z-8

UPDATE: Bottom line: First test shows a 23% improvement over SF props and 5% over APC.

Ok, I haven't flown it yet, but I'm sure it will work incredibly well.

While explaining why efficient, fixed pitch, props employ both taper and twist to keep spanwise lift distribution constant, and thus as close to the ideal elliptical plan lift distribution as possible, I ran across an old Cambridge text that explained why the ideal hovering helicopter blade actually concentrates lift more toward the center hub.

The idea is that by bunching lift closer to the center of the prop disk, hovering helicopters better isolate the total integral lift distribution from ever-increasing tip losses as the stationary vortex re-circulates downwash over and into the blade disk, whenever hovering above ground effect. Since the length of a 3D aircraft fuselage prevents 3D propellers from utilizing the benefits of ground effect (loosely defined as an altitude less than half the span) to break-up an ever increasing vortex, this is of obvious value to any 3D aircraft which can fly slowly on the prop instead of the wing.

Invention: My Z8-3D prop better isolates lift from a strengthening tip vortex by clipping 2 opposing blades of a 4-blade propeller, thus reducing the need to slowly increase power to sustain a hover. My prop design should provide a significant hovering boost to any 3D aircraft that can hang on the prop long enough to recirculate some air back through the prop disk.

Notes:

• Be sure to make the 2 short blades long enough to avoid installation losses resulting from a wide cowling, but not so long that they contribute to the 2 diameter blade vortex.
• Balance the prop in both dimensions
• A hover should be achievable at a slightly lower throttle setting, and require less power increase to sustain

Disregard the Z8 branding if someone else has already invented this. Will post hovering test results soon.

JetPlaneFlyer

Z6,

So if that is the most efficient design for hovering flight and it was known ages ago and published in the Cambridge text... how come no helicopter has ever used such a design?

Fact is you misread the article. It is disk loading that should, for the optimal prop, be constant. Uniform disk loading requires a blade loading that increases in a linear fashion toward the tip. The article states this very clearly and illustrates it with a graph (both attached).

Good luck with your prop through.. I'm sure it will work ok, just not quite as good as a correctly sized 'normal' prop.

z-8

This is a "fixed pitch" optimization. Your graphs are for constant chord, CP helicopters, with twist or no twist. Variable pitch blades with twist, rotated mechanically at the hub, allow heli's to turn the entire blade to achieve any lift profile they want, or in the case of RC, even create a massive negative lift distribution to hover upside down.

But yes, you are right, another approach is to put a constant speed prop with twist on an airplane or on your RC model. Great solution, but I'm pretty sure that constant speed props have been invented already.

rcers

So what 3D ship you flying with that 100w GWS only good for paint stirring prop?

Mike

JetPlaneFlyer

Z8,
'Uniform disk loading' is a design goal that applies equally to fixed pitch props.. The article I copied it from and which you originally found said or implied nothing whatsoever about the graph and calculations applying only to variable pitch fixed speed props... In any case it was you who said that your design was based on that article, so if it did only apply to fixed speed props why have you tried to base this design on your interpretation of the article?

Nowhere in the article does it say that blade loading should be greatest at the hub and decrease toward the tip.. In fact it clearly says and illustrates the exact opposite. This is the root of your error.

Interested to see the results of your hover tests with a comparison against a normal two blade prop of similar pitch and a diameter sized to give similar motor power (so slightly greater diameter than your 4 blade prop)

z-8

Hey I like that GWS prop! Incredible thrust for a 0.2 oz. I've used it on my 700W F8F, but the huge torque burns up my Turnigy 35-36c stand in motor after more than a few secs. Turning this prop is one of the reasons I'm developing a dual inline Super Tigre .10 twin (or is that .20?).

I'm going to try the Z8-3D blade profile on 3 planes

• 41" Great Planes Edge 540
• 37" Art Tech Yak 54 which I just assembled for blog review (first impressions later today)
• 34" Pitts S2B

Weight range is about 19-35 oz, RTF.

Sustained 25G40 mph winds this morning after my first (bone stock) Yak 54 flight. Forecast is 3-5 mph all day.

z-8

Obviously there is no hub thrust at the center point, and you want enough thrust for cooling only into an aircraft cowl, but that goes without saying. See my blog on motor selection for more detail on matching a motor/prop to an aircraft.

JetPlaneFlyer

That text is supporting what I have said and confirms as false what you are claiming..
The text is quite clearly talking about linear lift distribution increasing toward the tip. The text specifically refers to fig 3.7 (a) and (b) which illustrates this graphically and which I attached to my earlier post and attached again here

Case closed.

Steve

z-8

That figure reference and the sentence describing it is "for a rectangular blade" (no taper) and an "untwisted blade" (no twist). Those cases are for CP hubs and unrelated to anything I'm doing.

z-8

The Z8-3D prop is balanced and ready to go on both the Yak 54 and Edge 540. Here is the Yak installed thrust static data using a 1300 mAh 25C 3-cell using the stock indirect drive motor:

Amps - 15
Watts - 170
@ no Load V - 12.3

Well within reason, and thrust is well above 1:1. Just waiting on the gusty wind, forecast is for 3-5 mph Monday morning (just like today).

