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HomeAircraftHelicopterHIROBOHirobo SDX › D3 SWM SL rotor head
09-04-2018 09:48 PM  20 days agoPost 1
SD

rrNewbie

USA

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I have a recently built SDX with the D3 SWM SL rotor head. After flying it I have noticed thick, gray grease coming out of the rotor head assembly. The rotor head was preassembled at the factory and I did not take it apart. The helicopter flies well. Is it normal for excess grease to come out of the rotor head? I am wondering if I should take it apart and inspect it. Thanks.

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09-05-2018 12:42 AM  20 days agoPost 2
JLF92677

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Southern California

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If you are referring to grease coming out from the blade holders, then it is excess grease from the trust bearings. It was probably asssembled with perhaps more grease than needed. I would check that the blade holder button bolt is tight and secure.

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09-05-2018 01:53 AM  20 days agoPost 3
Dr.Ben

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Richmond, VA, USA

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Normal for Hirobo. They use a gray-black molybdenum grease. I'd have worried if some didn't sling out. You can vheck the spindle bolts, but Hirobo general does a goid job with torque and loctite.

Ben Minor

Peak Aircraft/Team Minicopter Team Futaba Team Kontronik USA

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09-05-2018 08:07 PM  19 days agoPost 4
SD

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USA

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Thanks for the replies. Yes, it is grease coming out from the blade holders. I am glad to hear that this is normal and is just excess grease from the thrust bearings. By the way, the manual states that the button bolts need to be replaced at regular intervals. How often should I be replacing the button bolts?

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09-06-2018 05:55 PM  18 days agoPost 5
JLF92677

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Southern California

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SD
By the way, the manual states that the button bolts need to be replaced at regular intervals. How often should I be replacing the button bolts?
Great question! Unfortunately Hirobo manual does not define “regular interval” time period or number of flights. Hence, it is left to one’s judgement. One can interpret “regular interval” when it is time to replace or relube bearings. However, at a minimum I would replace the blade holder/spindle button bolts if the rotor strikes the ground, as there is a possibility for over stressing the bolts. When replacing the button bolts make sure to replace them with genuine Hirobo bolts, as they are hardened steel bolts which aftermarket bolts may not meet the same tensile strength specifications. Also, it is very important not to exceed the max rotor head rpm specification limits.

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09-06-2018 06:59 PM  18 days agoPost 6
TMoore

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Cookeville, TN

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I don't use button head screws in rotor heads. It's a poor design choice. You can't get enough torque on them to do the job. Change them out with a set of SHCS' and washers.

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09-08-2018 06:03 PM  16 days agoPost 7
JLF92677

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Southern California

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TMoore
I don't use button head screws in rotor heads. It's a poor design choice. You can't get enough torque on them to do the job.
Never had a bid of problem with Hirobo rotor heads for more than 20 years of flying them.

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09-08-2018 07:37 PM  16 days agoPost 8
Dr.Ben

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Richmond, VA, USA

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Terry is right. I don't use them either. I use a 12.9 gr full size allen bolt. To give you an idea of proper torque, Minicopter specs about 80 in-pounds for the Diabolo 700. You can't apply that kind of torque to the button head bolts Hirobo uses. And neither Terry nor I use loctite that spindle bolt either. When torqued correctly, it never, ever, ever loosens up.

Ben Minor

Peak Aircraft/Team Minicopter Team Futaba Team Kontronik USA

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09-08-2018 08:20 PM  16 days agoPost 9
TMoore

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Cookeville, TN

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The first time I ever used loctite on a feathering spindle was on a Schluter Champion. I had to heat up the bolts to get them out and ruined the spindle. Never again. It's just not necessary to use loctite on these spindles but as Ben said you have to torque them to a spec and on this size fastener you just use the right tools. Spring bar style T wrenches from Eklind or a couple of torque wrenches from Harbor freight are your friends. There has to be some stretch on the tapped hole in the spindle to secure the bolts and that is exactly what gets stretched. Using hardened allen drivers is absolutely verboten here.

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09-09-2018 06:07 PM  15 days agoPost 10
JLF92677

rrApprentice

Southern California

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Dr.Ben
Terry is right. I don't use them either. I use a 12.9 gr full size allen bolt. To give you an idea of proper torque, Minicopter specs about 80 in-pounds for the Diabolo 700. You can't apply that kind of torque to the button head bolts Hirobo uses. And neither Terry nor I use loctite that spindle bolt either. When torqued correctly, it never, ever, ever loosens up.
Why are you comparing torque values for rotor head spindle bolts between Hirobo and Diabolo helicopters? The two are not even in the same class. The Diabolo is a speed helicopter pushing upwards of 150mph with rotor head speeds well north of 2000 rpms. Hirobo helicopter are F3C helis, some 3D with rotor head speeds of less than 2000 rpm. But you already know this. Hirobo spindle bolts torque value is 34.7 to 39.05 lbs-in vs 80 lbs-in for the Diabolo. Are you now questioning the adequacy of Hirobo’s design considering their reputation and the many World Championships they have won? Do you have data of Hirobo rotor heads coming apart because the spindle bold failed or came loose? I don’t think so.
TMoore
The first time I ever used loctite on a feathering spindle was on a Schluter Champion. I had to heat up the bolts to get them out and ruined the spindle. Never again.
You must have either used too much or the wrong Loctite. I have never had a problem releasing spindle bolts with blue Loctite.

