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Iris Instead of Grills

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marksorenson(at)sprintpcs
Guest

Posted: Sat Jan 28, 2006 7:12 am Post subject: Iris Instead of Grills

Hello all,



Can anyone tell me if it is practical to replace the grills on the front of my Yak with an Iris type grill.  Thanks.

------------------

Best Regards,

Mark-

678-GO-FLY-HI

--------------------

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rvfltd(at)televar.com
Guest

Posted: Sat Jan 28, 2006 8:48 am Post subject: Iris Instead of Grills

Mark,

It is done more now than in the past because of the rising cost of the

individual gill shutters has made the rather high price of the titanium iris

system more in line.  I have brought in 6 sets so far and all were installed

on CJ6's.  I have no stock right now but have some on order and should see

them in 60 days or so.  You have a CJ, or 52 or?  Contact me off list if you

need more info r give me a call at 509-826-4610.



Always Yakin,

Doug Sapp

rvfltd(at)televar.com



--

dsavarese(at)elmore.rr.co
Guest

Posted: Sat Jan 28, 2006 4:47 pm Post subject: Iris Instead of Grills

Only one question.  Why?

Dennis



---

HawkerPilot2015

Joined: 10 Jan 2006
Posts: 503

Posted: Sat Jan 28, 2006 9:18 pm Post subject: Re: Iris Instead of Grills

Mark,



I have an Iris setup on my Yak-50. Main reason is the airplane did not come with the gills when I bought it. I wanted something so I could control the temps and decided on the Iris. It has quite a few less parts and in the long run, was cheaper. I DO NOT have the titanium Iris. Mine are stainless steel. 



I am still working on a way to "control" them as they are fixed right now. My temps are right where they should be. The only thing I deal with is longer warm up times. 



Something else to think about. The gills add structure to the engine cowling where the Iris does not. Mark Bitterlich can add more to this. I have not had any issues with it so far but have quite a bit less time without the gills than Mark does. Mine is ROCK solid without the gills but I am not under the impression that that will remain true and am taking steps to prevent that.



As to Dennis's question why, I think it is a simpler system with less parts. It may also be cheaper. Dennis or Doug can answer that question though..



Tim

Doug, I am interested in talking to anyone who has mounted this system. Can you put me in touch with them?

dsavarese(at)elmore.rr.co
Guest

Posted: Sun Jan 29, 2006 6:18 am Post subject: Iris Instead of Grills

My interpretation was Mark was considering changing the standard cooling 

louvers over to the iris type.  I was just wondering why someone would want 

to do that unless their existing cooling louvers were severely damaged and 

cost prohibitive to repair.

Dennis



---

HawkerPilot2015

Joined: 10 Jan 2006
Posts: 503

Posted: Sun Jan 29, 2006 6:53 am Post subject: Re: Iris Instead of Grills

 	  dsavarese(at)elmore.rr.co wrote: 	
		  My interpretation was Mark was considering changing the standard cooling 

louvers over to the iris type.  I was just wondering why someone would want 

to do that unless their existing cooling louvers were severely damaged and 

cost prohibitive to repair.

Dennis



--- 	




Ahhh...yeah I would agree that it would not be worth the effort if the existing system is intact. 



If it aint broke...dont fix it.

BitterlichMG(at)cherrypoi
Guest

Posted: Mon Jan 30, 2006 3:27 pm Post subject: Iris Instead of Grills

Hello Mark,    

This is ANOTHER "Mark" so this is bound to get confusing.  Tim mentioned my experience in regard to flying without gills, so I thought I would bring my experiences in this regard to light.    

There have been a number of people who have replaced the gill system with the IRIS system, and the conversion is fairly simple.  One thing to keep in mind is that there are two different types of systems for controlling the IRIS.  The original system found on most Sukhoi 26's and their ilk used two cables in semi hard tubes that each fed to a round wheel on the IRIS itself.  In the cockpit there is a control LEVER that pulls on one cable at a time... obviously as you pull on one cable (and put it into tension) the other moves backwards and is slack and at that point the wheel on the IRIS pulls keeping it taught.   Just picture two cables attached 180 degrees apart to the outer rim of a wheel and you'll get the picture.    

