magnetos
Thread Starter
magnetos
a non flying friend (he did have some lessons many years ago) was questioning me about ignition systems on my aircraft, I have two stroke and 4 stroke Rotax engines in my 2 aircraft. His concern was about the reliability (or lack of) of magnetos fitted to aircraft engines and I said that the systems fitted to Rotax engines are basically fit and forget. Not so, he said, the systems fitted to Lycomings and Continentals in GA aircraft. Every 2 or 3 seasons.........
So what does go wrong with them? I have heard stories about impulser faults and, presumeably, the points are as prone to wear, adjustment and fatigue as they were when cars had points ignition systems.
Of course the Rotax circuits don't have any points or moving parts and seem to be much better for it.
Rans6...
So what does go wrong with them? I have heard stories about impulser faults and, presumeably, the points are as prone to wear, adjustment and fatigue as they were when cars had points ignition systems.
Of course the Rotax circuits don't have any points or moving parts and seem to be much better for it.
Rans6...
Join Date: Jun 2003
Location: EuroGA.org
Posts: 13,787
Likes: 0
Received 0 Likes
on
0 Posts
Mags (especially the single shaft dual mag types) are probably the weakest link (statistically) on an otherwise highly reliable Lyco/Conti engine, but they are fine if you follow the 500hr overhaul periods.
As Johnm says, they do not require external power and that is a really super safety feature.
Electronic ignition would be more accurate, of course, but aviation history is not exactly overflowing with reliable electrics and electronics - I think because very few people with a brain want to work in a company which brings out a new product every 20 years or so
As Johnm says, they do not require external power and that is a really super safety feature.
Electronic ignition would be more accurate, of course, but aviation history is not exactly overflowing with reliable electrics and electronics - I think because very few people with a brain want to work in a company which brings out a new product every 20 years or so
Join Date: Apr 2009
Location: New Zealand
Age: 38
Posts: 247
Likes: 0
Received 0 Likes
on
0 Posts
plugs, usually fouled.
Join Date: May 2001
Location: 75N 16E
Age: 54
Posts: 4,729
Likes: 0
Received 0 Likes
on
0 Posts
Never had a problem with the mags other than straight after overhaul! After the overhaul we broke down twice as the impulse spring stuck and we couldn't start the engine on the ground. It was very annoying and the second time we were away from home and by the time we got going we were racing sunset to get home.
A little trick from our maintenance organisation - wind the prop back twice then forwards, which appears to have released the spring and got us going. NOTE: They say DO NOT try this on a Continental engine as it will shear the vac pump shaft apparently.
Yes there are some good articles by John Deakin (search Avweb) about leaning on the ground, in fact he advocates doing the run up with highly leaned engine as this will tell you far more about the state of the mags and plugs than at full rich.
A little trick from our maintenance organisation - wind the prop back twice then forwards, which appears to have released the spring and got us going. NOTE: They say DO NOT try this on a Continental engine as it will shear the vac pump shaft apparently.
Yes there are some good articles by John Deakin (search Avweb) about leaning on the ground, in fact he advocates doing the run up with highly leaned engine as this will tell you far more about the state of the mags and plugs than at full rich.
Join Date: Apr 2003
Location: Midlands
Posts: 2,359
Likes: 0
Received 0 Likes
on
0 Posts
I have had 1 ½ mag failures in the air and just made it to a runway run by a parachuting club (Scotland) before I ran out of height.
The Rotax system is very good as it uses discharge capacitors, and providing the crank is rotating at 300rpm is independent of the conventional electrical system. The system is a fraction of the weight of a mag and does not have the 500h maintenance program, being totally maintenance free.
Rod1
The Rotax system is very good as it uses discharge capacitors, and providing the crank is rotating at 300rpm is independent of the conventional electrical system. The system is a fraction of the weight of a mag and does not have the 500h maintenance program, being totally maintenance free.
