Thread Tools
Old Apr 23, 2016, 06:08 PM
lu4414 is offline
Find More Posts by lu4414
Padawan
Brazil, SP, So Paulo
Joined Jan 2015
124 Posts
Help!
Design help

Hello,
Im trying to figure out how to design my first tailless plane, and i would like some advices.
So my goals is have a stable wing, with a maximmum wingspan of 130cm and that can fly on a 3s 2200mah. I want it to be efficient as possible!
So anyone do something similar? Can help me with some prop, motor, esc and airfoil ideas?
Best regards
lu4414 is offline Find More Posts by lu4414
Reply With Quote
Sign up now
to remove ads between posts
Old Apr 23, 2016, 07:31 PM
Artful Owl is offline
Find More Posts by Artful Owl
Registered User
Artful Owl's Avatar
New Zealand, Canterbury, Christchurch
Joined Dec 2011
792 Posts
what are you going to make it out of
Artful Owl is offline Find More Posts by Artful Owl
Reply With Quote
Old Apr 23, 2016, 07:46 PM
lu4414 is offline
Find More Posts by lu4414
Padawan
Brazil, SP, So Paulo
Joined Jan 2015
124 Posts
Quote:
Originally Posted by Artful Owl View Post
what are you going to make it out of
I have here EPO and depron, depending of the design suggestions i will chose the material
Thanks
lu4414 is offline Find More Posts by lu4414
Reply With Quote
Old Apr 23, 2016, 11:21 PM
Artful Owl is offline
Find More Posts by Artful Owl
Registered User
Artful Owl's Avatar
New Zealand, Canterbury, Christchurch
Joined Dec 2011
792 Posts
Both these materials are sheets? 3 to 5mm thick?
Artful Owl is offline Find More Posts by Artful Owl
Reply With Quote
Old Apr 23, 2016, 11:25 PM
Artful Owl is offline
Find More Posts by Artful Owl
Registered User
Artful Owl's Avatar
New Zealand, Canterbury, Christchurch
Joined Dec 2011
792 Posts
maybe something like this
FPV49 v4 Plans & Some Build Tips (10 min 20 sec)
Artful Owl is offline Find More Posts by Artful Owl
Reply With Quote
Old Apr 23, 2016, 11:29 PM
Artful Owl is offline
Find More Posts by Artful Owl
Registered User
Artful Owl's Avatar
New Zealand, Canterbury, Christchurch
Joined Dec 2011
792 Posts
this guys uses a different style of building you might find interesting
RPM314's blog
Artful Owl is offline Find More Posts by Artful Owl
Reply With Quote
Old Apr 24, 2016, 08:17 AM
lu4414 is offline
Find More Posts by lu4414
Padawan
Brazil, SP, So Paulo
Joined Jan 2015
124 Posts
Quote:
Originally Posted by Artful Owl View Post
Both these materials are sheets? 3 to 5mm thick?
The EPO is like 5cm thick and depron 5mm
Thanks
lu4414 is offline Find More Posts by lu4414
Last edited by lu4414; Apr 24, 2016 at 11:27 AM.
Reply With Quote
Old Apr 27, 2016, 12:27 AM
RPM314 is offline
Find More Posts by RPM314
Tailless fly-hard
RPM314's Avatar
United States, NY, Brooklyn
Joined Apr 2012
1,124 Posts
Thanks for the shout-out, Owl! Makes me feel all warm and fuzzy inside.

Quote:
Originally Posted by lu4414 View Post
Hello,
Im trying to figure out how to design my first tailless plane, and i would like some advices.
So my goals is have a stable wing, with a maximmum wingspan of 130cm and that can fly on a 3s 2200mah. I want it to be efficient as possible!
So anyone do something similar? Can help me with some prop, motor, esc and airfoil ideas?
Best regards
Well you can always just throw some stuff together, run it through a CG calculator and live with whatever comes out, but you can tailor the plane to be exactly what you want it to be if you're comfortable with a little algebra. There are certain steps you need to follow if you want to design a plane "properly", and they start off the same for all types of aircraft:

-Figure out what you want the plane to do
Looks like you already started in this section a little. Your first goal is efficiency, but what kind? Are you looking for a high lift to drag motorglider thing, a slow flying endurance plane with lots of flight time, or something that cruises efficiently at high speed? Another one of your constraints is being able to fly off of a 3s 2200. This is helpful, since it will narrow down the kinds of powerplants you will use. You have also constrained it to be 1300mm, which is helpful since it will make things simpler when you figure out how big you want the plane to be. It can limit your options, though.
Another big constraint that gets overlooked sometimes is handling. You already said you want good stability, but you need to remember that on tailless planes stability is very opposed to efficiency. Using reflex, washout and the correct CG you will have a perfectly flyable plane, but just remember that all things come in moderation.

