First taste of the sky

[leccyflyer]

First number is the prop diameter, second number is the pitch.

[David Davis 2]

Yes length always precedes pitch so a 12 x 10 prop is twelve inches long from tip to tip and moves the aircraft forward a theoretical ten inches with each revolution.

 

[toto]

So in my case the larger the pitch number, the further the model will travel per revolution. I wonder what the maximum pitch size would be for a 12 inch prop ?

 

Could be worth checking.

Toto

[David Davis 2]

Props are available in many sizes. I believe that competition aerobatic pilots back in the Eighties and Nineties flew with propellers with more pitch than the diameter but that was in the days of i/c engines. The biggest pitch available on a 12" propeller which I have been able to find after a brief search has a 12" pitch. https://stevewebb.co.uk/index.php?pid=ELP12012E&area=PROPS.

 

Please be aware that by using a propeller with such a coarse pitch the acceleration of your model on take off will be adversely affected. I hope you have a long runway at your club!

 

If you've got 1.5" clearance between the 12" propeller tip and the ground, you could fit a 13" diameter propeller and still have an inch clearance and you could always fit a bigger set of wheels as well. Just a thought.

[leccyflyer]

23 minutes ago, toto said:

So in my case the larger the pitch number, the further the model will travel per revolution. I wonder what the maximum pitch size would be for a 12 inch prop ?

 

Could be worth checking.

Toto

For a trainer you really don't want a prop with a coarse pitch - these are sometimes called square props, like a 5"x5", 6"x6" and so on and are designed for maximum speed, such as you would fit to a pylon racer. They are for fast flying models, but there is no such thing as a free lunch and, as I mentioned earlier, such coarse props come with undesirable side effects for launching and take off - more difficult to hand launch and get the model up to speed for take off. I've been known to drop an inch in pitch to improve the take off performance of a couple of models, going down from a 9x6" to a 9x5" - slightly less power, but better acceleration from a standing start.

[Learner]

1 hour ago, toto said:

They both weigh the size of your average small family car ....

 

 

Which is my point you dont want to turn a nicely flying trainer into a brick with wings!

[Learner]

Toto put your 12x8 prop on the motor bought for your sky 40 and try that on the watt meter with the 4 cell battery.

[David Davis]

FWIW, I've just been on the 4-Max site and looked up the details of my old Telemaster 40. On a 3547-800 motor, a 12 x 6 prop and a 4S 5000 Lipo current drawn was nearly 30 amps so 73 Watts per lb. This flew it well enough for a trainer. https://www.4-max.co.uk/customermodels34.htm

 

Of course I was not limited in the same way by prop clearence.

[leccyflyer]

1 minute ago, David Davis said:

FWIW, I've just been on the 4-Max site and looked up the details of my old Telemaster 40. On a 3547-800 motor, a 12 x 6 prop and a 4S 5000 Lipo current drawn was nearly 30 amps so 73 Watts per lb. This flew it well enough for a trainer. https://www.4-max.co.uk/customermodels34.htm

 

Of course I was not limited in the same way by prop clearence.

Yes, but that's a much smaller motor than Toto is using and a much higher kV, so much better suited to using that size prop on a 4s1p pack - you were getting at least 50% more power on that prop. The low kV and limit on prop size on Toto's model is robbing him of allowing the motor to develop any useful amount of power. We were flying sp600 motors 25 years ago giving just 200w on a 3lb airframe and you still hear folks complaining that they didn't work, for a 6lb model to have so little power they did really well to get the Domino to fly at all..

[David Davis]

1 hour ago, leccyflyer said:

Yes, but that's a much smaller motor than Toto is using and a much higher kV, so much better suited to using that size prop on a 4s1p pack - you were getting at least 50% more power on that prop. The low kV and limit on prop size on Toto's model is robbing him of allowing the motor to develop any useful amount of power. We were flying sp600 motors 25 years ago giving just 200w on a 3lb airframe and you still hear folks complaining that they didn't work, for a 6lb model to have so little power they did really well to get the Domino to fly at all..

 

 

Yes I agree on your last point!

 

If fitting a 12 x10 prop does not increase the current draw significantly his choices would appear to be to fit a smaller, more suitable motor or to fit his 6S LiPo.

 

He already has a Ripmax Quantum 40 which he bought for his Sky 40. This motor is marketed as having the same power as a 40 two-stroke glow so that would work if it were fitted to the Domino. http://www.ripmax.com/Item.aspx?ItemID=M-Q2-40 The larger motor could perhaps be used in the Sky 120 which Toto has already bought.