The newer method (and more preferable by far) is found on the newer SU-31's, and uses a HARD TUBE PUSH/PULL ROD very close to what controls the original YAK prop and gills.  If you get the NEWER IRIS, you should be able to use the existing YAK control that comes on the aircraft that used to control your gills.    

Ok, now the bad news.     

My YAK-50 came with the Les Crowder big spinner mod. (I mean as in HUGE.. looks good though, and I have been told that this is really a YAK-18T spinner, but I don't know for sure).  Anyway, this mod required all the gills to be removed.    

So, when I originally bought the aircraft, it had 110 hours on it since new, and away I went... no gills, no problem, who cares anyway?    

After about 150 additional hours or so, I started getting all sorts of cracking on the cowling leading edges.  Then the hollow tubes that the front of the top and bottom cowling are riveted to, started cracking too.  This problem became more serious as time went on, because at the same time, the little red tubes/struts that hold the cowl MOUNTING ring in place started to crack and break TOO!  These are the little adjustable things that bolt to the front of each cylinder and go straight out to the cowl mounting ring.    

At the time, I could not imagine what was causing all this.  When my cowl was closed, it closed fairly firmly on the front cowl ring I just described above.  I thought this might be the problem so I loosened everything up.  Wrong Answer. The problem got worse.    

I put soft fabric material between the mounting ring and the cowl ring.... this helped a little, but it could still easily be seen that things were just vibrating too darn much.  I might also mention that my two bladed prop was also out of balance quite a bit.  Balanced the prop.... and that helped, but did not STOP the problem.    

I then got the chance to study a YAK-52 up close and personal, and could see that those gills added quite a lot of support to that front cowl ring.  So, I made four adjustable struts out of stainless steel tubing.... identical in design and function to the ones coming straight out from the cylinder attachment points, but for these... I ran them out from the front of the engine supercharger cover (using the same mounting studs that the IRIS would attach to) HORIZONTALLY to the front cowl ring.  Four of them, one every 90 degrees.  These acted like spokes on a wheel, and gave back the support that the original gills had.    

Result?  Problem cured.  No more cowling damage... problem is 100% FIXED.     

This leads me to advise AGAINST putting an IRIS system on a YAK-50/52, UNLESS you also take additional steps to support that front cowl ring.  There are a lot of other factors involved here... such as: "What condition are your engine mounting rubbers in?"  Bottom line, the front of the cowls MUST MOVE WITH THE ENGINE, and if you take out the gills, you basically have a situation best pictured by imagining a person holding a HULA-HOOP out in front of himself with outstretched arms.  Then picture something/ANYTHING, "hanging from the hula-hoop itself"... you can see, there just is not any structural strength in that kind of assembly.  Put the gills in, and mount the gills to the engine itself, and you can see that the above picture regains all of its strength.    

By the bye, this is yet another reason to keep those leather mounting pads in good condition that are located on the engine itself.  These ALSO provide quite an amount of structural support to the whole upper and lower cowl.    

Sorry for the long post, but the details were needed in my opinion.     

Mark Bitterlich  

N50YK   

Here are some other interesting things that I learned the hard way about... last week!     

p.s.  Another tid bit for the YAK list.  The YAK-52/50/55 and the Sukhoi-26/29/31 AND the CJ-6, all use the exact same piston in the air-compressor relief valve.  This piston and seal are what you adjust to control the peak pressure in your air system in the aircraft.  Doug Sapp sells the whole assy. for the CJ.... and you can take it right apart, take out the piston and spring (and locking nut) and put the whole mess into your YAK, if you want to do that instead of repair what you have with a new rubber bushing.  Here's the TID BIT:  The YAK-52W (and I am GUESSING the YAK-52TW as well) has a DIFFERENT PISTON in the pressure relief assy.  It is slightly BIGGER and is NOT a direct replacement with all the others mentioned earlier. Why not?  Go figure.     

p.p.s.  YAK-52W guys... did you know that there is an emergency pressure relief valve behind the seat that allows you to eliminate emergency air pressure to the landing gear without having to crack fittings and jack and cycle the gear, if you ever do happen to open the emergency bottle valve?    

p.p.p.s.  For those aircraft with the manual engine starting valves (YAK-55, Sukhoi's) be aware that the rubber replacement tab for the starter valve MUST have a whole cut in the middle of it.  Ignore that fact, and the lever will work a few times and then fail forever. Trust me on this and save yourself a lot of head scratching.    

