Which prop to use?

[ATIS]

Not to put Mike on the spot but he sent my a message asking for some advise. He question is a common one amoung all pilots...which prop for my applications? He named his planes and motors which helps a lot but something that is needed as well is ESC size and the type of flying you want to do.

Here is is orginal question:

Hello ATIS, Can you give me your recommended prop suggestions for my applications? Everytime I try and pin down a decent prop size, I get so many suggestions of different sizes, I get confused and don't understand what to get. I am not knowledgeable to understand a lot of the jargon yet so I just want to get your opinion. I have a T-34 with the power 32, 60amp esc. I have been using a 4s battery and was told by LHS to use a 13x8 prop. Well, that prop was so thick that the nut barely screwed on but I tried it anyway. As soon as I powered it up, the nut flew off and broke that prop. So I used the 12x8 and seem to have good success with it. As for my Apprentice, I have a power 25 and also use the 12x8 prop. with the 4s battery. On my Corsair, I have an 800 watt Turnigy that is suppose to be equivalent with the power 32 and I use the 4s and use the 12x8 prop as well. What are your recommendations on props? Am I o.k. with what I have already? thanks a lot.

Before I answer I am going to point Mike (and everyone else to the "beginner section" as I have put together 2 very long threads that explain about 75% of the hobbies terms and provide explainations to a dozen topics from props, to esc's, to finishing foam. Yes, its in the beginner section but the info isnt all for the beginner and even I go back and reread some of it when I am having a senior moment. :opto:

Basic accronyms:

http://www.horizonrcflyers.com/forums/showthread.php?t=76

Beginner answers:

http://www.horizonrcflyers.com/forums/showthread.php?t=83

There is a lot of reading there but it will help you all out if you get in a rush to fly and cant get an answer to get you in the ball park.

Now to answer Mike's question:

T-34 on Power 32 with 4s... the APC 12x8E prop will give him lots of speed...if he wants to slower her down but still have a ton of thrust for good verticals and big loops I would suggest a APC 12x6E Prop on 4s.

The Apprentice on a Power 25 on 4s is over kill... I do not like the Power 25 on 4s as she is a higher KV motor and as such becomes amp hungry and flight times drop. The P25 on 3s with the stock prop or a APC 12x8E prop will work fine. If you want to stay with 4s then I suggest you drop to the APC 12x6E prop to slow her down a little and keep the wing on her.

For the Corsair I would follow the same rule as the T-34. (GLUE THE WING ON!!)

Now with all that said, anytime you make a prop change or change the number of cells in the lipo you need to test her on a watt meter to be sure you dont go over the ESC's rating or the motors rating.

I hope this helps Mike and others...it is not my intention to embarrass Mike in any way but his question and his choice of motor and plane combos are becoming very common, especially amoung beginners looking to "super charge" thier planes!

Off to fly...first day in 3 months that the winds are suppose to stay under 5 mph!! (and the temps are hitting 60*!)


http://www.horizonrcflyers.com/forums/images/misc/progress.gif

[WJCJR1]

Great information ATIS!

Wayne

Edit: That Corsair must COOK! The Blue Blurrr!

[Mike]

Edit: That Corsair must COOK! The Blue Blurrr!Yes it does. It loves visiting the clouds

[Mike]

The Apprentice on a Power 25 on 4s is over kill...

ATIS, let me quote you in an earlier post.

I prefer to over power my planes...thier like sports cars, they can never have too much power!!

[WJCJR1]

::tonguee: We all have different perceptions.

There are some planes that beg for more power and perform better with it. There are others, maybe like the Apprentice, that don't benefit much from being WAY over-powered because their ability to take advantage of this extra power is hampered by their physics.

It is kind of like someone who builds a Subrau WRX for AutoCross purposes then gets sent home earlier than the modded Malibu. The WRX guys says why would you do that to a Malibu. I look over and say because it was fun. You know how many looks I got at autocross? I had fun as heck doing it and the Porsches, Subarus, Stangs and other very NICE cars you'd expect to see at an Autocross event that went home before me went home mad because of no other reason then the Malibu didn't look all that sexy but had a great time and oh man how could they have a slower time than that thing.

Now definitely there's a point in which the Malibu, Apprentice, can not compete with the purpose built machines but are we really worried about the .001 seconds here? Or are we more concerned on having a great time.

Now nobody is snearing here but I never took those Autocross snears personally and honestly I had a better time enjoying myself rather than trying to 'look the look'. Be mindful of limitations (which ATIS was eluding to about over-powering certain planes), enjoy yourself to the fullest and never stop expanding your horizon.

Wayne

[ATIS]

Over power is nice, but remember the plane was designed for a certain amount of power so when you go over (or way over) the design limit things break so the need to reenforce areas becomes a need and that means more weight so your thrust to weight ratio drops and the planes performace will start to drop as well. (Wing loading increases so your stall speed is higher, landing speed goes up, take off speed has to be higher, etc)

[WingingIt74]

Can I assume this bit of info?


