Ducted fan aircraft

Homebuilt Aircraft & Kit Plane Forum

Help Support Homebuilt Aircraft & Kit Plane Forum:

henryk

Well-Known Member
Joined
Mar 8, 2010
Messages
7,402
Location
krakow,poland
Last edited:

raytol

Well-Known Member
Supporting Member
Joined
Dec 17, 2021
Messages
206
The reason is actually that few people have learned how to design ducted fans. That's the reason that George Wright and I wrote our book. Ducted Fan Design, Vol. 1, first published in 1997, now in its third edition. One of the early chapters lists the most common errors.
Thank you for your book. I used it to design the ducted fan in my first flying car. I found that keeping the tip clearences close in the composite structure was a problem. I ended up using a fan in a ring in a duct which also increased the mass flow. The flow straighteners are certainly worth doing and are a lot easier to make controllable than controlling the pitch of the fan blades.
 

henryk

Well-Known Member
Joined
Mar 8, 2010
Messages
7,402
Location
krakow,poland

Attachments

  • NotchedDuctedFan.jpg
    NotchedDuctedFan.jpg
    40.8 KB · Views: 0
  • WhatsApp Image 2021-12-02 at 12.53.43.jpeg
    WhatsApp Image 2021-12-02 at 12.53.43.jpeg
    34.8 KB · Views: 0
  • Screenshot 2022-01-01 at 23-16-29 Albi II – a new generation developmentAlbi II – a new genera...png
    Screenshot 2022-01-01 at 23-16-29 Albi II – a new generation developmentAlbi II – a new genera...png
    160 KB · Views: 0

piolenc

Active Member
Joined
Feb 17, 2013
Messages
28
Location
Negros Oriental, Philippines
Thank you for your book. I used it to design the ducted fan in my first flying car. I found that keeping the tip clearences close in the composite structure was a problem. I ended up using a fan in a ring in a duct which also increased the mass flow. The flow straighteners are certainly worth doing and are a lot easier to make controllable than controlling the pitch of the fan blades.
I'm having trouble visualizing your system - can you show a sketch? As for clearances in general, flow straighteners are useful because they can double as support struts near the propeller hub. They allow maintaining very narrow clearances between the rotor blades and the duct.
 

piolenc

Active Member
Joined
Feb 17, 2013
Messages
28
Location
Negros Oriental, Philippines
I'm hoping that folk with more shop experience than I have can help me. I am faced with actually building a ducted fan from the ground up, rather than simply designing one for others or analyzing the characteristics of an existing unit.
Although I have very little trust in reinforcement and resin suppliers here in the Philippines, I think I am probably stuck with composites, due to the complex shapes involved and the fact that I am building a small number of units.
Has anybody had experience building molds for the composite structure of a duct? My sketches are starting to look like the work of Maurice Escher.
 

Malish

Well-Known Member
Joined
Oct 11, 2013
Messages
829
Location
Russia. City of Volgograd
I'm hoping that folk with more shop experience than I have can help me. I am faced with actually building a ducted fan from the ground up, rather than simply designing one for others or analyzing the characteristics of an existing unit.
Although I have very little trust in reinforcement and resin suppliers here in the Philippines, I think I am probably stuck with composites, due to the complex shapes involved and the fact that I am building a small number of units.
Has anybody had experience building molds for the composite structure of a duct? My sketches are starting to look like the work of Maurice Escher.

I don't know what kind ducted fan aircraft you're building and what shape of the duct it's will have. Can you show your sketches of the duct?
In our aircraft ducts have shape like this:
Ducted fan design 024 (Large).jpg
And they have inner and outer skin. The outer skin is part of fuselage structure and to make the panels for it we used female molds, same kind you would use for fuselage or wing panel skin. But because inner duct skin must have smooth surface inside, we made male molds for it.
Our inside airduct looks like this:
DSC07684 (Large).jpg DSC07679 (Large).jpg P1310042 (Large).jpg
 