  

--

Ernie

Joined: 11 Jan 2006
Posts: 513

Posted: Mon Jan 30, 2006 4:23 pm Post subject: Iris Instead of Grills

do not archive

Dont apologize, thank goodness for Yak/CJ related posts



On 1/30/06, Bitterlich GS11 Mark G <BitterlichMG(at)cherrypoint.usmc.mil> wrote:

[quote]



 Hello Mark,



 This is ANOTHER "Mark" so this is bound to get confusing.  Tim mentioned my

 experience in regard to flying without gills, so I thought I would bring my

 experiences in this regard to light.



 There have been a number of people who have replaced the gill system with

 the IRIS system, and the conversion is fairly simple.  One thing to keep in

 mind is that there are two different types of systems for controlling the

 IRIS.  The original system found on most Sukhoi 26's and their ilk used two

 cables in semi hard tubes that each fed to a round wheel on the IRIS itself.

  In the cockpit there is a control LEVER that pulls on one cable at a

 time... obviously as you pull on one cable (and put it into tension) the

 other moves backwards and is slack and at that point the wheel on the IRIS

 pulls keeping it taught.   Just picture two cables attached 180 degrees

 apart to the outer rim of a wheel and you'll get the picture.



 The newer method (and more preferable by far) is found on the newer SU-31's,

 and uses a HARD TUBE PUSH/PULL ROD very close to what controls the original

 YAK prop and gills.  If you get the NEWER IRIS, you should be able to use

 the existing YAK control that comes on the aircraft that used to control

 your gills.



 Ok, now the bad news.



 My YAK-50 came with the Les Crowder big spinner mod. (I mean as in HUGE..

 looks good though, and I have been told that this is really a YAK-18T

 spinner, but I don't know for sure).  Anyway, this mod required all the

 gills to be removed.



 So, when I originally bought the aircraft, it had 110 hours on it since new,

 and away I went... no gills, no problem, who cares anyway?



 After about 150 additional hours or so, I started getting all sorts of

 cracking on the cowling leading edges.  Then the hollow tubes that the front

 of the top and bottom cowling are riveted to, started cracking too.  This

 problem became more serious as time went on, because at the same time, the

 little red tubes/struts that hold the cowl MOUNTING ring in place started to

 crack and break TOO!  These are the little adjustable things that bolt to

 the front of each cylinder and go straight out to the cowl mounting ring.



 At the time, I could not imagine what was causing all this.  When my cowl

 was closed, it closed fairly firmly on the front cowl ring I just described

 above.  I thought this might be the problem so I loosened everything up.

 Wrong Answer. The problem got worse.



 I put soft fabric material between the mounting ring and the cowl ring....

 this helped a little, but it could still easily be seen that things were

 just vibrating too darn much.  I might also mention that my two bladed prop

 was also out of balance quite a bit.  Balanced the prop.... and that helped,

 but did not STOP the problem.



 I then got the chance to study a YAK-52 up close and personal, and could see

 that those gills added quite a lot of support to that front cowl ring.  So,

 I made four adjustable struts out of stainless steel tubing.... identical in

 design and function to the ones coming straight out from the cylinder

 attachment points, but for these... I ran them out from the front of the

 engine supercharger cover (using the same mounting studs that the IRIS would

 attach to) HORIZONTALLY to the front cowl ring.  Four of them, one every 90

 degrees.  These acted like spokes on a wheel, and gave back the support that

 the original gills had.



 Result?  Problem cured.  No more cowling damage... problem is 100% FIXED.



 This leads me to advise AGAINST putting an IRIS system on a YAK-50/52,

 UNLESS you also take additional steps to support that front cowl ring.

 There are a lot of other factors involved here... such as: "What condition

 are your engine mounting rubbers in?"  Bottom line, the front of the cowls

 MUST MOVE WITH THE ENGINE, and if you take out the gills, you basically have

 a situation best pictured by imagining a person holding a HULA-HOOP out in

 front of himself with outstretched arms.  Then picture something/ANYTHING,

 "hanging from the hula-hoop itself"... you can see, there just is not any

 structural strength in that kind of assembly.  Put the gills in, and mount

 the gills to the engine itself, and you can see that the above picture

 regains all of its strength.



