912 throttle response hesitation

[BrendAn]

27 minutes ago, skippydiesel said:

To be human is to jump to  the most expensive/complex conclusion's/solutions to any situaton - I am staggered by the demonstration of this very human failing.

 

What of the BASICS????

 

We know very little about this engine, other than a few replacement parts have been fitted.

Have you forgot your medication again. 😁

[Blueadventures]

9 hours ago, BigDiggs88 said:

yea ok, interesting you do say that through because the manual does state about RPM variations after start, more so about rpm stability before retarding the throttle to look the reduction shock absorber but cant find anything about the advancement of throttle. I am aware smooth steady power adjustments are best. major concern was in the event of a go round you would want power on hand to recover, but the 3 -4 second hesitation was the concern. the advancement on throttle to have the issue is definitely quite aggressive. aircraft has only done high speed taxi runs at this stage till I'm happy with the gremlins. if you would have manual ref i could view just to put my mind at ease then id happily accept it. just want to determine if its operational error or a genuine issue.

 

Give Floods a call and they may be able to solve the issue and comment of fast throttle movements.  The POH for the Gazelle will state throttle operation method recommended on take off and other situations. How many hours have you done with this engine or other 912 Rotax? 

[BigDiggs88]

1 minute ago, Blueadventures said:

Give Floods a call and they may be able to solve the issue and comment of fast throttle movements.  The POH for the Gazelle will state throttle operation method recommended on take off and other situations. How many hours have you done with this engine or other 912 Rotax? 

ive only had the aircraft 3 months, i havent done any time with it other than high speed taxis as i am still undergoing flight training. (bit backwards buying before having a license i know) engine is due on both calendar and hours. engine has done 2160hours, running 98oct. Fuel was drained before i transported it (completely from wings, header tank) last inspection did show good leak down checks. i have come across a few issues since looking. inlet hoses not installed properly (inner edge of the scat hose curled up inside the inlet- restricting the inlet) the other had a tear just behind the hose clamp. as Skippy did mention back to basics. ill start from the tanks and trace the circuit back from there to eliminate any other unknowns but am confident i wont find much. failing that a phone call to Wal at Berts cant hurt before escalating to expensive options.

[BigDiggs88]

20 hours ago, skippydiesel said:

• How many hours?
• Has the engine/aircraft had its 5 year rubber replacement?
• Fuel type (RON) and age in tank?
•  "-carbs are balanced."  - Mechanical?/Pneumatic/Both? Technique?
• "- no change between choke on or off "This doesn't seem right - In my 15-18 years of Rotax 912 operation, I have never applied "choke" (an enriching device) to a running engine so don't know what happens however I would expect a very over rich condition and engine rpm to drop significantly.

 

Recomend joining the Rotax Owners Forum for specific technical assistance - https://www.rotax-owner.com/en/rotax-forum

engine is due on both calendar and hours. engine has done 2160hours, running 98oct. Fuel was drained before i transported it (completely from wings, header tank) last inspection did show good leak down checks.

I dont believe the 5 year replacement has been done looking through the logs but it has got new inlet adaptors from the carb to the inlet. thinking this has been an ongoing issue given fuel line replacements, on engine pump replacement and the inlet rubbers being new. apologies for the delayed response mate, trying to burn the candle at both ends.

[Blueadventures]

33 minutes ago, BigDiggs88 said:

ive only had the aircraft 3 months, i havent done any time with it other than high speed taxis as i am still undergoing flight training. (bit backwards buying before having a license i know) engine is due on both calendar and hours. engine has done 2160hours, running 98oct. Fuel was drained before i transported it (completely from wings, header tank) last inspection did show good leak down checks. i have come across a few issues since looking. inlet hoses not installed properly (inner edge of the scat hose curled up inside the inlet- restricting the inlet) the other had a tear just behind the hose clamp. as Skippy did mention back to basics. ill start from the tanks and trace the circuit back from there to eliminate any other unknowns but am confident i wont find much. failing that a phone call to Wal at Berts cant hurt before escalating to expensive options.

