Safety Officer

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  • Birthday 05/09/2008

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  1. Common causes of Vibration article in the safety Officer's blog
  2. Vibration Common Causes and Fixes I get many phone calls on vibration in owner’s aircraft. Here we’ll talk about some of the common causes, where to look and what you can do to help mitigate these vibration issues. Here is a common list, but is not all inclusive; 1. Carbs not synced properly. 2. Carb vent hose improperly placed or removed. 3. Carbs not opening equally or fully. 4. Prop blades not the same pitch or out of track. 5. Prop out of balance. 6. Aircraft wheels not balanced. 7. Old rubber engine mounts. 8. Mag drop difference too wide between ignition modules. 9. Trigger coil air gaps too wide. 10. Gearbox worn, damaged or in need of maintenance. So let’s address each of these. The carb sync (#1) should be fairly obvious to most now. The carbs should be synced at each annual / 100 hour inspection or anytime they have been removed for maintenance or you suspect a problem like vibration and you need to rule this in or out as the problem. Carb sync is vital to a good smooth long lasting running engine. You don’t want one side trying to run at 5100 rpm while the other may be trying to run at 5200 rpm. Sync those carbs. Once done it’s easy to keep them there. The carb vent hose (#2) that may be attached to the standard Rotax air box, a small clear plastic tube on the side of the carb under the carb bowl bale or some others have them routed to different places. These hoses should be as close to equal length as possible and be routed to the same area of pressure. If one hose has fallen off the side of the carb and the other is still attached it will cause the carbs to become unbalanced which will cause your vibration. Do not place these hose ends in the air stream outside the cowl. These only take a minute to confirm their attachment and placement. Check to see if the carbs open equally (#3) by moving the throttle from idle to wide open when the engine is off. You may see some signs of this during a carb sync, but most people don’t go above 3500 rpm for a carb sync so you need to double check this while the engine is off to see if they do in fact reach WOT at the same time or if one hangs up slightly. The prop blades all too often are not the same pitch (#4) from blade to blade. This is easy to double check and can be done with either a prop protractor and or a 12” digital level. Measure back from each tip 8”- 9” and put a mark on each blade. Make the blade out to your right level with the floor and then put the level on the back of the blade where you made the line from the tip. The blades should be no more than one tenth of a degree out from each other. That measurement seems small, but it is quite easy to accomplish. The Sensenich prop gauge pins are not accurate enough. Check them by hand with a prop gauge or level once you are close. To check tracking place a box underneath the bottom tip of a blade pointing straight down. Put a line on the box where that tip just barely touches the box. Then swing the other blade(s) around and see if they all cross at the exact same mark. If they don’t you’ll need to loosen the prop flange bolts and re-torque them to get the blades to all track over your line on the box. Prop blades now days are much better in balance (#5) than they were decades ago, but all props should still be dynamically balanced. All wood blades in humid climates can change due to moisture absorption. With all the new composites that aren’t susceptible to this anymore I’m not a fan of all wood blades. Even the main bolts change torque with humidity changes. A dynamic balance will not only help vibration, but will help save your gearbox from wear or damage. The heavier the blades i.e. long Warp Drive props the more important this becomes. I have never found an aircraft wheel (#6) in balance. Most do not ever think about the smaller aircraft wheel being out of balance as a vibration cause, but over the years I have cured many a vibration just by balancing the wheels. I always balance all new wheels I install. I see some occasionally that would need up to 20 x ¼ oz. weights to bring them in balance. If you failed to balance your wheels you would never find this huge disparity. These come off and go back to the distributor. What I normally see is 2 – 8 x ¼ oz. weights per wheel. It usually takes me about 3-5 minutes to balance a wheel after it’s off the plane. Don’t disregard this when you are looking for a vibration cure. Old rubber engine mounts (#7) are a common problem. Rotax wants a 5 year rubber replacement which I’m a fan of. This includes the rubber engine mounts. Rubber can get hard or soft from repeated heating and cooling cycles plus chemical exposure and just the ozone in the air. I replace these every time I do a rubber replacement on an aircraft. It usually isn’t hard or expensive. The mag drop vibration (#8) should be obvious when you do your mag drop check. Most see anywhere from 40 rpm – 100 rpm as a normal drop and usually both mags are within about 10 rpm – 30 rpm of each other. If you experience 300-1000 rpm drop then it’s time to troubleshoot your ignition system. There are documents out there that tell you how and where to look for ignition