Ducted propellors


#1

Just thought I would stir some thoughts on a ducted propeller idea. It may be very beneficial if designed correctly but also has the potential to be high cost, high drag, increased risk of failure. Any thoughts?


Ducted fans... No cage needed?
#2

Sounds interesting - I was thinking about individual prop surrounds just for cool look points but if you can make them so they increase efficiency with min weight increase then bravo
Cheers, Patrick


#3

Hmm maybe we do need a wiki.
Check out this answer from a few months back. Why four motors, instead of one motor?

Also the search is pretty good on this forum so don’t hesitate to try that before posting :slight_smile:


#4

Yeah I have briefly read elsewhere that for these low speeds the extra drag and weight of the ducts cancels out any possible efficiency gains and is maybe less efficient than no ducts for this style application. Also the unit wouldn’t fold up nicely into a small package do to the large ducts and I’d fear they’d be like mini sails when you get hit by the occasional gusting cross wind tossing you around. The only benefit they might have is slightly reducing noise levels but I thought I read you need a really tight tolerances between blade tip and duct wall for that to work.

I saw that same article and thought wow I gotta look into this but after reading about ducts I realized that if it’s not efficient at these speeds then its not worth it for what I want out of this paramotor rig.

I’m siked that if the weather kinda sorta looks good I can charge the night before and throw this rig and wing in the car in the morning and commute to work with it and go straight from work to my launch field right after work. With my gas paramotor there have been times I’m commuting home from work on a fantastic flying evening and I know that by the time I get home, get my hitch tray on, strap down the paramotor, get to the field, gas up, and preflight check the 2 stroke it will be to late in the day to fly.

I understand that if the weather doesn’t work out then I have to discharge the lipos using up a cycle on them if I don’t fly within two days. But to me that’s better to always have the option to fly than trying to commute with a stinky gas tank in the car and a 2-stroke strapped to a hitch tray on the back of my car. Even though I’d love for all props to be quieter I think the ducts would ruin the ease of portability that I am so looking forward to.
From the most recent video they posted I saw why that weird hole pattern is in the middle of the back plate, it’s cause the blade tips have to fit through there to fold it up, I believe. When I saw that I realized how much went into making this portable and large ducts would not make that possible.
Pretty sure those are the propeller tips poking through the back plate:


#5

Whoah sorry for the essay, I don’t post to forums ever so this is all new to me I’m usually just a lurker.


#6

Good catch! I was wondering about those holes.


#7

Good catch and good point. A serious design achievement. I assumed they were for cooling or weight reduction and they may double as that but I’m sure you’ve correctly identified their primary purpose.


#8

be sure to round off the edges of the prop holes as they tend to abrase the thin prop tips


#9

Who knows how to calculate the shroud profile in an airflow of 35-40km/h? The Capolight Blog shows a 0 axial velocity

This is my sketch

41


#10

Ryan I would be curious about this as well as a single motor seems more efficient than 4 smaller ones with potential for one of the four to go down as well. I know there are benefits in relation to twist not being a factor so much with four vs single prop, but other than that, I would think you could get better efficiency with a single prop.


#11

Could a ducted propeller resolve the need for the cage? Might be able to make the weight trade-off worthwhile in that case… and maybe we could even do a custom designed duct which is more aerodynamic. Seems like this is similar to the electric sudo-jet engines, but those seem to be less efficient.
Being round, they may not have significant windage from the sides… not much more than the paramotor/cage already presents anyway. I’d be interested to see some tests or comparisons regarding this… it does seem like there should be a more efficient method of generating thrust, and jet engines seem to be a really smart/efficient idea… but they rely on heat to work. (And can have a scary intake :wink: