Phil Heller

My Feedback: (9)

Jettpilot

Yes, I will always consider I have a lot to learn, even after soloing in 1946, private, instrument, and multi in '49 and having logged over 5000 hours in everything from a J-2 Cub to a B-29 (yes, they all had propellers - maybe jets react differently). As far as flying with me, I never lost a passenger - but in your case I could make an exception.

Cheers

Phil

Flyboy Dave

My Feedback: (21)

OK Guys....I have been asked to intervene in this thread via a "ticket", which
is basically a complaint. Here's the deal....good debate is hearty and fun.
However, bashing another Member....and not knowing what you are talking about
is a double no-no. I will edit out some non-helpful passages from this thread at
my own discretion.

I want to offer this advice to JettPilot....you seem to differ with the mainstream
theories of flight. That in itself is not a problem. The problem is....quite frankly....
you need to study up....your assumptions about flight are incorrect. The best
material available (to my knowledge) is the FAA ground school books. Trust me
on this, you will not find any opinions about flight in this study material.

Here's the deal....let me first say that I have been a Private Pilot since 1964.
There are four forces that act on an airplane....this is BTW the very first thing
you will learn in ground school....not the second or third.....the first thing.

1. Power....the engine and propeller that drives the plane forward.
2. Lift....the upward force provided by the wing of the airplane.
These are good things.....the next two are bad things.

3. Drag....the resistance of the airframe to forward motion. Example: stick
your hand out the window of your car going 60 MPH.
4. Gravity....yep, that darned old gravity will pull the airplane down, no matter what.

There are two things that will cause an airplane to go up. One of course is the wing.
The main force that can cause a wing to create lift is forward thrust, or POWER.

Without enough POWER, the plane will not achieve enough speed....and the wing
will not create enough lift to achieve flight....ie: the plane will not leave the ground.
If you do not have enough POWER....you can yank on the controls all day, until
you are blue in the face....you will not achieve flight.

There is only one force that can cause an airplane to fly....thrust forward (power).
The wing of course creates the lift. The wing itself however, can sit on the runway
for several generations without achieving flight, without any forward motion.

The only thing that will cause an airplane to climb (gain altitude) is POWER (thrust).
If you have enough POWER to achieve flight, and gain altitude....great. However,
if you reduce power to the point of negative lift....the point where drag and gravity
overcomes thrust and lift....the plane will descend....and eventually come in contact
with the ground. There is nothing you can do to forstall this eventuality.

Sit there on the ground in a plane with the engine at idle.....yank on the wheel (or
stick) for awhile....see if the plane leaves the ground (achieves flight).

FBD.

Rupurt

In simple terms, As a plane gains altitude it's potential energy increases, energy doesn't come from nowhere, in most cases the engine is responsible. Most engines direct there force in one direction, it is the job of the controls to point the plane where you want it to go. Whats so complicated?

JettPilot

My Feedback: (6)

IF what you say is correct Flyboy dave, why does every airliner in the world control altitude with PITCH ( autopilot ) and speed with autothrust (power) ??? Are you saying that the trillion dollar aerospace industry is incorrect on how they have set up autoflight systems on every airliner in the world ??

As far as mainstream, I think the aerospace industry, Boeing, Airbus, McDonald Douglas etc. have it right....

As many times as I have pointed this out, no one has even tried to answer this... People like to ignore facts that prove them wrong.

JettPilot

My Feedback: (6)

Flyboy,

You have edited some things you didnt like in my posts, but you ignore this by Phil. You are obviously biased on this subject and abusing your powers as a moderator by selective enforcement. If you are going to "clean up" this thread, then do it fairly...

Most moderators here in RC Groups try to be fair to everyone, you should do the same.

PlaneKrazee

My Feedback: (14)

Wow,

This thread went from setting the needles to allow for unloading in the air, hard manuevers and different fuel tank levels to a review of the basic principals of flight, sweet.

piper_chuck

My Feedback: (12)

Yes, instead they are too busy wading through the billions of possible motor, battery, controller, prop, and charger choices to actually do any flying.

bob27s

My Feedback: (19)

Let me try to answer this briefly (interesting thread at least... some good information put forth)

Jetpilot, you are correct about modern airliner flight controls. In cruise, the autopilot does dial in an altitude, and uses pitch to climb or decent to that altitude.

However, I think what you are missing here, is that the auto-speed is also active at the same time. They are inter-related.

