Matronics Email Lists :: View topic - Replacing throttle return springs

Matronics Email Lists
Web Forum Interface to the Matronics Email Lists

Get Email Distribution Too! FAQ Search Memberlist Usergroups Register

Profile Log in to check your private messages Log in

Replacing throttle return springs

Matronics Email Lists Forum Index -> RotaxEngines-List

View previous topic :: View next topic

Author Message

Catz631(at)aol.com
Guest

Posted: Wed Dec 26, 2007 5:34 am Post subject: Replacing throttle return springs

I own a Kitfox 4 with a Rotax 912UL .I was a recent purchaser of this aircraft and am trying to get to know the 912.It is a different 'animal" then the Lyc/Cont I am used to working on. (in fact I am going to Rotax 912 school in Jan)

  The throttle return springs on the Bing carbs are very strong and have been overiding the friction adjustment on my throttle no matter how hard I thighten them. It requires constant pull on the throttle to keep the throttle at idle.

   As a result.I went to a Vernier throttle which seems to have solved the problem as it will hold what I set.However, if I push the button the throttle immediately goes to the full power position. so I then installed weaker return springs and this seemed to solve the problem. One person I talked to told me to remove the springs completely but I didn't feel I should do this as the springs are needed,I think,In acheiving the full open position on the carb.

  Am I approaching this correctly ?

   I have had the engine quit on me several times during landing as it appears I am getting the idle back too low (around 1400 sometimes) At 1800 to 2000 rpm idle,this airplane is hard to get on the ground it just floats and floats.

   Any ideas would sure help.

                        Thanks,

                       Dick Maddux

                       Rotax 912UL



See AOL's top rated recipes and easy ways to stay in shape for winter.

  [quote][b]

Gilles.Thesee(at)ac-greno
Guest

Posted: Wed Dec 26, 2007 5:54 am Post subject: Replacing throttle return springs

Catz631(at)aol.com a écrit :

 	  Quote: 	
		   One person I talked to told me to remove the springs completely but I 

 didn't feel I should do this as the springs are needed,I think,In 

 acheiving the full open position on the carb.

  

The springs are needed when you use a flexible throttle cable. If you 
	


are using a rigid push-pull cable, things are different.

Another approach would be to modifiy your throttle friction. The 

diameter/leverage must be sufficient to ensure proper friction.

 	  Quote: 	
		     I have had the engine quit on me several times during landing as it 

 appears I am getting the idle back too low (around 1400 sometimes) At 

 1800 to 2000 rpm idle,this airplane is hard to get on the


	


Rotax advises 1600-1800. Try 1600, then 

BTW, do you have a positive idle stop on the throttle lever/vernier, as 

advised by Rotax ? One must not strain the carb stops.



Regards,

-- 

Gilles Thesee

Grenoble, France

http://contrails.free.fr

Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Wed Dec 26, 2007 6:54 am Post subject: Re: Replacing throttle return springs

Hi Dick,



You should have the springs. They are there for a couple of reasons. To make sure if you have a throttle cable failure the carbs will open full throttle and let you fly somewhere safe before you have to shut the engine down to land. It keeps constant pressure on each carb to help for equal opening when using the stranded type throttle cable.

Gilles is right you need the springs and you should be able to tighten the throttle linkage so it has enough friction to over come the spring tension with out any problems. 

You said your plane floats, compared to what. All planes have different landing characteristics. I have a Flight Design CT and that really feels like it floats compared to other planes and lands quick compared to let's say a glider or long wing plane. I doesn't really float bad, but different from what you are used to.

Your idle should be up to at least 1700, but better at 1800 rpm because of the vibration and pulsing of the engine on the gear box.

This is a Rotax recommendation. Maybe you could use more flaps on landing to land a little quicker? Slower approach?

