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slow flying MkIII's

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mdnanwelch7(at)hotmail.co
Guest

Posted: Thu Jun 03, 2010 6:23 am Post subject: slow flying MkIII's

Jason,

 

  Regarding your MkIII flying slower than other MkIIIs, I am sure you know it has an "attributable" cause.  By that I mean, there is a definite, definable, specific reason.....not

some nebulous unknown.

 

  For a comparison of one MkIII against another near identical MkIII, with virtually the same power input;

if someone else's MkIII flies faster than yours, then the only other possiblities are drag and propeller efficiency.

Your plane may have all kinds of unique differences than someone else's MkIII, and these will undoubtedly cause your plane to perform different (assuming the same power input)

 

  A couple of things NOT offered so far are your wing's incidences, compared to your horizontal stabilizers incidence.  

  The greater the difference between your main wing's incidences and your tailfeathers incidences, the more you main wings will "plow" through the air. (meaning---serious drag!!!!)

  

   When I did quite a bit of MkIII incidence research last year, I found some significant disparities between some of the MkIII's wings' incidences.  Example;  one guy "reports" as much as 2.5 degrees difference between his MkIIIX and the other MkIIIXs' wings vs hor stabs.  That's a lot!!

  Obviously, if in fact he is correct about his 2.5 degree difference with the other's angles, then his plane will fly VERY different than theirs will (either faster or slower).

  BTW, when I say "drag", it can come in the form of MANY ways.  Weight differences will vary drag, wing incidences, quality of workmanship, etc.  All these things, and more, can affect drag.

   Dana was correct when he reported " to double your airspeed, it will take 8 times the power.  You can see why John H's experience makes such sense......from the power of a Rotax 582 to a Rotax 912ULS, not a lot of change in airspeed.  So, the next big question is;

 How efficient is your propeller at converting that 100HP?  A "climb" prop will ALWAYS run out of pitch for higher airspeeds, compared to a "cruise prop!!  Maybe your solution is as simple as adjusting your prop's pitch to take a bigger bite at the air.  ???

  

   Have you used a digital level and read your airplane's angles compared to other MkIIIs, and the factory recommended settings?  (I can show you what I came up with, if you need me to.)

  

   There's not a lot of unexplainable reasons why your plane may not be as fast as other

 MkIIIs.  (Actually, there aren't ANY unexplainable reasons)  Your answer(s) will be either 

 A)drag, or 

 B) how your propeller is adjusted to transfer it's power to the air.

  

   Am I forgetting anything?

  

   Just my thoughts......

  

 Mike Welch

 MkIII CX

  

 PS.  I'm just back from my Alabama/Florida week-long vacation.   Sheesh!!!  Between the Kolblist and Aeroelectric---over 200 emails in a week!!!  Tough to catch up on!

  

 		 	   		  Hotmail has tools for the New Busy. Search, chat and e-mail from your inbox. Learn more.  [quote][b]

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Thu Jun 03, 2010 7:42 am Post subject: slow flying MkIII's

Mike:

  

 How about the high thrust line pusher configuration  of our Kolbs?  especially the heavier models?

  

 How does this affect Kolbs'  performance?

  

 How does this affect incidence of wing and  horizontal stabilizer?

  

 How does adjustment of flaps and ailerons affect  pitch trim?

  

 How's the best way to pitch a ground adjustable  prop for optimum

 climb and cruise?

  

 john h

 mkIII

  

  

 [quote]   ---

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

mdnanwelch7(at)hotmail.co
Guest

Posted: Thu Jun 03, 2010 9:20 am Post subject: slow flying MkIII's

Hi John,



 



  I hope you're healing okay.  Sorry to hear about your injuries.



  



  It would be easier to make comments inside your response, so.......

 



Mike:

 

How about the high thrust line pusher configuration of our Kolbs?  especially the heavier models?

 

How does this affect Kolbs' performance?

 

We're talking about one MkIII against all other MkIIIs, so a high pusher configuration isn't really in question (I would think).

 

 How does this affect incidence of wing and horizontal stabilizer?

 

  A high thrust line would likely want to push the nose down, I'd guess.  But still, with two Kolb MkIIIs, both with their engines in the same positions, a high thrust line most likely won't make one perform different from the other....if all other things were absolutley identical.

