How tight should the grips hold the blades?

[PaoloFCantoni]

As my helis have grown larger, the grips have held the blades tighter (both mains and tails).

My current blade settings are tracking almost "spot on", so I'm loath to change them. However, I'll be changing the blades in a while so I wondered if there was any mechanism for determining how tight to have the grips.

Some of the diagrams in the build give pretty precise tensioning instructions; such as the M3 screws into the bottom composite frame.

Any such instructions for the blades?

TIA,
Paolo

[Colin Broughton]

I cant find the video but i put heli horizontal with blades horizontal and give it a good jerk motion and they should just ever so slightly tilt towards the floor

[TheBum]

I like to keep my blades rather tight to prevent boom strikes on botched autos. There is plenty of mass in the blades for them to straighten out when they’re really tight.

[PaoloFCantoni]

Thanks, guys,

Food for thought. I have one of those luggage scales (with the hook) and I might see what "force" is required to overcome static friction on my current setup. I'll report back when I've tried it.

Paolo

[Michaelinpr]

On my 700 & 780 I tighten the blades just to the point that I have to hold the head to fold the blade back by hand. Meaning it is just slightly difficult to fold the blades by holding both blades at the same time. One will fold but it makes the other hard to fold once one blade has moved. Make sense? At this tension they basically act as described in Colin's test.

[jhamel]

Day 1 Part 3 - Blade Grip Torque (3 min 39 sec)

He goes over the detrimental effects of having the blades to loose like the helicopter possibly rolling over on the ground during spoolup or blades folding from fast spooling when bailing out of a botched autorotation. However, it is a bit unclear to me what detrimental effects one experiences when the blades are too tight.

[PaoloFCantoni]

Originally Posted by Michaelinpr

On my 700 & 780 I tighten the blades just to the point that I have to hold the head to fold the blade back by hand. Meaning it is just slightly difficult to fold the blades by holding both blades at the same time. One will fold but it makes the other hard to fold once one blade has moved. Make sense? At this tension they basically act as described in Colin's test.

I think mine are slightly looser than this, but still tight enough to pass the "jerk" test as described by Colin and shown in the video provided by curmudgeon.

FWIW, I measured the tension required to move the blades and it came to approx 200g measured at the far edge of the blade (@700mm), holding the head firmly in my other hand. That is, as I pulled the scale (and hence the blade) toward me, the scale built up to 200g and then the blade moved. There was a slight differential between one blade and the other which I have now correct, but nothing I'd consider significant.

I think, based on all the inputs, I'm happy with both the tracking and the tightness of the grips. So, thanks for all the input.

As to curmudgeon's question about the deleterious effects of too tight grips. If they are too tight to swivel properly, and the blades are out of alignment along the feathering shaft, might one expect some vibration to be induced due to the differential moment of inertia?

Paolo

[quinn]

Yes, if they are too tight you can get vibrations at lower head speed. Usually when I do low head speed flying, I'll flip to my highest head speed first to straighten the blades out, then go to the lower speed. Even then though, sometimes blades will lead or lag during certain maneuvers and can get stuck there giving occasional vibes so definitely don't want the blades too tight.

[TheBum]

I used to run the blades according to "conventional wisdom", which resulted in dings in my boom on botched autos. I run them tighter than most people because I don't want that happening again.