Predator b Uav design  
View related threads: (in this forum | in all forums)

Tower Hobbies
Enter up to 4 keywords or Tower stock numbers
Logged in as Guest



Users viewing this topic: none
  Printable Version
       

All Forums >> RC Airplanes >> Scratch Building, Aircraft Design, 3D/CAD >> Predator b Uav design
Page: [1] 2   next >   >>  

Login
Message << Older Topic   Newer Topic >>
Predator b Uav design - 4/10/2007 5:13:16 AM   
John Mason


 

Posts: 30
Joined: 8/1/2003
From: Tinker AFB, OK, USA
Status: offline 		I have always had a fascination for the predator uavs so i started designing a model of one.
What I have done so far:
I decided on a 1/8th scale of the original
66':99" wingspan
36.2': 54.3" fuse length
Weight not really sure hopefully under 8lbs
I started with the fuselage and designed the fuse formers first. I havent gotten to the dome on the front yet.
I am open to suggestions on an airfoil for the wing right now im pretty stuck on the clark y due the fact that this is my first project of this nature.
I have a question about the wing and how I should go about designing it, rib spacing, spars and the uniqe sweeping of the leading and trailing edges.

Heres a picture of what I have so far. please let me know if im making any fatal mistakes, im open to suggestions from anyone.

Attachments
Click to see fullsize image.
Click for fullsize 		Click to see fullsize image.
Click for fullsize 		Click to see fullsize image.
Click for fullsize 		Click to see fullsize image.
Click for fullsize
Click to see fullsize image.
Click for fullsize
       Post #: 1

RE: Predator b Uav design - 4/10/2007 5:19:23 PM   
Tall Paul



Posts: 4664
Joined: 6/23/2002
From: Palmdale, CA, USA
Status: offline 		The very high aspect ratio of the Predator B wing will be very difficult to build.
Foam shape, CF spars and Kevlar or CF cloth covering at the very least.
The long tail will need a LOT of ballast in the nose to compensate.
The small chord means the c.g. will be very critical.
The smaller version would be a better starting place.

_____________________________

Sparky Paul
http://www.angelfire.com/indie/aerostuff

(in reply to John Mason)
       Post #: 2

RE: Predator b Uav design - 4/10/2007 5:52:54 PM   
funkworks



Posts: 418
Joined: 3/24/2003
From: Houston, TX, USA
Status: offline 		I think you are on the right track. I built a U-2 with close to the same span. I put a .36 on the front and it all came out to about 7lbs after putting retracts and two digital cameras onboard. I would use a clark-y like you mentioned. I used a variation of the airfoil on my u-2 and I built up the wing using balsa. I have access to a lofting program to create wing ribs easy so its actually easier for me to use balsa. If you have access to foam cutting equipment then you can go that route. It helps to use differential on the ailerons also. You can also put your receiver, throttle servo and battery in the nose to help counterbalance the tail. Under 8lbs sounds possible. What do you plan on using for power? I think anything around a .46-.50 size would be plenty.. I actually thought about building one for myself. Let me know if you need a hand with the wing or anything else.

_____________________________

...will I see all my wrecked planes when I get to Heaven? www.thefunkworks.com
Revver Bro # 183

(in reply to Tall Paul)
       Post #: 3

RE: Predator b Uav design - 4/10/2007 5:58:20 PM   
funkworks



Posts: 418
Joined: 3/24/2003
From: Houston, TX, USA
Status: offline 		Each wing panel looks like it can be made in two panels. The first being the larger section, looks like just a simple taper to about 50% to 60% of the wing root and then the second panel is just the same chord that follows the leading edge angle...

_____________________________

...will I see all my wrecked planes when I get to Heaven? www.thefunkworks.com
Revver Bro # 183

(in reply to funkworks)
       Post #: 4

RE: Predator b Uav design - 4/10/2007 6:05:01 PM   
funkworks



Posts: 418
Joined: 3/24/2003
From: Houston, TX, USA
Status: offline 		...here is a pic of the u-2 wing panel framed up. I used a tapered spar that is wider at the root and gets narrower towards the tip. It helps stiffen up the wing near the root.