issues. It could just be a bad plug, too wide a plug gap, a bad plug boot, a bad connection at the plug boot where the wire screws in. If it is a large drop like 800+ rpm it may be a bad ignition module. These are all items you need to rule in or out. Always start with the most common, easiest and cheapest first. Do not just throw money at everything hoping to hit the jackpot. Most ignition issues are simple common issues. The trigger coils (#9) in the flywheel compartment can at times have too wide an air gap between the pick-up and flywheel trigger point. These are checked by using a feeler gauge and checking the gap tolerances listed in the Heavy Maintenance manual and setting them to the proper gap. These can even be off from the factory so check them before installing a new engine when they are easy to get to. You not only are checking the gap, but the screw torque for tightness. Gearbox (#10) care is important. As you look for your vibration issue consider the gearbox. It has maintenance service times at either 600 or 1000 hours. Using an automotive oil over a motorcycle oil can cause premature wear and damage. At your 100 and annual inspections you should be doing a gearbox friction torque check. Normal measurements that I usually see in the field is between 425-490 in. lbs. There is a low limit, but I personally don’t like to see anything in the 300 in. lb. numbers. It only takes a few minutes to perform. Checking the magnetic oil plug for debris at every oil change is another check for gearbox wear and damage. Prop strikes should have the gearbox removed and sent to a distributor for a special inspection. Gearbox’s when taken care of tend to last a long time, but there have been a few with excessive wear in early run hours. There have been some with the 912iS engine. These are the 10 common causes for unwanted vibration. Most are easy to fix and find. When trouble shooting start with the cheapest and easiest to rule in or out and progress to the harder least common when you do your checks. Whatever you do be methodical and don’t jump all around to exotic areas to check. Most Rotax issues are easy to find when you start at “A” and then work to B, then C and so on. I hope this helps some reduce any frustration in locating an unwanted vibration. Signed your friendly, Safety Officer.
  3. This may be interesting hearing from outside the US.
  4. When you guys get old you need glasses. One poll.
  5. Just an FYI, Here is an older Dynon bulletin from Dec. 2014 on the Kavlico fuel pressure sender. It addresses fuel pressure changes with altitude. If you don't have one of these then it is not an issue.
  6. In the Blog: Chasing the Perfect Idle RPM
  7. Chasing The Perfect Idle RPM The highs and lows Is there a perfect idle rpm for the 912 series engine? This seems to be a widely discussed and at times a hotly debated item on many forums. The simple answer is NO. Set the idle where you want and or need it, but do it for the right reason. A big discussion seems to be that if the idle isn’t set low enough I can’t land or I’ll float way down the runway. This answer may surprise you, but it shouldn’t and I’ll address this later in the article. The Rotax operator’s manual says the idle rpm should be no less than 1400 rpm. While you think about this remember that the manuals are written with different engines and configurations in mind and that you will need to adjust your final thinking along those lines that fit your personal aircraft and engine setup for the idle rpm. What do I mean about different considerations? You may have a 912UL 80 HP @ 9:1 compression or a 912ULS 100HP @ 11:1 compression and either one could be with or without a gearbox overload clutch. The 912UL without the overload clutch and a lower compression ratio can handle lower idle rpm’s better than the 912ULS with the higher compression with an overload clutch. Low idle rpm with the 912ULS just causes excessive wear from vibration and pulsation in the gearbox. Warm ups and long idling times in the 912 and 914 series engines should be above 2000 rpm. So what should we consider when picking an idle rpm? First think of being nice to your gearbox parts and second is setting the idle rpm so you don’t have to ride the brakes all the time. We have all been told time and time again not to warm up at low idle rpm due to excessive gearbox wear which is usually under 2000 rpm. You also don’t want too high an idle rpm for starting as this will make your starts much tougher. The choke and ASM system work best at starts with a lower idle rpm around 1600-1800 rpm. Landing rpm should be a last consideration and I’ll explain shortly. So what is the perfect rpm? There isn’t one, but there is an idle rpm range for each to consider. A reasonably good place to be would be between 1600-1800 rpm at operational oil temp and some like the twin 912 Tecnam can be higher due to its overall higher aircraft weight and tendency not to roll as easy as a lighter aircraft. The things that may come into play here is what engine you have and how heavy a plane do you own. This would take into consideration as to how much rpm it takes to make it roll for taxi. Heavy planes would need more and light aircraft less. This part is about saving the brakes or slowing for turns. (Just a quick note; Carbs should be synced at idle along with the higher rpms) Here’s the