Van's Air Force
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Best glide with/without flaps
- Thread starter swjohnsey
- Start date
Checked the flaps on the RV-4 to see how much I really had. I have no flap position indicator so I was setting take-off flaps by matching maximum down aileron deflection with turns out to be 16.7 degrees. Full flaps is 47.5 degrees. I put four marks on the leading edge of the flaps at 10, 20, 30 and 40 degrees. I think I will do some testing tomorrow to see if I get a better glide with 10 degrees of flaps.
You won’t, and testing will be difficult because best glide speed will change depending on flap deployment.
Your min rate of descent and max glide distances will be with flaps up
Remember TANSTAFL
There Ain’t No Such Thing As a Free Lunch.
Meaning that flaps do increase lift, but also increase drag, and very quickly the drag production exceeds the lift production.
Your method of matching flaps with aileron deflection is a good one, it’s a time tried method used by Bush Pilots for a very long time, it’s based on the theory that the manufacturer knew what they were doing and set aileron angle to where the aileron produces the most lift, before drag goes too high.
Many aircraft have three “notches” of flap, first notch produces lift with not much drag, second produces more lift, and much more drag, full flaps primarily produces drag, not much more lift than second notch but lots more drag.
Now on an aircraft that has excess thrust, min ground run can often be achieved with full flaps, this is because with enough thrust that large amount of drag can be overcome, if it’s light and has lots of power, I’d suspect an RV may fall into that category.
Pretty decent article explaining
https://www.experimentalaircraft.info/flight-planning/aircraft-best-glide-speed.php
Oh, and by the way, your method of marking flap degrees is exactly how they are marked on a Thrush Crop Duster, we had to put a light out there to illuminate the marking at night though.
Your min rate of descent and max glide distances will be with flaps up
Remember TANSTAFL
There Ain’t No Such Thing As a Free Lunch.
Meaning that flaps do increase lift, but also increase drag, and very quickly the drag production exceeds the lift production.
Your method of matching flaps with aileron deflection is a good one, it’s a time tried method used by Bush Pilots for a very long time, it’s based on the theory that the manufacturer knew what they were doing and set aileron angle to where the aileron produces the most lift, before drag goes too high.
Many aircraft have three “notches” of flap, first notch produces lift with not much drag, second produces more lift, and much more drag, full flaps primarily produces drag, not much more lift than second notch but lots more drag.
Now on an aircraft that has excess thrust, min ground run can often be achieved with full flaps, this is because with enough thrust that large amount of drag can be overcome, if it’s light and has lots of power, I’d suspect an RV may fall into that category.
Pretty decent article explaining
https://www.experimentalaircraft.info/flight-planning/aircraft-best-glide-speed.php
Oh, and by the way, your method of marking flap degrees is exactly how they are marked on a Thrush Crop Duster, we had to put a light out there to illuminate the marking at night though.
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You’ll almost certainly get off faster with that much HP, and such a light airframe.
When my Maule was light it got off fastest with full flaps because it had an IO-540 pulling on it.
However be careful. My Maule you could yank it off the ground at such a slow speed when it was light that you didn’t have enough right rudder to counter act torque.
Now I know nothing at all about an RV, never flown one, but work up to it in steps and watch for running out of right rudder.
I think some of the WWiI fighters may have had restricted power limits on take off based on not having enough rudder at slow speeds to counter the torque?
Never flown any of them either so that may be legend.
When my Maule was light it got off fastest with full flaps because it had an IO-540 pulling on it.
However be careful. My Maule you could yank it off the ground at such a slow speed when it was light that you didn’t have enough right rudder to counter act torque.
Now I know nothing at all about an RV, never flown one, but work up to it in steps and watch for running out of right rudder.
I think some of the WWiI fighters may have had restricted power limits on take off based on not having enough rudder at slow speeds to counter the torque?
Never flown any of them either so that may be legend.
fixnflyguy
Well Known Member
What I do
My -4 is , O320 160 HP, Sterba (more climb than cruise). Unless I'm on grass and looking to get off the ground quickest possible, I always take off zero flaps. These things perform so well I don't see a need, and I like to cruise climb anyway. I'd be focusing on keeping below max flap speed of 100mph not long after take-off, and its just another management point I don't need, even though I have electric flaps on the stick. I do enjoy seeing all the data points and performance numbers that others have expressed though! Its easy to drift into the STOL take performance envelope with an RV (compared to SPAM cans and what-nots)...then go really fast!
My -4 is , O320 160 HP, Sterba (more climb than cruise). Unless I'm on grass and looking to get off the ground quickest possible, I always take off zero flaps. These things perform so well I don't see a need, and I like to cruise climb anyway. I'd be focusing on keeping below max flap speed of 100mph not long after take-off, and its just another management point I don't need, even though I have electric flaps on the stick. I do enjoy seeing all the data points and performance numbers that others have expressed though! Its easy to drift into the STOL take performance envelope with an RV (compared to SPAM cans and what-nots)...then go really fast!
