RE: Props-More Myths Busted  
View related threads: (in this forum | in all forums)

Tower Hobbies
Enter up to 4 keywords or Tower stock numbers
Logged in as Guest



Users viewing this topic: none
  Printable Version
       

All Forums >> Glow Engines, Gas Engines, Fuel & Mfg Support Forums >> Glow Engines >> RE: Props-More Myths Busted
Page: <<   < prev  6 7 [8] 9 10 11 12 13 14 15   next >   >>  

Login
Message << Older Topic   Newer Topic >>
RE: Props-More Myths Busted - 1/12/2007 6:05:02 PM   
skiman762



Posts: 1166
Joined: 12/1/2005
From: Nashville, NC, USA
Status: offline 		There's no way that 5 secs in a hover is going to overheat an engine that is tuned properly and has a proper fuel system
I don't care what kind of fancy words you use to try to convince me
I'm not biting I have burned too many gallon of fuel to buy any part of that
There's another answer to his problem and it's not the prop



_____________________________

land of the FREE: you're free to get a JOB not a handout.
home of the BRAVE: they paid for it and you're enjoying it

(in reply to yallaair)
       Post #: 176

RE: Props-More Myths Busted - 1/12/2007 6:06:05 PM   
DarZeelon



Posts: 7084
Joined: 4/9/2003
From: Rosh-Ha'Ayin, ISRAEL
Status: offline 		B.E.,


Read through that thread again...
Even that high-pitch prop is only stalled while it is accelerating and only until if forms a vortex.

Within half a second it is no longer stalled.


You can spill more fuel on the fire now...

_____________________________

Dar Zeelon - ISRAEL - ddzeelon@gmail.com
MVVS - Jett - Nelson - Bolly - Mejzlik

(in reply to yallaair)
       Post #: 177

RE: Props-More Myths Busted - 1/12/2007 7:27:40 PM   
RVM


 

Posts: 1975
Joined: 3/12/2006
From: Sacramento, CA, USA
Status: offline 		So why doesn't someone analyze the effect different props have in the air? You would think, with all the research that has been done over the past 100 years, that this debate would be moot. Is there an aeronautical engineer anywhere around?

I fly with a bunch of aerospace engineers, and quite a few use low-pitch props on their Saitos and have no problems. Mathematically, they can show you why the props they choose are better for 3d type flying. In fact, a few plan every component of their aircraft out using nothing but numbers to determine which servo, how long the arms have to be to apply a certain amount of torque, the strength of various parts used in the construction, which engine, with what amount of nitro (based on our elevation), oil and methanol, and which prop etc. etc. The planes are usually near perfect the first day at the field.

I've never, nor have I ever seen anyone overheat an engine in 5-10 seconds of hovering, cowl or no cowl. If the cowl is that tight around the engine (or even if there isn't a cowl), and the engine temperature is so close to overheating that hovering for 10 seconds will overheat it, then I believe it would overheat in the same amount of time on the ground.

_____________________________

There is no substitution for human competition.

(in reply to DarZeelon)
       Post #: 178

RE: Props-More Myths Busted - 1/12/2007 8:39:20 PM   
jaka


 

Posts: 4526
Joined: 12/11/2001
From: Upplands Vasby, SWEDEN
Status: offline 		Hi!
Sorry Dar !
This is not my experience at all! I can hover my You Can Do .60 with my MVVS 15cc (.91) for as long I want without any overheating problems....but then I'm using just 15% all synthetic oil

_____________________________

Jan Karlsson Airracing products
MVVS, Motul "Micro" all synthetic oil

(in reply to DarZeelon)
       Post #: 179

RE: Props-More Myths Busted - 1/12/2007 10:44:06 PM   
DarZeelon



Posts: 7084
Joined: 4/9/2003
From: Rosh-Ha'Ayin, ISRAEL
Status: offline 		Jan,


The .91 engine I was referring to was an OS...

You don't have our weather either...

_____________________________

Dar Zeelon - ISRAEL - ddzeelon@gmail.com
MVVS - Jett - Nelson - Bolly - Mejzlik

(in reply to jaka)
       Post #: 180

RE: Props-More Myths Busted - 1/13/2007 3:56:59 AM   
skiman762



Posts: 1166
Joined: 12/1/2005
From: Nashville, NC, USA
Status: offline 		If it's a 2 stroke maybe one of there heli heads would fit and help his cooling problem
can't hurt to check

_____________________________

land of the FREE: you're free to get a JOB not a handout.
home of the BRAVE: they paid for it and you're enjoying it

(in reply to DarZeelon)
       Post #: 181

RE: Props-More Myths Busted - 1/13/2007 7:37:17 AM   
yallaair



Posts: 213
Joined: 1/1/2006
From: Floro, NORWAY
Status: offline 		Hava a look at the O.S. engines that was produced for "Byrofan" in the early 90's.... Clearly that one needed a big "HEAT SINK" head even, the fan can be condidered as "HIGH PITCH" propeller inside an airduct... I've tested the version without heatsink, and the result on lean running was very high temp. The temp got as high that the engine spitted out the plug!! the therads on the plug could not take the heat!! The plug melted 2 in. into the ice-covered airfield....

_____________________________

Darn the ground..... and the jumping trees

(in reply to skiman762)
       Post #: 182

RE: Props-More Myths Busted - 1/13/2007 8:15:55 AM   
DarZeelon



Posts: 7084
Joined: 4/9/2003
From: Rosh-Ha'Ayin, ISRAEL
Status: offline 		Yallaair,


If I recall correctly, the Byrojet engine was a pusher installation, with the engine out of the air-duct.

