Smallest Prop to Wingspan Ratio?!

[Flyingshark]

Half of my props are CCW, and the other is CW. If I give some angle thrust, can I still use the "opposite side" props by flipping them?

It's generally a bad idea to flip props like that. If you do, they'll just draw a lot of power without creating much thrust.

Part of what creates thrust is the airfoil-like curved shape of the propeller blade, but that only really works in one direction.

 

[quorneng]

My smallest prop to span ratio is 150 mm (a 6x3 folder) to 1280 mm.

But it is a very light glider so it doesn't need much power.

 

[Gnobuddy]

Monte C. wrote: "Do you want to plug numbers into equations or do you want to build planes?"

Those two things are not mutually exclusive, you know. There's absolutely no reason why you can't do both.

If you want to, you can plug numbers into equations and build a better plane by doing so. (This is how all full-size aircraft are designed, obviously. But full-size requires a heck of a lot more math.)

Math's not to your taste? You prefer rolling the dice? Sure. You can ignore the math, use TLAR (That Looks About Right) for everything, and these days, because we have so much excess power at our disposal, you can often still get the thing to fly.

I've known at least one guy who was an absolute genius at TLAR design. He would create the most outlandish-looking objects (like Alladin sitting on a magic carpet), and get them to fly. And he never used any math at all.

But that was the exception. Over the years, I saw a lot of money wasted by a lot of people who just used TLAR.

First they'd buy a motor, because it was on sale. Then throw a prop on it because their buddy said it was the right size. Mount the whole thing in whatever model they'd just finished building. But then, at the flying field, they'd find the model didn't have enough thrust to take off.

So they'd go and buy a bigger prop, throw it on, and try again. This time, they'd burn out the ESC, because it couldn't cope with the current draw.

Then they'd buy a bigger ESC, plug it in, and try again. This time it would be the motor that burned out, because the prop was too big for it all along. (That's why the first ESC burned out, but nobody did the math, so they didn't realize it.)

If they were unlucky, the motor would burn out in mid-air, and they'd crash the model because they didn't know how to glide and land it without power.

So they go off and buy a new airframe to replace the crashed one.

Then they go off and buy a bigger motor. Which puffs the lipo battery, because the lipo pack couldn't keep up with the current draw from the big motor and big prop.

Then they'd buy a bigger lipo battery, and the model would finally fly without crashing or burning anything.

But, by this time, the owner's wallet would be a good bit lighter. A fair bit of money had just been wasted on one burned out ESC, one burned out motor, one burned out Lipo pack, and one crashed airframe.

Along with the wasted money, there was also usually loss of enthusiasm. It's not fun having to waste lots of money and watch multiple expensive electronics doodads burn up before you ever get your model in the air. People who went through this more than once often walked away from the hobby altogether.

You don't actually have to do the math by hand. Back in 2004, I began to create WebOCalc because I wanted an easy way to do the essential math for myself. It took a few years for me to develop and refining the underlying physics model to get WebOCalc to work really well. Then I made WebOCalc free, and gave it away online, to anyone who wanted to use it. It works in your 'Web browser, on Windows, Macs, Linux, any operating system with a reasonably modern, standards-compatible 'Web browser. So nobody with a computing device is left out.

By 2009 or so, there were a bunch of other free online calculators to help with various aspects of electric RC plane design. Like "PeakEff" and the Adam One RC calculator, and lots more. Many seem to have disappeared in the dozen years since then 2009, though, as the RC flying hobby continued its decline, and the software creators eventually stopped paying their website hosting fees.

Dirt-cheap radio equipment, outrunner motors, and lipo packs have changed the game quite a bit since 2004. Nowadays it doesn't cost you as much money if you don't do the math, and have to replace burned-out ESCs, motors, and lipo packs.

-Gnobuddy

 

[Pieliker96]

Monte C. wrote: "Do you want to plug numbers into equations or do you want to build planes?"

Those two things are not mutually exclusive, you know. There's absolutely no reason why you can't do both.

