interesting idea, a couple of thoughts;
There is no plugin for autocad etc to do aero vehicle dynamics as a whole. You can get fea for mechanical, some programs for thermo and some fluid dynamics. Each program is more than several autocad full licences. The end result still wouldn't give the answer you're looking for. They do not generally contribute to one answer or even agree. Thats why wind tunnels are still required.
Hubless wheel bearings carry the load in a different plane to the concentric ducted fan design.
The hubless bearing generally is engineered for a relatively slow speed. Each fan would have to rotate much faster than a road wheel and you are componding the bearing speed since the two fans rotate in the opposite directions, doubling the effective working speed requirement for the bearing.
Are the two fans supposed to pass the same volume of air per unit time? A rough rule of thumb says the same amount of work (power) will move the same given volume of air what ever the speed and size of stream. If the concentric idea is to balance the torque produced by the fan disks then the inner disk will have to turn at a function of the ratio of the areas. If the inner is a 1/4 area its got to turn four times the speed. This will produce serous turbulent flow as the centre stream will be required to flow far faster than the outer stream. You've got boundary effects on the outsides of both fans.
Powering the rotors seperately would be interesting.
As thkoutsidthebox says, fairings or spinners do not help below certain airspeeds and at very low airspeeds are actually a hinderance.
How about concentric fans or prop blades like a helicopter, mounted on one common shaft system.
Any thoughts on controlling it?
Again, interesting, fun idea....
Last edited by fyffe555; 12-02-2006 at 05:40 PM.
Reason: can't spell....
1. you engineering guys develop:
____a. air volume/speed requirements to lift ~500lbs.(allow for some safety measure)
____b. divide that by 2 rings (inner smaller diam. and outer larger diam.) giving equal flow at same rpm.
____c. determine rpm of blades (based on available engine technology)
____d. size, shape and qty. of blades based on "a." & "c."
____e. determine adequate bearing configuration for fan rims.
____f. size of parachute to bring 500 lbs down safely in the probable emergency,(folded package size)
____g. what to drink when we achieve goal
2. No computer help so we need to build a scale model.
____a. What scale?
____c. what to drink when it flies?
Thanks guys for entertaining my idea.
Good point Carlo, there may be something already out there in the model industry that could help get things rolling.
Andrew, my point on the hubless wheels was just that you don't need to think center-minded anymore. The outer fan could be supported by some OD/ID bearings of some sort or another....not necessarily like a motorcycle wheel.
Each fan would be in their own bearing structure, I don't see where the compounding comes in.
I would suspect each fan would blow much different volumes of air at the same RPM. It could be the same but you are correct, the goal to me would be to balance torque. I do not know how else to stop the rotation unless you use a tail and rotor to keep you straight. And the outer fan could be much narrower if that results in a better match for the balance. Then I would just extend the motors out from the body to the centers between each fan.
The reason I was thinking each engine would both drive was for safety that possibly 1 engine could bring you down safely....nothing more. So if it makes sense to drive each fan a various different RPM's then I would hope that either remaining fan could also bring you down slower than a rock and still avoid using the chute.
Control in my plan comes from the ducts that lead from the top of the body(under fan) to the 4 corners at the base of the body....normally open air flows and gives some lift...close any 1 partially and you would begin to rotate..close all in back and go in reverse, close all in front and you go forward. Like I suggested earlier, it would not be a fast ride unless you could build in some kind of tilt to get the fans pulling you in a direction as well. The purpose for this would not in my mind be for cross country flight but possibly commuting 20-30 miles relatively quickly as the crow flies.
I was just trying to stay away from props as they have been done probably to death and they still don't fly much in this type application....they are not common. Concentric Fans?
Please remember I have no real idea of what I suggest....just thinking outside the box. ;-)
Generally the scale of model to build is 'the larger the better'! Smaller models give completely different aerodynamic characteristics to their full size brethren. I'd be thinking definately no less than 1/3 size, depending upon the size of the full scale vehicle. remember that some large rc models are what we can consider huge for models, so for something like this it may be worth thinking about your 'model' being a full size version, just with rc controls.