_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

thilo.kind(at)gmx.net
Guest

Posted: Wed Dec 26, 2007 11:06 am Post subject: Replacing throttle return springs

Hi Dick,



1400 RPM idle is too low. Rotax recommends something like 1800 at idle.



Also, the sprigs should stay on. Their purpose is to open the throttle in case of a breakage in the throttle linkage. There is at least one report in the archives about a gentleman who also removed / replaced the springs with disasterous results...



Thilo

-------- Original-Nachricht --------

 	  Quote: 	
		   Datum: Wed, 26 Dec 2007 08:31:01 EST

 Von: Catz631(at)aol.com

 An: rotaxengines-list(at)matronics.com

 Betreff: Replacing throttle return springs


	


 	  Quote: 	
		   I own a Kitfox 4 with a Rotax 912UL .I was a recent purchaser of this 

 aircraft and am trying to get to know the 912.It is a different 'animal"

 then the 

 Lyc/Cont I am used to working on. (in fact I am going to Rotax 912 school

 in Jan)

  The throttle return springs on the Bing carbs are very strong and have

 been 

 overiding the friction adjustment on my throttle no matter how hard I

 thighten 

 them. It requires constant pull on the throttle to keep the throttle at

 idle.

   As a result.I went to a Vernier throttle which seems to have solved the 

 problem as it will hold what I set.However, if I push the button the

 throttle 

 immediately goes to the full power position. so I then installed weaker

 return 

 springs and this seemed to solve the problem. One person I talked to told

 me to 

 remove the springs completely but I didn't feel I should do this as the 

 springs are needed,I think,In acheiving the full open position on the

 carb.

  Am I approaching this correctly ?

   I have had the engine quit on me several times during landing as it

 appears 

 I am getting the idle back too low (around 1400 sometimes) At 1800 to 2000

 rpm idle,this airplane is hard to get on the ground it just floats and

 floats.

   Any ideas would sure help.

                        Thanks,

                       Dick Maddux

                       Rotax 912UL

 

 

 

 **************************************See AOL's top rated recipes 

 (http://food.aol.com/top-rated-recipes?NCID=aoltop00030000000004)


	


-- 

GMX FreeMail: 1 GB Postfach, 5 E-Mail-Adressen, 10 Free SMS.

Alle Infos und kostenlose Anmeldung: http://www.gmx.net/de/go/freemail

Gilles.Thesee(at)ac-greno
Guest

Posted: Wed Dec 26, 2007 12:14 pm Post subject: Replacing throttle return springs

Thilo Kind a écrit :

 	  Quote: 	
		   Also, the sprigs should stay on. Their purpose is to open the throttle in case of a breakage in the throttle linkage. There is at least one report in the archives about a gentleman who also removed / replaced the springs with disasterous results...

   

Thilo,
	




The springs are there because many builders use *FLEXIBLE* cables. This 

is common practice in the ultralight community, but it has some 

drawbacks. Sometimes badly routed cables bind between throttle lever and 

cable outer case, leaving the engine at idle. That is because only the 

spring actuate the throttles at the carbs. Any undue friction in the 

cables leaves the pilot helpless.



On the contrary, no problem at all when one use a push-pull cable, like 

in most Lyco-Conti. This gives the pilot a positive action on the 

trhottles. In this case, the springs *may* stay in, but are not 

mandatory. Most airplanes don't have one.



Best regards,

-- 

Gilles

http://contrails.free.fr

thilo.kind(at)gmx.net
Guest

Posted: Wed Dec 26, 2007 2:31 pm Post subject: Replacing throttle return springs

Hi Gilles,



one very important function of the springs is to open the throttle fully in case of a breakup in the throttle linkage. This will ensure that the engine keeps running at max throttle and theplane thus is still flyable. I know of at least one case (should be in the archives somehwere) where a guy removed the springs for the reason you mentioned, lost the throttle linkage in flight, and the throttles on both carbs closed (due to engine vibrations). Very uncomfortable during take-off.... I highly recommed to leave the springs on and play with the friction of the throttle linkage instead.



