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Old Nov 25, 2012, 09:38 AM
Retired aircraft maintenance
Ken Gerrard's Avatar
United Kingdom, England, Wiltshire
Joined Oct 2009
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Hi Floey, Great 3 views thank you buddy downloaded and printed.
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Old Nov 25, 2012, 09:54 AM
Registered User
Singapore
Joined Nov 2007
434 Posts
I have to say I would also like to do an EDF version I am sure there will be a few issues but would like to give it a try.
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Old Nov 25, 2012, 10:22 AM
2014 EDF JET JAM We be Jamming
Kevin Cox's Avatar
St. Louis Intl, Missouri, United States
Joined Jan 1997
6,756 Posts
You guy might want to look at Gordon's thread.

http://www.rcgroups.com/forums/showt...ghlight=lightn
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Old Nov 25, 2012, 10:53 AM
Retired aircraft maintenance
Ken Gerrard's Avatar
United Kingdom, England, Wiltshire
Joined Oct 2009
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Smokin' Kevin ! Excellent material there buddy, all grist for the mill. Thank you so very much.
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Old Dec 03, 2012, 04:27 AM
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Norway
Joined Dec 2007
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Quote:
Originally Posted by Ken Gerrard View Post
Smokin' Kevin ! Excellent material there buddy, all grist for the mill. Thank you so very much.
Looked through Gordons Lightning and his exhaust duction I would say
not recomended.

http://static.rcgroups.net/forums/at...G?d=1116538877

Why? The exhust duct should be circular because the flow is very turbulent.

What he should have done was a split ducting (when using one fan) with two circular exhaust (like the original).
The split must be done like a snow plow see my attempt ...

http://www.rcgroups.com/forums/showp...3&postcount=16

This may not so crucial maybe on the Lightning (compared to the A-6 Intruder) since the
two exhaust are close to each other.
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Old Dec 03, 2012, 04:44 AM
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Singapore
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Interesting solution, it seemed to me on a first pass that better to use two small fans, ok there is the extra weight of another ESC but the exhaust would be two tubes. There is the other problem of the inlet duct which would need a Y duct. In looking at cutaway picture of the Lightning I noticed the engines were actually staggered in the fuselage, the lower one being in the bump under the wing and the upper one further back. This would at least solve the access issues with two fans on top of each other but would then make the inlet even more of a challenge.
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Old Dec 03, 2012, 06:00 AM
2014 EDF JET JAM We be Jamming
Kevin Cox's Avatar
St. Louis Intl, Missouri, United States
Joined Jan 1997
6,756 Posts
Quote:
Originally Posted by FLOEY View Post
Looked through Gordons Lightning and his exhaust duction I would say
not recomended.

http://static.rcgroups.net/forums/at...G?d=1116538877

Why? The exhust duct should be circular because the flow is very turbulent.

What he should have done was a split ducting (when using one fan) with two circular exhaust (like the original).
The split must be done like a snow plow see my attempt ...

http://www.rcgroups.com/forums/showp...3&postcount=16

This may not so crucial maybe on the Lightning (compared to the A-6 Intruder) since the
two exhaust are close to each other.
I will have to respectfully disagree. You would have more losses if you do a bifurcated exhaust over Gordon's oval method, which is a straight tube. The most important things like proper inlet and outlet FSA and the condition of the ducting has a greater impact.

I believe your work on the Kyosho A-6 showed benefits because you were simply improving a horribly designed ducting to start with (good job!). Gordon's exhaust design was spot on for efficiency with a compromise for scale appearance. EDF bifurcated ducting is used for scale appearance not system efficiency.
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Old Dec 03, 2012, 06:37 AM
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Norway
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Quote:
Originally Posted by Kevin Cox View Post
I will have to respectfully disagree. You would have more losses if you do a bifurcated exhaust over Gordon's oval method,
.
.
Thanks for Your respect but I suggest You try Gordon's oval against a
circular duct. I did when I was experiementing with my A-6 the oval duct
similar to Gordon's.

The oval was hopeless inefficient compared to my split/bifurcal duct, it was
just to do the split of the air correct.

