RE: I would like to dispel a myth here.  
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RE: I would like to dispel a myth here. - 9/6/2005 10:30:40 PM   
MJD


 

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From: Orangeville, ON, CANADA
Status: offline 		It is RC related.. RC airplanes fly the same way full scale do. I also hear the old "control altitude with power" wisdom tossed around by people who might not really understand what they are saying. Like "torque turns propellers, not horsepower" which showed up in a different thread in an attempt to wisely debunk a topic of discussion, but failed as it failed to take all factors into consideration in the situation.

On the subject of fuel mixture changes with altitude, understanding that issue helps explain why needle settings don't change in a significant manner in the few hundred feet altitude difference between the pits and where we fly, Maynard Hill and his altitude flights notwithstanding.
It also explains why if we live at 300' ASl, then drive to a fun fly in Colorado Springs, we may have to tweak our needles to achieve the best performance. Of course we check needle settings anyway, but knowing why is always better than just doing it out of habit.

Mike D.

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RE: I would like to dispel a myth here. - 9/6/2005 10:44:25 PM   
Bodge



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Status: offline 		MJD,

Absolutely: a smaller charge of both air and fuel occurs at higher altitude so you would think that the stoichiometries would be maintained. However, while gases compress and rarify, liquids don't - and while we call the fuel charge a gas it is not, it's an aerosol, i.e droplets of fuel remaining in the liquid phase and, for our concerns, uncompressible.

Since the liquid fuel remains (relatively) uncompressible, air most definitely does not. Therefore the density of the air will vary relative to that of the fuel according to height and will affect the mixture.

In other words, go higher and the air will become less dense, correspondingly less fuel will be drawn in, but the fuel will be relatively more dense than the air (because it's liquid and its density hasn't changed) and therefore the engine will run richer.

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RE: I would like to dispel a myth here. - 9/6/2005 10:47:14 PM   
William Robison



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Joined: 11/10/2002
From: Mary Esther, Florida, FL, USA
Status: offline 		Dave:

I think it's a matter of inertia as much as density, other things being the same. With the increased air flow, the venturi pressure goes down (Bernoulli's theorem) but the fuel, being more dense, will not accellerate as quickly as the air entering the engine.

Even then, the lessened density of the air at the higher velocity does not generate any amount more "Suction" than the higher density air at a lower velocity.

End result? You have to set the static mix a little rich to allow for the higher speed lower pressure air flow when the engine unloads.

Bill.

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RE: I would like to dispel a myth here. - 9/6/2005 11:26:43 PM   
RC-Captain



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quote:

you pitch the airplane 10 degrees nose down you are going to go down no matter how much power you add


does this hold true if the flaps on your plane are down ? My answer is no. Actually a model airplane will climb and can be landed with only the throttle if given enough room and the flaps set to a perfect degree.

Sorry for butting in on the fun. GL



RCF esq.

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RE: I would like to dispel a myth here. - 9/6/2005 11:31:41 PM   
William Robison



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From: Mary Esther, Florida, FL, USA
Status: offline 		FIEND:

What you have just said, is that in that state power DOES control altitude!

Bill.

< Message edited by William Robison -- 9/6/2005 11:32:07 PM >

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RE: I would like to dispel a myth here. - 9/6/2005 11:53:37 PM   
RC-Captain



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quote:

What you have just said, is that in that state power DOES control altitude!


agreed, I do it all the time , and it isn't easy but makes for the smoothest landings and all I am doing is copying the real airplanes, as we all know, they depend on thrust 100% for landings.

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RE: I would like to dispel a myth here. - 9/7/2005 1:56:19 AM   
JettPilot



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quote:

ORIGINAL: RC-FIEND

quote:

What you have just said, is that in that state power DOES control altitude!


agreed, I do it all the time , and it isn't easy but makes for the smoothest landings and all I am doing is copying the real airplanes, as we all know, they depend on thrust 100% for landings.


Pitch controls your altitude. You can have all the power in the world, if you are pitched down you will only hit the ground faster. You obviously need power to climb, but more importantly you need to pitch UP to climb first, and if there is enough energy the plane will climb. A plane will NEVER climb pitched down, power or not. Pitch controls altitude. (given there is enough airspeed and you dont stall.. Duhhh..)

Airliners fly in cruise and also do automatic approaches by using Autothrottles to control the speed, and by using the autopilot to control pitch and roll to keep the airplane on glidepath. Boeing, Airbus, and McDonald Douglas all use thrust to control speed on thier airplanes, and pitch to control the altitude, what a novel idea

I guess all the aerospace manfacutrers of the world got it all wrong and should be looking at redisigning their autoflight systems, because according to Garp and RC-FIEND they got it all backwards



< Message edited by JettPilot -- 9/7/2005 2:00:48 AM >

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RE: I would like to dispel a myth here. - 9/7/2005 2:11:27 AM   
RC-Captain



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Status: offline 		I am not talking about pitch as far as pointing the airplane in a path of flight. I am simply stating I can land with out ever touching my elevator. I simply hit my D switch the flaps come down and by controlling the speed of the plane it will climb or descend.

