Engine placement in the bypass
10-29-2002, 12:42 AM
#1
Engine placement in the bypass
I know that this question has been asked before but since it did not apply to me I let the answer go in one ear and out of the other!!!
When resting in the bypass, I need to know how far the turbine tailpipe should go into the S/S pipe. I have an AMT Mercury and even if I slide the turbine all of the way back in the bypass the tailpipe is still 1/2" to 3/4" from the exhaust pipe. Should the engine sit farther back? The plans show the turbine sitting in the middle of the bypass well forward of the S/S exhaust pipe. I don't want to cook the bypass....TIA
Kevin
When resting in the bypass, I need to know how far the turbine tailpipe should go into the S/S pipe. I have an AMT Mercury and even if I slide the turbine all of the way back in the bypass the tailpipe is still 1/2" to 3/4" from the exhaust pipe. Should the engine sit farther back? The plans show the turbine sitting in the middle of the bypass well forward of the S/S exhaust pipe. I don't want to cook the bypass....TIA
Kevin
10-29-2002, 01:02 AM
#2
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Engine placement in the bypass
My BVM Sabre conversion plan shows the end of the turbine exhaust is 1.5 inches from (in front of) the start of the inner tail pipe. The outer tailpipe is about 1/8 th of an inch behind the inner pipe.
hope this helps
Regards
Tom Watson
Sydney Australia
hope this helps
Regards
Tom Watson
Sydney Australia
10-29-2002, 01:16 AM
#3
Engine placement in the bypass
Tom,
Thanks for the quick reply. Since you are in Australia you might be familiar with the Trim F-86. This is the kit that I'm refering to. I believe that I've heard Tam comment about keeping the turbine close to the pipe. This may be on an open non-bypassed installation though.
Kevin
Thanks for the quick reply. Since you are in Australia you might be familiar with the Trim F-86. This is the kit that I'm refering to. I believe that I've heard Tam comment about keeping the turbine close to the pipe. This may be on an open non-bypassed installation though.
Kevin
10-29-2002, 03:00 AM
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Engine placement in the bypass
Kevin,
I don't know about the trim F86. My BVM sabre is being converted using the BVM conversion kit with full bypass. I havn't finished it yet and have not run the engine in the model. I can't see why there would be any difference with bypass or not. perhaps some of the more experienced modelers can answer. The back of the bypass is painted with BVM heatshield inside.
I suppose if the dimension from the turbine to the tailpipe is specificly indicated there must be a reason for it being so.
Regards
Tom Watson
Sydney Australia
I don't know about the trim F86. My BVM sabre is being converted using the BVM conversion kit with full bypass. I havn't finished it yet and have not run the engine in the model. I can't see why there would be any difference with bypass or not. perhaps some of the more experienced modelers can answer. The back of the bypass is painted with BVM heatshield inside.
I suppose if the dimension from the turbine to the tailpipe is specificly indicated there must be a reason for it being so.
Regards
Tom Watson
Sydney Australia
10-29-2002, 03:21 AM
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Euro Sport Build THE RED ONE
I do not know for sure about the AMT The Jet Cat manual gives measurements from the back of the turbine to the tail pipe it is 20 mm or 3/4" in a bypass system or not.
I would contact some one at AMT and see what they recomend
Don B Miniature Turbine Sales & Service Jet Cat Dealer
I would contact some one at AMT and see what they recomend
Don B Miniature Turbine Sales & Service Jet Cat Dealer
10-29-2002, 03:52 AM
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Engine placement in the bypass
You want the exhaust to fill the inner tube for best performance.
If you use a 10 degree expansion on all sides you will be close.
The size of turbine rear opening, the size of the inner pipe all
work to make this distance.
Darryl Usher www.acsip.com/~dgu
If you use a 10 degree expansion on all sides you will be close.
The size of turbine rear opening, the size of the inner pipe all
work to make this distance.
Darryl Usher www.acsip.com/~dgu
10-29-2002, 03:59 AM
#7
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Kevin,
These are the numbers right off of my BVM bypass kit for an AMT mercury. 1.2" from rear of tailcone to front edge of inner ss pipe.
outer is overlapping carbon bypass shell. It also shows that the inner ss pipe is cut .75" short of the outer one in the rear.
outer is overlapping carbon bypass shell. It also shows that the inner ss pipe is cut .75" short of the outer one in the rear.
10-29-2002, 06:54 AM
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kevin,
It depends to some extent on the design of the bypass, the diameter of the inner and outer exhaust ducts, the space between them, and especially the size of the bellmouth/splay at the front of the inner exhaust duct.
In most models the dimension from the back of the Mercury exhaust nozzle should be between 13mm - 15mm from the front edge of the bellmouth of the inner duct. Incorrect positioning of the turbine will give a noticeable loss of thrust, higher EGT's, and poor throttle-up. Incorrect positioning will DEFINATELY give higher exhust duct, and therefore fuselage temperatures. In extreme cases you could damage the tailpipe and/or fuselage.
