BigDiggs88

hi there,

I currently own a 97 model CA25 skyfox gazelle. this is the second year of owing this fun and rewarding little plane.  I am wanting to replace both the forward wing attach clevis (locks the wing into place when wings aren't folded) and the rear attachment bolt (hinge point for wing articulation)

Looking through the OEM parts manual, it doesn't reference these components. I have measured the hardware which is openly available but has anyone had any previous  knowledge of the material requirements for these components (S/S, cadmium plated, AN or MIL spec) wanting to ensure i am replacing these to the desired spec, there is no damage or reason for me to interfere with these, its just a piece of mind task.

any assistance would be greatly appreciated.

ok Gents, apologies for the delay in comms. has proven most challenging having an aircraft parked 400kms from where i live. since the original posting I'm now licensed and have my L1 certification, so it has bee quite a busy month.  Continuing on with the throttle hesitation issues between 3500-4000rpm i suspect that poor workman ship is to be the most likely culprit. Couple of things i wish to share, given the community has a wealth of knowledge and i fee obliged to return the favor for other aviators with similar issues.

- Carb vent lines were inspected and found one line had been cable tied against the engine support frame. (line was squashed) also wouldn't haven been helping the issue.

- one throttle control linkage (on the carb) was bent. was removed and straightened, both idle stop positions rigged so they were identical.

- one carby choke linkage was sticking, may not have been helping but was freed up with no issues.

- the diaphragms were removed and inspected. upon inspection there was physical debris under the diaphragm seats on both carbs. The rubbers were quite soft indicating they had been changed recently (no log book entries to say otherwise, purely a speculation). The pistons were cleaned, as were the seats and both carbs reassembled. This has actually appeared to have rectified the issue. the response is crisp and doesn't hesitate.

In a nutshell i think a lot of small things have lead to a big issue. the dirt under the seats could have been possibly been the most likely cause. I was hoping to take some photos and make this a little more visual, but when your focused on the issue at hand, its easy to forget to take the occasional happy snap.

again as a first time forum-er id like to thank the community for their assistance. 

On 20/11/2024 at 6:46 PM, 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.

ok to be clear, i have the full maintenance records of this aircraft right back from when it was a VH registered aircraft. i have an aviation back ground as an AME on VH aircraft as well as two other trade quols, but obviously applied to larger vehicles but similar principles apply.  All testing has been done, inspections performed in conjunction with an L2 maintainer. i just wish to iron this out before assumptions lead to things bigger than the problem at hand. i do apologise for the delay in communications given the fact i have been training and studying to do my license at the same time as this posting. as it stands i have run out of time as i don't live where the aircraft is hangered and will endeavor to sort the issue whilst sorting my L1 with RAAus. i do wish to thank the forum community for the shared knowledge as information is well worth its weight in gold. i will leave my post up till i have found the remidy and will share all, and any findings once rectified. 

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. 

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

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.

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.

13 minutes ago, Blueadventures said:

Are you moving from idle to full throttle over a four second period, the Rotax does not like fast throttle (like it sounds when you refer to "stab the throttle quickly" which is not correct application of throttle according to Rotax.)

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.

3 hours ago, turboplanner said:

No, Bing call the three stages Idle Range, Mid Range, Full throttle.

The needle usually plays the most important part in Mid Range so coming into Full throttle range where jet size plays the most important part, the engine should be clearing if it is fluffy in Mid Range.

 

This explains the sequence: chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://electricmotorglider.com/wp-content/uploads/2017/02/CV-Carb-Web.pdf

 

thanks mate ill have a sus when i get a chance

5 hours ago, Area-51 said:

If fuel related, 3000rpm and upward is the main jet circuit of the bing64 carbi. Check for incorrectly positioned tab or ruptured diaphragm or asymetric needle position height between carbis. (The diaphragms would be my first and easiest go to if everything outside looks correct). Check for a broken throttle arm or choke spring.

 

If electrical, check the resistor plug connectors for correct resistance and ignition leads for arcing through insulation to earth at the inlet manifolds or cylinder heads. Verify plug gaps are set correct.

 

Try opening throttle slowly and see if issue is still apparent; better or worse

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

9 hours ago, peterg said:

Are the plugs the correct ones for the 80HP ie not the 100HP plugs

yeh mate, double checked the the manual before purchasing the replacements and installing them

8 hours ago, turboplanner said:

See if the Manual shows the settings for the second stage. Might not be metering enough fuel in second stage.

Thanks buddy, if it wasnt metering the second stage properly would it not be across the entire upper RPM range where it becomes an issue?

Hi all, 

New to the group and having some issues with my Rotax 912 in my skyfox gazelle and am requesting some assistance. 

When advancing the throttle the engine appears to be rough through the 3000-4000rpm range, however when your backing off the throttle and then re-apply the power, like in the event of a go-around (again through the 3-4000range) the engine appears the sputter, and hesitate for about 3-4 seconds before recovering. The below has been checked, just looking to see if anyone else has potential ideas.

- Fuel filters new

- Fuel lines new

- On engine fuel pump new

- Plugs all new

- carbs are balanced

- ignition drops 60-80rpm L-R

- no change between choke on or off

- no change between AUX fuel pump on or off

- Inlet connections all inspected and re-fitted

- Air filter - clean and clear