# Experimental Ducted Fan Aircraft Designs

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#### nicknack

##### Active Member
As for the UL39, our concept was quite similar, but we wanted it to look a bit more like the F-35 . Both for me and my aerodynamics guy it doesn't make much sense to copy something and use it in a completely different aerodynamic regime.

Just think, speed, Reynolds, weight, etc. all being completely different, so why not start with a clean sheet? In addition: the L-39 is said to be a good trainer, but my aerodynamic guy and test pilot has many hours in military fighter jets and he said that most military jets fly marginal at best. I myself had the pleasure of a few hours in a F-16 and Eurofighter full motion sim. I would describe them too as "behaving good", the same way as any editor of a magazine would too.

Still, the flight behavior of a jet is nothing that I would sell with good conscience to any recreational pilot:
• super high pattern speeds
• low drag combined with high residual thrust (>20% at idle)*
• large turbo-lag (5s!!! for the PBS, up to 20s for the real big birds)
• small margins (like max. gear speed minimally above stall speed)
*makes it absolutely impossible to slow down to landing speeds without usage of spoilers

This is why the Beast One is designed to counter this as good as possible. For the 2-seat version, we considered the PBS +fan solution even before the UL39 guys, but we went away from it. First, the TP-100 is in a price range beyond of 100k (I forgot if 110 or 150) but uncertified and with a rather low life, as the TJ-100. Second, we asked Daniel Schuebeler if they could supply a fan of this size, as we know about the efficiency of their fan systems. He declined and said, that they won't dare touch anything above 25kW as for back then (hard to handle the rotational loads, even for carbon). Third, we had some concerns about the vibrations of the shaft and fan, as you have to cover 240kW over a wide variety of rpm's.

So in short, we considered it too expensive and too risky as for us to continue... Also, too expensive for any homebuilder and most guys with the sufficient money like to go to the next step for a "real jet".

#### nicknack

##### Active Member
You are right, used jets don't cost that much and owning it is the expensive part. Our Eurofighters in Austria for instance, have 70k running costs per hour (not including buying them!), while a Cessna Mustang is more in the 7k range, already including the leasing if flown enough hours.

The ultralight ducted fans have the big advantage of fuel consumption in the area of 5-10 gallons per hour and low maintenance costs of piston engines.

The Beast One (yes the one in the avatar ) has running costs comparable to a four-seater, as we intend it for the occasional flyer who doesn't want to buy a nightmare to come (when you loose 250k after an unintentional hot-start). Or just try to find a cheap mechanic to service your jet turbine, aren't many around. Main factors of Beast costs are the engine (rebuild sums up to ~150\$/h) and fuel consumption of ~15 gal per hour.
Those numbers sound sweet. Did you ever try to find out if pratt&whitney will sell you the PW610f, it’s got 900lb thrust and is a turbofan, very decent TSFC too compared to turbojets. Wonder what costs is like and overhaul cost. I heard those pw610f have TBO of 4000+hrs with IRAN in between.
Say, I tried some numbers:
1) 1000N thrust or 250lbs
2) 380kg or 840lb
3) time to 60kts or 30.7m/s = 11.66s
4) distance to rotate = 178m or 560ft
So for 50ft clearance 1500ft runway is enough?

#### Scheny

##### Well-Known Member
We didn't want to proceed with anything bigger than the DGEN, as there is already the Viperjet and honestly, this one I don't think we could beat no matter how much help I would get.

As for your numbers: with rotate at 65kt, actual liftoff would be rather at 85kt. Distance is then at best 280m (protection turned off, standing start) and my feeling would say that ~2000 feet will be sufficient.

#### nicknack

##### Active Member
We didn't want to proceed with anything bigger than the DGEN, as there is already the Viperjet and honestly, this one I don't think we could beat no matter how much help I would get.

As for your numbers: with rotate at 65kt, actual liftoff would be rather at 85kt. Distance is then at best 280m (protection turned off, standing start) and my feeling would say that ~2000 feet will be sufficient.
I concour with your numbers give or take depending on wing loading. But that's also kind of a narrow range between 16lb/sqft to 19lbs/sqft if we want to have something that can have a good fast cruise of well over 200kts. Can't have Va or Vno too low.
I think there's a market for a jet that's got 500nm/600nm range and can be extended to 900nm. Anything less than that it becomes just a pure weekend toy, in which case range doesn't even matter.
My reasoning is at 500nm, just barely enough for a 250kts+ aircraft to make a difference and enough time of flight to get to the FL100 to FL180.

The viper jet is a bit too far geared to the pure fighter/military trainer style. I am thinking more inline with something significantly faster than a SF260 or PC7 and no scrambling around for difficult to maintain engines or difficult to source parts and mechaics for ex-surplus military power units

Another example is even with funds, can't always guarantee that an ex military plane/equipment will always be properly maintained in civilian. Not all the know how is passed on, why else then is this knowledge of strategic national importance. One multi-milionaire/bilionaire who used to fly his own L-39 in US lost his life not for the lack of funds to maintain the plane but rather his "expert" maintainence shop wasn't aware that residual cleaner fluid can embrittle a hidden part of the canopy causing it to destruct structurally at high speed. Here's an indivdual whose business is aviation, lives and breathes flying and yet came to a tragic end flying his personal L39 commuter.