If you want to, you can plug numbers into equations and build a better plane by doing so. (This is how all full-size aircraft are designed, obviously. But full-size requires a heck of a lot more math.)

Math's not to your taste? You prefer rolling the dice? Sure. You can ignore the math, use TLAR (That Looks About Right) for everything, and these days, because we have so much excess power at our disposal, you can often still get the thing to fly.

I've known at least one guy who was an absolute genius at TLAR design. He would create the most outlandish-looking objects (like Alladin sitting on a magic carpet), and get them to fly. And he never used any math at all.

But that was the exception. Over the years, I saw a lot of money wasted by a lot of people who just used TLAR.

First they'd buy a motor, because it was on sale. Then throw a prop on it because their buddy said it was the right size. Mount the whole thing in whatever model they'd just finished building. But then, at the flying field, they'd find the model didn't have enough thrust to take off.

So they'd go and buy a bigger prop, throw it on, and try again. This time, they'd burn out the ESC, because it couldn't cope with the current draw.

Then they'd buy a bigger ESC, plug it in, and try again. This time it would be the motor that burned out, because the prop was too big for it all along. (That's why the first ESC burned out, but nobody did the math, so they didn't realize it.)

If they were unlucky, the motor would burn out in mid-air, and they'd crash the model because they didn't know how to glide and land it without power.

So they go off and buy a new airframe to replace the crashed one.

Then they go off and buy a bigger motor. Which puffs the lipo battery, because the lipo pack couldn't keep up with the current draw from the big motor and big prop.

Then they'd buy a bigger lipo battery, and the model would finally fly without crashing or burning anything.

But, by this time, the owner's wallet would be a good bit lighter. A fair bit of money had just been wasted on one burned out ESC, one burned out motor, one burned out Lipo pack, and one crashed airframe.

Along with the wasted money, there was also usually loss of enthusiasm. It's not fun having to waste lots of money and watch multiple expensive electronics doodads burn up before you ever get your model in the air. People who went through this more than once often walked away from the hobby altogether.

You don't actually have to do the math by hand. Back in 2004, I began to create WebOCalc because I wanted an easy way to do the essential math for myself. It took a few years for me to develop and refining the underlying physics model to get WebOCalc to work really well. Then I made WebOCalc free, and gave it away online, to anyone who wanted to use it. It works in your 'Web browser, on Windows, Macs, Linux, any operating system with a reasonably modern, standards-compatible 'Web browser. So nobody with a computing device is left out.

By 2009 or so, there were a bunch of other free online calculators to help with various aspects of electric RC plane design. Like "PeakEff" and the Adam One RC calculator, and lots more. Many seem to have disappeared in the dozen years since then 2009, though, as the RC flying hobby continued its decline, and the software creators eventually stopped paying their website hosting fees.

Dirt-cheap radio equipment, outrunner motors, and lipo packs have changed the game quite a bit since 2004. Nowadays it doesn't cost you as much money if you don't do the math, and have to replace burned-out ESCs, motors, and lipo packs.

-Gnobuddy

Rules of thumb and referencing existing designs will get you quite far. The most I've ever done in terms of calculations (besides CG, wing loading, thrust/weight) was one exceptional case where I did a weighted sum of every component of the plane and its position in the design phase just to make sure the CG would balance proper from the get-go. Looking at full-scale planes and copying the proportions and styles they use is perfectly valid: they've already done the engineering work, after all!

 

[Monte.C]

Monte C. wrote: "Do you want to plug numbers into equations or do you want to build planes?"

Those two things are not mutually exclusive, you know. There's absolutely no reason why you can't do both.

If you want to, you can plug numbers into equations and build a better plane by doing so. (This is how all full-size aircraft are designed, obviously. But full-size requires a heck of a lot more math.)

Math's not to your taste? You prefer rolling the dice? Sure. You can ignore the math, use TLAR (That Looks About Right) for everything, and these days, because we have so much excess power at our disposal, you can often still get the thing to fly.

I've known at least one guy who was an absolute genius at TLAR design. He would create the most outlandish-looking objects (like Alladin sitting on a magic carpet), and get them to fly. And he never used any math at all.