I spent a day with Philip Avonds testing this in his F-15 with interesting results, and Bennie and I have also done considerable testing on this in many customer models as well as pour own.
For reference, in the Avonds F-16 with a Mercury HP the distance from back of turbine exhaust nozzle to front on inner tube bellmouth should be 13mm exactly.
If you can tell me which exhaust and bypass you are using I can confirm excat dimensions that will work best.
Needed: diameter inner and outer ducts, size of bellmouth (normally 1/4" x 45 degrees), relative location front of outer and inner ducts at front, relative position outer and inner ducts at rear of model - and also distance that outer duct is inside the rear of fuselage. Also what type/manufacturer of bypass are you using?
Best regards,
Mike C
(AMT Netherlands/Holland)
In most models the dimension from the back of the Mercury exhaust nozzle should be between 13mm - 15mm from the front edge of the bellmouth of the inner duct. Incorrect positioning of the turbine will give a noticeable loss of thrust, higher EGT's, and poor throttle-up. Incorrect positioning will DEFINATELY give higher exhust duct, and therefore fuselage temperatures. In extreme cases you could damage the tailpipe and/or fuselage.
I spent a day with Philip Avonds testing this in his F-15 with interesting results, and Bennie and I have also done considerable testing on this in many customer models as well as pour own.
For reference, in the Avonds F-16 with a Mercury HP the distance from back of turbine exhaust nozzle to front on inner tube bellmouth should be 13mm exactly.
If you can tell me which exhaust and bypass you are using I can confirm excat dimensions that will work best.
Needed: diameter inner and outer ducts, size of bellmouth (normally 1/4" x 45 degrees), relative location front of outer and inner ducts at front, relative position outer and inner ducts at rear of model - and also distance that outer duct is inside the rear of fuselage. Also what type/manufacturer of bypass are you using?
Best regards,
Mike C
(AMT Netherlands/Holland)
10-29-2002, 11:40 PM
#9
Engine placement in the bypass
Mike,
The bypass and exhaust pipe are from Trim Aircraft. I used the slightly larger bypass intended for the KJ-66 type turbines just in case I sell the model down the road. (This way it would be easy to convert to either type engine.) Although it is slightly larger there is only about 5/8" clearance all of the way around the turbine. (Very nice bypass and dual walled exhaust pipe from Trim, by-the-way!!! Bypass is carbon fiber and the pipe is light yet very adequate.) I don't have the dimensions handy. I'll have to get them tomorrow. There is no bellmouth on the pipe. The pipe slides into the rear of the bypass for a tight, seamless, fit. If Ed or Kevin is monitoring this thread perhaps they could share some of the dimension #'s. This Trim Sabre is a very good kit and is a great value.
Kevin
The bypass and exhaust pipe are from Trim Aircraft. I used the slightly larger bypass intended for the KJ-66 type turbines just in case I sell the model down the road. (This way it would be easy to convert to either type engine.) Although it is slightly larger there is only about 5/8" clearance all of the way around the turbine. (Very nice bypass and dual walled exhaust pipe from Trim, by-the-way!!! Bypass is carbon fiber and the pipe is light yet very adequate.) I don't have the dimensions handy. I'll have to get them tomorrow. There is no bellmouth on the pipe. The pipe slides into the rear of the bypass for a tight, seamless, fit. If Ed or Kevin is monitoring this thread perhaps they could share some of the dimension #'s. This Trim Sabre is a very good kit and is a great value.
Kevin
10-29-2002, 11:50 PM
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Trim Bypass and Thrust Tube
Hi Kevin
Unfortunately, I don't have the numbers handy at the moment. I will open up the kit we have and take the appropriate measurements. You have the 1700/2300 bypass with your kit. The kit also has the option of coming with a 1200 sized bypass. Testing with the 1200 bypass/thrust tube combination has shown minimal thrust losses with a SimJet 1200 turbine.
Ed
Simply Blue
Unfortunately, I don't have the numbers handy at the moment. I will open up the kit we have and take the appropriate measurements. You have the 1700/2300 bypass with your kit. The kit also has the option of coming with a 1200 sized bypass. Testing with the 1200 bypass/thrust tube combination has shown minimal thrust losses with a SimJet 1200 turbine.
Ed
Simply Blue
10-30-2002, 12:15 AM
#11
Engine placement in the bypass
Ed,
Don't unseal anything on my behalf---This is something that can wait until tomorrow!!! No sense opening everything up as everything is sealed on their own protective bags. Thanks for the offer, though!!! I didn't know if you had one handy or not. I can't wait to get this bird in the air. The interlocking construction will be very strong. The size of this plane is between the BVM and the Fiber Classic versions. Every nut, bolt and screw is included as well as the bypass and dual wall S/S pipe.
Kevin
Don't unseal anything on my behalf---This is something that can wait until tomorrow!!! No sense opening everything up as everything is sealed on their own protective bags. Thanks for the offer, though!!! I didn't know if you had one handy or not. I can't wait to get this bird in the air. The interlocking construction will be very strong. The size of this plane is between the BVM and the Fiber Classic versions. Every nut, bolt and screw is included as well as the bypass and dual wall S/S pipe.
