So everyone knows that carb heat decreases engine performance. Yet when we check the heat during run-up, the manifold pressure increases.
Why is that? Shouldn't adding carb heat cause the intake air to become hotter and therefore thinner, and cause the manifold pressure to decrease?
Because manifold pressure sucks! Seriously though, the manifold pressure measures how much the engine is able to reduce the pressure between throttle and inlet valve by sucking air into the cylinder.
When you apply carb heat the air gets routed over a heat exchanger that uses some of the excess heat from the exhaust system to heat up the intake air, however the reason it becomes less dense, is because the pressure stays the same. If you look at the so called ideal gas law, you'll notice that pressure is a function of density and temperature, if you have a closed system, where the density can not change, increasing the temperature would indeed increase pressure. This is not a closed system however, so the pressure actually stays more or less the same and the density decreases, and it's not the reason for the manifold pressure increase.
The thinner air leaves the engine with less oxygen to burn and thus it produces less power, the RPM drops, causing the engine to "suck" less air into the cylinder, this gives the air more time to sneak passed the throttle, and the manifold pressure rises. For the same reason the manifold pressure rises (slightly) when you reduce the RPM for cruise. Any reduction in RPM, for whatever reason – engine damage for example – as long as the throttle doesn't move (or if you have carb ice, which has essentially the same effect as closing the throttle), your manifold pressure will actually rise. Remember, it seems counter-intuitive, but the engine is fighting a battle with the throttle, trying to keep the manifold pressure down by sucking the air out, while the throttle is trying to increase the pressure back to atmospheric by letting air in.
When the throttle is anything but wide open, the situation looks like this (image borrowed from the linked article)
It's related to the fact that the manifold pressure gauge, when the engine is stopped, will read ambient pressure, i.e. 29.92 inHg on a standard day at sea level, which is usually interpreted as "full throttle", it doesn't matter how the throttle is positioned. So it's not really showing how much fuel/air mix you're shoving into the engine. In fact, we're not shoving at all, the engine literally sucks it into the cylinder as the piston moves out of the way during the intake stroke. In this particular case with the engine off, it just means that enough air was able to sneak by the throttle and equalize the pressure. It is not flowing nearly fast enough to equalize the pressure as soon as the engine is running though.
So everyone knows that carb heat decreases engine performance. Yet when we check the heat during run-up, the manifold pressure increases. Why is that? Shouldn't adding carb heat cause the intake air to become hotter and therefore thinner, and cause the manifold pressure to decrease?
In some light aircraft, like a Cessna 172, the pitot tube is heated but the exterior static port isn't. The usual reason I've heard is that static ports are much less susceptible to icing, but why is that the case?
If I'm flying in conditions that are conducive to carburetor icing, and my carb-heat cable becomes in-operable, is there anything I can do to prevent engine failure if my carburetor starts icing up? Assuming there are no immediate landing-areas to stop and fix the problem.
As temperatures here in New York plunge toward (and below) freezing it's time for those of us without nice heated hangars to start thinking about pre-heating our aircraft before we turn the key. Lycoming SI 1505 tells me that "The use of pre-heat will facilitate starting during cold weather, and is required when the engine has been allowed to drop to temperatures below +10°F/-12°C (+20°F/-6°C for –76 series engine models)", but the general recommendations I've been given are to preheat if it's been below freezing in the last 4 hours. At what temperature does it start to become beneficial
Our Cessna 172P is equipped with a digital CO-meter rather than the traditional Quantum eye carbon monoxide detector. Today I was flying along in winter conditions, and naturally used cabin heat. During the flight, I heard some occasional short beeps, and couldn't figure out what it was. I looked at the CO-meter which has a red alarm light, but that light was definitely off. On the ground, after... and can tell if a reading of 10ppm is normal with cabin heat? Or should I be concerned our exhaust or heat exchanger is faulty?
Sorry for the slightly strange question, but Ryanair (Europe's Largest Low Cost Carrier) decided that seat back pockets took too much effort and got rid of them, and it appears the sick bags in the process. So the question comes up... What happens when Ryanair flights encounter turbulence? I can hardly imagine the Flight Attendants handing out bags ad-hoc when it's sufficiently shaky to cause motion sickness among the passengers.
When aircraft is at high altitude, atmospheric pressure will be too low but inside aircraft pressure is maintained such that it is comfortable for crew and passengers. But how is it maintained? As I understand that at higher altitude pressure difference can be too large which can deform the plane than how this is handled.
miles from a VOR. Therefore, when you're within those 22 miles, there's no practical difference between a MEA and a MOCA, right? If that's true, why is there an 1800 foot difference between
case, and average case for each location, altitude, and date in the future. I have searched and searched Google to no avail. Where can this wind data be found, and how can it be used in a commercial product? For those of you who don't know what the Boeing winds are, I found this description of their software product on am informal message board (not related to Boeing): PC WindTemp... navigation, or any other type of actual flight operations. PROGRAM FEATURES A seasonal and monthly database with global coverage from 1000 millibars (364 feet pressure altitude) to 10
WWII. They didn't have flight control computers back then, and the only control complaints I recall them having is that early versions had a tendency to flip over backwards when approaching stall speeds, well, that and the ground effects were pretty strong. But, no mentions of going into flat spins when going into hard maneuvers (that I recall). So how do they control that Y axis on flying wings...How do flying wings, like the B-2 Stealth bomber, actually keep themselves from yawing out of control without a vertical stabilizer? For the record, I assume this has to be a simple mechanics