 By the bye, this is yet another reason to keep those leather mounting pads

 in good condition that are located on the engine itself.  These ALSO provide

 quite an amount of structural support to the whole upper and lower cowl.



 Sorry for the long post, but the details were needed in my opinion.



 Mark Bitterlich

 N50YK



 Here are some other interesting things that I learned the hard way about...

 last week!



 p.s.  Another tid bit for the YAK list.  The YAK-52/50/55 and the

 Sukhoi-26/29/31 AND the CJ-6, all use the exact same piston in the

 air-compressor relief valve.  This piston and seal are what you adjust to

 control the peak pressure in your air system in the aircraft.  Doug Sapp

 sells the whole assy. for the CJ.... and you can take it right apart, take

 out the piston and spring (and locking nut) and put the whole mess into your

 YAK, if you want to do that instead of repair what you have with a new

 rubber bushing.  Here's the TID BIT:  The YAK-52W (and I am GUESSING the

 YAK-52TW as well) has a DIFFERENT PISTON in the pressure relief assy.  It is

 slightly BIGGER and is NOT a direct replacement with all the others

 mentioned earlier. Why not?  Go figure.



 p.p.s.  YAK-52W guys... did you know that there is an emergency pressure

 relief valve behind the seat that allows you to eliminate emergency air

 pressure to the landing gear without having to crack fittings and jack and

 cycle the gear, if you ever do happen to open the emergency bottle valve?



 p.p.p.s.  For those aircraft with the manual engine starting valves (YAK-55,

 Sukhoi's) be aware that the rubber replacement tab for the starter valve

 MUST have a whole cut in the middle of it.  Ignore that fact, and the lever

 will work a few times and then fail forever. Trust me on this and save

 yourself a lot of head scratching.

 --

dsavarese(at)elmore.rr.co
Guest

Posted: Mon Jan 30, 2006 5:12 pm Post subject: Iris Instead of Grills

Mark B,

 The Les Crowder spinner is purely a Les Crowder spinner and is  not an 18T spinner.  The 18T spinner retains the original cooling  louvers.  Here's a photo of an 18T with spinner.

 Dennis

  

 

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dsavarese(at)elmore.rr.co
Guest

Posted: Mon Jan 30, 2006 5:55 pm Post subject: Iris Instead of Grills

Mark,

 You comment - 

 "YAK-52W guys... did you know that there is an emergency  pressure relief valve behind the seat that allows you to eliminate emergency air  pressure to the landing gear without having to crack fittings and jack and cycle  the gear, if you ever do happen to open the emergency bottle valve? ", this  also applies to the TW.  However, regardless of the  fact that you can depressurize the actuator AND the shuttle valves by opening  these bleed valves, a shuttle valve can stick or not properly seal when the main  air pressure is re-applied to the now depressurized actuators and shuttle  valves.  Therefore it is a very good idea to perform a normal gear  retraction after any emergency gear system activation/operation, including the  depressurization.  It's better to be safe than sorry.

  

 Also, for those that did not know, the standard Yak 52, (which  of course does not have the additional bleed valve on the right side rear  console like the W and TW), you can discharge the air pressure in the actuators  and shuttle valves by squeezing and releasing the brake handle until all the air  is depleted in the actuators and shuttle valves as long as both the main and  emergency air valves are closed beforehand.

 Dennis

  

 [quote]   ---

cjpilot710(at)aol.com
Guest

Posted: Mon Jan 30, 2006 6:20 pm Post subject: Iris Instead of Grills

I had iris on my CJ/  M14p for several years.  I personally didn't like them.  I could never  get the engine warm enough.  Even full closed there was 1 to 1 1/4  inch gap opening.

  

 They looked terrible  unpainted so I painted them.  Than the paint scraped off while opening or  closing them.

  

 Also they rattled when  curious folks would move them with their hands.  They sounded cheap  and looked cheap.

