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HomeScale✈️AircraftScale HeliScale Helicopter Main Discussion Docs  Gazelle Build
08-19-2013 04:03 AM  7 years ago
heliadictaholic

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Hobart, Tasmania - Australia

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I did not change the mounting just added a few parts so nothing special to adjust the belt tention - the same process as you - yank on the motor and tighten the collar around the boom clamp. The biggest problem I will have is changing the belt when it starts to wear - but I can live with that.

It would be nice though to have someway of adjusting the belt tension that is more positive than just hand tension and tighten the collar.

When I need to change the belt, the easiest way is to remove the rotor head mechanics and then remove the boom pipe and motor mount, change the belt the slide the boom pipe back in.

Just wondering, during your build process, did you ever findout the KV of the stock tail motor? I have upgraded my motor to a Scorpion HK-3226-900KV based on someone elses tests, but I never found out the original KV.
I recon the easiest way is to connect one up and use a tacho on it.

Something interesting, I have one of the Turnigy digital tachos which can be set to read 9 blades, but I tried it on my fan, it could not read the revs. Maybe spinning too fast and having the tacho so close to the centre is outside of limits for the tacho.... or maybe the tacho is faulty
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08-25-2013 03:37 AM  7 years ago
Joel Rosenzweig

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Marlborough, MA - USA

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It would be nice though to have someway of adjusting the belt tension that is more positive than just hand tension and tighten the collar.
That's what I was getting at. I thought that perhaps you had figured out a solution for that. Getting the belt hand-tight, does not appear to be enough tension. My belt still buzzes under load, and it's only tensioned as far as I can go by hand.

I thought of making a belt tensioner, but it's just tight in that area. So whatever I machine will need to be tiny to fit. I think it's possible. I have not tried machining anything for that yet though. I'm not convinced that belt tension is the critical issue that I face, but a poorly tensioned belt is not helping me either.

I heard from Willis in the last couple of days. Apparently, they are moving their facility, and do not want to spend the time to do the power tests that we had been discussing, until after they finish their move. Willis tells me that he expects this to be sometime by the end of September. This is a long time to wait of course, and my flying season will be about over by the time I theoretically hear any news. That doesn't even get me a solution -- just some data to help narrow down the problem.

I can see that this is going to go unresolved for a while longer. I won't likely be test flying anything like this in the winter time, so if it takes as long as it is trending towards to get more information and an ultimate solution, I don't expect to have anything more until the spring time (April/May or so around these parts!)

If I hear anything from Willis before my flying season ends, and if I have any more to go on, I'll give it a try and report back. And, regardless, I'll update this thread with whatever info I get from Willis when he reports back to me.

This isn't the result I was looking for, but apparently, it's the result I have for now. I guess I signed up for yet another lesson in learning patience.

Joel
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08-25-2013 04:14 PM  7 years ago
Mojave

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Palos Verdes, Ca. USA

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Has anyone looked at the blade design of this unit? Maybe it's a matter of an incorrectly designed airfoil. Compare the blades to the vario and hirobo designs and see what you come up with. Blade profiles can be very sensitive to rpm and become inefficient when not run in the "sweet spot". Maybe by increasing the RPM, the problem is being exacerbated. Typically, when you increase the number of blades in the same plane, turning around 1 central hub, the system becomes less efficient. So blade profile becomes critical. Case in point would be the increased efficiency of a cascaded tail design. So, maybe this problem is not a product of not enough deflection in the control linkage. Just a thought...
Barry
All helis and planes have an expiration date stamped on them...you only find it after you crash!!
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08-26-2013 06:15 AM  7 years ago
heliadictaholic

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Hobart, Tasmania - Australia

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G'day guys,

Below is a pic which shows the fenestron blade profile - I took 2 photos and then traces as best I could.... I do not know anything about blade design for a fenestron. I spoke to a workmate who flies RC planes and he suggested that maybe a slightly thicker blade might be worth testing. If anyone has any recommendations for a blade profile to try, let me know. I will draw in 3D and get Wanfon prototype to quote the cost to CNC in a suitable plastic.

Also, attached is a pic on a possible belt tensioning device - might be worth trying....

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08-29-2013 10:22 PM  7 years ago
Joel Rosenzweig

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Marlborough, MA - USA

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Jim,

I don't quite understand how to tension your device. I see the serrated edges, but I don't see how to use a tool to tension it. It appears to me that you still have to tension it by hand then lock it down. Am I misunderstanding your drawing?

Barry,

It could be that the blades are poorly designed, but I have no basis for saying that. Given that, I have no particular design that would be a better candidate to use. And, making my own blades, is a little more effort than I'd like to invest at this point. Because it's not obvious that the blades are the problem, it seems like a lot of investment of my resources to make new blades only to have the fenestron fail to operate properly, again, at the end of the day. If Willis (of TF Model) thinks it needs new blades and if he provides them, then I'll gladly bolt them on the try. But at the moment, it just seems like way too much effort.