biggy! The next question is how much does the idle rpm affect my landing? Not as much as many want to believe and it’s more about piloting skills. No one usually sets their idle up excessively high and a 100 rpm difference at normal idle rpms (1600-1800) shouldn't make any big difference in a landing especially if you we're talking the difference between 1650 and 1750. Most set their idle rpms around 1600-1900 rpm for the ULS. High idle rpms makes you ride the brakes more on the ground. Being able to achieve a lower idle rpm usually reduces taxi brake use over the higher idle settings. I will have people swear that an 1800 idle rpm over a 1650 idle rpm makes them float way down a runway or they almost can’t land. We have to go back to Flying 101 in the student flight manuals. What controls the aircraft speed? Is it the throttle or the stick? Way too many tell me it’s the throttle. For the sake of this singular discussion let’s just talk about idle rpm and maybe up to 2500 rpm. The stick controls your speed not the throttle. If you have more rpm (or speed) on landing then pulling the stick back a tad farther will land you at the same speed as if the idle rpm were lower. Try it yourself. Pulling the stick back will increase angle of attack which will increase drag which reduces speed regardless of throttle setting and the plane will settle. This can be done in any phase of flight and is done during landings. We use this during slow flight practice as we pull back on the stick to reduce speed. It's the flare in landing. The plane at idle rpm will lose altitude and settle when the angle of attack and drag are increased. This is normal for jet landings and they leave throttle in to touch. I have many friends that leave a small amount of throttle in their 912’s to touch for better tail and directional control with the prop wash. I’m one of them. It’s not outlandish it’s just a different way and there is and always has been different configurations to land. You could if you wanted land at full stall at idle or 2500 rpm. The difference would be just a higher nose up at 2500 rpm because you had to increase the drag and angle of attack which helps reduce some lift to get the speed down to stall. Try a landing at idle rpm then try one at let's say 2500 rpm. The main difference should be that the stick is farther back with 2500 rpm to help slow the plane, but the touch speed should be the same. If you fail to pull the stick back farther will you glide down the runway and maintain a bit more speed, of course you will, but that’s piloting skills. On approaches and round out the idle speed will never get to 1600 if it was set there. Depending on the plane, pilot and approach speed the rpm will always be higher and what affects that more than any single item is your angle of attack which either increases the speed and the loading on the prop or decreases it. The more landing speed the more the prop turns due to some wind milling added to the idle rpm. So even at idle with a 1650 rpm the engine speed may still be around 2100 and decreasing after you round out or flare to land. You can actually turn the engine off if gliding at a safe altitude and unless you slow down the prop can still turn with the engine off. Last year this vary scenario was presented to a large fly-in group of pilots. Many knew the correct answer, but I was stunned at the number that thought idle rpm controlled their speed. They have had a change of mind after some demos that showed landings with an idle rpm set at 1600 and rpm left right to touch down at 2700 rpm. The only difference was the 2700 rpm group had to have the stick back a bit farther to land at the same speed as the ones set at 1650 rpm. 7 years ago some friends in the UK said they couldn’t land on a 300m grass strip unless the idle was set at 1500 rpm with an aircraft with a 14:1 glide ratio. I challenged them that it can be done at 2700 rpm and on an asphalt runway. We measured off 1000’ and I made 8 landings with 2700 rpm in half that distance. The key points are leave no runway behind you at touch and use the stick to control speed and to land at almost stall. It was quite easy. In Summary; What is the perfect idle rpm? Well that’s up to you, but most will be in the 1600-1800 rpm range depending on which 912 engine and aircraft they have. Does having an idle rpm set at 1650 rpm versus 1750 rpm make a difference in landing? Not if you realize it’s the stick that controls the aircraft speed (and prop loading) and not a 100 rpm difference in idle rpm. Lower idle rpm does help for taxi on the ground and if you decide to have a low idle rpm for landing just keep in mind you have the throttle and shouldn’t let it just idle at low rpms when just sitting on the ground.
  8. Just to let people know that these floats are the same, but have a dimple on the new floats. They are the same float material, but the difference is that instead of only two test performed before shipment they now get a third test and the new test is a pressure test. This process finds any floats susceptible to sinking. Any floats that you may have with marks on them or scratches DO NOT affect the float as far as fuel absorption. Floats technically can last for the life of the engine. What could wear out is the float guide and pin from vibration and rubbing over time, but even this isn't very prevalent.
