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Sep 16, 2019, 03:57 PM
KG7TTQ - Las Vegas
mark_q's Avatar
Quote:
Originally Posted by ninja_zx11
Thanks for sharing the info Mark!!

From your tests,it looks like APC props are more efficient than aeronaut folding props.
Not really
gr/watt values are only really relevant on multirotors where 100% of the lift is provided by the props. 3D planes also have an interest in high prop efficiencies.

-but-

We are flying fixed wing with all the lift being managed by the wing(s) and the motor and prop are running at sustained low RPMs. Basically you can't derive what is the most flight efficient prop from static bench tests. As an example, in one set-up using a 1100kv motor the (static) prop efficiency of the 9x6 is 4.48gr/W, a 9x7.5 is 3.21gr/W and a 9x9 is 2.8gr/W. What was found in actual flight testing however was the 9x7.5 required less power to cruise accross 1km than the 9x6 and the 9x9 was almost exactly the same as the 9x7.5.

This has to do with how much drag the plane has at a given speed and how much thrust, at that speed, the prop makes. If the prop is over-producing thrust, it will be more inefficient than a prop that is making more pitch speed than needed. The trick is to find a prop that makes exactly the thrust needed to overcome the airframe drag at exactly the pitch speed required to cruise. The only way to get there is buy a pile of props (I have hundreds!) and test, test, test. Bench testing gives only partial answers, none of which tell you how it will perform in flight

Mark
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Sep 16, 2019, 04:23 PM
Registered User
Quote:
Originally Posted by mark_q
Not really
gr/watt values are only really relevant on multirotors where 100% of the lift is provided by the props. 3D planes also have an interest in high prop efficiencies.

-but-

We are flying fixed wing with all the lift being managed by the wing(s) and the motor and prop are running at sustained low RPMs. Basically you can't derive what is the most flight efficient prop from static bench tests. As an example, in one set-up using a 1100kv motor the (static) prop efficiency of the 9x6 is 4.48gr/W, a 9x7.5 is 3.21gr/W and a 9x9 is 2.8gr/W. What was found in actual flight testing however was the 9x7.5 required less power to cruise accross 1km than the 9x6 and the 9x9 was almost exactly the same as the 9x7.5.

This has to do with how much drag the plane has at a given speed and how much thrust, at that speed, the prop makes. If the prop is over-producing thrust, it will be more inefficient than a prop that is making more pitch speed than needed. The trick is to find a prop that makes exactly the thrust needed to overcome the airframe drag at exactly the pitch speed required to cruise. The only way to get there is buy a pile of props (I have hundreds!) and test, test, test. Bench testing gives only partial answers, none of which tell you how it will perform in flight

Mark
You are correct Mark.Yes its not easy to find a perfect prop on the bench as we don't have wind tunnel to test the actual parameters that prop would face on the flight

After reading your posts,i now have better understanding how diameter and pitch effects the efficiency and how thrust,efficiency numbers get changed when prop actually faces incoming air during the actual flight.Its quite interesting
Sep 17, 2019, 09:21 PM
KG7TTQ - Las Vegas
mark_q's Avatar

Still Working on it!


MT#4 is showing its age so I spent the day in the shop working out some design ideas and changes for this next MT project, a three motor VTOL Mini Talon (Tri-Talon? )

I've been playing with all these parts for some time (kind of on and off) and have made a few changes that seem like they will be helpful. I extended the front motor pods 20mm from the original to get the props a bit farther forward. I also have now settled on the rear design useing a cone shaped mount that bolts directly to the original motor mount and has a 12mm CF tube for support forward to a cross brace.

All the parts together with motors shown and three BLHeli_32 ESC's weighs in at ~323gr so if you subtract out the Cobra 2221 and Hobbywing ESC (current setup) the overall weight add is 160gr. This will put my AUW close to ~1820gr. The front motors shown are Racestar 2508-1275kv units with 8x5 Graupner props. The rear motor shown is a Cobra 2208 but I will probably opt for a 2206-1800kv with a 6" HQBN prop.