 

How does adjustment of flaps and ailerons affect pitch trim?

 

  This would be one of those things I was referring to that would affect drag.

Of course, the adjustment of flaps and ailerons can create unneccessary

drag, making one MkIII fly slower than another.

 

How's the best way to pitch a ground adjustable prop for optimum

climb and cruise?

 

  By flight testing it.  He could read it's present angle.  Re-adjust it for a steeper pitch.  Go try it out.  Re-adjust, etc, etc.  At some point, he's going to have to make a decision on the setting he liked the best.  Some MkIII's may climb out like a rocket, but they give up some faster cruising speeds to do so.  Possibly an in-flight adjustable pitch prop might help in this regard.

  Speaking of props;

  Back when I was buying my engine (GEO w/ Raven Redrive) he recommended the Ivo In-flight adjustable.  Not having much experience, I went with his recommendation.  Maybe it was a good idea.  Maybe not.  I haven't flown with it yet, so I don't know.

  I have read lots of reports/opinions about other brands of props.  Most people seem to recommend Warp Drive.

  I have also heard that props in the "Less than 200 mph" range don't really need to be adjustable.  Maybe so.

  I suppose if I were shopping for a prop today, maybe I'd choose another brand.  Too late, tho, I already have one.  Not enough money to make the change.

 

  John,

 

  Were you possibly misunderstanding my response to Jason?  Did you think I meant ALL MkIIIs were slow?  If this is what you thought, you misunderstood me.  I think MkIIIs (all models) fly just fine!!!!  75 mph to 80 mph cruise is pretty darn good in my book!!!!

  I was simply making the observation that there are very few reasons why one virtually identical plane doesn't fly exactly like another.

Usually, these reasons are not too hard to figure out, either.  Drag, or prop efficiency.  Not too many reasons for two identical planes to not fly the same.

 

  Hope you heal quickly!

 

Mike Welch

 

 



---

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Thu Jun 03, 2010 10:12 am Post subject: slow flying MkIII's

Mike/Folks:

  

 When we build airplanes in our basements, we end up  with a lot of different airplanes with the same model designation.  Ain't  no two alike.  Too many variables.

  

 MKIIIs hit a brick wall about 95 mph.  At that  point additional thrust is consumed by the power it requires to overcome the  high thrust line.  You can't change that unless you go tractor or  reposotion thrust line to the center of mass.  Thus, similar cruise and top  speed by low to high powered engines.

  

 Adjustment/tuning of flaps and ailerons has a  dramatic affect on pitch.  Nose down adverse pitch is considerable because  of the high thrust line.

  

 I wrote about a good method of pitching a ground  adjustable prop for best climb and cruise recently.  Wide open throttle  (WOT), straight and level flight, just bump the red line for max continuous  rpm.  This produces optimum climb and cruise in a Kolb.

  

 I am anxious to read your flight report of your  inflight adjustable prop.

  

 In fact, I am anxious to hear your flight  reports.  You will gain a much better understanding of Kolb aircraft after  you actually fly one.

  

 I understand your post.

  

 Not all mkIII's are slow.

  

 I was curious what your response to my  questions would be.

  

 There is a lot more to it than props and  drag.

  

 No two Kolbs are built identically.

  

 Using my method of pitching the prop, you don't  give up climb for cruise, or cruise for climb. m If you over pitch or under  pitch, you will end up chasing your tail.

  

 Interesting to note:

  

 Using this method to pitch prop on two stroke  powered Kolbs, a new  two stroke out of the box with factory tuning and  proper expansion chamber will fly with EGT and CHT in the green, throughout its  performance band.

  

 Us old farts that have been flying Kolbs for a  while have not been sitting on our hands all these years.  I was 44 years  old when I built and flew my first Kolb aircraft.  That 26 years and many  experiments and test ago.  We pretty much know what we can expect from our  Kolbs.

  

 john h

 mkIII

  

  

 [quote]   



Hi    John,

 

  I hope you're healing okay.  Sorry to hear    about your injuries.

     

  It would be easier to make comments inside your response,    so.......



 

   Mike:

    

   How about the high thrust line pusher    configuration of our Kolbs?  especially the heavier models?

    

   How does this affect Kolbs'    performance?

    

   We're talking about one MkIII    against all other MkIIIs, so a high pusher configuration isn't really in    question (I would think).