  

 I ended up buying a  55's system and totally rebuilt it.  I made my own vanes (.020 T-3 bent  over and than cut to shape.  Spot welded along the trailing edge.)  I  had to weld up worn out holes in the outer ring and cam.  I than made a  simple jig and re-drilled them.  The only things original was the outer  ring, nose plate and cam.  I've had mine on now well over 300 hours showing  minor wear.

  

 Jim "Pappy"  Goolsby

cpayne(at)joimail.com
Guest

Posted: Tue Jan 31, 2006 4:00 am Post subject: Iris Instead of Grills

Mark G wrote:

 >

 >I ran them out from the front of the

 	  Quote: 	
		  engine supercharger cover 

 Hmmm, could that be the engine gearbox cover?

 >(using the same mounting studs that the IRIS would

 	  Quote: 	
		  attach to) HORIZONTALLY to the front cowl ring.  Four of them, one every 90

degrees.  These acted like spokes on a wheel, and gave back the support that

the original gills had.  

Result?  Problem cured.  No more cowling damage... problem is 100% FIX

 >

 I too have removed the gills but left the gill outer ring in place with the original mounting rods. Since I have the Crowder spinner in place now, I'm watching it all very closely. Another problem I have noticed on cowls without gills is that the cowl skin UNDER the lower mounting brackets tend to crack through around the bracket that holds the "donuts" the pins go through. Doublers on the skin are required.

 Craig Payne

gus.fraser(at)gs.com
Guest

Posted: Tue Jan 31, 2006 5:40 am Post subject: Iris Instead of Grills

Un the Sukhoi and my SP the whole cowl is MUCH stronger  than the standard 50/52 cowl. For example, the front of the cowl is shaped like  a wing there is baffling on the inside of the cowl that gives great strength.  Also there are support arms from all cylinders to the cowl (see attached  picture) I bet you have wondered what those bolts on the front of the cylinder  were for, well guess no more because they are the mounting for the support  arms.

  

 The diameter of the cowl opening is also slightly  smaller hence the gap on a 52 cowl when the flaps are  closed.

  

 Hope this helps

  

 Gus



 [quote]         From: owner-yak-list-server(at)matronics.com    [mailto:owner-yak-list-server(at)matronics.com] On Behalf Of Bitterlich    GS11 Mark G

Sent: Monday, January 30, 2006 6:22 PM

To:    'yak-list(at)matronics.com'

Subject: RE: Iris Instead of    Grills

   

   

Hello Mark,    

This is ANOTHER "Mark" so this is bound to get    confusing.  Tim mentioned my experience in regard to flying without    gills, so I thought I would bring my experiences in this regard to    light.     

There have been a number of people who have replaced the gill    system with the IRIS system, and the conversion is fairly simple.  One    thing to keep in mind is that there are two different types of systems for    controlling the IRIS.  The original system found on most Sukhoi 26's and    their ilk used two cables in semi hard tubes that each fed to a round wheel on    the IRIS itself.  In the cockpit there is a control LEVER that pulls on    one cable at a time... obviously as you pull on one cable (and put it into    tension) the other moves backwards and is slack and at that point the wheel on    the IRIS pulls keeping it taught.   Just picture two cables attached    180 degrees apart to the outer rim of a wheel and you'll get the    picture.     

The newer method (and more preferable by far) is found on the    newer SU-31's, and uses a HARD TUBE PUSH/PULL ROD very close to what controls    the original YAK prop and gills.  If you get the NEWER IRIS, you should    be able to use the existing YAK control that comes on the aircraft that used    to control your gills.     

Ok, now the bad news.     

My YAK-50 came with the Les Crowder big spinner mod. (I mean    as in HUGE.. looks good though, and I have been told that this is really a    YAK-18T spinner, but I don't know for sure).  Anyway, this mod required    all the gills to be removed.     

So, when I originally bought the aircraft, it had 110 hours on    it since new, and away I went... no gills, no problem, who cares anyway?        

After about 150 additional hours or so, I started getting all    sorts of cracking on the cowling leading edges.  Then the hollow tubes    that the front of the top and bottom cowling are riveted to, started cracking    too.  This problem became more serious as time went on, because at the    same time, the little red tubes/struts that hold the cowl MOUNTING ring in    place started to crack and break TOO!  These are the little adjustable    things that bolt to the front of each cylinder and go straight out to the cowl    mounting ring.     

