Review - Heim Joint's "Tennis Racket Effect" mod for helis

[Gutaaaooo]

Originally Posted by George Rillo

Are those the weight mods at the base of each blade grip? I love my furion but didn't know if it needed a kit. I was going to do some testing this weekend.

That is not a mod, it's how its made, stock form.

[Helico-pteron]

Why can't we just put nuts on both sides with a through bolt? Why does it have to be some specially designed weight screw assembly?

What exactly is this tennis racket effect? You guys mean bounce back?

[HEIM JOINT]

Originally Posted by Helico-pteron

Why can't we just put nuts on both sides with a through bolt? Why does it have to be some specially designed weight screw assembly?

What exactly is this tennis racket effect? You guys mean bounce back?

You may certainly do exactly that. Probably thousands of helis have a home made bolt, nut, washer, ball, ect. combo. There is nothing wrong with that. And if you test with some kind of force gage including your fingers you can add/remove weight untill you get low pushrod force.



But my Chinese bolt/nut sets have some advantages:

• They weigh less because the weight is concentrated further out from the blade feathering axis. This gives less additional centrifugal loading on the blade grip bearings
• The weights in each set are matched to within a few milligrams (.001g) to minimize any balance issues
• The nut on most styles is a metal self locking style so you can use loctite but fly immediately.
• You only have two pieces nut/bolt to mess with on a blade change. Not a stack of small pieces to loose at the field.
• They are precisely tuned at max speed using a force gage to give the lowest practical pushrod force.
• They save you time. A couple minutes to put mine on versus hours of your personal time doing trial & error testing.
• They add some Bling

When I am tuning the design of a nut/bolt set to get the forces close to zero. I am removing material from the end of the nut and bolt heads .003" at a time and testing the force each time. It is very sensitive. So thinking you are going to get close to zero force even when using somthing as small as a washer to tune with would certainly be luck.

Tennis raquet effect: Search HF for that and you will get a lot of info. I just dont have time right now to anwer this effectively but I will sometime.

Robin

[OICU812]

Robin, look forward to the release of your fix/improvement mentioned for the 250 for sure.

[Sam2b]

The only complaint I have is: the RPM of the tail rotor wasn't revealed. We know it is important to match the rpm in flight. That certainly matters. Otherwise this was a superb video presentation revealing critical information.

I use the G-force tail grips on my 600n and it has transformed the way the Spartan DS760 performs (using the JR8900G) and now with the Vbar. It is extremely smooth and consistent. So this mod (all of $2) is worth it's weight in gold.

When your tail is rock solid in the air AND smooth, your confidence may go through the roof. Just don't piro-flip better than me, okay?

[Sam2b]

Imagine the help the 90 size helicopter tails need!! Over 100mm of blade resistance, and using the same servo as the 50 size helis! Now imagine the performance increase...

[HEIM JOINT]

Originally Posted by Sam2b

The only complaint I have is: the RPM of the tail rotor wasn't revealed. We know it is important to match the rpm in flight. That certainly matters. Otherwise this was a superb video presentation revealing critical information.

I use the G-force tail grips on my 600n and it has transformed the way the Spartan DS760 performs (using the JR8900G) and now with the Vbar. It is extremely smooth and consistent. So this mod (all of $2) is worth it's weight in gold.

When your tail is rock solid in the air AND smooth, your confidence may go through the roof. Just don't piro-flip better than me, okay?

All tests I have done are at approximately max. headspeed for each heli. If it is just a tail run on the router I use the calculated max. tailrotor rpm for that heli. The tuning would still be good even if I did the tuning at slower rpm. The majority of the forces involved are the tennis racquet effect of the mass of the grips and blades not aerodynamic blade forces.

Robin

[HEIM JOINT]

Originally Posted by Sam2b

Imagine the help the 90 size helicopter tails need!! Over 100mm of blade resistance, and using the same servo as the 50 size helis! Now imagine the performance increase...

Imagine a servo motor pinion and first gear set for a servo that changes the gear ratio by a factor of two so your servo speed goes from .06 second/60 degree to .03 second/60 degree. Yes the torque will drop by a factor of two but who cares. My Chinese weights drop the pushrod force by a factor of at least 4 and in many case by a factor of 10.

Robin

[Sam2b]

The majority of the forces involved are the tennis racquet effect of the *mass* of the grips and blades not aerodynamic blade forces.

