HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Jun 05, 2012, 08:12 AM
Registered User
UK, Cornwall, Truro
Joined Feb 2009
381 Posts
Discussion
My first scratch build for a flying wing - advice please

Hi
I've been around on various forums, mainly Aerial Photography but have now developed an interest in a flying wing. I could buy one but I like to learn about things as well and enjoy the learning/ trying as much as the flying so I'm hoping to start from scratch and build one. My goal would be an all rounder, with FPV use and having something like a gopro on board.

Wings of interest to me so far have been the Zephyr, Knurrus Maximus and the Vega. They seem to be along the lines of what I'd like. I'm not looking to sell or exactly clone anything but there will be similarities if they are good models for me as a reference point.

I have been looking at cutting the wing from foam that is 900mm x 580mm and I want to get two wings (one plane) from one block of foam as that seems to make good economic sense.

I will add the ailerons after which in turn allows me to get slightly more wing surface from the cut from one piece of foam

I'm getting a total wingspan of 1500mm including a centre piece which I plan to add to give some extra equipment space and to avoid me having to cut into the wing span that I am able to achieve from the foam blocks which would give me less wing area.

So far I have picked up the following points from reading up on things - please can you advise me if I need to know more - and hopefully some good reading sources? I've learned a lot from this forum but to be honest when you have no specific idea it is easy to end up going around in circles.


Sweep
From what I can see this is measured from the quarter chord of the wing? In which case I seem to have 28 degrees (see images) I have no idea if this is good or bad but it seems to be in the regions of the other wings so I am guessing it is acceptable for this type of use?

Twist/Washout
I hope this is the right terminology. It would appear that I need washout (wing tips rotated tail up /nose down) in the order of perhaps 3 degrees? This as I understand it will help with stability and will help with smoothing out stalling characteristics?

Dihedral/Anhedral?
I'm at a loss on this one as to whether I should look at building any in and if so how you measure it? The wing will have a thicker chord than tip by design, and I'm not sure where the centre line of the tip (lets use no washout as a reference line) needs to be in comparison to the main root centre line. Is the tip line at the same height as the root line? Lower, higher? As the wing is tapered, if I have the wing tip higher but not outside of the outline of the root - is that dihedral? Or does it only become 'dihedral' if the tip goes outside of the line of the root? (Hope that makes sense)

Profile/Airfoil
MH 45 seems to be a good all round profile that is suitable for a swept wing design. Any reason not to use this one? I've come up with a bit of a squat variation of it to use for the tip as I think I've read somewhere that this is another way of helping with stability, by having a different profile should I use a different but standard profile here?

Please can you offer any advice/comments on the above?

If as I say there are any useful references please point me to them as well. Other than the CofG calculator I'm surprised there's not more in the way of a sticky with basic information - I feel as though I am missing something somewhere?

http://www.mh-aerotools.de/airfoils/flywing1.htm
http://www.nurflugel.com/Nurflugel/n_o_d/weird_02.htm
Ricky401 is offline Find More Posts by Ricky401
Reply With Quote
Sign up now
to remove ads between posts
Old Jun 06, 2012, 08:04 AM
Registered User
UK, Cornwall, Truro
Joined Feb 2009
381 Posts
No comments chaps?

Does anybody have any input one the dihedral/anhedral element of a flying wing? Should it have it and how do you measure it?

thanks
Ricky401 is offline Find More Posts by Ricky401
Reply With Quote
Old Jun 06, 2012, 12:38 PM
Mobius Cables... I got em'
chanyote66's Avatar
United States, TN, Oak Ridge
Joined Dec 2011
3,691 Posts
Quote:
Originally Posted by Ricky401 View Post
No comments chaps?

Does anybody have any input one the dihedral/anhedral element of a flying wing? Should it have it and how do you measure it?

thanks
Iv been messing with dihedral on my home built wings but have not found anything I like.

Using wingtips that only extend upwards, or extend upwards more than down creates some dihedral effects and helps stabilize the wing.

All of my builds are very simple and do not go nearly indepth as you are looking here. I fly FPV all of the time however I do not have a GoPro to test my design with.