  9. Just to be clear on the float exchange process. There are lots of orders out there pending so please be patient as only so many orders can be filled at a time. For Kodiak (Rotax Bahamas) customers areas: For non-certified engines (UL) In the USA, and in other regions where warranty service is administered by the ROTAX distributor Kodiak (American Samoa, Antigua And Barbuda, Argentina, Aruba, Bahamas, Barbados, Belize, Bermuda, Bolivia, Brazil, Cayman Islands, Chile, Colombia, Costa Rica, Cuba, Diego Garcia, Dominica, Dominican Republic, Ecuador, El Salvador, French Guiana, Grenada, Guam, Guatemala, Guyana, Haiti, Honduras, Jamaica, Martinique, Mexico, Netherlands Antilles, Nicaragua, Panama, Paraguay, Peru, Puerto Rico, Saint Kitts And Nevis, Saint Lucia, Saint Pierre And Miquelon, Saint Vincent And The Grenadines, Suriname, Trinidad And Tobago, Turks And Caicos Islands, Uruguay, Venezuela, Virgin Islands)... Customers with non-certified (UL) engines, that have affected serial numbers must contact their respective independent Service Centre, (iSC). At that time they may purchase the parts from the iSC. When the old parts are returned and the paperwork is submitted with valid serial number, a credit will be issued back to the customer. (The iSC will require the customer to return the old floats, tagged with the engine serial number, before the customer can receive a refund.) For customers who prefer to have the parts changed by a qualified independent Rotax Maintenance Technician, (iRMT), contact your service provider directly to make appropriate arrangements. __________________________________________________________________________________________________________ If you don't have an engine in the serial range, but did purchase individual floats within the affected time period these can be included, but you will need to have your invoice as proof of purchase. Your distributor you purchased from may be able to help you if you did not keep the invoice. _______________________________________________________________________________________________________ If you ordered directly from Bing these floats may not be covered.
  10. Read page 2 of SB-912-067 - SB-914-048. If your floats fall within the parameters listed on page 2 of the SB they get replaced whether they are bad right this minute or not. Tell them to read page two also. It is all floats within a certain time period and or serial number because there would be no way to tell if or when a float from this casting series would go bad. 1.1) Applicability All engines of Series 912 A, 912 F, 912 S and 914 F are affected, if at least one of following criteria applies: Criterion A) Engine Serial number: Criterion Carburetors: The part numbers and serial numbers of the carburetors: Criterion C) Spare parts: Further all engines are affected, which have been equipped during engine repair, maintenance or general overhaul as of July 01, 2012 with floats with the part no. 861184, which have not been marked (see page 7, chapter 3.3). NOTE: The carburetor and/or the float may have been removed from the initial engine and used on another one. Engines and/or carburetors with serial numbers higher than in criterion A or B have already been equipped with tested floats. To provide traceability the floats were marked as described in section 3.3. For relevant information, see the maintenance records and/or the logbook. 1.2) Concurrent ASB/SB/SI and SL In addition to this Service Bulletin the following Service Instruction must be observed and complied with: - Service Instruction-SI-912-021/SI-914-023, „Inspection of carburetors“, current issue. Engine type Serial number 912 A From S/N 4 410 957 up to S/N 4 411 048 inclusive 912 F From S/N 4 413 008 up to S/N 4 413 041 inclusive 912 S From S/N 4 924 408 up to S/N 4 924 838 inclusive 914 F From S/N 4 421 136 up to S/N 4 421 403 inclusive Carburetors Serial number 912 A/F 1/3 part no. 892500 - from S/N 116434 up to S/N 144101 inclusive 2/4 part no. 892505 - from S/N 115846 up to S/N 143886 inclusive 912 S 1/3 part no. 892530 - from S/N 121087 up to S/N 143702 inclusive 2/4 part no. 892535 - from S/N 120980 up to S/N 143505 inclusive 914 F 1/4 part no. 892520 - from S/N 116207 up to S/N 143799 inclusive 2/4 part no. 892525 - from S/N 120228 up to S/N 143310 inclusive and 1.1) Applicability All engines of Series 912 UL, 912 ULS and 914 UL are affected, if at least one of following criteria applies: Criterion A) Engine Serial number: Criterion Carburetors: The part numbers and serial numbers of the carburetors: Criterion C) Spare parts: Further all engines are affected, which have been equipped during engine repair, maintenance or general overhaul as of July 01, 2012 with