Electric Duct Fan (EDF) Self-Launch Glider?

[CLewis95]

Electric Duct Fan (EDF) Self-Launch Glider?

I have pondered this for some time now. Electric Duct Fan (EDF)
propulsion systems have been making strides in the RC model jet world
and are challenging the use of mini turbine jet engines (now used on a
number of full scale SL sailplanes) Battery technology regarding
power density and safety continues to improve at a rapid pace. (auto
engineer recently stated that within 5 years batteries will approach
the power density of gasoline ... hard to believe but ?? ) EDF
systems do not have the tremendously high exhaust temperature (~700°C)
and decibel level issues. (Though not as loud, the EDF systems sound
very similar)

Assuming:
- L/D 40:1 850 pound Sailplane (in my case Genesis 2)
- Cluster of (3) currently available EDF Units producing combined ~60
pounds STATIC THRUST (AFTER taking into account loss of efficiency do
to close clustering of intake ducts)
- Battery capacity for ~10 minutes full power .. no reserve
- 2,500ft Paved Runway .. No Tailwind :)
- Sailplane pre-positioned on runway (not taxied to runway)
- Goal altitude of ~1,500ft AGL

As a "sustainer" I am fairly confident this would yield some
success .. if only buying you ~10 miles :) What I would like to hear
from the hobby-physicists out there are comments on these questions:

1 - How detrimental is the loss of efficiency/performance when
clustering duct fan intakes in very close proximity?
2 - With sailplane starting from rest, how long would it take to
accelerate to flying speed? i.e. Would I need 3 miles of paved runway?
and/or .. Would the batteries be dead before the glider left the
ground? :)

I certainly am not proposing a "replacement" for jet turbines .. only
curious if the above scenario is at all feasible.

Thanks for comments!

Curt Lewis - 95
Genesis 2
Loves Park, IL USA

[CLewis95]

> Assuming:
> - L/D 40:1 850 pound Sailplane (in my case Genesis 2)
> - Cluster of (3) currently available EDF Units producing combined ~60
> pounds STATIC THRUST (AFTER taking into account loss of efficiency do
> to close clustering of intake ducts)
> - Battery capacity for ~10 minutes full power .. no reserve
> - 2,500ft Paved Runway .. No Tailwind :)
> - Sailplane pre-positioned on runway (not taxied to runway)
> - Goal altitude of ~1,500ft AGL

I should have added: "Starting from 1,000ft MSL"
Curt -95

[bildan]

On Jan 17, 12:53*pm, CLewis95 > wrote:
> Electric Duct Fan (EDF) Self-Launch Glider?
>
> I have pondered this for some time now. *Electric Duct Fan (EDF)
> propulsion systems have been making strides in the RC model jet world
> and are challenging the use of mini turbine jet engines (now used on a
> number of full scale SL sailplanes) *Battery technology regarding
> power density and safety continues to improve at a rapid pace. (auto
> engineer recently stated that within 5 years batteries will approach
> the power density of gasoline ... hard to believe but ?? ) *EDF
> systems do not have the tremendously high exhaust temperature (~700°C)
> and decibel level issues. (Though not as loud, the EDF systems sound
> very similar)
>
> Assuming:
> - L/D 40:1 850 pound Sailplane (in my case Genesis 2)
> - Cluster of (3) currently available EDF Units producing combined ~60
> pounds STATIC THRUST (AFTER taking into account loss of efficiency do
> to close clustering of intake ducts)
> - Battery capacity for ~10 minutes full power .. no reserve
> - 2,500ft Paved Runway .. No Tailwind :)
> - Sailplane pre-positioned on runway (not taxied to runway)
> - Goal altitude of ~1,500ft AGL
>
> As a "sustainer" I am fairly confident this would yield some
> success .. if only buying you ~10 miles :) *What I would like to hear
> from the hobby-physicists out there are comments on these questions:
>
> 1 - How detrimental is the loss of efficiency/performance when
> clustering duct fan intakes in very close proximity?
> 2 - With sailplane starting from rest, how long would it take to
> accelerate to flying speed? i.e. Would I need 3 miles of paved runway?
> and/or .. Would the batteries be dead before the glider left the
> ground? :)
>
> I certainly am not proposing a "replacement" for jet turbines .. only
> curious if the above scenario is at all feasible.
>
> Thanks for comments!
>
> Curt Lewis - 95
> Genesis 2
> Loves Park, IL USA

I think a large one meter EDF would make sense for a tow plane.
Ducted fans "sweet spot" is right in the towing speed range - that's
why they're popular with the new blimps. People talk about 8 - 10 Lbs
of thrust per HP at 60 knots. If so, that would allow a 60 - 80 HP
EDF tug provide the same tow performance as a 235 Pawnee.

