RE: .o49 engines by cox  
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 >> RC Airplanes >> "1/2 A" & "1/8 A" airplanes >> RE: .o49 engines by cox
Page: <<   < prev  1 [2] 3   next >   >>  

Login
Message << Older Topic   Newer Topic >>
RE: .o49 engines by cox - 4/15/2008 3:30:27 PM   
Bugzidor


 

Posts: 10
Joined: 12/22/2007
From: Bangkok, THAILAND
Status: offline
quote:

ORIGINAL: Mr Cox

Nice job, but I think there is an inherent problem with a carburator on a reed engine?
The reed only closes due to a higher pressure in the crank and that''''s fine at full throttle but near idle the restriction of the carburator gives an underpressure. This would be ok if it stayed constant but as the reed is shut (do to a higher pressure in the crank) the throttle is still "leaking" and the pressure will continue to rise on the wrong side of the reed... [:''(]

I think the TeeDee would be much better suited for a carburator, please feel free to prove me wrong.

I agree with you about the carb. on Tee Dee, which has more suitable, but, it also possible to use with reed type engine, eventhrough, the response time, might be slightly delayed. Anyway, what would be the effect, you expect to see on the ''leaking'' problem?

(in reply to Mr Cox)
       Post #: 26

RE: .o49 engines by cox - 4/15/2008 7:17:33 PM   
Mr Cox



Posts: 345
Joined: 7/20/2007
From: Gothenburg, SWEDEN
Status: offline 		I simply don''t think that the reed is able to operate and shut the inlet like it should, since it is only relying on pressure differences to do so.

(in reply to Bugzidor)
       Post #: 27

RE: .o49 engines by cox - 4/15/2008 8:33:34 PM   
digital_trucker



Posts: 1230
Joined: 2/4/2006
From: Dorr, MI, USA
Status: offline 		With that thinking, the reed should work just fine. The pressures inside the engine shouldn''t vary much with RPM, just the frequency of the pulses. Seems I heard somewhere that the limiting factor in a reedie''s performance is the reed...tends to float at high RPM. I''m betting the reed performs better at lower RPM - more time to overcome inertia.

_____________________________

I feel I can speak for 90% of humanity when I say 'durrrr'
Skype digital_trucker

(in reply to Mr Cox)
       Post #: 28

RE: .o49 engines by cox - 4/15/2008 8:48:48 PM   
Falco250


 

Posts: 56
Joined: 9/22/2004
From: Montreal, QC, CANADA
Status: offline 		The reed valve will be less effective when the throttle is closed down and the RPM and pressure differential are lowered,
which I think will cause a leaning out of fuel mixture. So you probably wont be able to acheive as low an idle speed
as with a rotary valve. You may have to richen overall mixture. But the concept does appear to work, especially with the choke tube throttle which inherently increases fuel mixture as you close down the choke valve.

(in reply to Mr Cox)
       Post #: 29

RE: .o49 engines by cox - 4/15/2008 8:49:59 PM   
Mr Cox



Posts: 345
Joined: 7/20/2007
From: Gothenburg, SWEDEN
Status: offline 		It is not the rpm itself that I'm after, it is the low pressure caused by the restrictive throttle that I think cases problems for the reed.

Maybe I'm looking for a solution to a problem that''s not there, but there is something about the reeds and a throttle that is not working well.

< Message edited by Mr Cox -- 4/15/2008 8:50:46 PM >

(in reply to digital_trucker)
       Post #: 30

RE: .o49 engines by cox - 4/15/2008 9:03:13 PM   
digital_trucker



Posts: 1230
Joined: 2/4/2006
From: Dorr, MI, USA
Status: offline 		There''s youtube videos of throttle-converted SS''s that idle beautifully. Of course, the QB didn''t idle so well, but I think that was just ''cuz of the lousy carb it had.

The proof will be in the numbers when he runs it...then we''ll all know.

_____________________________

I feel I can speak for 90% of humanity when I say 'durrrr'
Skype digital_trucker

(in reply to Mr Cox)
       Post #: 31

RE: .o49 engines by cox - 4/15/2008 9:30:02 PM   
rc2007


 

Posts: 165
Joined: 6/19/2006
From: , NV, USA
Status: offline 		propjobbill , are you saying that you reset the piston on a brand new engine? How does give you more performance and why do you have to do it on a new engine? Thanks.

(in reply to digital_trucker)
       Post #: 32

RE: .o49 engines by cox - 4/15/2008 10:41:28 PM   
jessiej



Posts: 1803
Joined: 7/6/2003
From: STATESBORO, GA, USA
Status: offline
quote:

ORIGINAL: rc2007

propjobbill , are you saying that you reset the piston on a brand new engine? How does give you more performance and why do you have to do it on a new engine? Thanks.