With a full FADEC, there are lots of small engine adjustments made too that are transparent to the pilots.

If you select to climb from FL 29.0 to 32.0, the plane will respond by pitching up gently, AND increasing engine thrust to maintain a consistant speed during that climb. Once at altitude, the plane levels off, and the resulting power setting is the thrust required to maintain that altitude. That thrust setting is generally lower than what it held during the climb phase, as the engines throttle back to maintain level flight in the most efficient manner.

To lift to a higher altitude and maintain it, you must create more lift. More lift, on a fixed geometry wing/airfoil, is created by greater forward velocity.

That catch 22 is that at higher altitude, lift becomes harder to generate (lower air density) and engine power is harder to generate. With a prop out front, it too produces less thrust at a given rpm. Eventually you reach a point where everything is maxed out, and that is the aircraft's 'service ceiling'.

Air density is everything. Most engines need air to breath just like you and I. At altitude, there is not much air. Turbo/superchargers help compress what little air is available to assit piston engines achieve higher altitudes. Jet engines, by their nature, are compressors, so they do not mind higher altitudes as much... but they too have limits.

The advantage of jet aircraft (airliners) is that jet engines tend to run ok in lower density air. They do produce less actual thrust at altitude, but that same lower density helps create less drag on the airframe at the same time. The speed of sound also changes with density/altitude. There is a balance to be found (called a performance and range curve). I'm sure you have seen one of these along the way.

Anyway.... just thought I would chime in here. I hope this is helpful.

Bob

Rv7garage

My Feedback: (10)

FBD- Thank for your post, and for trying to clean up this mess! I had no idea this thread would blow up like this.

(Wanna really watch the fur fly? Try to explain P-Factor! Ohhhh, my head.....)

Bob- yes. Pitch and power are tied together, at least if you want controlled flight.

Seriously, aside from the inevitable mud-slinging, I am really enjoying the good questions and answers we're getting here, and watching this thread evolve has been an eye-opener. Where do we go next?

rmh

This always happens when some try to ferret out the obvious ---

JettPilot

My Feedback: (6)

Thanks for your input Bob, you are very correct. The autopilot and auththrust work together to make for a smooth climb or descent, or approach. Forces in flight ALL interact with each other, but that is NOT the same thing as controlling an aspect of flight.

You can turn off the autopilot completely, and only have autothrust. Autothrust (power) controls the SPEED of the airplane .....

It is also possible to turn off the autothrust and fly with just the autopilot. The autopilot controls pitch which controls the ALTITUDE of the airplane.

This is ture on both Jets and Turboprops. So in the end, its exactly as I have said all along.... Boeing, Airbus, And the rest of the trillion dollar industry all agree and have built this into their airplanes. Power is what they use to control speed, and Pitch is what they use to control altitude...

LaCerne

My Feedback: (16)

When an MD-11 is climbing at "climb thrust", the Autoflight says it's controlling speed with pitch, when descending at "idle" it also says speed is controlled by pitch. Other times speed is controlled with the auto-throttles. I thought an MD-11 was considered an airliner, but perhaps I was wrong.

JettPilot

My Feedback: (6)

You are confusing what I have been saying La Cerne. You statement totally agrees with my last posts, it could not be more true !!!! When you are doing a maximum performance climb the autopilot us using pitch to acheive a certain speed because there is a fixed amount of thrust available, but it is still the ELEVATOR that the plane uses to pitch up and control its climb to acheive a optimum climb speed.

Same in the flight idle descent, the power is pulled off, and with no power the ELEVATOR is used to contorl descent to acheive given speed.

So in the end, its the ELEVATOR being used to control climbs and descents.

Your statment agrees with what I have been saying all along....

Rv7garage

My Feedback: (10)

JettPilot- this is not an attack on you, I just want you to understand.

I'm sorry, you are incorrect in your statements. Elevator (pitch) does nothing but control the angle of attack, which can have a brief but only temporary effect on altitude loss or gain. Power controls thrust, which is the only thing that overcomes drag and gravity, and which when used in combination with lift allows us to fly.

Example: With constant power, if you pull back on the elevator, you do nothing but increase the angle of attack, which will briefly show an altitude gain but quickly resume a new steady-state with a slower airspeed and higher angle of attack (drag is also increased as lift is increased). Google "behind the power curve".

