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Prop clearence on Kolb Mark 111 extra

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Frankd

Joined: 28 Mar 2008
Posts: 64

Posted: Fri Mar 28, 2008 4:43 pm Post subject: Prop clearence on Kolb Mark 111 extra

Hi Guys, 

 

This may not be a Kolb question per se, but you guys might know the answer. 

I am mounting a Jabiru 2200 on a Kolb Mark 111 extra with a Prince Aircraft 63" prop. (P/N 419.877,5557)

 

The clearance at the tip of the prop away from the Fuselage body near the tail tube is 2.5 inches. 

 

At normal operating RPM's , what flex should I expect at the tips of the prop?  Do I have enough clearance from the aircraft body? 

 

Also, is this a good engine/prop combo?  

 

Appreciate any input. 

Rgds

FrankD

rowedenny

Joined: 09 Mar 2008
Posts: 338
Location: Western PA

Posted: Fri Mar 28, 2008 5:25 pm Post subject: Prop clearence on Kolb Mark 111 extra

Frank,

That should be more than enough clearance. Mine only has 1.5 inch clearance, 

many have less.

Also, as long as your Jabiru is a newer model and not one of the first 

generation you will have plenty of performance.

The earlier Jab 2200 did not have nearly as much power as the current models 

and were not as viable.

I'll also post an old message from lister R Neilson regarding an X- tra with 

a 2200 that he saw at a fly in.

Stay tuned,

Dennis Rowe Mk-3, 2SI 690L-70



 	  Quote: 	
		   Hi Guys,



 This may not be a Kolb question per se, but you guys might know the 

 answer.

 I am mounting a Jabiru 2200 on a Kolb Mark 111 extra with a Prince 

 Aircraft 63" prop. (P/N 419.877,5557)



 The clearance at the tip of the prop away from the Fuselage body near the 

 tail tube is 2.5 inches.



 At normal operating RPM's , what flex should I expect at the tips of the 

 prop?  Do I have enough clearance from the aircraft body?



 Also, is this a good engine/prop combo?



 Appreciate any input.

 Rgds

 FrankD

JetPilot

Joined: 10 Jan 2006
Posts: 1246

Posted: Fri Mar 28, 2008 6:48 pm Post subject: Re: Prop clearence on Kolb Mark 111 extra

I don't know anything about your prop, but 2.5 inches on clearance from the boom is actually considered a lot of clearance for a Kolb, that is about what I have on my 912-S Xtra.   



Some people take the clearance down to an inch or so, but I don't want any chance of a strike.  The downside to having more clearance like we do is a little more pitch down with power, and more pitch up when you go to idle, but my plane flys great, so I am happy with a over 2 inches of clearance more for those sometimes rough startups.



Prop tips in general should not flex much, the centrifugal force of rotation keeps most props straighter when running than when stopped.   What kind of prop is that ???



Mike

_________________
"NO FEAR" - If you have no fear you did not go as fast as you could have !!!

Kolb MK-III Xtra, 912-S

Steve Boetto

Joined: 11 Jan 2006
Posts: 365

Posted: Sat Mar 29, 2008 4:33 am Post subject: Prop clearence on Kolb Mark 111 extra

In a message dated 3/28/2008 10:51:25 P.M. Eastern Daylight Time,  orcabonita(at)hotmail.com writes:

  	  Quote: 	
		  

Prop    tips in general should not flex much, the centrifugal force of rotation keeps    most props straighter when running than when stopped.   What kind of    prop is that ???



Mike

	
 Mike, I am not sure where you  got your info on prop flex. The tips of  an Ivo  Prop flex forward in excess of an inch. Other props flex less. On a  Kolb with an upswept boom this tends to increase clearance, However, it can  dramatically decrease clearance to the back of the wing.

  	  Quote: 	
		  

    

   Steve    B

Firefly 007/Floats

do not  archive

	


Create a Home Theater Like the Pros. Watch the video on AOL Home.

  [quote][b]

Frankd

Joined: 28 Mar 2008
Posts: 64

Posted: Sat Mar 29, 2008 9:52 am Post subject: Re: Prop clearence on Kolb Mark 111 extra

Thanks for the reply's everyone. 



The Prince Aircraft prop came with the engine when I got it.  It is listed in the Aircraft Spruce Catalogue and has unique drooping tips built in that is designed to enhance performance.. Its a wood core with glass finish and that is why I did not know about flex forward under power. 

Just to be clear, the clearance I measured is from the prop tip forward to the fuselage cage.  I have seen prop flex on Cessna's when in power run-up but it's minimal.  Since I don't have my wings attached yet, I did not even think about clearance from the training edge.. 



It sounds like there is enough clearance even if the prop does flex some, from your guys experience. I will continue as is. 



