Avid Airdale with Harley engine on barnstormers

[ne14Yah 0]

Correct the engine issues and CG check and go fly the dang thing!  If there were no issues or surprises with the crow hops, there is no reason to re-engineer it.

Allen, did you take a look at the picture that shows the prop and the cowl opening?  Did you notice that they are not parallel showing my engine to be canted up?  John Larson told me that any any engine should have a 1.5 degree down thrust line against the center line to counter P factor.  I want to make sure it is inherently safe to fly and the geometry is according to design.

[Allen Sutphin 705]

"P" factor  would be the left/ right line.  But its your plane, do as you think best. As for the picture, Ray Charles could see the difference, but you could shim the mount, engine, or redo the cowling. But if you don't know how it flys now, you wouldn't know the results of whatever you do. Positive or negative or no change. A lot of planes have a 1.5 deg down mount, a lot don't so you could be worrying about something that doesn't exist. My final comment on the subject!

[1avidflyer 1983]

I run a 64" 2 blade warp drive on my Jabiru.  Some guys go with 60" on their Jabirus.   While it's not maybe the most efficient set up for this type of plane, those props will fly these planes fairly well when the prop has the correct pitch.  Maybe your mechanic miss spoke, and meant to say over propped.  My understanding of terms is  underpropped = not enough prop.  Over propped = to much prop.  Not enough prop will allow the engine to over rev, to much prop and you wont make enough rpm to get all the power out of the engine.    Anyone else want to chime in??? Am I wrong in my termenalogy ??   JImChuk

[MnAvidFlyer 34]

I run a 64" 2 blade warp drive on my Jabiru.  Some guys go with 60" on their Jabirus.   While it's not maybe the most efficient set up for this type of plane, those props will fly these planes fairly well when the prop has the correct pitch.  Maybe your mechanic miss spoke, and meant to say over propped.  My understanding of terms is  underpropped = not enough prop.  Over propped = to much prop.  Not enough prop will allow the engine to over rev, to much prop and you wont make enough rpm to get all the power out of the engine.    Anyone else want to chime in??? Am I wrong in my termenalogy ??   JImChuk

Jim

I feel your explanation is correct. The first thing I would do is to set the static RPM as stated and also check the carbs and jetting.

Brooks

[ne14Yah 0]

"P" factor  would be the left/ right line.  But its your plane, do as you think best. As for the picture, Ray Charles could see the difference, but you could shim the mount, engine, or redo the cowling. But if you don't know how it flys now, you wouldn't know the results of whatever you do. Positive or negative or no change. A lot of planes have a 1.5 deg down mount, a lot don't so you could be worrying about something that doesn't exist. My final comment on the subject!

Allen, John Larson is an engineer and the designer of the Avid Mark IV/Airdale and others.  He advised me that P factor effects both the right/left and up/down torque tendencies.  Just reporting from what he said.  I greatly appreciate everyone's wisdom and advice!

[TJay 1041]

Allen, John Larson is an engineer and the designer of the Avid Mark IV/Airdale and others.  He advised me that P factor effects both the right/left and up/down torque tendencies.  Just reporting from what he said.  I greatly appreciate everyone's wisdom and advice!

And a pretty good one I love the Airdale But I do agree with others The airplane does fly so just have fun with it. About the engine bog that will probably go away when you take some pitch out of that prop.  Don't know till you try right. I think once you get it figured out you will love that plane. And if the engine don't work out for ya I think you could hang anything from a Rotax, Yamaha, Subaru, or even a Honda on it.