Rod1
Join Date: Jun 2003
Location: EuroGA.org
Posts: 13,787
Likes: 0
Received 0 Likes
on
0 Posts
Plug fouling is mostly caused by taxi without leaning the engine. I have not had a fouled plug for about 5 years, since I started doing that, religiously.
Whether iridium plugs help I am not sure. I have been using them for longer than that, and after 1000hrs they show no sign of wear.
Whether iridium plugs help I am not sure. I have been using them for longer than that, and after 1000hrs they show no sign of wear.
Join Date: Jul 2005
Location: SoCal
Posts: 1,929
Likes: 0
Received 0 Likes
on
0 Posts
The good news - only had a mag fail on me once.
The bad news - this happened in Birdsville, QLD, Australia
If you're unfamiliar with Birdsville, have a look at Google Earth....
A/c was a 210 and yes, the mags just had their 500 hour check done
The bad news - this happened in Birdsville, QLD, Australia
If you're unfamiliar with Birdsville, have a look at Google Earth....
A/c was a 210 and yes, the mags just had their 500 hour check done
Join Date: Jun 2003
Location: EuroGA.org
Posts: 13,787
Likes: 0
Received 0 Likes
on
0 Posts
That's why I usually get mags overhauled in the USA
I bought a spare magneto which lives on the shelf, so the overhaul is not time-critical.
I bought a spare magneto which lives on the shelf, so the overhaul is not time-critical.
Join Date: Nov 2001
Location: UK
Posts: 939
Likes: 0
Received 0 Likes
on
0 Posts
I've had one mag failure on the ground and one in the air, which was at almost exactly 100 hours post engine overhaul and the points actually snapped in flight. The only indication until power checks when safely on the ground was a slight drop in revs and a significant increase in EGT
Join Date: Aug 2006
Location: Sth Bucks UK
Age: 60
Posts: 927
Likes: 0
Received 0 Likes
on
0 Posts
P mag substitutes the original mag for electronic ignition with advance/retard and has a built in generator for it's own power supply.
By all accounts they significantly improve performance but AFAIK not for CAA approved use though.
By all accounts they significantly improve performance but AFAIK not for CAA approved use though.
Join Date: Jun 2002
Location: UK
Posts: 626
Likes: 0
Received 0 Likes
on
0 Posts
Mags on the whole are very, very reliable. And, sorry to explode the myth but the Bendix single drive, dual mag is just as reliable as any 'normal' mag. Okay, there is potential for a big problem if the single drive fails but can anyone quote an example of this actually happening?
500hr inspection is just that - an inspection. It may show up worn points, cam or other parts. What it doesn't do is tell you how long the ignition coil is going to last. Much the same for an overhaul. Don't be fooled into thinking it's a guarantee of 500 hours trouble free future use...
Impulse coupling springs do go weak and are often the cause of intermittent starting problems - impulse disengages at cranking speed but 'clicks' when turning the engine over by hand, just to put you off the scent. Gipsy Major mag tapping is to free stuck impulse couplings.
For some reason total mag failure seems to occur more often on the ground between flights rather than when airborne.
Bendix mag inspection is 4 years calendar time - inspection preiods aren't just by the hour.
Fouled spark plugs can be avoided by correct shut down procedures. Lycoming's advice is to run the engine at around 1700rpm (if it's clear behind) for 15-20 seconds then back to 1200rpm and mixture straight to idle cut off. The lead scavenging agents in 100LL work better at higher combustion chamber temperatures which is why the higher rpm run down and leaning whilst on the ground helps keep the plugs clean.
It isn't just the lower plugs that can get fouled. With an excessive mag drop during power checks, aggressive leaning may well clear the offending plug. Try it three times and if it doesn't work, don't fly - seek help. I heard of one aircraft owner who went flying round the circuit to try and clear the plug after leaning it didn't work. That didn't work either. So he flew one plug down to his maintenance facility some 30 miles away. Not a very good idea...