Thilo

-------- Original-Nachricht --------

 	  Quote: 	
		   Datum: Wed, 26 Dec 2007 20:19:33 +0100

 Von: Gilles Thesee <Gilles.Thesee(at)ac-grenoble.fr>

 An: rotaxengines-list(at)matronics.com

 Betreff: Re: Replacing throttle return springs


	


 	  Quote: 	
		   

 <Gilles.Thesee(at)ac-grenoble.fr>

 

 Thilo Kind a écrit :

 > Also, the sprigs should stay on. Their purpose is to open the throttle

 in case of a breakage in the throttle linkage. There is at least one report

 in the archives about a gentleman who also removed / replaced the springs

 with disasterous results...

 >   

 Thilo,

 

 The springs are there because many builders use *FLEXIBLE* cables. This 

 is common practice in the ultralight community, but it has some 

 drawbacks. Sometimes badly routed cables bind between throttle lever and 

 cable outer case, leaving the engine at idle. That is because only the 

 spring actuate the throttles at the carbs. Any undue friction in the 

 cables leaves the pilot helpless.

 

 On the contrary, no problem at all when one use a push-pull cable, like 

 in most Lyco-Conti. This gives the pilot a positive action on the 

 trhottles. In this case, the springs *may* stay in, but are not 

 mandatory. Most airplanes don't have one.

 

 Best regards,

 -- 

 Gilles

 http://contrails.free.fr

 

 

 

 

 


	


-- 

GMX FreeMail: 1 GB Postfach, 5 E-Mail-Adressen, 10 Free SMS.

Alle Infos und kostenlose Anmeldung: http://www.gmx.net/de/go/freemail

daberti(at)sbcglobal.net
Guest

Posted: Wed Dec 26, 2007 3:32 pm Post subject: Replacing throttle return springs

I know of 2 planes that lost throttle control with the solid cables on 

certificated airplanes so nothing about the throttle system is fool proof. 

Design for the worst case scenario for whatever cables you use but keep it 

simple!



---

Thom Riddle

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

Posted: Fri Dec 28, 2007 3:12 pm Post subject: Re: Replacing throttle return springs

Dick,



Most of the guys responding to you so far are flying airplanes with the 912ULS (100 hp) but your question was about the 912UL (80 hp) which is what we have in our Allegro 2000. The 100 hp engine may indeed need 1800 rpm idle but the 912UL does not. Ours is set for 1500-1600 rpm idle speed when fully warmed up. Setting it cold won't do you much good because it will change when warm. 



The Allegro is a floater too and anything above 1600 rpm idle (912UL) will make final approach difficult, just as you have experienced in your Kitfox. Roger and I have had this discussion before.... search the archives.



One thing no one has mentioned yet is this. When you buy someone else's experimental aircraft, you may be in for some unexpected surprises. Are you sure you have the Rotax/Bing supplied springs on the carburetors? If a previous owner lost them and bought stronger hardware store springs, instead of the more costly Rotax springs, this could explain the difficulty your were having with holding throttle position. 



Thom Riddle

FAA Powerplant Mechanic

hgmckay

Joined: 23 May 2006
Posts: 397

Posted: Sat Dec 29, 2007 8:31 am Post subject: Replacing throttle return springs

Thom: 

I have been following some of this discussion and since you and I both have

an Allegro 2000 with a 912UL engine I was curious as to how you are able to

idle your 912 at 1500-1600 rpm with out having the engine come off the mount

our tearing up your gearbox? I read Dick Maddux's reply stating that he had

terrible engine vibration and an actual in-flight engine stop at that low of

throttle setting. Have you changed something on the carbs (on your Allegro)

to allow such a low rpm? My 912UL begins to shake at about 1700. I try not

to go below 1800. From my experience, I agree with Dick that you cannot idle

a 912UL in the 1500-1600 rpm range and not have the engine violently

shaking.



I am also curious as to what airspeed you hold in your Allegro on your final

approach (under normal conditions), and what engine rpm you are turning on

final approach, and what your final touchdown speed is. As I turn from base

to final I am turning at 3000 rpm and an air speed from 65 to 70 with flaps.

