|Jun 16, 2012, 12:38 AM|
to fit a 90mm fan it has to be pretty bigto get a single fan in there...if your going T-38 you need it bigger as the inlets are very small on the 38,look at some pic of a 38 and a later model F-5 there is a big difference,also the nose ,canopy is diff on a 38.not sure you could do both planes,one or the other. the bigger the better,just scale the inlets to the fan. scale inlet ...what ever the size of the plane.
|Jun 16, 2012, 11:17 AM|
Take your pick, F-5, T-38 here a bunch of differant config 3 views I got these from Ed Waldrep awhile ago.
|Jun 16, 2012, 05:13 PM|
It looks like Sam started something interesting here.
The choice seems to be T38 or F5. At first glance the F5 seems to have more inlet area, but I would like to do some CAD measurements to confirm or dispel that.
The F5 does have Leading Edge Extensions, which would help in slow speed flight, more lift, and slower landings. However it also adds a small amount of additional drag. May not be a issue after I take a closer look at that.
The F5 is about 1 ft longer and wider (span) than the T38, and has 16 sq ft more wing area. Not a whole lot of difference when scaled down to 1/4 scale.
So let me study the 3 views that Andy was kind enough to post below and I will get back with my recommendations, shortly.
Meanwhile I would like to answer some of the questions you have asked below:
"AIR SALLY to fit a 90mm fan it has to be pretty bigto get a single fan in there...if your going T-38 you need it bigger as the inlets are very small on the 38,look at some pic of a 38 and a later model F-5 there is a big difference,also the nose ,canopy is diff on a 38.not sure you could do both planes,one or the other. the bigger the better,just scale the inlets to the fan. scale inlet ...what ever the size of the plane."
Doing both planes is a lot of work, so I would like for us to settle on one after I can get you the results of my study. Scaling the inlets to the fan FSA is one way to go, as you suggest, so I will also look at what length and wingspan we end up with if we do that.
"mike2663 Just curious are we talking construction along the "Wowplanes" line or more like what they did on the Falcon5 T-38 construction?"
The construction would be more along the "wowplanes" line. See my website at http://www.wowplanes.com. My A10 would be a good example to look at. The construction is not like a scratch build, where one starts with a block or a sheet of foam. Here we will have pre-cut parts, most already shaped. A few are profile pre-cut and need some minor sanding to get the final shape. The canopy is clear plastic and there may be some other parts in white plastic. The design is done in CAD and the parts are CNC cut by a computer. The quality of the cuts, the precision of the fit, the ease of assembly, is way better than manual foam cutting. I use white styrofoam because I can buy big blocks of it. That reduces the parts count and eliminates a whole lot of gluing that adds weight and failure points. The frame is also lighter and can be made just as strong, if not stronger, with strategic use of balsa, ply, and or carbon fiber.
|Jun 16, 2012, 08:45 PM|
I prefer The look of the T38, but you may have to cartoon the inlets a bit, or god forbid, add cheater holes. YUCK!!!!!!!!! Hope you can make a scale inlet work, so we don't have to resort to the two options above that everyone hates.
Your welcome Lee. I wasn't used to guys calling them LEX's till I came on these RC forums. LOL.
|Jun 16, 2012, 10:00 PM|
twin 70mm maybe????
I will look back over the CS fan threads and see if the FSA is listed.
Just an idea
idea: If the intake area is a major factor, i think the looks of the dual cockpit is the governing factor of WOW effect that might appeal to people more than a single seater. Does the F-5B have larger intakes than a T-38?
FYI vacation in New England, today at the Plum Island Jet meet, cloudy till after 4pm but temp was 65 high and winds from the NE. I thought about going south but all i can say is......WOW!, love the weather compared to the Ohio valley area!
Now FL in the winter would be similar so maybe head there this winter.
|Jun 16, 2012, 10:41 PM|
Well folks, I have some good news.
I scaled the 3 view so that the fuselage length would be 144 inches i.e. 1/4 scale.
Take a look at the attached cutouts from the 3 view.
Notice that on the full scale plane, the opening of the intake is cut at a slant, both in the vertical and horizontal plane. This effectively increases the intake opening area of the duct. Looking at the drawing in 2D gives us the wrong conclusion. But if we account for the slanted cuts and look at it in 3D, the intake opening is actually 12 sq in vs 8 sq in required by a 100 mm EDF.
From the opening towards the fan, the duct dimension in top view remains the same, but in the side view, it gradually increases. I verified that this keeps the area over 12 sq. in. till we reach the fan.
In other words, we don't have a problem of choking the fan if we build it to scale.
The other point is that for a jet this size, we really do need to have smooth intake ducts. Cheater holes create a lot of turbulence on entry to the fan and should be avoided where possible. For an EDF the intake turbulence is actually more harmful than the exhaust. By the time we get to the exhaust, the fan has already done its job.
So how the heck do I make the intake ducts, you may ask? Fear not, I plan on providing foam plugs for the intake ducts as part of the kit. You can wrap FG cloth around these plugs and dissolve the foam plug with gasoline once the epoxy has cured. Pretty simple way to make ducts. Of course there is some sanding and smoothing of the plugs that you will have to do.
So in summary, it looks like the T38 is a go for now. Next I have to look at the aeronautical / aerodynamic aspects to see how it will perform. Stay tuned.
|Jun 17, 2012, 02:53 AM|
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