If your not solo; I would not be doing high speed taxi runs as you will be in the air before you know it.  Wal is great to talk to; a full carb rebuild by him is a good option to set up for trouble free operations into the future; especially if it has not been done for a while and the needle, o rings etc and worn a perished.  I'll PM my contact should you wish to call.  Cheers.

[BurnieM]

Que ?

If it is expired on both hours and calender time how will you be (legally) flying it ?

[facthunter]

Quoi, Mon Dieu..  Nev

[Blueadventures]

6 minutes ago, BurnieM said:

Que ?

If it is expired on both hours and calender time how will you be (legally) flying it ?

MARAP Engine Condition report #23 and can't be used for training or hire.

[BurnieM]

Anybody got documentation for the MARAP process ?

[Blueadventures]

4 minutes ago, BurnieM said:

Anybody got documentation for the MARAP process ?

Best to phone RAA with aircraft details and they will advise if required for its category and send the documents and the form to be completed by an L2, annual requirement re engine condition report etc. (I have done a couple.)

Edited Tuesday at 11:22 PM by Blueadventures

[skippydiesel]

1 hour ago, BrendAn said:

Have you forgot your medication again. 😁

Naa!  - medication ? taking it by the handful -  ineffective!😎

 

We knew almost nothing of this engine & its service history. Without this background how can anyone give a hint of informed advice/opinion.

 

Starting to get a better picture.

 

• High time engine.
• Incomplete service history and or action on scheduled service.  
• Pilot/service provider, lacking in Rotax experince/knowledge - needs a mentor.

😈

 

 

[BrendAn]

1 hour ago, skippydiesel said:

Naa!  - medication ? taking it by the handful -  ineffective!😎

 

We knew almost nothing of this engine & its service history. Without this background how can anyone give a hint of informed advice/opinion.

 

Starting to get a better picture.

 

• High time engine.
• Incomplete service history and or action on scheduled service.  
• Pilot/service provider, lacking in Rotax experince/knowledge - needs a mentor.

😈

 

 

the bloke asked for advice and he got it. 

[onetrack]

With all the information provided, especially relating to the total engine hours, I'd expect the problem is related to an intermittent fuel flow blockage. The inlet hose problem is indicative of age-related problems.

Floating debris in fuel tanks will cause intermittent blockage, the inner lining on hoses separates, and can either peel back and create flow restriction, or simply bubble away from the join between inner and outer materials, and thereby partly block the line.

I've seen a tiny circular metal remnant from hole punching, slip into a fuel line out of the tank, and then act like a butterfly valve. Gun it, and the fuel flow went to near zero. Ease off the throttle, and the fuel flowed. It took a piece of wire shoved down the fuel line to remove the piece of metal.

[BrendAn]

2 hours ago, BigDiggs88 said:

engine is due on both calendar and hours. engine has done 2160hours, running 98oct. Fuel was drained before i transported it (completely from wings, header tank) last inspection did show good leak down checks.

I dont believe the 5 year replacement has been done looking through the logs but it has got new inlet adaptors from the carb to the inlet. thinking this has been an ongoing issue given fuel line replacements, on engine pump replacement and the inlet rubbers being new. apologies for the delayed response mate, trying to burn the candle at both ends.

hours and calendar time can be on condition for non training aircraft. they will just ask for an annual and 5 year replacement to be done.

but i thought gazelles were factory built which means you can't work on it. has to be an l2. i think your carb needles are worn because that causes the issues you describe. as blue said wal is the man to talk to.  very cluey and a gentleman as well.