    

    How does this affect incidence of wing and    horizontal stabilizer?

    

     A high thrust line    would likely want to push the nose down, I'd guess.  But still, with    two Kolb MkIIIs, both with their engines in the same positions, a high    thrust line most likely won't make one perform different from the other....if    all other things were absolutley identical.

    

   How does adjustment of flaps and ailerons affect    pitch trim?

    

     This would be one of    those things I was referring to that would affect drag.

   Of course, the adjustment of flaps    and ailerons can create unneccessary

   drag, making one MkIII fly slower    than another.

    

   How's the best way to pitch a ground adjustable    prop for optimum

   climb and cruise?

    

     By flight testing    it.  He could read it's present angle.  Re-adjust it for a    steeper pitch.  Go try it out.  Re-adjust, etc, etc.  At some    point, he's going to have to make a decision on the setting he liked the    best.  Some MkIII's may climb out like a rocket, but they give up    some faster cruising speeds to do so.  Possibly an in-flight adjustable    pitch prop might help in this regard.

     Speaking of    props;

     Back when I was buying my    engine (GEO w/ Raven Redrive) he recommended the Ivo In-flight    adjustable.  Not having much experience, I went with his    recommendation.  Maybe it was a good idea.  Maybe not.  I    haven't flown with it yet, so I don't know.

     I have read lots of    reports/opinions about other brands of props.  Most people seem to    recommend Warp Drive.

     I have also heard that props    in the "Less than 200 mph" range don't really need to be adjustable.     Maybe so.

     I suppose if I were shopping    for a prop today, maybe I'd choose another brand.  Too late, tho, I    already have one.  Not enough money to make the change.

    

        John,

    

     Were you possibly    misunderstanding my response to Jason?  Did you think I meant ALL    MkIIIs were slow?  If this is what you thought, you misunderstood    me.  I think MkIIIs (all models) fly just fine!!!!  75 mph to 80 mph    cruise is pretty darn good in my book!!!!

     I was simply making the    observation that there are very few reasons why one virtually identical plane    doesn't fly exactly like another.

   Usually, these reasons are not too    hard to figure out, either.  Drag, or prop efficiency.  Not too many    reasons for two identical planes to not fly the same.

    

     Hope you heal    quickly!

    

   Mike Welch

    

    

   [quote]     ---

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

mdnanwelch7(at)hotmail.co
Guest

Posted: Thu Jun 03, 2010 11:23 am Post subject: slow flying MkIII's

 

 John,

 

 

  .ExternalClass .ecxhmmessage P {padding-bottom:0px;padding-left:0px;padding-right:0px;padding-top:0px;} .ExternalClass BODY.ecxhmmessage {font-family:Verdana;font-size:10pt;}   Mike/Folks:

  

 When we build airplanes in our basements, we end up with a lot of different airplanes with the same model designation.  Ain't no two alike.  Too many variables.

 Yep!

  

 MKIIIs hit a brick wall about 95 mph.  At that point additional thrust is consumed by the power it requires to overcome the high thrust line.  You can't change that unless you go tractor or reposotion thrust line to the center of mass.  Thus, similar cruise and top speed by low to high powered engines.

 Ah, but then we're not talking about Kolb MkIIIs, anymore.  No fair changing the subject.

  

 Adjustment/tuning of flaps and ailerons has a dramatic affect on pitch.  Nose down adverse pitch is considerable because of the high thrust line.

 All forms of drag.

  

 I wrote about a good method of pitching a ground adjustable prop for best climb and cruise recently.  Wide open throttle (WOT), straight and level flight, just bump the red line for max continuous rpm.  This produces optimum climb and cruise in a Kolb.

 I think Jason might benefit from this method.  It may give him that extra speed he's looking for.

  

 I am anxious to read your flight report of your inflight adjustable prop.

 Yeah, you and me both!!  Being just a builder lost it's luster long ago.

  

 In fact, I am anxious to hear your flight reports.  You will gain a much better understanding of Kolb aircraft after you actually fly one.

 Understatement.

  

 I understand your post.

 Good.  I hate to be misunderstood.

  

 Not all mkIII's are slow.

 Obviously NOT!

  

 I was curious what your response to my questions would be.

 Hard to be totally accurate via email.  No personal input.  Sometimes you can't get a clarification before you have to respond.

