Ducted fan aircraft

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by jthunt, Mar 17, 2012.

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  1. Sep 23, 2019 #1541

    RSD

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    Some good information there Scheny. Looking at the Gates GT3 tables, if the engine hp and rpm fall outside the range on the table for a belt does the belt normally fail catastrophically the first time it hits full power, or does it just need to be replaced sooner than normal (for instance at every 100 hourly/annual inspection)?
     
  2. Sep 23, 2019 #1542

    Scheny

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    I used the belt for my ultralight human powered (pedal) boat. The power there is marginal, but the torque is enormous with up to 90Nm (which is about what the car of my mother in law has :p)

    I originally planned to build the 90° gear on my own, so I asked one of the best gear designers in the world if I can use his software once. At 100% design, the lifetime was calculated to be 10.000h. At 120% it went down to 200h and at 130% to single minutes. Unfortunately I don't have more data points, as I got a ready made drive for cheap and didn't need it anymore.

    I did not calculate it for the belt, as the bevel gear was the critical part, but I expect it to be similar. The stated numbers in the catalog are for lifetime endurance and the manufacturers offer correction values for start-up torque, etc.

    With a belt running at high power and speed you also get problems with vibrations (fortunately in the high frequency region, so more a noise issue) and static electricity. Some radio controlled helicopters use belts for the tail rotor and it can even affect radio reception.
     
  3. Sep 26, 2019 #1543

    Malish

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    Our fans are 27 inches in diameter and turning at 7000 rpm. We're still working on the fans design to increase their efficiency. Now they're producing about 1kgs(2,2lbs) per hp and our goal to get at least 1,5kg(3,3lbs) per hp of static trust. For our aircraft with 1,400kg(3,200lb) MTOW, the static trust of 600kgs(1,300lbs) with 400 hp engine, should be a good enough.
     
  4. Sep 26, 2019 #1544

    mm4440

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    When you increase hp into a fixed disc area the thrust per hp decreases; double the hp and maybe 50% more thrust. I think the lift fan from the F-35 produces about 1# of thrust per hp.
     
  5. Sep 27, 2019 #1545

    RSD

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    Presumably that is if you are using the same disc though? Would increasing the HP allow you to increase the number of fan blades?
     
  6. Sep 27, 2019 #1546

    mm4440

    mm4440

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    It is the disc area that is important. There needs to be enough blade area to absorb the additional hp but disc, blade swept area that limits thrust per hp.
     
  7. Oct 11, 2019 #1547

    Malish

    Malish

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    Here some photo's from news media, after MAKS 2019 international airshow. 74139f4d4543b125979baffb8d82baee14f0e1a90_703_469_c.jpg 8b52944b74f7e985b8c525555567890714df304ab_703.jpg 6b25fd3e0206cf8982fa9af3d087a68314692550c_703.jpg db399ba686451ecd04aa8e5599c07d641449a9ab5_703.jpg
     
  8. Oct 11, 2019 #1548

    henryk

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  9. Oct 11, 2019 #1549

    Malish

    Malish

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    Already flying!
     
    Last edited: Oct 11, 2019
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  10. Oct 11, 2019 #1550

    Malish

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    And one more nice photo. 7964655 (Large).jpg
     
  11. Oct 11, 2019 #1551

    henryk

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  12. Oct 13, 2019 #1552

    nicknack

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    Hi Malish, just wonder where the goal of 3.3lb per hp comes from is it to match the performance of a standard 150hp Cessna 172 that has ~465lb static thrust at full throttle ie 465/150 = 3lb/hp
    Also what do you expect for fuel consumption of the 400hp V8 LS engine at (a) full throttle 400hp and (b) cruise settings both cases at best altitude.
     
  13. Oct 13, 2019 #1553

    nicknack

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    Malish if you could allow another question, will a variable pitch ducted fan (assuming it is possible to make one) be any advantage or allow better thrust to speed matching at altitude
     
  14. Oct 13, 2019 #1554

    Malish

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    Ducted fan working is turbine - fan engine, but propelled by different power plant, no variable pitch would not will help. Please read theory of ducted fan
     
  15. Oct 13, 2019 #1555

    nicknack

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    Could you quote a few books, papers, that I can read on ducted fans... the more technical the better
     
  16. Oct 13, 2019 #1556

    Doggzilla

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    For some reason Ive not been getting notifications from this thread.

    Very nice pictures Malish!
     
  17. Oct 13, 2019 #1557

    Doggzilla

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    Malish, when you get a chance can you please check some performance for us.

    I see that it cruises at 187 and 15gph. Would you please test what speed it cruises at 10-11 gph?

    Most common prop aircraft cruise around 150mph/130kts at 11gph.

    If you can do 150mph at 10-11gph then it means your existing blades are efficient enough to compete against props in the 200hp power range. That would be better than the 172 or 182, which is more than acceptable for most pilots.

    If you can match that with two fans, it probably means a single fan could be used for 100hp and under without performance reduction.

    I am very curious to know how it performs at lower speeds.
     
  18. Oct 14, 2019 #1558

    Doggzilla

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    There is a specification page on the PJ site you may be interested in. Malish has already discussed a lot of this here so he’s just going to be repeating himself.

    Performance is 187mph on 15gph.

    The cruise efficiency is far higher than the max speed efficiency. I am certain that Malish will hit 3lbs at lower hp, but it seems to choke at max power.

    I think the reason this is possible is because props have a large dead zone in the center but ducted fans do not. The flow velocity equalizes across the entire cross section before leaving the exhaust.

    Previous ducted fans have had very short exhaust ducts and the flow may not have been stable compared to the long duct on the PJ
     
  19. Oct 14, 2019 #1559

    Vigilant1

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    Malish, I don't now who "us" refers to above. As for me--I hope you'll continue your test program exactly as you see fit. Congratulations on your continued progress.
     
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  20. Oct 14, 2019 #1560

    henryk

    henryk

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    file:///C:/Users/mbm/Downloads/Mechanika_2013_20.pdf

    =noise problems...

    http://www.icas.org/ICAS_ARCHIVE/ICAS2004/PAPERS/124.PDF

    =specific thrust=1.2 kG/HP.
     

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