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Old Jun 17, 2011, 09:08 AM
Jason
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United States, SC, Rock Hill
Joined Jun 2004
878 Posts
Got a question for you guys about pitch speed (and some of the basic physics behind our prop choices). I know for electric, we benefit from a higher pitch because of the efficiency. If efficiency weren't as big a concern, how come I've heard discussions on how a pitch of 10, which is the standard for a lot of gas setups, is not enough speed for electric? It works fine for gas engines, if we're turning the same prop at roughly the same rpm, shouldn't we get the same speed?

On another note, for curiosity sake, why is it that gas engines can't turn a higher pitch prop like we can with electrics?

I maidened my plane finally on Wednesday night at a friend's field. I went there to have a nice field for the maiden. Unfortunately the edge of the field on the opposite side is lined with about 2 foot tall grass and the field is more narrow than I'm used to. That, combined with the bigger plane that I am also not used to, and me not even considering any of this, ended with me landing far out on the edge of the runway. Gear caught the tall grass and ripped out. Was a pretty clean break out and I should have it repaired by the end of tomorrow. The biggest let down is I broke my Mejzlik 29x12 and have to wait for a replacement on that. In the meantime I do have a Xoar 26x12 I'll probably just throw on the plane to get it flying.

So this is why I starting wondering about the prop pitches. I called around looking for a replacement prop locally to get back in the air quicker, but everyone just carries props with a pitch of 10 in the standard gas sizes (28x10, 30x10, etc).
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Old Jun 17, 2011, 11:06 AM
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RiBell's Avatar
Canada, BC, Abbotsford
Joined Jan 2003
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Quote:
Originally Posted by super_nova View Post
Got a question for you guys about pitch speed (and some of the basic physics behind our prop choices). I know for electric, we benefit from a higher pitch because of the efficiency. If efficiency weren't as big a concern, how come I've heard discussions on how a pitch of 10, which is the standard for a lot of gas setups, is not enough speed for electric? It works fine for gas engines, if we're turning the same prop at roughly the same rpm, shouldn't we get the same speed?

On another note, for curiosity sake, why is it that gas engines can't turn a higher pitch prop like we can with electrics?
super-nova:
I'll give it a shot. Not saying that I'll be correct but it's my understanding.

~If the same prop is turning at the same RPM. By same prop I mean same brand and type. Not a Zinger vs Xoar vs Mejzlik. Not all 29x12 props have the same pitch. depending on the manufacture it can vary over 1"

~ My understanding about efficiency. Is the best flight possible with the least # of mah used from the battery, and lowest amp draw.
Has anyone carried a data logger and charted just how much power is needed per maneuver. Some might be shocked. might not be as much as thought.

~Gas guys don't care as much about efficiency as as an "electric guy" will. Just put in a bigger gas tank. The power from a gas engine is the same with 50oz of fuel in the tank as it is with 2oz in the tank. For a gas guy it's OK to use all the fuel in the tank for a flight. OK almost all of it as it's better to run out on the ground.

~ 10" pitch
Landing and down lines.
A gas engine need to keep running for the entire flight. Yes that's a pretty simple statement. When a gas airplane is landing. The engine is idling depending on the engine 1,000 to 1,500 RPM; with too much pitch the airplane just won't land. A friend of mine swapped out the prop on his 1/4 scale Stearman from a 22x8 to a 24 x6/10 both of them Zingers. It seems strange but he now has a lot less idle thrust and the airplane slow down and lands real nice. This is also helpful for the down lines. Something that has a bit of discussion here. Prop selection and how much brake to use.
Oh and the other one. If you put too big a prop on a gas engine it will overheat run lean, and most likely quit in flight. Never a good thing with big airplanes.
Rick
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Old Jun 17, 2011, 12:19 PM
Jason
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United States, SC, Rock Hill
Joined Jun 2004
878 Posts
The pitch explanation makes sense. I keep forgetting about the engine idle speed.

So the argument that a 10" pitch is not enough pitch speed on an electric, is that based just on efficiency? In terms of flying the plane, its going to pull just as well as a gas setup with that same prop right?

Jason
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Old Jun 17, 2011, 01:52 PM
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Canada, BC, Abbotsford
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Quote:
Originally Posted by super_nova View Post
The pitch explanation makes sense. I keep forgetting about the engine idle speed.

So the argument that a 10" pitch is not enough pitch speed on an electric, is that based just on efficiency? In terms of flying the plane, its going to pull just as well as a gas setup with that same prop right?

