three blade or 4 blade

[Shorts,David]

I must go faster. I can speed up the esc, but is there a more efficient 3 blade prop I could by trying? I'm using a MAS 11x6. Rimfire .32. Hubin timer. I'm getting 5.8 laps. 12 inch props will not fit without ruining stuff, like the prop. I saw a bunch of similar looking CF 3 blades at the last stunt contest. I hate to ask, but how much do they cost and where do I get them?

[Mike Alimov]

Larger diameter prop doesn't translate to higher speed. Higher pitch does.
But in your case, simply kick it up by about 800 RPM and see if you like it. Why complicate things?

[Ken Culbertson]

MAS 11-6 three blade is a fast prop. Don't understand why you're too slow with it. How big's your plane, what's your rpm, how long are your lines?

A CF three blade is about $60. I don't sell props anymore. Eliminator prop in the vendor section has some for sale.

Motorman

I use that exact prop and have no real issues.  I suppose I will switch to CF at some point. I have flown several of them and they are better but not for the reasons you are trying to solve.  What RPM are you using?  Mike and Motorman are right, you don't need more diameter and 6 is plenty of pitch.  The RPM range we run in is nowhere close to the high end of an electric. Bump it up.

Ken

[Brett Buck]

Larger diameter prop doesn't translate to higher speed. Higher pitch does.
But in your case, simply kick it up by about 800 RPM and see if you like it. Why complicate things?

    As a general rule, adding diameter and leaving the pitch and rpm the same will increase the speed substantially - because it is more efficient. In generally, you will have to run it more slowly to get the same airspeed, which tends to save the battery. That's the issue with just speeding it up as it is, 800 rpm seems to be about 25%-30% more power.

    Brett

[Shorts,David]

Thanks guys, that's very encouraging. I imagined everyone telling me to ditch the prop. I'll just kick it up and try again. Plane is a modified impact. 74oz with battery. Flew on 65s today. Barely made wingovers at 5.9 and 6 second laps. Obviously way too slow.
 

[Shorts,David]

    As a general rule, adding diameter and leaving the pitch and rpm the same will increase the speed substantially - because it is more efficient. In generally, you will have to run it more slowly to get the same airspeed, which tends to save the battery. That's the issue with just speeding it up as it is, 800 rpm seems to be about 25%-30% more power.

    Brett

Yeah, that's the catch I suppose. I may try cutting down a twelve inch a little bit and see if it clears. If my battery doesn't last. I'm running a 4s 4000. Was thinking about trying a 5s 3200, but I'd have to buy it first.

[jerry v]

Yeah, that's the catch I suppose. I may try cutting down a twelve inch a little bit and see if it clears. If my battery doesn't last. I'm running a 4s 4000. Was thinking about trying a 5s 3200, but I'd have to buy it first.

Rimfire .32 can handle easily 40 AMP draw on 4 cell 4000 lipo for 10 minutes. You can use 3 bladed 11x7 MAS prop, tractor or pusher.  I will recommend 5 cell battery, Rimfire .32 can handle that too. One more solution is taller landing gear. At least bigger diameter of the wheels.

Jerry

[Mike Alimov]

Plane is a modified impact. 74oz with battery.

I wish I had this data from your first post, I would not have recommended to stay with the 11" prop. A 74oz Impact is too much for this prop. We've been using this prop for 2 years and believe that about 64 oz is the limit for it. Switch to MAS 12-6 3-blade and you will have much better line tension on top. Make taller landing gear if you have to.
Also a comment on your powertrain. 4S systems use more current than 5S systems, and way more than 6S.  More current means more heat lost due to parasitic resistance (wires, motor, battery, etc).
I'm currently planning to put together a Score ARF, which will come out in the low 70oz range, and project needing a 6S 2800 mah battery to complete the pattern.
With the 4S setup, once you find the right prop and rpm to give you the desired lap time (probably around 5.1"), you may find that the system runs very hot, and there may not be enough capacity to complete the pattern.

[Ken Culbertson]

Thanks guys, that's very encouraging. I imagined everyone telling me to ditch the prop. I'll just kick it up and try again. Plane is a modified impact. 74oz with battery. Flew on 65s today. Barely made wingovers at 5.9 and 6 second laps. Obviously way too slow.