Haven't you ever flown a 2 channel toy plane that climbs when given full throttle and descends with less speed ? same concept different power source.

When my trainer had a dihedral wing I would climb to about 300-500 feet and put it into a nose dive and with out touching the elevator the nose of the plane would level out before coming any where close to hitting the ground.

I hope the two examples explain why speed can actually control the altitude.

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RE: I would like to dispel a myth here. - 9/7/2005 2:28:08 AM   
JettPilot



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Status: offline 		You are confused RC-FIEND, which is exactly STUDENT PILOTS are taught this line, because its easier for the "beginner" or less educated to understand . What happens is in your two channel airplane is that it has a fixed amount of elevator. When the airspeed increases the airplane PITCHES UP and it climbs. When power is taken off, the plane PITCHES DOWN and it descends. On a very stable airplane, this natural tendency can be used for a poor and primitive means of control, but its still the PITCH which makes the plane go up or down. Using this way to control the pitch is also very poor, because airspeed can change for many reasons an there is a serious lag in waiting for the pitch to adjust itself with no elevator control. This may work on the most stable little trainer model, but it is USELESS in full scale aircraft. No full scale aircraft is made without elevator.... If you lose the elevator its a VERY serious emergency, because its very difficult to hit the runway without it ! (at any speed) For those of you that are still to slow to understand, try this:


Kill your RC plane engine one day high up, and dive it down and then pull a bunch of up, the airplane will come out of the dive and CLIMB with no power as long as it has the airspeed... WOW

Now point your RC plane straight down, keep it pointed down and try to use the throttle to control the altitude, the airplane will continue to plummet to earth... amazing.

It would appear that Pitch controls the altitude doesnt it ????

Aerodynamics 101...


< Message edited by JettPilot -- 9/7/2005 2:30:05 AM >

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RE: I would like to dispel a myth here. - 9/7/2005 2:57:33 AM   
RC-Captain



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quote:

What happens is in your two channel airplane is that it has a fixed amount of elevator.


What happens is the speed of the plane controls the altitude, period. No up or down elevator . OH! there isn't a controllable elevator on a two channel plane, therefore it can't be included in your statement above.

Its easy to talk like you have every situation covered, but very hard to actually cover all situations with your talk. GL

RCF esq.

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I finally broke bread and bought a real charger , THE TRITON 2............

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RE: I would like to dispel a myth here. - 9/7/2005 3:03:44 AM   
JettPilot



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quote:

ORIGINAL: RC-FIEND

What happens is the speed of the plane controls the altitude, period. No up or down elevator . OH! there isn't a controllable elevator on a two channel plane, therefore it can't be included in your statement above.

Its easy to talk like you have every situation covered, but very hard to actually cover all situations with your talk. GL

RCF esq.


MANY two channel planes like yours have been dived into the ground at high speed, because they were PITCHED down. How many of those little 2 channel airplanes have been flown into the ground while pitched up ( FLOWN - not a stalled condition ) Speed obviously does NOT control altitude.

Its becomming quicly appearant that you are just not man enough to admit when you are wrong.

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RE: I would like to dispel a myth here. - 9/7/2005 3:03:57 AM   
William Robison



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From: Mary Esther, Florida, FL, USA
Status: offline 		JP:

No one is saying that when you are sitting at the end of the runway giving full down elevator will accelerate the plane for take off, nor is anyone saying that you need nothing but full throttle to pull out of a dive.

Just as in your example of the airliner on final and using power trim to control the descent - see, you are controlling the altitude with power changes. How 'bout that?

Go over to the thread I linked earlier and read post number five. It's not about maneuvering at all, it's about getting into a stable cruise at a given airspeed, and then changing only the pitch with the elevator, or the power setting.

If you started flying as a military type you have probably never flown anything but jets. And that makes it hard to understand aeronautics at low speed; even though you have the same thing at the higher speeds it's not as obvious.

I have many hours of jet and piston time, and I assure you all this works, A KC-97, a loaded C-124, my favorite (and most time in) B-57, even a B-52. But it's most obvious in a J-3 or a Super Cub PA-18. And it applies to our r/c planes - they all work in the same atmosphere, and under the same laws of nature.

Bill.

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(in reply to JettPilot)
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RE: I would like to dispel a myth here. - 9/7/2005 4:01:36 AM   
blw



Posts: 4569
Joined: 3/15/2004
From: Auburn, AL, USA
Status: online 		From some of the comments being argued here it appears that some people only know their trainers....barely. You know, the flat bottom, lots of dihedral types. Then, someone who does know engine tuning and aerodymics like W8YE tries to inject a little knowledge into the fray and that draws fire. It's okay to not understand anything about aerodynamics, airfoils, flight control surfaces, etc, but it's probably not wise to argue from a position of ignorance.

This all sure looks to be a troll fest by some Fred Huber wannabes. If you know about ol' Fred, he is long gone from RCU. I kinda miss his inflammatory style though.

I know that I can land a plane with either just throttle control, or just elevator control.....

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RE: I would like to dispel a myth here. - 9/7/2005 4:08:43 AM