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Sep 29, 2013, 04:13 PM
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Quote:
Originally Posted by JimDrew
With the Starfire, you don't have a choice because the fuselage tapers all the way to the tailcone. With other aircraft, like the F-15, F-16, F-18, etc. there is plenty of space to make the pipe the same diameter as the fan for as long as possible before the Y occurs (in the case of bifurcated pipes) or until the outlet needs reduced for the tail cone.

See the attached picture. This is for a single outlet, like a F-16. Notice that the pipe diameter is the same until the very end. This is the optimal design according to Cosmo-flo (a SolidWorks plug-in).
Jim, from my experience with Dynamax's I agree with you 100%, But I was wondering how you came up with 150 mm, as the taper length.

Larry E.

BTW did you get my email ?
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Sep 29, 2013, 08:30 PM
58mm is optimum according to Cosmo-flo. That gives the pipe I designed right at 1/2 pound total thrust loss. Larger diameter reduced the efflux and with no gain in thrust.
Sep 29, 2013, 08:34 PM
Quote:
Originally Posted by LJE4357
Jim, from my experience with Dynamax's I agree with you 100%, But I was wondering how you came up with 150 mm, as the taper length.

Larry E.

BTW did you get my email ?
Yes, I responded to your email.

I played with Cosmo-flo to determine the best angle that created the least amount of drag for necessary exhaust diameter. The real number was something like 151.xx mm, so I just made it 150mm. That is with a single exhaust. I don't recall what the angle length was for the bi-furacted pipe with the smaller diameter opening. It was shorter, like 90mm or something like that. I will have to check that.
Sep 29, 2013, 08:43 PM
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my tail piece dimensions


the inlet into the y pieces measures 5 1/4 in width and the height is 4 in. Basically two half circles 4in with a 1 1/4 filler in between. The 58mm/ 2.28 in outlets end with 4 3/4 in on center separation and the y tubes are tapered over a length of 7 in. It is rough sanded and filler is drying tonite on the foam. I will sand out tomorrow and post a picture.
Jim did you record amperages on F15 motor with the 58mm outlets, vs the larger ones you started with.
I intend to use a DYNE E Max on 12s setup to start with, based on what your F-15 performance seemed to be.
Last edited by jetjock50; Sep 30, 2013 at 11:59 PM.
Sep 30, 2013, 10:30 AM
There is no real difference in the amperage no matter what you make the outlet diameter. What you are after is the highest amount of thrust with the least amount of drag. So the outlets were "tuned" to provide the highest thrust with the smallest outlet. You can shrink the outlet, which will reduce the thrust and give you a higher efflux velocity. But, these war birds do not benefit from that. In fact, they suffer greatly because thrust is what pushes you through the sky. We know that an airframe's speed is limited by its drag. For the Yellow F-15, it doesn't matter how much thrust you have push it, it's top speed is right at 131MPH. We built a turbine version (32 pound thrust G130 turbine) and an EDF verison (~14.5 pounds of thrust - pre-inlet measurement). Flat and level, the speed was the same. On the up-line the turbine was incredible compared to the EDF, but all out flat and level speed was no different. As an experiment, we reduced the size of the EDF's outlets to increase the efflux velocity (reducing thrust) and that dropped the top speed considerably.
Sep 30, 2013, 09:36 PM
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tailpipe pics


Well here are some pics of the tailpiece. You can see the the lip at the inlet for inserting the exhaust duct into it..
Roger
Oct 01, 2013, 12:09 AM
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color scheme