-Figure out the rest of the constraints your plane needs to meet
Based on the 3 basic kinds of efficient flyers I noted before, you should choose the rest of your power system. This and this motor are middle-of-the-road kind of things, and they'll take a 10x6 and 8x4 prop on 3s, respectively. The first motor is definitely beefier, and should be used if you want to end up with a heavier and faster plane. The second one is kind of lighter gauge. You can go up to bigger motors and props for heavier planes, or if you want to go the super-light-endurance plane route you could probably get away with as little as a 1300kv 24g Blue Wonder motor. After that, a 20-30A ESC will do ya, based on what motor you choose. Then radio gear and servos are up to you, of course.
Then figure out how you're going to build it. There are lots of options; you could hotwire it out of blucore or EPP, you could make it out of folded-over foamboard like you see in my blog entries (and I got it from Ed at Experimental Airlines), or you could do KF airfoils and just make it out of flat foamboard sheets [these are ranked from most to least involved construction]. Or, of course you could use balsa or some nonsense, if you're a total square. This will also influence how you're going to reinforce it: hotwired wings need carbon or wood spars embedded in the top and bottom, folded wings need the spars tucked into the inside, but KF wings usually have to have a single big, heavy spar through the middle since they don't have depth or internal space. The construction method you choose will impact how heavy it ends up being more than the efficiency once it's flying, but you should make the decision based on what you are most comfortable building.
Then you need to figure out some aerodynamic stuff. First - what wing loading do you want? At the low end, 15g/dm2 is going to be very slow and floaty, like a Calypso motorglider if you've ever seen one. At the high end, 50g/dm2 is getting closer to EDF jet territory, and it'll make for a plane that flies solid at high speed. This decision should be based on what kind of efficient plane you want, as I said earlier. Next - what aspect ratio do you want? Some are tempted to say that higher is always more efficient, but this is not true, and there is an added dimension for tailless planes.
Aspect Ratio Sidebar - since there's a lot to say about it.
First off, know that right now I'm talking about changing the aspect ratio while keeping the wing area the same. So if you choose 1m^2 area and an aspect of 4, you end up with a span of 2m and a chord of 0.5m. Increasing the aspect ratio will directly decrease the drag due to lift, since you are increasing the span, and span has a bigger effect on lift induced drag than chord does. But if you change aspect ratio while keeping span constant, the reverse happens: higher aspect ratio means a smaller chord with the same span, so there is more lift induced drag because there is less wing area, so the wing needs to work harder. If you have already chosen your equipment and wingspan and wing loading, you have pretty much set what the aspect ratio will be. It might not be something you'll be happy with, so consider leaving your 1300mm constraint open to revision.
Higher aspect ratios will always mean smaller wing chords, which means higher parasite drag since the wing has a lower reynolds number. They also mean skinnier wings, which have to be heavier to have the same strength, and tend to be more flexible.
Aspect ratio also greatly affects the handling of flying wings. Having more wing chord (lower aspect ratio) is like having a longer "tail", so such planes will be more stable. They will also have a wider range of CG positions, since acceptable CG's are expressed as fractions of the chord, so longer chord=longer CG range. High aspect flying wings tend to be more touchy on the elevator, but this isn't a problem until you get to very high aspects, it just feels less mushy than a low aspect 'wing. Low aspect 'wings, even though they fell slightly mushier in elevator, they will have snappier rolling. So keep that in mind based on how you fly.

So an aspect ratio of 3-4 will be on the low side, and is a good fit for higher speed planes. Aspects of around 10 are good for planes that focus on the lower speeds for efficiency. 15 and up are usually found on sailplanes, and you'll have to make sure you reinforce it properly or you'll run a large risk of having it break. I'd say 6-8 is good middle ground if you can't make up your mind. This decision should be made based on what kind of efficiency you want and what kind of handling you'd like. Next - what taper ratio (tip chord divided by root chord) do you want? The biggest things you should worry about here are the fact that a lower taper ratio means more root chord for storing equipment, but it moves the CG point forward if the wing is swept back, so it'll be harder to balance. I'd say a reasonable range to pick from is 0.4 to 1.0, but just choose something in the middle if you're not sure and it'll work fine. Also know that more taper can lead to tip stalls. Last - how much sweep do you want? If you pick a specific value (particularly zero/plank) you will have to place your equipment to achieve this, maybe even in a fuselage pod to get them far forward enough. That is the easiest way. If you want to keep everything inside the wing, you'll need to calculate where the CG will end up for a given amount of sweep and check it against a CG calculator to see if they match up. If they don't, you need to change the sweep and try again. More sweep will make the plane more stable, have a wider CG range, and be less efficient.

-Figure out how big to make it
Hope you wrote all your choices down from before.
First, find the wing area. If you want to get all fancy, you can model how the airframe weight changes with wing area and solve the equations simultaneously wing the wing loading. Otherwise, just assume that the AUW of the plane will be twice the weight of the motor+battery+ESC+servos, etc (i.e. the electronics and airframe split the plane's weight 50/50) and you'll be close enough. Take the predicted AUW number and divide it by the wing loading, and you'll get the number for the wing area that gives you the wing loading you want.
Then, find the wingspan and chord. Aspect is span divided by chord, and wing area is span times chord, so the aspect ratio is span squared times the wing area you just found. You chose the aspect ratio, so solve for the wingspan. Then divide the span by the aspect ratio to get the average chord.
Then, find the root and tip chords. The taper ratio you chose gives you the equation [root*taper ratio = tip], and you know that their average is the average chord [(root+tip)/2 = average chord]. So solve the two equations and you have each chord.
You should already have the amount of sweep, so that's everything you need to plug into a CG calculator, like in this forum's sticky, to make sure it works. Congrats!

-Figure out the physical design
This means choosing the elevons (1/4 chord is usually good), making winglet shapes (you don't need a lot), figuring out a motor mount, placing your spars, routing your wires, devising access hatches, thinking up a fuselage pod if you need it, all that good stuff. Just use your intuition. I like using Sketchup for this since it's pretty freeform and lets you drag stuff everywhere and fiddle with shapes.


Or just ignore all this and be able to sleep for the next week. Your pick.
RPM314 is offline Find More Posts by RPM314
Reply With Quote
Old Apr 27, 2016, 04:12 PM
lu4414 is offline
Find More Posts by lu4414
Padawan
Brazil, SP, So Paulo
Joined Jan 2015
124 Posts
Quote:
Originally Posted by RPM314 View Post
Thanks for the shout-out, Owl! Makes me feel all warm and fuzzy inside.