At the time, I could not imagine what was causing all    this.  When my cowl was closed, it closed fairly firmly on the front cowl    ring I just described above.  I thought this might be the problem so I    loosened everything up.  Wrong Answer. The problem got worse.        

I put soft fabric material between the mounting ring and the    cowl ring.... this helped a little, but it could still easily be seen that    things were just vibrating too darn much.  I might also mention that my    two bladed prop was also out of balance quite a bit.  Balanced the    prop.... and that helped, but did not STOP the problem.     

I then got the chance to study a YAK-52 up close and personal,    and could see that those gills added quite a lot of support to that front cowl    ring.  So, I made four adjustable struts out of stainless steel    tubing.... identical in design and function to the ones coming straight out    from the cylinder attachment points, but for these... I ran them out from the    front of the engine supercharger cover (using the same mounting studs that the    IRIS would attach to) HORIZONTALLY to the front cowl ring.  Four of them,    one every 90 degrees.  These acted like spokes on a wheel, and gave back    the support that the original gills had.     

Result?  Problem cured.  No more cowling damage...    problem is 100% FIXED.     

This leads me to advise AGAINST putting an IRIS system on a    YAK-50/52, UNLESS you also take additional steps to support that front cowl    ring.  There are a lot of other factors involved here... such as: "What    condition are your engine mounting rubbers in?"  Bottom line, the front    of the cowls MUST MOVE WITH THE ENGINE, and if you take out the gills, you    basically have a situation best pictured by imagining a person holding a    HULA-HOOP out in front of himself with outstretched arms.  Then picture    something/ANYTHING, "hanging from the hula-hoop itself"... you can see, there    just is not any structural strength in that kind of assembly.  Put the    gills in, and mount the gills to the engine itself, and you can see that the    above picture regains all of its strength.     

By the bye, this is yet another reason to keep those leather    mounting pads in good condition that are located on the engine itself.     These ALSO provide quite an amount of structural support to the whole upper    and lower cowl.     

Sorry for the long post, but the details were needed in my    opinion.     

Mark Bitterlich 

N50YK    

Here are some other interesting things that I learned the hard    way about... last week!     

p.s.  Another tid bit for the YAK list.  The    YAK-52/50/55 and the Sukhoi-26/29/31 AND the CJ-6, all use the exact same    piston in the air-compressor relief valve.  This piston and seal are what    you adjust to control the peak pressure in your air system in the    aircraft.  Doug Sapp sells the whole assy. for the CJ.... and you can    take it right apart, take out the piston and spring (and locking nut) and put    the whole mess into your YAK, if you want to do that instead of repair what    you have with a new rubber bushing.  Here's the TID BIT:  The    YAK-52W (and I am GUESSING the YAK-52TW as well) has a DIFFERENT PISTON in the    pressure relief assy.  It is slightly BIGGER and is NOT a direct    replacement with all the others mentioned earlier. Why not?  Go    figure.      

p.p.s.  YAK-52W guys... did you know that there is an    emergency pressure relief valve behind the seat that allows you to eliminate    emergency air pressure to the landing gear without having to crack fittings    and jack and cycle the gear, if you ever do happen to open the emergency    bottle valve?     

p.p.p.s.  For those aircraft with the manual engine    starting valves (YAK-55, Sukhoi's) be aware that the rubber replacement tab    for the starter valve MUST have a whole cut in the middle of it.  Ignore    that fact, and the lever will work a few times and then fail forever. Trust me    on this and save yourself a lot of head scratching.    

   

--

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marksorenson

Joined: 31 Jan 2006
Posts: 15

Posted: Tue Jan 31, 2006 7:22 am Post subject: Re: Iris Instead of Grills

Again thanks for all your responses to my question.  My Grils are repairable I am sure  They close fine but when open they shimmy quite a bit durring my routine.  I do have the summer time ring, i guess that is what you call it, to install when it gets warmer.  I haven't taken a close look at it yet to see exactly how it goes on, but I was assuming that the entire support ring would come off and this would go on in its place.  My Yak is the 55M.  However listening to some of your comments I am not sure if removing the support ring is the way to go for my summer flying.  Currently I only use the grills for warm up and then once the power goes up it usually stays up for my routine and cooling temps isn't usually a problem as I don't have any enroute time to the box.