As I understand DF's, the bigger they are the more efficient they
are. Retracting a big DF into a SL glider would be a problem but
maybe if the duct were short, it could be rotated 90 degrees before
swinging down into the fuselage.

Why would this be better than the Antares large prop? Speed might be
an answer. The DF's cruise speed is likely to be higher than a large
slow turning prop. Speed would be useful to get to a lift area some
distance from the takeoff point.

[Martin Gregorie[_5_]]

On Mon, 17 Jan 2011 11:59:05 -0800, CLewis95 wrote:

No numbers, but:
- multiple impeller blades destroy efficiency due to interference
between the blades. Its similar to the inter-plane drag than makes
biplane less efficient than monoplanes. As a result, the fewer blades
the better, hence the superiority of the two blade propeller provided
speeds are low enough to avoid tip compressibility problems.
- a bigger diameter impeller is better because moving a given mass of
air slowly is more efficient for generating thrust than moving it much
faster as is required by the smaller impeller.

Against that, about a ducted fan can offer is reduced tip losses.

That has to make an Antares-style pop-up system that turns a large, two
blade prop a better bet than a ducted fan system.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

[CLewis95]

thx for comments so far ... another clarification to my "proposition"
here though:

I do understand why large, slow turning prop is more efficient. My
question is "How feasible would it be to use currently avaiable, off-
the-shelf EDF systems to achieve stated, limited goals?" .. the
trade off being much lower cost, simpler design, triple redundancy,
etc.

This EDF approach may never compete commercially or performance wise
with Jet Turbine or current conventional gas or electric prop
systems ... I'm just curious if adapting small EDF's could achieve the
very limited goals in my proposed scenario.

- 60lbs Thrust
- 10 minute duration (no reserve)
- Climb from 1,000' MSL to 1,500' AGL
- Using Paved Runway
- No taxi .. prepositioned on runway
- No tailwind component

While certainly not a feasible commercial solution .. it would be a
really neat experiment :)

Curt -95

[bildan]

On Jan 17, 3:20*pm, CLewis95 > wrote:
> thx for comments so far ... another clarification to my "proposition"
> here though:
>
> I do understand why large, slow turning prop is more efficient. *My
> question is "How feasible would it be to use currently avaiable, off-
> the-shelf EDF systems to achieve stated, limited goals?" *.. *the
> trade off being much lower cost, simpler design, triple redundancy,
> etc.
>
> This EDF approach may never compete commercially or performance wise
> with Jet Turbine or current conventional gas or electric prop
> systems ... I'm just curious if adapting small EDF's could achieve the
> very limited goals in my proposed scenario.
>
> - 60lbs Thrust
> - 10 minute duration (no reserve)
> - Climb from 1,000' MSL to 1,500' AGL
> - Using Paved Runway
> - No taxi .. prepositioned on runway
> - No tailwind component
>
> While certainly not a feasible commercial solution .. it would be a
> really neat experiment :)
>
> Curt -95

For a self launch - probably not. For a sustainer - maybe. Heck, you
could put 2 or 3 on a stick, poke them out a storm window and find
out.

[T8]

On Jan 17, 4:12*pm, bildan > wrote:
> *People talk about 8 - 10 Lbs
> of thrust per HP at 60 knots.

Well, y'know what they say about "talk".

Ole father physics says you get 5.43 lbf of thrust per hp (550 ft-lbf/
sec) at 60 knots if you can achieve perfect efficiency.

Reality will be substantially less than that.

-Evan Ludeman / T8

[Matt Herron Jr.]

On Jan 17, 3:08*pm, T8 > wrote:
> On Jan 17, 4:12*pm, bildan > wrote:
>
> > *People talk about 8 - 10 Lbs
> > *of thrust per HP at 60 knots.
>
> Well, y'know what they say about "talk".
>
> Ole father physics says you get 5.43 lbf of thrust per hp (550 ft-lbf/
> sec) at 60 knots if you can achieve perfect efficiency.
>
> Reality will be substantially less than that.
>
> -Evan Ludeman / T8

This may be another thread, but I like the idea of a microjet with an
electric main gear for takeoff assist. The electric main gear helps
accelerate the glider quickly and efficiently until the wheel leaves
the ground, say 40 knots. This means a jet glider needs less runway.
Also a jet is most inefficient at slower airspeeds. Of course you
could recover a little of the energy with regenerative braking during
the landing, but most likely you would just need to recharge the wheel
battery from the mains.