Well you can always just throw some stuff together, run it through a CG calculator and live with whatever comes out, but you can tailor the plane to be exactly what you want it to be if you're comfortable with a little algebra. There are certain steps you need to follow if you want to design a plane "properly", and they start off the same for all types of aircraft:

-Figure out what you want the plane to do
Looks like you already started in this section a little. Your first goal is efficiency, but what kind? Are you looking for a high lift to drag motorglider thing, a slow flying endurance plane with lots of flight time, or something that cruises efficiently at high speed? Another one of your constraints is being able to fly off of a 3s 2200. This is helpful, since it will narrow down the kinds of powerplants you will use. You have also constrained it to be 1300mm, which is helpful since it will make things simpler when you figure out how big you want the plane to be. It can limit your options, though.
Another big constraint that gets overlooked sometimes is handling. You already said you want good stability, but you need to remember that on tailless planes stability is very opposed to efficiency. Using reflex, washout and the correct CG you will have a perfectly flyable plane, but just remember that all things come in moderation.

-Figure out the rest of the constraints your plane needs to meet
Based on the 3 basic kinds of efficient flyers I noted before, you should choose the rest of your power system. This and this motor are middle-of-the-road kind of things, and they'll take a 10x6 and 8x4 prop on 3s, respectively. The first motor is definitely beefier, and should be used if you want to end up with a heavier and faster plane. The second one is kind of lighter gauge. You can go up to bigger motors and props for heavier planes, or if you want to go the super-light-endurance plane route you could probably get away with as little as a 1300kv 24g Blue Wonder motor. After that, a 20-30A ESC will do ya, based on what motor you choose. Then radio gear and servos are up to you, of course.
Then figure out how you're going to build it. There are lots of options; you could hotwire it out of blucore or EPP, you could make it out of folded-over foamboard like you see in my blog entries (and I got it from Ed at Experimental Airlines), or you could do KF airfoils and just make it out of flat foamboard sheets [these are ranked from most to least involved construction]. Or, of course you could use balsa or some nonsense, if you're a total square. This will also influence how you're going to reinforce it: hotwired wings need carbon or wood spars embedded in the top and bottom, folded wings need the spars tucked into the inside, but KF wings usually have to have a single big, heavy spar through the middle since they don't have depth or internal space. The construction method you choose will impact how heavy it ends up being more than the efficiency once it's flying, but you should make the decision based on what you are most comfortable building.
Then you need to figure out some aerodynamic stuff. First - what wing loading do you want? At the low end, 15g/dm2 is going to be very slow and floaty, like a Calypso motorglider if you've ever seen one. At the high end, 50g/dm2 is getting closer to EDF jet territory, and it'll make for a plane that flies solid at high speed. This decision should be based on what kind of efficient plane you want, as I said earlier. Next - what aspect ratio do you want? Some are tempted to say that higher is always more efficient, but this is not true, and there is an added dimension for tailless planes.
Aspect Ratio Sidebar - since there's a lot to say about it.
First off, know that right now I'm talking about changing the aspect ratio while keeping the wing area the same. So if you choose 1m^2 area and an aspect of 4, you end up with a span of 2m and a chord of 0.5m. Increasing the aspect ratio will directly decrease the drag due to lift, since you are increasing the span, and span has a bigger effect on lift induced drag than chord does. But if you change aspect ratio while keeping span constant, the reverse happens: higher aspect ratio means a smaller chord with the same span, so there is more lift induced drag because there is less wing area, so the wing needs to work harder. If you have already chosen your equipment and wingspan and wing loading, you have pretty much set what the aspect ratio will be. It might not be something you'll be happy with, so consider leaving your 1300mm constraint open to revision.
Higher aspect ratios will always mean smaller wing chords, which means higher parasite drag since the wing has a lower reynolds number. They also mean skinnier wings, which have to be heavier to have the same strength, and tend to be more flexible.
Aspect ratio also greatly affects the handling of flying wings. Having more wing chord (lower aspect ratio) is like having a longer "tail", so such planes will be more stable. They will also have a wider range of CG positions, since acceptable CG's are expressed as fractions of the chord, so longer chord=longer CG range. High aspect flying wings tend to be more touchy on the elevator, but this isn't a problem until you get to very high aspects, it just feels less mushy than a low aspect 'wing. Low aspect 'wings, even though they fell slightly mushier in elevator, they will have snappier rolling. So keep that in mind based on how you fly.

So an aspect ratio of 3-4 will be on the low side, and is a good fit for higher speed planes. Aspects of around 10 are good for planes that focus on the lower speeds for efficiency. 15 and up are usually found on sailplanes, and you'll have to make sure you reinforce it properly or you'll run a large risk of having it break. I'd say 6-8 is good middle ground if you can't make up your mind. This decision should be made based on what kind of efficiency you want and what kind of handling you'd like. Next - what taper ratio (tip chord divided by root chord) do you want? The biggest things you should worry about here are the fact that a lower taper ratio means more root chord for storing equipment, but it moves the CG point forward if the wing is swept back, so it'll be harder to balance. I'd say a reasonable range to pick from is 0.4 to 1.0, but just choose something in the middle if you're not sure and it'll work fine. Also know that more taper can lead to tip stalls. Last - how much sweep do you want? If you pick a specific value (particularly zero/plank) you will have to place your equipment to achieve this, maybe even in a fuselage pod to get them far forward enough. That is the easiest way. If you want to keep everything inside the wing, you'll need to calculate where the CG will end up for a given amount of sweep and check it against a CG calculator to see if they match up. If they don't, you need to change the sweep and try again. More sweep will make the plane more stable, have a wider CG range, and be less efficient.