I am going to change my opinion a bit here as well.  74oz is outside my comfort zone on prop size.  I live in the 55-65 range.  I have run the MAC 12-6 and did not like how it handled in corners but I learned years ago that the first step, not necessarily the last, in being under *powered* is the "S" value of the battery.  Now, I always go with the higher end of what my ESC and Motor supports and never under 5s in anything larger than a Twister.  There are tons of batteries out there that all have different weights.  With the new TP entries you can get a 6s that is very close in weight and dimensions to the 4s of a few years ago and it is only going to get better.  Keep in mind that as the "S" value goes up, the mAh required goes down ,ergo weight about the same.  Bottom line, before you start changing a lot of things, check your motor and ESC ratings.  If both will support a 6s battery, beg, borrow or steal one and give it a try. 

Ken

[phil c]

I must go faster. I can speed up the esc, but is there a more efficient 3 blade prop I could by trying? I'm using a MAS 11x6. Rimfire .32. Hubin timer. I'm getting 5.8 laps. 12 inch props will not fit without ruining stuff, like the prop. I saw a bunch of similar looking CF 3 blades at the last stunt contest. I hate to ask, but how much do they cost and where do I get them?

Master Air Screw uses the actual chord length of prop to assign pitch.  Everybody else, apparently, uses the back face of the prop, which can vary a lot along the blade length depending on the airfoil used.

Draw a simple more-or-less flat bottom airfoil.  Use a ruler and draw a chord line from the trailing edge to the center of leading  edge.  Draw a second line along the bottom of the airfoil

Do the same for a more-or-less symmetrical airfoil with the same "chord lines".  It's easy to see that the "everybody else" method to measure  pitch is highly subjective.  And what do you do when the thickness and airfoil of a prop blade changes from near the hub to the tip?

The "EBE" method works fairly reliably on wood props.  Virtually all use a blade shape that is flat most of the chord with any curvature limited to the front 5% +/- of the blade.

Most molded props use proper airfoils from blade root to the tip.  There really is no ideal way to measure pitch from the back face of the prop.  So at least one manufacturer, "Master Airscrew", just gets the pitch from the mold drawings.  Molded props have very limited variation in pitch anyway. If you do see some it probably was made that way on purpose.

[Shorts,David]

Well, how would this pack be for an experiment. Hopefully a successful one. I'll also buy the 12x6 and make it work. New gear legs if possible. Its a trike, that's why there isn't the normal clearance. Other things are changed too for a particular scale appearance. I don't expect it to win trophies, but sure would like to see it get its day in the sun.

It's a 2650 6s 40c. 
Another is much cheaper, 2700mah, 6s, but only 25C with 35 burst.
Weight doesn't matter too much because I have an ounce of lead in the nose I can widdle away at.

[Ken Culbertson]

It's a 2650 6s 40c. 
Another is much cheaper, 2700mah, 6s, but only 25C with 35 burst.
Weight doesn't matter too much because I have an ounce of lead in the nose I can widdle away at.

25C is normally plenty and for whatever reason, "C"'s add price and weight.  Maybe someone who knows the why's will chime in.

Ken

[David Hoover]

Why not try some shorter lines? 62' instead of 65' will get you from 5.8 seconds to a little over 5.5 and going to 60' will get you almost another 0.1 second.  It might be enough to get you over the hump and give a little feel for the plane at a shorter lap time before spending money on more serious equipment.

[Ken Culbertson]

Cutting Lap times by shortening lines does not make the plane go any faster and at that weight you have little choice but to make it fly faster or go to an active timer.   The Huben is a constant RPM timer so it is no help in giving you a boost in a maneuver.  One of the first suggestions was to add RPM's and I failed to ask then what RPM are you setting the timer for?  If it were me I would be getting the plane up to "operating" speed by whatever means were available then, once I knew how fast it needs to fly,  I would start working on efficiency.   

Ken

[Ken Culbertson]

We have been spending a lot of time discussing the virtues of 6s batteries but according to the Rimfire .32 specifications it is only rated for 3 and 4s batteries.  My Bad - increase RPM's and try the larger prop. 

Ken

[David Hoover]

Cutting Lap times by shortening lines does not make the plane go any faster

True for linear velocity but reducing the radius increases the angular velocity (shorter distance to travel/rev for same linear velocity) so reduces lap time and increases centrifugal force (line tension).  I thought it would be an easy, low cost way to determine the effects of a reduced lap time before making any serious changes to the power system.

[Ken Culbertson]

and increases centrifugal force (line tension)

It don't think it increases centrifugal force.  I will let someone that can do the f(x) thing better than me explain it. 

Ken

I have been taken to the woodshed on this one by someone that can do the f(x) thing.  It does increase line tension (on paper)

[Don Jenkins]

Why not try some shorter lines? 62' instead of 65' will get you from 5.8 seconds to a little over 5.5 and going to 60' will get you almost another 0.1 second.  It might be enough to get you over the hump and give a little feel for the plane at a shorter lap time before spending money on more serious equipment.