Anyone have the knowledge needed to size this battery and motor? Lets
say for two take-offs (one for a landout), 850 lb glider, good tire
traction up to 40 knots. Also, what kind of acceleration would be
reasonable to assume? The thrust of the jet would be added to the
wheel thrust, of course.

[Bruce Hoult]

On Jan 18, 11:20*am, CLewis95 > wrote:
> This EDF approach may never compete commercially or performance wise
> with Jet Turbine or current conventional gas or electric prop
> systems ... I'm just curious if adapting small EDF's could achieve the
> very limited goals in my proposed scenario.
>
> - 60lbs Thrust
> - 10 minute duration (no reserve)
> - Climb from 1,000' MSL to 1,500' AGL
> - Using Paved Runway
> - No taxi .. prepositioned on runway
> - No tailwind component
>
> While certainly not a feasible commercial solution .. it would be a
> really neat experiment :)

It seems to me to be far too little thrust to be useful, except as a
sustainer.

Back in 2000 I ran some calculations for various thrust levels for
glider takeoff using engines of a type where the thrust doesn't vary
with speed (i.e. rockets and, to a large extent, jets):

http://groups.google.com/group/rec.aviation.soaring/msg/37484c08689379af

At the time I was not aware of any jet or rocket-power gliders, but
there are now quite a number. I concluded that anything from 100 kg to
250 kg (220 - 550 lbf) of thrust looked very usable.

I see the "BonusJet" in fact has 240 lbf of thrust on a two seat
glider.

Bob Carlton has 225 lbf on his Super Salto. His earlier Silent had
twin 45 lbf engines for 90 lbf total. It obviously worked, but the
videos I've seen make the takeoff look pretty anaemic. I can only
imagine what it would be like with only 60 lbf!

I think these machines verify that my calculations in 2000 were in the
ballpark.

My constant thrust calculations are not as relevant to a prop or
ducted fan where the static thrust is quite a bit higher than the
thrust at 50 or 60 knots, and they're really starting to drop off
after 100 knots.

One conclusion that will still be relevant is that you use less total
energy for the launch if you have a reasonable level of thrust. WIth
low thrust you spend so much more time dragging the aircraft through
the air that you use a lot more energy in total -- my figures showed
17% more fuel needed with 50 kgf (110 lbf) of thrust compared to 100
kgf (220 lbf). WIth only 60 lbf available it would be a lot higher
again, because you'd be using a substantial proportion of the
available thrust just to fly straight and level. 120 lbf for 5
minutes or 180 lbf for 3m20 would be much more useful than 60 lbf for
10 minutes.

[Eric Greenwell[_4_]]

On 1/17/2011 11:59 AM, CLewis95 wrote:
>> Assuming:
>> - L/D 40:1 850 pound Sailplane (in my case Genesis 2)
>> - Cluster of (3) currently available EDF Units producing combined ~60
>> pounds STATIC THRUST (AFTER taking into account loss of efficiency do
>> to close clustering of intake ducts)
>> - Battery capacity for ~10 minutes full power .. no reserve
>> - 2,500ft Paved Runway .. No Tailwind :)
>> - Sailplane pre-positioned on runway (not taxied to runway)
>> - Goal altitude of ~1,500ft AGL
>
> I should have added: "Starting from 1,000ft MSL"
> Curt -95

I like the idea, but starting the quest with a sustainer, because 60 lbf
would be unsafe on a 850 lb glider. 2500 runway? You'd still be on the
ground, as it'd take ~40 seconds to get to 60 mph. One fan would just
keep you up; two fans would let you climb. You could try a single fan
most easily by mounting it externally - no retraction. You'd probably
learn a lot with little investment.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)

[Doug Greenwell]

