Following the thread about the F-14, I found a picture from the Gronau 2000 meeting with a DH-108 using a tandem fan setup.
What’s the benefit of using a tandem unit configuration? How does it really work?
Do you use two motors and two fans? Or is should two fans be connected to one big motor?




I would be happy if someone could explain this.

/Kim

Hi rcaviator,
the fan unit shown is the TF480 made by me. This one was modified by Dirk Woters to take the more powerful HP200s.

(For the danger of being blamed to post ads here, I will not post more details here, if you're interested, please mail me privately.
I don't want to stress the Admins more than I already do...at other place and I'm thankful that they let me )

The main advantage of a TwinFan is that you get the same power output at smaller diameter. That's what the TF was developed for (by Heino Dittmar, btw.) to be able to build scale intakes.

And as you get the same power output at smaller diameter the efflux velocity is greater...also intended, we want a jet to perform as such and achieve greater speeds. (But this yields the model, it has to be aerodynamically clean and able to achieve such speeds, Dirk Wouters' DH Swallow was (is) excellent in this respect)
The next advantage is that the engine "keeps pushing" still at higher speed, due to the higher efflux and the ability to "swallow" ram air pressure...

There are disadvantages, too, of course. The main is that it is more effort to build it (compared to a mass produced injection-moulded unit)
and that you need two motors (so your next question is already answered) but: of the cheaper type...

So in all the costs might be slightly higher and also the weight...but this is paid for by the forementioned advantages.

Another disadvantage: It is not so flexible in terms of power input, i.e. the motors and cell combination used, you cannot stick brushless 250W motors into it without modifying it...and as mentioned before Dirk did just that and built the TF2000 prototype which will, unfortunately, never show up as a kit, at least not by me...

I already talked about the working principle, but a little more:
2 fans, 2 motors, wired parallel, turning in OPPOSITE directions and sitting face to face to each other. But this means that the fans are NOT the same, and as mostly suspected the rear fan has NOT a coarser pitch.

So, I hope most questions are answered,
cheers, Ralf