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HelicopterBlades and Night Flying › Main blade tip design
11-29-2007 05:06 PM  9 years agoPost 1
jrvander

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Camp Foster, Okinawa japan

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I've got a question for the blades savvy public - what's the difference in tip shapes? Some have a very square tip such as SAB's, others are more rounded like Mavrriks, and still others have angled tips like Rotortechs:

Does a particular design favor one flying style over another? How about lift? I would think the rounded tips would generate less lift at the tip than a squared tip, but that may or may not be desireable at the very end. Any thoughts?

- Jon

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11-29-2007 10:06 PM  9 years agoPost 2
jrvander

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TTT!

Anybody?

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11-30-2007 08:47 PM  9 years agoPost 3
jrvander

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BUMP!

Anyone want to take a stab at this one?

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12-03-2007 01:13 AM  9 years agoPost 4
jrvander

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Again TTT!

I can't believe no one out there has an opinion about this question. Even subjective SWAG's are better than zero replies.

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12-03-2007 09:35 AM  9 years agoPost 5
kwikee

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Melbourne, Australia

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Maybe there's no replies 'cos it doesn't make any difference! I can't see there being a massive gain or loss in this area, angled or rounded must be fairly similar. The taper on the Rotortechs (called Carbontech's in Australia) may have some effect on laminar airflow, but I don't think it's noticable. FWIW I have flown all three tip shapes you've shown and each blade has its own characteristics, maybe or maybe not to do with the tip shape. You'd have to fly the exact same blade design with each tip to know for sure. Just go with what you like.

James

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12-03-2007 10:54 AM  9 years agoPost 6
The man

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I would think taper tip reduces the effective length of the blade thus less lift then slightly angled tip with the same length.

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12-03-2007 03:31 PM  9 years agoPost 7
helimatt

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Lafayette, IN

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Ending the lifting surface is a source of lots of designs and theories on what works best. Some are better than others- look at airplane wings. Large cruisers have tended towards tip sails or other upturned ends for better efficiency. Not practical (yet) on rotor blades, and anyway we want something that works equally well upside down. Some fun-fly types use tip end plates to help with extremely high angle of attack flight.

During the early parts of WWII rounded tips were regular fare for fighters and bombers (or elliptical on the Spitfire, but that was part of an overall attempt to tailor the wing toward some sort of supposed ideal lift distribution. Made for a very pretty wing). Then the Cadillac of all WWII beauties the P-51 just ended the wing with simple rounded tips- flat tip might have been even better, who knows. I think the unlimited Reno racers use basically squared-off tips.

Aerobatic aircraft usually just cut the tip off flat. Works fine. The R/C pylon racers have gone to some very extreme swept/tapered tips to improve their efficiency when pulling high "G's" in tight turns.

So for model helicopter rotors, its subjective and probably doesn't make a world of difference- just something a designer thought he'd try based on some theory, and once the molds are made and the blade flies just as well as any others they don't go changing it. The tip will affect a relatively small area of the total disk, might make a longer blade seem shorter if it is double tapered or such. The rotor blade tips are flying so fast in comparison to other model airfoils (except propeller blades) that tip designs for wings will probably not work so well on rotor blades. APC propellers are very interesting designs- very heavily thinned and tapered towards the tips. Effective for propeller airfoils running high relative airspeed.

However, we need to consider both efficiency, stability, and control feel. I have flown tapered MAH main blades on the Trex 450 helicopter and did not like their feel very much. They have a relatively thin airfoil however, and that might be part of the issue with those blades.

Rounded tip edges of some sort make it possible for the cloth to mold nicely in the layups, so we might never see squared-off tips for production blades.

Never, ever, ever, ever give up.

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12-03-2007 04:55 PM  9 years agoPost 8
Syclic

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Northern Hemisphere Ont.

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There are many things that give a blade its' flight characteristics - blade tip is just one of them.

The only way to compare the difference blade tips make would be to have the facility to make exactly the same blade (e.g. same airfoil, same chord, same span, same spanwise cg, same chordwise cg and the same weight, same rotor speeds, same pitch) with the only difference being the shape of the tips.

I know the designers for some manufacturers have done this and logged the data, and discovered the advantages and disadvantages of each relative to different airfoils....and I do not think they would be willing to come on a public form and give out the results of the real data they collected.

They spend thousands of dollars and a lot of time on real research - why would they want to make it available to their competitors for free??

But when they give their final designs to such top flyers as Scott Gray and others to try - they immediately feel the difference and only start using their blades (even if initially they had to pay for them and could get free blades from other manufacturers).

There are many manufacturing companies that are experienced in molding composite structures, but very few with a lot of experience and knowledge in the dynamics of rotor blades operating in the Reynold numbers region that we do. That is why some of us have actually found some wood blades that outperform some popular carbon fiber units on the market today.

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12-04-2007 02:26 PM  9 years agoPost 9
jrvander

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Great!

Alright, now we have some discussion points! I agree with the assertion that manufacturers need to keep their design secrets as proprietary info, but it looks like each company has their own take on what works best. Probably boils down to who is flight testing for them and what he likes in a blade.