-Figure out how big to make it
Hope you wrote all your choices down from before.
First, find the wing area. If you want to get all fancy, you can model how the airframe weight changes with wing area and solve the equations simultaneously wing the wing loading. Otherwise, just assume that the AUW of the plane will be twice the weight of the motor+battery+ESC+servos, etc (i.e. the electronics and airframe split the plane's weight 50/50) and you'll be close enough. Take the predicted AUW number and divide it by the wing loading, and you'll get the number for the wing area that gives you the wing loading you want.
Then, find the wingspan and chord. Aspect is span divided by chord, and wing area is span times chord, so the aspect ratio is span squared times the wing area you just found. You chose the aspect ratio, so solve for the wingspan. Then divide the span by the aspect ratio to get the average chord.
Then, find the root and tip chords. The taper ratio you chose gives you the equation [root*taper ratio = tip], and you know that their average is the average chord [(root+tip)/2 = average chord]. So solve the two equations and you have each chord.
You should already have the amount of sweep, so that's everything you need to plug into a CG calculator, like in this forum's sticky, to make sure it works. Congrats!

-Figure out the physical design
This means choosing the elevons (1/4 chord is usually good), making winglet shapes (you don't need a lot), figuring out a motor mount, placing your spars, routing your wires, devising access hatches, thinking up a fuselage pod if you need it, all that good stuff. Just use your intuition. I like using Sketchup for this since it's pretty freeform and lets you drag stuff everywhere and fiddle with shapes.


Or just ignore all this and be able to sleep for the next week. Your pick.
Man thanks a lot fot the help, i will write down some of my choices and if i please can get your opinion it would be great!
So first i pick the second motor that you reccomend with the 8X4 prop, for the wing loading i chosse 25g/dm2 and AUW if i do right will be a about 350g (2*50g of the motor+44g ESC=18g for the servos+188g for the battery ).I also choose 6 for aspect ratio and 0,7 for the tape ratio.
Calculating all i had:
Area of 14 dm2
Span of 91,64 cm
average cord of 15.26cm
root of 17.95cm
tip of 12.56cm
The data of CG is here http://fwcg.3dzone.dk/?wing_span=91....ow_mac_lines=0
All looks good on CG calculator and for sweep i chosse 20 degress( Random number based only on CG position, help here will be great).
Now for the construction i plan do something like you do on our models, but i don`t have a clue of how to do and calculate the need amount of washout, any tips?? Other point what about wing thickness??
Also a lot of thread here talks about profile (MH45, MH60 and others), what we calculate here is already a profile right?
The reinforcemnt of the wing and the more physical part of the design i still have to think about
Nothing more cool than do the math of that!
Again thanks so much for the help!!!
Best regards
lu4414 is offline Find More Posts by lu4414
Last edited by lu4414; Apr 27, 2016 at 05:12 PM.
Reply With Quote
Old Apr 28, 2016, 08:37 AM
BigShooter is offline
Find More Posts by BigShooter
Registered User
Joined Mar 2016
40 Posts
Quote:
Originally Posted by RPM314 View Post
Thanks for the shout-out, Owl! Makes me feel all warm and fuzzy inside.



Well you can always just throw some stuff together, run it through a CG calculator and live with whatever comes out, but you can tailor the plane to be exactly what you want it to be if you're comfortable with a little algebra. There are certain steps you need to follow if you want to design a plane "properly", and they start off the same for all types of aircraft:

-Figure out what you want the plane to do
Looks like you already started in this section a little. Your first goal is efficiency, but what kind? Are you looking for a high lift to drag motorglider thing, a slow flying endurance plane with lots of flight time, or something that cruises efficiently at high speed? Another one of your constraints is being able to fly off of a 3s 2200. This is helpful, since it will narrow down the kinds of powerplants you will use. You have also constrained it to be 1300mm, which is helpful since it will make things simpler when you figure out how big you want the plane to be. It can limit your options, though.
Another big constraint that gets overlooked sometimes is handling. You already said you want good stability, but you need to remember that on tailless planes stability is very opposed to efficiency. Using reflex, washout and the correct CG you will have a perfectly flyable plane, but just remember that all things come in moderation.

