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Old May 09, 2011, 12:47 PM
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I think the biggest thing we have to decide on is planform. do we go with the "traditional" looking sport plane, or do we go with something different?

as far as looks are concerned, personally I prefer the delta planform. everyone and their brother does the more traditional wing and not enough deltas are done. after saying that, I can see why less deltas are done for a sport jet. if the idea is all out speed, then the delta doesn't lend itself well to this ideal. deltas bleed speed very rapidly and require more power to maintain speed, especially as the AOA climbs, such as seen during a turn. this might not be such a great thing if you are involved in a speed trap event without the use of a dive. more energy is required to maintain the turn before the speed run, so it takes longer to transfer that energy once the turn is completed. for this reason, a planform such as the one shown by boredom would be more beneficial. than again, a delta is faster in a straight line and has less overall drag than a more traditional design. it's all about compromise and what you are willing to give up, in order to gain in other places.

I think we need to get a "kind of" firm number of who's all involved here. who actually wants to build this thing. based on that, it's going to be a vote I think. LOL. I'm happy either way, but my preference is towards a delta. mostly because I like them better, but also because it's something different than the norm.

as a side note................as I suggested before, I wonder if there's any way it could be engineered into the design, that wings could be interchangable. perhaps the whole belly of the beast could be removable and change planform from delta to traditional, depending on mood. also, perhaps a receptacle somewhere on the fuse for plug-in tail planes. i don't know, just sort of throwing ideas in there.
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Old May 09, 2011, 01:23 PM
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What about an ogive??
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Old May 09, 2011, 01:23 PM
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Frank, I can try to comment on your intake concerns................

with traditional intakes, the idea is that this style of intake provides the most ram pressure and flow volume. the tradeoff here is large drag losses associated with form drag and flow seperation.

with a NACA style inlet, if air is flowing horizontally and along a section of a streamline, where the speed increases it can only be because the air on that section has moved from a region of higher pressure to a region of lower pressure. consequently, the highest speed occurs where the pressure is lowest. interestingly, the NACA inlet also creates counter rotating vortices which help to deflect the boundary layer away from the inlet and allows more of that faster flowing, low pressure air to enter the inlet itself. the biggest problem is, that the NACA inlet cannot achieve the ram pressures and total volume of a protruding inlet design.

I believe this is where a combination of the two would be an asset. you have all the benefits of the NACA style inlet and all the beneifts of a protruding inlet, all combined into one efficient inlet design. because of the NACA inlet design, some of your inlet area can be "inside" the fuselage itself, which lowers frontal cross section, which in turn decreases form drag and lowers flow seperation. because of the addition of a NACA style duct, you also increase the ram capability of the protruding inlet design, by decreasing the pressure and increasing the speed of the flow. at the same time, you decrease the ingestion of boundary layer air, because the NACA inlet naturally spills this off. as we know, boundary layer air is a fan efficiency killer. I believe this is a win win situation for inlet design and the overall top speed of the plane will be much faster than with a protruding inlet only.

as you pointed out, the traditional design also provides lift over the airframe. this will still be the case as most of the inlet would still be the traditional protruding design, just more recessed into the fuselage. I'm also thinking that the typical NACA style inlet could be re-invented to a simple necking down of the fuselage in that area, instead of the more traditional looking NACA ramp/duct. I believe the narrowing of the fuselage creates the same pressure/speed change as the ramp does, but would also allow the air to flow more naturally into the inlet. what I'm not sure about, is if the vortices created by the NACA duct would be lost, due to no ramp walls being there anymore. for that reason, a traditional NACA duct might be better. again, it's all about compromise.

Rich
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Old May 09, 2011, 01:24 PM
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Quote:
Originally Posted by SMorrisRC View Post
What about an ogive??
ogive just oozes with coolness, doesn't it?
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Old May 09, 2011, 01:55 PM
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Rich: Man you know some good stuf..Thanks for the great explanation, this NACA inlet is all new to me. I have seen some models with the inlet that looked somewhat like this, mounted far at the rear of the model. Dose they work like NACA inlets?
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Old May 09, 2011, 09:15 PM
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if it's mounted towards the rear and is seperate to the air inlets, then it's possible that they added NACA inlets to draw in cool, high pressure air for the ESC or some other purpose for drawing in the air. NACA inlets are ideal for this purpose, but not completely ideal for feeding a turbine or ducted fan. but if one were to couple a protruding inlet and a NACA duct (such as seen on the cyclone bird), you combine the best qualities of both. of course, there are some tradeoffs, since one type does things better than the other and vice versa. however, I believe that combining them gives us what we want, which is better efficiency at higher speeds and air pressures.

when I was in school, we learned that the worst place you could put a NACA inlet was behind a wing, no matter where it's located on an airplane. the high speed, low pressure air flowing over the upper wing surface creates all sorts of nasty problems for a rearwards located NACA duct, especially as it approaches transonic speeds. for this reason, a NACA inlet is best placed ahead of a wing. another interesting bit of information is that NACA inlets are not great when higher AOA angles are reached, which is why a combination of NACA and pitot style intakes would be an asset.

after saying that, there are several aircraft that do very well with NACA inlets only. one that immediately comes to mind is the BD5.

the essential difference between the mechanism of a submerged NACA inlet and a pitot-type inlet (one that protrudes from the surface and faces directly into the wind), is that flow deceleration and pressure recovery take place in the internal ducting of the NACA inlet, whereas they occur in the free stream air ahead of the protruding pitot inlet. A pitot inlet with a well-formed lip can have very high pressure recovery over a wide range of flow rates, whereas a NACA duct tends to work best when speeds are above 100MPH and it can better take advantage of the pressure difference the ramps create.
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Old May 09, 2011, 09:25 PM
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As far as switch planforms at will, not a problem. The drawing I have now was really just for me to get an idea. It is way easier to build from scratch (or much much more simple parts) than it is modifying. The belly would be detachable and would hold the wings (and the tail section for the traditional). The only conflict would be the canard.