But that was the exception. Over the years, I saw a lot of money wasted by a lot of people who just used TLAR.

First they'd buy a motor, because it was on sale. Then throw a prop on it because their buddy said it was the right size. Mount the whole thing in whatever model they'd just finished building. But then, at the flying field, they'd find the model didn't have enough thrust to take off.

So they'd go and buy a bigger prop, throw it on, and try again. This time, they'd burn out the ESC, because it couldn't cope with the current draw.

Then they'd buy a bigger ESC, plug it in, and try again. This time it would be the motor that burned out, because the prop was too big for it all along. (That's why the first ESC burned out, but nobody did the math, so they didn't realize it.)

If they were unlucky, the motor would burn out in mid-air, and they'd crash the model because they didn't know how to glide and land it without power.

So they go off and buy a new airframe to replace the crashed one.

Then they go off and buy a bigger motor. Which puffs the lipo battery, because the lipo pack couldn't keep up with the current draw from the big motor and big prop.

Then they'd buy a bigger lipo battery, and the model would finally fly without crashing or burning anything.

But, by this time, the owner's wallet would be a good bit lighter. A fair bit of money had just been wasted on one burned out ESC, one burned out motor, one burned out Lipo pack, and one crashed airframe.

Along with the wasted money, there was also usually loss of enthusiasm. It's not fun having to waste lots of money and watch multiple expensive electronics doodads burn up before you ever get your model in the air. People who went through this more than once often walked away from the hobby altogether.

You don't actually have to do the math by hand. Back in 2004, I began to create WebOCalc because I wanted an easy way to do the essential math for myself. It took a few years for me to develop and refining the underlying physics model to get WebOCalc to work really well. Then I made WebOCalc free, and gave it away online, to anyone who wanted to use it. It works in your 'Web browser, on Windows, Macs, Linux, any operating system with a reasonably modern, standards-compatible 'Web browser. So nobody with a computing device is left out.

By 2009 or so, there were a bunch of other free online calculators to help with various aspects of electric RC plane design. Like "PeakEff" and the Adam One RC calculator, and lots more. Many seem to have disappeared in the dozen years since then 2009, though, as the RC flying hobby continued its decline, and the software creators eventually stopped paying their website hosting fees.

Dirt-cheap radio equipment, outrunner motors, and lipo packs have changed the game quite a bit since 2004. Nowadays it doesn't cost you as much money if you don't do the math, and have to replace burned-out ESCs, motors, and lipo packs.

-Gnobuddy

No need for such a long story. Boy you sure do have a point to make.

Far too many times I've watched someone ask a rather simple question and every other member jumps in with seemingly brilliant mathematical formulas that are actually barely related to the question at all, but designed to show us all that the member is an aeronautical engineering genius. There's an affliction that far too many members here are plagued with: Smartest Guy in the Room Syndrome. And they can't help but try to prove it with every word they type. Far too many times I've read complicated and worthless replies when the right answer is obvious and intuitive (to some of us).

Educated guesses are MY way to fly. With the emphasis on the educated part. And it serves me very well, thank you very much Mr. Nobody.

 

[FieldRC]

Monte C. wrote: "Do you want to plug numbers into equations or do you want to build planes?"

Those two things are not mutually exclusive, you know. There's absolutely no reason why you can't do both.

If you want to, you can plug numbers into equations and build a better plane by doing so. (This is how all full-size aircraft are designed, obviously. But full-size requires a heck of a lot more math.)

Math's not to your taste? You prefer rolling the dice? Sure. You can ignore the math, use TLAR (That Looks About Right) for everything, and these days, because we have so much excess power at our disposal, you can often still get the thing to fly.

I've known at least one guy who was an absolute genius at TLAR design. He would create the most outlandish-looking objects (like Alladin sitting on a magic carpet), and get them to fly. And he never used any math at all.

But that was the exception. Over the years, I saw a lot of money wasted by a lot of people who just used TLAR.