  

 There is a lot more to it than props and drag.

 Nope, props and drag.  That's all.  All the particular things you mentioned 

 are to affect props and drag (when talking about two identical airplanes)

 Since the subject is; ALL mKIIIs flying compared to Jason's MkIII, unless some goofball has changed his MkIII radically (Heads up, looking around), they should all fly the same, or very close to the same.  If one MkIII flies radically different, then the answer will be found in prop efficiency (which can be simply adjustment) or reducing drag.    And drag comes in the form of a million ways......workmanship, adjustments, engine fairings, incidences, parasitic drag, on and on.........drag.

  

 No two Kolbs are built identically.

 Neither are women.  Men, however, are all the same.  Am I right, ladies?

  

 Using my method of pitching the prop, you don't give up climb for cruise, or cruise for climb.  If you over pitch or under pitch, you will end up chasing your tail.  ( I think this is what Jason should check on)

 I think what you are describing is "an optimum pitched prop".  I think Jason may not have his prop pitched this way.  That's what I was talking about.

  

 Interesting to note:

  

 Using this method to pitch prop on two stroke powered Kolbs, a new  two stroke out of the box with factory tuning and proper expansion chamber will fly with EGT and CHT in the green, throughout its performance band.

  

 Us old farts that have been flying Kolbs for a while have not been sitting on our hands all these years.  I was 44 years old when I built and flew my first Kolb aircraft.  That 26 years and many experiments and test ago.  We pretty much know what we can expect from our Kolbs.

 Can't argue with experience....unless you're a fool.         Mike

  

 john h

 mkIII

  

  

 [quote] 



Hi John,

 

  I hope you're healing okay.  Sorry to hear about your injuries.

  

  It would be easier to make comments inside your response, so.......



 

 Mike:

  

 How about the high thrust line pusher configuration of our Kolbs?  especially the heavier models?

  

 How does this affect Kolbs' performance?

  

 We're talking about one MkIII against all other MkIIIs, so a high pusher configuration isn't really in question (I would think).

  

  How does this affect incidence of wing and horizontal stabilizer?

  

   A high thrust line would likely want to push the nose down, I'd guess.  But still, with two Kolb MkIIIs, both with their engines in the same positions, a high thrust line most likely won't make one perform different from the other....if all other things were absolutley identical.

  

 How does adjustment of flaps and ailerons affect pitch trim?

  

   This would be one of those things I was referring to that would affect drag.

 Of course, the adjustment of flaps and ailerons can create unneccessary

 drag, making one MkIII fly slower than another.

  

 How's the best way to pitch a ground adjustable prop for optimum

 climb and cruise?

  

   By flight testing it.  He could read it's present angle.  Re-adjust it for a steeper pitch.  Go try it out.  Re-adjust, etc, etc.  At some point, he's going to have to make a decision on the setting he liked the best.  Some MkIII's may climb out like a rocket, but they give up some faster cruising speeds to do so.  Possibly an in-flight adjustable pitch prop might help in this regard.

   Speaking of props;

   Back when I was buying my engine (GEO w/ Raven Redrive) he recommended the Ivo In-flight adjustable.  Not having much experience, I went with his recommendation.  Maybe it was a good idea.  Maybe not.  I haven't flown with it yet, so I don't know.

   I have read lots of reports/opinions about other brands of props.  Most people seem to recommend Warp Drive.

   I have also heard that props in the "Less than 200 mph" range don't really need to be adjustable.  Maybe so.

   I suppose if I were shopping for a prop today, maybe I'd choose another brand.  Too late, tho, I already have one.  Not enough money to make the change.

  

   John,

  

   Were you possibly misunderstanding my response to Jason?  Did you think I meant ALL MkIIIs were slow?  If this is what you thought, you misunderstood me.  I think MkIIIs (all models) fly just fine!!!!  75 mph to 80 mph cruise is pretty darn good in my book!!!!

   I was simply making the observation that there are very few reasons why one virtually identical plane doesn't fly exactly like another.

 Usually, these reasons are not too hard to figure out, either.  Drag, or prop efficiency.  Not too many reasons for two identical planes to not fly the same.

  

   Hope you heal quickly!

