S800 alternative props

[david.scarbrow]

Boris, yes I've had a few thoughts about that too. A Xaor prop is probably just a little softer than a Graupner prop...will the Graupner prop be too hard a material and become damaged due to being over-tightened on the shaft ? Should I place a suitable sized washer between the adapter and the prop. I can't check it out yet as I am still waiting for the recall changes to be made and completed on the booms...its been an awful long time for the DJI retailers to complete this.

 

[DennyR]

David,
when your Adapters arrive they will fit the Graupners perfectly with the correctly sized washer....

You must also use a 8 to 6mm insert.

 

[jes1111]

I already fly the 14x8 on most of my copters, on the hex with the Z15, and on the "fly long, fly far"-quad.

14x8 for hex with Z15:
https://vimeo.com/44931159

14x8 for long flight times (65min):
https://vimeo.com/38908434

14x8 for long distance (6,5km):
https://vimeo.com/47275644

I know that they will work great on the S800, I also have all the parts here to mount them, but until now I was just to lazy to do so and make a video. I might have some time over the weekend. There are not many props out there which can compete with the Graupners.

best regards

Ferdinand

Am I imagining things or are those props zip-tied onto the prop saver hub? How on earth do you get that balanced?

14x8 is theoretically too high a pitch ratio for hovering - interesting to see that it works well, but I can't help thinking it would be even better if Graupner did 14x4 and/or 14x5.

@Denny - are you a fan of wood props? You could try Xoar/JXF props on those nifty new adapters.

 

[FerdinandK]

Where did you get your "theoretical" results that 14x8 have a too high pitch ratio? The graupner props work as good as they do because of the high pitch (as well as e.g. the foxtech 15x7,5 with similar high pitch). I have seen no theoretical paper that would prevent 14x8 props to work on multicopter.

best regards

Ferdinand

 

[redridinghood]

Graupner 14x8 is a smaller prop and offer less thrust than a APC or JXF sized 14x8 prop.

 

[FerdinandK]

But it is still an ongoing myth, that props on multicopters have to be 14x4, 15x4, 16x4, we can talk on the diameter : pitch ratio, but the pitch needs to go up, as the diameter goes up. This is even on single - rotor helis the case. If you agree that (rc-sized) helis are flown in a pitch-range of up to 10°, this corresponds (approximately) to a diameter : pitch ratio of 2:1

best regards

Ferdinand

 

[redridinghood]

I agree, was only saying that a "real" 14x8 prop draws much more amps than a Graupner.

The Graupner 14x8 only gives 5-8% more thrust than a JXF 14x4. At least according to my not so pro tests.

 

[jffry7]

I have to agree with greater pitch comes greater amp draw but I noticed on all my graupner 8x5 10x5 11x5 and soon to get 14x8 (but now not enough stock at electricwingman because of Denny ) is that it shaped differently. the Pitch is concentrated on the middle slowly droppin and almost none on the edges. This is where I think Ferdinand is correct that this doesnt apply to the old ways but it works. 1yr ago everyone was saying slowfly is the way to go less vibration etc (MK days) but since I had WKM I find it Grapner offers the most stable flight but jumpy with to high gains, imho this is good for stabilizing the multirotor. The compromize of pitch/weight/design I guess makes it good.

Now if only I had ordered before Denny got their hands on the Graupner 14x8

 

[jes1111]

Where did you get your "theoretical" results that 14x8 have a too high pitch ratio? The graupner props work as good as they do because of the high pitch (as well as e.g. the foxtech 15x7,5 with similar high pitch). I have seen no theoretical paper that would prevent 14x8 props to work on multicopter.

best regards

Ferdinand

But it is still an ongoing myth, that props on multicopters have to be 14x4, 15x4, 16x4, we can talk on the diameter : pitch ratio, but the pitch needs to go up, as the diameter goes up. This is even on single - rotor helis the case. If you agree that (rc-sized) helis are flown in a pitch-range of up to 10°, this corresponds (approximately) to a diameter : pitch ratio of 2:1

best regards

Ferdinand

It's the science, Ferdinand - too high a pitch at too low an airspeed induces blade stall (separation of the airflow from the propeller's surface). "Pitch" doesn't produce lift, swept area (diameter) does. Pitch is increased for faster airspeeds (i.e. in the incoming air flow) and reduced for lower airspeeds. "Hovering" means zero airspeed, so the most efficient prop for hovering is one with a lower pitch ratio. As a rule of thumb, pitch ratio above 50% is "dangerous territory" for hovering. Greater pitch also induces more drag, therefore needing more power (watts) to keep it spinning.

Having said all that, your combination obviously works very well. By happy coincidence (and hard work/persistence, I'm sure), you've found a prop/motor/battery/AUW combination that produces great results. Which is why I only referred to it as "theoretically" too high a pitch ratio. The caveat is that if someone else sees you use 14x8 and tries them on their own craft they may get very different results (because their AUW, motor torque curve, etc. will most likely be different).

