View Full Version : Setting blade pitch..

srn4 - n/a
24-Mar-06, 12:30 PM
The time has come to set the required blade pitch on my fan http://hovercraft.org.uk/images/icons/smiley_icons/icon_smile.gif http://hovercraft.org.uk/images/icons/smiley_icons/icon_smile.gif http://hovercraft.org.uk/images/icons/smiley_icons/icon_smile.gif http://hovercraft.org.uk/images/icons/smiley_icons/icon_smile.gif http://hovercraft.org.uk/images/icons/smiley_icons/icon_smile.gif

A while ago I had a sketch that someone sent me that showed the measurements from the blade edges to the hub at each pitch setting to allow simple setup... does anyone have a copy of this?

If not, what other ways are there of getting an accurate pitch setting?

(I have a 9-9 5ZL 920)



nickyd - n/a
24-Mar-06, 01:55 PM

Your best bet is to set them at 45 degrees, you could use a square for this, then do a rev test on your engine. You maybe bang on your required revs with this which means you can just leave it. Otherwise back them all of a little and re check the revs. Keep doing this until your engine runs at the required revs when flat out.

You have to make sure all blades are at the same angle. The easiest way to do this is to clamp a piece of steel or similar to the engine frame so that it is just touching the laeading edge of the blade. Then you can spin the fan round and adjust the blades so that they all touch the piece of steel. You will then know that all the blades are at the same position.

The actual angle doesn't matter, so long as they are all the same and your engine runs at the required revs.

Hope this helps


srn4 - n/a
24-Mar-06, 03:21 PM
I know what pitch I want to set the blades to, I just cant figure out how to get them to that angle...

Trial and error might be a possibility, but with so many bolts its going to take hours!

tonybroad - n/a
24-Mar-06, 04:35 PM
I'll mail you a table for 5Z blades where you can measure the distance from the leading edge (or trailing edge) to the split in the fan hub

i'm at work at present and don't have it handy


Paul Fitz - n/a
24-Mar-06, 06:10 PM
This method is only partially possible with a 9-9 fan, because the blades overlap and it is difficult to then measure the distance. You will need to put 3 blades in and set the required angle, using the measurement method, mark the position of the hub split line on the base of the blades. You can then either do the same with the rest or fit all blades and using the 3 marked as a guide, do the first adjustment as suggested with a hacksaw blade or similar. They can then be finely adjusted the same way.

Dunc check your gmail address.

Hovertrekker - n/a
25-Mar-06, 11:33 PM

Perhaps this document will help you?

28-Mar-06, 07:05 AM
I know what pitch I want to set the blades...

Adjustable angles include 25; 30; 32.5; 35; 37.5; 40; 45 & 50 degree settings.

If you decide to use the pin settings, and together with the document Hovertrekker already put out, maybe these pictures will simplify things a bit.


Be sure you use the correct metal pins that generally come with the fan!

There should also be some markings on the bottom of the blade. Use a marker and you'll see them better.

Here is a german version with pictures that outlines the procedure a bit better. (...BTW. one of the sentences says the manufactures warranty expires if you do this, yet these seem to some pretty good instructions, don’t you think!!!)

jon_curtis - n/a
28-Mar-06, 11:53 AM
the pins that come with the fan are plastic!

Sean Atterbury - n/a
28-Mar-06, 12:42 PM
PLASTIC ????????

My Multi-wing came with mild steel pins..... http://hovercraft.org.uk/images/icons/smiley_icons/icon_rolleyes.gif

???????????????????????????? http://hovercraft.org.uk/images/icons/smiley_icons/icon_twisted.gif

Hovertrekker - n/a
28-Mar-06, 01:56 PM

Is there an english language version of that pdf? BTW - the pins on both my fans are plastic too. I don't think it matters much since the pins don't hold the blades in place once the bolts are tight.