At 21:45 17 January 2011, Martin Gregorie wrote:
>On Mon, 17 Jan 2011 11:59:05 -0800, CLewis95 wrote:
>
>No numbers, but:
>- multiple impeller blades destroy efficiency due to interference
> between the blades. Its similar to the inter-plane drag than makes
> biplane less efficient than monoplanes. As a result, the fewer blades
> the better, hence the superiority of the two blade propeller provided
> speeds are low enough to avoid tip compressibility problems.
>- a bigger diameter impeller is better because moving a given mass of
> air slowly is more efficient for generating thrust than moving it much
> faster as is required by the smaller impeller.
>
>Against that, about a ducted fan can offer is reduced tip losses.
>
>That has to make an Antares-style pop-up system that turns a large, two
>blade prop a better bet than a ducted fan system.
>
>
>--
>martin@ | Martin Gregorie
>gregorie. | Essex, UK
>org |
>

The duct does do a bit more than reduce tip losses - there's an
additional thrust component from the duct lip, which in the long run comes
from an increase in effective capture area. The airship people like them
because they are easier to vector for take-off ... plus there's the
reduced noise (acoustic shielding) and increased safety (blade
containment).

The big question for a self-launcher is how you retract a ducted fan - if
it's producing the same thrust as a prop, it's going to have a
similar(ish) frontal area, or else be really inefficient.

Doug

[Mike the Strike]

On Jan 18, 4:13*am, Doug Greenwell > wrote:
> At 21:45 17 January 2011, Martin Gregorie wrote:
>
>
>
> >On Mon, 17 Jan 2011 11:59:05 -0800, CLewis95 wrote:
>
> >No numbers, but:
> >- multiple impeller blades destroy efficiency due to interference
> > *between the blades. Its similar to the inter-plane drag than makes
> > *biplane less efficient than monoplanes. As a result, the fewer blades
> > *the better, hence the superiority of the two blade propeller provided
> > *speeds are low enough to avoid tip compressibility problems.
> >- a bigger diameter impeller is better because moving a given mass of
> > *air slowly is more efficient for generating thrust than moving it much
> > *faster as is required by the smaller impeller.
>
> >Against that, about a ducted fan can offer is reduced tip losses.
>
> >That has to make an Antares-style pop-up system that turns a large, two
> >blade prop a better bet than a ducted fan system.
>
> >--
> >martin@ * | Martin Gregorie
> >gregorie. | Essex, UK
> >org * * * |
>
> The duct does do a bit more than reduce tip losses - there's an
> additional thrust component from the duct lip, which in the long run comes
> from an increase in effective capture area. *The airship people like them
> because they are easier to vector for take-off *... plus there's the
> reduced noise (acoustic shielding) and increased safety (blade
> containment).
>
> The big question for a self-launcher is how you retract a ducted fan - if
> it's producing the same thrust as a prop, it's going to have a
> similar(ish) frontal area, or else be really inefficient.
>
> Doug

One technique to launch underpowered self-launchers is to auto-tow the
ship until it is airborne and then climb under power. The
acceleration and ground roll can be a significant problem at high
altitudes or on soft fields and the auto-tow is cheap and simple.

Mike

[Doug Greenwell]

At 11:56 18 January 2011, Mike the Strike wrote:
>On Jan 18, 4:13=A0am, Doug Greenwell wrote:
>> At 21:45 17 January 2011, Martin Gregorie wrote:
>>
>>
>>
>> >On Mon, 17 Jan 2011 11:59:05 -0800, CLewis95 wrote:
>>
>> >No numbers, but:
>> >- multiple impeller blades destroy efficiency due to interference
>> > =A0between the blades. Its similar to the inter-plane drag than
makes
>> > =A0biplane less efficient than monoplanes. As a result, the fewer
>blade=
>s
>> > =A0the better, hence the superiority of the two blade propeller
>provide=
>d
>> > =A0speeds are low enough to avoid tip compressibility problems.
>> >- a bigger diameter impeller is better because moving a given mass of
>> > =A0air slowly is more efficient for generating thrust than moving it
>mu=
>ch
>> > =A0faster as is required by the smaller impeller.
>>
>> >Against that, about a ducted fan can offer is reduced tip losses.
>>
>> >That has to make an Antares-style pop-up system that turns a large,
two
>> >blade prop a better bet than a ducted fan system.
>>
>> >--
>> >martin@ =A0 | Martin Gregorie
>> >gregorie. | Essex, UK
>> >org =A0 =A0 =A0 |
>>
>> The duct does do a bit more than reduce tip losses - there's an
>> additional thrust component from the duct lip, which in the long run
>come=
>s
>> from an increase in effective capture area. =A0The airship people like
>th=
>em
>> because they are easier to vector for take-off =A0... plus there's
the
>> reduced noise (acoustic shielding) and increased safety (blade
>> containment).
>>
>> The big question for a self-launcher is how you retract a ducted fan -
>if
>> it's producing the same thrust as a prop, it's going to have a
>> similar(ish) frontal area, or else be really inefficient.
>>
>> Doug
>
>One technique to launch underpowered self-launchers is to auto-tow the
>ship until it is airborne and then climb under power. The
>acceleration and ground roll can be a significant problem at high
>altitudes or on soft fields and the auto-tow is cheap and simple.
>
>Mike
>

