Did I really just gain 10 kts by replacing a failing magneto?

FORANE

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FORANE
Had a Slick magneto with 400 hours since rebuild that was going bad. It was harder starting when warm and ran rough when warm - most noticeable at idle. Finally, after a couple hour flight, it wouldn't restart. Replaced the failed mag with a rebuilt one.
Since replacing the mag, it starts much easier and runs noticeably smoother.
I've flown a couple 2 hour flights (in opposite directions) since mag replacement.
Both flights had about a 10 kt increase in groundspeed over my typical speed.
Was I just lucky with wind? Can mag replacement make such a difference?
 
Let me file an identical flight plan for your next flight...betcha get the headwinds both ways.
 
Had a Slick magneto with 400 hours since rebuild that was going bad. It was harder starting when warm and ran rough when warm - most noticeable at idle. Finally, after a couple hour flight, it wouldn't restart. Replaced the failed mag with a rebuilt one.
Since replacing the mag, it starts much easier and runs noticeably smoother.
I've flown a couple 2 hour flights (in opposite directions) since mag replacement.
Both flights had about a 10 kt increase in groundspeed over my typical speed.
Was I just lucky with wind? Can mag replacement make such a difference?

What was your AIRSPEED?

10kts seems pretty extreme unless the mag was like BLOWN

I guess if you’re only running on one mag you’re making less power and less power is less speed etc

Did you fix the slicks or upgrade to bendix?
 
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What was your AIRSPEED?

I guess if you’re only running on one mag you’re making less power and less power is less speed etc

Did you fix the slicks or upgrade to bendix?
Perhaps I should pay more attention to airspeed, but typically don't honestly. So long as I am out of the yellow in any significant bumps, I don't pay much attention to it in cruise. In takeoff and landing phases I do pay significant attention to airspeed; was trained to fly it by the numbers during these phases of flight...

Only replaced 1 mag, the impulse left mag. Bought a rebuilt one from QAA Quality Aircraft Accessories.
 
Perhaps I should pay more attention to airspeed, but typically don't honestly. So long as I am out of the yellow in any significant bumps, I don't pay much attention to it in cruise. In takeoff and landing phases I do pay significant attention to airspeed; was trained to fly it by the numbers during these phases of flight...

Only replaced 1 mag, the impulse left mag. Bought a rebuilt one from QAA Quality Aircraft Accessories.

If you weren’t paying attention to airspeed before then you have no reference to compare it to now. So you’ll likely never know just how much it did or didn’t improve.

As an aside, I’d want to know what a typical indicated cruise speed is to use a benchmark for all flights. If it is off, you need to figure out why. Maybe configuration is different or you’re picking up ice and getting slow. With no point of reference you won’t know.
 
..I’d want to know what a typical indicated cruise speed is to use a benchmark for all flights. If it is off, you need to figure out why. Maybe configuration is different or you’re picking up ice and getting slow. With no point of reference you won’t know.

And trim settings, especially for ice.
 
Let me file an identical flight plan for your next flight...betcha get the headwinds both ways.
 
Ice is easy for me to identify. The first place it shows up is the bottom of the canopy right in my direct field of view. In my plane I am pretty diligent at avoiding conditions where ice is a possibility.
 
I think your copilot was using the "force"...."those are not the droids you're looking for"..."your plane is going 10 knots faster" :)
 
If you gained 10 kts by replacing mag, you have been flying an unairworthy plane.
 
I remember when both of mine were overhauled and the timing set perfectly, it was a VERY noticeable difference in power.
 
If you gained 10 kts by replacing mag, you have been flying an unairworthy plane.
Almost everyone is flying unairworthy airplanes. It's not hard to find a defect that makes the airplane unairworthy. Unless the mechanic is very thorough at every annual, there will be stuff that wears or corrodes or comes loose or whatever. Not usually fatal unless it's ignored for too long. The law tends to regard a defect as being a defect once it's discovered.
 
Almost everyone is flying unairworthy airplanes. It's not hard to find a defect that makes the airplane unairworthy. Unless the mechanic is very thorough at every annual, there will be stuff that wears or corrodes or comes loose or whatever. Not usually fatal unless it's ignored for too long. The law tends to regard a defect as being a defect once it's discovered.

For a plane to gain 10 kts with a new mag, the plane has to have been flying 10 kts to slow in the cruise power settings and be no where near normal takeoff and climb values. A good pilot would recognize this issue and have a mechanic involved long before annual.

Almost everyone are not flying unairworthy airplanes. Just those who chose to do so.
 
What is that saying...oh yeah, "experience is what you get right after you needed it"
 
How are your marketing skills?
"FOR SALE: Magic Mag. Install it in your plane and gain 10kts! $4000."