I don't have a picture of the Hirobo blades. It would be interesting to know if the Hirobo blades have a different airfoil, and, if they are any stiffer, or dimensionally different in any way. If they were different, at least, we'd have something to go on. If they are the same, then I'd have to conclude it's not the blades.

Perhaps I'm just feeling a little burnt out on this project. I've put so much time into it so far, and don't have a working model to show for it. I'd like some hard evidence before investing more time and energy into it. That would be motivating, if I knew there was a high chance of success. So far, I have no carrot to go after.

Perhaps, when I hear from Willis at the end of September, there will be some good data there and it will illuminate a path forward.

Joel
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08-30-2013 12:00 AM  7 years ago
heliadictaholic

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Hobart, Tasmania - Australia

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G'day Joel,

The "sketch" is a sectional view through the mount and boom components. The serrated edge "is meant to indicate a thread". I have shown a pin which you would insert into a hole (shown) and rotate the outer part of the tensioner which would move the outer part toward the motor and force the motor mount outward hence tightening the belt. The inner part would be fastened to the boom with a couple of short fasteners....
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08-30-2013 12:05 AM  7 years ago
Joel Rosenzweig

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Marlborough, MA - USA

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Jim,

Your explanation makes so much more sense than what I gleaned from just the drawing. What a clever idea!! I like that very much.

Thanks for clarifying how that works. Very very good implementation.

Joel
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08-30-2013 12:44 AM  7 years ago
heliadictaholic

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Hobart, Tasmania - Australia

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Thanks Joel,

I am still waiting for the bearings and thrust races (slow boat from China) for my custom blade mount hub. When they arrive, I will setup my Aussie BT on a turn table as a test rig, (not painted and no main mechanics) and attach a digital scale to the tail and measure the force generated as the tail tries to spin the heli on its axis. Then I can test RPM and various pitch settings to see what I get. I will also 3D print a new inlet radiused lip and 4degree outlet ring to see if they make any difference. In the mean time, I will search the forums to see if I can get a blade profile for the Hirobo blades. If I can not find any details, I might have to order a set of Hirobo blades... =:-\

I stated a while back that I am not a competent pilot "yet" and I would hate to destroy a heli if I "lost the tail" So, lets see what we come up with in the hopefully "not too distant" future.....

Here are some pics of my upgrade fan parts. Not sure if the addition of the thrust bearings to each blade is going to make a difference to the servo load - but I think thrust bearings are a better way to go. I had to make the hub in multiple pieces to get the CNC cost down from $600 to $200
Each blade mount has 2 locating dowels and 1 M1.6 stainless fastener.

The actuator mount will make me feel a bit better that I have eliminated the 4 tiny screws into plastic....

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08-30-2013 04:34 AM  7 years ago
Mojave

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Palos Verdes, Ca. USA

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Nice looking machined parts!

Joel: I agree and sympathize with you. It's a great deal of effort to chase this ghost, not to mention the cash investment (on top of the original cost of the kit). I just threw the blade idea out there as a suggestion, hoping that someone would chime in with a comparison of the hirobo and vario blade designs. I sure hope that you guys can get this issue squared away before the next flying season.
Barry
All helis and planes have an expiration date stamped on them...you only find it after you crash!!
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09-19-2013 04:34 AM  7 years ago
heliadictaholic

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Hobart, Tasmania - Australia

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G'day guys,

I now have a picture of the Hirobo blade section. Have a look and let me know what you think....

I am no expert on aerofoil sections (nor anything else =:-\....) but something does not look right with the TFModel blade. The Hirobo looks to be a better aerofoil than the TFModel. The TFModel blade, almost looks as if it was designed with the top of the blade root on the bottom of the blade and the Hirobo looks correct. As I said, I am no expert.....

Any opinions? I am tempted to redesign the blades and have them CNC machined from plastic or even Aluminium - although, I recon aluminium might be twice as heavy. I will do the 3D model and check the weight difference.

The white blade and the blue outline in the pic is the Hirobo... I recon you already guessed that =:-)

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09-19-2013 08:29 AM  7 years ago
Mojave

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Palos Verdes, Ca. USA

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I'm no expert either, but the Hirobo blade appears to have a much more aggressive profile.
Barry
All helis and planes have an expiration date stamped on them...you only find it after you crash!!
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09-25-2013 04:18 AM  7 years ago
heliadictaholic

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Hobart, Tasmania - Australia

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G'day guys,

I redesigned the fan blade and made the aerofoil profile similar to the Hirobo profile.... I have had just one blade CNC'd at this stage to test the process and to determine the strength. The sample shows some machining marks which I hope can be sanded out. I am waiting for a price to have a set of 9 made - also 18 - also 27 blades (I have 3 fans)

I just realised that I missed a radius on the half round sections on the front and back of the blade where the pivot screw fastens into the blade.

Another option is to have them made from aluminium.... I know aluminium is probable twice the weight of plastic - but is this an issue - they are fairly lightweight anyway???

So - aluminium or plastic - descisions-descisions - it will probably come down to price and I recon there won't be much difference between plastic and aluminium....

Any comments?