Yes, but you would still need to be able to stow the fan in cruise?

I like the idea of some model airplane fans on a stick waved out of the DV
window :-) ... unfortunately, looking at advertised thrusts for these
units, I don't think they'd be up to it even as a sustainer.

[Evan Ludeman[_2_]]

There's an old rule of thumb that says that you need take off thrust
of about 1/4 your gross take off weight for satisfactory performance.
This holds true for a remarkably diverse range of aircraft, from J-3s
to jets. You can struggle off on less under favorable conditions, but
not a great deal less.

There's another rule of thumb that says that you get roughly 4.5 lbf
_static_ thrust for every hp in a typical propeller driven light
plane.

At 60 kts, a reasonable efficiency estimate for a light plane
propeller is 75%, yielding right around 4 lbf thrust per actual
developed hp at takeoff. That's about 800 lbf thrust for an L-19 or
any other 200 hp tow plane on a warm but not hot day. Plug in the
weight of your tow plane (fueled, with pilot) and various gliders it
could be towing and now you have some good semi-quantitative insight
into the relationship between thrust, weight and take off
performance.

-Evan Ludeman / T8

[T8]

There's an old rule of thumb that says that you need take off thrust
of about 1/4 your gross take off weight for satisfactory performance.
This holds true for a remarkably diverse range of aircraft, from J-3s
to jets. You can struggle off on less under favorable conditions, but
not a great deal less.

There's another rule of thumb that says that you get roughly 4.5 lbf
_static_ thrust for every hp in a typical propeller driven light
plane.

At 60 kts, a reasonable efficiency estimate for a light plane
propeller is 75%, yielding right around 4 lbf thrust per actual
developed hp at takeoff. That's about 800 lbf thrust for an L-19 or
any other 200 hp tow plane on a warm but not hot day. Plug in the
weight of your tow plane (fueled, with pilot) and various gliders it
could be towing and now you have some good semi-quantitative insight
into the relationship between thrust, weight and take off
performance.

-Evan Ludeman / T8

(some of you may see double post -- sorry about that: posted on wrong
account)

[CLewis95]

On Jan 18, 10:40 am, T8 > wrote:
> There's an old rule of thumb that says that you need take off thrust
> of about 1/4 your gross take off weight for satisfactory performance.
> This holds true for a remarkably diverse range of aircraft, from J-3s
> to jets. You can struggle off on less under favorable conditions, but
> not a great deal less.
>
> There's another rule of thumb that says that you get roughly 4.5 lbf
> _static_ thrust for every hp in a typical propeller driven light
> plane.
>
> At 60 kts, a reasonable efficiency estimate for a light plane
> propeller is 75%, yielding right around 4 lbf thrust per actual
> developed hp at takeoff. That's about 800 lbf thrust for an L-19 or
> any other 200 hp tow plane on a warm but not hot day. Plug in the
> weight of your tow plane (fueled, with pilot) and various gliders it
> could be towing and now you have some good semi-quantitative insight
> into the relationship between thrust, weight and take off
> performance.
>
> -Evan Ludeman / T8
>
> (some of you may see double post -- sorry about that: posted on wrong
> account)

Evan .. some have missed a few of the parameters I stated up front.
The "model" EDF unit I am refering to advertises 38lbs Static
Thrust ... I can cluster and raise/retract this "cluster" into the
large bay of the Genesis 2 area that was designed to house a BRS
system. (though I would experiment with fixed mount first if I ever
actually tried this)

So 3 x 38 = 108 lbs Thrust .. but I stated and proposed 60lbs Thrust
(56%) because..
1 - I did not want to push the envelope of the EDFs
2 - I felt the mfg specs were probably optimistic and under ideal
conditions
3 - I felt there must be SOME loss of efficiency having the intake
ducts clusters so close together (ie touching).
(I am still hoping to hear comments on this subject ... I cannot find
ANYTHING on the web)

