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Home✈️Aircraft🚁Helicoptere-AlignT-REX 500 › TRex 500, Scale Body Conversion issue
05-11-2018 04:07 AM  19 months ago
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Baton Rouge Louisiana USA

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TRex 500, Scale Body Conversion issue
My TRex 500 flew fine until I decided to insert the mechanics in a Scale Body.

I am using a Skookum 720 and pretty familiar with them. I have several and set up over 10 Heli's with this gyro.

First, I set my Head Speed to 1,800 rpms during the conversion. No other changes made except I went through the entire setup process with the Skookum 720.

I set everything up and it bench tested fine.

My first flight it was turning to the left, and I was having to give it right rudders to stay steady.

Shortly, I recheck and calibrated my tail settings about 5 times. After testing, I tried a few things to see if it helped, that's all it did was help.

The last two times I flew it, everything was working fine except the rudder. I constantly had to give it right rudder to stabilize the Heli.

I like to use my kill switch about 4 to 6 inches off the ground when landing. In doing so, as soon as I cut power, I immediately had to give it left rudder.

Long story Short. I did this two times. I bench tested the Heli with the main rotors removed, it never moved, and I didn't touch the tail. I tested and checked everything.

First thought, excessive main rotor torque due to the additional weight.

My theory is the mechanics/gyro will not handle the extra weight. I paid close attention to the tail rotor, and to keep it straight, the tail blades were struggling and I was pushing hard to the right to stay stable.

I may be way off with this, but I believe the extra weight is requiring several more degrees lift just to get it off the ground, therefore causing extra torque on the Heli.

The Skookum gyro is trying to correct, but the tail just doesn't have the strength to keep it straight. It's obvious just listening to the tail blades in action.

I am looking for suggestions. I thought about using larger tail blades, and maybe trying a lower head rpm setting.

What is your thoughts or suggestions. Everything else is working fine. I have a Trex 600 & 700, same gyro, both fly great, and my 500 did until I slipped it in a Scale Fuselage, AS 350. I love the Scale Body.

I have a MD 500 Scale Body on my TRex 600 and never had an issue with it flying. In Fact, it flew great!

I am a sport flyer, no 3D at all.

Thanks, Dennis
05-11-2018 05:04 PM  19 months ago
Heli Fanatix


Fountain Valley, CA

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Your Head Speed is about 1,000 rpm from normal HS. Usually at 2,600 we would have more tail authority.

Adding the scale body adds more mass and to be fair, your Trex 500 is not a Trex 600 and your Trex 700 is not the same as your Trex 600. There are forces at work that are out of the level of thought process at the moment.

This would explain why:
- you would have to constantly give right rudder to correct the torque of main blades.
- when you cut the power, you have to give left rudder to offset the right rudder you have been over compensating with

Typically the gyro would take care of this for you in the tail compensation. In the meantime:

- try a higher head speed
- maybe a little bigger tail on your 2 bladed tail just to test, at least a wider chord
- if the above two helps, consider a 3 bladed tail to give more tail authority?

So you kinda answered you own question sir
05-12-2018 04:30 AM  19 months ago


Baton Rouge Louisiana USA

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Thanks Scott for the reply,

All makes sense. Increasing head speed and trying larger tail blades makes a lot of sense. Plus there are the 2 easiest items to try. My tail rotor pushrod is secure, and is not giving during flight. Flight is smooth, no tweaking the gyro required there.

I wanted something smaller to practice with, but vibrations were always a problem with the 450's. This is the only reason I decided to try the 500.

Trying another gyro is another option.

The 600 is my favorite with the MD500 Scale Fuselage. NO problems with it.

Again, Thanks for the info, I will let you know how everything turns out. Hopefully I will get to fly this weekend. The weather is looking good.

05-12-2018 09:13 PM  19 months ago

rrKey Veteran

Morgan Hill, CA. USA

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Unless the T500 tailrotor drive shaft / pitch slider is the same as the 550 / 600, there will be no Align option for a 3-bladed tail.
RC-TEK has one for the 500, but it is kind of price-y

however, what you describe is not a "tail blowout".
You see that when a tailrotor RPM is too low or smallish blades.
A blow-out comes from the tail blades stalling (too much pitch for the blade size at too low an RPM) and the loss of counter-torque allows the tail to whip around (typically stopping around 180* from the original direction).

Yours is simply flying with right-rudder input needed. Not blowing out.

Here is something to think about:
Because of the low headspeed, the tailrotor may be running out of pitch travel or the servo arm is moving out of its best angle range.
Especially with the old-school Skookum (I used the 540 / 720 until I gave up on Skookum in general)

I would suggest starting with setting up the tail the way Align designed it.
1) Set the TR servo arm at 90* (use FBL servo travel to achieve that 90* point).
Once this is set, do not touch the servo's center point adjustment again.
2) Adjust the servo travel end points to achieve maximum "lock to lock" travel of the pitch slider.
It you cannot get lock-to-lock pitch slider travel, move the ball out one hole on the servo arm until you can get lock-to-lock pitch slider travel.
So far, this is the "typical" setup for a tailrotor.

This is the tricky part:
3) Set the 720's tail rotor to "Rate" mode. Normally, everyone flies in "Heading Hold" mode.
In the 720, that means the gyro gain on the TX is 0 to -100% (as I recall) instead of 0 to +100%.

Take off into a hover.
Be ready: You will have to fly the tail - something you may have never done before.
Apply rudder stick to counter the yaw.
Now land and adjust the tail-rotor control rod ball-links (longer or shorter) to add / subtract tailrotor pitch in the same direction you had to add rudder stick.
Fly it again and confirm you are adding less rudder stick.
Land, and adjust some more.

Do this until the heli heli will hover mostly without any constant rudder correction in one direction.
It should only need a little left or right input to maintain its heading.

4) Change back to Heading Hold mode and fly it normally.
+ > ÷
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