Of cause I might have done something wrong when I made the oval
but the result was so significantly better with the split that I pretty sure
(even if my experiementing was very primitve in a shed) that
it's correct. I've also tried to check with engineering books of fluid
and aero dynamics and as far I'm able to detect they support my views.
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Old Dec 03, 2012, 07:01 AM
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Norway
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Second thought

Got a second thought (I've not studied Gordon duct very closely just
the outlet)

If the internal ductin is made like my sketch to the left it's ok.
It's infact a split duct (section) but without wall in between.
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Old Dec 03, 2012, 10:37 PM
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LuvEvolution7's Avatar
St.Catharines, Ontario
Joined Jan 2009
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well, I can tell you that I made an oval duct for my Eurofighter and it was significantly better than the bifurcated duct. the top end was faster...................much faster. so not to argue Floey, but mine looked a lot like your pic on the right, just squashed down a bit more and it worked incredibly well.

great subject to build. there's not many around. you could contact Pontious and ask him about his Lightning. it's big. real big. Mick Reeves Lightning kinda big. LOL.
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Old Dec 04, 2012, 12:54 AM
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Norway
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Quote:
Originally Posted by LuvEvolution7 View Post
well, I can tell you that I made an oval duct for my Eurofighter and it was significantly better than the bifurcated duct. the top end was faster...................much faster.
.
.
hm it's too difficult (time consuming) this in text ...

I suggest You try this in a bench (when You got time):

Test 1. Measure thrust/air velocity (if possible) and amp draw fan only no duct.

Test 2. Same as above with circular duct (L~4 x fan length) same outlet area as fan.

Test 3. Same as above with conical duct outlet area 90% of fan.

Test 4. Same as above with the conical duct gradualy flattened (X/Y= 1/2) same outlet area.

Test 5. Same as 1. test with split duct (done optimal) total outlet area approx 90% of fan.

I found test 5 "better" than 4 but I had no way of measuring air velocity just RPM.
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Old Dec 04, 2012, 04:59 PM
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St.Catharines, Ontario
Joined Jan 2009
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I don't need to perform any of those tests on the bench to know if it worked better. I only need to see it in action when I flew it. plain and simple, the oval duct totally outperformed the bifurcated exhaust. the shape should be irrelevant, since it's all about area. all you are doing is squashing a circle into an ellipticale shape. also, as an added note, Dan Savage's F-4 performs wonderfully well with an elliptical exhaust too. you can argue numbers all you like, but the proof is in the flight testing. bench numbers don't mean that much to me. I just need to know installed numbers and then fly it and make sure it works.
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Old Dec 04, 2012, 09:01 PM
Da' Cajun
Boogie_'s Avatar
Lake Charles, Louisiana
Joined Jun 2009
2,866 Posts
This is all good stuff, and very timely for me.
I'm collecting parts now and about to start on my MiG 19. Which also has a similar twin exhaust like the Lightening and F-4.

I was planning on borrowing the oval duct idea like Dan did on his F-4. Too many have been built and successfully flown for it not to work.

I'm no fluid dynamics expert, but I can't see how there would be losses from an oval exhaust compared to a circle of equal area.
That said, I would be very interested in some solid comparative test data.

...or we could just wait and see what AirX has to say on it.
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Old Dec 12, 2012, 02:02 PM
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Norway
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Quote:
Originally Posted by Boogie_ View Post
.
.
I was planning on borrowing the oval duct idea like Dan did on his F-4. Too many have been built and successfully flown for it not to work.
.
.
I'm no fluid dynamics expert, but I can't see how there would be losses from an oval exhaust compared to a circle of equal area.
.
.
I'm not an expert in fluid dynamics either but high speed/velocity
turbulent flow will have less pressure drop in a circular duct than
an oval one (that is an physical fact ... as far as I'm able to detect)

But the air velocity in an oval duct may be higher (higher pressure loss)
than in a circular one so in the end the plane may go faster ... I'm not
sure about this ... LuvEvolution7 claims to have seen this in real life.

So far I've never seen a oval exhaust on any real jet plane. Inlet duct's are
mostly ovale but I believe it's to reduce drag. The early jet's had circular
inlets too.
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Old Dec 12, 2012, 07:56 PM
I make bad look so good.
SteveC68's Avatar
League City, Texas
Joined Sep 2006
2,512 Posts
http://www.rcgroups.com/forums/showthread.php?t=879830

This test by Stumax should be considered the last word on bifurcated exhausts. As long as the design is sound a bifurcated exhaust for all practical reasons is equal to a round exhaust.
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