Choosing Fixed Wing Motor and Prop. Some Golden Rules!

[@MHz-jl6wt]

Just renewed my subscription to eCalc. Thank you Lee and Marcus.

[@andywalker2992]

Brilliant. I spent months bench testing and optimising the thrust and lift motors on a differential thrust steer hovercraft. And then optimising the battery for the current draw the best weight compromise. This tool would have enabled much quicker optimisation to motors and prop and batery size. Will be signing up for this tool. Great stuff Lee and Markus. Keep up the good work.

[@user-lh4je7yg7m]

Very thankful for this video. Being new to the hobby, this and your other videos unlock many of the concepts that many of us new to the hobby struggle to understand. Appreciate all your excellent work. Thanks.

[@MCsCreations]

Fantastic conversation, Lee! Thanks a lot! 😃 Fantastic amount of knowledge here! Stay safe there with your families! 🖖😊

[@greatgandalf5233]

Great Gouge!! Wish they had this when I was going through Pensacola...

[@Painless360]

Huh?

[@johncarold]

Hi Mr. P Great video and series to make. If it was 40 years ago I could give you the best prop for the motor you was using. No more ! I could because we didn't have electric power, Nitro was so much easier. Now that we have so many different sizes and shapes and wires, we have to many to choose from. Thanks for making this series. Can't wait to see the rest.

[@Rob-vt1mz]

Perfect. I was just having a discussion at my local field about this and programming this type of data as one of the guys at the field did this on paper. Yes, paper. Great vid, great calculator.

[@Painless360]

Check out the other videos in the motor and prop series that looks at it in more detail.. Happy flying

[@adamhale6672]

What an excellent video! I haven’t found anything like it! One thing that is tricky in eCalc is matching a propeller to a motor for efficiency. Mathematically, you can graph efficiency vs advance ratio for a motor and prop which allows you to see how both efficiencies compare at different airspeeds. Ecalc seems to do this computationally a little bit, but I’ve always struggled to tell if I have a good match for my predicted cruise speed. Take a bit of guess work.

[@mikeb5556]

Very interesting and I can recommend ecalc. I have use it to design systems and it is good. As was coming across in the video, it is very easy to rob Peter to pay Paul in component selection and you need to find an optimum grouping of items for your particular requirement. Reasonably priced, and it can be subscribed for a short period, like a month if you have an intense design phase to need assistance with.

[@1FelixTheCat]

thank you Markus and Lee! more of this please! And then after you think you have the KV and prop diameter/pitch sorted.......the airframe parameters( IE: Clean versus dirty, airfoil etc. ) will once again try to convince you that maybe it is "black art" after all.

[@martinschyns1458]

Lea / Markus - Great intro video. I would love for you to do a series and get progressively deeper into this challenging topic. Personally I would love to see some graphs to explain the non linear relationships between Prop / Motor / Battery / ESC and Model ( Packaging & Operation) performances. Clearly there are physical boundary conditions as well - such as Size / Weight / Heat dissipation / Flight time / Battery energy density & power ratings. Currently I am trying to get into 3D flying and am grappling with the importance of higher battery S rating on flying performance. Keep up the great work. Thanks Martin

[@Painless360]

Thanks for the feedback. When you select a setup the tools provide a nice graph showing how many of those things work over the range. Stay tuned! :D

[@robertgoldbornatyout]

Well said thank you Markus and Lee! 👍👍👍

[@jagadishkumarmr531]

This is just amazing sir! Thank you Marcus for joining initiatives like this! Would like more of these.. especially on motors combination with the props. sir, it would be great if you could make video on using ECal for beginners.. because the interface looks a bit overwhelming...

[@ecalc-gettherightdrive5483]

Hi, we do have the expert and easy view - starting with the easy view might be an option www.ecalc.ch/motorcalc_mobile.php

[@Painless360]

Link to that simpler interface added to the description now too.. Happy flying!

[@jagadishkumarmr531]

@@ecalc-gettherightdrive5483 thank you!

[@simonlomax757]

Very helpful video with useful information to a person choosing a power system for my scratch built rc plane. Thank you. The channel is a godsend

[@christopherj3367]

It would be interesting to hear your views on the efficacy between a 2 prop and the latest craze of 6 prop's, thanks Marcus and Lee for an informative talk.

[@Painless360]

More blades = less efficiency. Adding more blades is all about increasing the total blade size so you get more thrust but you get additional incremental losses for each of the blades you add. For endurance and efficiency 2 bladed are the best options (if you have the room!) Happy flying!

