Derestricting Hyosung 125 Comet

Yeah, my bikes always seemed to run more smoothly on a crisp and chilly
morning...

 

On a chilly misty morning even more so. My Bandit just starts to
splutter and cough due to ice in the carbs.

 

*Woooooosh!*

 

Yes. But only with physics, unfortunately...

 

Whinging Courier wrote

I have always been a firm believer in the power of Esso Regular me.

 

Cold air = denser air = more gas getting into the pots, plus a cooler
incoming charge (same as having God's own intercooler).

You might think this would upset the mixture, but in cold weather fuel
is denser too, so it self-adjusts.

Next year's GP will be in Antarctica....

 

Heh, less of the little fucker please.

 

The wings work better in cooler, thicker air, but the engine does too. This
is because every intake stroke pulls in a higher mass of air, and therefore
each stroke can burn more fuel and produce more power.

On your average Cessna, you've got three primary engine controls: the
throttle, the mixture control, and the carb heat. All of these do roughly
what you'd imagine from the description.

You've also got a primer, which is a little pump that puts neat fuel into
the intake manifold. If you're starting the engine on a cold morning, you
give it two or three pumps, and then lock it down so it doesn't bleed fuel
and **** up your mixture. Then you set carb heat off, mixture rich,
throttle open a crack, mags on both and operate the starter. All of the
engine controls are left as is until after take-off, apart from things like
checking the engine runs acceptably on left and right mags separately, and
power checks. Once you're off the ground, climbed out and set course to
wherever you're going, you start dicking about with the mixture to find the
optimum for your power setting, altitude, air temperature etc. This is
called "leaning", and is a black art involving increases and decreases in
rpm as you dick about with the mixture knob. If you're climbing, you need
to repeat the exercise from time to time as air pressure and temperature
decrease. Some people spend their whole lives dicking about with the
mixture knob, especially on multi-engine and other complex types.

When you're doing a landing, you'll have the mixture set to rich, carb heat
on, throttle to what you need - the throttle controls rate of descent, the
attitude of the aircraft controls airspeed.

After landing, you get the carb heat off. As a rule, you don't use carb
heat at all on the ground, because it pulls unfiltered air from around the
engine cooling fins (air-cooled engine), and if you taxy through a puddle,
it could suck the spray into the engine (as well as any other muck or dust
that happens to be blowing about). Shutting down the engine, you close the
throttle, do a mag check, then haul the mixture knob right out to max lean.
The engine will die in a couple of seconds. Then mags off, shut down the
rest of the electrics, and you're done.

Well, now you do )

 

Chris,

A long shot but...

.... You aren't the Chris I was talking to about this very same subject at a
Jon, Mike & Loren's BBQ a few months back by any chance? The guy who learnt
at Oxford aviation?

If not then I really should get his email address

Dave.

 

Chris Cowley wrote

When you do the math for a prop you use the same basic sums as for any
wing and it includes a constant for air density. I suspect that in a
full size aeroplane you would be looking for constant revs from the
engine so you would need to feather the prop slightly on a colder day to
achieve the same overall effect.

A quick glance at the equations suggest to me that you are talking about
a fraction of a percent difference across "normal" ranges of air density
so in practice it probably makes bugger all difference.

 

The problem with being off sick is that I'm too crocked to spend the time
out on the bike. Still, things are moving into a post-crippled phase...

 

platypus wrote

You seem to be taking an awfully long time to get fixed, is everything
going ok?

 

Oh yes. It just took a while for the bones to knit. The other problem was
the shoulder blade: the arm had to stay immobilised, so what muscles I had
are more like soggy bogroll atm. But I can raise my arm over my head, I've
been sleeping in a bed for a few nights now, and I can change gear in the
car without yelling. I've been driving for a week now, and I may take the
Kontinent Krusher out for a trundle at the weekend.

Ta for asking, like )

 

platypus wrote

Not a problem, think nothing of it. Besides it gives me the chance to
point out that there are at least two things you are slow at.

 

That's "last a long time".

 

platypus wrote

Counting to two is not a long time.

 

The thing to remember is that, when you're hammering down the runway, the
wings aren't producing lift, and they don't until you reach take-off
airspeed, pull back on the stick and rotate the aircraft to create an angle
between the chord line of the wing and the relative airflow (angle of
attack). As drag is the price of lift, the drag is much less until
rotation - by which time, the aircraft is at flying speed.

Another benefit of cold air is that the same aircraft can fly higher in it,
because the power and lift both stay with you higher. It's also crisper and
nicer to fly in, too.

 

I haven't flown anything for nearly 10 years, but when I did, it was the
usual: ShiteOldCessnas, Cherokees, a Robin (once), a Beagle Terrier
(actually Beagle's demonstrator in a previous life), a Tripacer, a few
microlights, my mother's Rallye MS880B, gliders, a Supercub (once)...
That's probably about it.

You expected refinements like cabin heat in a Shadow? You can barely get
the pilot into a Shadow.

Started at Newtownards in Norn Iron, later places like Leavesden, Popham,
White Waltham, Blackbushe, Lasham, Nympsfield, Staverton.

 

The aircraft has less drag running along the ground than it has airborne,
because the wings aren't generating lift to take the weight of the thing, so
acceleration along the runway will always be greater than anywhere else.
The drag caused by skin friction, turbulence, and simply pushing the air out
of the way needs to be considered separately from the drag caused by
supporting the weight of the aircraft: the former will increase as speed
increases, the latter will not, as the weight of the aircraft doesn't
increase. Even chunky little trainers like the C150 are pretty slippery, so
airframe drag isn't going to be much of an issue at take-off speeds. I'd
suggest that the aerodynamic drag, which has to hold (say) a ton of aircraft
off the ground, would be hugely greater than the airframe drag. As the
aircraft's engine is specified to be able to hurl the thing down the runway,
into the air, and haul it up to around 15,000', I'd say that an 8% increase
in engine power would piss all over an 8% increase in airframe drag, because
the airframe drag is such a small part of the total load. Also, there won't
be an 8% increase in aerodynamic drag, because this is proportional only to
the weight of the aircraft.

Experience bears this out: I've flown on cold days, and the whole thing has
been more alive and responsive, climb-out has felt better, controls have
been crisper and more effective. OTOH the crash that killed my mother was
due to the aircraft failing to get properly airborne: short grass strip, max
weight, hot, windless day. Less drag, but less lift and less power from the
engine. If the pilot had remembered to put the flaps down it might have
helped.

Propellor pitch: the prop is matched to the engine power as well as the
airframe. If it's too fine, it'll let the engine over-rev at full power and
be inefficient in the cruise. If it's too coarse, it won't allow the engine
to rev to full power. Obviously it's a compromise, but in colder air, the
prop will have thicker air to bite into, and so will be able to take
advantage of the extra power from the engine and produce more thrust.

Don't hold your breath.

 

Excellent. Very reminiscent of the Sioux City crash.