As far as sloping the fuse inward, it would not create the same vortices as the NACA inlet. The NACA inlet is a more abrupt change in airflow due to a complete lack of airflow. The drastic shift in airflow would result in the vortices. Now if the fuse is sloped, then the airflow is gradually expanded in front of the inlet.
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Old May 09, 2011, 09:32 PM
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That raises more confusion on my part. What type of airflow does an edf like? If you say a NACA produces vortices, then this would mean that a turbulent airflow is desired. The NACA provides an elevated (and guaranteed) increase in airflow. But is that increased air smooth? (Yes I am asking two conflicting questions.)
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Old May 10, 2011, 12:44 AM
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LOL. yes the NACA inlet produces these vortices, but those vortices do not get ingested into the inlet. they swirl around the edges of the inlet and help to draw high pressure air into the inlet. imagine it to be like a vacuum cleaner. so to answer your question, the increased air is smoother and not turbulent. however, that changes as the AOA is increased, which is why you would also want a pitot (protruding) style inlet too.

I would ask that someone with more fan experience to answer your question about what type of air a fan "prefers", but as I understand it, they prefer a highly charged stream of air, with as little boundary layer as possible. the problem with this is long intake ducts. as the length of the duct increases, so does the thickness of the boundary layer and this robs performance of the fan. because of this, some fans do better with longer intake ducts, where some do not. it's the same way with cars and airplanes. long surfaces tend to increase drag coefficient because as air flows further backwards, the boundary layer becomes thicker and this creates drag. the same thing happens inside the intake duct(s) too.
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Old May 11, 2011, 05:12 AM
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Quote:
Originally Posted by LuvEvolution7 View Post
ogive just oozes with coolness, doesn't it?

There is only one type of aircraft that i know which used this "Style of wing design", may i say it starts with "C and ends with "E".....

So the 2nd beast seems to be on horizon!!...
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Old May 11, 2011, 06:30 AM
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Is it... Concorde? Wait no I take that back.
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Old May 11, 2011, 06:34 AM
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Quote:
Originally Posted by LuvEvolution7 View Post
LOL. yes the NACA inlet produces these vortices, but those vortices do not get ingested into the inlet.

but as I understand it, they prefer a highly charged stream of air, with as little boundary layer as possible.
I've done a bit of reading on these ducts over the last few days, as back at school we were pretty much told 'don't use them', but never given reasons why... You bring some interesting points up, hence the research (stretching brain cells hurts sometimes!)

I saw Wiki states the vortices 'spit' the BL out, but the only paper I could find (on dialup, the NACA paper is 12mb!) said at low speeds of around 60mph the momentum thickness was low enough to ignore. No help there.
I did find some flow vis, which shows the BL and associated vortex being ingested into the duct?
Any decent references on that point?

Also, you've said a fan likes "highly charged". As in, high pressure?
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Old May 11, 2011, 12:12 PM
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by highly charged, I mean the same energy as the free stream ahead of the plane. most intakes and duct systems only recover a percentage of this charged free stream. as in most competitions in life, the highest percentage wins. if a NACA inlet is done correctly, it can be as high as 94% recovery rate, but this depends where the inlet is placed on the vehicle. if a NACA inlet is placed towards the rear of a tapering vehicle, or in a location of constant area, a NACA inlet is not the way to go. the best location to place a NACA inlet is in a area of constant area increase, such as the rear section of a nose. this way, you can be assured that you have the maximum pressure rise and least amount of boundary layer before you draw in that air. this is why they put them on the hood of a car.

I believe the reason why we are told to ignore them on airplanes is the exact reason why they are used in cars.......................the ideal use of a NACA duct is where you require a large, low pressure front of air, such as required by a carburetor. this air volume is large and slow moving, so is ideal for this use. this is also the reason why it's used for cooling purposes, etc on airplanes. at lower speeds, this type of inlet serves little purpose on an airplane, other than creating a large front of slow moving air. so you can see that it's not very efficient as a powerplant feeder. this low speed range is where a pitot style inlet serves a better purpose, due to its very nature of operation. pitot style inlets recover the pressure and decelerate the air ahead of the intake mouth, so this makes them better suited to slower flight. NACA inlets do this inside the duct itself, which makes them better suited to speeds above 100MPH.

pitot inlets are draggy by nature, where NACA inlets have little drag associated with them...........there is some, but barely measurable. this is why I proposed a smaller pitot inlet, combining the extra area lost in the pitot with the area of the NACA inlet. we get less drag from the pitot and the extra area required for slower speeds, but also get the benefits of the NACA inlet at higher speeds combined with less drag of the pitot inlet at speed. I can't see this as anything other than a win win.
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Old May 11, 2011, 12:24 PM
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Sam, it's not only the Concorde with ogival delta wing. others have had the ogive delta. the prototype TU-144 had the ogive delta, but was later changed to double delta, because it performed better than the ogive. I think many tend to forget that the ogive design was tried with the Vulcan bomber, long before the Concorde was born. it's probably where they got the idea for the Concorde wing, along with the Olympus engines too.
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Old May 11, 2011, 01:14 PM
An itch?. Scratch build.
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Ogival delta wing ?

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