T-28 with an E-flite Power 15


Power 15:
Recommended Prop Range: 10x6–13x6.5
Voltage: 7.4–14.4V
RPM/Volt (Kv): 950
Resistance (Ri): .03 ohms
Idle Current (Io): 2.00A @10V
Continuous Current: 34A
Maximum Burst Current: 42A (15 sec)

Lipo:
Capacity: 4000mAh
Voltage: 3S1P / 3 Cell / 11.1v
Discharge: 30C Constant / 30-60C Burst
Weight: 315g (including wire, plug & shrink wrap)

ESC:
ElectriFly 45A Silver Series
45A of continuous current
50A surge currents
Includes a powerful 2.0A BEC

Using this Electric Motor Calculator:
http://www.brantuas.com/ezcalc/dma1.asp

Using a similar ESC, a 10x8 APC will give me 29.3 motor amps, which is nearly 90%.



In theory, I should be alright with this combination, am I correct? Yes, I know I need a watt meter to be right on.

[ATIS]

Yes, but where are you finding a APC 10x8E prop?? I have never seen one. I have flown the APC 10x7E prop (or on the same motor a APC 11x5.5E Prop for massive climbouts)

[WingingIt74]

Good point, I was looking at the regular 10x8.

How do I get more speed/thrust with the 3S?

[WingingIt74]

I guess I'm confusing myself. The Apprentice is a "BL15" swinging a 11x8 prop. Can the E-Flight Power 15 do the same?

[ATIS]

Should be able to as the KV should be similar.

[WingingIt74]

I guess this is where a watt meter comes in handy. The BL15 is an 840KV and the P15 is a 950KV. Could the lower KV allow it to swing a bigger prop?

[WJCJR1]

The brushless 15 may have a lower kV but it also has a lower Continuos Amperage rating and cooks whne you're too far over. The Power15 will take a beating before she cooks, just ask how I know!

SO yes the Lower kV accumulates less resistance since it is spinng the prop slower thus accumulating less amperage, heat (resistance). When I fly the Apprentice with the P15 on 4S I use a 11X5.5 or 10X7, with 3S I use the 12X6.

Not of course not EVERY motor is going to be exact but give me a prop to test on the P15 and I'll Watt it for you with 3S or 4S.

Wayne

[WJCJR1]

I ran a 12X8 APC Prop on the P15 with a 3200mAH 20C battery.

Set-up as follows:


E-Flite Power15

E-Flite Pro 60A ESC

E-Flite 3200 mAH 20C 3S Battery Fully Charged beginning static voltage of 12.57V

APC 12X8 E-Prop
Results

WOT; 35.43A, 384W @ 10.85V
3 Clicks Below WOT; 31.70A, 335W @ 10.56V
This is an older battery, a newer battery may provide a slightly higher Amperage as your battery being newer or having a higher discharge capacity may hold voltage higher whihc in turn rotates the motor quicker and increases Amperage. For my scenario and this battery pack the 12X8 would be fine as long as I did not run @ WOT all the time.

At 3 clicks below WOT yes she was turning slower but no by much and woohee she'd be cooking. I like to always check WOT and then a few clicks below, really amazing how much the amperage spikes those last few clicks of throttle.

So your question about the 11X8 you will have no trouble, you will be well below your motor and ESC's capacity. Without the validation of a test, which is more important than opinion, I'd say you could run WOT all day with that 11X8 and stay easily below the red zone.

Wayne

PS Remember 3S Battery not 4S! Run 4S with 11X8 WOT at any length and you will get in trouble.

[WingingIt74]

Do you have an idea what prop would give me the most speed and thrust with a 3S?

Let's say I set the P15 aside for my future Bonanza. What P15 equivalent could I put in the T-28 that will work with the ESC and Lipo I have?

I can't be the only one that finds all of this confusing. I know some of the other MFGs don't use the Power 15 designation. How can you compare apples to apples with out buying every apple in the orchard and testing for myself?

I did see that scorpion has a good chart on each motor, but then I'm back to guessing what size I'm looking at.

[WingingIt74]

Here's a nice list of specs, now what am I looking at...er...um..... for? ;)

http://progressiverc.com/Brushless_Motor.html

[WingingIt74]

OK, am I understanding this right.

A Power 15 is a 3512-950 ???


I assume this is Scorpions equivalent...
http://www.scorpionsystem.com/catalog/motors/s30_series_v2/SII-3014-830KV/

[WJCJR1]

Well CLSSY56 the 11X8 you'll gain some speed over the 12X8. The 12X8 will give you more thrust though. For flight times, mix of both I'd go 11X8. More hang time then 12X8. It is a give or take either way.

Now let us say you can't get ahold of the 11X8 and 12X8 for some reason a 10X10 on a 3S would be interesting. Should get great speed and reasonable thrust, you'll have more thurst than the APprentice on You should still be within your P15 and ESC's parameters even at WOT. Chew on that one a few minutes. Actually this should be the fastest prop of the three.

The only true way to tell is get ahold of the above 2 or 3 choices and give them a whirl and of course Watts test them.

