What a drag!

[Jim Mynes]

I just got my E-Vector 40 ARF put together. I figured the size and weight were similar to my Primary Force, so I used an identical Cobra 2820 and an identical APC 12x6 EP propeller, cut down to 11”. Powered by the same 4S 2800 batteries I fly in the PF, I dialed in a similar RPM for the Vector’s maiden flight. Lap times were 4.5 seconds, much faster than the PF at 5.1 seconds.
Now, the Primary Force weighs 45 ounces ready to launch, the Vector comes in at 48 ounces, and it has 36 more square inches. Should need more power, right?
The PF runs at 9100 RPM, the Vector got dialed back to just under 8600 RPM and was still faster at a 5 second lap. I’m still sneaking up on 5.2
Amp draw is much lower on the Vector as well.
All I can figure is that the electric gear all hanging out in the breeze on the PF is A LOT more draggy than I would ever have thought.

[bill bischoff]

Same line length and diameter?

[MikeyPratt]

I just got my E-Vector 40 ARF put together. I figured the size and weight were similar to my Primary Force, so I used an identical Cobra 2820 and an identical APC 12x6 EP propeller, cut down to 11”. Powered by the same 4S 2800 batteries I fly in the PF, I dialed in a similar RPM for the Vector’s maiden flight. Lap times were 4.5 seconds, much faster than the PF at 5.1 seconds.
Now, the Primary Force weighs 45 ounces ready to launch, the Vector comes in at 48 ounces, and it has 36 more square inches. Should need more power, right?
The PF runs at 9100 RPM, the Vector got dialed back to just under 8600 RPM and was still faster at a 5 second lap. I’m still sneaking up on 5.2
Amp draw is much lower on the Vector as well.
All I can figure is that the electric gear all hanging out in the breeze on the PF is A LOT more draggy than I would ever have thought.

Hi Jim,
Not sure of that one, but the P-Force is not draggy at all.  There has to be something in the set up that is way different, because my prototype flies on a OS FP 25 and one of my electric versions turn has a Cobra and uses a lot less power and battery than what you have listed.  Also there has been a bunch of P-F’s built with electric power systems not showing the usage you have.  Line size and length can have a big effect of drag so maybe it's a combination of a number of things.  A properly set up P-Force flies very good at 5 to 5.2 lap times and only burns 3 ounces of glow fuel and around 1800 or less per pack.   Let me know what you find.

Mikey

[Dennis Adamisin]

Hi Jim
APC made (at least) 3 versions of the 12x6E prop:
* The original thin version like to run around 8400 RPM
* They brought out a thicker version with higher rated max RPM that needed something like 9600 RPM
* I got them to revert somewhat and re-introduce a thinned out version as the 12x6 EP F2B.  This is a reverse pitch (CW, LH rotation, pusher  take your pick) and likes to run around 8800 RPM.

Thus I believe you may have gotten a different prodcution run (old stock/new stock?) of the 12x6. The F2B version has those letters molded in where the prop size is.  I do not know a "marker" for the earlier thin & thick versions.

[Jim Mynes]

Same line length and diameter?

Not only same length and diameter, but same set of lines and same handle.

[Jim Mynes]

Hi Jim,
Not sure of that one, but the P-Force is not draggy at all.  There has to be something in the set up that is way different, because my prototype flies on a OS FP 25 and one of my electric versions turn has a Cobra and uses a lot less power and battery than what you have listed.  Also there has been a bunch of P-F’s built with electric power systems not showing the usage you have.  Line size and length can have a big effect of drag so maybe it's a combination of a number of things.  A properly set up P-Force flies very good at 5 to 5.2 lap times and only burns 3 ounces of glow fuel and around 1800 or less per pack.   Let me know what you find.

Mikey

I’ve been flying my PF for maybe 3 years now. I really like it, and was in no way trying to imply that it was less than desirable. I just find it curious that there is such a difference in the RPM of the two airplanes.
My power installation on the PF is less than svelte. The ESC is mounted between the landing gear legs fully out in the wind. There are wires exposed, and Velcro straps holding all the components in place. If there is excess drag, I don’t blame it on the airframe.

