Experimental Ducted Fan Aircraft Designs

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vhhjr

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Still working on my version of this. So far I have data from an 11 inch diameter DF made with compressor blades from a Rolls Royce Avon engine. The first version had the blades mounted at the same 54 deg. angle of attack as in the Avon engine and. I then built a rotor with ground adjustable blades and found the sweet spot to be at a lower angle of attack. With a nine HP motor it topped out at about 25 lbs of thrust at 5000 rpm.

The next DSF is a 17 inch diameter one made with 12 blades from a Russian engine. The first hub also mounts the blades at a high angle of attack that limits the performance. With the nine HP engine the max RPM was 3000 and it also produced about 25 lbs of thrust. I then swapped the none HP for a 35 HP 2si 2 cycle engine and only have preliminary data for that combination. To date I have gotten 4000 RPM and about 35 lbs of thrust. I am currently making a new, variable blade angle hub for this fan and will keep you posted as to the results. Here's some of the initial data:
upload_2020-2-25_18-44-30.png
 

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Malish

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BTW=formula for Kf can help in comparation betwen
two DF with different dimensiones...
If formula is NOT designed for Ducted fan performance calculation - it's can't give acceptable figures.
On video they don't show thrust measurements, only talking about. But on the video their craft take off and flying don't look like it has 70kg of thrust.
 

Malish

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Still working on my version of this. So far I have data from an 11 inch diameter DF made with compressor blades from a Rolls Royce Avon engine.
Compressor blades are not designed for Ducted fan use - they design for different RPM's and have different twist and installation angel's. Also number of blades is very matters.
 

bmcj

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The key here would be developing a complete powerplant that can be integrated with multiple airframes. Like with electric aircraft, the problem is the lack of off-the-shelf solutions.
The obvious solution would be to take a jet turbine engine, add a gearbox to turn it into a turboshaft engine, then hook it up to the ducted fan in order to simulate a jet powered aircraft. :p
 

Hephaestus

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I think malish and Henryk are the ones to listen to here as if you recall - they're doing better than even our pros here have said is possible.

Some of the old theories of DF design have been tossed out in recent years - probably want to look at what they're saying.
 

vhhjr

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I just drove the 17" DF powered machine down our taxiway and back and got the fan a bit over 5000 rpm while recorded 55 lb of thrust.

When I was testing the 11" version with the blades at the same angle (~55 deg)as in the compressor they came from I got 14 lbs of thrust at 5000 rpm. I then built a hub with variable blade pitch and at 40 deg the thrust doubled at the same RPM. Twenty eight lbs of thrust on 8 HP isn't all that bad. Hopefully, the 17" fan will behave similarly with a new hub and the just installed 35 HP engine..

I went into using compressor blades knowing they weren't the best solution, but they are available and a place to start. Designing and fabricating DF blades does not appear to be a trivial endeavor.
 

Malish

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I just drove the 17" DF powered machine down our taxiway and back and got the fan a bit over 5000 rpm while recorded 55 lb of thrust.

When I was testing the 11" version with the blades at the same angle (~55 deg)as in the compressor they came from I got 14 lbs of thrust at 5000 rpm. I then built a hub with variable blade pitch and at 40 deg the thrust doubled at the same RPM. Twenty eight lbs of thrust on 8 HP isn't all that bad. Hopefully, the 17" fan will behave similarly with a new hub and the just installed 35 HP engine..
5000 rpm is way to low for 11" or even for 17" fan for good performance. Depend on blade design the installation angle should be 35 deg. or less.
This book's have good information for Ducted fan design:

http://massflow.archivale.com/ductbook.htm

DFD1.gif
51PHjfOlKNL._SY344_BO1,204,203,200_.jpg
 

vhhjr

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Thanks for the comment. I agree that my rpms are too low. My calcs show the safe limit for the 11" fan to be about 16,000 rpm, well under the sonic tip speed and for the 17" I have set 12,000 rpm as the limit for structural reasons. The 11" version was originally driven by a 12 hp Harbor Freight engine that never put out more than 9 hp output. Apparently, horses are smaller in China. The graph below shows the effect of blade angle on performance. Disregard the reference to torque on the "Y" axis as I pulled that off the graph to reduce the clutter. You're right about a lower blade angle as that was where I got the best thrust numbers. I am going to take the 17" fan apart shortly to install the blades on a new, variable pitch hub. When I do I will put the 11" fan back on and see how the performance is with the 35 hp engine that I now have on the test vehicle. The test vehicle has a CVT to ensure all the engine torque gets delivered to the fan. The graph below shows the maximum fan rpm between 6000 and 8000 rpm without having to change any drive pulley sizes. I will also be able to get some data at air speeds up to 30 mph

upload_2020-2-25_19-5-26.png
 

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vhhjr

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My ducts came out slightly out of round making the tip clearance range from 0.000" to 0.040". This is a bit too much, but I'm getting better at making them. Stepped ducts would help with this problem. Another possibility is an abradeable foam band that the blades scrape off. I have found that my turbines do increase slightly in diameter with increasing RPM so the foam might work.
 

Malish

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I will also be able to get some data at air speeds up to 30 mph
Look like you have good setup for testing your Ducted fan design. What is your goal - craft, this Ducted fan will be used? Why you decide to install so many blades with low hp engines?
Our PJ_II "Dreamer" fan's have five blades(new fan's will have six) and they propelled by 350 hp(175 hp per side). Airbus E-fan has 8 blades per fan.

PA222036.JPG thumbnail (8).jpg 20140715-airbus-e-fan-farnborough-001.jpg
 

vhhjr

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So many blades for two reasons:
1. I succumbed to the "more is better" line of thinking. The maximum I could fit on the 11" was 16 and 12 on the 17" fan. We also intend to remove blades and test with less blades. In the case of the 16 blade version we can run 8 or 4 and with the 12 blade we can go with 6 or 3.
2. The intention was to eventually drive the fans with a higher HP engine.

Originally, we had considered "untwisting" blades, but the stiffness of the blade materials made that impossible. Eventually, the intention is to make our own blades. We decided to put off that task until more was learned about the rest of the system.

We have another project using numerous, small (90 mm) EDFs on a full size aircraft. This aircraft is flying and we have done a lot of wind tunnel work on that system using subscale models and 50 mm EDFs from the RC model industry. The blade solidarity for these small turbines is very high as is the rotor hp/ft2. That model was a strong driver in choosing to maximize the number of blades in my DFs.
 

cluttonfred

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Here's a question from someone who knows very little about ducted fans....

Setting aside how to build it or how much it costs ore even what engine to use, what would the ideal fixed-pitch ducted fan look like for general aviation use? Let's say a maximum diameter including the duct of 1 m or less, so a fan diameter of 80 cm or less. What would the fan itself look like to get most thrust from a fan that size?
 

Vigilant1

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Here's a question from someone who knows very little about ducted fans....

Setting aside how to build it or how much it costs ore even what engine to use, what would the ideal fixed-pitch ducted fan look like for general aviation use? Let's say a maximum diameter including the duct of 1 m or less, so a fan diameter of 80 cm or less. What would the fan itself look like to get most thrust from a fan that size?
My guess is that HP, RPM, and design airspeed will be needed to make a rough estimate.
 

cluttonfred

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Let's say 100 hp at 5800 rpm for the engine, something like a Suzuki G13. Direct-drive would be easiest but the fan RPM could be whatever works since you could also use a "backwards" redrive to increase fan RPM. Let's say the fan optimized for cruise at 100 mph at 75% power.

My guess is that HP, RPM, and design airspeed will be needed to make a rough estimate.
 
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