I hear @Timbeck2 is looking to gain about 10kts.
 
... Both flights had about a 10 kt increase in groundspeed over my typical speed...
Yeah. In the trade, that's called a tailwind.
But how much did your TAS improve?
 
For a plane to gain 10 kts with a new mag, the plane has to have been flying 10 kts to slow in the cruise power settings and be no where near normal takeoff and climb values. A good pilot would recognize this issue and have a mechanic involved long before annual.

Almost everyone are not flying unairworthy airplanes. Just those who chose to do so.

It would take a serious increase in power to gain ten knots, alright. But getting the engine to run properly and produce its rated power will indeed improve cruise speed a little.

Power required to increase cruise speed is, I think, a function of the square of the increase in speed. To get a 10% increase you'd need a 21% increase in power. That's a lot of power.

As far a unairworthy airplanes, I am an experienced mechanic and have been a thorough inspector and a director of maintenance. I have inspected airplanes that have been looked after by other mechanics and have found many glaring deficiencies that put the airplane far out of airworthiness, and those defects have been there a long time. Many years. It makes one very cynical about either cheapskate owners or lazy mechanics. My generation has known for a long time that just about any airplane will have airworthiness defects if you look deep enough.

A chief place to look is the AD record for any airplane and check it against the ADs that pertain to it. You can often find that an ACS ignition switch is installed, but the mechanic has been doing the Bendix ignition switch AD for 25 years without ever getting under the panel and seeing what make it is. The ACS has a completely difference AD issue. A whole bunch of aircraft appliances have ADs against them: wheels and brakes, radios, seat belts, altimeters, vacuum pumps, magnetos, carbs, injector systems, and so on, and I have often found these completely overlooked. They don't normally come up in the typical FAA AD search function. You have to know what's in that airplane and go looking though the AD database. That takes time.

Then there are the defects inside closed-up places like wings and tailcone. Defects like seized control cable pulleys, worn and fraying cables, cracks in bulkheads, leaking fuel fittings, cracked and rotten fuel hoses. Control systems way out of rig. Corroded wheel bearings. Plenty of stuff that gets ignored because the mechanic didn't take the considerable time and effort to pull all the inspection covers off and get a good look inside. It's false economy. You know what a seized cable pulley does? Besides making the controls stiff, it abrades the cable as it skids over the pulley. Dirt and grit get embedded in the pulley and accelerate the damage. Eventually you're replacing both the cables and the pulleys, and replacing cables is an expensive proposition. All because nobody relubricated the pulley bearings.

Look at what the regs require. I've deleted some stuff for brevity and added a few comments:

Appendix D to Part 43—Scope and Detail of Items (as Applicable to the Particular Aircraft) To Be Included in Annual and 100-Hour Inspections
(a) Each person performing an annual or 100-hour inspection shall, before that inspection, remove or open all necessary inspection plates, access doors, fairing, and cowling. He shall thoroughly clean the aircraft and aircraft engine.


I have found inspection cover panel screws rusted solid in their anchor nuts. Haven't been out in a generation.

(b) Each person performing an annual or 100-hour inspection shall inspect (where applicable) the following components of the fuselage and hull group:

(1) Fabric and skin—for deterioration, distortion, other evidence of failure, and defective or insecure attachment of fittings.

(2) Systems and components—for improper installation, apparent defects, and unsatisfactory operation.

That takes a lot of looking. There are numerous systems that run through the airframe. Pitot and static, all of the flight controls, fuel lines, hydraulic lines, and so on.

(c) Each person performing an annual or 100-hour inspection shall inspect (where applicable) the following components of the cabin and cockpit group:

(1) Generally—for uncleanliness and loose equipment that might foul the controls.

It's often horrifying what one finds under the floors of some airplanes. Incredible debris packed in by mice, junk left by avionics technicians. Such junk can get between a cable and its pulley and jam it. Accumulated oil and dirt and so on. Corroded cables and other parts. Leaking fuel fittings, leaking so slowly that there's little odor, but a huge blue stain.

(2) Seats and safety belts—for poor condition and apparent defects.

Frayed seat belts, or belts that are 40 years old. They're made of nylon that UV and other factors slowly destroys so that if the airplane crashes they might not restrain the occupants.

(4) Instruments—for poor condition, mounting, marking, and (where practicable) improper operation.

Frequent United Instrument altimeters affected by ADs. Also frequent decaying vacuum and pitot-static lines. Sometimes find wiring and hoses being abraded by the control columns.

(5) Flight and engine controls—for improper installation and improper operation.

(7) All systems—for improper installation, poor general condition, apparent and obvious defects, and insecurity of attachment.

"All systems." Is your airplane up to snuff with its annual inspection of all its systems?
 
