Ducted fan aircraft

Homebuilt Aircraft & Kit Plane Forum

Help Support Homebuilt Aircraft & Kit Plane Forum:

piolenc

Active Member
Joined
Feb 17, 2013
Messages
30
Location
Negros Oriental, Philippines
what speed ranges are these fans operating at?
are they for filling the skirt or propulsion,both?
and what on earth are the nylon blades surviving,
that causes composite blades to fail?
I cant help but imagine its rocks and happless squireles
I looked into available fans when I first got interested in hovercraft, after emigrating to the Philippines. Having already written the ducted fan book, I was in a good position to evaluate them, and I was impressed by their availability, but not by their efficiency. Not surprising, as they are designed for industrial and domestic air-moving applications which are not very demanding. The fan that I am working on is for propulsion, and it does need to achieve the best possible efficiency given the rising cost of fuel. There are plenty of good data in the hovercraft literature on centrifugal and mixed-flow fans for use in inflating the cushion, and there too my primary concern is building a fan that is as light and durably as possible.
The speed range will be one that puts the blade tips at a low enough Mach number to avoid critical flow. Ideally, they would be directly driven, but that probably won't work out because the best small engines have a fairly high rpm at best efficiency, so I will have to also look into speed reduction, and all the fun stuff - particularly torsional vibrations - that goes with that.
 
Last edited:

piolenc

Active Member
Joined
Feb 17, 2013
Messages
30
Location
Negros Oriental, Philippines

"contaminating ring" =material ?

=blade tip/ring distance ?

BTW=Yours kit project in bad times ?
I think he means containment ring, for preventing pieces of a failed rotor from becoming high-speed projectiles. Logical material is aromatic amide (Kevlar) reinforced resin, and I think that is what they use. Stiff, strong and TOUGH - very useful for resisting ballistic impacts. They've obviously taken great pains to get the tightest possible rotor/ring clearances. I am puzzled by the high rotor speeds. They make sense for keeping swirl down and thus avoiding building a straightener, but they have several mounting struts that could easily be contoured as NPL straighteners. In that case they would still probably need gearing in the power train, to lower rotor speeds in this case, but that should make the rotor and final drive easier to design, though slightly heavier (more torque, greater weight). I would be very interested in how they selected the configuration that they are using, given the problems they certainly had to deal with such as near-critical flow on the rotor blades, skin friction and so on.
 

dog

Well-Known Member
Joined
Dec 29, 2019
Messages
807
here is a link to tests of small fans and the effects of changing the protective grills on noise and flow
with one interesting result that the more restrictive grills were progressivly noisier except for one pattern that is very restrictive and quiet
read "conclusions" at bottom
 

Malish

Well-Known Member
Joined
Oct 11, 2013
Messages
839
Location
Russia. City of Volgograd
here is a link to tests of small fans and the effects of changing the protective grills on noise and flow
with one interesting result that the more restrictive grills were progressivly noisier except for one pattern that is very restrictive and quiet
read "conclusions" at bottom

This is all about cooling fans and not real ducted fans that used for propulsion...
 

dog

Well-Known Member
Joined
Dec 29, 2019
Messages
807
This is all about cooling fans and not real ducted fans that used for propulsion...
yes ,and perhaps it is only general information
about the flow in ducts,and perhaps more usefull
to thinking about heat exchangers
though the one datum is notable in that the general rule of thumb that a restricted broken
flow will also be loud and noisy is not always
the rule and I think will scale to much larger systems
I will add the link to the heat exhanger thread
 

Steve C

Well-Known Member
Joined
Oct 6, 2008
Messages
165
Location
Lodi, CA
Naturally a propeller in open air will pull from everywhere, but it gets more linear as it moves forward.
 

henryk

Well-Known Member
Joined
Mar 8, 2010
Messages
7,412
Location
krakow,poland
Naturally a propeller in open air will pull from everywhere,

=NOT symmetric !

F thrust= a * m (of accelerated air)...

PS=dont forgott=


f.e. =1 cubic meter of air consist 0.65 kg *500^2=150 kJ Kinetic Energy !!!

=tornado vortex is selfsupplied...
dr Sorokodum modell=
 

Attachments

  • вихрь в трубе.mp4
    4.3 MB
Last edited:

piolenc

Active Member
Joined
Feb 17, 2013
Messages
30
Location
Negros Oriental, Philippines
There is a couple of really good hovercraft builders in the UK and the USA that can supply both the fan and the ducts for a very reasonable prices. I have used these on the hovercraft I have built and they worked well. The nylon fan blades are incredibly tough and will survive when composite ones will fail. Unless you are doing something really "out there" then my advise is to stick with the proven products.
I have some samples. They are all right for their original purpose - moving air through ventilation and air-conditioning systems - but I will need better efficiency than they can provide.
 

piolenc

Active Member
Joined
Feb 17, 2013
Messages
30
Location
Negros Oriental, Philippines
Last edited:
Top