Belt 6HV FBL conversion

[jperkosk]

Originally Posted by sutty

Forgive me for making a suggestion with no knowledge of the heli itself, but it looks to me like the blades are too loose. I think, and I do say think, I can see them collapse significantly on spool up. Sudden deceleration might have a similar if smaller reverse effect, but it could perhaps put it well out of balance. As I say, don't have experience of the heli, and I follow the logic of the wobbly skids argument, but as I say the blades did look particularly loose to me.

Cheers

Sutty

They are, Andy, I normally don't tighten the blades very much. This can be an issue on the spool-up, definitely, but shouldn't affect anything on landing, should it? I land, and hit TH. At this moment the blades are perfectly balanced, and the ESC is cut out so it can't interfere. Then the rotor head passes through this 6HV ground resonance zone, the heli starts shaking and the blades will start folding making things worse.

My gut feeling is you're correct, probably tight blades will eliminate the problem by helping the head pass through the resonance zone without folding the blades, but I'd still like to get rid of this resonance, it feels nasty.

[jperkosk]

Put just under 1900 mAh back into the Hyperions, that's 72% of nominal 2600 mAh capacity. So I'll keep the HS at 2000 RPM and the timer at 8 min for now, that should be fine for putting around the sky

[sutty]

Grant told me that loose blades can actually fold in certain auto conditions, which is why he runs his tighter than most. Autos are not something I concern myself with, but if they can fold under certain auto conditions, perhaps, and I do say perhaps, even on spool down you may get exaggerated and unequal lag in the blades, which would throw the balance off.

Perhaps couldn't hurt, as a trial, to run them tighter just the once to see. The only issue that I see from trying that is that if it is as a result of the ground resonance described, and you do get a tip over, tighter blades migh cause more damage to the blages?

Anyway, whatever the result, I will be interested to hear the outcome. I expect you're feeling a little disappointed at the moment.

Cheers

Sutty

[sutty]

One other thing Jerry. FBL is prone to differing levels of sensitivity of collective depending on the blades. All of my helis are now super sensitive on collective and a handful to land gently. I have just learned to cope, even in very bad wind where it is worse affected. Tried a modified pitch curve, with expo smoothing applied, but it didn't work for me. Your controller probably has a feature built in where you can smooth it out and tame it down though, so perhaps that could help. I only just found out that it was the blades that cause this as Walter, aka labmaster, the senior MB developer at BeastX has just made a post about it in the MB FBL forum. Even offered to send a guy a modied firmware version to help him out. Thought that was quite cool. Anyway, I knew about the issue, some say soft in the middle, some say very harsh, and all in all it comes down to the blades. Who'd av thunked it, lol.

Cheers

Sutty

[jperkosk]

OK, point well taken. Will move the head AND tighten the hell out of the blades .

Disappointed, not really... That thing was up in the air and didn't move much in gusts that were making ME brace up, German engineering at it's best. Unfortunately 6HV doesn't have the built-in wind indicator that nitros have , but I filmed the club's wind sleeve at the beginning of the first clip, so you can get an idea... Collective wasn't much of an issue, I managed to land softly all 5 times once I decided I just needed to wait out the worst of the wind up in the air.

But ground resonance ??? Give me a break...
https://www.helifreak.com/showthread.php?t=298874

Now I know how Panzer division commander felt when he had Moscow in sight, not much of opposition any more, and he found out his tanks engines all seized up in -40°C

So boy, it can fly, it just can't land afterwards

[DominicD]

Why on earth are you running blades loose ? You are always better off running them as tight as you can get.

[ragge1]

Originally Posted by jperkosk

Ragge, have you been landing on paved surface?

outside my house is asphalt and I do all my testing there , or if I just want to hover , no issues

[ragge1]

with the HW70 ESC , you get a kick with spoolup so you need to tighten your blades but it you update with the Turnigy firmware v: 1.07 then you are ok with loose blades ( not to loose ) link

[sutty]

Don't go mad Jerry, "tighten the hell out of them", lol. Gotto move in flight to help dampen pitching up tendencies and reduce vibration. See I've been reading the TDR manual Raf posted, lol. Just not so loose so that they collapse back when doing a fairly soft looking spool up.

Cheers

Sutty

[ragge1]

a small test for you Jerry , its dark outside and my wife with my cellphone , hope its not to dark my blade are abit loose

6HV test (0 min 53 sec)

[jperkosk]

Wow, as smooth as my Trexes!!!

1. Did you hit TH on landing or just pulled down on the stick in normal mode?
2. I definitely want the firmware upgrade. Got the HW programming interface with my FBL conversion order, but it turns out to be the simple LED one, can't flash the firmware with it, so I have to live with the kicking for another couple of months at least...