Still curious about your prop attachment method - are they zip ties?

Good article on propellers (though not multirotor-specific): http://www.stefanv.com/rcstuff/qf200203.html

 

[jffry7]

Ok Science makes sense, glad to know. Its good to point out so that others dont just plug them in fully loaded without testing. I personally use dummy weight before loading my camera gimbal on.

Thanks for the good info

 

[DennyR]

Guys
The underlying fact about Graupner versus APC is that although the 14x8 states a higher pitch angle, that does not translate into a constant angle of attack along the entire blade. It concentrates much of its higher angle at the hub which is what we want for better motor cooling and better stability. The AoA is nicely washed out towards the tips which helps efficiency. We don't want a lot of lift at the tips as this will cause tracking errors, be more unstable and create vibrations etc. At the end of the day I do expect some of you will want to experiment with some modified specials. I have made many versions of the APC by cutting and sanding them and then rebalancing them. I am waiting for this nice little voltage logger to come back into stock which will be great for a more accurate assessments. My view on 15" dia is that you MAY loose a little stability!

We have seen many times that the most efficient lifters are not the best for stability reaction. Graupner seems to have struck the right balance, but this will be an ongoing experiment, I'm sure of that.

Tip vorticies are very costly in terms of aerodynamic drag. that is because they act on a long lever arm from the hub.

BTW Guys don't forget to add your address in the paypal as my PM box keeps overflowing. Thanks

 

[FerdinandK]

@jes1111

You will have to redo your science. High pitch props (prop is fixed on the aircraft, aircraft at airspeed 0) will stall if the rpm is too high, but they will work (not stall) for low rpm. That is why people start their F5B (with e.g. 18x19 props) planes at 20% throttle. Thrust is produced as a combination of the "swept area" of the prop and air accelerated in that area. For a given pitch of the prop you can raise rpm to accelerate more the air , or you can do the same with lower rpm and a prop with higher pitch. If only the "swept area" would be the key, take a 14x0 and give it a try.

pitch-ration above 2:1 and "dangerous territory" is true coming from rc-planes, but not true for multicopter we run them at much lower rpm, than they run on planes.

Your link might shows basic info, but this is for sure not a scientific source of information. If you write this as an article in a scientific journal, they (including myself) will cut you into pieces.

I am flying the 14x8 in a wide range of load, I am using the 15x7,5 from foxtech, I also flew the Aeronaut 13x9 on the quad (which would work even better (more thrust ), but I am not able to balance the prop to get nice videos).

Yes there are zip-ties, Take a NX-motor, take a 14x8 and show be a better (more balanced way) to mount the prop on the motor. Just for your curiosity, the prop will also work with only one zip-tie, even more it will work (for some time) with no zip-tie.

best regards

Ferdinand

 

[DennyR]

It is a well proven fact that helis need to have a flexible head. only the very crazy 3D guys need to tighten it up a bit.

When considering these pitch angles I just checked the DJI (15x5) carbon and the pitch angle at the tips is very similar to the Graupner 14x8 so we are not comparing apples with apples here. In my view the DJI prop. focusses the max. lift at the wrong place along the blade.

 

[ChrisViperM]

The more you guys are arguing, the more I learn from you.....great thread and great people.

Chris

 

[FerdinandK]

@DennyR

Your are right, for sure the DJI 15x5 is by far not one of the best props the world has seen so far.

best regards

Ferdinand

 

[HeinzABF]

@DennyR

PM send.

Regards
Heinz

 

[DennyR]

I have extended the shaft length by 1 mm on the last batch to allow for a washer thickness on the Xoars.

I also checked into the request for 8 mm shaft and it is not possible because the PCD of the four counter bores will not allow that.

 

[ChrisViperM]

I was just checking for aluminium reducers 8mm - 6mm and almost fainted......the best price I could find (in a hurry) was one of our guys on the forum: http://www.multirotorforums.com/sho...m-Prop-Spacers-8mm-6mm-Reducers-Now-Available
...prices ranging up to almost $ 4,00 per piece with various vendors.

The most expensive place to buy raw material would be Amazon....and there you get a meter of seamless 8mm x 1mm tube for GBP 3,14.....http://www.amazon.co.uk/Round-Tube-8mm-1mm-Aluminium/dp/B005DR2GUM

Deeeeeeeeeeeeeenny.....any idea ???

Chris

 

[DennyR]

Hi Chris I am planning to start making these inserts next as the ones that are available don't cut the mustard.

Some people have asked why make the adapters out of 60/61. Well that is because the motor shaft extends to the base of the 6 mm adapter so if we used a cheaper material the shaft would break if you overtightened the prop nut.

Guys, could you please send your enquiries to dennyrowland@mac.com because my PM inbox cant keep up. Thanks.

 

[FerdinandK]

@Chris,

You can get the 8mm alu tubes at "baumax" or similar shops.

best regards

Ferdinand