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It would take a serious increase in power to gain ten knots, alright. But getting the engine to run properly and produce its rated power will indeed improve cruise speed a little.

Power required to increase cruise speed is, I think, a function of the square of the increase in speed. To get a 10% increase you'd need a 21% increase in power. That's a lot of power....

I think that's true for most of the stuff we fly - we are limited by drag. My Cardinal, for instance, wouldn't cruise a whole lot faster with double the horsepower. The Lancair 235 however, is a pretty slick machine and that same scaled up hot rod can be pulled much faster with a 550 (or even a 360) on the front. So I would submit that even small horsepower increases from proper magneto timing or a decent spark would be seen on the airspeed indicator more so than on most other airplanes.
 
Just one more reason why electronic timing and ignition is the way to go.. not a rube goldberg magnet setup
 
Now that I've given it more thought... All things considered, assuming a fixed pitch prop, if the cruise RPM is the same pre-magneto-repair and post-magneto-repair, to travel at a different speed, something aerodynamically had to have changed in order for TAS to change, i.e., CG, weight, etc.

A more efficient engine putting out more power might use less fuel at a given RPM, but won't go any faster unless the prop is going faster.
 
Now that I've given it more thought... All things considered, assuming a fixed pitch prop, if the cruise RPM is the same pre-magneto-repair and post-magneto-repair, to travel at a different speed, something aerodynamically had to have changed in order for TAS to change, i.e., CG, weight, etc.

A more efficient engine putting out more power might use less fuel at a given RPM, but won't go any faster unless the prop is going faster.
Was wondering the same though not sure that's a CS prop or not.. with a CS prop you could get the same RPM though if the engine is not making same power something else like FF or manifold pressure would likely be different too, along with airspeed
 
It is a MT prop with electric P-120-u control unit that allows for in flight pitch adjustment.
 
Using groundspeed is as good as a wild ass guess.
 
I"m no AP/IA but why can't you go up and turn the new mag off and see how much you slow down? o_O Just make sure you're close to an airport "just in case".
 
I"m no AP/IA but why can't you go up and turn the new mag off and see how much you slow down? o_O Just make sure you're close to an airport "just in case".
Flying home tonight or in the morning. Doubt my wife would like to see me try it. Good idea though.
Will see how it goes.
 
Now that I've given it more thought... All things considered, assuming a fixed pitch prop, if the cruise RPM is the same pre-magneto-repair and post-magneto-repair, to travel at a different speed, something aerodynamically had to have changed in order for TAS to change, i.e., CG, weight, etc.

A more efficient engine putting out more power might use less fuel at a given RPM, but won't go any faster unless the prop is going faster.

This is why the TCDS for an airplane lists the minimum and maximum static RPM for any of the propellers certified to be on that model. If the engine can't reach minimum static revs (brakes locked, full throttle, best mixture for RPM) there's something most likely wrong with the engine, less likely that someone has had the prop repitched coarser. If it runs up past the max RPM, the prop is wrong or worn/dressed well below the manufacturer's minimum widths and thickness at the various blade stations.

Make sure the tach is calibrated, or use a known accurate tach checker during the run. Many older airplanes have tachs that are well out of spec, usually under-reading. In Canada we have to check their accuracy annually and they must be within 4% of true RPM, and the tach placarded with the amount and direction of error if it isn't bang-on.
 
Static rpm is a good measure with a fixed pitch prop. My mt is adjustable and I recently adjusted the fine pitch electric stop. So, the static pitch isn't a well established number for my lancair at present.
 
Flew it in the dark for a couple hours. Did not turn off one or another mag to check for effect on airspeed, though I like the idea. It appears I have not gained kts with the new mag. It does run much smoother though.

I have heard claims of more speed, better fuel economy , easier starting, smoother running, etc with electric ignition. Are those claims true?
 
Power required to increase cruise speed is, I think, a function of the square of the increase in speed. To get a 10% increase you'd need a 21% increase in power. That's a lot of power.

Close but no cigar;)

Power required rises as the cube of the airspeed. Drag increases as the square but work done is force times distance so since when you go faster the work is done in proportionately less time you need to include an additional factor.

So to increase the airspeed from 100 to 110 you need (1.1 ^ 3) or 1.331 times the power. About 33% more.

Google - [airspeed power cube] produces a few hits. Sorry, I can't quickly see anything authoritative to list.
 
I"m no AP/IA but why can't you go up and turn the new mag off and see how much you slow down? o_O Just make sure you're close to an airport "just in case".

That’s actually a very good idea, and frankly about as risky as pulling carb heat or adjusting mixture in cruise
 
Just had to change my right mag. Failed within less than 4 hours of the left mag.
 
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