RE: Prop pitch cooling - the final word  
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All Forums >> Glow Engines, Gas Engines, Fuel & Mfg Support Forums >> Glow Engines >> RE: Prop pitch cooling - the final word
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RE: Prop pitch cooling - the final word - 2/18/2007 7:41:13 PM   
gkamysz


 

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From: Crystal Lake, IL, USA
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quote:

I believe the max speed of gravity pull is about 220 MPH and that is with steel balls. I not going to look this up ,but I believe this speed is attained in about 40 feet.


Believeing is different than knowing. And please do take the time to look it up, you will learn something. The basic information is here.
http://en.wikipedia.org/wiki/Terminal_velocity

The link below will give real answers to the terminal velocity of the falling sphere.
http://hyperphysics.phy-astr.gsu.edu/hbase/airfri2.html#c5

I'm sorry I jumped on speedsters other incorrect assumption trying to point out that he was looking at the cooling problem far too simply.

I'm done here. If I post again I will have data. Educating the ignorant has wasted enough time. Nobody is interested in my suggestions for experiments anyhow, I'll do them myself.

< Message edited by gkamysz -- 2/18/2007 7:55:48 PM >

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RE: Prop pitch cooling - the final word - 2/18/2007 7:53:43 PM   
speedster 1919



Posts: 1467
Joined: 12/17/2004
From: Martinsville, IN, USA
Status: offline 		Here is some human body posts on terminal velocity.
quote:

Note that terminal velocity for someone who is arms-out is around 150 ft/sec, about what you achieve with a 400' fall. Actually friction starts to be important when you get close, so it might take more than 400' to get to that speed. Anyway, it probably won't make sense to apply an OB mod for falling higher than +400. Although, if you curl up in a little ball you can get up to 450 ft/sec.
I also found a penny droped from the empire state building reachs a max terminal velocity of 45 MPH because of it's shape and weight.


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< Message edited by speedster 1919 -- 2/18/2007 9:03:38 PM >

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Hey Buddy -That was the most spectacular crash I've ever seen , That rolling cart wheel with parts slinging out was cool...

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RE: Prop pitch cooling - the final word - 2/18/2007 8:02:48 PM   
DarZeelon



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From: Rosh-Ha'Ayin, ISRAEL
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quote:

ORIGINAL: speedster 1919

....there are people that have actually survived falls of over 10,000 feet and lived. Rare yes and busted up yes. One in a million yes.



Randy,


The terminal velocity for a human, in spread-eagle posture, in sea level density, is about 60 m/s, which are about 134 mph.

If that skydiver goes head first from high altitude (the record was from over 60,000 ft.), he can go supersonic! And it will only take about 40 seconds to reach that speed.

Those people who survived high falls did not fall onto the sidewalk, near the Sears Tower... They fell into tall, forested areas, where tree branches progressively broke their fall, as well as just about every bone in their bodies and yes, they lived to tell about it...

Wiki Page.

A solid steel sphere, a shot-put ball, for instance, would reach well over 200 m/s at S/L altitude density.
It is much more dense than a human and has much less drag.

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RE: Prop pitch cooling - the final word - 2/18/2007 8:25:59 PM   
shakeelsid



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From: Dublindublin, IRELAND
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quote:

ORIGINAL: HighPlains

Always fun to see critical thinking in action.

where did you study roadrunner physics?


Road runner physics one on one (Yummy)

V=at (V=we, a=at it boy, t=till you get the roadrunner)
S=vt (S=soup, road runner soup, v= we, t=at tea time)
g=a (in earth's gravitational pull, g=Gee, a=at it boy)
v=gt (same as above, provided no atmosphere)
d=1/2 p S Cd V2 (Drag equation when there is atmosphere, a little complicated for coyote brain, but essentially, I need a rocket booster to catch a roadrunner)
Vsplat = a.t. (going too fast, smaller rocket,
ACME =

Ah you know the drill now

Can someone please add this to Wikipaedia's world of knowledge

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RE: Prop pitch cooling - the final word - 2/18/2007 8:38:26 PM   
speedster 1919



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From: Martinsville, IN, USA
Status: offline 		Greg What you showed me was crap -pure crap-I said the worlds tallest building where the atmosphere is thick and you give me a post of a 20 mile up freefall dive with barely any atomspere. I posted alot of terminal velocity maximums closer to ground level and they were way slower than most of you guys thought. Greg I can't converse with you because you keep changing the bar. I just give up. I gave real world examples and fairly accurate and tried to keep it simple . The simple fact remains --
The 4" pitch prop provided more than enough cooling.................

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Hey Buddy -That was the most spectacular crash I've ever seen , That rolling cart wheel with parts slinging out was cool...