 	  Quote: 	
		  From that point until I am over the runway threshold I try to hold a minimum

air speed of 65. After that I back off the throttle and as you say the
	


Allegro does want to "float" until touchdown. What is your experience?



Hugh  



--

Thom Riddle

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

Posted: Sat Dec 29, 2007 9:23 am Post subject: Re: Replacing throttle return springs

Hugh,



To get a 912 series engine to idle smoothly in the 1500-1600 rpm range requires careful mechanical and pneumatic (vacuum) synchronization of the carbs. The mechanical adjustments must be done first and can be done without running the engine. Once that is done, the engine must be fully warmed up to do a proper vacuum synchronization job. The best way to ensure it is warm enough is to fly it and then do the vacuum balance. This requires dual vacuum gauges. We bought ours from Lockwood (I think). The proper procedure for doing both of these is in the Rotax Line Maintenance manual.



If after reading the manual you have any questions, let me know. I know of several Rotax 912 owners who never synch their carburetors but it does make a difference if you want a smooth idle at 1600 rpm or less (warm). 



Speaking of gearboxes, we just finished removing, disassembling and inspecting our gearbox. The teeth on both gears looked new and only normal wear on the dog parts. The springs were still in new spec range too after over 500 hours in service. Lockwood gets a bundle for doing this, so if you want it done cheaper, send it to me. I'll do it for $100 plus parts and you pay the shipping. I'm an FAA certificated Power Plant Mechanic so can do it for any Rotax 9 series, including type certificated aircraft. Rotax recommends the gearbox inspection at 400 hour intervals and is required on S-LSAs, but not on experimentals. 



Our airspeed indicator reads a good bit high, about 7-8% in the final approach speed range so take that into account when I quote the IAS speeds I use.



On downwind I trim for 75 mph IAS with no flaps and about 3400-3600 rpm on the tach depending upon flying weight. Abeam the numbers I pull the throttle back to idle (don't recall what the tach speed is in flight) and maintain 75 mph through the turn to base and to final, gliding at idle all the way. Once on final the speeds I use depend on whether I'm flying solo or with a passenger. When dual, I use 70 IAS with zero flaps, then reduce IAS to 65 mph with 15 degrees of flaps, and then 60 mph IAS with full flaps until flare. When flying solo, I reduce these three final approach speeds by 5 mph each. 



As I said, I can't tell you what the engine rpm is in flight with the throttle at idle but I suspect it is in the 2200-2300 range and perhaps a bit less as my speed is reduced to 60 mph or less. Next time I fly I'll try to remember to note these tach speeds and let you know. This time of year we don't get many decent flying days.

_________________
Thom Riddle
Buffalo, NY (9G0)

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

hgmckay

Joined: 23 May 2006
Posts: 397

Posted: Sat Dec 29, 2007 1:15 pm Post subject: Replacing throttle return springs

Thom: 



I have not yet pneumatically balanced my carbs. I have a friend who has a

912S on his amphibian at our airport who has pneumatically balanced his and

has offered to help me do mine. I have read the Rotax procedure and I have

the equipment. At the moment, we, like you are waiting for some descent

weather to fly and do the sync. procedure. If we can get the idle speed down

to the 1500-1600 rpm range, I'll let you know.



My ASI is the one that came from Fantasy Air. I don't know how accurate it

is, but the numbers I quoted in my previous email to you are as INDICATED on

that instrument. It was interesting to hear that you pull the throttle back

to "idle" (1500-1600 rpm) and glide the plane all the way. Does this mean

you have pulled the throttle back to the throttle stop (i.e. can't pull it

back any farther)? How do you control your rate of descent if you do not use

your throttle? If you are a little low as you turn on final, I assume you

use the throttle to decrease your rate of descent as necessary to bring you

back to proper glide slope. Anyway, it was interesting to hear how you

handle your Allegro on landing.



