Experimental Ducted Fan Aircraft Designs

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Scheny

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Use helical gears, they are 5 times stronger at the same weight!!!

For 1:1 sizes they are available off the shelf for low money.
 

Urquiola

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Aug 23, 2013
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Madrid, Spain
Any specific comment on the use of a 'Counterpropeller'?: fixed vanes after the propeller blades, as vanes in turbines, changing the shape of helicoidal air flow from propeller into somethig more close to a linear, laminar flow.
There was a German inventor, R Wagner, proposing this, patent US1609978.
For sure the pass of propeller blades next to a fixed vane may induce vibrations, it's the engineers' expertise calculating this, but the results may not be clear.
I'd like having this type of arrangement in a Custer Channel Wing machine, and about this, I'm also not sure if the propeller placement in trailing side of Channel, the original Custer way, would yield same results as if put on leading edge, as in Antonov 'Izdelie 181', or over the thickest part of airfoil, or elsewhere. Blessings +
 

nicknack

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Jul 27, 2008
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I've followed the ul-39, and when the PBS TS100 Turboshaft Engine - PBS Aerospace came out, it seemed like they should do something experimental with it and the ul-39, even though that isn't EASA UL category. It looks like they might work something up like that as they have a rendering with what looks like the PBS TS-100: https://www.fs.cvut.cz/veda-a-vyzkum/vysledky/vysledky-projektu/ul-39-albi/ul-39-albi-ii/
Yeah, I’ve been following it too. The picture they have there is for a Turbohřídelový motor
Turbo shaft ie like a turboprop engine. Maybe they might get better TSFC numbers. I’ve wondered why not just use 2 pbs TJ100 and shove in a 100+ gallon fuel tank for a two seater and allow upto 160 gallons for a single seater operation.
keep the wing loading at under 18 to 20 lb/sqft. Performance will be enough for operations at 3000ft runways
Wing area = 91.5sqft so MTOW of around 1650 to 1900lbs
Thrust to weight will be 0.31 to 0.37.
And if TJ150s are used.... Thrust to weight goes to 0.42
That’s starting to get into the realm of real fighter jet numbers...
TJ100 consumes 30gallons at full takeoff power only usable for 5mins. Cruise at 50% power at FL150 consumes 16to18 gallons an hour. At FL250 improves to 14-15.5 gallon an hour.
 

nicknack

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I am waiting to see what kind of numbers the subsonex guys get with the new 2seat Jet they are developing. It will be a good data/reference point for a twin jet powered UL39 ALBI.
 

Scheny

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I am waiting to see what kind of numbers the subsonex guys get with the new 2seat Jet they are developing. It will be a good data/reference point for a twin jet powered UL39 ALBI.
Before we started the "Beast One" project (which uses the PBS TJ100), we wanted to start with a two-seater. Although the name suggests the TJ1500 has 50% more thrust, the TJ100 already provides 1200N, so the increase is only 25%.

For transport jet aircraft, the minimum thrust is calculated in a way, that it can climb OEI (one engine inoperative) at the minimum gradient of an SID. This means, that 2 engined jets are quite overpowered and 4 engined have the bare minimum. Now thrust is selected to be 1/3 of the weight for a twinjet and 1/4 of the weight for the real big stuff like the Antonovs.

With the JSX-2 having an MTOW of 450kg, the ratio is already quite bad at 1/3.8 which can be seen at the take-off rolls. With their two-seater, I am expecting it to have a thrust to weight ratio of 1/4.7. Honestly, I could not imagine it taking it off from ANY of the small airports we have here in Europe.

Our Beast One has 380kg MTOW, which means the ratio is ~1/3 and me and both my aerodynamicists consider this the BARE MINIMUM! In addition, last time I have asked PBS, the TJ-500 did not come with a generator sufficient for a plane of that size. We considered that no customer would like to buy a plane from us, which only runs the avionics from the generator and flaps/gear/etc. need to be run from a preloaded battery.
 

Doggzilla

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Was doing some math and it appears that ducted fans become much more suitable as weight increases.

The F-5 is considered one of the cheapest jets to operate, so I will use it as a reference point.

For a ducted fan to reach the same gross weight it would require 1500-1600hp.

A 1500-1600hp turbine uses a third the fuel at maximum power as the F-5 uses at cruise. But it can only go around 300mph, about 50% slower than a cruising F-5.

