TIA

I had to think about this for a second. But if I remember correctly, going back to high school physics, the terminal velocity between the two would be greater with the heavier weight. Therefore, given equal power sources, equal forces, and all other thigs being equal besides weight, the lighter object would indeed result in higher speed if neither ever reached the maximum velocity of the lighter object.

BUDMAN27

Say what?

Airbike

My Feedback: (6)

Sorry Ron, I'm with Budman..Say What?


High school physics; if you dropped two Predators from 1000' nose first, straight downline, the heavier one would hit the ground first.

F=ma bigger mass=bigger force acting on it while aerodynamic drag stays the same for identical objects.

Lighter plane creates less induced drag from less lift required.

But I thought the final conclusion was that a better flown line will have much greater impact on lap times than a slightly heavier plane.

Oh I understand the thought process of stacking everything you can in your favor, but for a newbie like me, I'll just do the simple things and not worry about the bugs on the leading edge or a couple of extra ounces.

djlyon

Airbike you slept through high school physics and you never read Newtons laws if you think the heavier object will hit first when the aero drag is the same.

Denis

HighPlains

My Feedback: (1)

Sometimes HS physics is not enough.

HighPlains

My Feedback: (1)

But airbike is correct as to which airplane would hit first.

Airbike

My Feedback: (6)

Djlyon,

did I miss something? heavier objects of the same size fall faster IN AIR (or other fluids too).

Whoever dropped the stuff off the leaning tower of Pisa just couldn't measure accurately.

....but then there was this giant threadmill...

BUDMAN27

Sounds like we need to get the TV show Myth busters involved with our problem, if you want to call it that.

HighPlains

My Feedback: (1)

No, this is where you turn off the TV and pick up a book.

TIA

Budman, your lighter air rifle pellets traveled at a higher fps than the heavier ones given the same force.

TIA

Dan,

Wrong theory. We’re not dropping planes from a building. Point A and point B are 90 degrees opposed to gravity. Gravity plays only a part in velocity.

Picture this. Two Predators exactly alike in every way, both being pulled by a power source, which produces exactly 6lbs. of thrust, only one plane weighs 3lbs., the other weighs 5.5lbs. Assuming both leave point A at exactly the same time and travel a perfectly straight line, which will arrive at point B first?

Weight is the enemy.

BUDMAN27

But like he was saying . Thats in a perfect world. What about a windy day. shouldn,t a heavyer plane be able to say on track better.

TIA

Hi Budman.

Mass and drag coefficients come to mind. I am just thinking Newtons first and second laws of motion.


Anyway if you're interested and have the time, check out this link for some really good reading.

http://www.auf.asn.au/groundschool/index.html

djlyon

You didn't miss anything Airbike. I missread what you wrote and then tried to cancel my post but I guess I failed.

Denis

Airbike

My Feedback: (6)

I think everybody agrees that a heavier plane will be slower for the same conditions. I don't even think the heavier plane is noticeably more stable in windy weather (we're talking just a few ounces here).

Reno, you missed some impromtu laps at Whittier last Sat afternoon. However, the local club guys got all upset at not following the AMA rules. (Well, really at a novice flyer that flew so wide, he was basically over the pits). They didn't get upset when we were doing laps really tight at the runway.

Anyways, its almost like no flying behind the "standard pilot flight line" except during an official event. So technically, no lap practice except the afternoon before the race and during the race. All other times, its against AMA rules.....[:@]

I think if we kept safety in mind, it shouldn't be a problem. We waited until others had landed before we launched. It's probably best to do lap practice only when there is hardly anyone there. A while back, the park police gave another flyer a hard time when he did some "laps" while standing on the runway.


What's the optimum CG for a quickie? I'm just trying to adjust battery location so that the plane will fly level without elev trim (drag). Is it better to be a bit nose heavy (perhaps more stable)? or is it better to have the CG farther aft (perhaps less tail downforce, less drag)?

TIA

Airbike,

Very true. There's theory, then there's reality. And for me, the reality is I need to learn to fly before I start worrying about catching up to the racers edge.

I was telling you in the past, I think, that I try & get up to the airstrip by 6-6:30 before anyone gets there. That is the exact reason! People will come unglued if you are out in the middle of the LZ flying circles along the safety-line when they are 3D'ing their Funtana's over your head. So I try to be the first one in the gate with everything ready, run out to the deck, and launch. By the time I've gone through a tank or two the other pilots have their engines warmed up already and starting to walk their planes out to depart.

It sucks for me but that just means I get my flying done early in the morning and then I can go home, cook breakfast for the awakening family, then start my list of honeydo's for the weekend. Not the coolest life, but someone’s got to step up and be responsible.

This Saturday I had my plane rebuilt and ready to go. So I thought! I got to the field at 6:30, ran out to the runway, fired the engine, was about ready to launch the AT-6 off and I couldn't get the plane to idle correctly. Then I noticed I couldn't get the engine to run right at all. Took the plane back to the pits and noticed I has lost a carb screw somewhere. O.S. uses two screws on the carb to mount it to the engine. One on each side. What was weird is that I had started the plane in the backyard the night before and everything ran great. Well I went back home and found the screw sitting in the spot on the patio where I had last started it. (I guess that was the good that came out of my adventure.) So no flying this weekend. Time to hit the simulator this evening maybe.

Shooting for next Saturday morning.

BUDMAN27

Adventures by reno from Califoria.

TIA

Sorry, I'll zip it.

BUDMAN27

i WASN,T SUGGESTING YOU DO THAT.

kane

Using the equation F=ma you can see that if you increase the mass, it would require more force to achieve the same acceleration. (9 units of force = 1 unit of mass x 9 units of acceleration, if you use 2 units of mass you would need 18 units of force to achieve the same 9 units of acceleration).

This also means that it will take more force to slow the heavier object down. This would explain why the heavier airplane seems to track better than the light one.

The lighter one will accelerate better from the start and better off of the turns. As the heavier airplane will resist changing it's state of motion more than the lighter one.

Having said all of that. I really don't think 4 oz makes that much of a difference.


(This holds true in the vertical direction as well. F=mg where g is the acceleration due to gravity, all this equation says it that two objects regardless of mass will accelrate towards the center of the earth with the same acceleration. This equation also represents weight. The more mass the more force present to start it moving and stop it moving acceleration will be the same)

HS physics what is that?

DK

daven

My Feedback: (1)

At 2 oz over, I can't tell a difference in how the plane flies.

Its about 4oz where I can start to "feel the difference", mostly on how it takes off (slower).

BUDMAN27

OK enough with the small talk lets go race.

Stand

Although acceleration is a factor, I believe the real effect of a heavier airframe is that it requires more lift. Given the same thrust, as the weight goes up the wing MUST fly at a higher angle of attack (AOL). A higher AOL generates more drag (CD) and therefore will fly slower in most aspects of flight except those where the ground is rapidly approaching.

BUDMAN27

There you go.

BUDMAN27

Well here is what I put on my bird.