Quantcast

Setting wing Incidence

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

Little Scrapper

Well-Known Member
HBA Supporter
Log Member
Joined
Jan 3, 2014
Messages
5,799
Location
Wisconsin
Hey guys. Question.

Baby Ace.

I’m currently working on the cabane structure and I need to set the incidence. I have a set of Baby Ace wings but want to use a Harry Riblett airfoil and use different ailerons etc.

Harry passed away but I did manage to have numerous conversations with him and we talked about wing incidence but I can’t remember if he said 1 degree or 2 degrees. I just cannot remember and it was so long ago I can’t find any notes.

How important is a one degree difference? While I can fabricate and build things I’m just not the engineering type so I’m looking for some guidance. Appreciate the help. Hope everyone is doing well.
 

PTAirco

Well-Known Member
Joined
Sep 20, 2003
Messages
3,577
Location
Corona CA
Most taildraggers, in my opinion don't have enough angle of attack in the three point attitude. So higher incidence there helps. Also means in cruise you have a better view over the nose. But tailplane incidence then comes into play too. If the Riblett airfoil has less or more pitching moment, that could affect things too.
 

TFF

Well-Known Member
Joined
Apr 28, 2010
Messages
13,826
Location
Memphis, TN
What is the chosen airfoil supposed to do different than the old? A faster plane would probably like less incidence while one flying slow would be more likely higher.
 

Rockiedog2

Well-Known Member
Joined
Dec 11, 2012
Messages
2,386
Rule of thumb for planes like Baby Ace, Legal Eagle etc
Set the wing chord line at +5 relative the plans HS chord line setting. Ball park setting. Trim as necessary from that. Ought not require very much.
Yeh Scrapper, I can put stuff together too but not much on the engineering. Managed to get by so far, with a little help from my friends.
 

Little Scrapper

Well-Known Member
HBA Supporter
Log Member
Joined
Jan 3, 2014
Messages
5,799
Location
Wisconsin
Appreciate the responses so far.

I’m changing airfoils because I can. I’m gonna build aluminum ailerons just like the Cub plans. Looking forward to it.
Harry told me what to expect as far as difference between the two but from what I recall it wasn’t much of a difference all things considered. It was a long time ago so my memory isn’t the best on the matter.
 

TFF

Well-Known Member
Joined
Apr 28, 2010
Messages
13,826
Location
Memphis, TN
When you lay a drawing over each other, how different are they? If they are mostly close, I would not change much. It will not fly bad. The stabilizer might have to be shimmed, but all these planes are a little different and they all end up working.

My parasol dream is to add some aerobatic symmetrical ailerons With some differential throw for the adverse yaw.
 

12notes

Well-Known Member
Lifetime Supporter
Log Member
Joined
Aug 27, 2014
Messages
1,113
Location
Louisville, KY
Since the airfoil on the Baby Ace is the Clark Y, I would guess the airfoil that is replacing it is the 30GA613.5, as that's the replacement suggested for the Clark Y in the Riblett book. The 13.5 at the end is thickness percentage, it may be a different thickness. That's just a guess, though. I can look it up and post some numbers tomorrow if you think that's a likely candidate.
 

wsimpso1

Super Moderator
Staff member
Log Member
Joined
Oct 18, 2003
Messages
7,267
Location
Saline Michigan
Scrap,

I think that the Riblett foil is a good choice. Understand that I do not know what the right answer is, but I hope to provide food for thought. A certain highly experienced tailwheel instructor you know might have some insight:

If we are trying to three-point land the beast, we want all three to touch together while the foil is tiptoeing into stall:
  • If the foil is still flying nicely when you get to three-point attitude and you touch down, I expect a bounce similar to what you get if the stick is not all the way back. Taking that same configuration all the way to stall has you putting the tailwheel on first, decreasing AOA with ground contact;
  • Going the other way, if it stalls with the tail up, all of your landings will be wheel landings, and the slow ones might be tough to manage;
  • Looks like too much incidence is better than too little, making PTAirco's advice look like a good plan;
  • Complicating all of this is that Harry's foil is not supposed to have a well defined stall - but well designed wings also tend to mush.
Airplanes fly on the wing. Set higher or lower incidence, and the wing will still fly at about the same alpha at same weight and airspeed, but your deck angle will change some. Then come the follow on stuff:
  • We align the horizontal stabilizer to put the elevator about in trail, usually at cruise. Remember that the tail operates in overall airflow modified by the downwash off the wing. Using the time proven monkey-see monkey-do engineering approach you should thus look at the difference in incidence between wing and tail of other airplanes, not the raw tail incidence to some arbitrary "level line". Rockiedog2's advice on this appears useful;
  • If you can adjust the tail incidence, either with a trim jackscrew or with shims or a series of holes, that will make life a little easier when it comes time to fly and adjust tail angle;
  • Then we align the prop (engine mount) to suit our mission - STOL may put preference on high alpha ops and a little more nose down angle on the engine. A preference for cruise efficiency will be aligned closer to the various factory angles.
I hope that this helps more than it hurts.

