R90 design flaw

[vandelescrow]

Well I finally flew my R90 3D yesterday and here is what happened,

1. While fueling for the 3rd flight I noticed chafing on sides of main fuel tank immediately in front of the vertical part of the plastic rear frame.
2. After landing 3rd flight, noticed tail rod guides broke loose
3. 4th flight engine not sounding right and flight aborted half way through. Found pieces of clutch liner have fallen out of clutch bell (factory installed). After dropping the engine noticed large pieces of clutch liner that could be pulled off using just your fingernail

Possible solutions

1. Sand the edges of the rear frame round so there is no edge to chafe the tank
2. Manual says “Add a tiny drop of CA glue to the pushrod guide after you finish building the entire helicopter.” I did not think this was adequate but they are the experts, right? More glue is needed than a tiny drop and perhaps even add some on both sides of guides after dry to create a lip preventing the guide from sliding
3. . Trying to remove the clutch bell is a royal pain!!! Due to a lip on the bottom side of the clutch bearing case, the clutch bell can not be removed with out removing the entire pinion gear subassembly. Also the clutch bell can not be passed through the hole in the fan casing. To remove the clutch bell I had to remove the main gears, lower bearing block and fuel tank, not to mention removing the engine and loosening almost all bolts on upper frame so the bearing case can slide. Also, in order to get to the two top forward bolts holding the bearing case, the pitch control frame has to have the bolts it pivots on removed so the entire assembly can be raised. Did I say royal pain?

All backlash will have to be reset due to a clutch liner? You will still have to remove quite a bit to remove the clutch bell but I think during assembly, the hole in the fan casing should be sanded so it is large enough to pass the clutch bell through it. The main gears will still have to be removed to give clearance for the bearing block, and pitch arm removed to get to the 2 screws still holding the block in place.

Has anyone replaced the bearing block with the metal one? Can the clutch bell be dropped once you remove the 6mm starter coupling?

How did it fly? I mainly just hovered to break the engine in but the presence of the heli due to the sound of the blades, WOW. On the first flight as I spooled the head up for the first time, the sound was incredible; it actually felt like the earth was vibrating (maybe it was my heart). While hovering with the nose to the left, the sound of the tail blades made the heli sound like a full size. Do I still have a smile on my face? The blades I’m using are the Curtis 710 SB, MAH 3d paddles, 105mm Kok extreme tail blades. I stabbed the throttle once (ok a few times) to see its climb out potential, even while running rich, The blades barked and it was instantly at least 20 feet higher altitude, the two guys standing on my sides watching the flight actually backed up, GRIN.

[Kinger]

On the fuel tank issue, take a piece of fuel tubing and glue it into the channel on the plastic tank mounts. This will keep the tank from rubbing the mounts even if you run a pressurized tank.

I've found that the best thing to do on the tail rod guides is to use thin CA and put a thin coating all the way around the boom. Then slide the rod guide over that section.

On the clutch bell removal, dremel the fan shroud so that the clutch bell can be dropped through it. Only takes a few minutes, but it makes removal MUCH MUCH easier and it doesn't seem to affect cooling.

[vandelescrow]

Kinger, Thanks for the reply
I'm not sure where you glued the fuel tubbing. The tank has two bumps on each side that fit into rubber gromets on the plastic rear frame. So the "channel" you mentioned, I'm not sure what you mean. I am running a pressurized system (YS 91SR).

About making the hole in the fan shroud bigger I would think would actualy aid in cooling letting the fan get more air.

Do you know of a way to drop the clutch bell with out having to remove the bearing block? There is a nut locktighted to the pinion on the top side of the lower bearing, the drawing in the manual looks like there is a lip on the bearing block preventing the lower bearing from sliding down.

Does anyone know if the metal bearing block is the same way? I am considering upgrading to it if it will make future repairs easier.

Thanks again

[Kinger]

Nope, as far as I know the bearing block has to come out when the clutch bell comes out. The block traps the bearing from coming free. If you dremmel the fan shroud you can just drop the entire assembly out through the bottom.

You are correct in that the fuel tank is held in by the 4 nubbies and the rubber grommets. However, when the tank is under pressure the sides will swell up and rub the inside of the plastic tank holders as you've seen. Inside the plastic mounts for the tank there is a channel that has been hollowed out when the plastic part was molded. You can glue a piece of fuel tubing in this small channel (it runs vertically up the sides of the tank) and when the tank becomes pressurized it will rub against this fuel tubing instead of the hard plastic.

