Metal cooling fan upgrade

[KouDy]

So there i am flying first tank and all of sudden RPM went nuts (like really high). I was confused what is happening so landing it and tried switch to change RPM with no effect. Shut down completely and after quick check i happened to me that one of the magnets fell off (ofc it had to be the one that sensor is reading ). So that was it for the day for me on nitro, after that i crashed small titan too (nothing big by the first look).

Now since i need to put new magnet in (i fortunately suspected this happens so i have pair magnets spare) i am thinking and being recommended by the folks on the filed to get metal clutch fan upgrade.
I am a little confused about which one to get tho.
Manual states that optional part is PV0106 but helikraft also has KL0049 which looks exactly the same as plastic AV0143.

Which one would you guys get when getting the upgrade?

Also getting aluminium boom "upgrade". It's 663mm long i guess that is ok since normal (carbon hybrid) one is 660mm right?

[Elgyn]

The cheaper one look like it might do a better job the way the fins are lined up but it has the shim already machined into it. That could be a problem since it the different thermal expansion rates between the steel clutch and aluminum hub use the shim to slide on.


Now that I'm done with over analyzing it... ...go with the cheaper one. I would

[KouDy]

Yes i ordered cheaper one. More appealing to me too. The more complex one is not on stock anyway...

[KouDy]

So how do you guys do magnets in clutch fan?
I followed Finless videos on Trex 600 with epoxy and all but not sure if it was just first time failure (becasue it was my first build) or if that's going to repeat.
Mix epoxy, put small drop into the hole in the fan, squeeze in the magnet and then try to create very thin layer of epoxy over the magnet to secure it. This is what i tried to do last time, not sure how can i improve it really...

I see my order is shipped already so i hope to get it on wednesday or thursday...

[NitroAl]

If RCT have machined the recesses into the top of the hub it will be fine with no chance of the clutch hanging up! I have been using the Kasama fans for a couple of years with no issues at all!
Quite often the reason the magnet has popped out is because there is air trapped in the recess behind the magnet! There are two ways to get around this, one is to drill a small (.5-1mm) hole through the fan in the middle of the recess (some fans already have a hole) the other is to dab a drop of epoxy right in the middle without touching the sides at all and inserting the magnet letting the epoxy push out the air!
Make sure you clean the surface of both the magnet and fan and you can scratch them up a bit so the epoxy has something to bite on to!

[KouDy]

Done with rebuild and upgrades.

Fan is awesome i can say. It's basically exact copy of stock plastic but all aluminium. Fins are curved a little for higher flow.
I changed tail boom to regular alu one. Also i have added 2 bearings for torque tube so now i will run 3 of them.
Also i got yellow skids. They look more green to me but ok. Now these have problem because they are slightly bigger than stock so clip on the canopy is a bit tight. Well i cut off a bit of them on bottom side and created little groove on the back side of the front skids so clip on canopy can hold there. Not sure if it's necessary but makes me feel a little safer.

Flight test will be tomorrow or sunday. I am looking for tomorrow but plans may change. Photos i will make and post tomorrow.

[johnbs8]

glad to hear that someones trying aluminum boom with torque tube. that TT boom is too expensive!! im sure it would work fine just nvr heard of anyone doing it yet.

[KouDy]

Yea i am not sure i know how to really compare alu boom with their CF boom from the point of view of flight itself. Installation was ok but there is nothing much to that...

[KouDy]

So the flights were smooth. No problems what so ever. Adding 2 extra bearings to torque tube and tail feels faster than it was.
No issues at all with alu tail boom so i can totally recommend it if you need cheaper parts (like me).

Metal fan i don't know. I expected higher air flow but maybe it was just too hot day. It's hard to measure the airflow of it. So by temperatures i couldn't hold my finger on the backplate of the engine for a second. Muffler had regular 180-200 degrees so everything was normal. Turned some 3 or 4 clicks on needle to rich and it was a bit more bearable for the finger to stay on the backplate but for sure not for 5 seconds or so. So i will see more later with more testing...

[KouDy]

Testing adjourned. Super cool thing happened today (sarcasm ofc).
So i was there flying with no problems and then i heard "bing!" like when metal dings on metal but it had no apparent affect on the flight itself but i landed anyway.
Quick inspection didn't reveal any lost screw or anything like that so puzzled on what is going on i pumped in new tank with intention to hover and hear for strange sounds. What surprise was when i started it and when idling on the ground we could hear clinging sound (metal on metal stuff). Like little bell ringing inside the engine so ofc i decided not to fly even a hover.