floats with the part no. 861184, which have not been marked (see Service Bulletin SB-912-067/SB-914-048, latest revision, chapter 3.3, page 7). NOTE: The carburetor and/or the float may have been removed from the initial engine and used on another one. Engines and/or carburetors with S/N higher than mentioned in criterion A or B have already been equipped with tested floats. To provide traceability these floats were marked as described in section 3.3 (refer to Service Bulletin SB-912-067/SB-914-048, latest revision). For relevant information, see the maintenance records and/or the logbook. For complete instructions and compliance to this Service Bulletin refer to Service BulletinSB-912-067/SB-914-048, latest revision, section 1.2 onwards. NOTE: Section 1.6) Approval: Is not required for engines of type UL (Series). Section 3) Accomplishment: In addition, persons with adequate typespecific training can perform the work. Engine type Serial number 912 UL from S/N 6 770 733 up to S/N 6 771 484 inclusive 912 ULS from S/N 6 780 228 up to S/N 6 783 917 inclusive 914 UL from S/N 7 682 154 up to S/N 7 683 662 inclusive Carburetors Serial number 912 UL 1/3 part no. 892500 - from S/N 116434 up to S/N 144101 inclusive 2/4 part no. 892505 - from S/N 115846 up to S/N 143886 inclusive 912 ULS 1/3 part no. 892530 - from S/N 121087 up to S/N 143702 inclusive 2/4 part no. 892535 - from S/N 120980 up to S/N 143505 inclusive 914 UL 1/4 part no. 892520 - from S/N 116207 up to S/N 143799 inclusive 2/4 part no. 892525 - from S/N 120228 up to S/N 143310 inclusive
  11. "Note that I have the same attitude toward owners of this forum who masquerade under the cognomen "Admin" and so forth and put out dogma with the picture of a dog, so don't take it personally." Ah come on Jim you know in your heart you really love us. A good belly rub and we'll hang with you all day.
  12. BRS Service Bulletin Just a quick look at the handle for cracks BRS Bulletin.pdf
  13. Yes it applies to all CT's.
  14. The stabilator is one of the most often over looked items in the pre-flight and especially the inspection. Most people aren't quite sure what to look for. This tip is aimed more at the pivot pin and nut torque. Grab the stab and move it fore and aft. Not up and down. If there is even the tiniest free play fore and aft then there is a very high chance the pivot pin nut needs to be torqued. If the stab has never been removed and had this checked after about 200+ hrs. then there is a good chance it needs to be torqued. It isn't the nut that comes loose, but just things settling and wearing in. I have found 90% of the CT's in the last 8 years to need the nuts re-torqued. I usually find them down around 90-120 in/lbs and they should be 200 in/lbs. The other minor issue is the rod end attachment pin for the trim tab. When you unscrew the 8mm nuts the pin may turn. usually one comes off without any issue, but the second nut turns the pin which shouldn't happen. The pin has a smooth area with no threads up against the mount. Use a pair of needle nose vise grips and secure it in that area. Remove the other not and then take the pin out. Clean the pin and the hole it goes into with lacquer thinner and then apply Loctite 480 to the pin and re-insert it into its mounting hole and center it. Allow it to set up a short time them re-install the stab and trim rod ends. Another tip. Before you slide the stab on take a piece of safety wire and attach it to the two loose trim tab rod ends, but only twist the wire 1-2 times because you are going to pull it off in a minute. As you slide the stab back in place pass the safety wire up through the hole the rod ends go into and use it to guide the rods up into there place. Once they are up inside remove the wire and place each corresponding rod end on the left or right side. All this may sound hard or tedious, but is all quite easy and doesn't take much time. If your stab has never been removed and had the pivot pin nut torque checked then you should at the next inspection. If it has been done then I haven't found any that has needed it again up to 1000 hrs or more. You can feel the free play fore and aft, but it may be subtle.
  15. Just for fun, The other day I wanted to know what the under the cowl temps were on two parts. The ignition modules and the reg/rec because 170F for the modules are a killer and after shut down there is no real place for heat to escape. I used a couple sets of temp strips on each. The ignition modules at their hottest which I assume was sitting for a few minutes after landing with no appreciable air flow was 130F. The reg/rec was 115F. These temps for the CT are well within any problem areas for the Rotax parts where heat can cause failures.