Thread Tools
May 11, 2019, 10:32 PM
Brett
pmanu's Avatar
Thread OP
Discussion

Under Camber wing help


I looking for a easy way to design a under camber wing and change parameters if need be,

cord section 200mm long with 3% thickness consents ,4% camber @ 40% cord

like this picture
Sign up now
to remove ads between posts
May 11, 2019, 10:37 PM
IMO ( In My Opinion ) →
balsa or carbon's Avatar
I build undercamber wings this way :
https://www.rcgroups.com/forums/show...2&postcount=28


Here is one of my planes that uses that type of construction :



FT Old Fogey-ish with 60" wingspan (1 min 56 sec)
May 11, 2019, 10:59 PM
Brett
pmanu's Avatar
Thread OP
I like it and it flys very nice indeed....But I have some 40mm thick foam I was hoping (but not fixed on it) to hot wire the shape in one go, or at least one per side with dihedral,
what was the current draw on the model to keep her in the air ?
thanks for sharing
Cheers
Brett
May 11, 2019, 11:34 PM
IMO ( In My Opinion ) →
balsa or carbon's Avatar
Quote:
Originally Posted by pmanu
I like it and it flys very nice indeed....But I have some 40mm thick foam I was hoping (but not fixed on it) to hot wire the shape in one go, or at least one per side with dihedral,
what was the current draw on the model to keep her in the air ?
thanks for sharing
Cheers
Brett
It has this motor with an 11 x 3.8 prop & 2200mAh 3S 30c battery , I've never measured the current draw .
https://hobbyking.com/en_us/hextroni...E&gclsrc=aw.ds
May 12, 2019, 07:07 AM
gpw
gpw
ďThereís no place like FoamĒ
gpw's Avatar
Pmanu, the absolute easiest way to make an undercambered airfoil is with the BendFoam jig … Made from salvage wood , quick and easy , reproducable, and you can vary the airfoil as you like … https://www.rcgroups.com/forums/show...ht=Bendfoam%20… and unlike rolled airfoils retains it's shape forever ...
Last edited by gpw; May 12, 2019 at 12:01 PM.
May 12, 2019, 08:10 AM
treefinder
springer's Avatar
+1 for what gpw said. Of course you will have to hot wire cut your foam down to the thickness you want. If you have a hot wire cutter, cobbling up a flat surface to slice 6mm sheets should be relatively straightforward. Once you get the foam to the foil shape you want, you can play a heat gun over the surface to help "set" the curve. Be prepared for a little relaxation, and perhaps another bending session to correct.
May 12, 2019, 10:02 AM
Build, crash...repeat
AleRRon's Avatar
Most people who go through the trouble of building and using a Hotwire cutter for wings make real airfoils. Why do you want to Hotwire an undercamber wing? Iíd suggest either hotwire cut a standard NACA airfoil or a Clark Y airfoil, or use flat sheet 3-6 mm foamboard like Dollar Tree foamboard or Model Plane Foam and simply roll and curve it into the shape desired. You can use the jig mentioned or just roll it with an implement like a rolling pin.
May 12, 2019, 08:10 PM
Brett
pmanu's Avatar
Thread OP
@gpw yes that is also a good way to bend up a wing, its hard to get thin foam here but heaps of insulation foam 15-40mm so didnt mind using my hot wire on some spare 40mm left over from a build project.

@Springer yes have a hot wire 1000mm long but thort if Im cutting why not cut the shape I need to start with ?

@AleRRon. the idea was slow flight max lift long duration using some recycled 18650 etc, I can see the airfoil section in video above flys very slow but wonder about how efficient the motor is running amp draw etc

the idea was to test Jef Raskin airfoil out also
https://bit.ly/2HffY52
Last edited by pmanu; May 12, 2019 at 08:11 PM. Reason: spelling
May 12, 2019, 08:35 PM
Build, crash...repeat
AleRRon's Avatar
OK I get it. Max lift. I could be wrong but I think the undercamber has a lot of lift but also lots of drag. Thatíll slow you down as you want, but the efficiency (power usage) may be poor too and your flight time may be shorter compared to a NACA airfoil.

A real airfoil is probably the best possible wing shape, but some of us scratchbuilders just want to use foamboard and came up with airfoil substitutes that still work really well on model planes and donít require a hotwire jig.