Billski
 

Rockiedog2

Well-Known Member
Joined
Dec 11, 2012
Messages
2,386
Leonard calls for zero on the HS relative the "backbone" reference on the fuse of the LEU (and I think all the eagles). He says mount the wing(4414) with the flat bottom at +2 relative the HS. The chord line of the wing is +3 from the flat bottom so what he's saying jives with the +5 rule of thumb for the class(speed) of planes we're talking about. Works good as long as the plane falls within the expected EWCG range. Unless that Riblett is something radical re the Clark Y I would just set it same as called in the Baby Ace plans and expect it to be easily adjustable with the HS aoi. But please don't do what I would do...I end up cuttin em up and redoing a lotta stuff
Buncha interesting stuff in here

 

TFF

Well-Known Member
Joined
Apr 28, 2010
Messages
13,826
Location
Memphis, TN
I don’t want to chase the rudder as much if it happens to roll upside down occasionally during flight. Anyway on the engineering side, why should one control fix another?
 

Little Scrapper

Well-Known Member
HBA Supporter
Log Member
Joined
Jan 3, 2014
Messages
5,799
Location
Wisconsin
Scrap,

I think that the Riblett foil is a good choice. Understand that I do not know what the right answer is, but I hope to provide food for thought. A certain highly experienced tailwheel instructor you know might have some insight:

If we are trying to three-point land the beast, we want all three to touch together while the foil is tiptoeing into stall:
  • If the foil is still flying nicely when you get to three-point attitude and you touch down, I expect a bounce similar to what you get if the stick is not all the way back. Taking that same configuration all the way to stall has you putting the tailwheel on first, decreasing AOA with ground contact;
  • Going the other way, if it stalls with the tail up, all of your landings will be wheel landings, and the slow ones might be tough to manage;
  • Looks like too much incidence is better than too little, making PTAirco's advice look like a good plan;
  • Complicating all of this is that Harry's foil is not supposed to have a well defined stall - but well designed wings also tend to mush.
Airplanes fly on the wing. Set higher or lower incidence, and the wing will still fly at about the same alpha at same weight and airspeed, but your deck angle will change some. Then come the follow on stuff:
  • We align the horizontal stabilizer to put the elevator about in trail, usually at cruise. Remember that the tail operates in overall airflow modified by the downwash off the wing. Using the time proven monkey-see monkey-do engineering approach you should thus look at the difference in incidence between wing and tail of other airplanes, not the raw tail incidence to some arbitrary "level line". Rockiedog2's advice on this appears useful;
  • If you can adjust the tail incidence, either with a trim jackscrew or with shims or a series of holes, that will make life a little easier when it comes time to fly and adjust tail angle;
  • Then we align the prop (engine mount) to suit our mission - STOL may put preference on high alpha ops and a little more nose down angle on the engine. A preference for cruise efficiency will be aligned closer to the various factory angles.
I hope that this helps more than it hurts.

Billski
Definitely helps, thank you for taking the time to write that out!

And thanks to the others as well!
 

simflyer

Well-Known Member
Joined
Sep 24, 2015
Messages
237
Location
Moravia
Since the airfoil on the Baby Ace is the Clark Y, I would guess the airfoil that is replacing it is the 30GA613.5, as that's the replacement suggested for the Clark Y in the Riblett book. The 13.5 at the end is thickness percentage, it may be a different thickness. That's just a guess, though. I can look it up and post some numbers tomorrow if you think that's a likely candidate.
Probably better Clark Y replacement would be TsAGI R-IIIa-12 or NACA 43013.5.
Interresting what I heard is, that time ago some builders set Clark Y AoA as bottom flat surface was zero.
btw most people think that Pipers are using Clark Y, buth they using USA35B and later versions added thickness on upper surface. Unfortunately haven't coords of this modified USA35B.
 

Pops

Well-Known Member
HBA Supporter
Log Member
Joined
Jan 1, 2013
Messages
8,526
Location
USA.
Friend of mine built a couple Baby Aces, second one, he built the ailerons like used on a Pitts. Made the ailerons much lighter than the ailerons built by the plans.

I always set the incidences of the wing and tail where the fuselage water line will be a couple degrees negative for better over the nose visibility when flying.
I usually set the wing and tail with about a 3.5 deg difference for a starting point. Usually the wing at + 4 degrees and the tail about +.5 degrees. The final setting will vary with the CG, etc. On the SSSC , at first I had to hold some up elevator for level flight, so I made the stab more negative with a 1/8" washer, that was to much, then I had to hold a little down elevator for level flight. Changed it to 1/16" washer, just right with the elevator trim tab at neutral.
Full up elevator trim was adjusted for my approach speed of 50 mph.
 
Last edited:
Top