruise, etc. 

A bit of a head scratcher alright and we just finished an engine mount inspection. Less than 30 hrs on the bucks and no sign of any cracks, loose bolts. 

Thanks again, Willy T.

[Av8r3400 1178]

When did you have the gearbox serviced last?

 

[Allen Sutphin 705]

Sounds like the problem is with the gearbox or engine instead of the prop. The 3 blade just made it seem smoother. The 2 blade just magnifies it a bit. My first instinct would be a gearbox issue.

[NorthIdahoAvidflyer 374]

Start with the easy stuff first. I go to great lengths to make my blades consistent in pitch. I raise the tail so the face of the prop hub is as close the 90 degrees to level as possible. Read the manufacturers pitch instructions to determine the exact location to take the pitch measurement. On my GSC it was 24 inches from the hub. On my Warp its at the tip. Once you locate that location use blue painters tape to mark the location on each blade. I have use an adjustable square to make the tape lines exact on each blade. When you check the angle of each blade the blade should parallel to the floor at a exact location each time. I use a level on the prop hub to place the blade 90 degrees to the floor then I adjust a painters stick (like the one use would use on a paint roller) to a length so I can roll either prop around and set the prop blade on top of the stick to bring it to the same location each time. Once I have all set up I determine a start pitch setting and use my calculator to figure out the correct reading on the electronic angle finder. Lets say you want 12 degrees. 90 degrees - 12 of pitch = 78 degrees. 78 will be the number you want to see on the electronic angle finder. 

Get a stool and set at the the end of the blade. Have the hub and blade bolts just tight enough to adjust the blades. Roll the first blade around and set in on the paint stick. Place the angle finder against the blue tape line and adjust the blade to 78 degrees. These angle finders are very sensitive so make small adjustments and let them settle. Roll the to the next blade and do the same. One you have both blades adjusted tighten the hub and blade per the instructions. 

It sounds like a lot of work but I assure you if you take the time the prop will run very true unless there is something else wrong. I have helped three guys adjust their blades ths way and they were amazed on how much smoother they ran. 

Here is a pic of the angle finder I use. 

If you have any questions PM me. 

 

Edited 4 Jun 2019 by NorthIdahoAvidflyer
Spelling

[Cloud Dancer 69]

New or old the first thing I would check is static balance on a home made string and hub center prop balancing device. Second while not usually a problem but I'd also check tip tracking from blade to blade. Set up a board or pole or tall back chair next to the prop and tape a pencil or some other pointy device at the tip of the prop and move the blade around until the other blade comes by and see if they are tracking exactly the same. With a couple of marks of bright marker or paint on the blade tips you can also start the engine and observe the marks from the side of the plane to see if one blade flexes more than the other causing the tip tracking to be different. Some composite blades don't get manufactured with the same amount of resin and even if balanced one may flex more than the other. One blade dialed into a slightly different pitch will also cause the tracking to vary from tip to tip while under load. Probably not your problem but it's something you can check if you run out of options. Sometimes the tracking issues are blade related and other times it could be a hub that was machined out of spec. You can mark the hub and swap the blades from side to side in these cases and see if the tracking issues follow to the new blade locations. If it does it's the blade, otherwise it's the hub or gearbox.

Edited 4 Jun 2019 by Cloud Dancer
clarification of content

[nlappos 413]

From my helicopter experience, I suspect bcbushcaddy that there might be some in-plane, lead-lag motion going on on one blade. The difference between powered flight and windmilling is that in powered flight the engine is pulling the blades around, and the blades have drag and therefore want to lag behind the hub a bit. In idle at forward flght, the blades are windmilling and therefore pulling the engine along, with the blades in the leading position. Could there be some lead-lag looseness on one of your blades?

[bcbushcaddy 27]

Thanks everyone for their thoughts, ideas, and contributions above. To update you, the 3 blade Warp is back on, the vibration is less as expected and best guess, given due consideration to the enclosed, is that its coming from the gearbox. It is nearing the 500hr mark and given the fact it is this load, unload scenario we feel its time to look deeper. We'll let you know what we find, here on this topic page. 

This is by no means a NR is bad and WarpDrive is good kind of posting, nothing could be further from the truth. The NR is absolutely gorgeous and a great option in the wide array of propellers. More to follow, have a great weekend!  

[1avidflyer 1983]

How did this ever work out if it did?  JImChuk