[ne14Yah 0]

As suspected, looks like the thrust line is an issue.  Spent the better part of 2 days dialing in the jetting.  Purring nicely now.  Straightened out a miss-rigged tail wheel to the rudder (canted off center relative to the rudder).  Prop pitch had been 10 degrees on one blade and 9 degrees on the other.  As mentioned, didn't seem to be producing enough airspeed, so increased to 13 degrees.  Producing 4600 rpm static, so in the ball park I suspect.  High speed taxing seems to feel like we are getting somewhere.  So, today was the day I was going to take her up.  Thankfully it was a nice cool morning with light wind down the runway.  Expected to get light around 40 or so, but nothing.  Increased to above 50 and knew something wasn't right.  Still nothing.  Made the mistake of forcing off the runway and the rodeo began.  Wild porpoising with it wanting to stick to the runway like a magnet.  Looks like we will be modifying the engine mount.  Should have trusted my instincts.  Thankfully, no harm done, but could have easily been a real bad day.

[1avidflyer 1983]

What was the static rpm before you adjusted the prop?   Not arguing with your assessment, but I still wonder why my Jabiru powered Avid flys fine with the prop perpendicular to the wing and yours doesn't.  Wonder also how the horizontal stabilizer lined up with the wing on each plane.  Maybe I'll put a straightedge on it when I go to the hangar after I finish typing this message.  Also, did you ever say what your CG numbers are?  JImChuk

[Allen Sutphin 705]

I guess I am getting ready to jump into the same thing with my model 2. Have to build an engine mount for it and as of right now plan on centering it on the fuselage, level with no offset. I can't seem to find a 503 mount for a model 2.

Edited 23 Mar 2019 by Allen Sutphin

[TJay 1041]

I guess I am getting ready to jump into the same thing with my model 2. Have to build an engine mount for it and as of right now plan on centering it on the fuselage, level with no offset. I can't seem to find a 503 mount for a model 2.

I got one for the Kitfox its 503/582 if you need some measurements I should just sell it because Ill never use it Maybe.

[Allen Sutphin 705]

I guess I am getting ready to jump into the same thing with my model 2. Have to build an engine mount for it and as of right now plan on centering it on the fuselage, level with no offset. I can't seem to find a 503 mount for a model 2.

I got one for the Kitfox its 503/582 if you need some measurements I should just sell it because Ill never use it Maybe.

I'd be interested in buying it if you decide to part with it.  If not maybe a couple good pictures? Thanks!  I plan on using a Hirth 55 hp but its the same mount.

Edited 23 Mar 2019 by Allen Sutphin

[ne14Yah 0]

I wasn't focusing on static rpm at the time I was playing with the jetting, so no static run before.  All it wanted to do was load up when reducing power.  It was obviously running too rich.  I spoke with a Harley guy who confirmed it and electronic timing was not advanced enough.  1Avidflyer, my wing is not a flat bottom chord like yours.  It's more semi-symetrical.  My instinct is telling me that the relative wind is not hitting the wing correctly.  It also has a lot of wash-out, so at the wing tips, the relative wind is on top of the wing.

[ne14Yah 0]

1Avidflyer, do you have any washout in your wing?  If so, how much?

[TJay 1041]

Glad to hear you got to fly it. 

[1avidflyer 1983]

Well before I went flying this evening I did some checking.  I pulled a string down the cord of the wing, (front to back) and when the sting was just touching the bottom of the trailing edge, I had the same dimention front and back on the horizontal stabilizer.  That is to say, the bottom front and back of the wing and the horizontal stabilizer are parallel  with one another.  I have the STOL/ Heavy Hauler style ribs, so it is not a flat bottom, but undercamnbered.  If I was you, that is something I would check out as well.  If the front of the stabilizer is to high, the tail will want to come up, but not the nose of the plane.  I have the standard wash out in my Heavy Hauler wings, about 1 1/4" if I remember right.  I'll ask again, and these are some numbers you should know without hardly thinking about it.  What is you empty CG in flying attitude?  What is redline supposed to be for this engine set up?  And some handy info, to know would also be: how much static thrust are you making at full throttle.  At 300 lbs and above, the plane should fly as far as power goes.   JImChuk

[ne14Yah 0]

Jim, on page 1 I laid out that for the most part the HS, wing root cord and thrust line are all parallel, but the thrust line is about .5 degree tilted back from being parallel.  You can see how severe it is tilted back in the close-up pic i posted.  I do not have any info regarding a "red line" other than a piece of red tape on the tach @ 5500.  The wash-out is about 3.5 degrees, what ever that works out in inches.  I don't have the CG info handy, but empty it is more forward in it's acceptable range - so more nose heavy.  I am hoping to measure static thrust soon.  Waiting on my IA friend to assist when he has some time.