I had already considered Mike's technique of short auto-tow to get
airborne and would consider that as an acceptable requirement.
Working backwards from your numbers, could I assume 60lbs Static
Thrust translates to about 15HP in flight? That is the kind of
estimate I am looking for.

thx Evan and All

Curt -95

[bildan]

On Jan 18, 9:40*am, T8 > wrote:
> There's an old rule of thumb that says that you need take off thrust
> of about 1/4 your gross take off weight for satisfactory performance.
> This holds true for a remarkably diverse range of aircraft, from J-3s
> to jets. *You can struggle off on less under favorable conditions, but
> not a great deal less.
>
> There's another rule of thumb that says that you get roughly 4.5 lbf
> _static_ thrust for every hp in a typical propeller driven light
> plane.
>
> At 60 kts, a reasonable efficiency estimate for a light plane
> propeller is 75%, yielding right around 4 lbf thrust per actual
> developed hp at takeoff. *That's about 800 lbf thrust for an L-19 or
> any other 200 hp tow plane on a warm but not hot day. *Plug in the
> weight of your tow plane (fueled, with pilot) and various gliders it
> could be towing and now you have some good semi-quantitative insight
> into the relationship between thrust, weight and take off
> performance.
>
> -Evan Ludeman / T8
>
> (some of you may see double post -- sorry about that: posted on wrong
> account)

There are a number of propeller calculators on the web. Entering the
prop diameter, pitch, airfoil etc. and the engine power and RPM
suggests a 235 Pawnee generates < 400 Lbs of thrust at towing speeds.

[T8]

On Jan 18, 1:08*pm, bildan > wrote:
> On Jan 18, 9:40*am, T8 > wrote:
>
>
>
> > There's an old rule of thumb that says that you need take off thrust
> > of about 1/4 your gross take off weight for satisfactory performance.
> > This holds true for a remarkably diverse range of aircraft, from J-3s
> > to jets. *You can struggle off on less under favorable conditions, but
> > not a great deal less.
>
> > There's another rule of thumb that says that you get roughly 4.5 lbf
> > _static_ thrust for every hp in a typical propeller driven light
> > plane.
>
> > At 60 kts, a reasonable efficiency estimate for a light plane
> > propeller is 75%, yielding right around 4 lbf thrust per actual
> > developed hp at takeoff. *That's about 800 lbf thrust for an L-19 or
> > any other 200 hp tow plane on a warm but not hot day. *Plug in the
> > weight of your tow plane (fueled, with pilot) and various gliders it
> > could be towing and now you have some good semi-quantitative insight
> > into the relationship between thrust, weight and take off
> > performance.
>
> > -Evan Ludeman / T8
>
> > (some of you may see double post -- sorry about that: posted on wrong
> > account)
>
> There are a number of propeller calculators on the web. Entering the
> prop diameter, pitch, airfoil etc. and the engine power and RPM
> suggests a 235 Pawnee generates < 400 Lbs of thrust at towing speeds.

Well, that's just not correct.

Some useful relations:

1 hp = 550 ft*lbf/sec

60 kts = 101 ft/sec

Apparent power = thrust * speed = brake hp * efficiency

Real world efficiency numbers are below 80%, typically 65 - 75% in
climb. Most light planes hit their best propeller efficiency in climb
or cruise/climb conditions.

-Evan Ludeman / T8

[T8]

On Jan 18, 1:08*pm, bildan > wrote:

> suggests a 235 Pawnee generates < 400 Lbs of thrust at towing speeds.

That pawnee, assuming gross wt of 1900# and an optimistic best L/D of
10 (in zero thrust condition) needs 190 lbf thrust just to maintain
level flight at best L/D. I think it's obvious that it produces much
more than twice this amount of thrust under full power....

-T8

[db_sonic]

Dont forget the speed controller for this thing would be a monster
with all the timing issues to go with it just like the RC model kind.
And one of the issues with EDF is the friggen heat from these
brushless motors spinning at such high rpms.
To save the bearings you have to design in some sort of liquid cooling
or heat sink. Then there is the inlet design.
...meaning development of the EDF for this may not be that easy.