So I am all for a simple uncomplicated, jet/jet fan/turbo-shaft/ducted fab with 300 to 700lb thrust with known maintenance risk for the educated/discerning individual. and easy enough, short range two seat to get transition jet training.

#### Scheny

##### Well-Known Member
100% right, nothing that I could add

#### Bille Floyd

##### Well-Known Member
I think the technology for a viable DF, for ultralight use ; it
may be getting closer ---- one day
Here is a 395mm EDF that puts out 58kg thrust. The amp draw
is kinda high ; and it takes a 45kw motor to make it work. 60Hp
to make 58kg of thrust ; well that isn't really efficient, but
maybe one day ?

from : Electric propulsion systems | Milan | EDFs

Internal cylinder diameter: 395 mm

Fan swept area: 1076.7 cm²

Weight with inlet lip and mounting brackets: 3,200 g,

Max. Thrust range: 750N

Max. Discharge speed range: 80m / s

Max. RPM range: 10,000 rpm

Max. Input power: 45kw

Allowed battery: 18S - 28S 30.000 + mAh

Permitted controller (ESC): 30kw - 45kw

Overall efficiency: 88%

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#### Malish

##### Well-Known Member
I think the technology for a viable DF, for ultralight use ; it
may be getting closer ---- one day
Here is a 395mm EDF that puts out 58kg thrust. The amp draw
is kinda high ; and it takes a 45kw motor to make it work. 60Hp
to make 58kg of thrust ; well that isn't really efficient, but
maybe one day ?
270 amp? It's a welding machine!

#### henryk

##### Well-Known Member
Allowed battery: 18S - 28S 30.000 + mAh
28 S=circa 100 V...
100 V * 30 Ah= 3 kW h ...
3 kWh *5 kg/kWh= 15 kg...

45 kW (max power)... 3 kWh/45 kW=0,07 h= 4,2 min !

45 kW/100 V=450 A !!!

"Weight with inlet lip and mounting brackets: 3,200 g, " +motor weight !?

#### Bille Floyd

##### Well-Known Member
...

45 kW (max power)... 3 kWh/45 kW=0,07 h= 4,2 min !
...
4.2 minutes is about right, for RC guys ; my F-35 with a 70mm
fan, can eat up a 14.8v, 3,200mah battery, in about 5 minutes.
It's a Really FUN, 5-min though !!

Efficiency is Not there , (Yet) ; but there are a Lot of people
that are working on a better solution ------- so maybe some-day ?

Bille

#### henryk

##### Well-Known Member
a better solution ------- so maybe some-day ?
=Oscillating Wing Propulsion =ZERO or MINUS(thrust!) drag anihilation?

#### pictsidhe

##### Banned
4.2 minutes is about right, for RC guys ; my F-35 with a 70mm
fan, can eat up a 14.8v, 3,200mah battery, in about 5 minutes.
It's a Really FUN, 5-min though !!

Efficiency is Not there , (Yet) ; but there are a Lot of people
that are working on a better solution ------- so maybe some-day ?

Bille
Ye cannae break the laws of physics, Jim.

#### WonderousMountain

##### Well-Known Member
The fans look good, but I agree these do not seem correct figures. The first pragmatic E-flyers will have a yuge lode of batteries. Also they will cost wads of cash.

#### henryk

##### Well-Known Member
"Ye cannae break the laws of physics, "

=no need in break,
we should finde the new laws of physic (NATURE)...

f.e=dr Sorokodum

#### Bille Floyd

##### Well-Known Member
Ye cannae break the laws of physics, Jim.
I mentioned something about were not there Yet ; but a lot
of people are working on it.
Look at the efficiency gain, when ya do counter rotating props ; I
haven't seen a DF , (model or full scale) that tried that yet. It
sure works for compressors used in turbo fan engines .

That is just , (1) example ; and i'm saying the laws of
physics for DF, haven't even begun , to be explored for, what "could"
be done, to improve efficiency .

Bille

#### pictsidhe

##### Banned
Yes, they have been fairly well explored. Ducted fans in both model and full scale have been made at over 75% efficient. There is not much gain that is possible without breaking the laws of physics... DFs almost always use stators, so little gain to be had from counter rotating. Make a DF to move more air, you increase the duct area and drag, negating the benefit of a bigger fan.
That said, it is very, very easy to make a DF that sucks, so there are a lot of mediocre ones out there. They can be improved upon.

#### henryk

##### Well-Known Member

=
to be explored for
-theory...

+some practice...

#### henryk

##### Well-Known Member

=CR Duct + EJECTOR DUCT !

+experiment.

=+++ !

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#### Fireflyer228

##### Member
I mentioned something about were not there Yet ; but a lot
of people are working on it.
Look at the efficiency gain, when ya do counter rotating props ; I
haven't seen a DF , (model or full scale) that tried that yet. It
sure works for compressors used in turbo fan engines .

That is just , (1) example ; and i'm saying the laws of
physics for DF, haven't even begun , to be explored for, what "could"
be done, to improve efficiency .

Bille
Not DF but electric aircraft with counter rotating props. This was a few years ago, so I wonder where this project is now. High power sport racer is how they describe it.