piolenc

Active Member
Joined
Feb 17, 2013
Messages
28
Location
Negros Oriental, Philippines
I don't know what kind ducted fan aircraft you're building and what shape of the duct it's will have. Can you show your sketches of the duct?
In our aircraft ducts have shape like this:
View attachment 130075
And they have inner and outer skin. The outer skin is part of fuselage structure and to make the panels for it we used female molds, same kind you would use for fuselage or wing panel skin. But because inner duct skin must have smooth surface inside, we made male molds for it.
Our inside airduct looks like this:
View attachment 130076 View attachment 130077 View attachment 130078
My project is much less complicated than yours. It is a propulsion unit for a hovercraft, a shroud with a chord that is shorter than its diameter. The means of holding it in accurate relation to the rotor is an NPL straightener, most likely with three vanes, as mentioned in my book and several others. So I need a rigid structure where the duct attaches to the straightener vanes and at the rotor station, but it can have slightly less demanding tolerances upstream and downstream. I've been fiddling around with a rigid ring for the straightener vane attachment, to which a composite nose section and tail section are attached.
 

Malish

Well-Known Member
Joined
Oct 11, 2013
Messages
829
Location
Russia. City of Volgograd
My project is much less complicated than yours. It is a propulsion unit for a hovercraft, a shroud with a chord that is shorter than its diameter. The means of holding it in accurate relation to the rotor is an NPL straightener, most likely with three vanes, as mentioned in my book and several others. So I need a rigid structure where the duct attaches to the straightener vanes and at the rotor station, but it can have slightly less demanding tolerances upstream and downstream. I've been fiddling around with a rigid ring for the straightener vane attachment, to which a composite nose section and tail section are attached.

Our ducted fan assembly have two main units(not counting fan):
1. Stator assembled from separate parts:
a) Contaminating ring(fan shroud)
b) Fan bearing assembly mounting housing
c) 7 structural vanes
2. Airflow straightener assembled from separate parts:
a) Tail pipe
b) Tail cone
c) 11 vanes

P8300659 (Large).jpg P9050038 (Large).jpg DSC07656 (Large).jpg
 
  • Like
Reactions: BJC

raytol

Well-Known Member
Supporting Member
Joined
Dec 17, 2021
Messages
206
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.
 

dog

Well-Known Member
Joined
Dec 29, 2019
Messages
740
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.
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
 

Malish

Well-Known Member
Joined
Oct 11, 2013
Messages
829
Location
Russia. City of Volgograd
So I need a rigid structure where the duct attaches to the straightener vanes and at the rotor station, but it can have slightly less demanding tolerances upstream and downstream. I've been fiddling around with a rigid ring for the straightener vane attachment, to which a composite nose section and tail section are attached.
What type of foam should I use?

Some info here may help.
Story 035 (Large).jpg Story 036 (Large).jpg Story 037 (Large).jpg Story 038 (Large).jpg
 

Malish

Well-Known Member
Joined
Oct 11, 2013
Messages
829
Location
Russia. City of Volgograd
Our molds to form the stator and airflow straightener units somewhat complicated and consist many different parts. Also it's very complicated to use them(forming in them) to get right result. For production we're looking to use 3D printer to form those units instead of using the molds.

P1140573 (Large).jpg P4120638 (Large).jpg P3250835 (Large).jpg P4170529 (Large).jpg
 

Malish

Well-Known Member
Joined
Oct 11, 2013
Messages
829
Location
Russia. City of Volgograd
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 don't know about nylon fan blades strength, but ducted fan blades should be made from metal(which is very expensive) or from carbon fiber, considering condition they're working at. Even with all this strength of metal or carbon fiber can provide, the ducted fan blades working under such load from centrifugal force, so they will act as gun shell if they fail, that is why fan should be placed inside of contamination ring(part of fan shroud).
 

Malish

Well-Known Member
Joined
Oct 11, 2013
Messages
829
Location
Russia. City of Volgograd
So I need a rigid structure where the duct attaches to the straightener vanes and at the rotor station, but it can have slightly less demanding tolerances upstream and downstream.

We have same design in our ducted fan layout, but with long tail and intake air ducts. Main structural unit is contaminating ring and stator(this one is also mount for the fan unit) and those two parts makes very rigid structure. Tail duct with airflow straightener and intake duct don't need to be so rigid.

P4170529 (Large).jpg DSC07653 (Large).jpg P4170528 (Large).jpg
 
Top