  

 Mike Welch

  

  

 [quote] ---

Jason Omelchuck

Joined: 07 May 2009
Posts: 120
Location: Portland Oregon

Posted: Thu Jun 03, 2010 12:02 pm Post subject: Re: slow flying MkIII's

Hello John,



What I read you as saying is your engine never will see the 5800 Max RPM (max for 5 min) under normal conditions (only if you are descending).  The max RPM you would ever see would be 5500 RPM and that would be at WOT in level flight.  



Jason



[quote="John Hauck"]  

 I wrote about a good method of pitching a ground  adjustable prop for best climb and cruise recently.  Wide open throttle  (WOT), straight and level flight, just bump the red line for max continuous  rpm.  This produces optimum climb and cruise in a Kolb.  

 [quote]

John Bickham

Joined: 10 Jan 2006
Posts: 170
Location: St. Francisville, LA

Posted: Thu Jun 03, 2010 2:53 pm Post subject: Re: slow flying MkIII's

Just to add to the little discussion on Mark IIIC speeds and their different speeds.



First thing that I wonder about is rear cage covering.  Is it a reasonable assumption that the faster machines may have the fuselage covered ala Ms P'fer.  Does this help reduce drag and provide cleaner are for the prop to bite on?



My personal opinion based on my experience we will never know what makes one Kolb model faster than another.  To explain....  Some of you might know that I bent my Kolb headed to MV in 2004.  Landed in short hayfield because of dumb pilot decision making.



Took the opportunity to make modifications that would make her a real XC machine.  Increased fuel capacity from 14 gallons to 22 gallons.  Made my own landing gear and put on the 8.50 x 6.0 tires.  Trying to imitate success.  The only other thing I did was make some new tube and fiberglass seats which ended up being lighter weight than my first attempt.  



Eventually put all back together and much too my surprise, the plane flew more than 10 mph faster.  Same engine, same prop/pitch setting.  Mike B talked about a sweet spot at a certain rpm.  Prior to the mods, my sweetspot was 4800 rpm and about 62 mph.  After the rebuild,  the sweetspot shifted to 5100 rpm and 75 mph.  I can't keep up with dem 100 hp 912's but I'm close and don't have to use as much or as expensive premium gas.



Just one more change that has to do with the fabric covered fueslage.  First build was one continuous piece.  This caused fabric drumming which may have increased the vibration, drag, and dirty air to prop.  Second covering after mods, I used John Williamson's method of individual pieces rolled up to next joint and start new section with overlap to next tube. 



The only other possibility is that when I hit the ground hard, I knocked the plane "into" trim????  Lucky I didn't break a leg or hand or worse  !!!



Fly 'em.  A few mph ain't nothing but about 5 minutes on a 150 mile XC leg!!!

_________________
Thanks too much,

John Bickham
Mark III-C w/ 912UL
St. Francisville, LA

I know many pilots and a few true aviators. There is a distinct difference that I have the greatest respect for.

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Thu Jun 03, 2010 4:00 pm Post subject: slow flying MkIII's

> What I read you as saying is your engine never will see the 5800 Max RPM 

(max for 5 min) under normal conditions (only if you are descending).  The 

max RPM you would ever see would be 5500 RPM and that would be at WOT in 

level flight.

[quote]

 Jason



 [quote="John Hauck"]

 I wrote about a good method of pitching a ground  adjustable prop for best 

 climb and cruise recently.  Wide open throttle  (WOT), straight and level 

 flight, just bump the red line for max continuous  rpm.  This produces 

 optimum climb and cruise in a Kolb.

  	  Quote: 	
		  


	




Jason/Ya'll:



That is correct.



With ground adjustable prop I pitch for max continuous rpm which is 5,500 

for both 912UL and 912ULS.



The 912UL and ULS can be operated continuously at WOT as long as it does not 

exceed 5,500 rpm.



I am not concerned with max power for 5 minutes unless I have an in-flight 

adjustable prop.



I have to settle for 95 hp instead of 100.  Never know the difference. 

Climb is exhilarating.



I never descend WOT, usually cruise power of 5,000, and normally do not 

exceed 5,500.



john h

mkIII

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

slyck(at)frontiernet.net
Guest

Posted: Thu Jun 03, 2010 4:11 pm Post subject: slow flying MkIII's

I think that aft covering makes some difference.  We need some responses from fast Kolbs (MkIIIs) that manage to

do without.  Personally, considering the kind of flying I do, a change would be a waste of effort.

