Threaded Fan

[ecofan_]

Hi all

I have the possibility to make a new fan for my stratus, but threaded, like the TT's ones.
So, I have some questions :

1rst : is it a good idea, because maybe Minair make unthraded fan for something.. (or maybe it is just to do only one fan for OS/YS/ other engines...) The precision of the thraded piece will be very good, so for the alignement there 'll be no problem

2nd : is it possible to put the fan into 2 pieces : the 'propeller' itself and the tube that goes on the engine shaft, by removing the two bolts ?

and 3rd : if the project work (it is for OS sz), 'll some poeple be interested in it ?

thanks, and again excuse my poor english !

[DavidH]

Don't know if you have checked. But on some of the engines the threads on the crankshaft are not that great. They are not put on the crankshaft square. So any type of thread on fan would not dial indicate and be precise. Just a thought, but I have seen this on some engines.

David

[ecofan_]

yes, sometimes it appears.. but the fan on thunder tigers heli are like that, and there arent any vibrations arent they ?

[EricLarson]

huge vibrations most of the time, but the plastic frame set hides it well. Dial indicate a TT fan after install or even dial a few main shafts and see what the results are :) You may be surprised.

The collet system is the most accurate, but the nut tightening down on the top collet is what causes the runout. This is fixed by a correctly made collet / nut. MA has the correct parts being made and they should be at the shop any time. Evey time we have installed the collet/nut the runout has been less than .001 and normally around .0005.

[DavidH]

ecofan,
Most pilots that have thread on fans don't dial indicate the fan to see if it is not correctly aligned. They know if it is not aligned, there is nothing they can do about it. Even the ones that use a dial indicator to check it and find it out of alignment. They fly it anyway, because there is no way to correct it with a thread on fan.
I am all for making things simpler, but there still has to be room for adjustment also.

David

[wattybotts]

One of the guys at our field is a machinist, and he decided to make a threaded fan for his tempest. It took him a few weeks to make, but after he was done, it ended up being perfect. He dial indicated the fan, and it ended up being .0005. He has been using this fan on his tempest for about 6 months to a year now, and he has not had any issues.

Just thought I would throw that out there...

[ecofan_]

thats sounds great !

maybe you know if he's got his DXF folders for the fan ? what engine is he using ?

thanks

Nicolas

[wattybotts]

maybe you know if he's got his DXF folders for the fan ?



I dunno??? :dontknow

He put it on a C Spec.

[david.read]

The Hirobo Freya has an upgrade alloy fan, it has a parallel tolerance fit and a wood-ruff key to anchor it to the crankshaft which already has a slot in it for a propeller.

All you need to do is statically balance the fan first, then install it with the key-way and Bob's your close relative.

This seems to be a very good way of installing the fan in my opinion.

'Happy dialing in' MA fans :)

David

[DavidH]

I dial indicate any fan. I don't care how it attaches to the motor. It is best to at least check the run out. I have seen helis shaking in flight. Ask them did they check the fan when they installed. They would say there was no need. I would get them to take the motor out and check the fan. They would be out sometimes up to .060 out. Get them dialed in if possible and within .002 and the heli would be smooth.

David

[david.read]

David,

How can you dial indicate a fan and be able to change the run out on a set up with no collets. :?:

I appreciate that if you only statically ballance a fan, this does not mean it won't have a wobble when on the crank.

David Read

[DavidH]

That is what I am saying. All fans need checked for runout with a dial indicator. Don't assume just because they are threaded onto the crank, there is no run out. I have seen threaded fans way out. There is nothing that can be done about it except get another fan and see if it is better. That is provided the crankshaft is not tweaked. Also the threads on the crankshaft are not always square. Won't mention any brands. But I know several motors I have seen that the threads on the crank were not put on the crank square.

David

[EricLarson]

Collets are not the only attachment means that can make the assembly straight, but they are slightly adjustable. Other means of attaching the fan have NO adjustment and you are stuck. Great for those that get lucky and the machine making the parts was setup perfect and it was a tues after the machinist had his 2 cups of coffee and was in a good mood. Most people don't want to thread a fan on, see the run-out greater than .001 or .002 and then have to buy another fan..........

Even when tolerances are held very tight, they are just that "tolerances" and you will at times get 2-3 parts at the high end of the tolerance range and you need adjust ability to make them work. Just how it is.

The new collet nuts MA has should make the process very simple and accurate most all of the time. You also have a slight amount of adjustment if necessary.

I agree 100% with David. If you want your model to last you need to dial in the parts on ALL models.

[mace]

I made A fan For my Tempest and this is why I feel it is better than Collet's.

The threads never align the fan they just tighten the fan against the inner race of the bearing !

The Bore .375+.0002-.0000 that sits on the crank is made the same time the BackFace and Diameter are made all in one sitting on a cnc lathe!!

Therefore all of these features all within .0001 of each other and manufactured on a 20 year old cnc lathe new lathes have runout of less than .00005 (typically it also depends on quality of lathe)
this machine can spit out 100 of these parts a day virtually identical with no operator interaction!!

The .0001 is runout of the bearings on this old lathe typical on older cnc lathes.

The crank is centerless ground at O.S engines and it spins in a bearing not to much room for this to have any runout I have indicator that can measure .00005 (50 millionths) and on all my engines from O.S. It reads no runout at the .00005 level !


An issue MA should consider with there colletnut (fix) is the condition of everyones existing fan.
I know for a fact that this will not work on my fan's As they are all messed up dented and scratched on vital surfaces (from trying to dial indicator them in )

I also believe that if the colletfans where one piece(not 2 pieces pressfit together) that people would be getting the fans runout to less than .0005 in 10 minutes

I would like to add that I have 3 MA birds and I am die hard MA I am not going anywhere,these heli's are Great !!!

This is the only thing I could ask for MA to improve!!!

Even if you make it a $75 ultra precision add on or after market fix I know alot of people the would buy it immediately !

loose the collets and 2 piece fan spend the money on one piece fans people will buy them from you !!!!!
(it is what they want) even the keyway idea is great alternative !!!!

P.S. Bobby the whole reason I made the fan was for the sz problem And yes it screwed on and read about .0003 on every dang surface of the fan it is sweet.

I agree with everyone that the fans should be tested for runout collets or no collets!!!!

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[EricLarson]

Nice part. I agree that is a good option.

There is a fix being MFG'd though :) It is the collet nut. So far when tightened the runout has been about .0005 every time. They are not expensive and will work with all of the existing fans.

Just FYI.

Thanks for sharing the info!

[Wayne]

Mace:

Hey, where is my fan anyway???? I've talked with Tim S about your fan, and your idea will work for the reasons you stated, that top lip on the cranks runs true. Part of the problem is the number of different engines out there all require slightly different fans, and it not in addition to knowing you need 8:18 or 8:45 or 8:27, you need to then order a kit with OS SZH Fan, C-Spec Fan, YS-91 Fan etc etc etc. That ends up being a real problem on the distribution end. As a machinist, you can imagine the cost of making one current fan out of a large hunk of aluminum.

But.... Your friends in MHA (me..) :glasses: are willing to take two off of your hands to do some extensive testing and then report back to you!

later

Wayne

[ecofan_]

Mmh
there are already differents type of stratus kits : YS / OSsz /Os cspec
might be a good alternative !