 

The existing power train with the 6S LiPo produces 462 Watts according to Toto's measurements.  In a 6lb model that would give 77 watts per pound which is close to my recommendation of 80 watts per lb.

 

As for cg concerns I note that the the 6S LiPo is smaller at 4800 mAh so probably only about 1.5 ozs heavier. 

 

If it were my model I would fit the smaller motor but then again, while respecting Toto's decision to change over to electric power,  I'd have gone with i/c from the outset...but then I'm a dinosaur! 😄

[Peter Jenkins]

Exactly so leccyflyer.  The problem is that Toto has been sold the wrong kv rated motor.  His motor has a 500 kv with a note to say use 15 inch props whereas the one that DD pointed to has an 800 kv so getting on for 60% faster rotation speed per volt.  That then can use a smaller diameter prop and produce far more power than he's currently getting.

 

As an example, I bought a second hand aerobatic aircraft that was being flown by a beginner in aerobatics.  He had a 425 kv motor that was really intended for a 6S setup but he was using a 5S setup and a 16x8 prop.  The performance this setup gave was anaemic to say the least as it was impossible to maintain speed on a vertical climb.  I had to resort to a 17x12 prop before I came close to the rated limit for the motor at which point all was fine except that there was almost no ground clearance now!  Changing the motor to one with a 585 kv allowed the use of a 16x10 prop and gave the required 1200 W with the current draw just within bounds.  It is rare to use full power for more than about 6 secs so that worked and still works fine.

 

This is one of the problems with electric power as there are so many variables that newcomers have to ask and don't know which answer to believe as all answers, as we have seen, appear to conflict.  

 

The best thing you can do Toto is to go with your 6S packs and see how things work out.  If you, or your instructor, feel you need more power, best solution is to swap out the motor for one with a kv or 800-900 and then you will probably be fine with the 4S pack.  That's a cheaper option than buying 6S packs.

[Cuban8]

3 hours ago, toto said:

So in my case the larger the pitch number, the further the model will travel per revolution. I wonder what the maximum pitch size would be for a 12 inch prop ?

 

Could be worth checking.

Toto

In all the electrical power plants I've specified for myself, I've never had to deviate from either 7 or 8 inch pitch props - diameter to suit the application of course. Models ranging from mini sport types to my 1500W aerobatic model (favourite party trick.....nose up, full wallop and accelerate vertically then spin down!) - I think you might be getting in a tad too deep at this stage of the game although I'd encourage experimentation as you gain understanding and experience.

I also find a digital spring balance a very useful tool to read static thrust as a comparison between props. Watts per pound is all very well but I like to know actually how much oomph the motor/prop is giving at full whack and comparing that to the flying weight of the model.

My estimate based on practical testing is that sport models and trainers will fly perfectly well on a max static thrust figure of between 50-75% of UUW. Plenty of power to get the model rolling smartly at take off and then ease off to suit when up and away. Vintage models that just need to potter about can get away with way less where overpowering can be a big problem. 1:1 or more to really get things going on a hot ship for the hooligans.

More than one way to skin a cat of course, and a little more too it than back in the day when one bought a .40 two stroke, fitted a 10x6 prop and that was that.

 

Edited November 6, 2023 by Cuban8

[toto]

I'll try the 6s packs before changing motors.

 

I have 8 x 6s batteries so no further purchase necessary. 

 

I am still going to try and get a more accurate fully loaded weight of the model just for peace of mind. Mrs toto knows the location of the baggage scales.

 

Cheers

 

Toto

[Cuban8]

3 hours ago, leccyflyer said:

For a trainer you really don't want a prop with a coarse pitch - these are sometimes called square props, like a 5"x5", 6"x6" and so on and are designed for maximum speed, such as you would fit to a pylon racer. They are for fast flying models, but there is no such thing as a free lunch and, as I mentioned earlier, such coarse props come with undesirable side effects for launching and take off - more difficult to hand launch and get the model up to speed for take off. I've been known to drop an inch in pitch to improve the take off performance of a couple of models, going down from a 9x6" to a 9x5" - slightly less power, but better acceleration from a standing start.

That's a very interesting post leccy. We don't usually have the advantage of variable/constant pitch props in the modelling world so our choice is very much a compromise to achive a good all round performance. I inherited a very nice electric 1930s style low wing racer from my late mate's estate and I was surpised that it had a 14x9 prop which had it lumbering off the deck and just generally feeling sluggish in flight. Sort of like driving a car with the brakes binding.

