Aircraft Engines

[Eglsfootball]

Why are small aircraft engines so much harder to start than engines in a car?

 

[bart]

You must not own any british cars built before 1970.

The answer most likely lies in newer cars having electronic ignitions with computers that monitor a variety of factors to deliver the precise amount of fuel and air to get a fast start.

In an aircraft with a piston engine, it is you that are in charge of deciding how much fuel and air is needed for a fast start.

With time and practice, it will be as easy as starting your Honda.

 

[Wankel7]

Trainers mostly have carburetors. Most likely your car is fuel injected. Like said above.

For example, most fuel-injected cars have air intake and temp sensors. These sensors tell the engines computer what the temp is in the air and the coolant. If it is cold it richens up the mixture during cranking. This assists in the starting process. There is a lot happening when you turn the key on a fuel-injected car.

Question? Do you fly in a cold climate? Do the people you rent the airplanes from preheat them?

Wankel

 

[Eglsfootball]

I fly in Mass. so right now yes it is a cold climate. The place where i rent does use preheaters. A few weeks ago it was really cold and on some of the planes even the preheaters wouldn't work. It seems that the planes are still harder to start than a carborated car. Why does a plane have a primer when carborated cars don't?

 

[Gulfstreamlover]

I have the same problem with the cold and piston engines, took me 10 minutes to start a Navajo the other day Man was I embaressed sitting on the ramp next to all those Gulfsteams and Falcons

 

[A Squared]

"Why does a plane have a primer when carborated cars don't?"

Carburated cars have a choke, older cars had manual chokes and newer ones have automatic chokes. the choke enriches the mixture for starting and warm up. That is not unlike what a primer does, although it's accomplished in a different manner.

Also, a car is generally turned off by switching off the ignition, this leaves the engine in a "primed" condition with a viable fuel-air mixture in the manifold and in at least some of the cylinders.

An airplane engine is generally stopped by shutting off fuel, which leaves little or no fuel in the induction system. A shot of prime even on a warm engine will usually result in a quicker start that just cranking the engine.

A cold carburated automobile engine, or one which has been sitting for a long time, will often not start readily. Pumping the accelerator a couple of times usually helps, as this works the accelerator pump which squirts gasoline into the induction system, much as a primer does.

 

[enigma]

The largest contributor to recip starting difficulties in most light aircraft is the ignition. Except the very latest production light aircraft, recips use magnetos to make the spark. A mag is basically a generator, it requires rotation to generate electricity and the starter just barely provides enough rotation to make a weak spark. Most mags use a device called an impulse coupler to connect the mag to it's drive, the coupler sort of snaps the mag, like cracking a whip, in order to speed up the generator portion and provide a stronger spark. Even with these devices, the spark at starting rotational speeds is weak. Additionally, most small recips are timed for optimum spark delivery at cruise speed. Your auto uses a pretty decent computer to figure out spark delivery down to the milisecond, your airplane delivers the spark on a schedule determined by an engineer using a slide rule in 1935. When you combine a weak spark with obselete fuel delivery systems, you get difficult starts.

In defense of mags, they are almost absolutely reliable. That being the main reason aircraft use them. Also, the faster the engine speed, the stronger the spark. Top fuel dragsters use mags and they obtain around 8000hp from 420 cubic inches.

regards,
enigma

 

[mar]

Simple philosophy = Safety + Reliability

Eglsfootball--Interesting questions.

If you look at the airplane engine from a design standpoint it's pretty darn simple, ain't it?

Really it's nothing more than 1930's technology.

I'm no engineer but if I were to design something that I wanted to be safe and reliable I'd try to keep it pretty simple.

Unfortunately the exorbitant cost of the average airplane engine is due to the phenomenon of "Product Liability."

In other words: Joe Sixpack does something stupid and kills himself. Overcome with grief (and a looming house payment) Mrs. Sixpack retains Mr Lawyer. Mr. Lawyer, per industry standard, charges 33.3% of any monetary settlement so has his own best interests in mind when he files suit against Mr. Deep Pockets, the manufacturer of the airframe, engine and seat belts.

Of course the airplane crashed because Mr. Sixpack made a downwind takeoff into IMC with water in the fuel tanks that he neglected to drain because he was high on Cocaine but thanks to Mr. Lawyer, the only point Mr and Mrs Juror can focus on is the fact that the engine quit causing Mr. Sixpack to sustain blunt impact forces to his cranium and torso--and how sad for Mrs Sixpack who is entitled to some compensation for her loss and suffering.

Welcome to the beautiful world of aviation tort law.

Fly safe, ok?

 

[A Squared]

In defense of mags, they are almost absolutely reliable.

Enigma,

Lucky you!, you haven't had the opportunity to wade through the reams of Airworthiness Directives which cover almost every component of most models of GA magnetos, maintain them, replace the impulse couplings, or enjoy many of the other aspects of owning and/or making your living with magneto ignition engines.