I use the KFm2 and KFm3 airfoils for simplicity.
chanyote66 is online now Find More Posts by chanyote66
RCG Plus Member
Latest blog entry: What does the FAA think of FPV?
Reply With Quote
Old Jun 06, 2012, 02:56 PM
I used to like trees
rchank's Avatar
United States, WA, Spokane
Joined Jul 2011
288 Posts
Ricky, Check out the Scratchbuilt Foamies forum for some good flying wing info from several talented builders.
rchank is offline Find More Posts by rchank
Reply With Quote
Old Jun 06, 2012, 03:53 PM
Registered User
UK, Cornwall, Truro
Joined Feb 2009
381 Posts
I do like the simple approach - maybe I'm over complicating things!

I never thought about the wingtips having that effect either. Interesting.

Thanks for the feedback! Much appreciated.

Quote:
Originally Posted by chanyote66 View Post
Iv been messing with dihedral on my home built wings but have not found anything I like.

Using wingtips that only extend upwards, or extend upwards more than down creates some dihedral effects and helps stabilize the wing.

All of my builds are very simple and do not go nearly indepth as you are looking here. I fly FPV all of the time however I do not have a GoPro to test my design with.

I use the KFm2 and KFm3 airfoils for simplicity.
Ricky401 is offline Find More Posts by Ricky401
Reply With Quote
Old Jun 06, 2012, 03:55 PM
Registered User
UK, Cornwall, Truro
Joined Feb 2009
381 Posts
Ah right - now why did'nt I think of that before?

Great idea. I'll go have a look now.

Thanks for taking the time to reply.

Quote:
Originally Posted by rchank View Post
Ricky, Check out the Scratchbuilt Foamies forum for some good flying wing info from several talented builders.
Ricky401 is offline Find More Posts by Ricky401
Reply With Quote
Old Jun 06, 2012, 03:55 PM
Mobius Cables... I got em'
chanyote66's Avatar
United States, TN, Oak Ridge
Joined Dec 2011
3,691 Posts
Quote:
Originally Posted by Ricky401 View Post
I do like the simple approach - maybe I'm over complicating things!

I never thought about the wingtips having that effect either. Interesting.

Thanks for the feedback! Much appreciated.
I have my FPV design on a post here... The "Stratos V" let me find a link... it might be a good one, not sure how big you want but its a 50" wingspan and has flown with an AUW of over 1300g

Here it is... http://www.rcgroups.com/forums/showthread.php?t=1619684
chanyote66 is online now Find More Posts by chanyote66
RCG Plus Member
Latest blog entry: What does the FAA think of FPV?
Reply With Quote
Old Jun 06, 2012, 04:05 PM
Registered User
Hagerstown, MD - USA
Joined Jan 2009
27 Posts
Also keep in mind that the sweep has some of the same stabilizing characteristics as dihedral. Many flying wings have sweep only, so that may be all you need. I haven't done it, but I wouldn't think that anhedral would be a good idea since it tends to be destabilizing in roll. The washout you are planning might help to reduce tip stall tendencies, but if you plan to fly inverted it will increase the tip stall tendency. I have no experience with this at all, but be careful if you do it. Washout is common on airplanes with more standard layout to assure that the stall occurs at the inboard part of the wing first.

Jim
Jim Marsden is offline Find More Posts by Jim Marsden
Reply With Quote
Old Jun 07, 2012, 02:31 AM
the answer 42 is
Switzerland, AG, Lenzburg
Joined Jan 2006
1,890 Posts
Hey what a long post, regarding the dihedral, the options and experiences are divided. In theory such wing will benefit from dihedral, and actually a swept wing will benefit from anhedral (negative dihedral). I have tested the three options +, - and 0 dihedral and there is not much difference, still my preference for High aspect FW is anhedral, for your case 0 dihedral will be still OK, build, test and report the anhedral also contributes to the stability of the wing, but maybe Norm can explain that better than me

the twist needs to be calculated appropriately to the airfoil you are using, you can find a great tool to calculate CoG and washout here http://www.tailwindgliders.com/Files.html and is free. On the bright side most of swept wings will fly OK with a reasonable amount of washout. But if you want your plane to really perform then take some time a calculate it

Do not forget that your elevons (alerons + elevators) are an integral part of your wing and airfoil so include them in your calculations.


good luck

EZ
Edwinzea is online now Find More Posts by Edwinzea
Reply With Quote
Old Jun 07, 2012, 01:58 PM
Registered User
UK, Cornwall, Truro
Joined Feb 2009
381 Posts
Thanks for the feedback chaps - feeling quite enthused about it. It'll take a while to get it all together but I'll feedback.