[Jim Mynes]

Hi Jim
APC made (at least) 3 versions of the 12x6E prop:
* The original thin version like to run around 8400 RPM
* They brought out a thicker version with higher rated max RPM that needed something like 9600 RPM
* I got them to revert somewhat and re-introduce a thinned out version as the 12x6 EP F2B.  This is a reverse pitch (CW, LH rotation, pusher  take your pick) and likes to run around 8800 RPM.

Thus I believe you may have gotten a different prodcution run (old stock/new stock?) of the 12x6. The F2B version has those letters molded in where the prop size is.  I do not know a "marker" for the earlier thin & thick versions.

You may be onto something here. Neither prop is the F2B version, but could be from different lots as you say.
But, I would expect the amp draw to be similar between the two. The PF, last time I checked, was pulling about 34 amps. The Vector was pulling 22 amps before I turned the RPM down one more time.
I think when I get the speed of the airplanes closely matched it might be fun to swap the propellers and see what happens.

[Dave_Trible]

I would think a lot of it is in aerodynamic differences beyond just the drag of components.  Wing loading, airfoils and very minor differences in level flight AoA could create a lot of difference in drag.  The airplanes are pretty different.  On my own designs I’ve seen just changing the cowling shape can show measurable differences on the stopwatch.

Dave

[Dennis Toth]

Jim,
Since you have the extra rpm with a low amp draw try de-pitching 1/8" of pitch at a time to get the lap time. If you are one 60' C to C I would aim for a lap time around 4.9.  The lower pitch will give more bit for pulling through second round in the wind. The IC setup with the OS 25 would use around a 4" pitch @ 11K ish. I think Dennis A has hit on the difference (assuming the same ESC & Timer), thin blades make a big difference in amp draw with not to much lose of pulling power.

If you can do a ground test between the two setups to see if swapping the props changes the amp draw. Let us know.

Best,   DennisT

[Jim Mynes]

https://hobbyking.com/en_us/carbon-fiber-propeller-12x6-black-cw-ccw-2pcs.html


https://hobbyking.com/en_us/aerostar-carbon-fiber-propeller-11x6-1pcs.html

Thanks for the links. The first one (set of two) gets less than glowing reviews. The second one looks interesting.

[Jim Mynes]

I would think a lot of it is in aerodynamic differences beyond just the drag of components.  Wing loading, airfoils and very minor differences in level flight AoA could create a lot of difference in drag.  The airplanes are pretty different.  On my own designs I’ve seen just changing the cowling shape can show measurable differences on the stopwatch.

Dave

Interesting. I have not considered all the variables, just the general size and weight being somewhat similar.
The PF started life as an ARF that I had to strip down and de-warp. Once it was straight(er) I slapped it together.
The Vector, also an ARF, is the first plane I have seriously fussed over with incidence meters, levels, squares, etc. to try to get it lined up as well as I can. It may not be perfect, but it’s as perfect as I could get it. Maybe that helped make it cleaner in the air.

[Jim Mynes]

Jim,
Since you have the extra rpm with a low amp draw try de-pitching 1/8" of pitch at a time to get the lap time. If you are one 60' C to C I would aim for a lap time around 4.9.  The lower pitch will give more bit for pulling through second round in the wind. The IC setup with the OS 25 would use around a 4" pitch @ 11K ish. I think Dennis A has hit on the difference (assuming the same ESC & Timer), thin blades make a big difference in amp draw with not to much lose of pulling power.

If you can do a ground test between the two setups to see if swapping the props changes the amp draw. Let us know.

Best,   DennisT

Hi Dennis,

The extent of my propeller magic is to balance them and maybe cut them shorter. I did discover that leaving the tips square makes lots of noise, so after I cut them shorter I give the tips a curvy shape.
I’ve never fooled with pitch, other than selecting a prop with more or less of it.
Mostly I run APC props because they’re readily available and inexpensive. I know they are not the best that can be had, but neither am I.
The power systems are identical except for the timer. KR in one, Hubin in the other. But I don’t see that as a factor in the different power required to fly what I thought were similar airplanes.
Will likely fly again Saturday. Can’t forget to add nose weight. It wanted to float forever, then land on its tail.

