Wing Root Fairings

[skippydiesel]

Simple question; - Why don't Sonex aircraft  (& many other metal home built aircraft) have wing root fairings?

AND

Would correctly designed wing root fairings, make any positive difference to handling/performance (speed)?

AND

An invitation, to anyone who has made & installed their own wing root fairings, to post photos and comment on changes to their aircrafts handling/performance

[facthunter]

LESS drag and more LIFT is why they put them there. It's not easy to  do it right so some don't bother to do it at all.  Nev

[spacesailor]

All Hummel aircraft have great wing root fairing .

Panelbeat on a bag of sand or a wooden former .

Make your pattern first in cardboard, when it fits best, cut your alloy to the cardboard pattern .

spacesailor

[IBob]

I made my own simple wing LE root fairings, as I didn't like the way the standard fairing (which just extends the LE shape inboard until it meets the windscreen) intrudes on the pilot's vision. They are just a flat aluminium shape, curved round, nothing 3D. I am a reasonable DIY pattern maker, but it was a surprisingly long job getting a pattern for the shape.
Sorry, I can't comment on performance as this was done before she flew. In the case of the Sav, I doubt there would have been any difference.

[facthunter]

It would only be worth doing on something  where they were  trying to get speed from and you'd do other things as well.   Nev

[skippydiesel]

I envisage a composite fairing that "smooths" the air flow at the leading edge of the wing root and then extends back  (above/below) to the flap. At the flap, the lower fairing would taper off to end jut before the flap max down position.  On top the fairing would continue past the flap and taper back into the fuselage to again smooth the air flow off the trailing edge of the flap.

 

No point in going to all this trouble for anything less than a 5 knot increase in speed, for a given engine setting/fuel flow.

[old man emu]

Sounds like it's a suck it 'n' see proposition.

[Thruster88]

Most Van's aircraft do not have wing root fillets including the later models like the RV14. Have seen some on a RV4, if they made any difference they would be more common. If they made a 5 knot difference they would be on every RV.

[facthunter]

Not often done with Hi wings, Mostly with below floor level wing spars Any decent larger design after 1938 OTA would have them  DC-3 on. I don't think it has anything to do with the flaps down position. If you look  at image's of piston airliners with people exiting the rear door you'll see the fairings. 

  They work alright and were developed in wind tunnels.  Nev

Edited March 23, 2023 by facthunter

[spacesailor]

One Hummel Bird builder went to extreme with cleaning up to the best he could !.

The result was great . More top speed for less fuel.

61 mpg ( American  ) at 140 knots . ( 3.8 L / 100 KMTRS  )

 

spacesailor

 

[skippydiesel]

2 hours ago, Thruster88 said:

Most Van's aircraft do not have wing root fillets including the later models like the RV14. Have seen some on a RV4, if they made any difference they would be more common. If they made a 5 knot difference they would be on every RV.

Yeah but almost all composite aircraft do - especially the European ones, that tend to use Rotax 9 series engines.

 

Complexly biased observation - Europeans & Japanese seem to have inherited a thrifty (small capacity engine motivation & streamlining) approach to vehicles & aircraft design, probably related to WW2 privation (during & after) that our American cousins do not have.

[spacesailor]

Ooops 

skipprdiesel

Those Hummel Aviation planes are American . 120 flying at last count. 

spacesailor

[skippydiesel]

6 hours ago, spacesailor said:

Ooops 

skipprdiesel

Those Hummel Aviation planes are American . 120 flying at last count. 

spacesailor

An exception to every biased comment 😁

[Ian]

If you're going down this path you probably want advice from someone who's already devoted a good chunk of their life to minimising drag.

Around the 37 minute mark is where he gets into shapes to minimise drag.

I think that fact that he managed to exceed 200mph with less than 65hp is a pretty good reference.

 

 

[skippydiesel]

Thanks Ian - I have actually seen/heard of Mike Arnold before - well worth the revisit

[Thruster88]

I wonder if Mike may have tuned that Rotax 582 2 stroke to produce a lot more than the stock 65hp @6500rpm. There were plenty of knowledgeable 2 stroke tuners at that time. 

[RFguy]

I think the "there is no point unless it makes a 5 knot difference" statement  is not the right way to look at it.
Many  5 knot gains come from numerous 1 knot gains all put together.

[Old Koreelah]

Too plurry right, Glen! Every little bit helps.

I put lots of work into streamlining my Jodel, mostly to increase the distance it would glide if the noise stops.

Not much you can do about the friction on fabric, but easy to reduce the form drag of wheels, etc. My tests showed up to 13% reduction in fuel burn from my wheel spats.

[skippydiesel]

2 hours ago, RFguy said:

I think the "there is no point unless it makes a 5 knot difference" statement  is not the right way to look at it.
Many  5 knot gains come from numerous 1 knot gains all put together.

This is already a "slippery" aircraft able to deliver approximately 130 knots indicated (145TAS) 5200rpm @ 6500ft with a whole of sortie fuel burn of 12.5L/hr (Hobbs).