On a related note, what is the ideal incidence of the engine thrust line in relation to the wing bottom?  Should it be the same incidence?   I got an engine mount from Titan aircraft to fit the Jabiru to the MkIII Extra and would like to verify incidence before I bolt it all down finally. 

Now at the stage of spraying silver on all the fabric so aiming to have it all ready for flight THIS year...  thats as close as I will aim for.. 

Good feedback.. Thanks

f

ElleryWeld(at)aol.com
Guest

Posted: Sat Mar 29, 2008 4:20 pm Post subject: Prop clearence on Kolb Mark 111 extra

I understand that Prince P-Tip Propeller is  a  good match for your application  However I think you are going to need more  of an extension on your prop to give you more room between the back of your  Fuselage Trailing edge of wings and your prop,  some of the other guys on  this list was explaining they had less clearance  than what you have but  they was talking about clearance between the prop tip and the Boom tube not the  back of there Fuselage  Just trying to verify this info correctly for  you  

  

 Ellery in Maine 

 do not archive

  

  In a message dated 3/29/2008 12:55:33 P.M. Eastern Standard Time,  frankd(at)foundrynet.com writes:

  	  Quote: 	
		  -->    Kolb-List message posted by: "Frankd"    <frankd(at)foundrynet.com>



Thanks for the reply's everyone.    



The Prince Aircraft prop came with the engine when I got it.  It    is listed in the Aircraft Spruce Catalogue and has unique drooping tips built    in that is designed to enhance performance.. Its a wood core with glass finish    and that is why I did not know about flex forward under power.    

Just to be clear, the clearance I measured is from the prop tip    forward to the fuselage cage.  I have seen prop flex on Cessna's when in    power run-up but it's minimal.  Since I don't have my wings attached yet,    I did not even think about clearance from the training edge.. 



It    sounds like there is enough clearance even if the prop does flex some, from    your guys experience. I will continue as is. 



On a related note, what    is the ideal incidence of the engine thrust line in relation to the wing    bottom?  Should it be the same incidence?   I got an engine    mount from Titan aircraft to fit the Jabiru to the MkIII Extra and would like    to verify incidence before I bolt it all down finally. 

Now at the    stage of spraying silver on all the fabric so aiming to have it all ready for    flight THIS year...  thats as close as I will aim for.. 

Good    feedback.. Thanks

f





Read this topic online    here:



http://forums.matronics.com/viewtopic.php?p=173455#173455

	




Create a Home Theater Like the Pros. Watch the video on AOL Home.

  [quote][b]

mdnanwelch7(at)hotmail.co
Guest

Posted: Sat Mar 29, 2008 4:53 pm Post subject: Prop clearence on Kolb Mark 111 extra

 	  Quote: 	
		  

 Just to be clear, the clearance I measured is from the prop tip forward to the fuselage cage. I have seen prop>flex on Cessna's when in power run-up but it's minimal. Since I don't have my wings attached yet, I did not even>think about clearance from the training edge..


	


 	  Quote: 	
		  Frank


	




  Frank,



  I don't think everyone understood your reference correctly, regarding the prop clearance.  I, for one, thought you were referring to the distance from the blade tip, to the boom tube.  That is the usual measurement when people 

talk about prop clearance.



  If you are talking about only 2 1/2" clearance from the blades to the back of the fuselage, then, NO, I do not think you have enough clearance.  Although I am very not familiar with Prince "P tip" props, and how much they flex, I think for air cavitations reasons alone, you'd want to get a prop extension.



  I can imagine a scenario where you may pull up into a powered climb, and flex that prop just enough to contact the back of the fuselage.   It seems entirely possible to me.   It may not be likely, but I think it "possible".  The catastrophic results would not seem to be worth the chance, I would think.



  Another thing to consider is; no matter what testing and observations you do on the ground, you never can fully tell how the flexing will act in the air, under a climbing load.



  I believe the absolute minimum distance you need between the back of the fuselage and the front of the prop blades is at least 4", and 6" would be even better to aim for.



  This is definitely a subject you want to investigate, and have a proper remedy to.  I'd highly recommend calling the Prince Prop company and asking to speak to their man'in'charge, and see what he says.



  Doesn't a prop extension seem like a good idea, in this case, knowledgable Kolb guys?



Mike Welch

MkIII



PS.  The prop flex on my Cessna 172 is probably a 3/4"...if it's that much.   That's because it is solid aluminum alloy.  A composite prop will flex many times what a solid aluminum one will, and they are made to do just that, namely flex.