[TJay 1041]

Well before I went flying this evening I did some checking.  I pulled a string down the cord of the wing, (front to back) and when the sting was just touching the bottom of the trailing edge, I had the same dimention front and back on the horizontal stabilizer.  That is to say, the bottom front and back of the wing and the horizontal stabilizer are parallel  with one another.  I have the STOL/ Heavy Hauler style ribs, so it is not a flat bottom, but undercamnbered.  If I was you, that is something I would check out as well.  If the front of the stabilizer is to high, the tail will want to come up, but not the nose of the plane.  I have the standard wash out in my Heavy Hauler wings, about 1 1/4" if I remember right.  I'll ask again, and these are some numbers you should know without hardly thinking about it.  What is you empty CG in flying attitude?  What is redline supposed to be for this engine set up?  And some handy info, to know would also be: how much static thrust are you making at full throttle.  At 300 lbs and above, the plane should fly as far as power goes.   JImChuk

Jim thanks for taking time to do that good helpful info

[TJay 1041]

As suspected, looks like the thrust line is an issue.  Spent the better part of 2 days dialing in the jetting.  Purring nicely now.  Straightened out a miss-rigged tail wheel to the rudder (canted off center relative to the rudder).  Prop pitch had been 10 degrees on one blade and 9 degrees on the other.  As mentioned, didn't seem to be producing enough airspeed, so increased to 13 degrees.  Producing 4600 rpm static, so in the ball park I suspect.  High speed taxing seems to feel like we are getting somewhere.  So, today was the day I was going to take her up.  Thankfully it was a nice cool morning with light wind down the runway.  Expected to get light around 40 or so, but nothing.  Increased to above 50 and knew something wasn't right.  Still nothing.  Made the mistake of forcing off the runway and the rodeo began.  Wild porpoising with it wanting to stick to the runway like a magnet.  Looks like we will be modifying the engine mount.  Should have trusted my instincts.  Thankfully, no harm done, but could have easily been a real bad day.

Don't want to argue with you because I'm not like that but maybe it just takes  different style to fly this thing.  I know Tom Said it flew really good and you said your mechanic flew it 3 times with no surprises other than lack of power. Maybe there is nothing wrong with it just a lot heavier than your kitfox 2 was? Just throwing it out there.  Either way just get it flying you'll enjoy it.

[ne14Yah 0]

Finally able to get briefed from my IA friend who hopped it down the runway.  He said it "just doesn't want to fly."  He barely was able to get it a couple of feet in ground effect after "prying it off of the runway."  He suspects it's a combination of not enough prop, low lift wing design and not enough wing incidence (Not sure of the thrust line issue - will look into it more when he's out next).  I sat right seat on his 3rd run to monitor engine gauges and on that run, he said we were at 65/70 mph and it would not fly.  He also commented that he did not feel it was safe to fly it around the patch.  I wish I had that information prior to my attempt the other day.   We will be discussing needed changes hopefully this week when he is out to test another prop and check pulls.  Bottom line, I am not going to be able to 'just fly it and have fun.'

[ne14Yah 0]

Anyone have  HH STOL wings they want to sell?  Or perhaps some insight as to how someone can assemble the parts needed to build a set?  I had originally planned on doing so anyway, but now it looks like a priority.