[@ayoaina_fpv]

Great stuff Lee! Awesome! 02:39 glad to see you didn't 'hand over to yourself' in public lol

[@guypehaim1080]

You have multuple gear ratios in an automobile transmission because the engine produces a limit of horsepower(kW) which is esentially torque X speed. To get the car to move initially, you have to overcome the static inertia. To do this, we choose 1st gear, for example, the ratio of which has the highest mechanical advatage and thereby provides the most torque to the driveshaft and rear axle. As the car accerates and we are shedding static inertia, we choose successive gears (gear ratios) each of which have lower and lower gear ratios. What we are doing in this process is trading torque for speed. We stop choosing additional gear ratios when we reach the speed we want to maintain. We now are operating with the ratio that satisfies both the speed we want to maintain and to propel the load on the drivetrain and engine. This process allows the engine to operate at a resonable speed in each gear for a given speed of the car. When discussing propellers, I think it safe to say the torque in the equation is determined by the pitch of the propeller, I.E., the bite the propeller makes into the air ahead of it. The speed of course is the number of revolutions per minute of the motor at a given set of conditions.

[@theartandscienceofflight9239]

Very interesting. Thanks for putting this together and posting. I had not considered the possibility of a prop stalling, but with the explanation it makes sense as a possibility.

[@jvalovcik]

Recalculate looks great but what do you do if you can’t find all the info about your motor and it is not on your list. Do you go under airplane for fixed wings?

[@zbynekchmela7778]

Great video, thank you guys! I’m hungry for more.

[@AerialWaviator]

Would love to hear what Markus and Painless350 have to say about tractor vs pusher configurations and how it effects efficiency. example: how to use a tool like eCalc to account for effect of prop being behind fuselage, or wing? Also a discussion of twin vs single motors would be nice.. A number of models offer the option of twin, or single motor configuration. Why favour one vs. other? What rules of thumb if any, on prop size, motor sizing?

[@TeamYankee2]

This is just what I'm after for my Bixler2... a better motor and prop

[@muhammadyounosraz5698]

It was quite interesting and informative to watch this video. Thank you . Is it possible to explain the amont of change in thurst by changing the dia and the prop.eg.is the thurst developed by a prop 10x5 is equal to 11x4 prop

[@Painless360]

It is, see the other videos in this series where we cover that very topic in some depth..

[@koalatails6391]

Good video. Education without information overload. The 60% rule is something that I never heard of before. I have a 1100mm T28 Trojan, the stock prop is 9.5 x 7.5, it’s an aggressive looking prop but the plane never achieves a high speed. Is it possible the plane never reaches a fast enough speed to allow the prop to work efficiently? Or to put it another way... Does this model suffer from prop-stall of some degree, all the time?

[@Painless360]

What motor and ESC are you using?

[@koalatails6391]

@@Painless360 ESC is an eflite EFLA114OW 40amp Bec. I believe the motor is the original Parkzone T28, it has no markings that tell size or kv. Only a sticker “CE Horizon Hobby Inc”.

[@koalatails6391]

@@Painless360 I found the online manual for the model, it lists a “480 outrunner motor.

[@jimbrown563]

This brings up a question that I've been wondering about for ~20 years ........ Why has no manufacturer come out with a flexible Variable-Pitch-Prop. We certainly have the trick-materials and Computer-Analysis-Tools to achieve this goal, and it could perform miracles in increasing Model Performance, in both Fixed-Wing, and Multi-Rotor designs. I, certainly, would be willing to spend ~3X to ~4X the price for a high-performance working example. BTW, this is currently standard practice on many Fishing-Boat Electric "Trolling-Motors". Even an Automatic / Mechanical / Centrifugal System could easily be implemented for Models, just like almost every WW-II War-Plane had. They were called "Constant-Speed-Props, because their main job was to keep the Engine operating in its most efficient RPM-Range at various Air-Speeds and Loads. And, something that was not directly addressed, a "Stalled-Condition" will cause tremendous "Drag" and excessive Motor-Loading, therefore causing excessive Current-Draw, and can quickly over-heat the Motor if continued for more than ~10-Seconds or so. . .

[@Painless360]

They exist but as fragile and tricky as CP heads for helis..

[@jimbrown563]

@@Painless360 There's more than one way to skin a Cat. I was referring to "Flexing" under load, rather than a complex Mechanical-Linkage.

[@scottyh72]

@@jimbrown563 You want less pitch at full throttle (thrust) and more pitch (efficiency) at cruise. So a flexy prop won't really work.

[@jimbrown563]

@@scottyh72 It doesn't work that way. It has everything to do with the LOAD on the Prop, which has everything to do with the Forward-Air-Speed. The desired outcome is to maintain a constant LOAD on the engine, we are not talking about a Car Transmission here.

[@frasersteen]

Ecalc is amazing. I've spent more time on that than any other single rc thing. It's brilliant and surprisingly accurate. The one problem I have with it is that I cannot build out a few options in a spreadsheet. I'd love to graph some of the figures so I can understand the mechanics better. For example, max power vs prop pitch, diameter vs motor efficiency etc. If there anywhere where the maths is accessible without needing masters level understanding of aerodynamics?

[@Painless360]

Let me add that to the list for potential future videos.. Thanks Fraser

[@adamhale6672]

I’ve had the same experience with ecalc. I also wish that I could see more of how it handles in non-static conditions. If you want a great resource for the math and calculations behind much of this, my university’s flight vehicle design textbook is very straightforward, clear, and open source. It can be found on the BYU ME415 syllabus page under the textbook section. Comes up pretty quick on Google.

