Inline IC engines    Gallery
View related threads: (in this forum | in all forums)

Logged in as Guest



Users viewing this topic: none
    Search This Thread  
 
Printable Version

All Forums >> Glow Engines, Gas Engines, Fuel & Mfg Support Forums >> Glow Engines >> Inline IC engines
Page: [1]

Tower Hobbies Get Coupon Codes Brands  
Login
Message << Older Topic   Newer Topic >>
Inline IC engines - 5/3/2007 1:02 AM   
R/CFlorin


 

Posts: 104
Score: 100
Joined: 12/28/2002
Last Login: 9/11/2012
From: Ontario, Canada
Status: offline 		I'm not sure if this is the right forum to post this question...
I've got 2 cox TD 09 engines wth throttle/carburetor and i'm thinking to put them inline, with a puller and a pusher prop. I've done a bit of research and the second propeller (pusher) would have a higher pitch so the incoming air can be accelerated even more.
The front pulling propeller could have more blades to get a more amount of air, say 3 blade pull prop at front and 2 blode higher pitch pusher prop at the back.
The throttles would be controlled by a single servo between the engines.
Would this setup work, or is it worth to try out of curiosity?
Thanks.


Hide Signatures
       Post #: 1

RE: Inline IC engines - 5/3/2007 1:12 AM   
w8ye



Posts: 36486
Score: 318
Joined: 12/11/2001
Last Login: 6/19/2013
From: Shelby, OH, USA
Status: offline 		Sounds pretty good to me

But one .20 engine will have more power and be more efficient than two .09's

_____________________________

Attended the CutFinger Institute of DirtNap University for years but never did graduate....
Recipient, Mangledhand award August 2008
Club Saito Member #7
Original AMA #31261

Hide Signatures

(in reply to R/CFlorin)
       Post #: 2

RE: Inline IC engines - 5/3/2007 1:20 AM   
pe reivers



Posts: 6558
Score: 646
Joined: 1/23/2002
Last Login: 6/18/2013
From: Arcen, , NETHERLANDS
Status: offline 		Why not!
The front prop should be a larger two blade though to adapt the prop diameter to the prop wash, which narrows down behind the first prop due to Bernoulli's law.

_____________________________

Pe, (www.mvvs.nl), MVVS, MOKImotor, RCexl, MTW, Xoar, Mejzlik.
Blessing in ignorance? There is sanctuary in analysis.

Hide Signatures

(in reply to R/CFlorin)
       Post #: 3

RE: Inline IC engines - 5/3/2007 5:58 AM   
blw



Posts: 7679
Score: 655
Joined: 3/15/2004
Last Login: 6/18/2013
From: Opelika, AL, USA
Status: offline 		Pe,

At first, I agreed with you. But, my guess is that the rear prop could end up working with only disturbed air from the forward prop. I made a quick sketch to show the reduced column of disturbed air from the pressures of the forward prop. My guess is that this column of air would be the swirling slipstream, or P factor air, also further disturbed by the fuselage. This could mean that the rear prop would experience uneven pressures around the disk. This could lead to vibrations and unequal efficiencies.

I've not seen this explained, so it is all a guess. It would seem that an equal sized or larger rear prop would bring in clean air near the blade tips to equalize the airflow more. I'm sure this has all been figured out much better.



Attachments
Click to see fullsize image.
Click for fullsize


_____________________________

The ultimate responsibility of pilots is to fulfill the dreams of the countless millions who can only stare skyward...and wish.

"It doesn''t take but one Auburn man to be a majority" -
Coach Pat Dye

Hide Signatures

(in reply to pe reivers)
       Post #: 4

RE: Inline IC engines - 5/3/2007 7:36 AM   
downunder



Posts: 4373
Score: 123
Joined: 10/10/2002
Last Login: 6/18/2013
From: Adelaide, AUSTRALIA
Status: offline
quote:

ORIGINAL: w8ye
Sounds pretty good to me

But one .20 engine will have more power and be more efficient than two .09's

Except he's talking Cox Tee Dee 09's which are really gutsy engines

The pull/push system works on full size planes so I guess it'll work fine with models. My only reservation is on the rear engine with its plain bearing where the thrust is pushing backwards on the crankshaft.

Hide Signatures

(in reply to w8ye)
       Post #: 5

RE: Inline IC engines - 5/3/2007 10:04 PM   
pe reivers



Posts: 6558
Score: 646
Joined: 1/23/2002
Last Login: 6/18/2013
From: Arcen, , NETHERLANDS
Status: offline 		edited:

a counter rotating of the tractor and the pusher tend to even out the swirl. Yet efficiency goes down the drain because a narrower column of air is accelerated, much increasing the apparent prop disk load. It was no success in German WW2 fighters, but that is no reason not to do it in a model airplane.
After a quick failure mode analisys I think Downunder is right, the Cox pusher needs a hardened steel or phosphorbronze shim between the prop drive washer and the crankcase.
[/quote]


< Message edited by pe reivers -- 5/3/2007 10:05 PM >

_____________________________

Pe, (www.mvvs.nl), MVVS, MOKImotor, RCexl, MTW, Xoar, Mejzlik.
Blessing in ignorance? There is sanctuary in analysis.