Something to consider about line length is longer lines gives you a larger operating envelope.  Meaning maneuvers are flown larger because the further out you go 45 degrees gets higher.  This allows bigger, heaver planes more room to turn and larger stunts are easier to perform, at least for me.

I also have found the APC F2B 12 x 6 pusher prop to work much better than their standard 12 x 6 pusher.  I swapped props on my 69 ounce SV-22 and it made such a significant difference I had 2 of my flying buddies change motor direction using the F2B prop on their SV-11's and it worked better than their 3 blade Igor props, they don't cost $50 either, give one a try!

Don

[Ken Culbertson]

Something to consider about line length is longer lines gives you a larger operating envelope.  Meaning maneuvers are flown larger because the further out you go 45 degrees gets higher.  This allows bigger, heaver planes more room to turn and larger stunts are easier to perform, at least for me.

I also have found the APC F2B 12 x 6 pusher prop to work much better than their standard 12 x 6 pusher.  I swapped props on my 69 ounce SV-22 and it made such a significant difference I had 2 of my flying buddies change motor direction using the F2B prop on their SV-11's and it worked better than their 3 blade Igor props, they don't cost $50 either, give one a try!

Don

Don was that the 2 blade?  I tried that on a much lighter ship (55 oz) and didn't like it at all and went back to the MAS 11 x 6 three blade.  Is it possible that weight was the factor?  FYI, I try and fly all of my ships at 5.5 on 62' lines.  I don't always suceed!

Ken

[GerryG]

In support of what you are saying Don. I was flying my RSM Mustang using an APC 11 1/2 x 6 at 9400 RPM for a 5.2 sec lap time. I changed to an APC 11 1/2 x 6 F2B and was able to reduce RPM to 9100.

[David Hoover]

It don't think it increases centrifugal force.  I will let someone that can do the f(x) thing better than me explain it. 

Without going into fancy math: linear (tangential) velocity stays the same but with shorter lines you're making a sharper turn so the force required to maintain that turn is greater than for a shallower (longer lines) turn.

[Istvan Travnik]

The formula of centripetal acceleration is v^2 / r
The force is: m x v^2  / r
Where is: v = speed of the plane, r=real flying radius , m=mass of the plane.

Regarding the wind and turbulences, there is no doubt, the best is to fly  maximal speed, and to use maximal radius (length of line).
In my observations, that means at least 1500 grams of minimal mass ("weight"),  that means round 53 ozs minimum, at .015 dia. 7-strand Sullivan lines.

If something enforces to use .018 lines, the suggested minimal weight is surely bigger. Sorrowfully I have no experience with.
Istvan

[Ken Culbertson]

Shortening the lines and keeping same airspeed will increase centrifugal pull, or whatever it's called.
Lengthening the lines and keeping the same lap time will increase the line pull.
There are plenty of centrifugal force calculators in internet, just feed in the figures and see the result, if you cannot calculate it yourself. L

You are absolutely correct.     The old rule of thumb longer lines more pull assumes the same lap time.

Ken

[Shorts,David]

I need more airspeed for air velocity over control surfaces. I assume the same thing that happened with my ringmaster. I fly slow and it mushes the corners something awful. I sped it up and I've gotten a few decent scores with it. 

[Howard Rush]

I have a 74 oz. Impact that flies fine with either an Igor 11" prop or Igor 12" prop.  I use full 70' lines and fly 5.2- to 5.3-second laps.  I've been advised not to use shorter lines.  I use about 800 2000 mA-hr out of a 6s 2800 mA-hr battery.  I think that's about the same amount of energy as your battery.  I wouldn't worry about resistance losses in the wire unless you have 24 gauge or so wire. 

Igor's props are designed using some science, so they're pretty efficient.  They have three blades apiece, weigh about 16 grams, and cost about $50 each after you pay shipping. 
I used the APC F2B props for awhile.  They are very efficient, but the Cox-Resinger and Igor props flew so much better stunt that it was worth replacing my 5S batteries with 6S batteries to turn them. 

Edit: I haven’t got the hang of this subtraction yet.

[Shorts,David]

Thanks everyone. I'll make some changes and be back with my report in a few days.
David

[Ken Culbertson]

Thanks everyone. I'll make some changes and be back with my report in a few days.
David

David - please check the rating on your motor before trying the 6s battery.  I ruined a motor by putting a 6 on one only rated to 4.  It ran but it never ran well again.

