RoCkaZ
Mar 31, 2009, 06:51 PM
Hello and greetings from Lithuania! :cool:
This is my first post in this amazing forum, so don't be very critical about it. I promise to adapt and behave :rolleyes:
I am willing to build a slow and very stable electric airplane, mostly for FPV/Video'ing. I have very little knowledge in aerodynamics and even less theory/practice in actually building models. Also, beeing kinda giant-o-maniac and sick for challenges, I am going for something with the wingspan of 3 to 4 meters (118-158 inches). Also, for some reason I believe, that "slow and very stable" doesn't go with "small and compact".
Concering my knowledge and experience, I do not expect this "size decision" to be a logical one, but having the model itself is not the primary goal here. Building, failing/learning and that "mine from scratch" feeling is half of the joy. Oh yeah, did I mention I like making BIG stuff?
Here's a little requirements "spec" for myself:
Slow. I'm not sure of the numerical value, as I am terrible at "imagine it fly" to "meters per second" conversion. But as slow as possible with the stability preserved.
Stable. I haven't seen much of those onboard videos, that would be really smooooth and stable. It's always that little roll jigling... Is it possible to overcome that, and is it compactible with "slow"?... Let's find out ;)
Electric. Mabe it's due to zero experience with IC, maybe it's just the price and simplicity. But I want it to be electric. Oh yeah, the enviroment-friendly :) Besides, it's not gonna be 3D/aerobatic plane, so the power plant shouldn't be very big and powerfull.
Collapsible (built from smaller parts) for easier transportation.
As I haven't got any clue what should I start with when designing, I improvise. First I define some "global" properties, as I think of them at present moment (those might change later):
Wing: on top, dihedral, tapered and swept back - for stability. Quite long - for more lift.
Fuselage: minimal, starts in front of the wing's leading edge and ends with it's (the wing's) trailing edge. Only two spars (no "volume") from the wing's trailing edge to hold the tail.
Tail: fairly large horizontal and two vertical stabilizers. Only elevator for control, no rudder.
Motor/propeller: pusher, on the back of the fuselage. The front is reserved for camera :)
Of course, there's also an airfoil to be chosen. Now that's a tough one - there's like a zillion of them. I guess it should be something very cambered and thick - for low speeds. So I quickly google'd and read some online literature about aerodynamics/airfoils. Please correct me if I got it wrong: first I need to now the target cruising speed, wing chord and flying altitude. Then I compute the Re and play around with profili2? Yet, a lot to choose from...
Having everything above put into Google SketchUp, I have this:
http://img142.imageshack.us/img142/8282/sloshark1.th.jpg (http://img142.imageshack.us/my.php?image=sloshark1.jpg) http://img142.imageshack.us/img142/5951/sloshark2.th.jpg (http://img142.imageshack.us/my.php?image=sloshark2.jpg) http://img142.imageshack.us/img142/9105/sloshark3.th.jpg (http://img142.imageshack.us/my.php?image=sloshark3.jpg) http://img142.imageshack.us/img142/7035/sloshark4.th.jpg (http://img142.imageshack.us/my.php?image=sloshark4.jpg) http://img142.imageshack.us/img142/1461/sloshark5.th.jpg (http://img142.imageshack.us/my.php?image=sloshark5.jpg)
All of this is just for very high level visual purposes, and not much into details. Wingspan is 4 meters (~158 inches). Chord is 40cm (~16 inches) root to 30 cm (~12 inches) tip.
Currently I am planning the wings and the fuse to be cut of foam. It might sound weird, but it looks easier to be built, faster to prototype and I have a CNC foam cutter at home :) I just wonder, how much of weight do I gain in comparison to using balsa/covering tape? The wings would be enlightened from inside:
http://img142.imageshack.us/img142/3593/sloshark7.th.jpg (http://img142.imageshack.us/my.php?image=sloshark7.jpg)
The wings would be made of four removable panels + center panel with fuse. Rear lids gives access to ESC, front lid and detachable nose - to the rest of flight control and video electronics. The battery will probably live under the front lid, but I'll see that when adjusting the CoG:
http://img135.imageshack.us/img135/1189/sloshark9.th.jpg (http://img135.imageshack.us/my.php?image=sloshark9.jpg)
I'm also considering a kind of suspension, that would hold stuff together:
http://img528.imageshack.us/img528/5443/sloshark8.th.jpg (http://img528.imageshack.us/my.php?image=sloshark8.jpg) http://img142.imageshack.us/img142/3913/sloshark6.th.jpg (http://img142.imageshack.us/my.php?image=sloshark6.jpg)
It would made of aluminum, and would consist of:
Wing holding elements (the two airfoil profiles in the sides and the tubes between them)
Fuse and battery holder (the stick to the front)
Tail holders (the two sticks to the back)
Some rectangular plates to hold everything together
The reason for this suspension is for the separate parts of the plane to be independant from each other and just to be statically linked and held by it (the suspension). For example: the motor pushes only the suspension, which in advance "hangs" on the wing, and pushes the rest of the plane. The fuse is only an aerodynamic box/container for the electric components. The gear will (most probably) also be attached only to the suspension. It's hard to write down the thoughts, but I hope You get the idea.
