HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Apr 03, 2013, 07:38 AM
quad lover
United States, MI, Ann Arbor
Joined May 2009
166 Posts
Question
prop guards and flight performance/efficiency/what works and why?

the title says it pretty well. This is my quad. It is a DJI Flame Wheel 450, with some Gens Ace motors, and the 30 amp DJI ESC's, and NAZA FC. The foam prop guard I have put on it has caused a significant decrease in flight time and a jump in amps used.

I don't have a watt meter or anything, but the weight of the entire foam addition, with lights and glue, and everything, is 195 grams. Total weight without battery = 917 grams.

My question is this: why does this thing cause so much drag, even though it's not even in the prop wash, and what can I do to make it better, if anything. What other easy (within reason) prop guard designs have people tried that did not decrease flight times by any significant amount? Any successful designs out there?

I've been looking around, trying to find one, buy one, build one, design one, for a long time, without success. They have all had some problem or another, and this latest one caused a significant drop in flight times, by about 1/3!
john-doe is offline Find More Posts by john-doe
Last edited by john-doe; Apr 03, 2013 at 09:41 AM. Reason: add picture
Reply With Quote
Sign up now
to remove ads between posts
Old Apr 03, 2013, 09:42 AM
Hovering my 85" Katana
Robert Youens's Avatar
Austin, Texas
Joined Mar 2006
924 Posts
My experience indicates that your problem isn't drag induced by prop guards, it is weight added. Consider doing a test, adding weight vs flight time. I think it will open your eyes to the impact of this single variable. I postulate that you will see the same loss of flight time regardless if the weight is simple increased or similar weight in prop guard is added.

The single largest factor in flight time is prop loading. To over simplify, drop weight or increase prop size to increase flight time. I say, "over simplify" since increasing prop size must be associated with adjustment to power and flight control.
Robert Youens is offline Find More Posts by Robert Youens
Reply With Quote
Old Apr 03, 2013, 10:09 AM
quad lover
United States, MI, Ann Arbor
Joined May 2009
166 Posts
Wow, that is actually even more helpful than I had hoped for. Prop loading (I'm thinking you mean something along the lines of how much energy is used by a given propeller at different payloads) is something I never even thought of, at all.

But if you're saying that the energy used by a given propeller across different payloads (and thus different RPMs) has a highly exponential curve, then I can see why the change in weight would cause a drastic loss of efficiency, and thus flight time, beyond that which could be explained by the weight alone.


You've given me a lot to think about. If you have any links or anything that you can point me to for good reading, that would definitely be useful too. Great info. Thanks!
john-doe is offline Find More Posts by john-doe
Reply With Quote
Old Apr 04, 2013, 05:34 PM
Registered User
United States, OR, Portland
Joined Aug 2011
462 Posts
Even though you made a 'guard', you've also made is propellor "shroud" as opposed to a propeller 'duct'. The duct being longer, and usually discussed under the term 'ducted fan'. The fans create a much higher pressure difference between the inlet and outlet - and a higher prop loading ( total force created by the prop divided by the swept area of the prop).

The shroud has the aerodynamic consequence of preventing radial airflow off the prop tips and thereby reducing tip vortices (energy loss). BUT, the inlet and outlet shapes have to be smooth and specifically shaped, and the tip clearance has to be very small. Most people seem to have found the benefit is so small, it doesn't offset the weight. Also the other exposed area tends to make the quad more susceptible to wind (remember, not all wind is horizontal)

Do Google search on "quadcopter prop shroud" for pics and more info.
Good luck with the project.
Jim
Jem3 is offline Find More Posts by Jem3
Reply With Quote
Old Apr 04, 2013, 10:24 PM
quad lover
United States, MI, Ann Arbor
Joined May 2009
166 Posts
very good! Even more helpful info. I may end up building a ducted fan type setup (something more aerodynamic and efficient than what I've got).

And definitely some bigger motors and props! Thank you for the tip(s).
john-doe is offline Find More Posts by john-doe
Reply With Quote
Old Apr 04, 2013, 10:49 PM
Too Many Thread Subscriptions
TheFernMan's Avatar
United States, FL, Miami
Joined Jul 2012
2,117 Posts
Don't waste your time and just fly without that huge thing around and break props like the rest of us. Once you get better, you won't be breaking as many props
TheFernMan is offline Find More Posts by TheFernMan
Reply With Quote
Old Apr 04, 2013, 11:20 PM
quad lover
United States, MI, Ann Arbor
Joined May 2009
166 Posts
Quote:
Originally Posted by TheFernMan View Post
Don't waste your time and just fly without that huge thing around and break props like the rest of us. Once you get better, you won't be breaking as many props

Well I thank you for the sentiment, but actually I've never broken a prop (at least not on a quad). Then again, a quad is the only aircraft I've ever had that leveled itself when I dropped the transmitter.

The reason for the prop guard is only one: safety. It all goes back to an incident I had years ago. I used to fly powered paragliders. One night I was working on mine in the garage, because the engine wouldn't start. So since I had it apart, the cage was off, and VERY unexpectedly, the engine started on the lightest pull (a pull-start engine). It came at me, and since the throttle was in my hand, I squeezed it all the way down in reaction (a flynch reaction, as I tried to shield myself from this lunging machine), and the prop thus got up to as high an RPM as it could in the half second before it hit me. I was in shock, and lay on the ground for a moment, before I had someone drive me to the ER. I was as lucky as I could have been, with no permanent damage, just lots of blood from my shoulder. But it nearly gave me PTSD, and to this day, I insist on guards like this one. Plus, I like to fly in close quarters.

PS that thing had a 4 foot propeller, and a 25 HP engine.
john-doe is offline Find More Posts by john-doe
Reply With Quote
Old Apr 04, 2013, 11:25 PM
Registered User
CG Photo's Avatar
United States, CA, Fresno
Joined Feb 2013
1,199 Posts
I find that I loose about one minute of flight time for each 100 grams of weight I add to my Hexa F550.
CG Photo is online now Find More Posts by CG Photo
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Cool Watch how our motor performs in 3D hovering flight YXmotor Indoor Pattern/F3P 3 Jan 30, 2013 12:09 PM
Discussion EZ V929 Performance Prop Upgrade ! harrye Mini Multirotors 11 Jan 13, 2013 06:16 PM
Discussion Differences in flight performance on Tricopter FCs. acetech09 Multirotor Electronics 1 Jan 06, 2013 02:16 AM
Discussion My prop guard idea - will this work? TheNiceGuy Multirotor Talk 18 Jun 02, 2012 08:56 AM
Discussion Why is 2 blade prop more efficient then 3 blade prop? butters149 Modeling Science 30 Sep 05, 2008 11:36 PM