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slingshot thrust line

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tc1917(at)bellsouth.net
Guest

Posted: Mon Oct 25, 2010 2:12 am Post subject: slingshot thrust line

I am going to jump in here because I believe the SS has the engine thrust 

line too far back.  I hope you get this pic of my SS with the 912.  The 582 

had about the same thrust line as my 912 only adjusted for the power.  If 

you dont raise the back of the engine on the mount you will be virtually 

pushing the nose over.  The entire airframe will be fighting.  You MUST 

raise the rear mounts from 3/4 to maybe 7/8 of an inch (one guy went more 

than that) in order to correct the angle of attack.  I bet you have a really 

heavy stick or a lot of bungee stretch to compensate.  At 7/8 at the rear of 

the mounts, you will be able to fly virtually hands off at your regular 

cruise rate and not have to fight it on take off.  I bet you got a handful 

when you firewall the engine at take off.  Not just my opinion, fact on this 

one and if you dont believe, well, fight it in the air.  Raise the rear of 

the engine a little at a time and you will see the difference in the first 

quarter inch.  You will notice the angle of the blade in relation to the 

boom.  This really works.  Trust me.  Ted Cowan, Slingshot, 912UL, zoom zoom

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aoldman(at)xtra.co.nz
Guest

Posted: Mon Oct 25, 2010 9:46 pm Post subject: slingshot thrust line

Yep that worked for me on the MK111c. Packed the back up with 2 washers. 

There is a slight pitch up when you throttle back  from cruse rpm by about 

200 rpm . The pitch up is so slight that it is no more than a "be aware this 

will happen" it is normal, when some one is flying the Kolb for the first 

time . I was trying to get the prop away from the boom at the bottom to 

reduce noise. Not sure that worked , but I like the way it fly's now . I 

have never measured the angles . Just changed things a little and went 

flying .

Down under

MK111c

Thom Riddle

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

Posted: Tue Oct 26, 2010 3:01 am Post subject: Re: slingshot thrust line

Ted,



You are correct regarding full power take-off. It becomes a handful quickly so I don't add full power until I'm airborne, and then only gradually.



I guess I'll try a little at a time as others have suggested but will probably end up with about what you have. My concern is that the Jabiru mount is a steel pad virtually identical in size to the steel pad on the Kolb and is 2 or 3 inches square or perhaps larger. So it is not like the Rotax that have vertical bolts through the slightly flexible Lord mounts. It is steel to steel which means I will need tapered shims. The Lord mounts have horizontal bolts between the steel tubing Jabiru mount and the Jabiru engine which you can see clearly in one or two of Chris's photos, and in the attached photo from my SS.



This is why it is not just a matter of simply inserting washers. If it was that simple it would have been done long ago.

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.
- Anonymous

pj.ladd(at)btinternet.com
Guest

Posted: Tue Oct 26, 2010 6:46 am Post subject: slingshot thrust line

<<You are correct regarding full power take-off. It becomes a handful 

quickly so I don't add full power until I'm airborne, and then only 

gradually.>>



When you are airborne is NOT when you need to apply full power.



Back to basics. Were we not all taught to apply full power GRADUALLY and 

increase speed GRADUALLY?. If that is done then all the normal corrections 

of rudder and stick should take care of problems. Too much power too soon, 

before you have full control and the torque will get you.

The phase when we are all vulnerable is when we are low so grab height as 

quickly as you can. That means full power BEFORE you leave the ground.

Don`t we run full power checks to make sure that full power is available for 

take off?

I am a comparative newbie on the Kolb compared to some of you but I flew my 

Challenger, with the same problem of a high mounted pusher for some while 

and the same applies

Of course the Challenger with a tricycle gear didn`t have quite the same 

problems as a tail dragger

How about cutting the Kolb boom down to get rid of the rear weight and 

convert to trike u/c. It was done with the Thruster, probably the most 

numerous type in the UK. When I had one in the early days it was a tail 

dragger but there are very few left now. New ones are built with a trike u/c 

and nearly all the old ones have converted. I am surprised that one of you, 

with the freedom which you have to Experiment hasn`t had a go at that.

