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Heads and Rotor Blades Heads and Rotor Blades Discussion


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Old 02-26-2015, 06:08 AM   #1 (permalink)
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Default Scale flying rotor blades?

I was told its better to use glass fiber (heavier thicker) rotor blades for scale flying heli . The regular align blades are more for 3d flight? Suggestions please
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Old 05-12-2015, 09:30 PM   #2 (permalink)
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I know a lot of guys on here are using spin blades. semi symmetrical. I've been out of the hobby for a little while due to going back to school for two years, so I don't know if those are still available.
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Old 05-12-2015, 09:34 PM   #3 (permalink)
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Try these?

http://www.empirerc.com/spinblades-m-73.html?y=6&x=10
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Old 05-13-2015, 02:42 AM   #4 (permalink)
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emederos:

For what seemed like the longest time, I was convinced that semi-symmetrical blades were the answer for scale flight. They appeared to have more lift and use less power but recently, I changed my tune. I have been flying an MD500 TOW Defender, which is no light weight machine, using Rotor Tech semi-symmetrical blades and I thought those were very good. They are well made and are narrower than most normal blades but I thought that I needed thinner blades for a more scale look.

The 500 does take thin blades in real life compared to many other helicopters but it is not that easy to find blades suitable. Spin Blades fit the job very well and look amazing on the machine when it is static but we don't put our models out as static displays, we fly them. The scale direction of rotation of the Hughes design is counter-clockwise like a majority of full size helicopters but our models for the most part, rotate clockwise. There must be a simple explanation for that but I have yet to find the definitive answer.

For the past three years, I have been flying this helicopter with tail blades on the correct side and rotating the correct direction. The main blades have been going the wrong way and the main reason is that no one makes semi-symmetrical blades for helicopters under 800mm that rotate counter-clockwise. I spent days looking on the net and never found one manufacturer that made narrow cord scale semi-symmetrical OR symmetrical blades, period. I found one that made smaller blades, HeliTec, but they were still very wide compared to Spin Blades. I was stuck with keeping things as is until two people convinced me that symmetrical was the way to go for best flight performance.

Semi-symmetrical blades (like the wings in trainer model aircraft) create lift at 0 degrees pitch but have a nasty tendency to balloon in gusts, high speeds, and heavy winds. Symmetrical blades might create a bit more lift in a gust but it is equal top and bottom therefore being smoother in flight. This is really noticed when you are hovering a helicopter as a gust will tend to make the disk create more lift and therefore make the helicopter climb on the spot. Symmetrical blades create lift equally above and below the blade centerline so it is the angle of attack that is where we get the change in altitude of the helicopter. The airfoil gives the blade the power to create the lift it needs at a small angle of attack

Before I took the steps to change the direction of rotation of my helicopter, I gave a full set of symmetrical blades a trial at my club. They not only produced more lift than the much narrower Spin Blades, they used a bit less power over the duration of the flight. The airfoil on a thinner blade will not produce as much lift as a larger section airfoil but there are other factors that can effect blades like drag. The bigger the blade frontal area, the higher the drag, but when you have a well designed blade and airfoil, the overall performance gain is noticeable. The angle of attack of the narrow blade is higher than the angle of attack of the larger blade where they produce the same lift.

In gusts, my helicopter is no longer as susceptible to bouncing up and down in a hover and when you are trying to do clearing turns in front of judges, that is very important. These blades are pretty much the same size as 3D blades but they do have different balance points and weight distribution, compared to 3D blades, that helps them perform well with most sport and scale helicopters that we fly. I am using Rotor Tech 600mm carbon fibre composite symmetrical blades on my TOW Defender and 550mm versions on my CH-139 with excellent results. My last large helicopter, an AS350, may one day get the set of symmetrical 570mm blades I have set aside for it, but it is only being flown for sport at the current time (could be that I am also a bit lazy to paint up another set of blades right now, too, lol).

I know this is a bit long but it took three solid years of flying the 500 to come to this conclusion. Some will agree with me, others may not, but so far, I am convinced well enough to completely rework my TOW Defender so that the main rotor goes the correct direction and that has taken almost an entire day to do. I hope this helps.

Don

PS: The real MD500's blades are symmetrical as are most commercial blades with a few notable exceptions.

Last edited by Keyrigger; 05-13-2015 at 09:38 AM..
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Old 05-13-2015, 05:16 AM   #5 (permalink)
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Don

These guys make a 5 blade set of narrow chord LH/CCW blades down to 580mm.

http://derblattschmied.com/epages/5b.../5_Blatt/600mm

I am using the LH 820mm wider chord for my EC-145, and they are very nice blades - perfectly balanced, and very nicely finished. I have only had 2 proper flights so far, but very happy so far.

I think it depends on the asymmetrical blades. I have been happy with my little 465mm Spin blades on my UH-1N, and the HeliTec blades, but the "plastic" TF Model asymmetrical scale blades that RCA (and a few others sold) a couple of years ago were terrible.

They had lots of lift (in a hover) but used about 15% more power than my cheap HK GF symmetrical 600mm blades, and were so flexible that they tended to have tracking issues, and porpoised in FF. Got rid of them pretty quickly.

Colin
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Old 05-13-2015, 09:35 AM   #6 (permalink)
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Hi Colin:

Yes, I didn't mention the name but referred to them in the message as the company that did make CCW turning blades that were smaller than 800mm but were still a wide cord blade. I don't think I will be installing semi-symmetrical blades ever again on a model. Now I need to get used to the way this helicopter will take off with a CCW head. Even the little BO-105 from Blade took a bit of getting used to as it is CCW rotating. All part of the learning curve. Take care.

