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| Scale Helicopters Discuss scale helicopters, tips, tricks and scale construction threads |
Topic Review (Newest First)
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| 03-27-2017 09:27 PM | |
| bensidus197217 |
Re: Four blade fly barred head Well I tried to true the head but the aluminum is too soft so the first chatter on the lathe pretty much finished off the centre bore. now I will scrap the head, take a break and come up with plan "C". |
| 03-26-2017 05:07 PM | |
| bensidus197217 |
Re: Four blade fly barred head Once I was able to clamp the head to the main shaft properly I then checked to see if things were out of round. The head was .010 out of round which would cause a nasty vibration. See the pictures below where I set up my dial indicator to check just how bad it was. |
| 03-26-2017 05:03 PM | |
| bensidus197217 |
Re: Four blade fly barred head First thing was to check out the balance problems. The grips and feathering shafts were as much as a gram out of balance each, I'm still working on that part. Second was the head itself, the first thing I noticed was the bolt that clamps the bottom of the head to the main shaft would not clamp properly. I milled .080 off both sides of the head that slides over the shaft to make it more flexible. That worked now it clamps tightly. |
| 03-22-2017 09:25 AM | |
| Cougar429 |
Re: Four blade fly barred head Other than a balance or physical problem you may be running into a conflict between the two systems. By their very nature flybars are a stability system to negate short duration deviances from their starting point. What that means is any sudden input from either your own control or externally such as a wind gust are dampened as the system resists that change. There is also another function. Rather than straight mass as with the early Bell designs we have aerodynamic paddles on the end to use as magnifiers of our control inputs. This allows for much less costly servos with adequate output and sensitivity than otherwise would be necessary to work the main blades in the fractions of degrees they move during each rotation. Basically, we fly the flybar and the main blades follow along. With a FBL unit the servos have to move the main blades directly. This is the reason servos and linkages need to be tight enough to prevent variations in blade angle away from what is requested. I'm wondering if yours is setting up an oscillation between the flybar and servo controlled blades. This would likely be evident after each control input and may settle down or amplify with time. A physical imbalance would show at any RPM regardless of input, but some specific ranges would be worse as the frame resonance is reached. In real life several helis got into ground resonance, some to the point of destruction. One other thought would be if phasing was off even slightly. If your control phasing was different between the two systems it may have one fighting the other. |
| 03-20-2017 03:44 PM | |
| bensidus197217 |
Re: Four blade fly barred head Thanks Dar and Don I will check out those wires you mentioned. You are right about how it functions, the fly bar controlled blades do have some lift to them but not much. I will have a better idea about control once I get the head properly balanced. The heli does seem as responsive as a normal fly bar head. It is fairly stable in hover even with all the shaking going on, that too will improve. The fly bar arrangement can be altered to do a better job of hiding it and the head could be more scale now that I have a good lathe and milling attachment. I plan on getting a MD500 body for it and made it just as good as you would in let's say grade two or three ha ha. |
| 03-19-2017 10:25 PM | |
| Keyrigger |
Re: Four blade fly barred head Jim: I noticed that a couple of wires are close to the main gear. That might catch them and do a bit of damage. If I understand your head design, the pitch is active only on the two blades connected directly to the swash plate. The other two have zero pitch but are altered in angle of attack by the flybar and its propensity to remain unchanged in its rotation about the main shaft. I am not sure that it will affect the flight much more than working against the other blades when you enter forward flight. As you move the stick forward to get the helicopter started moving, the blades, under the control of the flybar, will tend to pitch up but at a 45 degree angle to the path of flight. In a hover, it may well keep it nice and stable but do be very careful when you first go to move forward. Take care. Don |
| 03-19-2017 05:07 PM | |
| Helidar |
Re: Four blade fly barred head WOW now thats impressive, awesome engineering |
| 03-19-2017 05:03 PM | |
| bensidus197217 |
Re: Four blade fly barred head Took it out today to try it and make the needed adjustments. Biggest problem is vibration which got better after adjusting the phasing and flybar location, but I'm still not happy with it. What I will do is put the complete head on my blade balancer and see if I can get it better balanced. All things considered it flew well for the problems it had. Here are some pictures of it after flight I will take a video once I get the bugs out of it. |
| 03-01-2017 07:06 PM | |
| bensidus197217 |
Re: Four blade fly barred head Almost done still have to tighten the clamp bolt then I will strap the training wheels on and adjust the fly bar blades for a slight even lift. Hopefully tomorrow I will get the fly bar blades set up, that will be interesting The amount of lift I want will be enough to compensate for the extra weight. Those that say it can't auto rotate would be right, even if I could I can't, who knows maybe it will. Keep in mind there are no plans for this so I couldn't repeat it exactly,all a case of maybe this will work. |
| 02-26-2017 07:55 PM | |
| bensidus197217 |
Re: Four blade fly barred head Made in 1944 and when I pulled it apart it showed having signs of very little use. Now to become skilled at using it! |
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