Traders - What are your hobbies?

[Mike805]

Quote from Lucrum:



Fan is mounted to the engine and I'm working on getting the shaft aligned using a dial caliper. After which I'll mount the bearing, already attached to the fan, to a stand supporting the fan on both ends.

Why not just buy something well engineered, get it machined professionally? While I applaud your efforts, that fan looks a bit hokey...

The thing is going to be spinning really fast, right? Aerospace engineers have put in a ton of effort into fan effiecieny over the years. The curvature/shape of the blades can provide orders of magnitude increases in terms of efficieny/noise.

Won't low efficiency just increase the load on your engine? Shouldn't you be making sure that the least amount of power is wasted?

Not trying to be an ass here, just asking.

Mike

 

[Lucrum]

Quote from Mike805:

Why not just buy something well engineered, get it machined professionally? While I applaud your efforts, that fan looks a bit hokey...

To my knowledge there is nowhere to simply order a machined version of what I need in terms of dimensions or materials. Any existing fan suitable for my project would probably be part of a turbofan engine, they're usually constructed titanium and would cost WAY more than I hope to spend on the entire project. Also I'm using mostly wood and composites which will both absorb vibration and have better fatigue qualities than metal.
My fan is not as smooth as it could be, but IF I get past the testing phase with it I'll put some more work into it before installing it in the plane. Also the center hub portion won't see any airflow. And while it's not a "pretty" as it might be it should be strong enough.
It's made from a laminated black walnut core with 6 layers of .009" S-glass.

The thing is going to be spinning really fast, right? Aerospace engineers have put in a ton of effort into fan effiecieny over the years. The curvature/shape of the blades can provide orders of magnitude increases in terms of efficieny/noise.

6500 RPM at take off power. There is NO doubt a qualified engineer could design a better fan than I have. IF I could find someone qualified and willing. Truth is though not nearly as much engineering knowledge and experience is even available for this relatively unique utilization of a fan as there are for turbine powered fans and reciprocating engine powered propellers. This is kinda in between. With the fan in the rear of the plane and both the engine and the fuel tank between it and the cockpit, noise really wasn't a major concern for me. And if your thinking in terms of turbofan jet noise, my blade tips will be operating at much lower mach numbers than those fans do and therefore, theoretically, should not be as loud.

Won't low efficiency just increase the load on your engine? Shouldn't you be making sure that the least amount of power is wasted?

Yes but then ultimate efficiency isn't my goal, if it was I wouldn't be using a ducted fan to begin with. I'm only expecting/hoping for 60% propulsive efficiency while a typical propeller can yield 80% or more.

Not trying to be an ass here, just asking.

I didn't take it that way at all.

 

[Epic]

Lucrum,

Did you consider taking a block sander to it? Followed up with some finishing epoxy, another hit with the sander, work up to like a 800 grit. Then finish it off with a nice high gloss catalyzed paint.

I would think it would cut down the friction of the blades quite a bit.

BTW, what are you using for the ducting?

 

[Lucrum]

Quote from Epic:

BTW, what are you using for the ducting?

Thin plywood for the inlet and exit areas and due to the many compound curves fiberglass for the transition between front and rear sections.

 

[William Rennick]

Lucrum,

I just now went through this thread. Are you building a damned jet? Keep posting on your progress. Doing something like this takes hard work, smarts, and brass balls. This truly is fascinating, best of luck with your noble endeavor.

Rennick out

ps. One of my hobbies is firing golf balls with a lob wedge at the big dinner bell hanging in my apple tree.

 

[nutmeg]

In the shade of the old apple tree. She picked up her dress for me.

 

[Lucrum]

Quote from William Rennick:

... Are you building a damned jet? ...

No William it's a jet look-a-like powered by a rotary engine and a ducted fan. Same basic idea as the radio controlled ducted fan "jets", only bigger.

http://www.e-fliterc.com/Products/Default.aspx?ProdID=EFL7075

http://www.ductedfans.com/Ducted_fan_impellers_EDF_units.html

http://en.wikipedia.org/wiki/Ducted_fan


I have a lot of testing to do on the fan though before I proceed with the rest of the plane. Not only testing the obvious structural strength but also testing for torsional resonance issues. If I can't make the fan/shaft/engine combination work then I'll revert to plan B. A more traditional pusher propeller configuration, probably with a cranked delta wing.

 

[rew]

Quote from stock777:

I aspire to this championship in my spare time



A mans grasp can never exceed his reach

OMG, the most politically incorrect sport ever invented!

 

[WinstonTJ]

Lucrum...

Awesome project!!! I'm jelous of not having a decent work space... I'm relagated to wrenching on 2-wheeled vehicles on the NYC sidewalk at the moment!

A few questions/comments, I mean no offense at all but have a bit of composites experience (from the sailing and automotive industry).

What is the scale of this thing? Are you making this up as you go along or is that from a kit? Have you considered using a vacuum bag and epoxy resin combined with some foam and/or honeycomb vs. wood? What about using carbon/kev weave and kevlar at higher stress points?

My concern with you not bagging that fan is that when things are under load and stress you will find that the resin will be more brittle than the fiberglass and may start to crack - that combined with the weight of the extra resin is a very bad thing I would think...

Also, is that a proven driveshaft method? Seems like the rods may have torsional strength issues - and wrapping it with loose wet cloth is going to be tough to balance. Have you thought about using an outer layer of Kevlar there too - since its much more resilliant to shattering vs. the carbon which could shatter and go through into the cockpit if you are sitting on top of it.

Are you going to balance the driveshaft and the rotary fan together? Are you using a flex disc between the motor and the driveshaft?

Cool project!!!

 

[Lucrum]

Quote from WinstonTJ:

...What is the scale of this thing? Are you making this up as you go along or is that from a kit?

Latest iteration is 24' long with a 17.5' wingspan, the fan is approximately 30" in diameter.

Have you considered using a vacuum bag and epoxy resin combined with some foam and/or honeycomb vs. wood? What about using carbon/kev weave and kevlar at higher stress points?

I considered most of the available techniques and materials. I chose a wood core partly for it's vibration dampening properties and partly for ease of fabrication. You may already know but wood is still commonly used for propellers.

My concern with you not bagging that fan is that when things are under load and stress you will find that the resin will be more brittle than the fiberglass and may start to crack - that combined with the weight of the extra resin is a very bad thing I would think...

Excess resin is a bad thing and you may very well be correct that bagging would have been better. If this fan doesn't test satisfactorily I'll consider bagging if I try a new fan.

Also, is that a proven driveshaft method? Seems like the rods may have torsional strength issues - and wrapping it with loose wet cloth is going to be tough to balance. Have you thought about using an outer layer of Kevlar there too - since its much more resilliant to shattering vs. the carbon which could shatter and go through into the cockpit if you are sitting on top of it.

It's not proven, the diameter and materials I chose were partly to keep the shafts critical frequency twice as high as what I intend to rev the engine and ease of construction. I've never used it but it's my understanding Kevlar is a little difficult to cut and wet out properly which is why I avoided using it.

Are you going to balance the driveshaft and the rotary fan together? Are you using a flex disc between the motor and the driveshaft?

I balanced the fan and shaft/flywheel coupling separately. I'm going to try not using a flex disc at first. The whole ducted fan/shaft is an experiment to say the least, and one with a relatively high technical risk at that. But I knew that going in, it's simply the price for exploring a full size DF jet look a like.