On a separate note, SD opening post was with regard to “gray grease coming out of the rotor head assembly” followed by “How often should I be replacing the button bolts?” I am not sure how or why this post is now debating Hirobo spindle bolts torque values? I don’t know if SD is new to the hobby or not (joined RR on 8/3/2018), but this discussion sure does not help “beginners” get started, only adds to more confusion and deters on their confidence. Wonder why RR traffic is at an all-time low…?

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09-10-2018 09:18 PM  14 days agoPost 11
payne1967

rrElite Veteran

uk

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I've never used Loctite on my spindle bolts and have re-used them many times without failure

for those that have voiced about the Hirobo head and the speed it can handle, my SDX50 with the plastic head had the carb on an OS55 go south and the head was clocked at over 3000 rpm before I landed the model
the whole heli was checked over and nothing had failed Hirobo side of things
on the carb the barrel had worn sucking in lots of air
a new carb sorted the engine

www.alcesterhelicopterclub.bmfa.org

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09-10-2018 10:09 PM  14 days agoPost 12
TMoore

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Cookeville, TN

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JLF92677
Dr.Ben
Terry is right. I don't use them either. I use a 12.9 gr full size allen bolt. To give you an idea of proper torque, Minicopter specs about 80 in-pounds for the Diabolo 700. You can't apply that kind of torque to the button head bolts Hirobo uses. And neither Terry nor I use loctite that spindle bolt either. When torqued correctly, it never, ever, ever loosens up.
Why are you comparing torque values for rotor head spindle bolts between Hirobo and Diabolo helicopters? The two are not even in the same class. The Diabolo is a speed helicopter pushing upwards of 150mph with rotor head speeds well north of 2000 rpms. Hirobo helicopter are F3C helis, some 3D with rotor head speeds of less than 2000 rpm. But you already know this. Hirobo spindle bolts torque value is 34.7 to 39.05 lbs-in vs 80 lbs-in for the Diabolo. Are you now questioning the adequacy of Hirobo’s design considering their reputation and the many World Championships they have won? Do you have data of Hirobo rotor heads coming apart because the spindle bold failed or came loose? I don’t think so.
TMoore
The first time I ever used loctite on a feathering spindle was on a Schluter Champion. I had to heat up the bolts to get them out and ruined the spindle. Never again.
You must have either used too much or the wrong Loctite. I have never had a problem releasing spindle bolts with blue Loctite.

On a separate note, SD opening post was with regard to “gray grease coming out of the rotor head assembly” followed by “How often should I be replacing the button bolts?” I am not sure how or why this post is now debating Hirobo spindle bolts torque values? I don’t know if SD is new to the hobby or not (joined RR on 8/3/2018), but this discussion sure does not help “beginners” get started, only adds to more confusion and deters on their confidence. Wonder why RR traffic is at an all-time low…?
Good for you and BTW this isn't the beginner site. Just because my experience doesn't correllate with yours doesn't mean I'm wrong. Besides I'm not here to inspire confidence, you get that on your own. If you ask questions you get answers, if the thread drifts so what. That can happen in the course of normal conversations. If you want how to guides or want to minimize thread drift go to the Instructables website, I'm sure will find what you're looking for. If I sound pissy so what, I'm older now and I have way more experience than most . Don't like my answers; I dont care.

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09-23-2018 01:53 AM  2 days agoPost 13
John Benario

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Las Vegas

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While I value any advice from Terry and Dr. Ben, I do use Loctite on my spindle bolts. Clean bolts with a little bit of 290 and snug just enough not to bell mouth the end of the spindle. This method has worked for me with no failures since the late 80's.

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09-23-2018 01:31 PM  2 days agoPost 14
wjvail

rrKey Veteran

Meridian, Mississippi

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John Benario
While I value any advice from Terry and Dr. Ben, I do use Loctite on my spindle bolts. Clean bolts with a little bit of 290 and snug just enough not to bell mouth the end of the spindle. This method has worked for me with no failures since the late 80's.
One more data point... I'm with John on this one. I clean and Locktite and also use 290. John used the word snug but also said just enough not to bell mouth the end of the spindle. I think that is to say tighten really damn tight. Me, I use a couple of L Allen wrench. My goal is to stretch or pre-load that bolt if possible.

Just for kicks... Here is an on line centripetal force calculator.
http://www.calctool.org/CALC/phys/newtonian/centrifugal

I plugged in a few rough numbers:
Radius (approximate CG of a 700mm blade): 500mm
Angular Speed (head speed): 2,000
Mass (Weight of blade): 200 grams

The resultant force is nearly 1,000 pounds (986lbF). That is static force on a spindle bolt in a steady-state hover. Notice I plugged in fairly benign numbers. Loads will only go up with maneuvering and over-speeding. With nearly 1/2 a ton pulling on a single m6 bolt my goal is to make sure it stays in place.

