Ducted fan aircraft

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RSD

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May 19, 2019
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The best belt on the market at the moment is the GT3. It has superior power capability and in addition higher lifetime, still it is limited to where it can be used.

Belts are categorized in pitch, meaning the length between two teeth, and width. The 8mm pitch is limited to 5500rpm and the 14mm is limited to 4000rpm (on the smaller gear!). In terms of power, the 8mm would only handle 200hp at maximum width, so it would be wise to use the 14mm in the first place.

The values can be exceeded for short time (if other parameters allow it), but at this deviation I don't see how you could put this in your aircraft (at least not for the 2x200hp version).
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)?
 

Scheny

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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)?
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.
 

Malish

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Oct 11, 2013
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BTW I wasn't suggesting that Malish go to an 800 hp motor, but rather was interested in his thoughts on what (if any) benefit could be gained by combining his design with a much larger motor - curious to know whether more hp would benefit given that they are relatively small fans (look to be about 24 inches in diameter).
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.
 

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.
 

RSD

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May 19, 2019
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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.
Presumably that is if you are using the same disc though? Would increasing the HP allow you to increase the number of fan blades?
 

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.
 

nicknack

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Jul 27, 2008
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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.
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.
 

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
 

Malish

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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
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
 

nicknack

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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
Could you quote a few books, papers, that I can read on ducted fans... the more technical the better
 

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.
 

Doggzilla

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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.
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
 

Vigilant1

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