Opposite: You can certainly control altitude loss with application of elevator, but as the end goal is to arrive on the ground in a controlled manner, you had better reduce power before you reach Vne (your wings fold and you're dead). Ever heard about dive bombers that were lost before they invented dive brakes? Any autopilot will do what a smooth pilot can do manually: Pitch for climb/descent and then apply/decrease power for a desired fpm.

Another way to look at it is this: Even if you are at full power (regardless of Vne) you can only pull back so much before you cease climbing (reach a new stady state, where you have effectively given yourself enough drag to artificially induce a service ceiling) or stall the wing (which can happen at any speed, stall is only a function of angle of attack).

Pitch controlls angle-of-attack only (which in the end only controls your airspeed), and power-being the only thing that allows ascend in the first place- is what in the end controls altitude. Thrust is what gets us up there in the first place!

rmh

Here we go round the mulberry bush -the mulberry bush the mulberry bush--

MJD

My Feedback: (1)

Makes perfect sense to me - if "climb thrust" is a fixed setting, then for sure you would control speed with pitch. More pitch, steeper climb, lower airspeed. Less pitch, shallower climb, higher airspeed. As alluded to in another post, climbing means increasing potential energy. If the power (energy expended per unit time) setting is fixed then the shallower climb rations less power to climb rate and more to increased airspeed and subsequent increased drag. Vice versa.

Same true for descent, where gravity replaces engine thrust. Point the nose down and the aircraft will accelerate until lift and drag equal gravity. Pitch it up more and it will slow down due to the higher Cl of the wing producing more lift at a given airspeed. It is still seeking an equilibrium.

However, at other times when speed is controlled by auto-throttles - isn't the autopilot or the organic pilot controlling pitch to ensure that increased speed does not result in an unprogrammed climb??? Someone has to. If the airplane is stable in the pitch axis, then added power will result in climb.

Mike D.

p.s. I still say that everyone here has a grasp of the concept but the real debate seems to be how to express the same observations and understandings!

bob27s

My Feedback: (19)

What can I say

if an aircraft is flying along at level flight speed, and the nose is elevated for climb, the plane will decelerate. If power is not increased, the plane will contiune to decelerate and eventually reach stall speed.

There is no free lunch. It requires energy to overcome gravity.

Just for info, my training is in aerospace. Worked commercial and military projects. Worked with most of the guys who wrote the flight control software.

Rv7garage

My Feedback: (10)

I think you're right. Or are you???[sm=confused.gif]

rmh

How about throwing in phugoid oscillations as a simple explanation?
(the craft speeds up -climbs -slows - drops -speeds up etc., ad infinitum

MJD

My Feedback: (1)

This subject is no fun anymore. Let's start a new thread on torque versus horespower!

Aggggggggggggggggggghhhhhhhhhhhhhhhhhhhhhhhhhhhhhh hhhhhhhhhhhhhh!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!

Rv7garage

My Feedback: (10)

So start it already. Torque is generally measured in mass over distance, correct? I'm less than sure about horsepower- is there a time factor involved?

Rv7garage

My Feedback: (10)

Good example. In a stable airplane, they will eventually smooth out, etc.

JettPilot

My Feedback: (6)

Sorry Buddy, I just couldnt let that one slip by I like your thread about the engine richness and altitude and I never meant to hijack it, I apologise for that [&o] ... It just kind of happened [:'(] You are obviously a really smart guy and like to see through the "myths" and the garbage most people beleive, that is a quality in a person that I really admire !!! Keep up the good work !

Unfortuately you have the disadvantage of being involved in General aviation for to long where they pound in the power controls pitch thing since day one. They do it to simplify the concept for new students, but its still wrong. If you ever go to Air Force flight school, and get low on approach and try to pitch up your T-38 by adding more power, you will find yourself a smoking hole in the ground [:@]

If you ever get to fly bigger and faster airplanes, you will see that the autopilot and autothrust systems are set up exactly as I have said, and as LaCerne also states. Its always the elevator controlling the pitch of the airplane...

Rv7garage

My Feedback: (10)

Oh, hell Jett- I think we've been having a mis-communication this whole time. I could have sworn that you were saying that pitch controlled altitude! I think now that MJD was really right- we all understand the concept, we just don't articulate it the same way. Are we at least in agreement that pitch=angle-of-attack, and that excess power is what gives us altitude in the end?

rmh

I think I go get my phugoid looked at -