I would like it to be as efficient a tourer as I can make, that is within reason. The reason in this instance is mainly time : I am already committed to returning this aircraft to my workshop, to make changes, that I hope will make a big difference to its cooling systems. Fabrication & installation of  simple wing root fairings, may not extend its non flying sojourn by more than a few days.  I am no longer in the first flush of youth, so time spent on  "numerous 1 knot gains"/ incremental improvements is , for me, time wasted, when I could be up flying. The wing root fairings will be discarded if they do not make a a measurable improvement.

[Ian]

Looking at the Sonex shaped in the image below, the base of the wing might be making a high drag expanding "nozzle" mentioned in the  video.

To reduce the drag flattening this section until the end of the wing might help.

A somewhat quick and dirty approach using something like CNC machined foam or 3D printed parts might be a lower labour approach. Using something like freecad could facilitate this approach.

Another quick and dirty would be model some foam and cover it with duct tape.

[skippydiesel]

On 29/03/2023 at 10:44 PM, Ian said:

Looking at the Sonex shaped in the image below, the base of the wing might be making a high drag expanding "nozzle" mentioned in the  video.

To reduce the drag flattening this section until the end of the wing might help.

A somewhat quick and dirty approach using something like CNC machined foam or 3D printed parts might be a lower labour approach. Using something like freecad could facilitate this approach.

Another quick and dirty would be model some foam and cover it with duct tape.

Hi Ian,

 

"To reduce the drag flattening this section until the end of the wing might help" - end of wing? Do you mean the inboard wing/flap intersection with the fuselage?

 

Sonex plans call for a quite small piece of angled aluminium, to be attached to the fuselage, above each flap. after trim adjustments have ben completed/finalised.

 

This is not supposed to be a flap "stop"  (may act as such) more of a gap seal. My theory is that this could be enlarged and shaped to be somewhat more aerodynamic. I envisage it starting in the vivacity of the wing spar and continuing back behind the flaps/trailing edge.

 

EG Europa - Zenith - schematic of laminar flow going turbulent over flap (wing root?)

 

[Ian]

On 02/04/2023 at 11:16 AM, skippydiesel said:

To reduce the drag flattening this section until the end of the wing might help" - end of wing? Do you mean the inboard wing/flap intersection with the fuselage?

Yes, From the diagram (which may or may not be accurate), the rear of the wing is attaching to the fuselage in a section which is reducing. ie both sides are converging towards the tail. 

To reduce drag the section should be attempting to remain straight.

The sections for the pictured wing root appears to be trying to achieve this straight line effect but its a bit hard to actually assess.

[Thruster88]

On 23/03/2023 at 9:18 PM, skippydiesel said:

Yeah but almost all composite aircraft do - especially the European ones, that tend to use Rotax 9 series engines.

 

Complexly biased observation - Europeans & Japanese seem to have inherited a thrifty (small capacity engine motivation & streamlining) approach to vehicles & aircraft design, probably related to WW2 privation (during & after) that our American cousins do not have.

While owners of RV aircraft might not have thrift in mind we all want to go faster, hence my comment. It would also be weird not to have a wing fillet on a composite airframe, regardless of the engine choice.  

 

Readers will need to read thread for context.  

[spacesailor]

Not just ' go faster ' .

But those extra ' gap filler's ' will make your fuel go the extra mile .

So fairings and spats , will pay for themselves in the long run. 

 

61 mpg  about 98 klmtrs on 4 ( four ) litres on mogas 

spacesailor

 

 

[Area-51]

Wing root flares are not what many might think when it comes to flight performance gains.

 

In straight and level AoA trajectory there are no substantial gains between the same aircraft using or not using wing root flares. This should not be confused by the seperate criteria and affects of wing root to fuselage corner fillet. Although the flare does incorporate the corner fillet aspect they both provide alternate results. For the speeds of most ultralights corner fillets of 50mm radius provide a better reduction of interference drag than those of 10mm. For wing root flares 100mm to 150mm radius corner fillets at the flare provide much better results than 50mm fillets; there is no advantage going larger than this other than to cause discussion.
 

 

The two images above present this aspect of straight and level AoA flight (3.25deg incidence included). Both models return nominally equal Drag and Lift results within this flight mode regardless of air speed.

 

Where the wing root flare excels is within the intermediate AoA flight modes where the wing is transitioning through 4deg to 6deg AoA. Within this narrow band the flare reduces vortex turbulence generated by the contrast of upper and lower transient flow rejoining by channeling the free stream toward a more gradual reunification. This reduction in Drag on the aerodynamic example pictured, at 100kt and 6deg AoA, the flared wing provides about 65kg more Lift and 20% less Drag compared to the non flared model. This would occur during a situation such as a rate one turn, or, raised nose attitude cruise due to heavier AUW, or, glide approach. This aspect described above is presented in the two images below, the blue areas represent turbulent slower velocity air, the red represents higher velocity air, green represents free stream velocity of 100kt. Outside of this narrow performance band the wing root flare provides no advantage or hinderance.

 

 

So to conclude wing root flares are most effective during bank turns. They allow for tighter turns to be achieved over their non flared counterpart, and a more efficient cruise at higher AUW.

 

"No lawnmowers were harmed during these scientific experiments."