Now THAT aught to start a new thread

Cheers



Pat

rickofudall

Joined: 19 Sep 2009
Posts: 1392
Location: Udall, KS, USA

Posted: Tue Oct 26, 2010 6:48 am Post subject: slingshot thrust line

Thom, I don't have a Slingshot, but I do have a small machine shop. You draw up the shims you need and I'll make them for the cost of material and mailing. If you're using AN3 bolts to attach the Jabby engine mount buying 16 new bolts shouldn't set you back more than $20 and neither will any shims. $40 seems awfully cheap to fix a problem and put your mind at ease. 



Rick Girard



On Tue, Oct 26, 2010 at 6:01 AM, Thom Riddle <riddletr(at)gmail.com (riddletr(at)gmail.com)> wrote:

 	  Quote: 	
		   --> Kolb-List message posted by: "Thom Riddle" <riddletr(at)gmail.com (riddletr(at)gmail.com)>

 

 Ted,

 

 You are correct regarding full power take-off. It becomes a handful quickly so I don't add full power until I'm airborne, and then only gradually.

 

 I guess I'll try a little at a time as others have suggested but will probably end up with about what you have. My concern is that the Jabiru mount is a steel pad virtually identical in size to the steel pad on the Kolb and is 2 or 3 inches square or perhaps larger. So it is not like the Rotax that have vertical bolts through the slightly flexible Lord mounts. It is steel to steel which means I will need tapered shims. The Lord mounts have horizontal bolts between the steel tubing Jabiru mount and the Jabiru engine which you can see clearly in one or two of Chris's photos, and in the attached photo from my SS.

  

 This is why it is not just a matter of simply inserting washers. If it was that simple it would have been done long ago.

 

 --------

 Thom Riddle

 Buffalo, NY (9G0)

 Kolb Slingshot SS-021

 Jabiru 2200A #1574

 Tennessee Prop 64x32

 

 

 “Everyone is entitled to his own opinion, but not his own facts.”

 Daniel Patrick Moynihan

 

 

 

 

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 http://forums.matronics.com/viewtopic.php?p=317062#317062

 

 

 

 

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-- 

Zulu Delta

Kolb Mk IIIC

582 Gray head

4.00 C gearbox

3 blade WD

Thanks, Homer GBYM

It is not bigotry to be certain we are right; but it is bigotry to be unable to imagine how we might possibly have gone wrong.

  - G.K. Chesterton



 



  [quote][b]

_________________
The smallest miracle right in front of you is enough to make you happy....

Thom Riddle

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

Posted: Tue Oct 26, 2010 7:01 am Post subject: Re: slingshot thrust line

Rick,



Thanks a bunch for your offer. I will gladly take you up on it. I'll get the drawings to you as soon as I can. Have to take some dimensions first, probably not until the weekend.



Thanks again.

_________________
Thom Riddle
Buffalo, NY (9G0)

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

Dana

Joined: 13 Dec 2007
Posts: 1047
Location: Connecticut, USA

Posted: Tue Oct 26, 2010 8:35 am Post subject: slingshot thrust line

At 10:44 AM 10/26/2010, Pat Ladd wrote:



  	  Quote: 	
		  How about cutting the Kolb boom down to get rid of the rear weight and convert to trike u/c. It was done with the Thruster, probably the most numerous type in the UK. When I had one in the early days it was a tail dragger but there are very few left now. New ones are built with a trike u/c and nearly all the old ones have converted. I am surprised that one of you, with the freedom which you have to Experiment hasn`t had a go at that. 	


 Most of us prefer taildraggers... why take a perfectly good airplane and put a training wheel on it? 



 -Dana



 do not archive

 --

  Politicians and diapers have one thing in common.  They should both be changed regularly, and for the same reason.    [quote][b]

John Hauck

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

Posted: Tue Oct 26, 2010 9:01 am Post subject: slingshot thrust line

Gang:

  

 I feel like Dana.  I like Kolbs the way Homer  designed them.

