Ducted Fans

Hang on – did you really mean a Swift flying?! 😮

Sorry, I meant Sea Hawk!

CFM Glint

I have a particular interest in ducted fans, as I was asked once to develop a design proposal, to replace a three bladed pusher propellor driven by a Rotax engine with a ducted fan.

The aircraft was to be called the CFM Glint. I will post a drawing of it here soon. It was a flying wing, designed and developed by a friend called David Cook, of CFM Shadow Ultralight fame. Only one was made, but it never got to the stage where the fan was installed. I believe that the aircraft still exists, but was never flown.

Thanks for digging up the Channel wing – glad to see PL hit a similar tracking it down problem!

As for the Italian CC-1, it was generally held to be a dead end at the time, once tried. I don’t think anyone would have found further development worthwhile as dcollins has said. Incidentally there’s a scale model of the previous concept in the Zuccoli collection in Queensland. (See pics)

In most ‘innovations’ theres a ‘hump’ of low credibility, high cost, low return to overcome before it becomes viable, and it’s possible to argue that mankind has a weakness to develop the familiar and safe to death, rather than accept and develop something innovative and unfamiliar – hence my personal hate of ‘if it looks right, it flies right’ post-hoc justification…

Back on topic, the Custler did offer some innovation, being something like a ‘blown’ wing – so development there would might have been interesting…

Cheers

“RobAnt: The CC2(N1) looks very interesting – given it’s date, you can’t help but wonder what would have been achieved by further development as technology improved.”

This was a dead-end technology unfortunately, quickly surpassed by the jet engine. A ducted fan offered no advantages over free propellor driven aircraft. It had less acceleration, much higher fuel consumption, less range, and poorer acceleration. The gas turbine was the holy grail technology.

. . . as it says on the web site to which my link is pointing!

A ‘Custer Channel Wing’ is on display at the MAAM (Mid-Atlantic Air Museum) in Pensylvania.

Got it! Custer Channel Wing, see here:

http://www.aerospaceweb.org/question/aerodynamics/q0022b.shtml

JDK – it was the Channel Wing, and I am looking for it in my archives . . .
They are arranged by manufacturer, so my filing system is stumped!

The CC2(N1) looks very interesting – given it’s date, you can’t help but wonder what would have been achieved by further development as technology improved.

Ummm.

I remember a twin engined aircraft, American 1950s IIRC, that had a wing with a half duct (like a wing with a ‘U’ half-way along it) with the prop running in it – a sort of semi-ducted fan. Anyone know the history / story?

Hang on – did you really mean a Swift flying?! 😮

The main disadvantage of DF over props in models is the accelearation, you have to be very careful about your energy management during manoeuvres, to ensure that you carry your speed through.

The commentator at Elvington last year made a similar comment about the (full size) Supermarine Swift that was displaying, so I assume that the early jets had a similar issue compared to the props they were used to

My knowledge of ducted fans is limited to models and only then from reading about and seeing them. Gas turbines are beginning to take over but there are still a few die-hard enthusiasts out there.
It may be because of the scale effect mentioned above but they run at extremely high revs, up to 30,000 last I heard, and have very poor acceleration. Once they’re off the ground and up to flying speed it’s only the scream of a piston engine that spoils the effect.

I suppose it’s also possible that as they are generally used to get rid of the prop on a scale jet model, it’s probably not the optimum way to use one.

Italian Ducted Fan

The ultimate development of the ducted fan was the Caproni Campini CC2 (N-1).

See this website:

http://www.airbornegrafix.com/HistoricAircraft/ThingsWings/CC2.htm

Ducted fans compared to free props.

Hi RobAnt

Pay attention, here’s the science bit… 😉

If any one comes up with some model aircraft comparisons, I will be intersted. Because of Reynolds number, air density, skin friction, etc, aerodynamics does not scale as you might expect between very small models, and full scale applications, so for a full scale application:

Advantages of a ducted fan over a free prop.

Better ground handling safety. Quieter, fan blade tips can run with reduced losses in theory because the duct can hug the fan with minimal gap.

Advantages of a free prop over a ducted fan.

A free prop will draw in a larger volume of air, for the same disc diameter, and will therefor produce greater thrust. It is a lighter assembly. It will produce less drag. It will have better fuel consumption correspondingly. A free prop has more static thrust, which is better for take-off, and general acceleration.

Also, for a ducted fan to produce the same thrust as a free prop it has to turn faster, hence worse fuel consumption.

Ahh yes, the “Slipstream” movie plane.

What I’m really trying to get at is whether there is any kind of performance advantaged offered, or disadvantage caused, by ducting a piston aero engine.

Yes it has been done, the Edgley Optica was powered by a ducted fan, as was an experimental version of the Islander (reistration G-FANS?). Doubtless there have been others.

Steve.