Groove gear fairing

[Birdseyeview]

I've been looking at past postings on various drag reducing fairings but never came across one that would streamline the rectangular cross section of the grove gear under the fuselage. I bent a sheet of .060" thick lexan and shaped it to fit around the gear seen in the attached photos. The lexan is light, strong and flexible so I'm trying it out but I honestly don't expect a measurable improvement in airspeed. I miss the building phase and needed a project to keep from getting bored. I also put a fairing that came with my kit behind each gas cap. I shaped the bottom edges of these small fairings to conform to the curve of wing, pressed it into some of the light foam that came with my kit and glued it down to the wing with silicon RTV. I held it in place while the RTV set up using a small C clamp.
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[FoxbuilderWill]

I suspect your gear fairing is actually increasing drag on your plane.
There was a guy named Mike Arnold who built a small plane powered by a rotax 582 and for awhile was the world record holder of a aircraft weighing less than 660lbs. He was the first person a far as anyone knows who managed to build a man carrying aircraft with a flat plate drag area <= to 1 sq ft. His 3km closed course speed record was 213 mph. Pretty good on just 60 hp(he figured his non optimal exhaust cost him 5 hp).

In any case he made a video detailing his drag reduction techniques.

The most relevant portion for your gear leg fairing starts about minute 40 to 52.

https://youtu.be/rxvoDbZpoY8?feature=shared

[Birdseyeview]

Foxbuilder, Thanks for the link to that very interesting video on drag reduction. The principles revealed in that video would seem to confirm your suspicion that I may have inadvertently increased drag by creating a drag increasing "nozzle effect" between the fuselage skin and the trailing edge of my fairing. Without testing this in a wind tunnel its impossible to tell how much drag there was before and after my mod but the video makes sense and gave me an idea on how to eliminate the "nozzle effect" drag at the trailing edge. My idea would be to change the cross section of the fairing from the symmetric cross section I currently have to one with a flat top surface running parallel to the skin of the airplane and to make the bottom surface with all the curved streamline in it from front to back. That should reduce or eliminate the drag caused by the nozzle effect at the trailing edge. I think my next attempt to construct such a fairing will make for another fun project. Thanks again for the tip.

[Eric Page]

Larry, if I understand your proposal correctly, it seems to me that your idea would create an inverted wing cross section that would generate downward lift, counter to the main wings. Also, any parasite drag reduction the fairing creates might be replaced by induced drag, both from the downward lift of the fairing and from the increased wing lift required to offset the fairing lift.

Just thinking out loud here. I could be out to lunch; as I have proven in multiple forum posts, I am not an engineer!

[Birdseyeview]

Eric, thanks for your thoughts - this fairing of the grove gear gets more complex with each iteration and this complexity may explain why no one has seemingly come up with the magic bullet that I could find so far. It may be that the flat plate forward surface of the rectangular gear cross section is in fact the least drag creating shape after all. Having said that an engineer friend of mine thought that most of the drag on such a flat plate surface is usually on the down wind side of the plate. I wonder what Kitfox does for their streamlined grove gear on their Speedster model?

Another possible iteration may be to place a triangular cross section length of foam just in front of, but not connected to the gear cross plate. This foam piece could be glued down to the fuselage fabric to act as a forward ramp for the air to slide over the gear surface while allowing the gear to flex during landings. This would prevent any air from entering the gap between the fuselage bottom fabric and the top of the gear plate. Something similar could be attached to the fuselage just behind the gear plate, again not quite touching the gear. I saw something similar to this on the front side of the gear in an old post but I didn't see anything on the back side, where most of the drag tends to be created. If this idea was without a down side I suppose the foam pieces could be enclosed in fabric to better hold it in place on the fuselage. Any thoughts and/or constructive criticism are welcome.

[FoxbuilderWill]

I've been thinking a lot about drag reduction on my build and I've heard from different sources that putting a bulge on the belly of some aircraft makes them faster. It's the case when adding a cargo pod to a super cub (but that's possibly just smoothing out the horribly disturbed air from the landing gear) and on another forum someone posted a pic of a business jet with a bulge on the belly and said that made the plane faster.
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I'm not necessarily sold on that idea since the designer may just have needed to get the wing structure lower to increase cabin room then had to fair it.

But I have been looking at whales and interestingly the humpback whale which has to migrate long distances without eating is much flatter on the top than the bottom. Definitely not apples to apples but it's still fluid dynamics.

So my best guess would be to completely fair in your gear legs where they go across the belly and see what happens.

Eric, thanks for your thoughts - this fairing of the grove gear gets more complex with each iteration and this complexity may explain why no one has seemingly come up with the magic bullet that I could find so far. It may be that the flat plate forward surface of the rectangular gear cross section is in fact the least drag creating shape after all. Having said that an engineer friend of mine thought that most of the drag on such a flat plate surface is usually on the down wind side of the plate. I wonder what Kitfox does for their streamlined grove gear on their Speedster model?

Another possible iteration may be to place a triangular cross section length of foam just in front of, but not connected to the gear cross plate. This foam piece could be glued down to the fuselage fabric to act as a forward ramp for the air to slide over the gear surface while allowing the gear to flex during landings. This would prevent any air from entering the gap between the fuselage bottom fabric and the top of the gear plate. Something similar could be attached to the fuselage just behind the gear plate, again not quite touching the gear. I saw something similar to this on the front side of the gear in an old post but I didn't see anything on the back side, where most of the drag tends to be created. If this idea was without a down side I suppose the foam pieces could be enclosed in fabric to better hold it in place on the fuselage. Any thoughts and/or constructive criticism are welcome.

[Slyfox]

seems to me you can just put a covering over the whole area without an opening between the bottom of the airplane and the bottom of the spring gear and do much better, just my opinion. If you have the radiator in front of this area I'm sure you are going to be defeated on the whole thing anyway, that's how my model 4 is. take care.

[airlina]

On my Series 5 I knew I wasn't gonna be happy with the unfinished look of the gear under the fuse so during my build I fabricated this fiberglass fairing to reduce drag and give that area a more finished look. With the flex of that part of the gear during landing , it was important to leave that part open , so just front and aft are faired as you can see in the pics. Bruce N199CL

[bbs428]

"On my Series 5 I knew I wasn't gonna be happy with the unfinished look of the gear under the fuse so during my build I fabricated this fiberglass fairing to reduce drag and give that area a more finished look. With the flex of that part of the gear during landing , it was important to leave that part open , so just front and aft are faired as you can see in the pics. Bruce N199CL"

Wow! That's really nice! I like the look and its functionality.
I'm sorry I didn't catch this detail before my plane was done Bruce, or I might have done something similar.

No matter which way you go Larry, if it helps to reduce some drag, that's a good thing! Just have to keep it as light weight as possible.

[Slyfox]

On my Series 5 I knew I wasn't gonna be happy with the unfinished look of the gear under the fuse so during my build I fabricated this fiberglass fairing to reduce drag and give that area a more finished look. With the flex of that part of the gear during landing , it was important to leave that part open , so just front and aft are faired as you can see in the pics. Bruce N199CL

yes that's what I'm thinking right there.