  

 I have experience flying and demonstrating the  first Sling Shot powered with a 582.  I did not detect any adverse flight  characteristics with it.  Flew a TV videographer at Lakeland.  Had fun  wringing out the SS, low level through the cabbage palms and pastures south of  Lakeland.  There is a Kolb video clip with part of that flight on it on  Youtube.

  

 I also have experience flying TNK's Rotax 912ULS  SS.  No perceived problems with it.

  

 I can not remember if there was any kind of  modifications to the engine mounts.  I think if there were, it would have  been pretty obvious to me.

  

 I experimented with different thrust lines with my  FS and my mkIII.  Always going back to the factory recommended  settings.

  

 When I take off in any model Kolb, I go full  throttle immediately, but like any other aircraft, I don't jam the throttle  forward.

  

 Kolbs are good aircraft.  The only aircraft I  fly.  We have some pilots that seem to have problems flying them.   Maybe they need more training and flight time.  

  

 I am not saying that individuals that change the  engine thrust line is wrong.  Everyone is free to do as they wish with  experimental aircraft.  I am saying I could not find justification in my  Kolbs to keep changes I  made.  Maybe I was doing it wrong.   ;-(

  

 My own personal opinion.

  

 john h

 mkIII - 3,000.00+ hours airframe

 912ULS - 440.00+ hours engine

 [quote]    Most of us prefer taildraggers... why take    a perfectly good airplane and put a training wheel on it?    



-Dana

 

[b]

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

jbhart(at)onlyinternet.ne
Guest

Posted: Tue Oct 26, 2010 5:33 pm Post subject: slingshot thrust line

At 07:15 AM 10/25/10 -0700, you wrote:

 	  Quote: 	
		  


	


Thom,

 	  Quote: 	
		  

The other problem with this that Chris alluded to is that the point and 
	


angle at which the thrust is acting is so far aft of the CG that it results 

in a significant nose down pitching moment when adding power, more so I 

believe than if the thrust was parallel to relative wind. 

 	  Quote: 	
		  


	


The nose down rotation due to the addition of power is caused by the thrust 

line (moment arm) passing above aircraft vertical cg.  The higher the thrust 

line the greater the moment arm and the more the nose wants to go down. To 

compensate, one must apply stick back pressure to maintain constant level 

flight.  This in turn applies additional load to the tail which must also be 

picked up by the wing.  This effect is not influenced by the point of thrust 

application, pusher or tractor if the thrust line is parallel to the 

relative wind.



If the thrust line is angles up to and above the relative wind. then point 

of application can have some effect.  As above one would expect greater nose 

down effect as the thrust line is rotated upward for the pusher 

configuration as this again increases the moment arm relative to the 

vertical cg.  Also if the thrust vector is not parallel to the relative 

wind, power factor will be present.  One can detect this by making steep 

banks to the right and to the left.  If power factor is present, the plane 

will bank much easier or feel more solid in one direction than the other. 

I added an attachment to help describe what is going on.  It can be seen at:



http://jackbhart.com/firefly/pf&thr.jpg



Jack B. Hart FF004

Winchester, IN

aoldman(at)xtra.co.nz
Guest

Posted: Tue Oct 26, 2010 10:21 pm Post subject: slingshot thrust line

Yep ,got me why would you put a wheel on the front of a Thruster. Learned to 

fly in one of those  . Did my first 100 hrs in one . Not many proplems with 

that wheel way out the back. It was a early one that was built for a 447 but 

was running a 503 so round outs tended to be a bit sudden. You could wheel 

it on sooo smooth you could hardly feel it was on the ground. My instructor 

hated that . Three point it he would say ,I did get good at that after a 

while.

Downunder

MK111c

pj.ladd(at)btinternet.com
Guest

Posted: Wed Oct 27, 2010 1:16 am Post subject: slingshot thrust line

Not many proplems with that wheel way out the back.>>



Hi,

I had none.. Aftre coming from gliding the Thruster was the machine I 

trained on and didn`t know that threepointing was supposed to be difficult.