Of course building full size and full weight increases the costs exponentially since you can no longer buy r/c aircraft parts for testing and you have to go to regular aircraft manufacturers and engine manufacturers. Its basically a trade off between as big as you can afford while trying not to be too small. If you have a multi million developmental budget then of course the sky's the limit....so to speak!
Im working on a design of my own at the moment, I have been since last May. I have a two year design program drawn up. Sorry I can't post pics for a bit, but will at a later date. I've gone through a number of design changes and sourced most of the parts. Im tooling up at the moment and starting to build the initial proof of concept prototype at the beginning of February all going well. I've sourced most parts for both a scale prototype and a full scale version, but the full scale version was running at over 6 times the cost to build a prototype, and that's not including staying in line with any regulatory considerations. The scale I decided upon in the end is 1/2 scale, which allows me to remain within a reasonable budget for the initial prototype by using model aircraft parts (Approx €1000).
As intimated to above, you can't get a program to just calculate everything, at least not without getting it specifically made for you. If you can I'd be extreamly surprised, please let me know! The factors involved are phenomenal, your talking about the movement of multi-billions of air molecules, with huge variables ranging from the altitude and humidity to the exact shape, size and distances from your fans that your vehicle is. Supercomputer multi million dollar government physics lab kind of stuff. Unfortunately.
There are hobby type programs out there, some are free online or VERY cheap and used for analysing aerofoil data. However, the accuracy of the data is questionable, but can be useful for getting a general idea, in fact, Im using one myself! But I havent seen anything for calculating the thrust from ducted fans like you need to. In fact, I havent even found one for props, and have to do all the calculations myself the old fashioned way...great fun! ...
Two engines for safety is great, but if you have a working parachute system then its not really necessary. However, two engines can be advantageous because you may be able to get the same power out of a smaller weight using two smaller engines which are lighter than one bigger one.
How about moving your ducts to the base of your vehicle, two front and two rear. And have their output adjustable like you said, or possible having fully adjustable pitch outlets also. Anyway, when you direct some thrust solely out of the rear vents, because the vents are at the base and rear, the rear base will lift and the front base will drop, the aircraft will tilt forwards, allowing the main fans to then provide forward motion also. But remember when the main fans provide some forward motion also, that said force is being taken from the thrust providing lift and the thrust will have to increase. Theres more to this again, such as the operation of the ducts, the thrust out of the ducts, the operation of the front & rear ducts in concert etc but its an idea.
The reason that props "have been done" is because they are very efficient for moving large volumes of air at slow speeds. Unlike for example, jet engines, which move small volumes at high speed. Dont dismiss props as being old. I know ducted fans have that cool factor, but take a step back to think that maybe props would be a possible alternative. They might look less new and improved, but they may also be a better choice. I considered both in detail and decided upon props, but again, lots of money could change this to fans if you have it!
Im not that up on the intimate details of ducted fans, but I believe that your rims in the pic above would be unsuitable as the shrouds on ducted fans have to go slightly above and below to trap the air, so the shrouds need a flat (Or matching the blade edge) verticle surface inside. Ducted fans also have very tight tolerances between the edge of the fan blades and the shroud which have to be engineered very closely. They are not common because of the expense in making them, and they have their own considerations. Although with modern techniques and materials their time is probably coming. Again, I can't be sure because I dont know the characteristic comparisons between fans vs props. That would be interesting to see, any idea anyone?
Also Im thinking '6 bladed prop' instead of 'ducted fan'. A 6 bladed prop is 6 times more efficient than a single blade (Very rare but they do exist), twice as efficient as a 3 blade etc. By efficient I mean that it literally provides 6 times the thrust of a single blade.