Attachments
Click to see fullsize image.
Click for fullsize


_____________________________

...will I see all my wrecked planes when I get to Heaven? www.thefunkworks.com
Revver Bro # 183

(in reply to funkworks)
       Post #: 5

RE: Predator b Uav design - 4/10/2007 10:53:14 PM   
John Mason


 

Posts: 30
Joined: 8/1/2003
From: Tinker AFB, OK, USA
Status: offline 		Do you think I need the carbon fiber tube in the fuselage?

I really like you u2 and im contemplating using your wing design and modifying to work in my application. What size is the root chords and tip chords on the us wing. Im looking for an 8 in root and 4-5" tip chord.
I could use all the knowledge you have about wings of this nature.
A new photo of the progress.



Attachments
Click to see fullsize image.
Click for fullsize 		Click to see fullsize image.
Click for fullsize

(in reply to funkworks)
       Post #: 6

RE: Predator b Uav design - 4/11/2007 2:27:18 PM   
funkworks



Posts: 418
Joined: 3/24/2003
From: Houston, TX, USA
Status: offline 		Looks good. I really dont think you need a CF tube if you plan to sheet the structure. You will want to beef up the area where the wing and tail fins attach to the fuse to disperse the stresses. Just make sure you have a way to keep all the formers straight while you are sheeting the fuse. I think my u-2 wing had a root chord of about 12 inches and a tip chord of about 6inches with a panel length of 45inches each. I added about 2 degrees of washout to the tip also. I used a tapered main spar and some sub spars with sheer webs. The wing is solid even though the only lite ply I used was for the wing root rib. I had trouble with one flight and the model nosed into the ground. I thought the whole thing was destroyed. The nose of the model was smashed pretty good and I had to rebuild the whole section forward of the intakes. The model hit so hard the wings folded forward to where the front of each wingtip touched the ground. The aluminum tube absorbed all the impact and the spring that holds the halves in place just snapped clean allowing the wings to move free. I had to just replace a little covering on one wingtip and cut away the metal tube from the fuse. I was shocked...those little suckers are tough. I'll come up with something for you based on the info you gave me.

_____________________________

...will I see all my wrecked planes when I get to Heaven? www.thefunkworks.com
Revver Bro # 183

(in reply to John Mason)
       Post #: 7

RE: Predator b Uav design - 4/12/2007 2:38:35 AM   
John Mason


 

Posts: 30
Joined: 8/1/2003
From: Tinker AFB, OK, USA
Status: offline 		Some more work on the fuse. I romoved the cf spar and changed the profile on the top. I also started on the formers for the nose.
The fuse formers are 6in on center.


Attachments
Click to see fullsize image.
Click for fullsize

(in reply to funkworks)
       Post #: 8

RE: Predator b Uav design - 4/17/2007 9:16:14 PM   
John Mason


 

Posts: 30
Joined: 8/1/2003
From: Tinker AFB, OK, USA
Status: offline 		Some more work on the fuse. I decided to mold the nose out of fiberglass to accomplish the complex curves.Still debating over wing designs.
The fuse will be completly sheeted and possibly glassed.

Attachments
Click to see fullsize image.
Click for fullsize 		Click to see fullsize image.
Click for fullsize

(in reply to John Mason)
       Post #: 9

RE: Predator b Uav design - 4/19/2007 4:55:54 PM   
John Mason


 

Posts: 30
Joined: 8/1/2003
From: Tinker AFB, OK, USA
Status: offline 		Do you guys think I should go with a built up wing or a sheeted foam core wing? The root chord is 8.1" and the tip chord is 4" with a half span of 47" and a clak y foil. Im leaning towards a built up wing because it is what iam familiar with.