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RE: Prop pitch cooling - the final word - 2/18/2007 8:41:47 PM   
speedster 1919



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quote:

ORIGINAL: HighPlains

Always fun to see critical thinking in action.

Speedster, where did you study roadrunner physics?

BY the way . What is roadrunner physics????????????

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Hey Buddy -That was the most spectacular crash I've ever seen , That rolling cart wheel with parts slinging out was cool...

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RE: Prop pitch cooling - the final word - 2/18/2007 9:36:52 PM   
JNorton



Posts: 3135
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From: Montague, MI, USA
Status: offline 		Roadrunner physics like in the cartoon. It's something like Wiley E saws off a tree branch and falls down with the branch. The next panel the Roadrunner saws off the branch and it stays in the air while the tree falls down on top of Wiley E.
John

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RE: Prop pitch cooling - the final word - 2/18/2007 9:51:40 PM   
proptop



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Joined: 10/18/2002
From: Rome, NY, USA
Status: offline 		I was thinking it was a 440 beats a 383? (ba-doom-boomph, rim shot )

But seriously folks...I agree that a 4" pitch prop will provide more than adequate cooling when breaking in an engine. I have done it...more than once I might add.

The only times I have experienced an excessive amount of heat build-up with a shallow pitch prop is during a prolonged hover...and I think that has more to do with the engine having to pull the fuel from a longer distance, especially when the fuel level has been burned off.
It's kind of like a catch 22 though, when you're hovering, because the airplane balances better for a hover when it's a little tail heavy (as in a lot of the fuel been burned off ) but you risk over heating the engine because it can go lean.

< Message edited by proptop -- 2/18/2007 9:59:41 PM >

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RE: Prop pitch cooling - the final word - 2/18/2007 10:42:18 PM   
Jim Thomerson



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From: Austin, TX, USA
Status: offline 		A genera truism, not directed at anyone in particular.

Before you can learn something new, you have to accept that your present understanding of the subject is somewhere between incomplete and totally wrong.

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RE: Prop pitch cooling - the final word - 2/19/2007 3:00:39 AM   
Sport_Pilot



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From: Acworth, GA, USA
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quote:

This is not correct. The cooling changes as a natural logarithm, as a function of the airspeed (a).
(cooling = Xln(a), where a>0)


By exponential, I only meant that the rate of cooling increases less and less as the air speed increase. I was not trying to get that specific.

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RE: Prop pitch cooling - the final word - 2/19/2007 3:07:11 AM   
Sport_Pilot



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quote:

ORIGINAL: JNorton

Sport Pilot
Cold junction offset helps eliminates errors introduced by ambient temperature.
http://www.ecnmag.com/article/CA508469.html?ref=nbra
Commercial controller using differential input to implement a cold junction offset.
http://www.omega.com/ppt/pptsc.asp?ref=DP26&Nav=temp04
John


I am not an electical engineer and I don't doubt that there is a method to compensate for part of the sensing element being exposed to the air. However, I don't see any claim in the above that this compensates for this efect. Even if they do, it would still be better that the element be completly emerged in the medium being measured, not a small part of it on the medium and most of it in the ambiant air, or the heated cooling air. This would be the case with a cylinder shaped wire or probe touching the side of the engine. Anyway I doubt Downunder was using such a sophisticated device.


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RE: Prop pitch cooling - the final word - 2/19/2007 3:13:57 AM   
Sport_Pilot



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quote:

The air could pass over the fins at 1000 MPH but the simple fact is The heat transfer rate is a set factor between cylinder,crankcase and fins and will transferr heat just so fast and at a certain air flow the heat can be taken away no more faster.


It is not a set factor, but the heat removed will at a certian point increase very little as airspeed increases, till the airspeed creats enough friction to create significant heat itself, but we are nowhere near those velocitys.

My point about the thermocouple is that at least part of it should be completely inside the engine. I was not the one trying to show super duper circuits to compensate.

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RE: Prop pitch cooling - the final word - 2/19/2007 3:16:46 AM   
Sport_Pilot



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quote:

ORIGINAL: Hobbsy

It's as simple as , the arm chair mechanic loses and the hands on mechanic who actually did a test wins.


No prize, but if he did not convince the armchair mechanic, he did not accomplish his goal.


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RE: Prop pitch cooling - the final word - 2/19/2007 3:19:08 AM   
Sport_Pilot



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From: Acworth, GA, USA
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quote:

this very interesting and rather pointless discussion that I've enjoyed immensely.


At least I can agree with that!

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RE: Prop pitch cooling - the final word - 2/19/2007 10:57:57 AM   
JNorton