Kevin
10-30-2002, 06:33 AM
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Trim Sabre & Mercury HP
Hi Kevin,
OK. Seen your post. If you can give us some dimensions we can give you a definitive turbine position. Will check the thread when I get back from the office today - but time difference between Netherlands and US will mean you have to wait a few hours, sorry!
Surprised that there is no bellmouth, there really should be a small one at least. But sure it will work fine 'cos Tony Roessen knows what he's doing, and having built and flown a couple of his sabres I can tell you they are great.
Bennie had a Trim F-86 also (for a short time) with a Mercury in it, and it was ballistic!
'Till later....
MIke C
OK. Seen your post. If you can give us some dimensions we can give you a definitive turbine position. Will check the thread when I get back from the office today - but time difference between Netherlands and US will mean you have to wait a few hours, sorry!
Surprised that there is no bellmouth, there really should be a small one at least. But sure it will work fine 'cos Tony Roessen knows what he's doing, and having built and flown a couple of his sabres I can tell you they are great.
Bennie had a Trim F-86 also (for a short time) with a Mercury in it, and it was ballistic!
'Till later....
MIke C
10-30-2002, 10:55 PM
#13
Dimensions
The dimensions of the bypass are as follows: Intake---4 1/4" in diameter. Exhaust---3 1/4" in diameter. Width at widest point---5". Overall length from the leading forward edge lip to the start of the S/S pipe---12". (The inner portion of the pipe slides about 1" deep into the bypass) This is plenty large enough for the Merc. I just would like to know the optimum placement of the turbine within this bypass for max results. TIA!!! Kevin
P.S. Mike, So the Sabre flew well with the Merc!!!! Good to hear---now I really can't wait to get mine going!!!! I also have an Avonds turbine F-16 on the boards. Another great kit!!! I also received my Super Bandit on Monday. It looks as though I may need another Mercury HP for the Super Bandit. (Or better yet, a Pegasus!!!) Kevin
P.S. Mike, So the Sabre flew well with the Merc!!!! Good to hear---now I really can't wait to get mine going!!!! I also have an Avonds turbine F-16 on the boards. Another great kit!!! I also received my Super Bandit on Monday. It looks as though I may need another Mercury HP for the Super Bandit. (Or better yet, a Pegasus!!!) Kevin
10-31-2002, 04:08 AM
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Engine placement in the bypass
Hi Kevin,
Just line up the front of your Mercury engine with the front of the turbine shown on the plan and this will give you the optimal placement of the engine.
Your concern was that the engine does not sit far back enough into the SS duct and that you will cook the bypass, but this is not the case. The bypass is designed to move the airflow around the engine and "hug" the exhaust nozzle at the back of the engine creating a cooling effect.
We developed the larger duct system utilizing the TJT3000 and even at the hottest points of the engine, bypass and SS duct temperatures were only 45 degrees celsius!! The Mercury is smaller in diameter than the other engines (TJT3000/Simjet1700/2300/JetcatP80) that the duct system is also suitable for, so there is a larger airgap between the Mercury and the bypass - meaning the Merc will run slightly hotter than the larger diameter engines, but still not enough to even come close to cooking the bypass.
We do not use bell mouths, although they work, they have a loss of dynamic performance. Besides extensive testing of the larger duct system we also created our smaller duct system using the Simjet 1200 and we had ZERO loss of performance with our enclosed design (We were able to obtain 13.5lbs thrust in our test Sabre and the engine test-run report from Simjet states 13.5lbs).
As always, if you require assistance please feel welcome to contact us at anytime,
Best Regards,
Tony Roessen
Trim Aircraft – Australia
Just line up the front of your Mercury engine with the front of the turbine shown on the plan and this will give you the optimal placement of the engine.
Your concern was that the engine does not sit far back enough into the SS duct and that you will cook the bypass, but this is not the case. The bypass is designed to move the airflow around the engine and "hug" the exhaust nozzle at the back of the engine creating a cooling effect.
We developed the larger duct system utilizing the TJT3000 and even at the hottest points of the engine, bypass and SS duct temperatures were only 45 degrees celsius!! The Mercury is smaller in diameter than the other engines (TJT3000/Simjet1700/2300/JetcatP80) that the duct system is also suitable for, so there is a larger airgap between the Mercury and the bypass - meaning the Merc will run slightly hotter than the larger diameter engines, but still not enough to even come close to cooking the bypass.
We do not use bell mouths, although they work, they have a loss of dynamic performance. Besides extensive testing of the larger duct system we also created our smaller duct system using the Simjet 1200 and we had ZERO loss of performance with our enclosed design (We were able to obtain 13.5lbs thrust in our test Sabre and the engine test-run report from Simjet states 13.5lbs).
As always, if you require assistance please feel welcome to contact us at anytime,
Best Regards,
Tony Roessen
Trim Aircraft – Australia