-Figure out the rest of the constraints your plane needs to meet
Based on the 3 basic kinds of efficient flyers I noted before, you should choose the rest of your power system. This and this motor are middle-of-the-road kind of things, and they'll take a 10x6 and 8x4 prop on 3s, respectively. The first motor is definitely beefier, and should be used if you want to end up with a heavier and faster plane. The second one is kind of lighter gauge. You can go up to bigger motors and props for heavier planes, or if you want to go the super-light-endurance plane route you could probably get away with as little as a 1300kv 24g Blue Wonder motor. After that, a 20-30A ESC will do ya, based on what motor you choose. Then radio gear and servos are up to you, of course.
Then figure out how you're going to build it. There are lots of options; you could hotwire it out of blucore or EPP, you could make it out of folded-over foamboard like you see in my blog entries (and I got it from Ed at Experimental Airlines), or you could do KF airfoils and just make it out of flat foamboard sheets [these are ranked from most to least involved construction]. Or, of course you could use balsa or some nonsense, if you're a total square. This will also influence how you're going to reinforce it: hotwired wings need carbon or wood spars embedded in the top and bottom, folded wings need the spars tucked into the inside, but KF wings usually have to have a single big, heavy spar through the middle since they don't have depth or internal space. The construction method you choose will impact how heavy it ends up being more than the efficiency once it's flying, but you should make the decision based on what you are most comfortable building.
Then you need to figure out some aerodynamic stuff. First - what wing loading do you want? At the low end, 15g/dm2 is going to be very slow and floaty, like a Calypso motorglider if you've ever seen one. At the high end, 50g/dm2 is getting closer to EDF jet territory, and it'll make for a plane that flies solid at high speed. This decision should be based on what kind of efficient plane you want, as I said earlier. Next - what aspect ratio do you want? Some are tempted to say that higher is always more efficient, but this is not true, and there is an added dimension for tailless planes.
Aspect Ratio Sidebar - since there's a lot to say about it.
First off, know that right now I'm talking about changing the aspect ratio while keeping the wing area the same. So if you choose 1m^2 area and an aspect of 4, you end up with a span of 2m and a chord of 0.5m. Increasing the aspect ratio will directly decrease the drag due to lift, since you are increasing the span, and span has a bigger effect on lift induced drag than chord does. But if you change aspect ratio while keeping span constant, the reverse happens: higher aspect ratio means a smaller chord with the same span, so there is more lift induced drag because there is less wing area, so the wing needs to work harder. If you have already chosen your equipment and wingspan and wing loading, you have pretty much set what the aspect ratio will be. It might not be something you'll be happy with, so consider leaving your 1300mm constraint open to revision.
Higher aspect ratios will always mean smaller wing chords, which means higher parasite drag since the wing has a lower reynolds number. They also mean skinnier wings, which have to be heavier to have the same strength, and tend to be more flexible.
Aspect ratio also greatly affects the handling of flying wings. Having more wing chord (lower aspect ratio) is like having a longer "tail", so such planes will be more stable. They will also have a wider range of CG positions, since acceptable CG's are expressed as fractions of the chord, so longer chord=longer CG range. High aspect flying wings tend to be more touchy on the elevator, but this isn't a problem until you get to very high aspects, it just feels less mushy than a low aspect 'wing. Low aspect 'wings, even though they fell slightly mushier in elevator, they will have snappier rolling. So keep that in mind based on how you fly.

So an aspect ratio of 3-4 will be on the low side, and is a good fit for higher speed planes. Aspects of around 10 are good for planes that focus on the lower speeds for efficiency. 15 and up are usually found on sailplanes, and you'll have to make sure you reinforce it properly or you'll run a large risk of having it break. I'd say 6-8 is good middle ground if you can't make up your mind. This decision should be made based on what kind of efficiency you want and what kind of handling you'd like. Next - what taper ratio (tip chord divided by root chord) do you want? The biggest things you should worry about here are the fact that a lower taper ratio means more root chord for storing equipment, but it moves the CG point forward if the wing is swept back, so it'll be harder to balance. I'd say a reasonable range to pick from is 0.4 to 1.0, but just choose something in the middle if you're not sure and it'll work fine. Also know that more taper can lead to tip stalls. Last - how much sweep do you want? If you pick a specific value (particularly zero/plank) you will have to place your equipment to achieve this, maybe even in a fuselage pod to get them far forward enough. That is the easiest way. If you want to keep everything inside the wing, you'll need to calculate where the CG will end up for a given amount of sweep and check it against a CG calculator to see if they match up. If they don't, you need to change the sweep and try again. More sweep will make the plane more stable, have a wider CG range, and be less efficient.

-Figure out how big to make it
Hope you wrote all your choices down from before.
First, find the wing area. If you want to get all fancy, you can model how the airframe weight changes with wing area and solve the equations simultaneously wing the wing loading. Otherwise, just assume that the AUW of the plane will be twice the weight of the motor+battery+ESC+servos, etc (i.e. the electronics and airframe split the plane's weight 50/50) and you'll be close enough. Take the predicted AUW number and divide it by the wing loading, and you'll get the number for the wing area that gives you the wing loading you want.
Then, find the wingspan and chord. Aspect is span divided by chord, and wing area is span times chord, so the aspect ratio is span squared times the wing area you just found. You chose the aspect ratio, so solve for the wingspan. Then divide the span by the aspect ratio to get the average chord.
Then, find the root and tip chords. The taper ratio you chose gives you the equation [root*taper ratio = tip], and you know that their average is the average chord [(root+tip)/2 = average chord]. So solve the two equations and you have each chord.
You should already have the amount of sweep, so that's everything you need to plug into a CG calculator, like in this forum's sticky, to make sure it works. Congrats!

-Figure out the physical design
This means choosing the elevons (1/4 chord is usually good), making winglet shapes (you don't need a lot), figuring out a motor mount, placing your spars, routing your wires, devising access hatches, thinking up a fuselage pod if you need it, all that good stuff. Just use your intuition. I like using Sketchup for this since it's pretty freeform and lets you drag stuff everywhere and fiddle with shapes.


Or just ignore all this and be able to sleep for the next week. Your pick.
That sounds simple enough
BigShooter is offline Find More Posts by BigShooter
Reply With Quote
Old Apr 28, 2016, 09:13 AM
nmasters is online now
Find More Posts by nmasters
internet gadfly
nmasters's Avatar
Colorado
Joined Aug 2006
2,399 Posts
Yes, airplanes are simple machines, but designing them well is not always easy.