But this also means at about 50% power it’s using about 1/5th the fuel. This is the really important part. Having 5 times the loiter time means it is vastly better suited to ground support, where staying overhead for long durations is extremely important.
 

nicknack

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Before we started the "Beast One" project (which uses the PBS TJ100), we wanted to start with a two-seater. Although the name suggests the TJ1500 has 50% more thrust, the TJ100 already provides 1200N, so the increase is only 25%.

For transport jet aircraft, the minimum thrust is calculated in a way, that it can climb OEI (one engine inoperative) at the minimum gradient of an SID. This means, that 2 engined jets are quite overpowered and 4 engined have the bare minimum. Now thrust is selected to be 1/3 of the weight for a twinjet and 1/4 of the weight for the real big stuff like the Antonovs.

With the JSX-2 having an MTOW of 450kg, the ratio is already quite bad at 1/3.8 which can be seen at the take-off rolls. With their two-seater, I am expecting it to have a thrust to weight ratio of 1/4.7. Honestly, I could not imagine it taking it off from ANY of the small airports we have here in Europe.

Our Beast One has 380kg MTOW, which means the ratio is ~1/3 and me and both my aerodynamicists consider this the BARE MINIMUM! In addition, last time I have asked PBS, the TJ-500 did not come with a generator sufficient for a plane of that size. We considered that no customer would like to buy a plane from us, which only runs the avionics from the generator and flaps/gear/etc. need to be run from a preloaded battery.
Any idea what happened to the Price Induction DGEN 380/390. I thought that would have been a better option with 600 to 900lb thrust Class and a TSFC of 0.7 ish.... Never heard any further news since 2018
 

Scheny

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Vienna, Austria
Also, something for the UL
Any idea what happened to the Price Induction DGEN 380/390. I thought that would have been a better option with 600 to 900lb thrust Class and a TSFC of 0.7 ish.... Never heard any further news since 2018
I had two very long phone calls with their sales rep as it was our first choice for the two seat version. Without an ongoing series production, the price per unit has tripled and lies above (larger model) competition. In addition, there are some engineering hours required for fitting it which go into a range we could not afford and the generator was not yet within design specs (but would have been more than sufficient for us).

Made me very sad this didn't work out. The DGEN is built for a design cruise speed in the 210-250kt range, making it even more efficient at low speeds.
 

nicknack

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Jul 27, 2008
Messages
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Also, something for the UL

I had two very long phone calls with their sales rep as it was our first choice for the two seat version. Without an ongoing series production, the price per unit has tripled and lies above (larger model) competition. In addition, there are some engineering hours required for fitting it which go into a range we could not afford and the generator was not yet within design specs (but would have been more than sufficient for us).

Made me very sad this didn't work out. The DGEN is built for a design cruise speed in the 210-250kt range, making it even more efficient at low speeds.
Oh that’s a real shame.. it was pretty much the only high bypass turbofan in this size. PBS is after all a turbojet so unless they redesign it into a turbofan, thrust isn’t going to go up and tsfc numbers are not going to go down much.
 

nicknack

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Joined
Jul 27, 2008
Messages
43
Also, something for the UL

I had two very long phone calls with their sales rep as it was our first choice for the two seat version. Without an ongoing series production, the price per unit has tripled and lies above (larger model) competition. In addition, there are some engineering hours required for fitting it which go into a range we could not afford and the generator was not yet within design specs (but would have been more than sufficient for us).

Made me very sad this didn't work out. The DGEN is built for a design cruise speed in the 210-250kt range, making it even more efficient at low speeds.
By the way what’s your opinion about the turboshaft proposal by the UL 39 Albi team. It has the PBS TP100 driving a fan
and maybe putting out some residual jet thrust from exhaust. If I remember correctly from the article about the TP100 equipped RV10, the exhaust provided some thrust too. TSFC should be better?
Turbo shaft TJ100 provides 241shp, if fan can produce 2lb thrust/HP, that will be around 482 to 500lb thrust.
1591604135848.jpeg
 

Scheny

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Vienna, Austria
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".
 

TiPi

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Aug 25, 2019
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Mackay (AUS)
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.
Remember that they were designed to be UNSTABLE and are only becoming flyable through a large computer with hundreds of inputs. Turn that computer off and they are just tumbling bricks. For any replica aircraft to be flyable by a recreational/private pilot, the airframe will need to be redesigned aerodynamically to be stable without a computer.
 
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