Wayne

[WingingIt74]

An 11x8 should be over on the Continuous Current and Under the Burst in Flames Current of 42A, right? Is the Continuous Current, the point where the motor is the most efficient and therefore get as close to that number as I can?

[WingingIt74]

According to the motor calculator I posted earlier.

P15
Master Airscrew 11x8 (I assume this is closer to the stock apprentice prop)
3s-4000 (custom)
CC Phoenix 45

Motor Amps: 43.097
Pitch Speed: 63.7 mph
Thrust: 73.1 oz


So, should you do 90% of the Burst or Continuous? OR be close to the Continuous as you can?
• 90% of 34A = 30.6A
• 90% of 42A = 37.8A

[WingingIt74]

Same scenario for the Bonanza, E-Flite calls for an APC 11x8E. It can also weigh 4.5 lb (72oz) which is heavy compared to my 42.5oz T-28.

Motor Amps: 39.691
Pitch Speed: 65.1 mph
Thrust: 77.1 oz

I've got to be missing something here some where? These numbers are closer to 90% of Burst.

[WJCJR1]

Continuous maximum current is NOT most efficient current. It is the highest current you can carry 100% of the time. It is your 100% Duty Cycle rating, hardest point you can push it for 100% of the time.

The 11X8 will be under your 34A Continuous, at least it would for me with my batteries. I see you added a link to an online calculator I have always found the online calculators to be a little high in their calculations/projections. It may be my E-Flite, FlightMaxx and TP batteries just can't deliver as the fictitious batteries in the calculator can.

Getting the Watt meter woudl be the best thing you coudl do to learn a lot about the interaction between Thrust/Diameter, Speed/Pitch and how those correlate between battery capacities and types. I have been amused at the information this simple Watt meter provides.

As a matter of fact, a gentleman at my airfield this passed weekend, cooked a battery in his hopped up Super Cub. He has a Power-Up 480 motor with a 40A ESC and cooked a 1800mAH 15C battery. Doing the math a 1800mAH X 1.5 (15C) this battery can deliver a continuous 27A. He flew for about 5-6 minutes WOT then the play started dogging real bad he came in to find his battery bloated and had to cut it out of the plane as it had expanded to a point it was not able to be pulled out. I told him he had cooked it and described exactly how. Terry did not believe immediately this motor was capable of pulling more than what the battery could deliver. We hooked up a separate battery to the plane revved her up with the Watt meter inline and YUP over 31A! He was an easy 15% over the capacity of the battery and PUFF!

Wayne

[WingingIt74]

Continuous Current seems to be both the most efficient current and 100% Duty Cycle. Anything over, will eventually overheat the motor and slow it down? So, if it comes down to Duty Cycle, 90% of Burst is probably a good number as long as you are not WOT 100% of the time. Am I correct?

I know it would be nice to have a Watt Meter, but then how many props from the orchard do I have to buy to find the right one? For example, a watt meter is ~$50, then you buy 4 props @ ~$5 each, total of ~$70 that could be saved if the right combo could be picked from a certain % or -2A under the Burst.

[ATIS]

Also remember that E props are lighter then SPORT...so they take less pwer to turn. the 10x10 is a sport prop and thats a lot fo pitch to turn so it could hurt your over all performance by holding back your max rpms. I would look to get to 30amps at WOT.

[tkrahlin]

::tonguee: We all have different perceptions.

There are some planes that beg for more power and perform better with it. There are others, maybe like the Apprentice, that don't benefit much from being WAY over-powered because their ability to take advantage of this extra power is hampered by their physics.

Wayne

Yepper ::tonguee:

I just had a situation yesterday with my Apprentice running the Power-25 with a 4s x 3300mAh x 2c battery.

I usually run a 12x6e prop, but I wanted to do some ‘trial runs’ using a 12x8e. When I held the plane between my ankles and did my run up, JJ pointed out the tail feathers fluttering in the prop wash.

As expected she's faster and takes longer to get up to speed. However, the situation came about when I was descending from altitude at full throttle (not a straight dive – descending). When I eased back on the elevator to level out, nothing happened. So I eased back a little more and still nothing. Once I reduced the throttle, I was able to regain pitch control. It took you longer to read this than it took for it to happen, but it was real. I duplicated it twice more -- but higher.

Rather than take a chance on blowing out windows in the nearby houses, I went back to the 12x6e.
.

[WJCJR1]

Did you Watt that setup? Have concern you are over Burst or maybe you never went to WOT.

I bet it flew with command.

Wayne

[tkrahlin]

Did you Watt that setup? Have concern you are over Burst or maybe you never went to WOT.

Wayne

"...never went to WOT" --- Have we met? ::tonguee:

I did watt the setup, but you don't want to know... If I told 'ya, ATIS' head would "asplode".

Seriously, like ATIS has said many times, quality parts are worth the money.

E-Flite, Castle Creations and Thunder Power.
.

[ATIS]

let me up my life insurance and verify my medical is paid before you post numbers!!

The apprentice benefits more from an increase in thrust more then speed.