--------.~.
--------/V\
------//----\\
-----/(------)\
----(^^)---(^^)
--Norm
nmasters is online now Find More Posts by nmasters
Reply With Quote
Old Apr 28, 2016, 11:12 AM
RPM314 is offline
Find More Posts by RPM314
Tailless fly-hard
RPM314's Avatar
United States, NY, Brooklyn
Joined Apr 2012
1,124 Posts
Quote:
Originally Posted by lu4414 View Post
Man thanks a lot fot the help, i will write down some of my choices and if i please can get your opinion it would be great!
So first i pick the second motor that you reccomend with the 8X4 prop, for the wing loading i chosse 25g/dm2 and AUW if i do right will be a about 350g (2*50g of the motor+44g ESC=18g for the servos+188g for the battery ).I also choose 6 for aspect ratio and 0,7 for the tape ratio.
Calculating all i had:
Area of 14 dm2
Span of 91,64 cm
average cord of 15.26cm
root of 17.95cm
tip of 12.56cm
The data of CG is here http://fwcg.3dzone.dk/?wing_span=91....ow_mac_lines=0
All looks good on CG calculator and for sweep i chosse 20 degress( Random number based only on CG position, help here will be great).
Now for the construction i plan do something like you do on our models, but i don`t have a clue of how to do and calculate the need amount of washout, any tips?? Other point what about wing thickness??
Also a lot of thread here talks about profile (MH45, MH60 and others), what we calculate here is already a profile right?
The reinforcemnt of the wing and the more physical part of the design i still have to think about
Nothing more cool than do the math of that!
Again thanks so much for the help!!!
Best regards
Awesome! It sounds like the power system you chose will be a good match for the airframe.

If you want to put in the work, you can calculate where the CG will end up based on the location and masses of all components, like I did in the spreadsheet I attached below. If the cg ends up in front of the target given to you by the CG calculator (i.e. tail heavy) then you increase the sweep angle and try again until it works.
If not, I'd say from experience that 25 degrees will get you closer to your target, and then you can build in a little pod or nose extension so you can move the battery around to meet the CG target after you build. The motor can also be moved forward/back for this purpose too, you just have to cut out some of the trailing edge to go forward.
Either way will get you what you want. Your choice.

You said you had 5mm Depron to build with? That's good. If you want to build folded wings with it, you'll have to take a little extra care since depron doesn't like to fold as much as some other foams, but you should be fine, other people have built folded depron wings before.
Like I linked to before, Ed from Experimental Airlines has a bunch of detailed videos about building folded wings, which is actually how I got started building my own planes. So watch that series of videos and you should have a good idea of what to do. You'll need a covering material, either tape or iron-on laminate are the popular choices, to protect the foam and also to keep the foam board from splitting when you fold it, which is particularly important with depron.

There is a very long and complicated discussion to be had about washout, but if you just want to improve the stall behavior it gets pretty simple. 2-3 degrees will be enough, and you could either make the wing twist throughout the whole wing (most basic), only twist that 2-3 degrees in the inboard half (focuses more on lifting power/efficiency), or only twist in the outboard half (focuses more on tip-stall-proofness). Any way will be fine, so you pick there.

If you want to store the electronics inside the wing, the thickness at the root is necessarily dictated by how much space you need for the battery. Otherwise and at the wing tip, you should aim for a 9-12% thickness over chord ratio for best efficiency.

Unless you want to go through the considerable trouble of making a lot of jig pieces, it's best to stick with a flat bottom airfoil like Ed makes in his videos. You can make specific airfoils like the MH60 out of foam board, but like I said in needs a lot of jigging and extra time. I wouldn't recommend it for this build, since the effort to payoff ratio will be pretty whack.

Reinforcement if pretty simple. You can take a big spar (like 5+ mm carbon rod or 1/4"+ wooden dowel) and put it through the center of the wing, parallel to the span, and leave it at that. This way has a slight weight penalty and it ignores the outboard parts of the wing, which is fine for a small plane like yours if you don't do wingtip launches and stuff.
Or, you can take a couple of smaller spars (3mm carbon or 3/16" wood) and glue them into the tops and bottoms of the foam blocks that give the wing its depth. No wrong way to do this as long as they are securely glued in, are as far apart from each other as you can get them, and they don't interfere with having a smooth outside surface. This way is usually a bit lighter and a lot stiffer than the other way, but since the spars usually get interrupted by the battery (if you store the battery inside the wing), you have to put a small center spar in anyway.
You won't need to do it for this plane, but if you ever build something seriously fast that can pull a lot of G's, you'll probably need to do both the keep it stiff.


Keep at it Lu, you're doing good work.

Quote:
Originally Posted by BigShooter View Post
That sounds simple enough

What I just gave in my first post was an extremely condensed version of Dan Raymer's design philosophy that he gives in the book "Simplified Aircraft Design for Homebuilders", which is itself a very condensed version of the processes used by professional aircraft firms. Check out the weight and balance calculator for my current design, attached below, if you want to see just how complicated this can get for a model plane. Then imagine how complicated a Boeing is. Then have a panic attack.
RPM314 is offline Find More Posts by RPM314
Reply With Quote
Old Apr 28, 2016, 08:08 PM
lu4414 is offline
Find More Posts by lu4414
Padawan
Brazil, SP, So Paulo
Joined Jan 2015
124 Posts
Quote:
Originally Posted by RPM314 View Post
Awesome! It sounds like the power system you chose will be a good match for the airframe.

If you want to put in the work, you can calculate where the CG will end up based on the location and masses of all components, like I did in the spreadsheet I attached below. If the cg ends up in front of the target given to you by the CG calculator (i.e. tail heavy) then you increase the sweep angle and try again until it works.
If not, I'd say from experience that 25 degrees will get you closer to your target, and then you can build in a little pod or nose extension so you can move the battery around to meet the CG target after you build. The motor can also be moved forward/back for this purpose too, you just have to cut out some of the trailing edge to go forward.
Either way will get you what you want. Your choice.