Good Luck - Ken

[Shorts,David]

David - please check the rating on your motor before trying the 6s battery.  I ruined a motor by putting a 6 on one only rated to 4.  It ran but it never ran well again.

Good Luck - Ken

Sure, I will. But I'm going with a bigger prop and timer settings first before I switch my battery.

[Shorts,David]

Okay, quick update. They were sold out of MAS 12x6 3 blade.
So, here's some other props I have.
APC 2blade 13x5.5 cut down to 12 inches.
A CF aerostar 2blade 12x? maybe 6 that I got from Hobbyking long ago for some forgotten purpose.
And an APC 3 blade 11x7 I also got long ago but forgot why, maybe for this plane.

I'm still trying to get the 12x6 MAS 3 blade. I think 12 inches will clear but wouldn't want to put a CF $50 prop on it.

[Ken Culbertson]

Sure, I will. But I'm going with a bigger prop and timer settings first before I switch my battery.

Given all that has been said here - good call.

Ken

[Shorts,David]

Okay, I just switched props to measure efficacy prior to changing my rpm. Using the MAS 3blade 11x7, I was getting 5.8 laps and pretty loose, like, pulling my handle down to my pocket on wingovers.
Today I switched to the 2blade APC 13x5.5 cut to 12". I think I'll just stick with that one for now. I got about 5.7 although considerably more tension on the wingover. Possibly my imagination? I went to the APC 3 blade 11x7 and it stunk. 6.2 second laps, motor clearly unwinding too much, but it still pulled overhead on the wingover and vertical 8. So, I figure my plane is light enough.

I did discover that my lines are not 65', but 67.5'.
I've just been doing 2 minute flights.
I think next time I'll kick up the rpm, change the flight time, and go for my first pattern with my plane. I think I'll increase the elevator throw at the horn, and decrease the sensitivity at the handle. If successful, I've got my plane for Golden State...maybe.

[Mike Alimov]

David, I still have concerns about your setup.  5.7 second laps?...  Here are a few thoughts and suggestions, if I may:
1. If at all possible, consider switching to a 6S 2800 mAh setup (yes, that would require different batteries and motor.  If need be, I can loan you the entire power package for the Golden State, along with a MA 12-6x3 prop; we just finished our last contest for the season).  Notice that a 6S system is drawing on average 20A in flight, while your 4S system will be drawing 27A - a huge increase in current, which means it will run very, very hot.  Even if the motor and ESC survive, the batteries may puff up in a few flights.  If this happens, send the bill to Howard, as he said not to worry about the current-induced heat.
2. After your 2-minute test flights, check how much % of the battery you are using per minute using a battery checker, and multiply that by 5.5 (typical pattern takes about 5 min 30 sec).  If you get anything more than 80%, you may not have enough battery capacity for a full pattern.  Solution: see #1 above.
3. If you must stay with the 4S setup, then at least switch to 60' (eye-eye) lines.  I'm serious.  Same linear speed but smaller flight radius will give faster lap time and better line tension (remember centrifugal force: mV^2/r, where r is flight radius: the smaller the radius, the greater the force).  Bonus: you will get through the pattern faster, and may have enough battery capacity.
4. Is it possible to convert it to a 2-wheel / taildragger?  Less air drag = less energy required to fly.  Just a thought.

[Dennis Toth]

Dave,
You haven't stated what rpm you are running. The MAS props seem to be under pitched by about 1". If you look at typical rpm for a normal 6" (7" on MAS) you should be at around 9600 - 9800 to get around 5.3 lap on 65' C to C. One thing you could consider is to sand in some undercamber to the MAS prop. Only need about 1/64".

Best,    DennisT

[pmackenzie]

Slow lap times could be due to ESC governor settings: either incorrect target RPM, or improper ESC setup in the first place.

What ESC are you using, and what program settings?

[Ken Culbertson]

Slow lap times could be due to ESC governor settings: either incorrect target RPM, or improper ESC setup in the first place.

What ESC are you using, and what program settings?

I had a similar problem with a Cobra 2826 on a 4 cell battery.  I had moved the ESC from a plane using 5cell and forgot to change the setting.  No matter what RPM I set the Huben at it produced about 2000 less.  Found the problem, fixed it and life was good.  It could also be the number of polls in the motor doesn't match the ESC.  Everything works, it just doesn't do what you want.  Makes you want to go back to a needle valve and tach....for about 5 seconds

I just read through and I can't find where you told us what ESC you were using.  I am only familiar with Castle and Spin.  Castle has a cell setting but I don't think it has an "Auto" mode, I could be wrong.  The Spin line will auto detect your battery cells or you can state it.