I don't intend flying upside down so a bit of twist should be ok I think. I'll keep reading up on things (which is proving to be quite interesting) and I'll have a look at this calculator and see what it comes up with for twist etc.

thanks again
Ricky401 is offline Find More Posts by Ricky401
Reply With Quote
Old Jun 07, 2012, 11:03 PM
internet gadfly
nmasters's Avatar
Colorado
Joined Aug 2006
2,153 Posts
Quote:
Originally Posted by Edwinzea View Post
Hey what a long post
A detailed description is good but one question at a time is easier to deal with.

Quote:
my preference for High aspect FW is anhedral, for your case 0 dihedral will be still OK, build, test and report the anhedral also contributes to the stability of the wing, but maybe Norm can explain that better than me
If you really want to be accurate dihedral should be measured at the leading edge. So if you have a tapered wing with the highest point of the top skin of the root and tip sections at the same height the nose of the tip will be just a tiny bit higher than the root nose and you'll have a very small amount of dihedral. Some guys build their 'wings with the lower surface flat on the building board because of this effect but I think it's so small that it won't make much difference. The reason that some builders pay attention to such a small detail is that dihedral is detrimental to a smooth flight in swept 'wings. This is because the dihedral effect of sweep depends on the speed. If you have too much you'll get an annoying oscillation in pitch and roll called "dutch roll" at low speed. With 28 degrees of sweep you don't need any more dihedral and in fact will probably want to reduce the effect so that your picture doesn't wobble. Tip fins that hang down below the wing can help with that and offer an easy way to adjust it

Quote:
twist needs to be calculated appropriately to the airfoil you are using, you can find a great tool to calculate CoG and washout here http://www.tailwindgliders.com/Files.html and is free. On the bright side most of swept wings will fly OK with a reasonable amount of washout. But if you want your plane to really perform then take some time a calculate it
Yep that's a good tool. A lot easier for most people to use than my weird a$$ work flow.

Quote:
Do not forget that your elevons (ailerons + elevators) are an integral part of your wing and airfoil so include them in your calculations.
Good point. A lot of people aren't sure of that one. I'd like to add that full span elevons rob lift from the inboard half of the wing without doing anything more for pitch than small elevons that are only outboard of MAC.


--Norm

ps The 'wing I'm working on will be flat on top for the inboard panels and anheadral on the outboard panels (sort of flattened out gull wing). And my center section will a wedge instead of a rectangle as in Ricky401's drawing. That will allow me to cut my wings out with the root edge square with the leading edge
nmasters is offline Find More Posts by nmasters
Last edited by nmasters; Jun 08, 2012 at 08:17 PM. Reason: spelling
Reply With Quote
Old Jun 08, 2012, 12:11 PM
Registered User
UK, Cornwall, Truro
Joined Feb 2009
381 Posts
thanks Norm
fair point about the length of post - I was coming at it from the other way where people might be saying - well this bit depends on what you are doing with that bit, and I wanted to show I'd at least made and effort to do some reading first.

I'll try and keep the posts simple now we're up and running.

That 'dihedral effect of sweep' is another interesting read - thanks, and I've added it to my library. I guess what you are saying explains the use of anhedral on Maxi swifts? I wondered about that but someone said it was to take out some of the stabilisation effect which kind of makes sense now seeing this info.

I'm trying to envisage your plan Norm, sounds interesting and cutting the blocks that way is interesting too and might allow different uses of the foam block to get different size wings so I'm going to have a quick experiment with that too.

Anyway - thanks for the feedback - much appreciated.

I've got the calculator here and have started putting in details - and I've downloaded and am trying to get my head around XFLR5. Bit tricky but I think I'm getting there.

All good progress in my education!

I'll keep you updated on how I get on and perhaps ask questions one at a time.
Ricky401 is offline Find More Posts by Ricky401
Reply With Quote
Old Jun 08, 2012, 01:22 PM
the answer 42 is
Switzerland, AG, Lenzburg
Joined Jan 2006
1,890 Posts
XFLR5 is a great tool but I have found it too optimistic with CoG on flying wings. So I use both tools excel sheet for CoG and XFLR5 for the washout and genereal improvements. It works great for standard gliders thought

EZ
Edwinzea is online now Find More Posts by Edwinzea
Reply With Quote
Old Jun 08, 2012, 10:21 PM
internet gadfly
nmasters's Avatar
Colorado
Joined Aug 2006
2,153 Posts
Quote:
Originally Posted by Ricky401 View Post
fair point about the length of post - I was coming at it from the other way where people might be saying - well this bit depends on what you are doing with that bit, and I wanted to show I'd at least made and effort to do some reading first.
No criticism was intended. Actually I thought that that was a very good opening post. The ability to thoroughly describe your goals in writing is a very useful skill. I can only wish I had it I tend to proses information in small bits.