First they'd buy a motor, because it was on sale. Then throw a prop on it because their buddy said it was the right size. Mount the whole thing in whatever model they'd just finished building. But then, at the flying field, they'd find the model didn't have enough thrust to take off.

So they'd go and buy a bigger prop, throw it on, and try again. This time, they'd burn out the ESC, because it couldn't cope with the current draw.

Then they'd buy a bigger ESC, plug it in, and try again. This time it would be the motor that burned out, because the prop was too big for it all along. (That's why the first ESC burned out, but nobody did the math, so they didn't realize it.)

If they were unlucky, the motor would burn out in mid-air, and they'd crash the model because they didn't know how to glide and land it without power.

So they go off and buy a new airframe to replace the crashed one.

Then they go off and buy a bigger motor. Which puffs the lipo battery, because the lipo pack couldn't keep up with the current draw from the big motor and big prop.

Then they'd buy a bigger lipo battery, and the model would finally fly without crashing or burning anything.

But, by this time, the owner's wallet would be a good bit lighter. A fair bit of money had just been wasted on one burned out ESC, one burned out motor, one burned out Lipo pack, and one crashed airframe.

Along with the wasted money, there was also usually loss of enthusiasm. It's not fun having to waste lots of money and watch multiple expensive electronics doodads burn up before you ever get your model in the air. People who went through this more than once often walked away from the hobby altogether.

You don't actually have to do the math by hand. Back in 2004, I began to create WebOCalc because I wanted an easy way to do the essential math for myself. It took a few years for me to develop and refining the underlying physics model to get WebOCalc to work really well. Then I made WebOCalc free, and gave it away online, to anyone who wanted to use it. It works in your 'Web browser, on Windows, Macs, Linux, any operating system with a reasonably modern, standards-compatible 'Web browser. So nobody with a computing device is left out.

By 2009 or so, there were a bunch of other free online calculators to help with various aspects of electric RC plane design. Like "PeakEff" and the Adam One RC calculator, and lots more. Many seem to have disappeared in the dozen years since then 2009, though, as the RC flying hobby continued its decline, and the software creators eventually stopped paying their website hosting fees.

Dirt-cheap radio equipment, outrunner motors, and lipo packs have changed the game quite a bit since 2004. Nowadays it doesn't cost you as much money if you don't do the math, and have to replace burned-out ESCs, motors, and lipo packs.

-Gnobuddy

I've been very fortunate to get good measurements/specs on my stuff and so far nothings burnt out. I thank HK and those calculators for giving good numbers.

 

[FieldRC]

It's generally a bad idea to flip props like that. If you do, they'll just draw a lot of power without creating much thrust.

Part of what creates thrust is the airfoil-like curved shape of the propeller blade, but that only really works in one direction.

Got it. I'll save the reverse props for "reverse" angle thrusts, pushers, two engine designs ect.

 

[Flyingshark]

Monte C. wrote: "Do you want to plug numbers into equations or do you want to build planes?"

Those two things are not mutually exclusive, you know. There's absolutely no reason why you can't do both.

If you want to, you can plug numbers into equations and build a better plane by doing so. (This is how all full-size aircraft are designed, obviously. But full-size requires a heck of a lot more math.)

Math's not to your taste? You prefer rolling the dice? Sure. You can ignore the math, use TLAR (That Looks About Right) for everything, and these days, because we have so much excess power at our disposal, you can often still get the thing to fly.

I've known at least one guy who was an absolute genius at TLAR design. He would create the most outlandish-looking objects (like Alladin sitting on a magic carpet), and get them to fly. And he never used any math at all.

But that was the exception. Over the years, I saw a lot of money wasted by a lot of people who just used TLAR.

First they'd buy a motor, because it was on sale. Then throw a prop on it because their buddy said it was the right size. Mount the whole thing in whatever model they'd just finished building. But then, at the flying field, they'd find the model didn't have enough thrust to take off.

So they'd go and buy a bigger prop, throw it on, and try again. This time, they'd burn out the ESC, because it couldn't cope with the current draw.