Despite the good things about mags, the future is ignition systems like the Rotax 912. In fact the Rotax 912 is the engine of future GA. Be it in Rod's MCR01, my RV-12 or an IFR certified Tecnam P2006T twin.
PS No vacuum pump likes being turned backwards (same ones are fitted to Continentals as Lycomings). The carbon vanes are set to sweep (angled backwards) in the chamber and they can break and jam if turned the wrong way, causing the pump drive shaft to fracture (as it is designed to do to prevent potential engine damage).
500hr inspection is just that - an inspection. It may show up worn points, cam or other parts. What it doesn't do is tell you how long the ignition coil is going to last. Much the same for an overhaul. Don't be fooled into thinking it's a guarantee of 500 hours trouble free future use...
Impulse coupling springs do go weak and are often the cause of intermittent starting problems - impulse disengages at cranking speed but 'clicks' when turning the engine over by hand, just to put you off the scent. Gipsy Major mag tapping is to free stuck impulse couplings.
For some reason total mag failure seems to occur more often on the ground between flights rather than when airborne.
Bendix mag inspection is 4 years calendar time - inspection preiods aren't just by the hour.
Fouled spark plugs can be avoided by correct shut down procedures. Lycoming's advice is to run the engine at around 1700rpm (if it's clear behind) for 15-20 seconds then back to 1200rpm and mixture straight to idle cut off. The lead scavenging agents in 100LL work better at higher combustion chamber temperatures which is why the higher rpm run down and leaning whilst on the ground helps keep the plugs clean.
It isn't just the lower plugs that can get fouled. With an excessive mag drop during power checks, aggressive leaning may well clear the offending plug. Try it three times and if it doesn't work, don't fly - seek help. I heard of one aircraft owner who went flying round the circuit to try and clear the plug after leaning it didn't work. That didn't work either. So he flew one plug down to his maintenance facility some 30 miles away. Not a very good idea...
Despite the good things about mags, the future is ignition systems like the Rotax 912. In fact the Rotax 912 is the engine of future GA. Be it in Rod's MCR01, my RV-12 or an IFR certified Tecnam P2006T twin.
PS No vacuum pump likes being turned backwards (same ones are fitted to Continentals as Lycomings). The carbon vanes are set to sweep (angled backwards) in the chamber and they can break and jam if turned the wrong way, causing the pump drive shaft to fracture (as it is designed to do to prevent potential engine damage).
Join Date: Jun 2003
Location: EuroGA.org
Posts: 13,787
Likes: 0
Received 0 Likes
on
0 Posts
Okay, there is potential for a big problem if the single drive fails but can anyone quote an example of this actually happening?
The single shaft dual mag engines are rare anyway.
No vacuum pump likes being turned backwards
I have also built up an electrically powered vac pump rig (for erecting vacuum horizons) and the capacitor-start motor had no trouble running the vac pump in either direction, at 1300rpm. I can't remember which direction I ended up running it in the end but it worked equally. This was the very common 215CC pump. Certainly the myth that the vanes shear off following any reversal (like turning the prop backwards) is a myth - I ran it for hours in either direction.
Join Date: Apr 2010
Location: IRS NAV ONLY
Posts: 1,230
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by smarthawke
Despite the good things about mags, the future is ignition systems like the Rotax 912. In fact the Rotax 912 is the engine of future GA. Be it in Rod's MCR01, my RV-12 or an IFR certified Tecnam P2006T twin.
The problem with aircraft piston engines are - as IO540 says - no development, we still have newly developed engines with carburetors, which have catastrophic air-fuel mixture ratios between cylinders (sadly even many injected engines with factory-made injectors don't offer much improvement), and I could go on and on and on about it. I think aviation industry should look to engines used in todays cars, you see technology as: variable valve timing, electronically controlled ignition, accurate piezo-injectors, 4 valves per cylinder, etc. Looking at this, it almost seems as if we were flying aircraft made in Stone Age