Hugh



--

Thom Riddle

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

Posted: Sat Dec 29, 2007 7:01 pm Post subject: Re: Replacing throttle return springs

Hugh,



The idle rpm I'm talking about (1500-1600) is on the ground with the throttle fully closed. In flight that fully closed throttle (to the throttle stop) in a glide at 75 mph results in a good bit higher rpm which I am guessing to be in the 2200-2300 range, but this is just a guess. 



The secret to near perfect landings every time in any airplane is a stabilized approach. In the Allegro, I always plan my pattern (800' AGL) so that when abeam the numbers at idle power I can glide to an easy power off landing. This turns out to be about 1/4-1/2 mile away from the runway on downwind depending upon cross wind. Abeam the numbers I close the throttle and hold 75 mph and begin my idle power glide. I continue the downwind leg past the numbers about 15 seconds (adjusting for headwind component by subtracting one(1) second for each 5 mph of headwind component) and turn base, then turn final when I get there and stabilize approach on final and slow to 70 mph. From abeam the numbers up to this point I am at fully closed throttle and gliding. Once stabilized on final I can tell if my current glide path is about right or too long (never short) and apply flaps and hold the speeds I stated before depending upon my anticipated touch down point. Using approximately a 15 second downwind extension I am always plenty high to make the runway if I have a power failure. If the pattern altitude is 1000' AGL I would have to make the downwind extension longer than 15 seconds, closer to 20 seconds. I adjust the flaps and speed as necessary on short final to touchdown where I want, sometimes needing to slip to get it down shorter. I never have to add throttle once I begin my stabilized approach abeam the numbers. All I have to do is judge my landing point once on final and use the flaps and stated speeds as required to make my intended landing point. 



This is NOT how I was taught 40+ years ago. It is what I found to be the easiest and safest approach method for me in simple aircraft. I am not a big fan of big patterns for many reasons, not the least of which is that when in the pattern I want to always be able to glide power off to a safe landing. We are not flying 747s on 3 degree glide slopes on ILS approaches, so this method keeps the pattern small and operations quicker for everyone in the pattern. I hope this helps.

_________________
Thom Riddle
Buffalo, NY (9G0)

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

l_luv2_fly(at)yahoo.com
Guest

Posted: Sat Dec 29, 2007 7:19 pm Post subject: Replacing throttle return springs

Hi all,

  

 I just wanted to share my experience with carburettor balancing.  I purchased the vacuum gaauges from Lockwood aviation, but for some reason I was never able to get them balanced nicely.  In particular I would find I had a vibration in the range of 3200 ~ 3500 RPM.  

  

 Any how I purchased a TwinMax carburettor balancer.  This thing is awesome, it has variable sensitivity and I can get them nuts on using this thing.  I am able to idle my 914T ar 1500 RPM nicely.  It makes quite a difference to my Europa during the landing phase.  If you google TwinMax you can find several suppliers.  Try [url=http://www.adventuremotogear.com/twinmax.mgi?mgiToken 9HJXUUF]http://www.adventuremotogear.com/twinmax.mgi?mgiToken 9HJXUUF[/url]

  

 Cheers,  Paul

  

 N378PJ

 http://www.europa.net.nz/363/index.html

 [quote][b]

Thom Riddle

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

Posted: Sun Dec 30, 2007 5:07 am Post subject: Re: Replacing throttle return springs

I keep hearing many folks on this list saying that 1800 rpm is minimum recommended idle speed for the 9 series Rotax engines. Can someone show me in the Rotax Documentation (not Lockwood) where it says that? The reason I ask is that the attached file is a snapshot from my 912S Installation Manual. 



As you can plainly see it says IDLE SPEED AROUND 1400 RPM. I'm going to piss off some folks here with my next statement. If you can't get yours to idle smoothly at less than 1800 rpm, perhaps you ought to have a professional mechanic do it for you, because something may be amiss in your procedure or your engine.