This clearly does not constitute a good cooling setup and it does require the heat-sink head for sufficient cooling, especially with the high output this engine must produce, at 22K...

Ducted fans like Kress, BVM and Turbax were tractor installations, with the engine in direct air-flow; and required no cooling intensification, due to high speed direct flow on the cylinder and the head.

_____________________________

Dar Zeelon - ISRAEL - ddzeelon@gmail.com
MVVS - Jett - Nelson - Bolly - Mejzlik

(in reply to yallaair)
       Post #: 183

RE: Props-More Myths Busted - 1/13/2007 9:53:11 AM   
speedster 1919



Posts: 1467
Joined: 12/17/2004
From: Martinsville, IN, USA
Status: offline
quote:

What I found was that I could directly control the engine temperature of the engine with the needle (that has been my point all along) but because I was using less oil I was able to richen the engine and still have reliable power. Peak rpm with this fuel and prop is 13,000 (tested without tape and rags). I was able to comfortably run the engine at 12,000 rpm and 190 deg. This is only 1,000 off peak and solidly 2 cycling. If I back the needle out further yet, to around 11,500, the temp dropped into the 150 deg range. The bottom end was not warm. Not cool. It was full on cold. The max temp I saw with any settings was 240 deg.



As typical this test is missing the base or constant factor. I don't care what the wrapped up temp is at 12,000 RPM.
I want to know what the temp was at 13,000 and then richen to prove amount of fuel would cool.

The test of a good idle is to let run for 30 seconds to see if set right. Alot of flyers hold plane nose up in air for a few seconds to test for lean setting. Now a 20 second hover would be a max test of fuel system because if you think about it ,you try to get fuel tank level with carb and most of us know 1" down presents a problem sometimes. Now in a hover I would say your pulling fuel up from bottom of tank 6-12 inches- tank too low. Duh -it's going to be lean.

< Message edited by speedster 1919 -- 1/13/2007 10:11:59 AM >

_____________________________

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

(in reply to yallaair)
       Post #: 184

RE: Props-More Myths Busted - 1/13/2007 1:42:41 PM   
Hobbsy



Posts: 10678
Joined: 12/2/2001
From: Colonial Beach, VA, USA
Status: offline 		Is it worth considering that in the hovering condition the muffler pressure is high.

_____________________________

"I have gone faster backwards, upside down and on fire than most people have gone at all" Don Garlits

(in reply to speedster 1919)
       Post #: 185

RE: Props-More Myths Busted - 1/13/2007 2:06:44 PM   
B.L.E.


 

Posts: 1305
Joined: 8/27/2005
From: Austin, TX, USA
Status: offline
quote:

ORIGINAL: speedster 1919

The test of a good idle is to let run for 30 seconds to see if set right. Alot of flyers hold plane nose up in air for a few seconds to test for lean setting. Now a 20 second hover would be a max test of fuel system because if you think about it ,you try to get fuel tank level with carb and most of us know 1" down presents a problem sometimes. Now in a hover I would say your pulling fuel up from bottom of tank 6-12 inches- tank too low. Duh -it's going to be lean.


Anytime you firewall the throttle at low speeds, the planes forward acceleration can easily put more g-forces on the fuel than gravity can with the nose up, so a static nose up engine run is not nesessarily the worst case situation for leaness, particularly with planes that have a thrust to weight ratio greater than 1 to 1.
Have you ever taken a ride in a high performance car and felt the acceleration push you back in the seat when the driver stepped on the gas? That also happens to the fuel in the fuel tank when your plane accelerates out of a hover or during take off.

(in reply to speedster 1919)
       Post #: 186

RE: Props-More Myths Busted - 1/13/2007 4:19:11 PM   
yallaair



Posts: 213
Joined: 1/1/2006
From: Floro, NORWAY
Status: offline 		Have experienced this leanout during forward acceleration several times. Cured with slightly rich needle-setting... Have not tried a pump, but guess that will help a lot.... Mounting the fueltank far away from the carb just increases the problem.

_____________________________

Darn the ground..... and the jumping trees

(in reply to B.L.E.)
       Post #: 187

RE: Props-More Myths Busted - 1/13/2007 6:08:07 PM   
RVM


 

Posts: 1975
Joined: 3/12/2006
From: Sacramento, CA, USA
Status: offline 		I just run a regulator on my glow engines. I don't have to worry about them leaning out. They run much mroe consistently as well.

_____________________________

There is no substitution for human competition.

(in reply to yallaair)
       Post #: 188

RE: Props-More Myths Busted - 1/13/2007 6:56:12 PM   
B.L.E.


 

Posts: 1305
Joined: 8/27/2005
From: Austin, TX, USA
Status: offline 		Not to mention that you can have the fuel tank located there the CG doesn't change from full to empty.

(in reply to RVM)
       Post #: 189

RE: Props-More Myths Busted - 1/13/2007 7:56:45 PM   
RVM


 

Posts: 1975
Joined: 3/12/2006
From: Sacramento, CA, USA
Status: offline 		Yup!


quote:

ORIGINAL: B.L.E.

Not to mention that you can have the fuel tank located there the CG doesn't change from full to empty.



_____________________________

There is no substitution for human competition.

(in reply to B.L.E.)
       Post #: 190