Here is the color scheme I intend to use, it was the 1996 RCAF demo plane. I have so much scale documentation on this plane it is crazy. I spoke with the pilot on the phone and he went over to the hanger and shot a couple of rolls of pictures. Pretty cool of him, I thought.!! That is how long this plane has been sitting around in my shop, sick isn't it?? LOL
Oct 01, 2013, 09:26 AM
That's definitely a unique scheme!
Oct 02, 2013, 08:31 PM
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tail pipe


wow, I thought that surely some one would comment on the tailpipe I have shaped up????
Roger
Oct 03, 2013, 09:21 AM
That doesn't connect directly to the fan, does it? There needs to be as long as possible tube from the fan outlet to where the Y split begins. Ideally, you want those smaller diameter tubes as short as possible too.
Oct 03, 2013, 01:14 PM
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exhaust duct


Jim,
No, it goes clear back at the tailcones. Total length of the piece is 9 1/2 inches, which leaves an exhaust duct to be made approximately 16 inches long from the fan to that tailpiece The inside of the Y measures 5 3/4" to the outlets
Roger
Last edited by jetjock50; Oct 03, 2013 at 01:23 PM.
Oct 04, 2013, 02:01 PM
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stabilator pivot point


I went all the way around to get back to where the article listed in the edf Yellow twin f-18 build said it should be. Which is exactly where the AMA guidelines for large models require it to be.(Not that this is a "large model" by their definition).
I just needed to learn how to calculate MAC (mean aerodynamic chord), once that line is established they want the pivot at 23% of mac. Long and short of it is, the stock Byron pivot point is 3/32" ahead of that location. I am not going to change that. I will try to static balance them, which, is required in the large model airplane guidelines. Whew!!!!!
Oct 05, 2013, 12:18 AM
Quote:
Originally Posted by jetjock50
Jim,
No, it goes clear back at the tailcones. Total length of the piece is 9 1/2 inches, which leaves an exhaust duct to be made approximately 16 inches long from the fan to that tailpiece The inside of the Y measures 5 3/4" to the outlets
Roger
Perfect!
Oct 05, 2013, 09:06 AM
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planning ahead


Now that the inlet and tailpipe plugs are made, I am just waiting on the cash to get the Jet Legend stab mechanisms, some glass cloth and resin. I have also made a template for stab mechanism mounts/rear former. Since that former will now carry the entire load of stab and servo motion. I am making it wrap around the fuse more, and using 1/4 ply in stead of the stock little 1/8 ply units. I am modifying the stabs as well. I have cut off the leading and trailing edges and will epoxy balsa trailing edges and will sandwich a piece of .040 carbon fiber in between the foam and the leading edge balsa. I will notch out the foam and take two pieces of ply, which will be laminated around the pivot rods which have little anti rotation rods thru them. Then epoxy those assemblies into the foam stabs being careful to keep the pivot rods centered and straight. After that I will fiberglass the stabs. And then static balance the stabs. A bit of weight gain here, but well worth it I feel, to gain some solid stabs. As I have this conversion in my head, that, the gear doors and Jet Legend retracts should be the only weight gains. Oh and the inlet ducting. LOL
In spite of the fairly large size of this plane, it seems that I need to build it from the tailcones forward. I will, need to get the wing mounts squared away at the same time though in order to maintain the alignment of the wings and stabs. Will get some pics of all this as I proceed
Roger
Last edited by jetjock50; Oct 05, 2013 at 09:15 AM. Reason: add ons
Oct 11, 2013, 10:20 PM
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messing around with some scale details


While I am awaiting the arrival of the JL stab mechanisms. I cut out the appropriate panel on the nose of the plane and made up a "spot light" which is typical of a CF-18. Used the reflector and light, from a mini-mag flashlight, and used the panel I cut out with the right size hole dremeled in it. Epoxied some 1/32 ply strips around the opening in the fuse and mounted it with bvm panel screws. I have a small paddle switch laying around which hooks up to a 9v battery, which really lites it up.. Also cut out the gun ports on the nose and epoxied some balsa under them so I can do some shaping for those ports then fill and sand them. I will post pics of these tomorrow. I sold my sport plane (sig king kobra) to buy the mechanisms and resin and glass cloth. I am so ready to get this moving.
Roger


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