I agree except I feel strongly about the blades' wind resistance forces in effect additionally. One evidence is the increased torque (about double) required by the servo to deflect the blades.

Can we see a test with 105mm tail blades installed?

[HEIM JOINT]

Originally Posted by Sam2b

I agree except I feel strongly about the blades' wind resistance forces in effect additionally. One evidence is the increased torque (about double) required by the servo to deflect the blades.

Can we see a test with 105mm tail blades installed?

My testing shows an increase in going from a 90mm blade to a 105mm blade but not double. The picture below is the weights for the T600/700 Kasama. The bolt/nut set in the back is for the 90mm blades (600) and the set in the front is for the 105mm blades (700) notice the diference in the head thickness on the two sets. Yes some of what you are seeing is perspective but the 700 weights have heads that are 1mm (.0394")thicker. This is proof that a significant part of the tennis racquet forces are from the blade mass distribution being concentrated in a chordwise direction. I will agree that after about 20 degrees of pitch in a stationary test, aerodynamic forces start to be seen as an increase in pushrod force especially in the larger (600 and up) helis

Robin

[Sam2b]

Actually when I said "double", I was referring to the test before adding the blades, and then the test after adding the blades. ~15oz with out the blades, ~30oz with the blades.

Excellent footage and info. Thanks.

[3D Aviator]

Hey guys, I hope everything is well with all!!!

I'm sorry if I missed it, but is the mod for the Trex 450 V2 out yet?

Also, a big thanks to all, especially Heim Joint and Finless, for your hard work to make this average joe's heli fly that much better!!!!

[HEIM JOINT]

Originally Posted by 3D Aviator

Hey guys, I hope everything is well with all!!!

I'm sorry if I missed it, but is the mod for the Trex 450 V2 out yet?

Also, a big thanks to all, especially Heim Joint and Finless, for your hard work to make this average joe's heli fly that much better!!!!

They will start shipping this week.

Thanks, HJ

[Rªzª]

Hey HJ. Got my set of 500 and 600 weights. Thanks much. I was wondering tho, how efficiently are you balancing them now-a-days? Just wondering if you're getting feedback that is reason enough for adjustments to not remove so much of the torque. I've heard by a few that the mods are too balanced and you are removing too much of the torque which allows slack and play in the tail system to be more prevalent than it should be. I don't know if this is still the case tho.

I don't really understand the physics behind the effect you are counteracting here, but if I wanted to "tweak" my set could I just remove a tiny bit of weight to the inside (pointing towards the boom) weight so that I can add back a little more torque if I feel that the tail has too much play?

[HEIM JOINT]

Originally Posted by Rªzª

Hey HJ. Got my set of 500 and 600 weights. Thanks much. I was wondering tho, how efficiently are you balancing them now-a-days? Just wondering if you're getting feedback that is reason enough for adjustments to not remove so much of the torque. I've heard by a few that the mods are too balanced and you are removing too much of the torque which allows slack and play in the tail system to be more prevalent than it should be. I don't know if this is still the case tho.

I don't really understand the physics behind the effect you are counteracting here, but if I wanted to "tweak" my set could I just remove a tiny bit of weight to the inside (pointing towards the boom) weight so that I can add back a little more torque if I feel that the tail has too much play?

Yes you can remove material from the heads of the bolt and or nut to add back some more pushrod force. Just try to make your bolt and or nut weights match to keep things in ballance. My designs are now leaning toward leaving some residual force to keep a small load on the tail system.

Thanks for the feedback, It helps make products better. HJ

[jefierro]

Originally Posted by HEIM JOINT

They will start shipping this week.

Thanks, HJ

so you are taking orders now? looking forward.

[Motorman007]

Hey guys put your orders in so Heim can make a other run of his bolts again. So, I can get a set or 2..

Thank Heim for a great IDEA.

Motor

[levelflight]

Originally Posted by wrobijns

The TREX600 uses the same bladegripps as the 700.
But the tailblades on the 700 are bigger.
Can i still use the 600 mod on the 700, even if it may be off a bit.

And can I use anything for the Bade400? (indoor play thing)

You can swap the T-rex 450 tail on your 400 and then install the mod.

[progunpilot85]

got a set of these for a Raptor 50?

[HEIM JOINT]

Originally Posted by Raptorman37

got a set of these for a Raptor 50?

It is on the list. I am having a hard time keeping up with the Trex helis. I should be doing the raptor50 in the next few months.

Thanks HJ