Jason
Same prop same RPM same airplane same weight; there is no reason why the flight performance should be different. The prop doesn't care if itís hydrocarbons or electrons supplying the spinning force. If itís spinning at the same RPM the HP vs watts argument is nil, as the power is the same that should be basic physics.

I belive that the higher pitch props are able to spin slower; and as such there is a greater aerodynamic efficiency as well. It's got to have something to do with physics and aerodynamics. (way is over my head)
There have been some gear reduction set-ups for gas engines.
Which reminds me. Something else to think about gas engines make their power at a fairly high RPM compaired to a big outrunner motor. That will also be a requirement for less pitch on a gas engine

Just look at full size airplanes prop RPM is quite slow. Yes I am also aware it's to keep the tip speed of the prop from breaking the sound barrier but come on now 5000 HP @ 900 RPM. That's a lot of pitch.
Rick
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Old Jun 17, 2011, 03:55 PM
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Vancouver BC Canada
Joined Jul 2006
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I have never heard of a real good explanation as to why higher pitch propellers are more efficient but I have certainly found that assuming that the pitch is inline with the KV of the motor and how fast you want the airplane to go.

The big problem is that there are so many variables including the pilots own personal preferences!

I broke my A100-8 motor (bearing) so I am back to using my backup motor the A100-10 with a 27x12 Xoar propeller. Seems to be about the same power curve but quieter given the lower RPM. Efficiency seems to be about the same or slightly less than the A100-8 and the Xoar 24x12.
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Old Jun 28, 2011, 12:50 PM
Jason
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United States, SC, Rock Hill
Joined Jun 2004
878 Posts
I finally made it out for a full day of flying. I'm still waiting on my prop (Postal Strike up here in Canada, which just ended, has been delaying it) so all I had on hand was a Xoar 26x12. Did not feel like the best prop for the job, but it worked for now.

First thing I noticed, was the plane felt heavy. This was expected with 15Ah of battery on board, but I didn't like it. Without the wheel pants on, it weighed in at 34.66lbs So after a couple flights I swapped to just 10Ah and things were much better. Weight with that setup was 30.78lbs. The plane felt a lot better in the air and on landing. So last night I went to work on lightening it. With my 3P setup I had 3 sets of arming switches and a relatively heavy splitter. Pulled that all out, and it weighed 10oz. I replaced it with a simple Y harness weighing 1.8oz. Also had built an air scoop to help with airflow, decided I didn't need that, and lightened the motor box. All together I was able to remove 14.6oz plus whatever came off sanding things smooth. Replaced it with just the 1.8oz Y harness for the batteries.

So weight right now is almost dab on 30lbs. I'll need to weigh again for an exact measurement. I'm also planning to swap out my 2200mah Rx packs for 1000mah packs I have on order. That should be good for 3-4 flights easily and I can recharge or swap them with another set after that. Will save me just over 4oz in weight there. I'm also thinking about pulling out my turbo regulator and running straight lipols. Another 2.5oz. On a contest day I can recharge them after a flight and the voltage drop during the flight should be really low to the point where someone of my skill level will never notice it

Given Geoff's experience, I'm worried 10Ah won't be enough for sportsman on a windy day, even if I am 3.5lbs lighter than his setup. It certainly won't leave much in reserve, so I've ordered a set of 5800mah to mimic Geoff's setup. My final weight should be somewhere around 30.5lbs with those. Now I'm really wishing I had gone with the Predator motor, which would leave me around 29.5lbs.

I haven't pulled the data from my castle creations esc logger. But I did tach and get an amp reading with a clamp on meter just for interest sake:

Xoar 26x12
Hacker A100-10
CC ICE160HV esc
Fresh 12S2P 10Ah 20C packs - 130amps max current, 6000rpm
After 8-10 minutes of mixed flying - 117amps, 5760rpm

Once I get my Mejzlik 29x12, I'll get more results.

Jason
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Old Jun 28, 2011, 02:23 PM
Team Hacker
Geoff Dryer's Avatar
Vancouver BC Canada
Joined Jul 2006
1,169 Posts
Quote:
Originally Posted by super_nova View Post
I finally made it out for a full day of flying. I'm still waiting on my prop (Postal Strike up here in Canada, which just ended, has been delaying it) so all I had on hand was a Xoar 26x12. Did not feel like the best prop for the job, but it worked for now.

