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MTA Hobbies . Model Rectifier Corp . RCHover

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e-Align T-REX 450-500-600 > T-REX 450 My chinese weight mod
 
 
e12ry
Heliman
Location: A.S.A.C.

thx tail_boomstrike....
what do u use for the weight.... bearing or ball linkage....??

- Let's Fly Guys.....!!!!!
11-27-2007 12:54 AM
 
 
Richardmid1
Senior Heliman
Location: Leeds, England

I had the same problem with wagging after I tryed this mod and had to turn the gain right down which defeated the object!
11-30-2007 11:55 AM
 
 
Gary H
Senior Heliman
Location: Minnesota USA

e12ry, I am going to try the bearings, I think they weigh more, we will c soon.

Gary H
11-30-2007 12:52 PM
 
 
helimatt
Elite Veteran
Location: Lafayette, IN

Tail_BoomsStrike, excellent post and in my opinion quite complete and correct. Good illustrations, thanks for putting this together.

By the way, the force which tends to throw an orbiting mass outward is "centrifugal", while a force which holds a mass in toward the center is "centripetal"

The word used in the post "centrifetal" = "centered toward the baby".

I think the bounce during stops that some have after the mod might mean that there is too much weight added- try putting something lighter in place of what was used to somewhat decrease the counterbalance affect. Too much mass added would then make the grips want to move to a 90deg pitch orientation (too far), or float a bit which, if there is some slop in the system would make the tail control have a difficult time finding center.

Interestingly, I tried this with one ball on one side of the grip (didn't have a longer bolt at the time) and it made no apparent improvement. I think this unbalanced the grip and put too much moment load on the grip bearings. Gonna try a better setup next time I mess with the 450.

As for different ways to do this mod.. a third option is the NIX tail assembly which has counterbalance mass integral to the grip design as it comes.

http://trextuning.com/nix_tail_assembly.php

I'd like to try this one when I have $80 or so to spend on the little heli.

Never, ever, ever, ever give up.
11-30-2007 01:53 PM
 
 
Ken Filloon
Senior Heliman
Location: Highland, Michigan

I put 5 more flights on the Trex with the tail mod last night flying in a golf dome.
All I can say is, Iam impressed with the way this mod works.
The tail has a very solid locked in feel during fast backwards inverted and inverted tail in funnels. Piro rates are very consistent and strong. I really like this mod and recommend giving it a try.
12-01-2007 03:09 AM
 
 
Tail_BoomStrike
Veteran
Location: Virginia Beach

Quote 
The word used in the post "centrifetal" = "centered toward the baby".

centripetal force means "center seeking" force.


So "centrifetal", should be "center seeking" fetus...

Thanks for the correction BTW...

Oh, centrifugal almost sound like "frugal" it could maybe mean center seeking cheap bastard....
12-01-2007 05:29 AM
 
 
martinic
Veteran
Location: NB, Canada

Quote 
I'd like to try this one when I have $80 or so to spend on the little heli.

GForce is making Trex 450 weighted tail grips (GFT6010) and dealers have them listed for $26 US. RC Hover has them listed, but they're not in stock. That's better than $80 for the NCIX ones. I also wouldn't be suprised if Align offered weighted grips soon.
12-01-2007 10:11 AM
 
 
DenisS
Key Veteran
Location: Essex, UK

Somewhere around 1986 or 1987 I think Robert Gorham was doing this mod to his Cobras and stuff, and I think the design of the early Xcell tail blades incorperated the leading edge weight to offset the forces, so there is nothing new with this idea (as with many other ideas). I'll try to find the article in one of my old mags. He used longer bolts with nuts and washers to 'tune' the response.
Denis

Crash 'n Lurn
12-05-2007 06:41 PM
 
 
heli_headcase
Key Veteran
Location: Hovering around Atlanta

More Info...

Tail_BoomStrike: Very good pictures and diagrams. Yeah, the "inward seeking fetus" had me confused but I got over it

As to the weighted X-Cell tail blades - the weight was an extension of the blades' root, probably intending to counter the natural tenancy of the blade mass to force the blades to lead (vs lag) in the grips. It's not at all effective as it only makes matters worse as far as this subject of servo loading is concerned. I'd like to hear of Gorham's testing as this a bit of news to me. FYI: Gazaur has two e-heli's, the Poseidon and Mars, that feature bullet-shaped weights on the leading edge side of the blade root. They claim this weight removes the tenancy for the blades to lead also.

Now on to the Chinese weights again. Read my posting down at the bottom of this thread and then check my gallery under the Heli-Max MX400, Heli-Max MX450XS and Dragonus 450 Elite headers for my tail grip mods. Try not to read or look at everything else. You'll never get out alive

http://runryder.com/helicopter/t357197p1/?p=3019877#RR


HHC

So many heli's - too little time...
12-05-2007 09:49 PM
 
 
Tail_BoomStrike
Veteran
Location: Virginia Beach

HH

I see the wisdom in the mod in your link......