I got a PM from a friend who thinks that that tapered tip design is more aggressive in cyclics but not as good in autos as a squared tip would be. Maybe that's the trade off between tip designs?

Edit: This is interesting - Same company, different blade lengths, different tip designs.

- Jon

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12-30-2007 02:46 AM  9 years agoPost 10
Chopper

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Stow,Oh- oops, I mean St Louis, nope Stow again,

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Ya know, through the years, there have been a lot of different designs on the market. There was once a "BURP" blade with a real....engineered tip....one only an engineer would like. It worked, but in the overall, it was forgotten.
There are just sooooo many different flight parameters to measure blades. Some people like hanging autos, some like quick cyclics, some want stable hovering and straight tracking. Tip design is only one element in the overall performance of the blade, and some like a particular blade for it's performance, and it is more the weight distibution and airfoil than the tip that defines the performance.
My favorite all time blade was the 680 ZigSaw blade. It had the best of all performance, but when I changed to the 90 ships, The 700 Ziggy was not the same.
There is a "progressive" blade that was designed to try to even out the lift along the length of the blade. It worked, but the newer designs out perform this design. There are blades with washout that were tried, and most went away too. It seems that trying to get the lift inboard is not really a beneficial thing after all. The blades with good loift at the tips seem to work the best in overall performance for sport flying.
The SAB 710 is a big blade and will auto forever. If the tip was changed to more of the Zig Saw or the Rotortech tip, it may loose some of the bottom end auto performance. Then again, it could speed up more on the auto giving you more head speed before the flair. It could load the disk a bit less, but have less "pop" for hard cyclic maneuvers. You get blades that are based on your flying style and use those, despite (or because of) what the new HOT kids are flying.
In the end, most of the blades on the market now have airfoil differences and CG differences that seem to affect the performance more than tip design. It seems that any "clean" way to end the blade works for the most part.
This only applies to the larger 690 -710 blades. The smaller sizes have a whole 'nother set of parameters to work on. So when you ask a blanket question, What is best"??? Then you need to follow up with the size and weight of the heli, the type of flying, the manner in which you fly, the motor and available HP to swing the blades, and all of the other variables that go into making that right choice for YOUR combination. Then you can get 147 opinions from 146 people.

Paul Soha is a free agent now. Wow.

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12-30-2007 03:13 AM  9 years agoPost 11
wings19

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Tucson, AZ

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One thing I know from being a real world pilot is that the main idea behind different tip designs has to do with wingtip vortices. The idea is to minimize the vortices which form off the ends of the wings. They create turbulence and they are a side effect of creating lift which means they cause drag as well.

This is why you see airliners having the winglets at the end of the wings. They don't allow the air to spill over the end which creates the spiraling motion of the vortex.

With helis, I can see why you wouldn't want these vortices even more because the blades are flying in the same place in a hover. If you could take away those vortices you would have less drag and more lift. That is why when you get within a wingspan of the ground you get into ground effect which is an area of less drag and you tend to float. With helis you require less collective when closer to the ground because the ground doesn't allow the vortexes to form fully.

Nick
If the wings are traveling faster than the fuselage, it's probably a helicopter

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12-30-2007 04:56 PM  9 years agoPost 12
Chopper

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Wings19, that is where I was going in my previous post on having a "clean" tip design. It seems that most of the blades on the market have a decent tip design. Reducing the vortice (by chord and thickness changes) reduces parasitic drag, but it also (effectively) moves the lift inboard unless you use winglets or Horner tips. It is like running a slightly smaller blade in the overall performance of the blade. The trend now, especially with the higher performance and power to weight ratios of the current helis is to maximize lift on the entire blade. The engines seem to be able to handle the extra drag, and a lot of guys are going for all of the "pop" they can get with a blade. The vortex drag is rather insignificant when pulling 10 Gs and powering 50 mph vertical collective slams. So again, it all depends on what type of performance you want from a blade.

Back in 1990, Don Chapman showed up at a field with Horner tips (inverted winglets) on his blades. The engineering is sound, but the results in flight performance was not worth the effort to make the changes. NHP was famous for the square tip. They flew just fine.

Does the tip design make a difference? Sure. But moving the lift inboard never seemed to help the heli fly better in any appreciable way.

Paul Soha is a free agent now. Wow.

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12-31-2007 02:41 PM  9 years agoPost 13
wings19

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Tucson, AZ

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I fly giant scale 3D planes also and being a full scale pilot helps to understand why the plane does certain things. It also helps in deciding which design and props would work better for what I want to do with the plane.

One thing I've noticed though from real full scale aviation to models is that some things don't affect us as much in the RC world. I think to some extent blade tips and things of that sort aren't extremely crucial since we have so much of a power to weight advantage. At least not as much as these things have an effect in full scale. In 3D planes and helis, the engines being used in comparison to the plane(or heli) size and weight have enough power to handle much more drag without looking back.

Nick
If the wings are traveling faster than the fuselage, it's probably a helicopter

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