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gaman(at)att.net
Guest

Posted: Sat Mar 29, 2008 6:04 pm Post subject: Prop clearence on Kolb Mark 111 extra

Frank,

   my mk-3C W2200 jabiru has more clearance  than that.You may want to contact Kolb as they had a mount for Jabiru at one time .I think wing/flap clearance will be more of a concern than rear of  fuselage.As best I can recall I have almost a foot of fuselage clearance.High rpm props make a lot of noise on a pusher,and my MK-3 is no exception.The 2200 is a sweet running engine.

                                     G.Aman,MK-3C Jabiru 2200,298 hrs.



---

j.codd(at)btopenworld.com
Guest

Posted: Sun Mar 30, 2008 12:48 am Post subject: Prop clearence on Kolb Mark 111 extra

Hi Frank, here in the UK we all run Jabiru  2200's on our Mk3 Xtras, your main clearance problem will be propellor to the  flaps/torque tubes on the wing, New Kolb supplied our engine mounts for the  Jabiru equipped Xtras, and you will also need the 2 1/2" prop shaft extension  supplied by Jabiru.

 I also use the Prince P tip prop, a 62" x 41",  these props are ideally suited to the Jab in the Xtra, but don't forget that  they have anhedral and when loaded up in the climb they twist and reduce  pitch to get a better climb, I believe this moves the tips forward which would  bring the tips nearer to the flap/aileron torque tubes than a simple static  measurement would indicate, I would suggest a phone call to Donny at Prince  Propellors would be adviseable to see what movement forward (if any) there is on  this prop in the climb, 

 Rgds, John Codd, Mk111 Xtra, Jabiru  2200.

  

  

  

  

 [quote]   ---

rowedenny

Joined: 09 Mar 2008
Posts: 338
Location: Western PA

Posted: Sun Mar 30, 2008 4:46 am Post subject: Prop clearence on Kolb Mark 111 extra

Thanks Ellery,

 That is correct, I was refering to boom clearance, I have a  lot more than that to the trailing edge.

  

 Denny rowe

 [quote]   ---

JetPilot

Joined: 10 Jan 2006
Posts: 1246

Posted: Sun Mar 30, 2008 7:24 am Post subject: Re: Prop clearence on Kolb Mark 111 extra

Frank,



It does seem that you are talking about prop clearance from the prop to the Fuselage structure forward of it, not clearance to the boom.   If that is the case, 2 1/2 inches is not enough.   Even though the prop blades to do not bend much in flight ( Someone quoted 1 inch ) which sounds reasonable..  The engine is mounted on Rubber mounts, and it is possible for the engine to twist, and move around a bit in its mounts.  This small but normal movement of the engine will translate to a much larger movement at the prop tips.   Combine the bit of prop twist you get forward, with the engine movement, and its very possible that the prop could strike the structure that is only 2 1/2 inches forward.



I have a 4 inch spacer between my Rotax 912-s and prop.  If the prop is to close to the wing / fuse, you will get more noise, more beating on the fabric from the prop.  If the prop does hit something forward of it, its a pretty good bet that it will come apart and cause not only an engine out, but could rip the engine from its mounts, making the aircraft uncontrollable.  This is a pretty serious safety item, which is why I used over 2 inches from my boom, and a 4 inch spacer to give me lots of room between the prop and the wings.



Mike

_________________
"NO FEAR" - If you have no fear you did not go as fast as you could have !!!

Kolb MK-III Xtra, 912-S

JetPilot

Joined: 10 Jan 2006
Posts: 1246

Posted: Sun Mar 30, 2008 7:34 am Post subject: Re: Prop clearence on Kolb Mark 111 extra

[quote="Steve Boetto"]



Prop flex forward in excess of an inch. Other props flex less. On a  Kolb with an upswept boom this tends to increase clearance, However, it can  dramatically decrease clearance to the back of the wing.

 [quote]



Steve

    

Given a 70 inch prop, and that I have more than 6 inches of clearance between my prop and wings,  I consider 1 inch of flex to be minimal    I think the engine twisting in is rubber mounts has more potential to change clearances than flexing of the prop.  The two strokes start pretty smooth, but the 912's have a lot of travel in the rubber mounts, and can move around quite a bit on start.  I do not have any figures on this, but I would bet that gyroscopic forces move the engine around a bit in flight also.  It does not take much engine movement to translate into more than 1 inch at the prop tips.

Mike

_________________
"NO FEAR" - If you have no fear you did not go as fast as you could have !!!

Kolb MK-III Xtra, 912-S

by0ung(at)brigham.net
Guest

Posted: Sun Mar 30, 2008 8:02 am Post subject: Prop clearence on Kolb Mark 111 extra

Doesn't a prop extension seem like a good idea, in this case, knowledgable

Kolb guys?



Mike Welch

MkIII

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


	


YES   a prop extension helped a bit with performance (3mh) , less noise, and

less worry.



Boyd

MkIII c  

912ul 3 inch ext, on warp prop.

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