And yeah I forgot to mention the blade has more profound effect on the tails tendency to center 0* pitch. The aerodynamic combined with centrifugal force acting on it.....

Double sided chinese weight though provides and almost zero tendency for the blades to track 0*..... And it works on both side of the 0* pitch, compared to the one you did which reduce the load on the servo only at rest , when no rudder input......
12-07-2007 08:54 PM
 
 
heli_headcase
Key Veteran
Location: Hovering around Atlanta

Clarification needed.

Quote 
Double sided chinese weight though provides and almost zero tendency for the blades to track 0*..... And it works on both side of the 0* pitch, compared to the one you did which reduce the load on the servo only at rest , when no rudder input......

I don't follow what you're trying to say. Maybe you're implying the single-ended weight (on the right-hand side) of the tail grip only works when pitch (for counter torque OR assisting torque) is commanded. If I'm understanding that as your evaluation then I have to tell you the single weight works perfectly for both directions.

There's a good and bad side to the single and double weights. If you think of a static "skids down" hover with a clockwise rotating main rotor, the tail blades are producing thrust to push the tail boom to the left. The tips of the tail blades are effectively coning towards the left. The tail blades are causing bending forces on the tail grips and hub. If a single weight is installed so its mass is on the left side of the tail grip/blade set, the outward centrifugal moment on the weight will provide as a lever into the grip and counter the bending tenancy of the coning blades. Neat, huh? Too bad I'm not using that method of thinking for all my tail rotors but there's a reason. The space available on the left of all these tail rotor systems is limited by the location of the pitch changing mechanism. A shorter length of weight stand-off means more mass is needed to provide the required amount of "anti-tennis racquet" effect. More weight means more load on the already stressed tail rotor hub and bearings.

I've never checked the grip bending action vs the weights inboard or outboard but my mechanical sense is pretty good and my theory should stand up to strong scrutiny. Anyway, does this cover your concerns? If not, please try again to explain the problem here.


HHC

So many heli's - too little time...
12-07-2007 09:22 PM
 
 
Tail_BoomStrike
Veteran
Location: Virginia Beach

HH

I thought about what you just explained.... Indeed you are correct.... Single sided chinese weight would provide the same result....

For others that reported they experienced wagging when they did the mod.... Try replacing the bearings on the grip..... Mine worked flawlessly for several weeks... Then started developing wags.... troubleshooting revealed that the bearings in one of the grips went bad and no longer operate smoothly...... I can't attribute this to the chinese weight mod, since the bearings were almost a year old, and had been through several crashes..... I had it replaced, and once again operating smoothly. This time I will find out how long will the bearings last with the added weights.......
12-08-2007 12:58 AM
 
 
Justin911
Senior Heliman
Location: San Diego, CA - USA

thats a killer idea.. i think i will do that to mine instead of drilling the blade grips and running a chance of messing it up!
12-08-2007 01:20 AM
HOMEPAGE  
 
 
Tail_BoomStrike
Veteran
Location: Virginia Beach



Above is what I believe the tennis racket effect......

In the bottom drawing, it shows the tennis racket is attached to a spinning pole by a string, so it can change angle freely. The yellow line shows the heavy ring of the racket is not aligned to the plane of rotation. At center of the racket, air can flow freely, so weathervaning to the wind is considered non-existent, that's why tennis racket and not ping pong paddle was used. So basical, if the racket twist away from this orientation, which it will, it's all due to centrifugal force. Now, the centrifugal effect on the mass of the ring is suppose to be directed outward from the center of the plane of rotation as a straight line tracking the circular plane. Not at an angle from the circular plane plane. So the natural tendency is that the heavy ring of the racket will seek the plane of rotation and flatten as in the top drawing....

So as with our tail rotor blades unless we add weights at 90* angle, the "tennis racket effect" and the weather vaning due to its flat surface causes the natural tendency to return to 0* pitch. This put a lot of load to the tail servo.......
12-09-2007 03:58 AM
 
 
heli_headcase
Key Veteran
Location: Hovering around Atlanta

You got it!

That's a clear diagram. I like it.

As to the aerodynamic flattening effect - That only happens if the blade airfoil is "stable", meaning it wants to go flat and not go divergent. Stability is had from the airfoil center of pressure location vs the center of mass (gravity). I don't think I can describe all the varying factors involved on a pure engineering level but have a good basic understanding of the interaction of the forces involved, good enough in fact that I can design from scratch a tailless (flying wing) aircraft with "perfect" handling qualities and no stability issues. The single tail blade consists of a real airfoil and is subjected to all the physical laws any other wing experiences. Saying this, there are no tail blades that are inherently stable and all want to change pitch (positive or negative) if left to fly unrestrained in a straight line. The location of the blade anchor point, the bolt at its root, relative to the center of mass of the blade, gives the blade a forward or leading tenancy in relation to its pivot or "feathering" axis. This places more blade area forward of the feathering point and makes for a blade that is trying to add pitch to itself without outside input.

It's the "self pitching effect" I was investigating on my Concept 60 which then uncovered the "tennis racket effect". Clearly the centrifugal flattening force is overcoming the self pitching or our tail rotors would behave rather erratically.