[Dennis Toth]

Jim,
Might be worth swapping props and checking the rpm and current draw. I would try a 5 pitch APC on the Vector.

Are you going to Palmetto next week?

Best,    DennisT

[MikeyPratt]

Hi Dennis,

The extent of my propeller magic is to balance them and maybe cut them shorter. I did discover that leaving the tips square makes lots of noise, so after I cut them shorter I give the tips a curvy shape.
I’ve never fooled with pitch, other than selecting a prop with more or less of it.
Mostly I run APC props because they’re readily available and inexpensive. I know they are not the best that can be had, but neither am I.
The power systems are identical except for the timer. KR in one, Hubin in the other. But I don’t see that as a factor in the different power required to fly what I thought were similar airplanes.
Will likely fly again Saturday. Can’t forget to add nose weight. It wanted to float forever, then land on its tail.

Hi Jim,
OK, now I know it was an ARF and that helps a bunch.  The ARF P-Force has a ton of rudder offset, that and the components hanging in the air will cause a fair amount of drag.  Next time out, set the rudder offset to almost 0 with a max of 1/16” to the out side of the circle.  That should help reduce the amp draw and level it out.

Later,
Mikey

[Steve Helmick]

Mike is probably onto something here: Yaw! Especially with a profile, a significant difference in yaw would show an equally significant change is drag and power requirement. Might be worth some testing and adjusting one plane or the other.

Something else, already touched on, is the prop tips. I had an interesting thing happen to me when I was flying my Fancherized Twister with a TT 11 x 4.5 prop. It would typically flash to 11.3+K rpm when I pinched off the muffler pressure hose while warming it up. Then, I buzzed that prop and fuzzed up the tips. When I got home, I trimmed the diameter to 10.75" and left them pretty square. That prop would not get up to 11.3K. I reworked the rework and don't recall that I ever got that prop to run as fast. Looking at the stock tips, they're very sharply tapered, which made me think "HMMMMM. I sure screwed up way back in the '60's, when I was flying speed!"

By the way, I have since re-carved tips on APC props and even completely re-carved APC props, and those worked very well. Those were 12-5 and 12.25-3.75, both reworked to 11.5" diameter. The 12.25 was completely reshaped and is still a back-up prop for my .46VF.  Steve   

[TDM]

You are comparing two planes with completely different wings. Sure a profile will drag more but the bigger impact comes from the wing design. If line length is the same and you use same motor prop  combination, trust the results you get from the electronics like how much you put back in the pack as that is pretty reliable. If you run the motor at lower RPM that is because yo have a cleaner aerodynamics. Just compare the power usage before and after to see how much better this is. Electrics are consistent and are a good go to place to investigate and compare thighs.

[MikeyPratt]

https://hobbyking.com/en_us/carbon-fiber-propeller-12x6-black-cw-ccw-2pcs.html


https://hobbyking.com/en_us/aerostar-carbon-fiber-propeller-11x6-1pcs.html

Hey MM,
Have you tried that prop before?  What was the amp usage and thrust and all the specs for the model used?  I’m thinking I may try one on the XL (12 X 6).

Mikey

[Jim Mynes]

Electrics are consistent and are a good go to place to investigate and compare thighs.

My wife does not approve of that idea.

[Jim Mynes]

Jim,

Are you going to Palmetto next week?

Best,    DennisT

Palmetto is on my radar. More than likely Sunday only.

[Steve Helmick]

"Electrics are consistent and are a good go to place to investigate and compare thighs."


"My wife does not approve of that idea."

Suddenly, the appeal of electrics is more clear to me...  Steve

[Dane Martin]

"Electrics are consistent and are a good go to place to investigate and compare thighs."


"My wife does not approve of that idea."

My wife and I compared thighs. No surprise, she won.

[TDM]

Since we are in the investigating realms here I will check the XOAR props in the near future. I put a flight on a 13X6 XOAR prop and was impressed. What is even more impressing id that on pitch gauge they are exactly what they claim to be. If I was checking a 6in pitch prop it was 6in pitch.  I think they CNC the blades then finish and balance them too. XOAR PJN series that is.