(in reply to John Mason)
       Post #: 10

RE: Predator b Uav design - 4/20/2007 3:39:28 AM   
batchelc


 

Posts: 176
Joined: 11/8/2004
From: Wichita , KS, USA
Status: offline 		That wing is going to be very high aspect ratio like a glider. You may want to ask some glider folks. I know they have used both methods with sucess. In either case you may want to consider some flat carbon fiber tow on the top and bottom of the spars.

_____________________________

--------------------------------
http://www.wichitapilot.com

(in reply to John Mason)
       Post #: 11

RE: Predator b Uav design - 4/20/2007 6:41:02 AM   
ptxman


 

Posts: 351
Joined: 7/31/2002
From: Calgary, AB, CANADA
Status: offline
quote:

.... I am open to suggestions on an airfoil for the wing right now im pretty stuck on the clark y due the fact that this is my first project of this nature. I have a question about the wing and how I should go about designing it, rib spacing, spars and the uniqe sweeping of the leading and trailing edges.


Thats a really cool project, nice cad work too. Certain aspects of the wing construction would be challenging for a first-timer, but you should know its not outside the scope of what modelers are doing in other diciplines. Everybody starst somewhere & if you genuinely like your project, you will learn whats required to build it & ultimately succeed!

Re wing construction, I think the closest comparable work is being done by the DLG (Discus Launch Glider) crowd. Their wings have airfoils with comparable or thinner max thickness (5-8% MT foils I believe), somewhat similar high aspect planforms, sometimes multi paneled like your project & actually pretty high loads. A popular method they have perfected is hot wire cutting foam cores (either manually or through CNC services who do this), install appropriate spars/reinforcement & vac bag kevlar or similar cloth skin. So many of the issues pertaining to strength, materials, control surface actuating & hinging, dimensional accuracy, surface finish, even painting have been dealt with.

You can do a net search on 'DLG' & I think they still have a forum on yahoo groups. Or just hop over to this group & you will have a few nights of useful surfing:
http://www.rcgroups.com/hand-launch-96/

particularly if you do a search on keywords like 'bagging' or 'supergee' there are some good build threads with lots of pics & details, ex:
http://www.rcgroups.com/forums/showthread.php?t=246671
http://www.rcgroups.com/forums/showthread.php?t=99866
http://www.rcgroups.com/forums/showthread.php?t=179297

The old school ribs/spars/sheeting method might be getting taxed pretty severely on this dimensional planform. There just isnt a lot of material to work with & the net result strength weight will probably not be as good as the DLG method. Having said that, your cad files are a direct plug-in to laser cutting services which would be cost effective & remove a lot of scrollsaw grunt work. Laser parts would be dimensionally very acurate (kerfs in the low-thou range) & you can be creative about how parts notch & index together to yield a strong yet light structure. But because its not a WW1 rib & cloth model, its basic manual sheeting & glassing & finishing thereafter...

The next option is cadillac, but if you have access to someone with a cnc router/mill, your (presuming 3d surface files) are perfect to develop plugs & molds. Thats a whole ($$) world unto itself, but something to be aware of. Maybe you want to build som espares while you're at it or share some kits with friends?

Re airfoil, there probably isnt much wrong with Clark Y for the primary task intended: lifting a fuse load on a popsicle stick wing surface & flying around upright & moderatley (c/w weight adding gangly landing gear gear & maybe some RC spy telemtry hardware) . There are probably better airfoils out there that might assist you though:
- something that would give comparable or better lift/drag polars, but possibly be even thicker max%. Your main challenge will be bending stresses so the thicker the spar depth, the stronger the structure... until 'too thick' interfers with aerodynamics.
- a foil that may be suited to flap employment. This gives you the best of both worlds, ability to safely takeoff if weight becomes an issue & retract them back when flying around.
There are more qualified people than me to help with this, but be aware there are programs like Profili which are useful to simulate (2d) airfoil performance, have hundreds of available airfoils in their database & the ability to tweak/modify/export coodinates to your cad program.
http://www.profili2.com/eng/default.htm

Good luck!

(in reply to John Mason)
       Post #: 12

RE: Predator b Uav design - 5/1/2007 4:43:42 AM   
John Mason