Hide Signatures

(in reply to pe reivers)
       Post #: 6

RE: Inline IC engines - 5/3/2007 10:10 PM   
gkamysz



Posts: 3397
Score: 120
Joined: 6/24/2003
Last Login: 2/6/2012
From: Crystal Lake, IL, USA
Status: offline 		Efficiency of counter rotating props close together actually improves slightly. There are NACA documents that are available. In the case of a model were the prop selection is limited, se what works best. A conventional twin setup would outperform what we are discussing by quite a bit.

_____________________________

Greg

Hide Signatures

(in reply to pe reivers)
       Post #: 7

RE: Inline IC engines - 5/3/2007 10:47 PM   
R/CFlorin


 

Posts: 104
Score: 100
Joined: 12/28/2002
Last Login: 9/11/2012
From: Ontario, Canada
Status: offline 		Thank you for all your replies.
I have some things unclear though - shouldn't the rear prop be smaller in diameter and higher in pitch? If the first prop already accelerates the air, it would be normal to have the second propeller move at higher RPM that the first one to accelerate the air even more right?
Since the engines are cox td 09, i've heard that the best propeller for that is a 7x3.5 (i already have a 7x3), so I am thinking to get a 6x4 pusher propeller for the rear engine.
As for the reinforcement between the prop drive washer and the crankcase for the rear engine, does the incoming air create that much pressure to affect the crankshaft of the rear engine?
thanks.

Hide Signatures

(in reply to gkamysz)
       Post #: 8

RE: Inline IC engines - 5/4/2007 1:26 AM   
pe reivers



Posts: 6558
Score: 646
Joined: 1/23/2002
Last Login: 6/18/2013
From: Arcen, , NETHERLANDS
Status: offline 		The conclusions are correct.
It is not a reinforcement for the crank that you need nor the inrushing air creating problems; just a washer to take the thrust of the rear engine. As a pusher, you will get aluminum to aluminum for thrust bearing material. This is not the best combination, hence the need for a thrust washer made of steel or bronze.

_____________________________

Pe, (www.mvvs.nl), MVVS, MOKImotor, RCexl, MTW, Xoar, Mejzlik.
Blessing in ignorance? There is sanctuary in analysis.

Hide Signatures

(in reply to R/CFlorin)
       Post #: 9

RE: Inline IC engines - 5/4/2007 6:54 AM   
IronCross



Posts: 2409
Score: 100
Joined: 8/18/2002
Last Login: 2/14/2011
From: NearBy, AZ, USA
Status: offline 		Apparently Cessna engineers weren't aware of all the above problems when they designed the 337 Tractor/Pusher config you describe... You might check out KMP's model of the 337 KMP,, I talked to them at the West Coast IMAA flyin at Castle.. They seemed to think any too engines within the specified range would work just fine... No big deal... I think there are a couple threads on here about the plane and engines also... Been awhile though...

_____________________________

Inside every older person is a younger person wondering what the hell happened

Hide Signatures

(in reply to pe reivers)
       Post #: 10

RE: Inline IC engines - 5/5/2007 4:47 PM   
MarkNovack



Posts: 1552
Score: 100
Joined: 2/9/2002
Last Login: 10/14/2010
From: Nameche, BELGIUM
Status: offline 		I was thinking Dornier Arrow.

< Message edited by MarkNovack -- 5/5/2007 4:49 PM >

Hide Signatures

(in reply to IronCross)
       Post #: 11

RE: Inline IC engines - 5/7/2007 7:59 AM   
blw



Posts: 7679
Score: 655
Joined: 3/15/2004
Last Login: 6/18/2013
From: Opelika, AL, USA
Status: offline 		Ironcross- I was thinking the same thing. This is much different than a counter rotating prop system.

_____________________________

The ultimate responsibility of pilots is to fulfill the dreams of the countless millions who can only stare skyward...and wish.

"It doesn''t take but one Auburn man to be a majority" -
Coach Pat Dye

Hide Signatures

(in reply to MarkNovack)
       Post #: 12

Page:   [1]
All Forums >> Glow Engines, Gas Engines, Fuel &amp; Mfg Support Forums >> Glow Engines >> Inline IC engines
Page: [1]





Jump to:


 
Google 



Search | Marketplace | Event Calendar | Local Clubs | Magazine | Product Ratings | New Products | Discussion Forums

Photo Gallery | Instructor Search | Field|Track|Marina Search

Advertisers | Hobby Vendor Resources | Rate Manufacturers | Sign In/Sign Up

SITE MAP!   : :   FORUM RULES

RC Universe is a service of Internet Brands, Inc. Copyright © 2001-2013.

Charities we support that also need your help
Yorkie Rescue | Humane Society | ASPCA | Crohn's-Colitis America


1.547RCU1