The Challenger was easier though although I always landed with the weight 

firmly on the mains and the nose held high

Cheers



Pat

pj.ladd(at)btinternet.com
Guest

Posted: Wed Oct 27, 2010 6:05 am Post subject: slingshot thrust line

put a training wheel on it? 



Dana,  

 love it...training wheel heh  heh

  

 I bought a Kolb because I fell in love with the  design about 3 airplanes back. Then the opportunity came about. I had been in a  Eurostar partnership which dissolved and I found myself with about 20K not  earmarked for other things.

 This coincided with a distributor picking up the  import rights from another company who had decided not to sell |Kolbs any  more.

 So the Kolb became available in the UK  at the  time I had some cash.

 Having trained on the taildragger Thruster the  thought of going back to a rear wheel after the trike u/c Challenger was not a  problem. In fact, once I got back into the habit, and with differential  footbrakes it was nearly as easy to handle as the trike u/c.

 Although I am well pleased with my Mk111Xtra I  cannot forget the ease of ground handling  which goes with a `training  wheel`. No problems with weathercocking or nosing over if I braked too hard and  very little trouble keeping straight even if the throttle was pushed flat out  from a standing start. No different handling on grass or tarmac even in a brisk  sidewind.

 Must be a good reason why the military went for a  wheel up front after about the DC3 and the B-17.

  

 Training wheel.......

  

 Cheers

  

 Pat

   [quote][b]

Richard Pike

Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee

Posted: Wed Oct 27, 2010 6:41 pm Post subject: Re: slingshot thrust line

Ok, for those of you that think a MKIII would be better with a nose (training) wheel, here's your chance to put your money where your mouth is. I have for your inspection a Gen U Wine nose wheel for a MKIII, $15 for the trouble to box it up plus what ever shipping turns out to be.



All 4130 steel construction, made from Gen U Wine cub jury struts plus what ever else I had handy. Built in pitot and static air tubes, already calibrated. Remove 6 of the the screws that attach the nose cone and screw it in place. Non-swiveling, so you no longer have to worry about running off the runway. 



The only thing it is good for is it allows you to do full throttle run ups with two aboard without having to worry about standing the airplane on it's nose.



Why did I make it? I don't remember, but as Butch Cassidy said to Sundance Kid in the movie, "It seemed like a good idea at the time."



Richard Pike

MKIII N420P (420ldPoops)

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pj.ladd(at)btinternet.com
Guest

Posted: Thu Oct 28, 2010 2:56 am Post subject: slingshot thrust line

I have for your inspection a Gen U Wine nose wheel for a MKIII, $15 >>



Gee, thank you Richard. Such kindness. You are all heart



However to make this a working proposition I am afraid that there may be 

other expenses incurred.



1) making the wheel swivel



2) under the general heading of moving the weight off the rear wheel

a)slide the boom forward

b) transfer the engine from the top of the cockpit to the bit of the boom 

which is now sticking out the front

c)reverse the engine to make a tractor configuration, (this will make the 

whole thing quieter)



3) It is probable that with the low position of the protruding boom (and 

engine)the cockpit will blank the airflow to the tail unit so perhaps that 

should be transferred to another boom protruding from the rear of the 

cockpit top.



4) With the propellor now being mounted low the u/c legs will have to be 

lengthened to give the prop ground clearance



5) The cockpit door will now be so high that a small ladder should be 

carried.



6) These changes will certainly move the  MAUW outside the limits of  the UK 

`microlight` spec. and this will incur extra insurance, a different flying 

license which will mean   more training and new exams to be passed. 

Different rules for maintenance will apply and I shall have to employ a 

mechanic.



You can see Richard that the costs do not stop at $15 so in view of my 

impecunious state I am sorry that I shall have to refuse your kind offer.



However it is heartwarming to see how members of this wonderful List are so 

keen to help out others.