You said you had 5mm Depron to build with? That's good. If you want to build folded wings with it, you'll have to take a little extra care since depron doesn't like to fold as much as some other foams, but you should be fine, other people have built folded depron wings before.
Like I linked to before, Ed from Experimental Airlines has a bunch of detailed videos about building folded wings, which is actually how I got started building my own planes. So watch that series of videos and you should have a good idea of what to do. You'll need a covering material, either tape or iron-on laminate are the popular choices, to protect the foam and also to keep the foam board from splitting when you fold it, which is particularly important with depron.

There is a very long and complicated discussion to be had about washout, but if you just want to improve the stall behavior it gets pretty simple. 2-3 degrees will be enough, and you could either make the wing twist throughout the whole wing (most basic), only twist that 2-3 degrees in the inboard half (focuses more on lifting power/efficiency), or only twist in the outboard half (focuses more on tip-stall-proofness). Any way will be fine, so you pick there.

If you want to store the electronics inside the wing, the thickness at the root is necessarily dictated by how much space you need for the battery. Otherwise and at the wing tip, you should aim for a 9-12% thickness over chord ratio for best efficiency.

Unless you want to go through the considerable trouble of making a lot of jig pieces, it's best to stick with a flat bottom airfoil like Ed makes in his videos. You can make specific airfoils like the MH60 out of foam board, but like I said in needs a lot of jigging and extra time. I wouldn't recommend it for this build, since the effort to payoff ratio will be pretty whack.

Reinforcement if pretty simple. You can take a big spar (like 5+ mm carbon rod or 1/4"+ wooden dowel) and put it through the center of the wing, parallel to the span, and leave it at that. This way has a slight weight penalty and it ignores the outboard parts of the wing, which is fine for a small plane like yours if you don't do wingtip launches and stuff.
Or, you can take a couple of smaller spars (3mm carbon or 3/16" wood) and glue them into the tops and bottoms of the foam blocks that give the wing its depth. No wrong way to do this as long as they are securely glued in, are as far apart from each other as you can get them, and they don't interfere with having a smooth outside surface. This way is usually a bit lighter and a lot stiffer than the other way, but since the spars usually get interrupted by the battery (if you store the battery inside the wing), you have to put a small center spar in anyway.
You won't need to do it for this plane, but if you ever build something seriously fast that can pull a lot of G's, you'll probably need to do both the keep it stiff.


Keep at it Lu, you're doing good work.




What I just gave in my first post was an extremely condensed version of Dan Raymer's design philosophy that he gives in the book "Simplified Aircraft Design for Homebuilders", which is itself a very condensed version of the processes used by professional aircraft firms. Check out the weight and balance calculator for my current design, attached below, if you want to see just how complicated this can get for a model plane. Then imagine how complicated a Boeing is. Then have a panic attack.
Thanks again man, for build material i also have 5cm tick foam, maybe cut it with hot wire may be a good choice? Also about the washout, i didnt catch maybe its my poor english skill
And the wing thicknnes are also not so clear, if i build a thicker wing i will get more efficient and lift, but less speed?
And the last i know that the math indicate that my 91cm span will do great but isn`t it too low? I remember that in the firsts posts 130cm seems low, so what about 91?
Again sorry for the lot of questions...

Really think about what boeing enginners does its pretty amazing, im still on high school maybe one day i get there

Best regards
Lucas
lu4414 is offline Find More Posts by lu4414
Last edited by lu4414; Apr 29, 2016 at 06:31 PM.
Reply With Quote
Old May 02, 2016, 07:24 PM
RPM314 is offline
Find More Posts by RPM314
Tailless fly-hard
RPM314's Avatar
United States, NY, Brooklyn
Joined Apr 2012
1,124 Posts
Quote:
Originally Posted by lu4414 View Post
Thanks again man, for build material i also have 5cm tick foam, maybe cut it with hot wire may be a good choice? Also about the washout, i didnt catch maybe its my poor english skill
And the wing thicknnes are also not so clear, if i build a thicker wing i will get more efficient and lift, but less speed?
And the last i know that the math indicate that my 91cm span will do great but isn`t it too low? I remember that in the firsts posts 130cm seems low, so what about 91?
Again sorry for the lot of questions...

Really think about what boeing enginners does its pretty amazing, im still on high school maybe one day i get there

Best regards
Lucas
Sorry for the long wait, I've been trying to find time to sit down and write another long post but this turned out pretty short.

For the materials, like I said before do whatever you're most comfortable with. Hotwiring will let you make a specific airfoil section and EPO is probably more durable than Depron, so that could be another advantage. Weigh your options and choose what you want. If it doesn't work as well as you'd like you can always make another plane!

So washout is changing the angle of attack of the airfoil along the wingspan. To keep it simple, I've told you restricted options on how you make that happen. You can twist the whole wing, so the root is at 3 degrees, the middle of the span is at 1.5 degrees, and the tip is at 0 degrees. Or you can put it inboard, so that the root is at 3 degrees, the middle is 0 degrees, and the tip is 0 degrees. Or you could put it outboard, so the root is at 3 degrees, the middle is at 3 degrees, and the tip is at 0 degrees. I already said what each distribution tends to do to the plane's performance. Mixing two kinds will of course mix the behaviors too.