I'm not planning any of the electric/power stuff yet, as I haven't got a clue of how much this whole thing will weight. I just think that the motor/prop combination would be something that could produce static thrust of 50-70% of the whole weight. Maybe there's a way to calculate the volume of a 3D object? That would make it really easy to estimate the weight of the plane.
Next doubt is about the ailerons. I'm not sure where to put them and how big should they be. Initially I thought they'd be ~1/8th of the chord and 1/2 of one wing panel's length, and be positioned on the very end of the wings. But I'm very concerned about the response in control at low speeds. I am considering another option - two puller motors/props on the middle wing panels in the front of the wing and ailerons behind them. I guess that should make it more responsive. Or maybe I should just make them wider (1/3-1/4 of a chord) and longer (through the whole side panel)?
Some other considerations:
V-Tail. Lot's of UAV's and gliders seem to employ it, so I guess there's a good reason for that? It's just both of those types are the "fast models" and mine is (supposed to be) a slow one.
Horizontal stabilizer as elevator. I was just wondering - why should I build two surfaces (one static and other one controlable), when I can make just one controlable and of the total length of the two? Too responsive/sensitive? But I'm talking low speeds :/
A lower wing's aspect ratio by making a longer chord. Currenty it is 35 cm average, and since I'm dealing with low Re numbers (120000 @ 5 m/s), making the chord larger is the only way I see. I wonder, what parasitic effects does a wider wing make? And how to choose the right aspect ratio...
... and the rest of the parameters :confused:
So, that's about enough of me for today. I would love to hear something from You, the real professionals at this addictive hobby :) Any ideas, critics, theory references and anything else about this topic (or at least close to it) will be appreciated. And please excuse me for my english, as it is not my native language.
P.S. 1 The name SloShark is because of the vertical tail stabilisers, that look like that... thing on the back of a shark :D
P.S. 2 Due to the lack of time and financial stuff this is gonna be a long and slow project.
This is my first post in this amazing forum, so don't be very critical about it. I promise to adapt and behave :rolleyes:
I am willing to build a slow and very stable electric airplane, mostly for FPV/Video'ing. I have very little knowledge in aerodynamics and even less theory/practice in actually building models. Also, beeing kinda giant-o-maniac and sick for challenges, I am going for something with the wingspan of 3 to 4 meters (118-158 inches). Also, for some reason I believe, that "slow and very stable" doesn't go with "small and compact".
Concering my knowledge and experience, I do not expect this "size decision" to be a logical one, but having the model itself is not the primary goal here. Building, failing/learning and that "mine from scratch" feeling is half of the joy. Oh yeah, did I mention I like making BIG stuff?
Here's a little requirements "spec" for myself:
Slow. I'm not sure of the numerical value, as I am terrible at "imagine it fly" to "meters per second" conversion. But as slow as possible with the stability preserved.
Stable. I haven't seen much of those onboard videos, that would be really smooooth and stable. It's always that little roll jigling... Is it possible to overcome that, and is it compactible with "slow"?... Let's find out ;)
Electric. Mabe it's due to zero experience with IC, maybe it's just the price and simplicity. But I want it to be electric. Oh yeah, the enviroment-friendly :) Besides, it's not gonna be 3D/aerobatic plane, so the power plant shouldn't be very big and powerfull.
Collapsible (built from smaller parts) for easier transportation.
As I haven't got any clue what should I start with when designing, I improvise. First I define some "global" properties, as I think of them at present moment (those might change later):
Wing: on top, dihedral, tapered and swept back - for stability. Quite long - for more lift.
Fuselage: minimal, starts in front of the wing's leading edge and ends with it's (the wing's) trailing edge. Only two spars (no "volume") from the wing's trailing edge to hold the tail.
Tail: fairly large horizontal and two vertical stabilizers. Only elevator for control, no rudder.
Motor/propeller: pusher, on the back of the fuselage. The front is reserved for camera :)
Of course, there's also an airfoil to be chosen. Now that's a tough one - there's like a zillion of them. I guess it should be something very cambered and thick - for low speeds. So I quickly google'd and read some online literature about aerodynamics/airfoils. Please correct me if I got it wrong: first I need to now the target cruising speed, wing chord and flying altitude. Then I compute the Re and play around with profili2? Yet, a lot to choose from...