A change to a 13x7 transformed it and did surprise me at the all round positive improvement. Much crisper throttle response being particularly welcome - not a rocket ship but sometimes that's not always what one needs for a relaxing afternoon's flying.   I suppose I could fiddle with it further but it performs nicely now and Watt readings are sensible at about 350W at full chat for a four pound 'plane running 3S. Cruises comfortably with lazy aeros at 1/2 - 2/3 throttle. Nice.

[Caveman]

Just to put my thoughts into this discussion; below is a photo from the first post in Toto's Domino build thread. The manufacturers recommended motor for this model is a Rimfire 46.

 

The Rimfire motor is, according to this website (RIMFIRE .46 42-60-800 OUTRUNR (bestrcshops.com)  800kV and is suitable for 5-6S batteries, and prop size 10x5 - 11x5. As Toto already has this motor then it would seem sensible to install this motor, together with a suitable prop, the current (no pun intended) 60A ESC and use the 6S batteries already to hand.

 

No worries about prop clearance and bags of power!

 

 

As Peter says, the Thumper 500kV motor is not a suitable match for this plane, it needs too large a prop which the Domino cannot sensibly accommodate.

 

I work on a 40 2 stroke giving approx. 650W and a 46 approx. 750W running on 5% nitro fuel so the Rimfire motor look to be spot on.

 

Keep the 500kV motor for a larger, future project.

 

GDB

 

 

 

[toto]

As mentioned in one of the posts above, I have a Quantum 11 40 800kv brushless motor 4250 fitted in the Sky 40.

 

Would that be a better match .

 

Power output max 980w

KV RPM 800

 

It's similar to the rimfire as stated in Cavemens post above and would let me run with a 10 x 5 - 11 x 5 prop.

 

Toto

[Peter Jenkins]

40 minutes ago, toto said:

As mentioned in one of the posts above, I have a Quantum 11 40 800kv brushless motor 4250 fitted in the Sky 40.

 

Would that be a better match .

 

Power output max 980w

KV RPM 800

 

It's similar to the rimfire as stated in Cavemens post above and would let me run with a 10 x 5 - 11 x 5 prop.

 

Toto

That would be far better Toto.  I should swap them over and you will instantly have much more power available with either of the two props.  The 11x5 will provide more power but check on the wattmeter that it stays within the ESCs limit current wise.  Don't exceed 980 W on the motor although in reality, once in the air then the power output drops as the prop will unload.  It is load on an electric motor that makes it put out the power.

 

Sounds like a cost free solution.

[aidan mcatamney]

On my Hangar 9 Meridian which is sold as a 40 size plane.  I have it flying with a Power 60 motor which is 470Kv.  Along with this set up I have a 6s lipo 5000 and a 15x8 Apc electric prop.  I also put larger Dubro low bounce wheels on the plane and this gives me plenty of ground clearance.  The Meridian flys  beautifully with this electric set up and it balances out perfectly.  

[David Davis]

I'd be interested to see what figures you get from the Quantum II 40 on the wattmeter.

[Learner]

3 minutes ago, aidan mcatamney said:

On my Hangar 9 Meridian which is sold as a 40 size plane.  I have it flying with a Power 60 motor which is 470Kv.  Along with this set up I have a 6s lipo 5000 and a 15x8 Apc electric prop.  I also put larger Dubro low bounce wheels on the plane and this gives me plenty of ground clearance.  The Meridian flys  beautifully with this electric set up and it balances out perfectly.  

Hanger 9 meridian is for 10cc which is a .61

[toto]

Hi David,

 

I'll swap over the motor for the Quantum 40 and put the Watt Meter on. I'll do the same two tests to allow a comparative reading ...... same prop .... same two battery sizes and the same 60 A ESC.

 

Only a motor swap.

 

Hopefully I will get the chance to do this tonight. I'll do my best.

 

Cheers

 

toto

[Philip Lewis 3]

I would be very carefull putting a  six cell pack hrough a motor with 800KV, 22.2 volts X 800 less 20% loss is 14.208 RPM, your amps could hit new heights!

[Cuban8]

18 minutes ago, Philip Lewis 3 said:

I would be very carefull putting a  six cell pack hrough a motor with 800KV, 22.2 volts X 800 less 20% loss is 14.208 RPM, your amps could hit new heights!

Alarm bells are ringing - the magic blue smoke awaits. Just run some figures based on a 12 dia prop and it ain't pretty.

[David Davis]

Toto is going to try the Quantum 40 motor on 4S first. A basic trainer will not need more than a 4S power pack. I'd forget about 6S with the Quantum 40 if I were you Toto.

[toto]

Maybe I should just call it a day and 4un the set up I have with the 6s batteries. 

 

If that potentially fits the bill then let's leave it at that.

 

Toto