First thing I noticed, was the plane felt heavy. This was expected with 15Ah of battery on board, but I didn't like it. Without the wheel pants on, it weighed in at 34.66lbs So after a couple flights I swapped to just 10Ah and things were much better. Weight with that setup was 30.78lbs. The plane felt a lot better in the air and on landing. So last night I went to work on lightening it. With my 3P setup I had 3 sets of arming switches and a relatively heavy splitter. Pulled that all out, and it weighed 10oz. I replaced it with a simple Y harness weighing 1.8oz. Also had built an air scoop to help with airflow, decided I didn't need that, and lightened the motor box. All together I was able to remove 14.6oz plus whatever came off sanding things smooth. Replaced it with just the 1.8oz Y harness for the batteries.

So weight right now is almost dab on 30lbs. I'll need to weigh again for an exact measurement. I'm also planning to swap out my 2200mah Rx packs for 1000mah packs I have on order. That should be good for 3-4 flights easily and I can recharge or swap them with another set after that. Will save me just over 4oz in weight there. I'm also thinking about pulling out my turbo regulator and running straight lipols. Another 2.5oz. On a contest day I can recharge them after a flight and the voltage drop during the flight should be really low to the point where someone of my skill level will never notice it

Given Geoff's experience, I'm worried 10Ah won't be enough for sportsman on a windy day, even if I am 3.5lbs lighter than his setup. It certainly won't leave much in reserve, so I've ordered a set of 5800mah to mimic Geoff's setup. My final weight should be somewhere around 30.5lbs with those. Now I'm really wishing I had gone with the Predator motor, which would leave me around 29.5lbs.

I haven't pulled the data from my castle creations esc logger. But I did tach and get an amp reading with a clamp on meter just for interest sake:

Xoar 26x12
Hacker A100-10
CC ICE160HV esc
Fresh 12S2P 10Ah 20C packs - 130amps max current, 6000rpm
After 8-10 minutes of mixed flying - 117amps, 5760rpm

Once I get my Mejzlik 29x12, I'll get more results.

Jason
Glad to hear got got some flights in. I just flew in a contest this last weekend with the A100-10 and the 27x12 propeller. I flew pretty big and used a little over 4000 of the 5800 mAh batteries. I think you will be fine with 4 6S-5800s considering hour setup will be a tad lighter.

On another note, the IMAC contest last weekend was at the Red Apple Flyers field in Wenatchee WA. This is one of the nicest fields that I have ever visited. 600 foot paved runway, Full facilities including showers and power at every light pole and bench. This is an electric flyers dream field!
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Old Jun 28, 2011, 03:20 PM
Jason
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United States, SC, Rock Hill
Joined Jun 2004
878 Posts
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Originally Posted by Geoff Dryer View Post
Glad to hear got got some flights in. I just flew in a contest this last weekend with the A100-10 and the 27x12 propeller. I flew pretty big and used a little over 4000 of the 5800 mAh batteries. I think you will be fine with 4 6S-5800s considering hour setup will be a tad lighter.

On another note, the IMAC contest last weekend was at the Red Apple Flyers field in Wenatchee WA. This is one of the nicest fields that I have ever visited. 600 foot paved runway, Full facilities including showers and power at every light pole and bench. This is an electric flyers dream field!
I just found Xoar makes a 3 blade 26x12 I may try out. Do you have any numbers on that 27x12? Like RPM, Amp draw, Watts. I can't remember if you already listed some in this thread for that combo...And what make was it?

That field sounds great! Have you flown off a paved runway before? I have once and it felt like I was taxiing on ice! Having power on a field would be so nice. But I set myself up pretty nice. 2000watt generator, 2400watts in power supplies and 2 FMA PowerLab 8 chargers. With 2 flight packs and parallel charging, I can basically fly non stop. I picked up a cheap 2000watt (1600 continuous) Champion generator. So far its working out well at a fraction of the cost of a honda. Only time will tell how well it holds up.
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Old Jun 29, 2011, 01:46 PM
Jason
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United States, SC, Rock Hill
Joined Jun 2004
878 Posts
I've got another theory question for everyone After the discussion a couple pages back about 3 blade props, I really want to try one out, just to see how it does. Anything I can get to help keep airspeed consistent is a plus in my books.