Having everything above put into Google SketchUp, I have this:
http://img142.imageshack.us/img142/8282/sloshark1.th.jpg (http://img142.imageshack.us/my.php?image=sloshark1.jpg) http://img142.imageshack.us/img142/5951/sloshark2.th.jpg (http://img142.imageshack.us/my.php?image=sloshark2.jpg) http://img142.imageshack.us/img142/9105/sloshark3.th.jpg (http://img142.imageshack.us/my.php?image=sloshark3.jpg) http://img142.imageshack.us/img142/7035/sloshark4.th.jpg (http://img142.imageshack.us/my.php?image=sloshark4.jpg) http://img142.imageshack.us/img142/1461/sloshark5.th.jpg (http://img142.imageshack.us/my.php?image=sloshark5.jpg)
All of this is just for very high level visual purposes, and not much into details. Wingspan is 4 meters (~158 inches). Chord is 40cm (~16 inches) root to 30 cm (~12 inches) tip.
Currently I am planning the wings and the fuse to be cut of foam. It might sound weird, but it looks easier to be built, faster to prototype and I have a CNC foam cutter at home :) I just wonder, how much of weight do I gain in comparison to using balsa/covering tape? The wings would be enlightened from inside:
http://img142.imageshack.us/img142/3593/sloshark7.th.jpg (http://img142.imageshack.us/my.php?image=sloshark7.jpg)
The wings would be made of four removable panels + center panel with fuse. Rear lids gives access to ESC, front lid and detachable nose - to the rest of flight control and video electronics. The battery will probably live under the front lid, but I'll see that when adjusting the CoG:
http://img135.imageshack.us/img135/1189/sloshark9.th.jpg (http://img135.imageshack.us/my.php?image=sloshark9.jpg)
I'm also considering a kind of suspension, that would hold stuff together:
http://img528.imageshack.us/img528/5443/sloshark8.th.jpg (http://img528.imageshack.us/my.php?image=sloshark8.jpg) http://img142.imageshack.us/img142/3913/sloshark6.th.jpg (http://img142.imageshack.us/my.php?image=sloshark6.jpg)
It would made of aluminum, and would consist of:
Wing holding elements (the two airfoil profiles in the sides and the tubes between them)
Fuse and battery holder (the stick to the front)
Tail holders (the two sticks to the back)
Some rectangular plates to hold everything together
The reason for this suspension is for the separate parts of the plane to be independant from each other and just to be statically linked and held by it (the suspension). For example: the motor pushes only the suspension, which in advance "hangs" on the wing, and pushes the rest of the plane. The fuse is only an aerodynamic box/container for the electric components. The gear will (most probably) also be attached only to the suspension. It's hard to write down the thoughts, but I hope You get the idea.
I'm not planning any of the electric/power stuff yet, as I haven't got a clue of how much this whole thing will weight. I just think that the motor/prop combination would be something that could produce static thrust of 50-70% of the whole weight. Maybe there's a way to calculate the volume of a 3D object? That would make it really easy to estimate the weight of the plane.
Next doubt is about the ailerons. I'm not sure where to put them and how big should they be. Initially I thought they'd be ~1/8th of the chord and 1/2 of one wing panel's length, and be positioned on the very end of the wings. But I'm very concerned about the response in control at low speeds. I am considering another option - two puller motors/props on the middle wing panels in the front of the wing and ailerons behind them. I guess that should make it more responsive. Or maybe I should just make them wider (1/3-1/4 of a chord) and longer (through the whole side panel)?
Some other considerations:
V-Tail. Lot's of UAV's and gliders seem to employ it, so I guess there's a good reason for that? It's just both of those types are the "fast models" and mine is (supposed to be) a slow one.
Horizontal stabilizer as elevator. I was just wondering - why should I build two surfaces (one static and other one controlable), when I can make just one controlable and of the total length of the two? Too responsive/sensitive? But I'm talking low speeds :/
A lower wing's aspect ratio by making a longer chord. Currenty it is 35 cm average, and since I'm dealing with low Re numbers (120000 @ 5 m/s), making the chord larger is the only way I see. I wonder, what parasitic effects does a wider wing make? And how to choose the right aspect ratio...
... and the rest of the parameters :confused:
So, that's about enough of me for today. I would love to hear something from You, the real professionals at this addictive hobby :) Any ideas, critics, theory references and anything else about this topic (or at least close to it) will be appreciated. And please excuse me for my english, as it is not my native language.
P.S. 1 The name SloShark is because of the vertical tail stabilisers, that look like that... thing on the back of a shark :D
P.S. 2 Due to the lack of time and financial stuff this is gonna be a long and slow project.