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09-25-2013 04:22 AM  7 years ago
Joel Rosenzweig

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Marlborough, MA - USA

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Hi Jim,

My only comment is, make me a set. :-) At least, if it can be made at some price that doesn't make my head explode.

I'd use a harder plastic than what TF Model uses, since the Hirobo plastic is stiffer. I got to feel the Hirobo blades just a week ago on an EC-120.

Aluminum blades would probably be fine, too. Maybe even better, since they would be stiffer, and machine very nicely.

Joel
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09-25-2013 05:23 AM  7 years ago
Mojave

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Palos Verdes, Ca. USA

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I'm on the edge of my seat, waiting for the next episode of "As the Blade Turns" But seriously, very nice job on the blade and I hope that your issue was as simple as a blade profile. Regarding the plastic VS aluminum issue: The aluminum will probably have less tendency to deflect under load, but if plastic works for hirobo, why not keep it cheap during the experimental process? Unless the price difference is negligible, then my vote goes to aluminum. IMHO, if need be, you can go with a much more aggressive profile with aluminum, as you won't need as thick of a center section in the blade chord for rigidity.
Barry
All helis and planes have an expiration date stamped on them...you only find it after you crash!!
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09-25-2013 07:03 AM  7 years ago
heliadictaholic

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Hobart, Tasmania - Australia

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Guys,

Prices for aluminium and plastic options...

Note the blade profile is not necessarily final - if you guys could maybe talk to club members who might be better at aerofoil knowledge than I am, and provide a sketch of a preferred blade profile. I can update the model no problem before we go to CNC..... I would prefer not to be the one to produce another not satisfactory blade.....

Also Note that I am not sure of the strength of the plastic option. I asked for a strong plastic - I know nothing about plastics....

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09-25-2013 11:44 PM  7 years ago
heliadictaholic

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Hobart, Tasmania - Australia

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RE:fenestron blades - will the link below work for fenestron blades?

Have a look at this link to airfoil online design.....

http://airfoiltools.com/plotter/index
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09-25-2013 11:50 PM  7 years ago
Joel Rosenzweig

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Marlborough, MA - USA

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Before you make a blade...
Before you make a blade or any more parts, it would benefit you and all of us really, if you performed a measurement of fenestron power consumption first. As it stands you don't know if you need any of the upgrades you are proposing. It's quite possible that your fenestron works great and it's only mine that are problematic.

Joel
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09-26-2013 01:03 AM  7 years ago
heliadictaholic

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Hobart, Tasmania - Australia

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G'day Joel,
I am in the process of assembling the fans with the updated thrust race type blade mounts and the replacement of the plastic actuator mount with aluminium.

You should see my work bench.. I have got fan bits all over the place.....

As soon as I get things back together, I will do some tests. As part of the test, I will 3D print an alternative radiused intake lip on the duct.

I am leaning toward getting the aluminium blades - just because the TFM blade profile just looks wrong..... I might hold off ordering for a couple of weeks to see how things go with the tests....
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09-26-2013 04:24 AM  7 years ago
Joel Rosenzweig

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Marlborough, MA - USA

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I bet your blades will be fantastic. There's no harm in making them. I would just like to know if the fenestron may work for you without them. If you get the before and after data, then you'll know if the blades were "the" item that needed a fix, and that will help any of us who are trying to resolve fenestron problems. That is, if the blades fix it, then at least we can all order these replacement blades.

I used to own the Vario fenestron which worked fine in my EC-135. There wasn't much to those blades, and they were OK. The Cinescale fenestron uses blades that are different, but I can't say they are any more or less aerodynamically (is that a word?) correct than anything else available. The Hirobo blades and the TF Model blades LOOK fine relative to what else is available. It would be great if we could pinpoint the actual issue.

At this point, I'm still trying to figure out just what could be changed on the fenestron to make it move more air. For all I know, it's operating at peak efficiency already and will never move more air no matter what blades on bolted onto it. It may simply be that the helicopter weighs too much for the amount of thrust this fan unit can provide. I'm not sure how anyone will make the helicopter lighter and balance nose heavy at the same time, but ....

I think that, if I could get my hands on a Hirobo fenestron, that would be the best test. I could determine if that fenestron worked any better than the TFModels one. Though, I don't expect that finding a Hirobo fenestron will be trivial.

Joel
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09-26-2013 06:41 AM  7 years ago
PETER ROB

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Devon UK

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leaning toward getting the aluminium blades
Are these blades available and from where or whom
Will they be a special order from someone like 'M'blades?
I have a selection of fenistron units with Vario plastic and CF blades, also CF blades from Cine-Scale
Like it has already been noted, weight seems to be the deciding issue with fenistron units

I was in London a few month's back collecting a helicopter, Mark had made his own fenistron unit also carbon fibre blades, i saw it on a test rig but as yet is not on a model

Another thing I have seen was something Mike Pattison did a few years ago, that was to line the internal dia of the fenistron duct so there was the minimum of clearance at the ends of the blades
I tried this and the only downside, was I had a hard landing and the blades chewed a groove in the lining material lucky for me I had used thin layers of milli ply, so no real damage
Peter R
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