Your other comments about magnetos are technically accurate, but they are not particularly reliable in the context of today's technology: Impulse couplings fail, coils develop faults, magnets weaken, distributor blocks crack, distributor gears shed teeth, distributor arms and terminals erode and pit, breaker points pit, breaker cam followers wear.

We in aviation (myself included) are very fond (perhaps overly so) of the fact that the magneto is a neat device which will continue the keep the engine running with no external source of electricity. Don't let that fool you into thinking that magnetos are reliable. Pound for pound, a magneto probably absorbs much more than it's share of maintenance and inspection hours and dollars than any other componnent of your average GA airplane.

Why do you think we have 2 of them? Yes, complete failure of a magneto will result in complete failure of an engine ... but then so will complete failure of a carburator, oil pump, or a camshaft...and there's only one each of those per engine.

 

[enigma]

Enigma,

Lucky you!, you haven't had the opportunity to wade through the reams of Airworthiness Directives which cover almost every component of most models of GA magnetos, maintain them, replace the impulse couplings, or enjoy many of the other aspects of owning and/or making your living with magneto ignition engines.

OK, I was overly optimistic. Get MAR and ya'll sue me

I will basically stand behind my point that small recip mags are reliable, maybe I give them too much credit, but they work pretty well.
A point, (no pun intended) the vast majority of my flight time has been in machines in which you figure fuel by the pound, and I suspect that yours has been in birds that buy Aeroshell by the barrel. You have much more experience with mags than I do, so I'll change my stance in deference to your experience.

I still fix autos on the side, and I can tell you that modern automotive ignitions are not bulletproof either. They work better, than points but not perfectly. I guess the truth is, any system capable of delivering 25K to 50K volts is hard to keep running perfectly.

regards,
8N

 

[mar]

Hey man, leave me out of it!

As far as I'm concerned it's all PFM.

Ask me where the battery is located on the aircraft and I'll point to the switch labeled 'BATT' and say, "...at the other end of that switch."

Who cares really? I'm just a trained monkey--on the evolutionary scale that's one step above personal injury lawyers.



Oh crap. Please lay off the evolution reference.

 

[Cardinal]

Eglsfootball - There's a fair chance that your CFI learned to fly in Florida and doesn't have any more experience than you in getting a really cold piston engine to light off. First, preheating it makes it easier, and can save you considerable embarassment. If not available, try this:
Once you have the aircraft fully configured to start, and after priming normally, unlock the primer and pull it all the way out, and leave it out. You now have some fuel in the plunger on "ready reserve." Crank the engine, and it will burp along for a few seconds and start to die. At this point smoothly push in the primer, and this will provide the richer mixture that you need to get the 'ole girl running. If your spit is freezing before it reaches the ground, you might even need an extra pump or two during that first 20 seconds or so. Don't go crazy with the primer though, you can potentially flood the engine, start a fire under the cowl, etc.

 

[Eglsfootball]

I'm going flying today and its 10 degrees. We'll see how fast i can get the engine started. lets hope the heat works too, because last time it stopped working at 4,000 feet and it was colder than today. good thing i love flying!

 

[enigma]

I'm going flying today and its 10 degrees. We'll see how fast i can get the engine started. lets hope the heat works too, because last time it stopped working at 4,000 feet and it was colder than today. good thing i love flying!

Eagle, your inflight stoppage should be investigated before you fly again. It probably has nothing to do with hard cold starting.
You obviously succeeded in a restart, but I wouldn't temp fate.

good luck,
enigma

 

[avbug]

Why are small aircraft engines so much harder to start than engines in a car?

They're not. It's a pilot issue. I can't count the number of times I've seen pilots crank a starter past it's duty limits, kill a battery, and once even melt the terminals off a battery.

This isn't the engine's fault. It's the pilot's fault, and most of the time it comes back to inadequate training.

If you turn three blades and the engine doesn't fire, then stop turning and figure out what you're doing wrong. Either there's a problem with the engine, or you're doing something wrong. Find out what it is, and don't waste your time cranking.

The possible exception is the radial engine, for reasons too numerous to list here.

 

[Wankel7]

Eagle, your inflight stoppage should be investigated before you fly again. It probably has nothing to do with hard cold starting.
You obviously succeeded in a restart, but I wouldn't temp fate.

good luck,
enigma

I think he ment the heat stopped working

Never the less. I would look into why the heat stopped working too.

Wankel

 

[kevdog]

1-800-LYCOMINGS

 

[Eglsfootball]

I think he ment the heat stopped working

i did mean the heat stopping and today i went up and it worked fine.

 

[enigma]

I think he ment the heat stopped working

Never the less. I would look into why the heat stopped working too.

Wankel

that's my mistake for the year, now i've got to stay on my toes.



enigma