Miniature aircraft did what they thought best in their plastic tail blade design in the inception of the X-Cell line of helicopters. The blades were molded plastic with two charicteristics no longer seen on today's blades: Weighted Roots by using extra material in front of the attachment bolt and a "Reflexed" trailing edge, an "up elevator" trim if you will. I'm willing to bet the up trip helped reduce the servo load at hover pitch, tail trim neutral. This would probably provide a mild tail thrust to counter main rotor torque under hover conditions only. I need to test this theory some time.


HHC

So many heli's - too little time...
12-09-2007 04:25 AM
 
 
jhamlinjr
Veteran
Location: Milledgeville, GA, United States

So what is best, one sided weight or one on each side?
12-09-2007 05:07 AM
 
 
Tail_BoomStrike
Veteran
Location: Virginia Beach

My preference is of the double sided, since I do more 3D flying than scale flying.....
12-09-2007 05:23 AM
 
 
heli_headcase
Key Veteran
Location: Hovering around Atlanta

What is the "best" anyway...?

Quote 
So what is best, one sided weight or one on each side?

In my opinion, you'd have to compromise and put as much weight on the inboard and outboard sides as needed to get a hint of self-centering and then try biasing the weights *toward the direction of thrust*. For a clockwise turning main rotor, with the tail rotor situated on the right (starboard) side of the tail boom, more weight should be on the left side of the grips...assuming most of your flying is using nose-right tail commands.

If you're primarily flying 3D and the tail is pushed hard both ways, there's not much reason to worry about the weight bias unless you gravitate toward hard tail moves that cause the heli chassis to rotate the same direction as the main rotor system. If that's the case then again, try to place the majority of the counterbalance mass on the left of the grips. Make sure the pitch mechanism isn't contacted by the weights.

Follow?


HHC

So many heli's - too little time...
12-09-2007 05:25 AM
 
 
jhamlinjr
Veteran
Location: Milledgeville, GA, United States

Gotcha! Im into 3d so I guess it wouldnt matter. I was checking out the G-force grips on Rchover. I wonder when they will be available? I would like to try those out.

heli headcase- Damn impressive gallery! Did you work with NRI and the Autocopter Express A or someone that had one?
12-09-2007 05:41 AM
 
 
DenisS
Key Veteran
Location: Essex, UK

As promised I have found the article regarding this mod-it is reproduced here from Radio Controlled Helicopters, Autumn/Winter 1985. There were no diagrams but the explanation seems clear enough. John Wallington is still around I'm sure. I thought it was Robert Gorham but I was wrong (it WAS a long time ago).

Improving tail stability and gyro response
One such innovation which recently came from John Wallington — current British FAI Champion and manager of "Slough Radio Control Models" is the use of bob weights on the tail blades to increase stability and tail control.
Last article we talked about increasing the gyro rate until the tail started to wag then turning the rate back until it stopped. However gyro feedback can still be produced by changing conditions or forward speed. Even if you have a second rate to utilize, this still does not cover all eventualities.
We also looked at lateral centre of gravity balancing of the main rotor blades and how this helped the general stability and performance of the blade if it was about 25% to 30% of the chord.
This seems to apply equally to the tail rotors and if the chord wise C of G is adjusted similarly stability increases.
Unfortunately most tail blade holders are of light construction to keep the rear of the helicopter as light as possible. Therefore the tail blades must also be kept light to prevent too much centrifugal force pulling them from the holders. Adding any extra weight to the leading edge of the tail blades would be distinctly dodgy (colloquial expression for 'definitely not on mate'.
So to make the C of G further forward John uses small weights attached to arms, bolted to the tail holders themselves and projecting forward in the direction of rotation.
These of course must be balanced and identically positioned to prevent any tail vibration.
I experimented with thin strips of aluminium about one and a quarter inches long, one quarter of an inch wide and about 1mm thick. These were bolted to the tail holder using the two bolts already in position which held the two halves of the tail holders together. I used the upper two bolts to get the strip as near to the tail blade as possible and bolted one strip to each holder so that it projected forward at 90° to the tail blade. They can be put onto the front or the back of the holder. I had already put a 3mm hold in the leading end of each strip and proceeded to experiment with bolting various lengths of 3mm bolt into the holes to bring the tail C of G forward. The exact weight I cannot tell you as it depends on the speed of the tail rotor. Certainly if you have too much the tail becomes dead and too little causes no noticeable change from normal. When it is about right you can turn the gyro rate up to nearly full without tail wag and the stability is pure magic!
Note — I used the smallest bolt possible in the end but I am still testing as the next stage is to increase tail response on the servo and then start the whole process again.
Reproduced from an article by John Griffiths in Radio Controlled Helicopters Autumn/Winter 1985
Hope you all appreciate this, took me looking through about 200 copies in my workshop before I found it on my bench at home

Crash 'n Lurn
12-17-2007 09:21 PM
 
 
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e-Align T-REX 450-500-600 > T-REX 450 My chinese weight mod
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