Still a ton to do learning the new APM parameters for this Convergence style control system. I will be sticking with a Matek F405 with an added servo power buss for the tilt rotor servos. I've chosen 13.8gr TowerPro MG92B hi-torque units (3.1kg*cm). Probably overkill but I think that's a good thing

Cheers all,
Mark















Sep 17, 2019, 09:27 PM
Registered User
Wow!! great idea!!Thanks for sharing.
Sep 17, 2019, 09:34 PM
Registered User
Bill0's Avatar
You are truly amazing.. Thanks for sharing all you work.
Sep 17, 2019, 10:27 PM
Registered User
Will you install a tilt servo for the rear motor or just cant it? Thinking about torque compensation.
Sep 18, 2019, 01:12 AM
Registered User
To mark_q!
Can I get files.stl from this project?
Best regards,
Serhii from Ukraine!
Sep 18, 2019, 02:56 AM
Maker of things
DangerFlite's Avatar
Quote:
Originally Posted by Danne1700
Will you install a tilt servo for the rear motor or just cant it? Thinking about torque compensation.
This. Doesn't the rear motor need to tilt on a tri?

damn awesome setup though, looks excellent

Painted my new toy, still waiting on parts to finish the build though



Anyone had good results with Hobbyking's low-temp covering film? I ordered some but have never used films before. Book covering was a fail
Sep 18, 2019, 03:07 AM
RC fanatic
Quote:
Originally Posted by DangerFlite
This. Doesn't the rear motor need to tilt on a tri?

damn awesome setup though, looks excellent

Painted my new toy, still waiting on parts to finish the build though



Anyone had good results with Hobbyking's low-temp covering film? I ordered some but have never used films before. Book covering was a fail
I covered my fx61 with black HK film but not sure if it's the low-temp version you mention. It looks awesome though and covered really well.


Sent from my Nexus 6P using Tapatalk
Sep 18, 2019, 06:52 AM
Maker of things
DangerFlite's Avatar
did you manage to cover the fuselage? I can't imagine it's going to go well for me
Sep 18, 2019, 06:59 AM
Registered User
Atx_Heli's Avatar
Quote:
Originally Posted by DangerFlite
This. Doesn't the rear motor need to tilt on a tri?

damn awesome setup though, looks excellent

Painted my new toy, still waiting on parts to finish the build though



Anyone had good results with Hobbyking's low-temp covering film? I ordered some but have never used films before. Book covering was a fail
No, yaw is handled by tilt in front motors....btw @markq, be sure that the range of tilt is ~15-20 back to straight forward....~110 deg total....
Sep 18, 2019, 07:41 AM
Registered User
Another tidy build Mark. Where is the tricopter CG? Is it close to the normal MT CG??
Sep 18, 2019, 11:44 AM
Registered User
JamDan's Avatar
Quote:
Originally Posted by mark_q
MT#4 is showing its age so I spent the day in the shop working out some design ideas and changes for this next MT project, a three motor VTOL Mini Talon (Tri-Talon? )
Looks great Mark! It’ll be exciting to see how it performs.
Last edited by JamDan; Sep 18, 2019 at 11:49 AM.
Sep 18, 2019, 12:29 PM
KG7TTQ - Las Vegas
mark_q's Avatar
Quote:
Originally Posted by DangerFlite
This. Doesn't the rear motor need to tilt on a tri?

damn awesome setup though, looks excellent

Painted my new toy, still waiting on parts to finish the build though



Anyone had good results with Hobbyking's low-temp covering film? I ordered some but have never used films before. Book covering was a fail

Then best shrink cover I have found for EPO is Hanger9 Ultracote. The full thickness (heavy) versions have a lower temp and much better adhesion than Monokote or Oracover brands. I have never tried the HK covering so I can't comment on it.

Here is a link - Hanger9 Ultracote

Mark
Last edited by mark_q; Sep 18, 2019 at 12:48 PM.
Sep 18, 2019, 12:45 PM
KG7TTQ - Las Vegas
mark_q's Avatar
Thanks all for the kind words and extra motivation to keep me going!

@Danne1700
@DangerFlite
As Atx_Heli states, yaw is handled by tilting the front motors so the rear motor is just stationary. This is completely handled by the awesome APM software.

@Greyukrck
When I have completed design changes and testing and actually get her airborne I will do an article on the build and release all the parts - stay tuned...

@Atx_Heli
Thanks! Of course I have this info from our earlier correspondence . Currently the tilt can go 16 degrees rearward before coming to within 6mm of the wing surface and I still have to add in a hard-stop to make sure this is as far as it goes. I may lengthen the motor mount piece to get more but for now this is where I will try it. I may also add a thin skid plate to where the prop would touch if it flexed enough...

@StuntDouble
I am assuming I will be able to move the CG back, hopefully to about 70mm near where the proper CoL (center of lift) should be for the wing. I'm betting this is part of the "tuning" I will be doing as it may have a large effect on transition from hover to forward flight.


Mark


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