[Eric Greenwell[_4_]]

On 1/18/2011 3:56 AM, Mike the Strike wrote:

> One technique to launch underpowered self-launchers is to auto-tow the
> ship until it is airborne and then climb under power. The
> acceleration and ground roll can be a significant problem at high
> altitudes or on soft fields and the auto-tow is cheap and simple.

Bungee launch without the hill! That would enable you to launch
unassisted: stretch the bungey out the runway, climb in, trigger the
release of the bungee, and WHHoommp! You are going 45 knots and off the
runway.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)

[Eric Greenwell[_4_]]

On 1/18/2011 9:09 AM, CLewis95 wrote:

> Evan .. some have missed a few of the parameters I stated up front.
> The "model" EDF unit I am refering to advertises 38lbs Static
> Thrust ... I can cluster and raise/retract this "cluster" into the
> large bay of the Genesis 2 area that was designed to house a BRS
> system. (though I would experiment with fixed mount first if I ever
> actually tried this)

Can you give a link to the EDF you are considering?

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)

[CLewis95]

On Jan 18, 6:42*pm, Eric Greenwell > wrote:
> On 1/18/2011 9:09 AM, CLewis95 wrote:
>
> > Evan .. some have missed a few of the parameters I stated up front.
> > The "model" EDF unit I am refering to advertises 38lbs Static
> > Thrust ... I can cluster and raise/retract this "cluster" into the
> > large bay of the Genesis 2 area that was designed to house a BRS
> > system. *(though I would experiment with fixed mount first if I ever
> > actually tried this)
>
> Can you give a link to the EDF you are considering?
>
> --
> Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
> email me)

These are (2) units that I have been watching for ~ 2 years now..
hoping next generation would be stronger:

TF 8000 (28lbs Max Thrust)
http://www.ductedfans.com/TF_8000.html

DS 94 HST (22lbs Max Thrust)
http://www.ductedfans.com/Schuebeler_%20HST_%20from%20Ducted%20Fans.html

I just noticed in reviewing these links that the Max Thrust is stated
as 28lbs on TF 8000 ... I was using 20lbs for assumptions x 3 =
60lbs. In a previous reply I incorrectly said "3 x 38 = 108 rated max
thrust" .. I should have said "3 x 28 = 84 rated max thrust" ... again
I am using 60lbs for assumed thrust.

There are a number of purpose built electronic speed controllers for
these units.

Curt - 95

[Steve]

On Jan 18, 7:43*pm, CLewis95 > wrote:
> On Jan 18, 6:42*pm, Eric Greenwell > wrote:
>
> > On 1/18/2011 9:09 AM, CLewis95 wrote:
>
> > > Evan .. some have missed a few of the parameters I stated up front.
> > > The "model" EDF unit I am refering to advertises 38lbs Static
> > > Thrust ... I can cluster and raise/retract this "cluster" into the
> > > large bay of the Genesis 2 area that was designed to house a BRS
> > > system. *(though I would experiment with fixed mount first if I ever
> > > actually tried this)
>
> > Can you give a link to the EDF you are considering?
>
> > --
> > Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
> > email me)
>
> These are (2) units that I have been watching for ~ 2 years now..
> hoping next generation would be stronger:
>
> TF 8000 (28lbs Max Thrust)http://www.ductedfans.com/TF_8000.html
>
> DS 94 HST (22lbs Max Thrust)http://www.ductedfans.com/Schuebeler_%20HST_%20from%20Ducted%20Fans.html
>
> I just noticed in reviewing these links that the Max Thrust is stated
> as 28lbs on TF 8000 ... I was using 20lbs for assumptions x 3 =
> 60lbs. *In a previous reply I incorrectly said "3 x 38 = 108 rated max
> thrust" .. I should have said "3 x 28 = 84 rated max thrust" ... again
> I am using 60lbs for assumed thrust.
>
> There are a number of purpose built electronic speed controllers for
> these units.
>
> Curt - 95

How about downsizing the fans a little and using them as combined air
extractor and boundary layer suction/boundary layer control devices
which give some thrust. They could blow air along each side of the
fuselage tail across the lower part of the rudder and suck air from
the intake vents and possibly from small slots cut into the top wing
skin. Not a sustainer but it might increase the L/D by a fair
amount.