I think the general rule of thumb when going from 2 blade to 3 blade, is to drop an inch or two on the diameter. Unfortunately, the Mejzlik 3 blades are a lot of money just for testing, but I found Xoar makes 3 blade props in electric variants even.

I wanted to try a 27x12 but Xoar doesn't make a 3 blade in that size. The have a 26x12 but I can't find the electric version in stock, only the gas version. They do have a 28x12 electric which I found in stock in the States and could order. The 26x12 gas prop would probably be similar to the 27x12 that Geoff likes. Do you guys think the electric 28x12 would be too much for the hacker a100-10 (150kv)? It would be the electric version so it would be lighter and less load I would hope than a similar sized gas prop...

Just looking for people's opinions, I know unless someone has run these exact combos, you can't give definite yes/no answers.
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Old Jun 29, 2011, 03:04 PM
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Moss, Norway
Joined Jul 2003
437 Posts
Hello.
The dutch MVVS supplier, Pe Reivers, has made a very good "propeller power calculator" which he has posted on his internet site, http://www.mvvs.nl/
Look under "utilities" in the menu at the left hand side.
There you can compare different propellers etc. based on expected rpm.
The load factor for a three blade propeller is 1.5 times that of an equivalent two blade propeller.
What power level are you looking for?
(Suggestion: Put in the values you actually got with the Xoar 26x12 for comparison, adjust power factor, efficiency etc. to reproduce the result you got. Then use similar figures for different propeller dimensions. Use some judgement for expected rpm values, keeping in mind that these will drop somewhat when you increase the load.)

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Old Jun 29, 2011, 03:14 PM
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Vancouver BC Canada
Joined Jul 2006
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Originally Posted by super_nova View Post
I just found Xoar makes a 3 blade 26x12 I may try out. Do you have any numbers on that 27x12? Like RPM, Amp draw, Watts. I can't remember if you already listed some in this thread for that combo...And what make was it?

That field sounds great! Have you flown off a paved runway before? I have once and it felt like I was taxiing on ice! Having power on a field would be so nice. But I set myself up pretty nice. 2000watt generator, 2400watts in power supplies and 2 FMA PowerLab 8 chargers. With 2 flight packs and parallel charging, I can basically fly non stop. I picked up a cheap 2000watt (1600 continuous) Champion generator. So far its working out well at a fraction of the cost of a honda. Only time will tell how well it holds up.
It is my understanding that a 3 blade propeller is less efficient that a 2 blade so I have avoided them.

I have flown off pavement before. I prefer to land on grass as my 5" wheels tend to roll forever on pavement.

I have a 1000 Watt generator but it was nice not to have to have to pack it along with carrying a gas can.
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Old Jun 29, 2011, 03:24 PM
Jason
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United States, SC, Rock Hill
Joined Jun 2004
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Geoff if you get a chance sometime to take some measurements, I'd be interested to see your amp draw, watts and rpm on the 27x12. Which I'm assuming is a Xoar?
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Old Jun 30, 2011, 11:16 AM
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Originally Posted by super_nova View Post
Geoff if you get a chance sometime to take some measurements, I'd be interested to see your amp draw, watts and rpm on the 27x12. Which I'm assuming is a Xoar?
I will measure it for you this weekend. It is a Xoar 27x12 (regular wood)
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Old Jul 02, 2011, 05:47 PM
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Vancouver BC Canada
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Originally Posted by super_nova View Post
Geoff if you get a chance sometime to take some measurements, I'd be interested to see your amp draw, watts and rpm on the 27x12. Which I'm assuming is a Xoar?
Took some measurements today.

Hacker A100-10 Motor
Hacker 170 ESC
Xoar 27x12 (wood) Propeller
12S2P Flighmax 6S 5800 mAh 30C Batteries

Static Measurements
160 Amps
7400 Watts
6000 RPM
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Old Jul 02, 2011, 07:36 PM
Barefoot Birkinsomething
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United States, CA, Hayward
Joined Aug 2004
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Originally Posted by Geoff Dryer View Post
Took some measurements today.

Hacker A100-10 Motor
Hacker 170 ESC
Xoar 27x12 (wood) Propeller
12S2P Flighmax 6S 5800 mAh 30C Batteries

Static Measurements
160 Amps
7400 Watts
6000 RPM
thats REALLY wierd...on my a100-10 (brand new from gravesrc) i have a 29x12 on it, as per recommendation, and i got about the same amp draw, maybe just a tad more. i believe i got around 165-170 on a fresh set of packs.
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