[1avidflyer 1983]

I think you are barking up the wrong tree looking for a different set of wings.  I do have a set however that need the rib tails repaired.  These airplanes are not that complicated.  Speedwings have flown these planes ok with a lot less wing area then what you have.  Here are some actual numbers that I would like to see you produce.  Actual location of the CG in inches.  Actual washout in the wings, (use a 4' level and tape measure to see how much difference there is between the most inboard rib front to back and the most outboard rib front to back)  Check both sides for that matter to make sure the wings aren't way out of rig with each other.  Actual diameter of the prop.  And for that matter, Is the prop turning in the correct direction.  Don't laugh at that one, there were posts about this plane about a year ago, and the warp drive prop that was on there then was backwards.   The warp drive label should be on the back side of the blade.  In other words, you should be able to see it from the cockpit.  What is the ratio of the reduction drive?   Lastly, this back and forth on the computer is nice, but I think sometimes an actual conversation with immediate back and forth is more helpful to arrive at a solution.  

PS  here is the old thread where the prop is on backwards.  www.avidfoxflyers.com/index.php?/topic/5671-airdale/#comment-50957

 

Edited 25 Mar 2019 by 1avidflyer

[ne14Yah 0]

-  W&B shows datum at leading edge of wing.  Forward CG is 11.185 aft.  Aft CG is 16.5.  With 200 lb pilot and 90 lbs of fuel, the CG is 14.28  Dry weight is 744.  Gross is 1400 design/1320 legal.

-  Washout is 2 3/4" on right wing 2 3/8" on left wing. Left wing can be adjusted.  Right is fixed.  Leading and trailing edges are straight.

-  Prop is 68 1/2" diameter, right hand turning in right direction.  Blades facing proper direction.

-  1.92:1 belt reduction drive

*  With horizontal stabilizer held up at level, the left wing experiences negative incidence (relative wind hitting top surface).

[1avidflyer 1983]

-  W&B shows datum at leading edge of wing.  Forward CG is 11.185 aft.  Aft CG is 16.5.  With 200 lb pilot and 90 lbs of fuel, the CG is 14.28  Dry weight is 744.  Gross is 1400 design/1320 legal.

Those are the same CG numbers on other Avids as well, so if your calculations are correct, 14.28" is certainly a good place to be in and shouldn't be your problem.  

-  Washout is 2 3/4" on right wing 2 3/8" on left wing. Left wing can be adjusted.  Right is fixed.  Leading and trailing edges are straight.

I looked at my manual, and it says that for the Aerobat wing you want 1 1/2" wash out, and 2" washout for the Heavy Hauler wing.  I'm guessing the length is the determining factor here more then the different style of rib.  That measurement is made on the spars from front to back, so if you went with the whole wing, from leading edge to trailing edge, it seems like your are the ball park on the amount of washout. I scanned a couple of pages from the manual that show this stuff.  I'll add those pages at the end.

-  Prop is 68 1/2" diameter, right hand turning in right direction.  Blades facing proper direction.

-  1.92:1 belt reduction drive

If you could turn 5500 your tip speed would be about 78% of the speed of sound, so that's not in a bad place.

 

*  With horizontal stabilizer held up at level, the left wing experiences negative incidence (relative wind hitting top surface

 

Have a look at the last picture, if it's drawn to scale, it looks like what you describe.  and yet that plane flys fine.  Don't think that is your problem either.  Ever figure out how much static thrust you are developing?

 

 

 

 

Edited 28 Mar 2019 by 1avidflyer

[ne14Yah 0]

I measured the washout from the underside of the leading edge to the trailing edge.  Would be greater than from spar to spar, so probably was set at 2".  The static rpm is 4600 with 13 degrees pitch - about 2400 then at the prop on the ground.  With the airframe being stretched 16" over a standard Avid MK4, would the CG be slightly different or would you expect it to be the same?

[1avidflyer 1983]

I don't think stretching the fuselage changes the CG envelope for the wing.  It would of course move the actual location of the CG for that plane rearward, just like adding weight to the tail would.