Then they'd buy a bigger ESC, plug it in, and try again. This time it would be the motor that burned out, because the prop was too big for it all along. (That's why the first ESC burned out, but nobody did the math, so they didn't realize it.)

If they were unlucky, the motor would burn out in mid-air, and they'd crash the model because they didn't know how to glide and land it without power.

So they go off and buy a new airframe to replace the crashed one.

Then they go off and buy a bigger motor. Which puffs the lipo battery, because the lipo pack couldn't keep up with the current draw from the big motor and big prop.

Then they'd buy a bigger lipo battery, and the model would finally fly without crashing or burning anything.

But, by this time, the owner's wallet would be a good bit lighter. A fair bit of money had just been wasted on one burned out ESC, one burned out motor, one burned out Lipo pack, and one crashed airframe.

Along with the wasted money, there was also usually loss of enthusiasm. It's not fun having to waste lots of money and watch multiple expensive electronics doodads burn up before you ever get your model in the air. People who went through this more than once often walked away from the hobby altogether.

You don't actually have to do the math by hand. Back in 2004, I began to create WebOCalc because I wanted an easy way to do the essential math for myself. It took a few years for me to develop and refining the underlying physics model to get WebOCalc to work really well. Then I made WebOCalc free, and gave it away online, to anyone who wanted to use it. It works in your 'Web browser, on Windows, Macs, Linux, any operating system with a reasonably modern, standards-compatible 'Web browser. So nobody with a computing device is left out.

By 2009 or so, there were a bunch of other free online calculators to help with various aspects of electric RC plane design. Like "PeakEff" and the Adam One RC calculator, and lots more. Many seem to have disappeared in the dozen years since then 2009, though, as the RC flying hobby continued its decline, and the software creators eventually stopped paying their website hosting fees.

Dirt-cheap radio equipment, outrunner motors, and lipo packs have changed the game quite a bit since 2004. Nowadays it doesn't cost you as much money if you don't do the math, and have to replace burned-out ESCs, motors, and lipo packs.

-Gnobuddy

The problem with recommending lots of math up front is that it creates a barrier of entry for newbies. Wasting money makes me lose enthusiasm for something, but so does having to jump through a million mathematical hoops to get there. (I even count myself as a person who enjoys math, but not when it's stopping me from flying.)

Investing a lot of time to optimize a design is IMO only a good idea when you're flying very expensive things (and hopefully you're not flying those until you have plenty of experience to draw on), but the beauty of foam board and the FliteTest method is that it's not expensive at all (compared to 1000+ dollar planes).

The electronics from an FT power pack can be reused in multiple planes and are already matched to each other for you, and the airframe itself costs about $10 in materials. With that kind of investment, it's a lot easier to feel comfortable with throwing some pieces of foam together and learning by doing. You can worry about the math later on if you need to.

EDIT:
Sorry for hijacking your thread @FieldRC!

 

[cbf123]

The electronics from an FT power pack can be reused in multiple planes and are already matched to each other for you, and the airframe itself costs about $10 in materials. With that kind of investment, it's a lot easier to feel comfortable with throwing some pieces of foam together and learning by doing. You can worry about the math later on if you need to.

I totally agree with this, but at least once a week I see someone on rcgroups.com or reddit who's trying to piece together a motor/battery/ESC/prop combo from Banggood/Aliexpress/Ebay that'll work for their custom-built "that looks about right" airframe that they've assembled. And they have already bought the motor, so they need other bits to match.

For people on the tightest budget, the FT power pack is more expensive than buying the major components separately. Way faster and easier though.

 

[SSgt Duramax]

I totally agree with this, but at least once a week I see someone on rcgroups.com or reddit who's trying to piece together a motor/battery/ESC/prop combo from Banggood/Aliexpress/Ebay that'll work for their custom-built "that looks about right" airframe that they've assembled. And they have already bought the motor, so they need other bits to match.

For people on the tightest budget, the FT power pack is more expensive than buying the major components separately. Way faster and easier though.

They sell motor esc combos on ebay that are matched and work well. They even tell you what props to get. It isnt like power packs are a mystery. The plans and packs tell you what to buy.