[@ds-3d283]

PERFECT thank you

[@SteveJohnstoneNG3D]

Great video Markus and Lee, thank you!

[@skypilot23]

yesterday flying I had this exact topic come up with my friend- I usually tend to go up an inch in diameter and pitch from stock and see how it flies- maybe check the amps with a meter if I'm feeling anal haven't burned up an esc yet- watching out for heat very timely video and my thanks

[@frankyflowers]

cool. does anyone use variable pitch on planes like the helicopters that fly upside down? what if we used gears to power a two folding props with one motor and it uses one for takeoff and one for cruising and the other folds. would that work?

[@JuanRodriguezArchitect]

Question: what's the percentage of efficiency loss if a prop is softener or flimsy vs a more rigid prop? Is there any loss? Does the prop material effect thrust?

[@adamhale6672]

That would be represented by a P constant change. If you know the brands of rigid vs flimsy props you could try to view that change in ecalc. I couldn’t give you a percentage and I don’t know how significant it would be. Folding props also rotate forward when turning, but still have great efficiencies.

[@PhilWare1]

I suppose thats why variable pitch or constant speed propellors are now standard in full size aircraft. I wonder if these are possible to scale down for RC models?

[@Painless360]

They are available but they are very delicate. More like the CP heads from a heli...

[@PhilWare1]

@@Painless360 Maybe the way that technology is constantly improving they will become more common in the future thereby eliminating discussed trade off :-)

[@Painless360]

I'm not holding my breath. From my long time flying helis - CP setups are a pain in the backside to setup and get spot on and then break at the merest hint of a blade strike meaning another 2 hours setting it all back up. Choosing a good fixed pitch prop setup is not tricky when you know the rules of thumb/tips.

[@PhilWare1]

@@Painless360 I also suppose the benefits of increased efficiency in fixed wing RC propellers is not as big an issue as it is in the real world, so not a problem that really needs fixing in the first place! Thanks for the video, great stuff.

[@MrNikse]

As usual great video, i have a doubt regarding the temperature limits of the motor, is the temperature of the motor directly related to the power and amperage?. For lower kv motors putting a larger prop does not exceed the power limits of the motor but it shows overtemperature >80 deg when tested on ecalc.

[@Painless360]

Excellent question. This is one we ran out of time to cover so will cover it next time if we get enough interest. Thanks for asking..

[@adamhale6672]

I’ve also found that ecalc gives a very safe (overestimated) temperature prediction. Getting the red letters doesn’t necessarily spell out failure, but can indicate when you’re getting close.

[@maxdragon91]

Fantastic video, great content!

[@michaelo2l]

Great video very useful... booked-marked eCalc ;)

[@ais_robotic]

Assalamu alaikum vai, can you help me please ?? I am using Apm2.8. my problem is when I rool posative by hand monitor shwing nagative diraction! I finding result and tired..... no result found youtube and other site... please try to say what can I do vai.

[@Painless360]

No need to post a question twice. I've answered on your first post..

[@stevefox7961]

Thank you brilliant stuff

[@aerialimagery3216]

It would be interesting to know how airframe drag affects this. If one setup gives you 25% more thrust be 10% less speed is it possible the model would still go faster because the extra thrust better overcomes the airframe drag.

[@Painless360]

An increase in prop speed will give a faster model but as drag increases exponentially with speed it will only be a smaller increase. So twice the prop speed will not be anywhere near twice the speed in practice.

[@jackd6134]

Ah the beauty of variable pitch prop in manned airplanes.

[@Painless360]

Indeed, a lot of problem sorted when you select fine or coarse pitch ;D

[@TheRattleSnake3145]

Another reason more blades are less efficient is due to the preceding blade causing dirty air for the blade following. Fewer blades gives each blade a cleaner/better bite.

[@ecalc-gettherightdrive5483]

correct - turbulent air (dirty air) adds more drag on the blade too

[@_Amilio_]

Awesome vid thanks 👍

[@TeamYankee2]

in a very vague way that anyone can understand... diameter determines the 'grunt' and pitch determines the speed of the plane. Then it gets technical...

[@daniebecker7704]

Hi, quick question, if I use a low pitch prop and increase the rpm, can I also get a 5th gear prop for my plane with enough thrust? Thanks for a great video.

[@Painless360]

It's a tradeoff. You could have a setup for easier launches and a setup for higher speeds... Happy flying

[@srnunan4783]

When u try to buy a motor or prop for a fixed wing these days,, all you find is quad motors. It’s like nobody flies fixed wing anymore

[@Painless360]

Loads about but not usually stocked by those shops who focus on quads. Check out places like 3DXR...

[@adamhale6672]

I find that I often buy my props direct from where I want now days. APC is my go to, sometimes places like Master Airscrew work if I need different sizes. I almost always get what I need and shipping isn’t too bad.

[@scottyh72]

You are not looking hard enough. Plenty of motors for fixed wing. BadAss, KO, Cobra, Sunnysky all make fixed wing motors.