|Feb 27, 2012, 01:10 PM|
Tail rotor set up for 450 size MD500E
I tried to do a search but so far I haven't found the answer to my challenge. Here goes: I installed an old Align 450 SA frame into my new Align MD500E (Blue tail) fuse. I thought it was going fine i.e. tail rotor was spinning freely and in the right direction i.e. up into the main rotor wash CCW, no binding or hitting of servo arms with full cyclic and collective movements. But then when putting in rudder input - left I think - the tail rotor blades hit the scale tail boom. Now, I had centered the servo arm on the rudder servo (Hitec HS 81) by passing the gyro to get my 90 and then re connected gyro and so on. I did have to reverse both rudder and gyro channels to get the tail moving the correct direction.
Since I have to make travel adjustments using the gyro (Futaba GY401) potentiometer and the scale fuse pretty much makes access to the gyro impossible I am faced with having to disassemble the tail again to get the mechanics out and make the adjustment. I will mark the location on the tail slider before taking things apart so I have a good idea where to set the limit so the blades don't hit the boom.
Anyone else run into this issue and if so what was your solution? A friend of mine suggested cutting a hole in the fuse to get a long screwdriver down to the gyro. Not sure I am crazy about this idea but neither am I happy about having to disassemble the tail to remove from the fuse...
|Mar 15, 2012, 06:30 AM|
Joined Feb 2008
Unfortunately, your friend is correct. To properly adjust travel on the 401 via the potentiometer, you will have to drill a hole in your fuse. It doesn't have to be a gaping hole just big enough for your "tweaker" screwdriver device. The "pot" on the 401 will limit travel. HOWEVER, with this travel limit that you just imposed you WILL lose tail authority. There are "workarounds" to this and it falls within two basic camps (or schools of thought, if you prefer):
A. Speed up the tail. This can be done (and has been in the past, a user/poster here has done it; a.k.a SUPERHORNET). From what I have read and remember, he was successful. That being said, the modifications to the tail drive were not for the meek or the timid. Basically he replaced the gearing within the tail drive assy in total. Normally the 450's run with about a 4 :1 (guestimate, it is acually is a little higher..but I'm getting old, and I don't remember the exact figure..this is close enough). With this stock gear ratio this was acceptable for pod and boom, and everybody was happy. Whe scale in 450 expanded, then the issue became more appearant. With the enclusion of some fuses, you lost a little in the tail, so hence people playing around to fix. Usually however if you keep her two bladed, you don't see too much of an issue. This issue always presents itself when going multi-blade (i.e more than two main blades). There are several posts and threads by him, your best bet is to do a search on this forum for them. But be prepared to do some modifications, and spend some dough doing so.
B. Multi-blade your tail / upsize your tail blades. Ok, I lumped these two diverse options in one catagory because in the end result you attain the same goal .. MORE tail rotor surface area pushing air to correct the tail. Basically stated, you can either purchase a mutli-bladed tail rotor (more blades, more air movement) , or you can attempt to get a 500 sized tail blade to fit a 450 hub. There is one more option that requires less sanding, but you kinda get into the "McGyver" thing with it. It is possible to cobble together a tail hub using 500 sized grips and fit it to the 450 tail drive shaft. I have done it, I never really tested it out, due to once I built the unit, I started to re-think the weight of the assy turning on the 450 drive shaft (it is smaller in diameter than the stock 500 shaft). I have one built, but never flew it. The problem with going bigger in blade/s is the amount of mass that you are moving, and the fact that you have to heavily modify the blade, hub, ect. to do it. Add that to the fact that the little sucker is turning at a high rate of speed, well... I just get kinda "antsy" about the whole thing.
What I ended up doing is going multi-blade on my tail. I use a three bladed tail with stock 61mm blades. The weight difference should be evenly spread at 120 degrees across your rotor disc, and should present less of an issue for you (my opinion here..and no, I don't work for NASA, or Hughes, or Bell). I have found that with my Hughes 500D with the 5 blade mains, this works well for me. There are a few posters out there that will say this isn't scale looking enough, but I don't care. If you really care that much, there are guys here that have done the "cascaded" 4 bladed tail. This was an option that Hughes put out and so it does look more scale. The cascade design is the type that the AH-64 uses in its tail rotor system. The mods aren't two terrible, but to me, it seemed like a case of money (parts for mods) vs. work/effort (time, wich means more to me than money these days) for something that really, for me, was relatively minor in my book. You can make up you own mind about it. Do a search in the forum for "cascade tail" and you should find some stuff.
I hope through my ramblings this will present you some options. In short, yes you have a problem. How you eventually fix it, is up to you; as it is your heli after all, and all the badgering about which method is better than the other, in the end doesn't matter a hill of beans..you have to fly it regardless...
Hope this was helpful for you,
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