[jperkosk]

Originally Posted by DominicD

Why on earth are you running blades loose ? You are always better off running them as tight as you can get.

Haven't ever spooled up fully a stock Belt CP with the blades super-tight, have you?

Seriously, helps with the self-alignment of the blades in flight, reduces vibrations. I will set-up SL bailout in the SK720 so I need to keep the vibs as low as possible.

Obviously, tight blades have some drawbacks, too, as you were kind to point out AFTER my 6HV has tipped over (just kidding, really appreciate all your input)

[ragge1]

I hit the TH , like of used to that

[dauste]

Originally Posted by sutty

Don't go mad Jerry, "tighten the hell out of them", lol. Gotto move in flight to help dampen pitching up tendencies and reduce vibration. See I've been reading the TDR manual Raf posted, lol. Just not so loose so that they collapse back when doing a fairly soft looking spool up.

Cheers

Sutty

Just to give you guys an idea of how tight Grant runs his blades... I was helping packup his helis in Venlo and went to fold the blades back... it didn't happen! He looked over and said 'You may need to put your knee on those to start them off'

He was right, I actually did need to stick me knee on the grips!

[jperkosk]

Wow, that's tight alright !

Apparently Grant hasn't flown his stock Belt CP in a while either, has he ?

[sutty]

Hey, I was all for super tight blades based on what Grant showed me with his. First hand experience of this just like Dave, but despite how he might run them and what Dominic is saying, I cannot get way from what I just recently read in the TDR manual. That guy really knows his stuff. You can tell simply from reading the manual, not to mention that he has designed what is practically a world beating heli himself, so if he says they need to move in flight then I think they need to move. I quoted it in another thread recently, but he states, just like in the Belt-CP guide, they should be tight enough not to move under gravity when the heli is tipped on its side, and not much more. He then explains that this should be for all helis not just his and that it reduces vibrations and pitching up in forward flight.

If it helps any, to the best of my limited ability to explain what happens, and for those who might not know and want to, it is because the advancing blade, in forward flight, if the blades are stiff, will generate more lift as the airspeed will be higher over this blade when compared to the retreating blade. This causes a torque to be applied to the spinning rotor disc, essentially a gyroscope. A little counter intuitively, or at least to me, instead of causing the heli to roll to the right, gyroscopic precession causes the disc to pitch up, at a point 90 degrees to the applied torque. (We've all seen the strange motion of a gyro when a force is applied to the gimbal frame. Doesn't make sense to me, but it happens.)

Allowing the blades to move in the grips means that the higher airspeed over the advancing blade, and therfore higher drag, subjects the blade to sufficient force such that it will be forced back at an angle and lag behind the retreating blade. As it lags it is less efficient, and produces less lift, thereby significantly reducing the additional lift that it would have produced if the blade was fixed. Reducing this differential lift lessens the torque and therfore minimises the pitching up tendency.

Sorry if no one wanted to know, but I think it is kind of cool.

Cheers

Sutty

[DominicD]

Your idea of loose and Hensleit's idea of loose might be very different. Trust me on this one you will want to error on the side of too tight. The blades will move in flight, you will NOT be able to crank down on the 6HV grips enough to prevent this (the nylock will strip LONG before you get it tight enough to prevent the blades from shifting in flight). If the blades are too loose when you bog the head the blades will lag behind a little, which means they can get closer to the boom and potentially cause a boom strike.

Tighten the grips down, just not so much you strip out the inside of the nylocks.

[Castel]

^^^ That is actually pretty cool and a great explanation, thanks for sharing.

[sutty]

Originally Posted by DominicD

Your idea of loose and Hensleit's idea of loose might be very different. Trust me on this one you will want to error on the side of too tight. The blades will move in flight, you will NOT be able to crank down on the 6HV grips enough to prevent this (the nylock will strip LONG before you get it tight enough to prevent the blades from shifting in flight). If the blades are too loose when you bog the head the blades will lag behind a little, which means they can get closer to the boom and potentially cause a boom strike.

Tighten the grips down, just not so much you strip out the inside of the nylocks.

Yeah, that's fair enough Dominic, but the guy we were talking about, you couldn't move them without putting your knee on the head. Hensleit's idea of tight is clealy described in the manual. They should be tight enough just so as to not fall down when the heli is tipped on its side. As I said I don't know the 6HV first hand, so I was unaware that you couldn't get them ultra tight due to the design. Agreed you certainly don't want a boom strike in flight.

Cheers

Sutty

[jperkosk]

Nice one, Andy .

Don't want to sound like I'm pulling your leg again, but the wind has died almost completely now, sun is out full blast as it is most of the time, so time to slap these boom supports back on 6HV (CA on the nylon thread has dried out overnight), some sunscreen on my face (SPF15 will do this time of the year) and off to the field for another test flight !