Finally ....I firmly believe that the reason personal air transport has not developed faster is because the aviation industry worldwide has become SO INCREDIBLY OVER-REGULATED. Seriously, its crazy. Its well regulated for current technology in use, but regarding the development of a completely new aircraft, the amount of red tape and paperwork basically makes it impossible for an individual to fly something they designed and built themselves. Look at how difficult and expensive it is to just buy a small aircraft kit and get it registered to fly. With something like this you basically will end up with some aviation authority bozo who knows cessnas and 747's coming out at every stage of the construction process to see if your new aircraft, which he knows nothing about, is going to be safe to fly. Also, to actually sell and use something like a personal air vehicle, your talking huge legislative changes, because obviously every person who buys one of these can't go through the current Private Pilot training and testing and certification. This is not so bad in the good ole US of A, because you have different airspace classes, and if Im not mistaken, this could be flown by anyone, to and from work or whatever, in ClassD airspace. But in Europe we dont have seperate airspace classes like that, and its a headache to even think about.
So, the point is that you should build a prototype as a model whatever size (I joined the local Model Aeronautical Society! ), then build the full size as a model and see if you can find investors or whatever. If I eventually get to a full size version Im going to just build it and fly it away from crowded area to see how it goes without telling anyone. If they get a radar blip at ATC I dont care because Ireland doesn't have any F16's to scramble to investigate.
12-04-2006, 09:17 PM
Ok.....I guess you have convinced me to go back to work on my little router. When you start talking governmental bureaucracy I'm outta here. Last thing I need is more stress in my life.
I really do appreciate the information you have so graciously shared. I hope it didn't keep you up too late. That was a huge post! Somebody will benefit from it, I am sure.
I wish you well in your project and good luck with your test flight. I'll watch this post from time to time to see if anyone is keeping it going but I don't think it will be me.
maybe after I get my router going........cnc propeller/fan blades........hmmmm...
01-05-2007, 08:30 PM
Not sure if you are still here but I remember this from my childhood time: http://www.virtuallystrange.net/ufo/...o/avrocar.html
You were looking at diffeant designs of lift of an person...hummmmm, Old tech but maybe you could revie it..lol...have fun!
08-03-2007, 04:40 PM
Hi diarmid..... Sir i am a mechanical student from Pakistan and am only 20 years of age.... i have to give a final years project in about 10 months as im doing mechanical engineering. I was interested in this Springtail vehicle alot since the last two years. But as im just a novice thus i couldnt know if i ever will be able to make it or not. But you sir look like an expert and seems to me as if you have invested some time in this Springtail machine... Sir i wanted to ask you that should i take it on as my project.... What i mean to say is that is it do-able ? Your reply will mean alot to me. Thank you!
08-03-2007, 06:55 PM
diarmaid is no longer a member of cnczone, but I think you misunderstood him. He did not have anything to do with the SpringTail, and only found info about it on the internet. He was simply starting from ideas like you.
Originally Posted by Faisal Durrani
It is certainly 'do-able' but requires a lot of effort and research depending upon your aeronautical engineering knowledge so far. To actually design and build such a system also requires money, even in the scale prototype stage. Also, you can't just build a Springtail, its copyrighted, you have to think of something new.
08-04-2007, 12:03 PM
TO: TNKOUTSIDTHEBOX. Thank you sir, ya i really did misunderstand him. And i have not enough knowledge of aeronautics so i have planned to give up on the springtail project on your advice. Thank you again.
08-04-2007, 12:12 PM
The Road Marking Machine Project !
I have noticed this forum is filled with many experts who give very vital and detailed help to those who are seeking it... I have been given this project of a road marking machine that paints a yellow continous strip on the edges of the road... the old version was man pushed... thus there was no quantized speed plus no idea of how much paint be sprayed from the nozzle gun onto the road.... it was all dependent on the skill of the worker using it. I wanted to ask you people that as the machine does have a gasoline motor and a compressor what can i do to make it "automatic". Im sending its picture so that it can be easyh for you to come up with your creative ideas. Thanks!
11-11-2008, 11:40 AM
??The beginning of a SCUD MISSLE LOL
02-19-2009, 11:16 AM
Hello guys im new to this site but i am glad i found it. Diarmaid i think you and fyffe's ideas are cool. I have been working on an idea similar to the solotrek. With a helicopter you can auto rotate and so have a fallback system, with your system you have no controlable fallback so you need to add one, parachute maybe... Kona tours
02-20-2009, 01:11 PM
The obvious fallback as you allude to, would be a ballistic parachute system. These have been used effectively on light aircraft now for a number of years.
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