# Ducted Fan Pseudo-Jets

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#### sanman

##### Well-Known Member
=expected/estimated Specific Thrust ? [kG/kW]

BTW= CR Fan (Stator less !)...

=references...(many !)

Wow, that looked cool -- but it was electric ducted fan, right? What diameter are those fans?
Can counter-rotating ducted fan be done with mechanical transmission? Or will it be too heavy?

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#### sanman

##### Well-Known Member
I came across this software for modeling things like ducted fans & turbines - anybody heard of this?

#### henryk

##### Well-Known Member
Can counter-rotating ducted fan be done with mechanical transmission? Or will it be too heavy?
CR Differential mechanical Reductor (circa 3: +/- 1) ,for 100 HP drive is only 3 kg , 0.1 m diametr...

electric variant see= CRFLY.

+ EJECTOR (low speed buster)

#### Malish

##### Well-Known Member
How do you mean more shallow? You just mean shorter ducts? How does that keep intakes farther away from fan?

Duct turning radius should be larger and angle of turn should be as less as possible. On UL-39 ALBI they should placed the fan farther back from side air intakes, that will make air ducts with less degrees of turn(more shallow).
As now, there very sharp two almost 90 degrees turns in very short distance - this creates airflow separation and air turbulence in front of the fan and this causing loss of DF effectiveness!

#### Malish

##### Well-Known Member
And note also the flow straighteners behind the strongly twisted fans. This is almost as important.

You're right - airflow straightening stator behind the fan will increase thrust of DF for more then 10%

##### Well-Known Member
Would the high static thrust potential of a DF help with an amphibian aircraft?

I'm thinking of something with high-ish inlets without the high CoG & thrust line.

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#### Malish

##### Well-Known Member
+cooling in duct system dont help...?

Radiator cooling intake should be placed outside of duct(under fuselage) and exhaust could be made into the duct and fan should be located behind of radiator
Right now radiator cooling duct is taking some space of fan duct - and this is not good...

#### Malish

##### Well-Known Member
Would the high static thrust potential of a DF help with an amphibian aircraft?

May be...

#### copec

##### Well-Known Member
Radiator cooling intake should be placed outside of duct(under fuselage) and exhaust could be made into the duct and fan should be located behind of radiator
Right now radiator cooling duct is taking some space of fan duct - and this is not good...
View attachment 120034

I believe their intent was to augment thrust by adding the engine heat while keeping the outside of the plane looking the same without additional intakes. It was definitely a much bigger compromise to keep the fan that far forward.

#### nestofdragons

##### Well-Known Member
Supporting Member
Hey, i see a lot of possible troubles when trying to design intakes for ducted fans, so ... why not use the idea of Burt Rutan? A asymmetrical installed engine. He did it on the Ares and it works fine. Intake-duct is a perfect line.

#### nestofdragons

##### Well-Known Member
Supporting Member
I am just thinking out loud now. Would a ducted fan need to be small if he was installed angled?

At first, after looking at the Ares, i thought yes, but then i started drafting. In this draft you see the fuselage no longer in center and a huge duct beside it. If all is placed so CG is still central if will be less of a difficulty than a fully asymmetrical airplane like the BV141.

At first i was thinking "how do i make a nice connection between prop and engine", but ... if you simply place the engine at the same angle, that problem is gone. Placing engines at angle is not a problem at all.

Just for fun i placed a asymmetrical tail.

#### Malish

##### Well-Known Member
A asymmetrical installed engine. He did it on the Ares and it works fine. Intake-duct is a perfect line.

Looking at 3 view drawing of this aircraft I don't see asymmetrically installed engine.
For me, engine is perfectly in line with centerline of fuselage - only air duct intake on left side of it. Two vertical tails can easy hold this small aerodynamic disbalance caused by single side air intake
Also on the right side of fuselage look like large gun(similar as on A-10 aircraft) is located - that is why engine air intake is located only on left side - gun smog(when it's fire) wouldn't get to the engine and stall it!

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#### cluttonfred

##### Well-Known Member
Supporting Member
IIRC, the reasons for the asymmetric intake on the Ares were 1) accommodating an engine, pilot, and a big gun in a very small airframe and 2) ensuring that the gun gasses wouldn't get sucked into the engine and cause it to stall. That's even clearer in the unbuilt two-seat variant envisioned by Scaled Composites. Note that the engine itself is installed at an angle and slightly off-center, but the actual jet-pipe directing the flow does appear to be straight and centered.

#### nestofdragons

##### Well-Known Member
Supporting Member
IIRC, the reasons for the asymmetric intake on the Ares were 1) accommodating an engine, pilot, and a big gun in a very small airframe and 2) ensuring that the gun gasses wouldn't get sucked into the engine and cause it to stall. That's even clearer in the unbuilt two-seat variant envisioned by Scaled Composites. Note that the engine itself is installed at an angle and slightly off-center, but the actual jet-pipe directing the flow does appear to be straight and centered.

View attachment 120084
i do think that the small angle of the exhaust is less a problem than the sharp angles which we saw in the intakes of the other designs. I would go for this kind of ducted fan proposal. Problem might be to get CG in center. Ares has the gun as counterweight for the engine. But ...it might have a very easy solution to get it done for a small jet looking homebuilt.

#### cluttonfred

##### Well-Known Member
Supporting Member
i do think that the small angle of the exhaust is less a problem than the sharp angles which we saw in the intakes of the other designs. I would go for this kind of ducted fan proposal. Problem might be to get CG in center. Ares has the gun as counterweight for the engine. But ...it might have a very easy solution to get it done for a small jet looking homebuilt.

Yes, there would be very slight losses due to the duct but nothing major. I have always liked the Ares configuration, with or without the asymmetric elements. With wider spacing of the booms it would also make a very elegant pusher prop design, probably needing to move the center section trailing edge forward for prop clearance without an extension shaft but then you could sweep the outer panels back to compensate if needed.

#### Woodenwings

##### Well-Known Member
RFB fan trainer. And some good reading

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#### Malish

##### Well-Known Member

Yes, this two very good books to read - I learned a lot from them about DF theory and design

#### J.L. Frusha

##### Well-Known Member
Supporting Member
@Malish

I used to have several of Bob Hovey's books, especially those on structure and aerodynamics that involved the Whing Ding II. At one point I had his phone number, but his wife said he was no longer interested in aircraft and was totally focused on breeding roses. Wish I'd been able to talk to him myself.

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I just came across an RC Ducted Fan of the Martin X-24A Lifting Body... Aerofred has it as the "Mystery Wing" It was designed by the same people that designed the X-24A Lifting Body.

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