"Well, Nothing bad can happen now."

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09-24-2018 03:07 AM  1 day agoPost 15
Dr.Ben

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Richmond, VA, USA

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Little detail in this discussion because I really hate misinformation. The torque specs I mentioned for interest and comparison for Minicopter were stated in the Diabolo 600 manual, not exactly a speed model. Minicopter makes a lot more models the the S. Speed versus nonspeed model has exactly nothing to do with how tight a spindle bolt should be tightened anyway. Proper torque and the method used to apply it are the same for both models.

Interested numbers Bill. I don't put a torque wrench on mine either, but I also achieve what you term as damn tight with a long L wrench on one side and a T wrench on the other. I ceased using loctite about 15 years ago after, without any exception and lenth of time the model had been flown and in many, many models and countless service cycles, the spindle bolts, when loosened, always broke (breaks) free with that satifying pop/crack experienced builders know so well. In contrast, almost every instance of a loosened spindle bolt of which I had direct knowledge, the bolt had plenty of loctite, often red, but completely inadequate installation torque. I spent a sh....t load of time and multiple years flying Hirobo heads, and those button head spindle bolts are one place, like Terry with his 3+ decades as a master machinist, that I simply do not believe the fastener choice is correct for proper torquing of that diameter of screw.

Ben Minor

Peak Aircraft/Team Minicopter Team Futaba Team Kontronik USA

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09-24-2018 03:24 AM  1 day agoPost 16
John Benario

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Las Vegas

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Centrifugal force is easy to calculate.

Revs^2*R*m

The key is keeping units straight.
Revs = RPM/60*2PI
R=CG of blade in proper units
M=mass of blade in proper units.

If you use grams for weight, you need to convert to Kilograms and then use meters for R. Result in Newtons.

If you use ounces for weight you need to convert to pounds and then to slugs (unit of Mass in our system (divide pounds by 32.2)) and use feet for R. Result in pounds

Team highest quality
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John's Ultimate building school

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09-24-2018 05:08 AM  1 day agoPost 17
TMoore

rrMaster

Cookeville, TN

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wjvail
John Benario
While I value any advice from Terry and Dr. Ben, I do use Loctite on my spindle bolts. Clean bolts with a little bit of 290 and snug just enough not to bell mouth the end of the spindle. This method has worked for me with no failures since the late 80's.
One more data point... I'm with John on this one. I clean and Locktite also with 290. John used the word snug but also said just enough not to bell mouth the end of the spindle. I think that is to say tighten really damn tight. Me, I use a couple of L Allen wrench. My goal is to stretch or pre-load that bolt if possible.

Just for kicks... Here is an on line centripetal force calculator.
http://www.calctool.org/CALC/phys/newtonian/centrifugal

I plugged in a few rough numbers:
Radius (approximate CG of a 700mm blade): 500mm
Angular Speed (head speed): 2,000
Mass (Weight of blade): 200 grams

The resultant force is nearly 1,000 pounds (986lbF). That is static force on a spindle bolt in a steady-state hover. Notice I plugged in fairly benign numbers. Loads will only go up with maneuvering and over-speeding. With nearly 1/2 a ton pulling on a single m6 bolt my goal is to make sure it stays in place.
If we are discussing an 8mm feathering spindle with a 5mm bolt, providing that the spindle is properly machined I don't think bellmouthing is going to be an issue. The yield strength of a 5mm grade 12.9 bolt is far in excess of what a rotor blade can generate at speed(1100mpa). The are three determining factors at play here plus one other factor that will go nameless for the minute, one lies in the machining of the feathering spindle and more importantly how the threads are generated in the end of the spindle, what their class of fit is and thread percentage, Feathering spindle material spec and the other is whether or not there are any stress factors built into the design and manufacture of the bolt. There are other factors but in the overall scheme of things are rather minor for the purposes of discussion.

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09-25-2018 01:24 AM  12 hours agoPost 18
wjvail

rrKey Veteran

Meridian, Mississippi

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I've never completely liked button head screws. Sure they have their place. They look nice when bolting a frame together. They'll save a few grams too.

I've never like the fact they use a smaller hex driver than a similar socket head screw would. A m3 bolt uses a 2.5mm driver if it's a socket head screw but the same m3 bolt uses a 2mm driver if it's a button head. That is NOT what I'm looking for in a spindle bolt. Not only is the driver smaller but the depth of the hex in the bolt head isn't as deep on a button head. A smaller driver with less purchase area just doesn't seem to make sense for a structural fastener.

As for using Locktite on spindle bolts... I think I use it out of habit. Now, it more like superstition. I just do it as part of the routine. And you're right, nothing makes a more satisfying crack as popping a spindle bolt loose. There is that moment when the wrenches are flexing and you know it's about to snap, and then a nice crisp crack.

"Well, Nothing bad can happen now."

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09-25-2018 01:32 AM  12 hours agoPost 19
JuanRodriguez

rrProfessor

The Villages, Florida

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Loctite for me all the way .... cheap insurance !!!

Been there, done that and old enough to know better.....

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