# Ducted fan aircraft

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#### rv6ejguy

##### Well-Known Member
The Hines aircraft is complete nonsense. 300 knots carrying 6 people on 300 some hp using ducted fans- not going to happen.

Where do all these people using 300-350 hp V8s pull their fuel flow numbers from? 300hp, BSFC .40 (really generous)= 120 lbs./hr.= 20 gal./hr. yet they say 10. How?

The fastest Reno Sport class racers (tiny 2 place, highly refined aircraft) take at least 350hp to do these speeds at these altitudes. These guys are going to do it on less hp with way more flat plate area AND with ducted fans which are nowhere near as efficient as propellers.

2000fpm climb on this hp, this weight with this cruise speed using fixed pitch fans- again, not going to happen.

I'd be interested in seeing their drive system for the fans too.

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#### Apollo

##### Well-Known Member
...Where do all these people using 300-350 hp V8s pull their fuel flow numbers from? 300hp, BSFC .40 (really generous)= 120 lbs./hr.= 20 gal./hr. yet they say 10. How?
It's the same magic that drives their fuel cost assumptions - take a look at footnote #3:

3. Automotive fuel is assumed to cost $2.00 per gallon and aviation fuel is assumed at$2.80 per gallon.

Guess their website hasn't been updated for many years, or it slipped through. The propulsion system is an interesting concept though. Aside from their overly optimistic predictions, it would be interesting to discuss the technical merits.

#### topspeed100

##### Banned
Any news about the efficiency of this vehicle ?

#### rv6ejguy

##### Well-Known Member
Any news about the efficiency of this vehicle ?
Just a training/ proof of concept aircraft with likely short endurance and it has not flown yet to my knowledge but at least it is built and looks well thought out. The electric taxi feature is now being tested on airliners to save fuel also. Would be interesting to see how it works in flight.

#### Vipor_GG

##### Well-Known Member
I won't argue that but I think my odds aren't too bad flying low over water
As a former water skier I can tell you that water is very hard when you hit it with any speed.

#### henryk

##### Well-Known Member
Just a training/ proof of concept aircraft with likely short endurance and it has not flown yet to my knowledge but at least it is built and looks well thought out. The electric taxi feature is now being tested on airliners to save fuel also. Would be interesting to see how it works in flight.
Opublikowano 24 cze 2013
EADS Innovation Works video of the e-Fan electric aircraft built with France's Aero Composites Saintonge. E-Fan has batteries in the wing providing 50kW of power to two electric ducted fans and a motor driving the mainwheel, which is used for taxiing and to help acceleration on takeoff

#### yellow_submarin

##### Well-Known Member
Given the diameter of these fans, the efficiency is likely to be pretty close to 0 ...

#### henryk

##### Well-Known Member
Given the diameter of these fans, the efficiency is likely to be pretty close to 0 ...
-from russian experiment\diameter 0.6m\=380 kG thrust from 300 HP motor...

#### yellow_submarin

##### Well-Known Member
And that's clearly not as good as a 1.8m propeller. Plus you can get additional thrust by working the shroud to act as an airfoil, but I don't think this is what has been done here. I don't really get the aim to go for electric and meanwhile ruin the propulsive efficiency. I considered going for twin shrouded propellers on my design, and that's fine, provided you keep the diameter large enough. I expect they have run through calculations to conclude that this is the best option. I would find it legit if the aircraft aimed at fast cruise speeds, but it does not actually look like it ?!

#### rv6ejguy

##### Well-Known Member
-from russian experiment\diameter 0.6m\=380 kG thrust from 300 HP motor...
So about 50% less than a propeller...

#### henryk

##### Well-Known Member
but=

Pegasus MkIII Specifications
Powerplant 200 Hp fuel injected: Lycoming IO-360
Recommended Time between overhaul (TBO): 2000 hours
Electrical System: 12 volt
Propeller: 6 ft. ducted constant speed Hartzell HCE2YK
Static thrust: 1320 Lbs

=circa 600 kG from 200 HP!

#### rv6ejguy

##### Well-Known Member
Seems hard to believe this figure when most 200hp engines driving propellers are below 1000 lbs.

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#### henryk

##### Well-Known Member
Seems hard to believe this figure when most 200hp engines driving propellers are below 1000 lbs.
=proper duct=circa +40% thrust!

#### Aircar

##### Banned
The Mississippi state uni Marvel had the best integrated ducted propeller in my view --the drag of the duct was written off against the tail surfaces as well and was also of fairly large diameter and not sucking the fuselage back . Even so I believe that this approach was not pursued further (tried by Bede on the BD 2 also and the formula one racer Pushy Galore/ Miller racer ) Hovey's book on ducted fans and a more recent one that I don't have are the best references .

#### rv6ejguy

##### Well-Known Member
Static thrust is not very meaningful as far as aircraft performance goes. While ducted fans are cool, to my knowledge, no aircraft using them has exceeded the performance of propeller driven designs using the same engine. If anyone has some actual examples showing otherwise, I'd be interested to see the information. Most good propeller setups generate around 4 lbs. of thrust per hp, I find it very hard to believe that simply putting a duct around a prop or especially a small diameter fan could approach 6. If the tip losses on a prop were that high, we wouldn't have props with over 80% efficiency these days. Pitch has a lot to do with static thrust numbers for a given diameter so these figures might not be very comparable. Lower pitch might give more static thrust but less in-flight performance, especially cruise speed. The duct also creates drag and a central duct with the adjacent fuselage structure or long duct length, plus blocking flow from the engine profile, even more drag not to mention inlet and exit airflow disturbances. It would seem that twin ducts with the engine enclosed within the fuselage would allow higher duct efficiencies at the expense of more duct drag.

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#### yellow_submarin

##### Well-Known Member
That's because there is confusion here between duct and shroud. A duct is basically a tube helping reducing propeller tip loss. The gain exists but is marginal. But a duct is generally to be considered as length equal to diameter. When shorter, it's called a shroud. Shrouds should work in a different manner, using an airfoil (NACA 4412 with an elliptical LE seems to work quite good) with the lift side INSIDE the duct to produce a lifting force with an axial component increasing thrust. In this case, there is propeller thrust, and duct thrust. The duct thrust can be as high as 100% of the propeller thrust and even higher. But it reduces with the forward speed. A way to increase the duct thrust is to use a modified propeller with large tip twist accelerating even more the airflow on the lift side of the airfoil. Such propeller shrouds are useful for aircrafts not exceeding 200 km/h. Now what I don't get here is the reason that brought them to reduce propeller diameter. Unless they want to reach speeds as high as 500 km/h, I can't see no reason to justify the efficiency loss.

##### Moderator
A bigger prop should theoretically always be more efficient than a duct of the same diameter. If you're not limited by a low prop rpm, by regulations (blade containment), noise, reducing damage potential or desired looks, I don't see the point of using a duct?

#### djschwartz

##### Well-Known Member
+1 on what Aude says. The ducted (or shrouded, who cares!) fan attempts at a Formula One racer went significantly faster when the duct (or shroud) was simply removed.

#### yellow_submarin

##### Well-Known Member
Yes a propeller will probably have a better efficiency without a duct which represents a lot of drag.

But concerning the shroud, it DOES make a difference. Provided a shroud is always considered to be airfoil-shaped to provide its own thrust. Obvisouly it only works for speeds at which the duct thrust is superior to its drag. A Formula One, for instance, is too fast to see the benefits of a shroud. Remember that the the duct thrust is maximal at nil speed and decreases as advance ratio increases (speed).

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