Brought the heli home and put it apart (took out engine on skids). Now the problem was apparent. One of two screws holding the clutch to the fan got snapped in half and upper part went ballistic (loud bing sound was probably when the flying out part hit the muffler and fell to where ever). Now clutch was little loose on the other screw which caused the clinging sound when engine was idling.

There are 2 scenarios in my investigation :

1. Screws were not tight enough. Some smaller vibration caused one to snapped and the created ringing.
   1. They were not tight because of my own mistake.
   2. They were not tight because of the fan itself (the holes are not deep enough to get both of them completely tight)
2. Screws were tight enough but just got loose in process of flying by vibration.

During removing the fan the nut holding it on crankshaft got destroyed ofc (that poor nut took too much beating) so getting new one there is unavoidable.

I tried to screw the other screw back and it fits tightly. I am going to use stronger than blue threadlock on these. Super strong 680 or weaker red 272. I will see but likely i will actually also put threadlock to the shoulder of the fan to glue the clutch to it for more firmness.

So now i have to figure out how to get that bit of the screw out without damaging the threads in the fan. Yes the screws were threadlocked ofc.

In the meantime i am not sure how to approach this. Should i get the same fan again? No idea tbh...

[see_e_oh]

I experienced same problem with the aluminum fan on my 5th flight. Threw it in the trash. The stock fan is much stronger (and way cheaper)! Not one problem with any stock rappy fans, ever.

[KouDy]

I want to give it another shot with using stronger threadlock so ordered another one.
I am going to take measurements of everything there on the fan, note them and compare them with measurements of original plastic one. I expect they will be the same tho. Everything was fitting correctly so i tend to think this was really installation problem from my side.

Either way when it's mounted after 2 tanks i am going to pull the engine assembly out and check if everything is firm and in place.

[carlos]

KouDy
The screws were probably too long, you done them up tight but they were bottoming out in the bottom of the hole and not holding the clutch down hard onto the hub.
Common problem with those cheaper fans.

[KouDy]

So inspected the arriving clutch fan.
Measures are exactly the same as the original plastic with one small difference. And it's a big one. Just like indicated by carlos the holes are not deep enough.
No matter i thought, i will just grab 2 screws and make them shorter. After all i had PV1357 ordered from earlier. Well these screws are not there inside. Fortunately in this package i ordered spare body frame holders PV1349 where 2 of those screws are present, 2 are longer. Which is also weird because in original kit there are only small ones.
So anyway taking them i grinded about 2mm off. I will post photos later but now the screw goes in nicely into the full metal fan.

[KouDy]

So i took time to take photos of the screws and bringing them here.
For this metal fan upgrade it seems to me that the holes are a little random in depth. None the less i took the time and grinded off 2 screws. As mentioned before they are not in those mixed screws bag (or there are more types of bags and i picked "wrong" one ).
Visual difference in screws is following :

Measures for the shortened screw are 10.9mm (with head and all) and original has 12.85mm. I guess 10mm screws are ok for this one.

Now one word tho. Since this was my third installation of the fan, the engine shaft saw some action already. Unfortunately i forgot to take the photo of it so i will try to describe. When you look at engine, shaft going out can be divided to 3 parts. First par is with threads. It is where where you screw on the fan and nut. Second part is same diameter as first but without threads for nut. Third part is with larger diameter and fan shrouds over it all the way down to the washer when you screw it down. Now i found out on the third part there must have been some kind of remains of the thread lock (yes sounds weird to me too). What happened to me was i tried to screw on the fan. Now i was totally not able to screw it all the way down. With threadlock getting dry i decided to eventually pull it back out. Man that was harsh. I destroyed epoxy on the sensor completely but finally managed to unscrew the fan back. That larger diameter part on the shaft looked weird so i used very fine sand paper on. What a change. Whatever was there was that fine that i was not able to feel it with fingers but screwing was almost impossible. After this little cleaning there was not much of the hold up and thread lock is getting dry on the nut now

[KouDy]

So i got few tanks in with my little screw mod and everything looks solid and firm. I may take engine out to check but i expect to see nothing special there. If you get the upgrade, get shorter screws for clutch or grind stock to make them shorter...