Where I notice most of my wear is on the inner ring close to the crank.  The holes are so elongated that there are a couple that are almost worn through the edge.  I was first wondering if there was a replace ring part available for rebuilding the grills.  The Iris just seemed like a simple device and just as functional.  Maybe that isn't exactly the case.  Again, thanks for all the imput.

_________________
Mark Sorenson
Tigerbatics N921GRrrrrr

pilot8kcab(at)hotmail.com
Guest

Posted: Tue Jan 31, 2006 10:50 am Post subject: Iris Instead of Grills

Mark,



I have the Sukhoi Iris on a Yak-55 without any problems.  The second owner 

installed them, I'm the 3rd owner and would guess they've been on the plane 

for atleast 3 years or more.  The Yak-55 and 55M cowls are very similar, the 

only differences I noticed were some extra cooling gills as well as enlarged 

cooling gills in the sides and an extra access panel.  I have another friend 

who flew a Yak-55M without any grills or Iris (in the Northeast during 

Spring, Summer and Fall only) in airshows for years and he also had no 

problems.  In the Yak-55 with the iris fully expanded I would estimate there 

is about 2 inches of clearance between the cowling and the iris.



That being said I've occasionally wondered if there is a differences in 

terms of engine longevity between using the grills and the iris as I would 

think the grills server to increase or decrease air flow to the engine 

fairly uniformly over the length of the cylinders whereas the iris when 

operated from fully closed to fully expanded would tend to increase the air 

velocity at the upper ends of the cylinders as it decreased air at the lower 

ends presumably resulting in a thermal gradient across the cylinder from the 

base to the heads.  At their extreme with the iris fully expanded in the 

Yak-55 and 2 inches clearance from the cowl, the air is accelerated thru 

that 2 inch space directed toward the tops of the cyliners only.  Again this 

is only an "hmmmm, I wonder...." on my part.



If you want more or need details such as photos, let me know and I'll see 

what I can do.



Scott





----Original Message Follows----

From: "marksorenson" <marksorenson(at)sprintpcs.com>

Reply-To: yak-list(at)matronics.com

To: yak-list(at)matronics.com

Subject: Re: Iris Instead of Grills

Date: Tue, 31 Jan 2006 07:22:00 -0800






Again thanks for all your responses to my question.  My Grils are repairable 

I am sure  They close fine but when open they shimmy quite a bit durring my 

routine.  I do have the summer time ring, i guess that is what you call it, 

to install when it gets warmer.  I haven't taken a close look at it yet to 

see exactly how it goes on, but I was assuming that the entire support ring 

would come off and this would go on in its place.  My Yak is the 55M.  

However listening to some of your comments I am not sure if removing the 

support ring is the way to go for my summer flying.  Currently I only use 

the grills for warm up and then once the power goes up it usually stays up 

for my routine and cooling temps isn't usually a problem as I don't have any 

enroute time to the box.



Where I notice most of my wear is on the inner ring close to the crank.  The 

holes are so elongated that there are a couple that are almost worn through 

the edge.  I was first wondering if there was a replace ring part available 

for rebuilding the grills.  The Iris just seemed like a simple device and 

just as functional.  Maybe that isn't exactly the case.  Again, thanks for 

all the imput.



--------

Mark Sorenson

Tigerbatics N921GRrrrrr





Read this topic online here:



http://forums.matronics.com/viewtopic.php?p=8424#8424





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BitterlichMG(at)cherrypoi
Guest

Posted: Tue Jan 31, 2006 10:52 am Post subject: Iris Instead of Grills

Mark you can fix that inner ring by having all the holes welded up and then redrilled.  Sounds like a pain in the rear, but it is not all that difficult really.    

By the way, I have no experience with 55's.  It is possible that their cowl is much stronger in design than the 52/50 design.  For example the Sukhoi design is MUCH stronger than the YAK's.    

Good luck,    

Mark Bitterlich  

  

--

BitterlichMG(at)cherrypoi
Guest

Posted: Tue Jan 31, 2006 10:56 am Post subject: Iris Instead of Grills

Yes, that  would be the engine gearbox cover.  Thanks for the correction.  

  

 Mark

  

 [quote]   --

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