Wing thickness is defined as the thickness divided by the chord (t/c), so if you have 10mm thick and 100mm chord the t/c ratio is 0.1, or 10%. For airplanes of this size and speed, about 9% thickness usually gives you the best drag and L/D. More thickness means more drag and less efficiency, but higher maximum lift. It also means a stiffer and stronger wing, and more space for your stuff. You have to decide what best fits what you want. Personally, I try to get everything I can inside the wing, which means my wing thickness has to be bigger than my biggest component (this way is more challenging). Some people make a bigger compartment in the center for the battery and things so that the rest of the wing can be thinner. Again, this is another choice you have to make.

There is not really such a thing as "too low". 91cm is smaller than 130cm, and 130cm is smaller than 180cm, and 180cm is smaller than 250cm. 91cm is also bigger than 80cm, and 80cm is bigger than 65cm. There is no one "correct" wingspan, there is only what kind of performance a certain wingspan gives you. If that performance is not what you set out to get, then the wingspan is not a good fit for your project. But I can tell you that a 91cm span plane with a 3s 1400kv power system will be sporty and maneuverable. If you don't want a snappy, quick plane then you should scale up the wing so everything happens slower.
For 3s flying wings, in my experience wingspans of around 100cm make the "best feeling" airplanes. So your plan right now will make a good little airplane. If what I've described is not what you want, you are free to change it. It's your decision.

Best of luck, and keep pushing!
-RPM
RPM314 is offline Find More Posts by RPM314
Reply With Quote
Old May 03, 2016, 06:07 PM
lu4414 is offline
Find More Posts by lu4414
Padawan
Brazil, SP, So Paulo
Joined Jan 2015
124 Posts
Quote:
Originally Posted by RPM314 View Post
Sorry for the long wait, I've been trying to find time to sit down and write another long post but this turned out pretty short.

For the materials, like I said before do whatever you're most comfortable with. Hotwiring will let you make a specific airfoil section and EPO is probably more durable than Depron, so that could be another advantage. Weigh your options and choose what you want. If it doesn't work as well as you'd like you can always make another plane!

So washout is changing the angle of attack of the airfoil along the wingspan. To keep it simple, I've told you restricted options on how you make that happen. You can twist the whole wing, so the root is at 3 degrees, the middle of the span is at 1.5 degrees, and the tip is at 0 degrees. Or you can put it inboard, so that the root is at 3 degrees, the middle is 0 degrees, and the tip is 0 degrees. Or you could put it outboard, so the root is at 3 degrees, the middle is at 3 degrees, and the tip is at 0 degrees. I already said what each distribution tends to do to the plane's performance. Mixing two kinds will of course mix the behaviors too.

Wing thickness is defined as the thickness divided by the chord (t/c), so if you have 10mm thick and 100mm chord the t/c ratio is 0.1, or 10%. For airplanes of this size and speed, about 9% thickness usually gives you the best drag and L/D. More thickness means more drag and less efficiency, but higher maximum lift. It also means a stiffer and stronger wing, and more space for your stuff. You have to decide what best fits what you want. Personally, I try to get everything I can inside the wing, which means my wing thickness has to be bigger than my biggest component (this way is more challenging). Some people make a bigger compartment in the center for the battery and things so that the rest of the wing can be thinner. Again, this is another choice you have to make.

There is not really such a thing as "too low". 91cm is smaller than 130cm, and 130cm is smaller than 180cm, and 180cm is smaller than 250cm. 91cm is also bigger than 80cm, and 80cm is bigger than 65cm. There is no one "correct" wingspan, there is only what kind of performance a certain wingspan gives you. If that performance is not what you set out to get, then the wingspan is not a good fit for your project. But I can tell you that a 91cm span plane with a 3s 1400kv power system will be sporty and maneuverable. If you don't want a snappy, quick plane then you should scale up the wing so everything happens slower.
For 3s flying wings, in my experience wingspans of around 100cm make the "best feeling" airplanes. So your plan right now will make a good little airplane. If what I've described is not what you want, you are free to change it. It's your decision.

Best of luck, and keep pushing!
-RPM
Thanks for your time again man, you are really making a big diference!
Maybe a scale up the wing for 111cm for get a 18g/dm2 wing load and hopefully a still good felling plane but a bit slower and more efficient.
So i will probably go with hot wire, and in that case i plan to use MH45 airfoil, are someone already try it?
I still thinking a lot in thickness, if i want to put baterry inside i will had considerably increase thickness, and decrease speed and add drag, but if i dont i will had to come out with a pod or something like that will add weight and maybe drag, so i still had to figure it out Suggestions?
Just more one, 1400kv motor looks good but im seeing a lot of low kv motor (750-850kv), like that http://www.hobbyking.com/hobbyking/s...ner_Motor.html, claim to be very efficient with a considerable larger prop (9X6), are you try something like this before? How the plane behaves? Worth the extra autonomy?
Again cant thanks you enough
Best regards
lu4414 is offline Find More Posts by lu4414
Reply With Quote


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion Help me design my graphics for my biplane mensite Electric Plane Talk 9 Oct 10, 2015 07:36 AM
Discussion Old clips from the wing. Plans coming out very soon, need help on structural design. TarikAgcayazi Foamies (Scratchbuilt) 1 Oct 01, 2015 02:58 PM
Help! Need help regarding glider designs for a project evilkudos Free Flight 11 Aug 12, 2015 04:41 PM
Help! Help me to Design RC parts for a small fishing bobber khjortg Submarines 4 Aug 08, 2015 02:43 PM
Help! help needed with tab and notch designing yashodhanp Scale Kit/Scratch Built 8 May 16, 2015 10:13 AM