Don
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Old 05-14-2015, 04:43 AM   #7 (permalink)
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Don

The blades I linked above are 43mm chord. By comparison many symmetrical are over 50mm (Zeal 600mm are 55mm, Spin are 58mm), so I would consider 43mm to be narrow chord - perhaps not the narrowest around (the Spin asymmetrical 5x 600mm blades scale blades are 35mm wide, but are only RH/CW), but narrower than most symmetrical blades never the less.

I decided to deliberately go with the HeliTec wide chord blades (I bought 2 pairs of the 64mm wide x 820mm instead of a 4 blade set of the 53mm wide x 820mm multiblade set) as they were closer to the real EC-145 blade dimensions). The appear to fly just fine so far, and are not power hungry compared to my other helis.

CCW is definitely something to get used to and I always struggle a bit at first when swapping from CW to CCW - the banked turns are noticeably different.

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Old 05-14-2015, 09:51 AM   #8 (permalink)
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Hi Colin:

If I didn't mention this point in my post, here is the main reason for changing. When hovering a set of semi-symmetrical blades in gusty conditions, the helicopter does bob up and down. IRCHA and the Cajuns were the proof of that pudding and having some of the best scale pilots and judges look at it and comment about it was ample enough for me to make the change. For the sport flyer, it will not make a bit of difference to their enjoyment of flying unless the porpoising is horrendous in FFF. None of my helicopters, when flown with semi-symmetrical blades, ever exhibited that trait so I was spared that tendency and never had to fight that in competition. It is not that the bobbing is moving the helicopter feet at a time but much less and when under the watchful eyes of judges, it might as well be a mile. Some day, one of those manufacturers will come out with a narrow cord symmetrical scale blade and when they do, I have three helicopters ready to try them. Until then, what I have will do the job. Take care.

Don
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Old 05-14-2015, 01:11 PM   #9 (permalink)
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Quote:
Originally Posted by Keyrigger View Post
If I didn't mention this point in my post, here is the main reason for changing. When hovering a set of semi-symmetrical blades in gusty conditions, the helicopter does bob up and down.

Don
I gotta say, the little bit of flying I have done with my Cobra, which has semi symmetrical blades on it, experiences this exact phenomenon. At first I wasnt sure if I had a loose mechanical system or something funny in my TX programming, but couldnt find anything amiss there . But yea, in the hover, wind would cause the heli to rise and fall quite dramatically with zero collective input. I have some symmetrical blades I will try. Sounds like they may help stabilize the hover altitude in wind.

Thanks for sharing your info guys!
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Old 05-17-2015, 04:14 PM   #10 (permalink)
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this is a good source for scale blades "smaller than 800 size"...
http://derblattschmied.com/epages/5b.../4_Blatt/500mm

may come handy...

gh
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Old 09-07-2016, 04:08 AM   #11 (permalink)
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When I brought my 500 size H500MD secondhand with a 5 blade custom titanium head, it had scale narrow cord blades, while they looked good when it was not flying, they flew like c**p, popping out of track 5-10mm at random, the power changes even in the hover were hugh,basicly not nice to fly
I brought the heli to fly, so I brought 3 sets of Align black 500 blades. The LHS weighed 6 sets and gave me the closest 3 .
They took a bit to balance and get the CofG the same,they also where 1/2 the weight of the scale blades, the model now flys well. sure they look a bit oversize when not turnings, but you can't tell at idle up 2. You still have to give it the respect a heavy multy model requires, but I get 11 min out of it with a 4500 6S battery
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Old 09-07-2016, 09:28 PM   #12 (permalink)
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I have flown a 600 Scale MD500E and currently a 700 scale version. I used Spinblade 600mm on the one and 700mm asymmetrical blades on my present heli.

For my sport type flying of these helis I found the Spinblades to be excellent. The key (for me) was to install turnbuckle type link rods to allow for precise adjustment of the blades for tracking. Once dialed in they performed wonderfully.

The model weighs 12.2lbs. It hovers at 3.8deg @ 1300RPM.

Blade weight will affect your power train. My 700 size blades weigh in at 83g each x 5 = 415g

Keyrigger is correct that a symmetrical blade will dampen the gusts as there is being generated on top as well as 'lift' being generated downward on the underside of the blade vs. the Semi-symmetrical which has very little on the bottom side... so for a given gust the semi-symmetrical will have virtually all the lift go to the top of the blade as opposed to the symmetrical which will split it between the top and the bottom at a ratio dependent on blade angle.

For me I really like the scale look of the Spinblades in static and I am more than happy with them in flight...but I don't do scale competitions.
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Old 09-08-2016, 05:58 AM   #13 (permalink)
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A bit more on blades, some advantages on symmetrical blades that help is as the pitch changes there is only a very small center of pressure change compared to that of semi-symmetrical blades so the cord CofG of the blade & center of pressure remain the same, thus the load back on the system remains constant. what you don't want is the center of pressure to move forward, as this (at least in real helis) will cause a blade to dive, and sweep forward, more so with min pitch and on the advancing blade, this cause track change and dynamic balance change, making it hard to keep smooth/stable in all aspects of flight. Semi symmetrical blades thave much more twisting loads, thus diffrent sections have diffrent presure movement as the airflow speeds change . We have limit on such small blades to build in the required torsional strength.
Hence why early real heli blades are symetrical, plus early blade manufacture had limitations in manufacture, mainly with metal blades. Over the last few years as advanced design and manufacturing of composite blades has improved with design to improve performance & noise reduction has become more important, we see swept tips, strange shape blade, multiple aerofoil changes, even swept down tips on full size heli's such as AW189, NH90's. Maybe we will see some of that in our models soon
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