BB, lots of  pipes in the breeze.



On 3, Jun 2010, at 6:53 PM, John Bickham wrote:



 	  Quote: 	
		   

 

 Just to add to the little discussion on Mark IIIC speeds and their different speeds.

 

 First thing that I wonder about is rear cage covering.  Is it a reasonable assumption that the faster machines may have the fuselage covered ala Ms P'fer.  Does this help reduce drag and provide cleaner are for the prop to bite on?

 

 My personal opinion based on my experience we will never know what makes one Kolb model faster than another.  To explain....  Some of you might know that I bent my Kolb headed to MV in 2004.  Landed in short hayfield because of dumb pilot decision making.

 

 Took the opportunity to make modifications that would make her a real XC machine.  Increased fuel capacity from 14 gallons to 22 gallons.  Made my own landing gear and put on the 8.50 x 6.0 tires.  Trying to imitate success.  The only other thing I did was make some new tube and fiberglass seats which ended up being lighter weight than my first attempt.  

 

 Eventually put all back together and much too my surprise, the plane flew more than 10 mph faster.  Same engine, same prop/pitch setting.  Mike B talked about a sweet spot at a certain rpm.  Prior to the mods, my sweetspot was 4800 rpm and about 62 mph.  After the rebuild,  the sweetspot shifted to 5100 rpm and 75 mph.  I can't keep up with dem 100 hp 912's but I'm close and don't have to use as much or as expensive premium gas.

 

 Just one more change that has to do with the fabric covered fueslage.  First build was one continuous piece.  This caused fabric drumming which may have increased the vibration, drag, and dirty air to prop.  Second covering after mods, I used John Williamson's method of individual pieces rolled up to next joint and start new section with overlap to next tube. 

 

 The only other possibility is that when I hit the ground hard, I knocked the plane "into" trim????  Lucky I didn't break a leg or hand or worse [Twisted Evil] !!!

 

 Fly 'em.  A few mph ain't nothing but about 5 minutes on a 150 mile XC leg!!!

 

 --------

 Thanks too much,

 

 John Bickham

 Mark III-C w/ 912UL

 St. Francisville, LA

 

 I know many pilots and a few true aviators.  There is a distinct difference that I have the greatest respect for.

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=299936#299936

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Fri Jun 04, 2010 2:58 am Post subject: Re: slow flying MkIII's

Speaking high thrust lines, wing incidence and HS incidence, I am wondering if the numbers on my SS are "correct". I will call Kolb and ask but thought maybe someone on the list might know what the design calls for on the SS. Attached is a drawing I borrowed from Jack Hart and edited the numbers to match my SS. 



It seems to me that the difference between my wing incidence and HS incidence (7 degrees) is greater than it should be, but this is just a guess. It also seems to me that my thrust line angle is way too high (3.5 degrees pointed up relative to wing bottom, and 10.5 degrees above HS incidence). 



Any thoughts from those who know would be appreciated.

ThomSSangles.jpg

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_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Fri Jun 04, 2010 6:04 am Post subject: slow flying MkIII's

Thom:



Lot of variables in thrust line because of the design of the engine mount.



I insure I have the hardest Lord  Mount to help reduce movement on the 

mkIII.



I learned about engine excursion with my FS/447 that was equipped with 

softer Lord Mounts during engine run up while tied down.  The engine rolled 

right and forward, loading up the right front Lord Mount.



By chance I discovered how much a problem this was at WOT in the FS.  During 

a test, at WOT, the FS would not exceed 75 MPH.  I rolled off throttle until 

I unloaded the engine, then very slowly came back in with power, very 

slowly,  The FS increased speed to 85 mph.  I'm sure it was caused by 

misalignment of thrust line.  Nursing power back in kept the thrust line 

more in line as power and speed increased.



My theory on mkIII thrust line is:



912 rotates opposite two strokes, loading left front mount.



At rest, 5/8" spacers raised the front of the engine bringing thrust line 

parallel with the bottom of the wing.  In flight, thrust brings the thrust 

line back to where it was at rest.  I tested this with a flight to Point 

Barrow, Alaska, and back.  Performance figures were the same as enginge 

mounted in stock configuration on another flight to Point Barrow, Alaska, 

and back.