Cheers



Pat

Richard Pike

Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee

Posted: Thu Oct 28, 2010 4:57 am Post subject: Re: slingshot thrust line

 	  pj.ladd(at)btinternet.com wrote: 	
		   <snip> 

You can see Richard that the costs do not stop at $15 so in view of my 

impecunious state I am sorry that I shall have to refuse your kind offer.

However it is heartwarming to see how members of this wonderful List are so keen to help out others.



Cheers



Pat 	




Wow - and I thought my wife knew how to haggle...   So - I need to send it to you for nothing plus pay you $15? (You don't work for our current political administration do you?)



Richard Pike

MKIII N420P (420ldPoops)

rickofudall

Joined: 19 Sep 2009
Posts: 1392
Location: Udall, KS, USA

Posted: Thu Oct 28, 2010 5:43 am Post subject: slingshot thrust line

Pat, You've misunderstood the application. Here are two pictures of the original application for this type of augmented landing gear on a somewhat larger scale. It's a nose over wheel just like that used on the Barling Bomber. No need to add all that extra stuff, just bolt it on and be on your way. If you apply too much power too early, your plane comes over on it's nose and continues on its merry way. I'm surprised the regulators in the EU haven't made it a requirement already.  



Rick



On Thu, Oct 28, 2010 at 5:53 AM, Pat Ladd <pj.ladd(at)btinternet.com (pj.ladd(at)btinternet.com)> wrote:

 	  Quote: 	
		   --> Kolb-List message posted by: "Pat Ladd" <pj.ladd(at)btinternet.com (pj.ladd(at)btinternet.com)>

 



 I have for your inspection a Gen U Wine nose wheel for a MKIII, $15 >>

 

 Gee, thank you Richard. Such kindness. You are all heart

 

 However to make this a working proposition I am afraid that there may be other expenses incurred.

 

 1) making the wheel swivel

 

 2) under the general heading of moving the weight off the rear wheel

 a)slide the boom forward

 b) transfer the engine from the top of the cockpit to the bit of the boom which is now sticking out the front

 c)reverse the engine to make a tractor configuration, (this will make the whole thing quieter)

 

 3) It is probable that with the low position of the protruding boom (and engine)the cockpit will blank the airflow to the tail unit so perhaps that should be transferred to another boom protruding from the rear of the cockpit top.

  

 4) With the propellor now being mounted low the u/c legs will have to be lengthened to give the prop ground clearance

 

 5) The cockpit door will now be so high that a small ladder should be carried.

 

 6) These changes will certainly move the  MAUW outside the limits of  the UK `microlight` spec. and this will incur extra insurance, a different flying license which will mean   more training and new exams to be passed. Different rules for maintenance will apply and I shall have to employ a mechanic.

  

 You can see Richard that the costs do not stop at $15 so in view of my impecunious state I am sorry that I shall have to refuse your kind offer.

 

 However it is heartwarming to see how members of this wonderful List are so keen to help out others.



 

 Cheers

 

 Pat 

 

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 ="_blank">http://www.matronics.com/contribution

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-- 

Zulu Delta

Kolb Mk IIIC

582 Gray head

4.00 C gearbox

3 blade WD

Thanks, Homer GBYM

 It is not bigotry to be certain we are right; but it is bigotry to be unable to imagine how we might possibly have gone wrong.

 - G.K. Chesterton

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_________________
The smallest miracle right in front of you is enough to make you happy....

pj.ladd(at)btinternet.com
Guest

Posted: Thu Oct 28, 2010 11:46 pm Post subject: slingshot thrust line

I'm surprised the regulators in the EU haven't made it a requirement  already.  >>

  

 Hi Richard,

  

 I am sure they are thinking about it.  After  seeing the picture of the `training wheel` in use I can quite see that my  worries about the `knock on` effects of fitting the wheel were groundless.   I think that the ladder may still come in useful.

  

 Pat

 



   [quote][b]

pj.ladd(at)btinternet.com
Guest

Posted: Thu Oct 28, 2010 11:46 pm Post subject: slingshot thrust line

(You don't work for our current political administration do you?)



I am Obama`s best (only) friend.



Pat

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