[F10]

15 hours ago, BigDiggs88 said:

if you advance the throttle slowly the engine responds but you can feel slight hesitation during normal operation. more prominent when you stab the throttle quickly. Hesitates for about 3-4 seconds and pulls through the rev range just fine. Not a vibration, more so a sputter as the engine responds to the throttle advancement.  Plug gaps should be fine as i replaced them all. cheap and quick but no real improvement. throttle arms are all good and choke cables all connected with no breakages. ill have a play later and see if the others show any signs of causing the issue

These are Bing constant velocity carbs, opening the throttle butterfly will cause the slides to rise up, withdrawing the needle from the diffuser, letting more fuel into the venturi. Are the slides moving freely? Nev correct, the rubber diaphragms in the dashpots could be leaking slightly. If the slides don't rise up, you will have a short term leaning of the mixture. Consider cleaning carbs and renew needles and rubber diaphragms. Private message me, I can give you the contact details for two members of the Yarram Aero Club, who know a lot about Rotax 912 UL engines and Rotax engine tuning. 

 

Enjoy your Gazelle! I have one and have had an absolute ball flying mine! A fun and viceless little aircraft.  And before we see posts making you feel less of a pilot, because of their claim that the Gazelle is soooo easy to fly it's almost not an aeroplane....like the famous and beloved Piper Cub, about which it is said "A  Cub can almost kill you"....so too, disrespect it and the Gazelle (like any aircraft) can hurt you, badly. 

[BigDiggs88]

6 hours ago, Blueadventures said:

If your not solo; I would not be doing high speed taxi runs as you will be in the air before you know it.  Wal is great to talk to; a full carb rebuild by him is a good option to set up for trouble free operations into the future; especially if it has not been done for a while and the needle, o rings etc and worn a perished.  I'll PM my contact should you wish to call.  Cheers.

i when i say high speed taxi runs its with my instructor. cheers

[BrendAn]

6 hours ago, Blueadventures said:

If your not solo; I would not be doing high speed taxi runs as you will be in the air before you know it.  Wal is great to talk to; a full carb rebuild by him is a good option to set up for trouble free operations into the future; especially if it has not been done for a while and the needle, o rings etc and worn a perished.  I'll PM my contact should you wish to call.  Cheers.

i know of someone who did exactly that. he left the ground and panicked,   cut the throttle stalled the left wing. wrote off his $30,000 plane and went to hospital for a few days.

[BigDiggs88]

12 minutes ago, BrendAn said:

i know of someone who did exactly that. he left the ground and panicked,   cut the throttle stalled the left wing. wrote off his $30,000 plane and went to hospital for a few days.

bit more smarts in my head than i let on. im actually renewing my license at the same time im trying to get the Gazelle sorted. if its not safe it dont fly. 

[skippydiesel]

4 hours ago, BrendAn said:

the bloke asked for advice and he got it. 

The quality of any advice, can only be proportional to the quality of the information supplied.

 

 I am shore the respondents meant well but best to ask for as full an information picture as possible, before charging off down rabbit holes.

 

Now that more information has been provided, it is fairly clear that the engine needs a thorough inspection (by a suitably Rotax experienced person), major service and possibly action on Rotax AD's etc,  not implemented.😈

[Blueadventures]

5 hours ago, skippydiesel said:

The quality of any advice, can only be proportional to the quality of the information supplied.

 

 I am shore the respondents meant well but best to ask for as full an information picture as possible, before charging off down rabbit holes.

 

Now that more information has been provided, it is fairly clear that the engine needs a thorough inspection (by a suitably Rotax experienced person), major service and possibly action on Rotax AD's etc,  not implemented.😈

Hearing that an instructor is involved it's interesting that he has not provided advice and connection to an engine service person.  Seems the instructor is leaving it up to the owner to sort the engine issue and is prepared to run a time expired engine with unknown maintenance history.  A very good instructor would not do such in my experience as they would ensure the aircraft is airworthy and if asked provide advice on required work before operation of the aircraft.

[turboplanner]

11 hours ago, Blueadventures said:

Hearing that an instructor is involved it's interesting that he has not provided advice and connection to an engine service person.  Seems the instructor is leaving it up to the owner to sort the engine issue and is prepared to run a time expired engine with unknown maintenance history.  A very good instructor would not do such in my experience as they would ensure the aircraft is airworthy and if asked provide advice on required work before operation of the aircraft.

It's troll time again by the look of it.

[BrendAn]

7 hours ago, turboplanner said:

It's troll time again by the look of it.

What do you mean.