29-Mar-06, 04:06 AM

Is there an english language version of that pdf? BTW - the pins on both my fans are plastic too. I don't think it matters much since the pins don't hold the blades in place once the bolts are tight.

Sorry, no English version is available at this time, but the pictures are pretty much self explanatory I think. Let me know what you have trouble understanding, and I can translate it for you.

I have used the plastic ones in the past, and now I prefer the metal ones. In some rare cases, the plastic ones can get pinched, and are therefore in my opinion less accurate. If you snug up the hub bolts to a point where you can still move the blades a bit, you'll find that the plastic ones can have just a little bit more play than the metal ones. I guess the plastic ones, (…if used at all?), can be just fine on the 4 and 5 inch wide Z blades, but using the pin’s on the much bigger P6Z's is a must! I've seen one of the other German crafts try it without them once. Needless to say, it didn't work, and they had a catastrophic failure. Using the metal ones was also a recommendation made to me by one of the sales engineers, during the time when I had visited the factory in Germany.

One little hint for keeping the pins from moving during the assembly process. I’ve found myself using a tiny tab of grease, or better yet, a dab of red lock-tight to keep the pins inside the correct grove. I like to believe this helped in keeping the angle all the same, while putting the rest of the blades in place.

Sean Atterbury - n/a
29-Mar-06, 05:02 AM
Greese, good Idea http://hovercraft.org.uk/images/icons/smiley_icons/icon_rolleyes.gif I am using a small piece of insolation tape, this way when you take them out again they do not fall and get lost, that has already happened, nothing like lying face down for an hour looking for a damb pin. http://hovercraft.org.uk/images/icons/smiley_icons/icon_cry.gif

OK maybe only a cuple of minutes, would'nt want to fall asleep. http://hovercraft.org.uk/images/icons/smiley_icons/icon_lol.gif

Michel - n/a
29-Mar-06, 06:47 AM
Hello Jonathan,

you can replace plastic pins by a headcut bolt, it works, for grease, if you don' t want to see grease leak on blades and duct, use an adhesive tape ( office thin one ), it will glue just enough time to put them all. And with a marker you can eventualy write the setting on it. With a little chance, it will be readable next time you dismount the hub.

A friend of mine never uses pins, so as to change angle with hub on place, he never had any trouble, I suppose he uses something to avoid blades bases to turn, like a block.

jon_curtis - n/a
29-Mar-06, 11:46 AM
i never use the pins, certainly not with my rotax 503, 50 odd hp is not enough to turn the blades in the hub.

i must admit i didnt like the look of the plastic pins and did make some stainless ones to use, before i ditched the pins all together, as they are not needed with 5z blades and 50 odd hp.

my rotax with a gearbox does take some very fine tuning on the fan, only a couple off mm, on each blade can make a couple hundred rmp difference on fan max and tick over speeds! my pitch is certainly not bang on 45 or 50, its between! but i can't fine tune the fan speed with the correct pulley ratios!

i would be interested to get some informed opinion on the exact power point of which a set of pins are required?

a word of warning tho! i would not use locktite anywhere near the fan blades! locktite can reacte with various types of plastic, making it break down and embrittle! i dont know if it will effect glass filled nylon, but i do know i would not like to find out!

Michel - n/a
29-Mar-06, 09:22 PM
It' s hard to say you have a risk of blade turn above XX hp. It happens with vibrations + shock + wrong tightening + prop speed.........

If you never encountered the problem, good for you, when it happens: either it' s slow and just uncomfortable ( vibrations, strange noise, revs up or down , loss of power ) or it' s sudden and you may explode the whole set of blades, and may be more.

My opinion is : I don' t try.

On aircrafts, prop turn at generally 2500 - 3000 revs, at that speed, prop base suffers several TONS of effort; change scale , on a 90 cm diameter prop like mine , or 1, 4O m on my diesel, I had' nt computed , but I think it should be several hundreds of kilograms, amongst them, how many are trying to make your blades turn ?