Quote:
I'll try and keep the posts simple now we're up and running.
Thank you bot don't change your style just for me. You may find that I bring more chaos than light to the conversation.

Quote:
That 'dihedral effect of sweep' is another interesting read - thanks, and I've added it to my library. I guess what you are saying explains the use of anhedral on Maxi swifts? I wondered about that but someone said it was to take out some of the stabilisation effect which kind of makes sense now seeing this info.
You'll find that many of the best flying swept 'wings may look superficially similar but in fact are subtly different. That's because there is always more than one way to solve a problem and an experienced designer can make a wing work in spite of some weird feature that another, equally experienced, designer considers a mistake. After all it is a hobby and for the most part we're self taught so we figure out novel solutions. It's nice to build a plane that performs flawlessly the first time it leaves the ground but that doesn't often happen. Even Boeing had to fix the nose gear door on the first 777.

Quote:
I'm trying to envisage your plan Norm, sounds interesting and cutting the blocks that way is interesting too and might allow different uses of the foam block to get different size wings so I'm going to have a quick experiment with that too.
It may not be the most efficient use of your material unless you just happen to have an 18 degree wedge left over after cutting your wings. I'm progressing very slowly with mine because of other responsibilities (poor time management actually) A couple days ago while "watching" a bunch of 8 year olds play slow pitch softball I realized that instead of cutting a triangle off the root of each wing to set the sweep I could add a wedge and this wedge can have any profile I want


Quote:
I've got the calculator here and have started putting in details - and I've downloaded and am trying to get my head around XFLR5. Bit tricky but I think I'm getting there.
Those are good tools and many people get good results from them. I find XFLR5 useful for working on airfoils but I haven't had time to figure out the airplane analysis part. Curtis' spreadsheet looks very nice but I had already been working on my own kludge that includes that formula for some time. It fits my personality and workflow so I use it. As far as finding the CG I use a graphical method and measure that to determine the static margin to put into the spreadsheet. It's weird and by some standards probably backwards but I get the numbers I want.



Quote:
I'll keep you updated on how I get on and perhaps ask questions one at a time.


--Norm
nmasters is offline Find More Posts by nmasters
Reply With Quote
Old Jul 01, 2012, 07:26 AM
Registered User
UK, Cornwall, Truro
Joined Feb 2009
381 Posts
Well, I've been reading up more and found out some very interesting stuff about the fundamentals of flying, how things work etc.

I've also done some more planning. XFLR5 is 'very' slowly starting to make sense and I have a model wing drafted up in the design. I'm trying now to figure out how to get the polars for the MH 45 airfoil into it as I think I need that to do that last page of the Flying Wing Calculator Spreadsheet

I've been here

http://www.mh-aerotools.de/airfoils/mh45koo.htm

and dowloaded the pef file for the polars (I thnk that's right?) but in XFLR5, when I try to import polars, I get an error message which says 'no UFO with the name ; obsolete : could be found - the polars will not be stored'.

I feel like having done so much reading, measuring up, planning etc that I'm so close and that if I can get this data for the last page of the calculator I'll be ready to start cutting so can anyone help tell me what I'm doing wrong here?

thanks
Ricky401 is offline Find More Posts by Ricky401
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion Looking for some advice on my first micro-ish build C₄H₁₀ Scratchbuilt Indoor and Micro Models 12 Jun 24, 2012 11:34 PM
Discussion MY first scratch build! Micro Zephyr flohio117 Foamies (Scratchbuilt) 12 Apr 19, 2012 11:18 PM
Discussion Building my "First" flying wing - The Raptor MyGeekShow Flying Wings 0 Mar 10, 2012 06:02 AM
Discussion My First Wing, and My First Scratch Build Shazbot996 Flying Wings 9 Aug 25, 2007 05:33 AM