I am exploring all ways to make airfoils. I have already given up with hot wire cutting. Now i am experimenting by folding depron ( I am using material that you lay under parquet). I just want to know if this airfoil would work. I am planning the wingspan to be around 2,3 m because I want the wing loading to be low.
Does airfoil shape matter ?
- Thread starter Noob777
- Start date
JasonK
Participation Award Recipient
quorneng
Master member
Noob777
If the foam underlay is rigid enough you certainly can make a wing that way and it is possible to do so without any ribs or spar. Each wing half is made up of just 4 pieces! It relies entirely on the strength of the foam.
Note the foam has been sanded on the inside of each skin to give a fine trailing edge.
The two foam shear webs are caefully sized and positioned to give an almost symetrical wing section which in this case is for an EDF.
The wing has a relatively low aspect ratio and a thick built up root but it is likely some reinforcement would be required for a glider type high aspect ratio wing.
This is the skinniest unreinforced wing I have done so far using this method.
This wing has a more normal wing section (more camber top than bottom) for a reasonable glide performance.
Pianted with acrylic foam safe paint.
Don't be shy to experiment.
If the foam underlay is rigid enough you certainly can make a wing that way and it is possible to do so without any ribs or spar. Each wing half is made up of just 4 pieces! It relies entirely on the strength of the foam.
Note the foam has been sanded on the inside of each skin to give a fine trailing edge.
The two foam shear webs are caefully sized and positioned to give an almost symetrical wing section which in this case is for an EDF.
The wing has a relatively low aspect ratio and a thick built up root but it is likely some reinforcement would be required for a glider type high aspect ratio wing.
This is the skinniest unreinforced wing I have done so far using this method.
This wing has a more normal wing section (more camber top than bottom) for a reasonable glide performance.
Pianted with acrylic foam safe paint.
Don't be shy to experiment.
Linkster
New member
JasonK - one of the questions I have is about KFm wings is this: What is the depth of the step needed?
Regarding step placement for the wings in the KFm family, the "diagrams" (in the FT post you reference) all mention the step placement at some specified percentage of the wing chord...got it...easy enough.
Then each configuration references step "thickness" being 7-9% or 8-12%...
Percent of what? The wing chord?
I've been through every post (seems like) on rc forums and I can't find squat...
I think it is me just being stupid and the 7-9% means 7-9% of the wing chord.
Can you or anyone confirm this (what the 7-9% is in reference to, pls, rather than my stupidity)?
Thx.
leaded50
Legendary member
KF wingfoil ( Kline–Fogleman airfoil ) The purpose of the step, it is claimed, is to allow some of the displaced air to fall into a pocket behind the step and become part of the airfoil shape as a trapped vortex or vortex attachment. This purportedly prevents separation and maintains airflow over the surface of the airfoil.
- and seen here in this file, they say % of the cord on many of versions...
In FT article this is written : "Note the percentage thickness refers to each sections total thickness vs the total chord of the wing, and not the height of the step. The height of the step is only determined by the thickness of your foam sheet. Steps can be raised to give more height and the step effect increases proportionaly with both height and air speed."
https://www.flitetest.com/articles/kfm-wings-a-basic-explanation
- and seen here in this file, they say % of the cord on many of versions...
In FT article this is written : "Note the percentage thickness refers to each sections total thickness vs the total chord of the wing, and not the height of the step. The height of the step is only determined by the thickness of your foam sheet. Steps can be raised to give more height and the step effect increases proportionaly with both height and air speed."
https://www.flitetest.com/articles/kfm-wings-a-basic-explanation
Attachments
quorneng
Master member
KF wings work well at model sizes where the boundary layer is relatively very thick and the surface drag proportionally high but they do not work well at full size. NASA did a series of wind tunnel tests and could find no advantage over the equivalent conventional one.
I suspect for smaller models the fact that the boundary layer is positively broken at a specific point (the step) means predictable handling characteristics whereas with a small conventional wing section the high relatively viscosity means the laminar flow break away point is unpredictable with correspondingly sudden & large changes in the centre of pressure.
I suspect for smaller models the fact that the boundary layer is positively broken at a specific point (the step) means predictable handling characteristics whereas with a small conventional wing section the high relatively viscosity means the laminar flow break away point is unpredictable with correspondingly sudden & large changes in the centre of pressure.
Linkster
New member
Like I said, my stupidity doesn't need confirmation.
Thanks for pointing this out. I have no idea how I missed this.
LOL
Linkster
New member
In my search for the answer, I read a number of papers and a PhD thesis that pretty much confirmed that there's no benefit at full scale. Based on what I read, what you say makes sense.
THX, M8.
Yes, your airfoil will work. The airfoil will not prevent your plane from flying, something else might, but the airfoil will work.
Would a different airfoil work better? Yes, but it depends on what you want. Some airfoils are for speed, some are for lifting heavy loads, some are for endurance, that is flying for a longer time.
How much difference will a better airfoil make? Maybe 5%, maybe 30%, depending on your goals, but not 2-3 times better.
Similar threads