Travis Brown, Kolb Aircraft, provides me with the hardest Lord Mount 

available.  In addition, I insert a 2" fender washer on top the two front 

mounts.  This prevents the thrust from depressing the front mounts more than 

about 1/8" to 1/4".



Two major factors working against our mkIII's is high thrust line and the 

way the prop wash hits the tail section.



The lower the engine is mounted on the airframe the faster the mkIII will 

fly.  My engine is absolutely as low as it can be without hitting the root 

tube.



My mkIII and the other faster mkIII's have fully enclosed fuselages with the 

rear of the fuselage faired and not cut off square or not covered at all.



So, remember when you are standing there looking at your engine sitting on 

top of your Kolb at rest,  it will not be in the same position when you are 

flying.



john h

mkIII



---

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Fri Jun 04, 2010 10:17 am Post subject: Re: slow flying MkIII's

Thanks for your thoughts on Lord Mounts, John.



My mounts are very hard rubber and the engine does not appear to move much at all when tied down and run up. Unfortunately, the wet sump on the Jabiru is pretty deep which requires a fairly high mounting. My prop (only 64" diameter) clears the boom tube by at least 5-6" at rest.



My question for you (and/or others) is this. The static (at rest) thrust line of the my engine is pointing upwards 3.5 degrees relative to the bottom of the wing. Is this about right, assuming my mounts are plenty hard? Note that the axis of the motor mount bolts is not vertical like on the Rotax but parallel to the longitudinal axis of the airplane. However I can still raise one side/end vs the other because this mount bolts to the Kolb engine tube. Not sure this shows in the attached photo, but that is all I have right now and my camera keeps quitting on me. Guess it is time for a new one.

Jabiru Engine Rt Rear cropped.jpg

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Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
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John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Fri Jun 04, 2010 10:34 am Post subject: slow flying MkIII's

Yes, as a guesstimate 3.5 deg sounds about right.



john h mkIII

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John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

by0ung(at)brigham.net
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Posted: Sun Jun 06, 2010 7:34 am Post subject: slow flying MkIII's

My question for you (and/or others) is this. The static (at rest)  thrust line of the my engine is pointing upwards 3.5 degrees relative to the  bottom of the wing. Is this about right, assuming my mounts are plenty hard?  Note that the axis of the motor mount bolts is not vertical like on the Rotax  but parallel to the longitudinal axis of the airplane. However I can still raise  one side/end vs the other because this mount bolts to the Kolb engine tube. Not  sure this shows in the attached photo, but that is all I have right now and my  camera keeps quitting on me. Guess it is time for a new  one.



--------

Thom Riddle

 	  Quote: 	
		  >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

  
	


 not sure about the sling shot.....   the   bottom of the mkIII  wing has 9 deg positive incidence in  flight.   if I read your post correctly you would add 3.5 deg to  that,  assuming the SS  has the same 9 deg in flight  (plus or minus), adding the 3.5 would make the front of the engine  pointing up at 12.5 deg in flight.  guess I am going to have to measure my  mike  this week...  guess in my mind I would think the engine should  have less incidence than the bottom of the wing.   making the prop  more perpendicular to the line of travel.  

  

 or am I missing something?

  

 Boyd Young

  

  

   [quote][b]

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Sun Jun 06, 2010 7:48 am Post subject: Re: slow flying MkIII's

Boyd,



That is my thought too. I would think that at cruise, the thrust line should be fairly closely aligned with the relative wind.  



BTW, I measured the angles again yesterday and came up with a little different numbers but still seems the thrust line is pointing too far up. The reason for the difference in measurement was I used the prop hub this time instead of the top of the engine.



My Slingshot wing bottom chord has an incidence of 7.5 degrees relative to the boom tube and horizontal stabilizer (parallel to boom tube). The thrust line (static) is 9.5 degrees relative to the HS & boom tube, so the engine is point up only 2 degrees rather than 3.5 degrees. But it still seems to me that it should be more aligned with relative wind at cruise AOA. 



If my SS flies at cruise with an AOA of 7.5 degrees (guess) then the thrust line (very hard mounts so not perceptible tilting under power) is not parallel to relative wind by about 9.5 degrees. 



ON THE OTHER HAND...

Perhaps this is by design to help offset the effect of the high position of the thrust line. Still waiting to hear back from Travis on this question.

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
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