[db_sonic]

On Jan 18, 5:43*pm, CLewis95 > wrote:
> On Jan 18, 6:42*pm, Eric Greenwell > wrote:
>
> > On 1/18/2011 9:09 AM, CLewis95 wrote:
>
> > > Evan .. some have missed a few of the parameters I stated up front.
> > > The "model" EDF unit I am refering to advertises 38lbs Static
> > > Thrust ... I can cluster and raise/retract this "cluster" into the
> > > large bay of the Genesis 2 area that was designed to house a BRS
> > > system. *(though I would experiment with fixed mount first if I ever
> > > actually tried this)
>
> > Can you give a link to the EDF you are considering?
>
> > --
> > Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
> > email me)
>
> These are (2) units that I have been watching for ~ 2 years now..
> hoping next generation would be stronger:
>
> TF 8000 (28lbs Max Thrust)http://www.ductedfans.com/TF_8000.html
>
> DS 94 HST (22lbs Max Thrust)http://www.ductedfans.com/Schuebeler_%20HST_%20from%20Ducted%20Fans.html
>
> I just noticed in reviewing these links that the Max Thrust is stated
> as 28lbs on TF 8000 ... I was using 20lbs for assumptions x 3 =
> 60lbs. *In a previous reply I incorrectly said "3 x 38 = 108 rated max
> thrust" .. I should have said "3 x 28 = 84 rated max thrust" ... again
> I am using 60lbs for assumed thrust.
>
> There are a number of purpose built electronic speed controllers for
> these units.
>
> Curt - 95

The second one looks like it pulls 180 Amps -> 10 KW which puts it at
the very high end of the modeling spectrum.
Probably somewhere in the 30,000 to 40,000 rpm range.

yeah, 40KW and you are getting there.

[JJ Sinclair[_2_]]

On Jan 17, 11:53*am, CLewis95 > wrote:
> Electric Duct Fan (EDF) Self-Launch Glider?
>
> I have pondered this for some time now. *Electric Duct Fan (EDF)
> propulsion systems have been making strides in the RC model jet world
> and are challenging the use of mini turbine jet engines (now used on a
> number of full scale SL sailplanes) *Battery technology regarding
> power density and safety continues to improve at a rapid pace. (auto
> engineer recently stated that within 5 years batteries will approach
> the power density of gasoline ... hard to believe but ?? ) *EDF
> systems do not have the tremendously high exhaust temperature (~700°C)
> and decibel level issues. (Though not as loud, the EDF systems sound
> very similar)
>
> Assuming:
> - L/D 40:1 850 pound Sailplane (in my case Genesis 2)
> - Cluster of (3) currently available EDF Units producing combined ~60
> pounds STATIC THRUST (AFTER taking into account loss of efficiency do
> to close clustering of intake ducts)
> - Battery capacity for ~10 minutes full power .. no reserve
> - 2,500ft Paved Runway .. No Tailwind :)
> - Sailplane pre-positioned on runway (not taxied to runway)
> - Goal altitude of ~1,500ft AGL
>
> As a "sustainer" I am fairly confident this would yield some
> success .. if only buying you ~10 miles :) *What I would like to hear
> from the hobby-physicists out there are comments on these questions:
>
> 1 - How detrimental is the loss of efficiency/performance when
> clustering duct fan intakes in very close proximity?
> 2 - With sailplane starting from rest, how long would it take to
> accelerate to flying speed? i.e. Would I need 3 miles of paved runway?
> and/or .. Would the batteries be dead before the glider left the
> ground? :)
>
> I certainly am not proposing a "replacement" for jet turbines .. only
> curious if the above scenario is at all feasible.
>
> Thanks for comments!
>
> Curt Lewis - 95
> Genesis 2
> Loves Park, IL USA

I don't think a ducted fan is the way to go, but I could get excited
about an electric sustainer in the nose if available for say10K with
folding prop, controller and battery. Nose weight of the motor is
counter balanced with battery in aft fuselage, but they wont 25K for
the one installed on a LAK-17.
JJ

[Eric Greenwell[_4_]]

On 1/20/2011 6:41 AM, JJ Sinclair wrote:

>
> I don't think a ducted fan is the way to go, but I could get excited
> about an electric sustainer in the nose if available for say10K with
> folding prop, controller and battery. Nose weight of the motor is
> counter balanced with battery in aft fuselage, but they wont 25K for
> the one installed on a LAK-17.

Possibly, a folding propeller design like the Carat uses would make
installation a lot easier. The battery, controller, motor, and propeller
might be available for $10K total, but you need a battery/motor guy to
complement your composite construction skills. Any Genesis owners like that?

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)