[Laurens]

You can dremel the edges of the fanshroud to make the hole just a little bit bigger. If you done that all you have to do is loosen the hex adapter and your ready.

I use clear tape around the tail rod guides to keep them from moving. Even when glueing them down I'd still use it. If the front or rear rod guide breaks loose it can block the rod from moving and thus making your heli piro constantly, even with your engine off. When you don't glue them down they can move on their own, making them line up better.

[vandelescrow]

Thanks, I understand now about the fuel tubing.

On one of my R50s, till I found some rod guids that fit better to the tail boom (I think they were from Goebee) I used washers on both sides of each guide. Rubber washers that would go in the faucet in your kitchen sink. These would prevent the guide from sliding along the boom but could rotate so they would always be lined up. I thought about doing that on the R90 but I thought if they can rotate, they would not prevent the rod from flexing. I can see it possibly flexing when doing hard piroetts but only when the rod is pushed toward the rear. What do you think? Is allowing the rod to flex bad or using these washers a good idea?

[ferincr]

On the tank issue you can also glue some of the soft fluffy side of velcro (instead of fuel tubing) to the inner side of the frames to avoid the chaffing to the tank.

[Raven_darkcloud]

You can slide a zip tie under the guide and it will wedge it in place. Cut the exess off when done. The trex 600 uses this and it works great.

[Ah Clem]

Vandlescrow,

I am sorry to hear that you had trouble with your ship, but am grateful to you for posting your findings.

I will inspect the fuel tank on mine for wear.

I have not had the tail pushrod guides come loose (I probably used a lot more CA than the instructions recommend, but will be inspecting them again.

So far, the clutch liner on mine is fine, but it has always engaged a bit later than I would like (there have been threads on this subject.

Can you replace the clutch lining while the bell is still installed (or is the shroud in the way). I have replaced the liner in the Raptor 50 without removing the bell (I did drop the engine).

[vandelescrow]

The clutch liner came out in chunks where the seam was. During removal of the rest of the liner I noticed they only glued half of the liner, the bottom half (toward the open side of the bell) and nothing was holding the other half.

Ah Clem, I'm sure you could replace the liner still in the heli but it would be difficult, not only getting the old one completely out but getting your fingers in there to put the new one in.

BTW, I sent an E-mail to heliproz asking them if the metal bearing block would make this job easier. They said no, the bearing block will still have to be removed and suggested removing the servo tray. Well last night I used the sanding disk on my dremel to make the hole in the fan shroud big enough to slip the bell through. The main gear will still have to be removed to get the bearing block past it but should be alot easier. Hopefully there won't be a next time.

[Kinger]

You should not have to remove the main gear to drop the clutch bell once you have sanded the fan shroud. At least I didn't anyway.

[vandelescrow]

Found a new thing to keep an eye on. I finaly been able to break the rebuit engine in and noticed the tracking was a bit off. After looking I noticed the seesaw was loose and would wiggle. The two screws that hold the seesaw to the head were locktighted but backed out for some reason. I relocktighted them and will keep an eye on them.

Just thought yall would want to know to keep an eye on it.

Also I upgraded the tail to the Goebee belt driven, no more stripped gears in the tail for me. It seems to be working just fine, only had to adjust the tension once, other than initial install. The gear that comes with it (autorotation gear) is much more sturdy than the TT. It has a metal "collar" (I guess you could say) that bolts to the gear just like the one way bearing does to the main gear. Don't have to worry about worping the gear by tightening the bolt to tight. When I ordered it from Goebee via phone, I had allot of questions. One question was "will the TT carbon boom fit with this mod?" the answer is no because the boom is actualy longer than the TT. Not sure how much longer, I have not measured them yet, will have to get back to you on that, but it is like making the 90 into a Titan 90

[JimLerch]

Also I upgraded the tail to the Goebee belt driven, no more stripped gears in the tail for me.

Hmmm???? More info on this mod please :YeaBaby: What parts are needed, any pictures? (Not a fan of Torque Tube tail drives..)

[vandelescrow]

Here is a link to it http://www.gohbee.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=GB111&Category_Code=1110
Everything you need is included and it comes almost completely assembled, $140. They sell a "speedup gear" (you need 2 for $25 each) where the tail will spin faster. I do not have them yet but wondering what it will do to the gain on the gyro.

P.S. everything you see in the photo is included