I imagine propjobbill does it for the same reason I do. I have found the fit on new Cox engines variable. Aside from any effect on performance a sloppy rod/piston fit will accelerate wear.

jess

(in reply to rc2007)
       Post #: 33

RE: .o49 engines by cox - 4/16/2008 6:02:38 AM   
air-madness


 

Posts: 140
Joined: 2/27/2007
From: , IN, USA
Status: offline 		That''s exactly, I mean exactly what I''ve done! I used an AP .061 carb though. I have been meaning to post some pics. My wife and I are in our newly constructed home now, I just need to get the things from my mother-in-laws house over to this one. I may even post some pics of our new home; I''m very proud of it.

I don''t have any problems at all with idle, transition or the likes, however, it does have a rather high idle. Who cares though, I now don''t have an .049 screaming constantly.

_____________________________

What goes up must come down (sometimes hard), so build a SPAD and save some cash, man.

(in reply to Bugzidor)
       Post #: 34

RE: .o49 engines by cox - 4/16/2008 12:53:14 PM   
Andrew


 

Posts: 1903
Joined: 2/4/2003
From: Murray, KY,
Status: offline
quote:

ORIGINAL: jessiej


quote:

ORIGINAL: rc2007

propjobbill , are you saying that you reset the piston on a brand new engine? How does give you more performance and why do you have to do it on a new engine? Thanks.



I imagine propjobbill does it for the same reason I do. I have found the fit on new Cox engines variable. Aside from any effect on performance a sloppy rod/piston fit will accelerate wear.

jess


Same here.

_____________________________

the "other" andrew
I'm not older than dirt, but I can remember when it was patent pending

(in reply to jessiej)
       Post #: 35

RE: .o49 engines by cox - 4/16/2008 6:07:46 PM   
Clay Walters


 

Posts: 117
Joined: 1/5/2008
From: Simpsonville, SC, USA
Status: offline 		I feel fortunate so many knowledgable .049 folks are around. After fussing for days with a formerly great running Black Widow that had been put away and permitted to gunk up; I ordered a couple of the Sure Starts even though a good many threads/posts had me wondering about how good they''d be.

Well, I''ve run-in two of them now and have to same I am impressed. Seems like they''d properly headspace just from running. At any rate, I just removed the stack off the back and bolted them to a Slickmount. They run for 11-12 minutes on a tank while they''re rich and breaking in. You can see the grey residue running off the block as they wear in and then clear up at the same time they smoothout. Who knows how long one will last but as smooth as they are going I have to wonder what the clues are that a piston reset needs to be performed?

Genuinely curious,

Clay

(in reply to Andrew)
       Post #: 36

RE: .o49 engines by cox - 4/18/2008 2:03:04 PM   
gcb



Posts: 2385
Joined: 10/24/2002
From: Port Ewen, NY, USA
Status: offline
quote:

ORIGINAL: Clay Walters
...Who knows how long one will last but as smooth as they are going I have to wonder what the clues are that a piston reset needs to be performed?

Genuinely curious,

Clay


Clay,

With the backplate off, turn the prop until the piston is partway up and hold it there until gas escapes past the piston and it will hold that position. Now VERY GENTLY rock the prop just enough to see movement in the crankshaft but not move the piston. There will be a little slop on the lower end at the crankpin. Any extra slop of the conrod moving without the piston moving is ball-socket slop. You can see it if you look up into the bottom of the piston.

Another way is to remove the piston and, holding it so you can see the bottom, push and pull on the conrod. Very slight looseness is tolerable. Ideal is little or no slop, without binding.

The faster you run the engine, the closer the fits need to be. In all honesty, I ran Cox engines for many years of sport flying without owning a reset tool. But then it was sport flying with no more than 25% nitro, ~22% oil, and usually a large (6x3) prop.

George

(in reply to Clay Walters)
       Post #: 37

RE: .o49 engines by cox - 4/18/2008 5:32:54 PM   
Clay Walters


 

Posts: 117
Joined: 1/5/2008
From: Simpsonville, SC, USA
Status: offline 		Thanks George. I recently purchase a 5.5-? prop since it was the only .049 prop the shop had -but haven't tried it yet. (That's how it was actually labeled!)

Still using a couple of 6-3 windsor props I have from 20+ years back and have started looking to see who carries the small stuff. Dissappointed to see it start drying up and suspect a revival of interest at some point. (Seems like that's how it always goes)

In the meantime, now that my interest has been revived I need to locate sources.

Unless you think the 5.5 (don't recall pitch) will introduce problems I guess the 12,000 rpm range gives me minimum exposure?

Regards,

Clay

(in reply to gcb)
       Post #: 38

RE: .o49 engines by cox - 4/18/2008 6:05:04 PM   
chevy43


 

Posts: 1023
Joined: 6/9/2006
From: Santa Cruz, CA, USA
Status: offline 		There is a member here ( Skaliwag ) who is a Cox Guru and has a website with Cox engines and parts and lots of nice kits and hardware etc for 1/2a and small planes. He has been a big help to me. His website is: www.selecthobbies.com

(in reply to Clay Walters)
       Post #: 39

RE: .o49 engines by cox - 4/21/2008 7:23:44 PM   
Bugzidor


 

Posts: 10
Joined: 12/22/2007
From: Bangkok, THAILAND
Status: offline