Will Aldridge
Well-Known Member
I have a kitfox model 1 I'm rebuilding. I intend to pay as much attention to drag reduction as possible.
The main goals are:
1. Reduce fuel consumption at cruise( it's a backcountry plane so increasing playtime before having to come back out for fuel)
2. With a Vne of 100 mph I won't win any races but climb rate is also related to drag and at high density altitude climb rate really suffers, so drastically improve climb rate.
3. Learn something while doing it.
There are a number of well known ways to reduce drag on a kitfox which I'm planning on, the following list is what's already in progress or on my mind:
1. Pvc leading edge "cuffs" for the wing. The early model kitfox wings use the round aluminum tube spar as the leading edge, the model 4 with a Riblett designed airfoil has a pvc leading edge for a proper airfoil profile. Others have used this on the early models and in general report 1-2 mph better cruise, 1-2 mph lower stall and maybe 100 fpm better climb rate. Ive purchased this from kitfox and will install it before recovering the wings.
2. The wing strut attach points are terrible drag producers. Haven't decided how I'm going to tackle that but it's on the list.
3 The gas cap on top of the wing is supposedly worth a couple mph in cruise and lower stall speed if faired (not to mention making the aircraft stall more straight ahead if you only have a tank in one wing like I do).
4. Landing gear is cub style with a cabane. Definitely going to need a fairing for the cabane. I'm trying to decide if I should fair each tube in the gear leg individually or just fair the aft edge of the rear tube and cover the whole thing. Maybe someone can comment on the increased wetted area of covering the whole gear leg vs having the 1 tube in front of the other? I'll also be working on a way to fair the fear leg attach points at the fuselage.
Ok there's more I'm going to do that I'll save for later but looking at the fuselage I see a place that I bet causes some drag and Ive got a couple ideas to run past you guys.
In the attached image you can see there's a somewhat abrupt transition between the flat side of the fuselage where the door is and where the fuselage starts tapering towards the tail. Ive had 2 ideas about addressing this issue:
1. Hysol a piece of wood to the side of lower longeron that smooths the transition.
2. Add a couple vortex generators at that point.
Problem with option 1 is that I'm not sure if the fabric will do what Id like. It might just create a saddle between the lower longeron and the stringer running down the middle of the aft fuselage, in which case I might need to add some kind of material under the fabric for a few inches aft of the seat back tubing to hold the fabric out. Although I'm willing to spend a few pounds in weight on the whole airframe for drag reduction, I have a feeling that the drag reduction for the weight might not be worth it.
Using VG's would look like a bandaid (and maybe not work at all)
Opinions?
The main goals are:
1. Reduce fuel consumption at cruise( it's a backcountry plane so increasing playtime before having to come back out for fuel)
2. With a Vne of 100 mph I won't win any races but climb rate is also related to drag and at high density altitude climb rate really suffers, so drastically improve climb rate.
3. Learn something while doing it.
There are a number of well known ways to reduce drag on a kitfox which I'm planning on, the following list is what's already in progress or on my mind:
1. Pvc leading edge "cuffs" for the wing. The early model kitfox wings use the round aluminum tube spar as the leading edge, the model 4 with a Riblett designed airfoil has a pvc leading edge for a proper airfoil profile. Others have used this on the early models and in general report 1-2 mph better cruise, 1-2 mph lower stall and maybe 100 fpm better climb rate. Ive purchased this from kitfox and will install it before recovering the wings.
2. The wing strut attach points are terrible drag producers. Haven't decided how I'm going to tackle that but it's on the list.
3 The gas cap on top of the wing is supposedly worth a couple mph in cruise and lower stall speed if faired (not to mention making the aircraft stall more straight ahead if you only have a tank in one wing like I do).
4. Landing gear is cub style with a cabane. Definitely going to need a fairing for the cabane. I'm trying to decide if I should fair each tube in the gear leg individually or just fair the aft edge of the rear tube and cover the whole thing. Maybe someone can comment on the increased wetted area of covering the whole gear leg vs having the 1 tube in front of the other? I'll also be working on a way to fair the fear leg attach points at the fuselage.
Ok there's more I'm going to do that I'll save for later but looking at the fuselage I see a place that I bet causes some drag and Ive got a couple ideas to run past you guys.
In the attached image you can see there's a somewhat abrupt transition between the flat side of the fuselage where the door is and where the fuselage starts tapering towards the tail. Ive had 2 ideas about addressing this issue:
1. Hysol a piece of wood to the side of lower longeron that smooths the transition.
2. Add a couple vortex generators at that point.
Problem with option 1 is that I'm not sure if the fabric will do what Id like. It might just create a saddle between the lower longeron and the stringer running down the middle of the aft fuselage, in which case I might need to add some kind of material under the fabric for a few inches aft of the seat back tubing to hold the fabric out. Although I'm willing to spend a few pounds in weight on the whole airframe for drag reduction, I have a feeling that the drag reduction for the weight might not be worth it.
Using VG's would look like a bandaid (and maybe not work at all)
Opinions?