P.S. The Yak flew great considering on the first flight considering the light wing loading and initial winds of 8-10 mph, ending with a harrier landing into a gusty 25 mph on the nose! Will have initial (bone stock airplane) impressions on the blog soon.

rcers

You know this is how people lose all credibility.

That propeller can not handle loads anywhere near 700w. That prop flies apart, or flattens blades at power levels WELL below that.

I have used it and found it to be one of the least efficient propellers I have ever used. I watched 4 of them on a C-130 a friend flew. He was running under 200w and had issues with that prop shedding blades and flattening to the point it was useless.

Why on earth would you make that claim?

Why don't you shoot a quick vid of that prop at 700w with a meter, tach and show us your setup?

Mike

Nitro Blast

Tuned in.

I too am no fan of orange props.


Things in black and white are not always as they are in the real world.


There will only be one result in putting an orange prop on a wet fuel motor, an explosion of orange shrapnel.

groundrushesup

Now Now, don't be so conventional.

I, for one, eagerly await the confirmation of this breathtakingly ingenious breakthrough in applied aerodynamic science.

Z-8 - are you by any chance a patent clerk in your spare time?

Standing by
GRU

z-8

Well, if it helps any, the stock A-T Yak 54 prop is that glow in the dark color that doesn't even glow in the dark.

z-8

Ok, what do I get if I do?

firemanbill

The ability to say I told you so. So let's see it!

kyleservicetech

A while back, I had a model with one of those orange props. Prop was something like 12 inches diameter, power was a geared brush motor running about 100 watts. You could actually hear that prop fluttering at more than about 50% power.

Nitro Blast

Z-8, let me throw this out for some perspective...

No disrespect in your desire to create something new, but consider the fact that there are many, many professional propeller companies out there. In the years they spend on R&D, plus the advancements in technology, you would have to have some belief that those companies would have already been through the development you are doing at least to the point where it is not worth pursuing.

Honestly, if it was better to design it as you show, SOMEONE would have taken it to market by now, right?

If not, I would be shocked. Propellers have gone through the whole range of designs from single blade to multi blade through the ages. From fan blades to boat props, none of them have blades that are different sizes. I do not wonder why.

I will however be in line as one of the first to congratulate you if in fact you have turned over a leaf no one else has. I would give more credit to a 'real' prop design, not a plastic coffee stirrer from GWS. Get a 4 bladed Master Airscrew, and work that one into your design and test that.



One more item, consider not making such incredible claims with your announcements...

"New invention revolutionizes 3D aircraft hovering performance" I still have not seen that.

could read:

"New propeller concept could revolutionize aircraft hovering performance" and is not a false statement.

z-8

Uhh, well, let me think on that. That doesn't sound very fun. I was hoping for more, especially given that 175W per blade is a minuscule task for any prop. Can't you do better?

I think I should hold out for more.

z-8

Humor. It's all about toys, afterall.

firemanbill

Hold out for all you smart alec...

NJSwede

Was the entire thread intended as a joke? That would explain a few things.

In your extremely convoluted introduction seem to say that you want to move the thrust closer to the hub and thereby reducing some of the tip vortices. The irony is that it's the tip vortices that completely kills the design. Here's why:

1) You're shortening the blade while keeping the same tip shape as the longer blades. All you do is to increase the relative effect the vortex is going to have on your blade. In other words, you have the same vortex, but less thrust (because the blade is shorter). Where's the gain in that? You were talking about an "infinite wing" with lift tapering off to zero at the tip. That actually makes sense in terms of reducing tip vortices. But shortening the airfoil seems to be the opposite of making it infinitely long. Not good. (Edit: Well, actually the vortex decrease because you decrease the tip speed. But you only decrease it at the expense of thrust. It's a wash, at best)

2) By shortening the blade, you move the inevitable tip vortex inwards. Each short blade will leave behind it a trail of disturbed air that is going to hit the next blade smack in the middle of the thrust generating area of the longer blades. Sure, the forward motion will make you fly past some of the disturbed air, but since turbulence typically fans out like a "funnel" from the source, you're sure to hit some. Not good at all. (Edit: Since the idea was supposedly to optimize for hover, there is no forward speed, so the disturbed air will definitely hit the neighboring blade)

TDisaster

It sure ended up that way. Seems once his idea was picked apart it was the easy way out without looking like a fool.

Just my take. Too bad he can't deny comments here, eh?

z-8

The whole hobby is about having fun. Lighten up and you'll enjoy life a lot more and more toys will come.

Not that uncommon...

z-8

Many will be happy to learn that I have given up on the orange paint stirrer. Now it is yellow. PZ Fw-190 spinner works well and is easy to run with either a 2 or a 4-blade, as it slides over the hubs from front to back.