Ken

[Shorts,David]

Thanks for all the input. So, a few days ago I tried a few changes in props, timer settings, and switching my 4 cell practice pack to a borrowed 5 cell pack.
With the MAS 12x6x3 I was turning 8200 rpm, and getting a 5.65 lap with the 67.5 lines. I flew for four minutes and had 40% left on the 4 cell pack with minimal heat. However, 5.65 still struggled a bit and I didn't attempt all the stunts.

Then I did an hours worth of changing settings on the ground with the timer. Oh, I also discovered that using my old ESC, which is a chinese something from hobbyking, that the Hubin Jetti Spin setting worked rather decently, but the rpms were not accurate, so I made a conversion chart using my Tach. However, today I just stuck my spare Castle 50 in the plane. It works much better and I am set for next time at about 8600 rpm. I'll see how it flies.

The only remaining question is that of battery life for 5:30, which I haven't tried yet. Maybe Wednesday I'll try again. Long term, I'd rather have 5 cells than four cells, so I'll just go with my borrowed 5 cell, but it is only a 2800. Really long term, this is a scale-ish aircraft, and I just want to get through 2 patterns at Golden State. If I can beat my dad, then I'll make a bigger investment in it.

[Ken Culbertson]

Thanks for all the input. So, a few days ago I tried a few changes in props, timer settings, and switching my 4 cell practice pack to a borrowed 5 cell pack.
With the MAS 12x6x3 I was turning 8200 rpm, and getting a 5.65 lap with the 67.5 lines. I flew for four minutes and had 40% left on the 4 cell pack with minimal heat. However, 5.65 still struggled a bit and I didn't attempt all the stunts.

Then I did an hours worth of changing settings on the ground with the timer. Oh, I also discovered that using my old ESC, which is a chinese something from hobbyking, that the Hubin Jetti Spin setting worked rather decently, but the rpms were not accurate, so I made a conversion chart using my Tach. However, today I just stuck my spare Castle 50 in the plane. It works much better and I am set for next time at about 8600 rpm. I'll see how it flies.

The only remaining question is that of battery life for 5:30, which I haven't tried yet. Maybe Wednesday I'll try again. Long term, I'd rather have 5 cells than four cells, so I'll just go with my borrowed 5 cell, but it is only a 2800. Really long term, this is a scale-ish aircraft, and I just want to get through 2 patterns at Golden State. If I can beat my dad, then I'll make a bigger investment in it.

If my math is right going the full 5:30 (I use 5:40 to give me two extra laps to deal with wind shifts) is going to put you around 20% remaining.  That should be fine.  Everybody around here uses 5s or 6s 2800's.  I use 5s and, depending on the wind, get down with around 19-25% left.  Too low for storage but well above minimums.  Bottom line, I would run it down to 10% if it meant beating your Dad.

I will restate my caution at using a motor not rated for the voltage.

Now go win something - Ken

[Shorts,David]

Slow lap times could be due to ESC governor settings: either incorrect target RPM, or improper ESC setup in the first place.

What ESC are you using, and what program settings?

Good news. I now have my first pattern under my belt on this plane. I had to call Castle to remember what I was doing to program the new esc. I still used my 4 cell 4000 because it's my only battery big enough to attempt a whole pattern on this size plane. I kicked up my rpm to 8400, and set the timer for a fairly short 5:15, just cause I wanted to check the heat build up and all and see what was left over. Motor and ESC were cool, but battery was fairly warm as Mike or others suggested it would be.
I only had 14% left on my battery, which I don't mind too much for all the more I'll be using it, but I may still break down and buy some bigger 5cells this week and reprogram everything. (electric is not my first choice, except for certain airframes like this one.)

Of note, I was doing 5.8 laps before and couldn't get the plane to turn on the bottom of the top loop on the vertical 8, nor on the third corner of the hourglass. Today it turned just fine and...I was still doing 5.7-5.8 laps. Big surprise, because it flew better with the CL governor programmed correctly to provide consistent power.
I think I will switch to my 65' lines to get a little faster, and kick the rpm up a hair.

I nicked my MAS 12x6x3 twice, so, no CF's in my future with this plane.

[Mike Alimov]

David, if you are landing with 14% battery, the system is running on the rugged edge of maximum capacity.  Any more increase in RPM will lead to dramatically more power consumption (remember drag grows as a square of speed), and you might brown out the battery.
Keep current settings and shorten the lines to 60' eye-eye.  You'll be rewarded with more line tension.