Since you have the Hotwire and could cut either one, Iím not sure that cutting a constant flat section undercamber wing is better.

I guess you just have to try one and see what happens. Itís just foam after all!
May 13, 2019, 02:29 AM
Brett
pmanu's Avatar
Thread OP
Quote:
Originally Posted by AleRRon
OK I get it. Max lift. I could be wrong but I think the undercamber has a lot of lift but also lots of drag. Thatíll slow you down as you want, but the efficiency (power usage) may be poor too and your flight time may be shorter compared to a NACA airfoil.

A real airfoil is probably the best possible wing shape, but some of us scratchbuilders just want to use foamboard and came up with airfoil substitutes that still work really well on model planes and donít require a hotwire jig.

Since you have the Hotwire and could cut either one, Iím not sure that cutting a constant flat section undercamber wing is better.

I guess you just have to try one and see what happens. Itís just foam after all!

I agree with you that in the video above and other undercamber wing videos I have watch the motor sounds like it is about half throttle, dont get me wrong I love the idea of high lift and having a floater but not at the cost of battery usage. the way Jef Raskin speaks it should work fine 3% thick 4% [email protected] % .
It was trying to find some easy software to print the airfoil section off
May 13, 2019, 11:30 AM
Build, crash...repeat
AleRRon's Avatar
I don't have a hotwire jig but I thought all you needed was a template for the wire to ride over, don't you? Can't you just print the picture to the size you need and use it to cut a wood or metal template? I am asking out of relative ignorance but after having seen some hotwire setups, so I don't really know for sure how you go about it.
May 13, 2019, 04:26 PM
Brett
pmanu's Avatar
Thread OP
Quote:
Originally Posted by AleRRon
I don't have a hotwire jig but I thought all you needed was a template for the wire to ride over, don't you? Can't you just print the picture to the size you need and use it to cut a wood or metal template? I am asking out of relative ignorance but after having seen some hotwire setups, so I don't really know for sure how you go about it.
I have no way to measure and then change the setting if need be, say if I wanted to try max camber at 30% apart from using a ruler I guess, but I have a computer so be easyer to use printer try adjust etc etc if that makes sense
May 13, 2019, 04:38 PM
treefinder
springer's Avatar
Pmanu; you can do all that you want with a freeware cad program like sketchup, design it and change it as you like, then print out the template to cut the hotwire template. Since you have a 40mm piece of foam, I'd slice a few sheets of 6mm thick off it and try bending them on a bendfoam like fixture, then you can still cut a UC section or a full conventional airfoil section if you want. I think you will find it really difficult to cut the thin section with a wire cutter. Most of the wing cores are pretty thick sections not the really thin one you show. You will be essentially cutting the offal and the 'scrap' will be the actual section you want. I don't think it will be particularly stable though, I'd expect it to be pretty floppy. The foam sheets like MPF and fanfold have a "grain" due to the way they are extruded that you can exploit, but a thick block won't exhibit much of that, I would expect.
May 13, 2019, 05:58 PM
Build, crash...repeat
AleRRon's Avatar
pmanu
sometimes old school rulers, straightedges, and pencils and paper are better than computers. Computers can make us all crazy just trying to figure out how to make them do what you want. I've used both methods and paper/pencil is far simpler and still works pretty well. Just sayin.
May 13, 2019, 06:10 PM
gpw
gpw
ďThereís no place like FoamĒ
gpw's Avatar
Back before all that , some even traced the edge of their trainers ( athletic shoes) as a pattern for airfoils … The “Adidas “ airfoils …

GeneBond always recommended 4/40 undercambered airfoil , his planes always flew Great ...
Latest blog entry: Lost plans


Quick Reply
Message:

Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Question How to dope an under-cambered wing without it shrinking away Sackie Scale Sailplanes 2 Apr 24, 2016 07:34 PM
Question Covering a Convex / Under-cambered wing. Taxus812 Painting and Finishing Tips 4 Mar 05, 2016 01:33 PM
Question is there a maximum angle you can make an under-cambered wing? sbrunsen The Builders Workshop 3 Jan 31, 2016 08:57 PM
Discussion Help....covering an under-cambered wing? talehevvy Scale Kit/Scratch Built 7 Mar 02, 2007 10:23 PM
Pitch reactions with under camber wing? Steve McBride Power Systems 10 Mar 31, 2002 10:00 AM