As the owner operator of your airplane, you are entitled to set your idle speed at anything you want. If you are happy with 1800, then so be it, but don't tell me THE MINIMUM RECOMMENDED IDLE SPEED is different from what the Rotax Installation Manual says unless you can document that in another Rotax Document.

idle speed.jpg

Description:

Filesize:

55.02 KB

Viewed:

655 Time(s)

_________________
Thom Riddle
Buffalo, NY (9G0)

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

Thom Riddle

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

Posted: Sun Dec 30, 2007 5:29 am Post subject: Re: Replacing throttle return springs

Paul,



I'm glad to hear that you are able to get your engine to idle at less than 1800 rpm. I was beginning to think that I was some sort of real world evil wizard like my alter ego, Lord Voldermort of Harry Potter fame. do not archive

_________________
Thom Riddle
Buffalo, NY (9G0)

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

daveaustin2(at)primus.ca
Guest

Posted: Sun Dec 30, 2007 9:04 am Post subject: Replacing throttle return springs

Thom,

Please don't piss us off.

Dave Austin  601HDS - 912, Spitfire Mk VIII

l_luv2_fly(at)yahoo.com
Guest

Posted: Sun Dec 30, 2007 10:46 am Post subject: Replacing throttle return springs

Hi Thom,

  

 I should add a few other comments.  My engine is a 914T and if I understand it correctly it has the same compression ratio as the 80HP engines, so my experience might not be relevant for the 912S.

  

 The other experience I can share is that although my idle is set in the 1500 ~ 1600 range, I typically see 2200 RPM on short final with the throttle closed due to the windmill effect, so I can say (for my aircraft at least) that a lower idle speed is unlikely to result in an engine stoppage.

  

 The other pratice I have adopted is to once I have exited the runway is to set my throttle to 1800 RPM for taxi.

  

 Just as an FYI, with careful adjustment I can get the idle down lower, but as others have mentioned it really sounds like "rattle and roll" going on under the cowling so its  probably not a great idea.

  

 BTW, I am still trying to debug my loss of boost at altitude, but is way too cold to work in the hanger at the moment.

  

 Cheers,  Paul

       Be a better friend, newshound, and  [quote][b]

Fergus Kyle

Joined: 03 Jun 2007
Posts: 291
Location: Burlington ON Canada

Posted: Sun Dec 30, 2007 11:22 am Post subject: replacing throttle return springs

Thom -

	I was interested in your approach/landing thoughts (and figured you

for Air Force training, way back), and agree with all your thinking BUT am

unsure of the 912 characteristics - so put this in for thoughts.

	We were always taught two final processes:

1	Always give the engine a quick burst to keep 'er warm on final and

ready for overshoot,

2	Always throttle off during the approach to hear if the warning horn

indicates gear not locked down.

	This may not apply to Rotax (not flying yet) so might be redundant

and perhaps the gearhorn is equally unnecessary. Just a thought.

Cheers, Ferg

Thom Riddle

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

Posted: Sun Dec 30, 2007 12:02 pm Post subject: Re: Replacing throttle return springs

Ferg,



If the Rotax 9 series engine has its idle speed set appropriately (fill the rpm you prefer) and the carbs are synchronized well, and there are no other problems with the engine, then the engine will be ready for full power in prep for a go-around or balked landing, without "blipping" the throttle occasionally on final. In my opinion there are two reasons for this. One the automatic mixture control (alt. compensating) feature of the Bing 64 carbs precludes over-rich running and fowling of the plugs due to prolonged idle speed operation. The second reason is that the heads are liquid-cooled so the engine does not normally experience wide temperature swings over short time periods when gliding at idle speed. These features (and others) make the Rotax 9 series engines superior to (but more complex than) the 50's and 60's vintage Lycoming, Continental, Franklin etc.  air cooled aircraft engines.

_________________
Thom Riddle
Buffalo, NY (9G0)

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

Display posts from previous:

	Matronics Email Lists Forum Index -> RotaxEngines-List	All times are GMT - 8 Hours
Page 1 of 1

Jump to:

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum