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Old Jan 29, 2008, 06:47 PM
Life begins at transition
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Great minds think alike I've got the Dell as well, had no issues whatsoever. In CAD a good screen is important. Likewise, make sure the video card has hardware acceleration AutoCAD can use. Commands like DVIEW are useless otherwise.
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Old Feb 07, 2008, 07:02 AM
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Nem3 you have made excellent work. I believe that I only need is the intake and exhaust ducting with MF480 in the middle.
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Old Feb 07, 2008, 07:05 AM
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Please I need the file in AutoCad format.
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Old Feb 07, 2008, 10:39 AM
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Originally Posted by dimigav
Please I need the file in AutoCad format.
All in good time my friend. I have finally completed the new version of the intakes. Now they have a constantly shrinking area all the way to the fan. Now I can concentrate on getting some stringers and other supports. Once that's completed it all comes down to cutting out the parts to check for fit and finish. Then I will release the plans for all.
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Old Feb 07, 2008, 12:00 PM
smug in granny panties
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good deal nem. all the work can be a pain but good ducting is gonna be important on this kind of model. I went through like 20 fronts and backs on mine before I was happy. cause you start out at 100 percent performance for your fan then every bend and angle it starts to go down, and if vectoring is expected every darn percent counts! lol cause even in perfect setup your picking acceptable losses for vectoring on the back side. course for me I made things worse for myself on mine cause I was also chasing weight and size, and went a tad on the small side, so tight confines didnt help.

Barry
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Old Feb 07, 2008, 02:40 PM
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I know what your talking about. I am actually considering redoing my exhausts. I have yet to check and see what the area is in between the start and end shape I used. So I may still go that route since you bring up a very good point. If I use thrust vectoring, which I plan to, the exhaust should be more intensively designed than the intakes were. I will also most likely do the same thing I did on the intakes.

My goal was to have a constant area all the way to the fan blades. The problem is that the spinner cone on the front of the fan takes up a lot of area. And most intakes do not take that into account. So what I did with the new ones, is account for the area that is taken up by the spinner. So the intakes continue shrinking, from 31.65 sq. cm down to 29.10 sq. cm. at the start of the spinner. Then the intake follows the contour of the spinner to keep a constant 29.10 sq. cm. area all the way to the fan blades.

So for the exhaust I will have to utilize the same concept. I'll have to put tail cones on the fans (already have them) and make the exhaust follow the contour of the tail cones to keep a constant area to the end of the duct. The only question that really remains for me is what to end the duct at. My thought is that if I do thrust vectoring, I should keep the exhaust @ 100% FSA, and use the nozzles for getting it down to the desired 70 or 80%. The problem with that is that the nozzles are very short. And this would create a pretty abrupt change in the airflow. So should I make the exhaust duct for from 100% FSA down to 85 or 90% FSA, and then have the nozzles do the rest.

In tests that I have done with a long exhaust tube, cutting the exhaust down to 90% did not produce much change in either air velocity or static thrust. But this may be different up in the air. So who knows?
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Old Feb 08, 2008, 02:54 AM
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Quote:
Originally Posted by nem3
...............
My goal was to have a constant area all the way to the fan blades. The problem is that the spinner cone on the front of the fan takes up a lot of area. And most intakes do not take that into account. So what I did with the new ones, is account for the area that is taken up by the spinner. So the intakes continue shrinking, from 31.65 sq. cm down to 29.10 sq. cm. at the start of the spinner. Then the intake follows the contour of the spinner to keep a constant 29.10 sq. cm. area all the way to the fan blades............
I think that this is not a good idea.
If you follow the spinner shape your ducts will have an abrupt deviation and this can cause a lot of drag even if section area is held constant.
I would rather go this way:The duct at spinner should have the same diameter of the fan.
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Old Feb 08, 2008, 03:11 AM
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Well its kind of a catch 22. You either do it the way I do, or the way you suggest. Either way you end up with a problem. If you do it your way, the entire intake would have to be roughly 130% of the FSA. And once the air got to the spinner section, there would be an abrupt change in area and velocity. Or you could start off with a 100% FSA intake and then go to the fan dia. But then your going from small to big to small again. The would be two changes in area and velocity. I know that many won't agree with me and that O.K. I would rather try it my way and see what happens, than just say it'll never work.

Any ways here are a few more pics to help you guys sleep at night. It's 2:10a.m. and I think I'll be heading off to bed now.
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Old Feb 08, 2008, 04:46 AM
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I think your on the right tack nem, causebest way is leave it smaller then go out at spinner at spinner length and shape. if i have a fan with a 2 inch long spinner, i make the divergance that size right at the fan, even if i only have 80 percent FSA. cause really as long as its spinner shaped, its no more turbulant to the air than the spinner itself right? and the air wont care or see it cause its goung right around the spinner anyway and wants to go out a bit at this point anyway, it only will see the diameter its traveling in. its worse to have it too big cause air will get in there and go almost all the way back and will have nowhere to go, except to churn and cause drag till fan decides to process it.

Barry
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Old Feb 08, 2008, 09:40 AM
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Hi nem3,
I agree with Barry and think you right on with the duct shape. It's looking very good.

Hey, after taking a close look at the drawings I got a dumb question. How are you getting those batteries in and out? Removable nose?

Dan Eaton
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Old Feb 08, 2008, 10:49 AM
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Hi nem -
Your CAD skills are very good, I am envious!
I have a few observations about ducts that you may find entertaining.

In my opinion, in an inlet duct, air flows fastest at the center of the duct, and slower near the duct walls. This is due to friction, air viscosity, surface effect, boundary layer, whatever you want to call it.
Since the air is traveling faster in the middle of the duct, it becomes more important to streamline the center. Most of the supplied fans give us these big, blunt, spinning obstacles right in the middle of the fastest moving airstream. Some way needs to be found to move the air gently away from the center. Perhaps a model rocket nosecone (the long graceful kind) in front of the fan spinner would help. The nosecone could be supported by a thin wall across the diameter of the inlet duct.

The outlet duct is a differant matter. Since the fan imparts a large 'spin' on the airstream, centrifugal force might tend to force a lot of the airflow outwards, towards the duct walls. Any corners, (as in square outlets), might restrict the aftward flow, and have the same affect as necking down the outlet.

The above is presented not as proven fact, but rather, as an opinion. Your mileage may vary.

Darn F22s are very duct intensive!

Ron
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Old Feb 08, 2008, 11:24 AM
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Quote:
Originally Posted by eatond
Hi nem3,
I agree with Barry and think you right on with the duct shape. It's looking very good.

Hey, after taking a close look at the drawings I got a dumb question. How are you getting those batteries in and out? Removable nose?

Dan Eaton
Thanks Dan and Barry. I am glad to see I am not the only one thinking along these lines. But like I said, even if I am wrong, the only thing lost is a little bit of time. But we gain the knowledge of how to make ducts better and more efficient. My only wish is that I had the time and resources to actually test both theories.

As far as the batteries. The battery compartment has an opening where the canopy is. Its just not apparent because I have not cut those bulkheads off yet. On my other F22, I made the canopy out of foam and it was removable. I am thinking I will do something similar as it was very easy to make the other one that way. But I am unsure what I am going to do around the canopy area at the moment.

Ron, I totally agree with you. I was thinking the same thing. In fact I have been racking my brain thinking about that for weeks. The problem is that if you put something like a nosecone in the intake, you are imparting more wall turbulence because now there are two surfaces the air must travel along. And then a third or fourth wall just to support the nosecone. I am sure though, that your thinking would most likely result in a more effecient, less blunt intake. The question is if the gain is worth the loss.

My other thought about the straightline of the intakes. With the geometry of the intake versus exhaust of the F22. Some part of the ducting must deviate from a straight line. In my opinion it is better to have the intake curved than the exhaust. For starters the exhaust is where your going to want the greatest efficiency, since the only thing you can do after the fan is lose. Also, the curve of the intakes may end up a mute point once the plane is actually in the air, and air is being force into it. Now I am sure if the intake were to make a couple of 90 degree turns, that would be bad. But the little bit of offset I am dealing with should not impose a huge loss. At least less of a loss than if I were to use the same amount of offest on the exhaust.

Oh, btw Ron, thanks for your kind CAD words. This is the first thing I have ever done in 3D in ACAD. I have been a long time CAD user at work with 2D drawings.
Nick
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Old Feb 08, 2008, 12:45 PM
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Hey Nick,

Awesome work as usual! How are you gonna cut those bluk heads out with such great percision ? (hehehe ) man, I hope you know someone with a cnc router! (you have my computer fixed yet )

Dude, I gotta give you credit,,, this guy has never built an airplane, never used balsa... to this. Keep it up cheif! Can't wait to throw it into the ground for you when I hand launch that puppy

taus
www.cuttingedgecnc.com
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Old Feb 08, 2008, 01:01 PM
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Originally Posted by tauscnc
Hey Nick,

Awesome work as usual! How are you gonna cut those bluck heads out with such great percision ? (hehehe ) man, I hope you know someone with a cnc router! (you have my computer fixed yet )

Dude, I gotta give you credit,,, this guy has never built an airplane, never used balsa... to this. Keep it up cheif! Can't wait to throw it into the ground for you when I hand launch that puppy

taus
www.cuttingedgecnc.com

Ha ha ha smart @@@. Never going to let you launch this one. I do know someone with a CNC. Its a little big for something this size, but I have regular access to it. So that's O.K.

And yes your puter is done. Oops, forgot to put you modem card back in.
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Old Feb 08, 2008, 01:39 PM
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cause even in a perfect world things can go into the ground, that's why I create files and go right to a plug, otherwise you got one shot, but build a plug you get many! lol On my F-22 as with a lot of my builds I kinda do a blend of cnc and hand made parts, cnc for precision and important parts, and hands so it gets done in fast time. but either way I do the plug so I can make more.

Barry
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