HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old May 03, 2013, 06:48 PM
Registered User
RC Erik's Avatar
United States, FL, Naples
Joined Oct 2011
169 Posts
Discussion
25% Cub air ducting for ESC - Motor

I saw Joe Smith do this on some of his larger 3DHS electric planes, thought I would try it for the Cub. I know its not a work of art but its my first attempt.
RC Erik is offline Find More Posts by RC Erik
Reply With Quote
Sign up now
to remove ads between posts
Old May 03, 2013, 06:49 PM
Registered User
RC Erik's Avatar
United States, FL, Naples
Joined Oct 2011
169 Posts
More pics
RC Erik is offline Find More Posts by RC Erik
Reply With Quote
Old May 03, 2013, 06:49 PM
Registered User
RC Erik's Avatar
United States, FL, Naples
Joined Oct 2011
169 Posts
And final -
RC Erik is offline Find More Posts by RC Erik
Reply With Quote
Old May 03, 2013, 07:00 PM
Registered User
RoysRC's Avatar
United States, FL, Naples
Joined Sep 2011
17 Posts
Wow, very niiiice!
RoysRC is offline Find More Posts by RoysRC
Reply With Quote
Old May 20, 2013, 03:54 PM
...design-build-fly-publish...
eye4wings's Avatar
Ware, herts. U.K.
Joined Sep 2008
3,480 Posts
Hi Erik,
I am sure properly ducting incoming air towards motor and ESC will have good effect - but are you aware that for every square inch of intake you need one and a half square inches of free outlet?

With planes like the Cub that can be tricky to achieve. Maybe leave the side windows open? - lots of pilots fly their cubs open.

I assume that as you are going to the trouble of ducting you are running motor and ESC close to their top limits of power?

Robin
eye4wings is offline Find More Posts by eye4wings
Reply With Quote
Old May 22, 2013, 06:16 AM
Supersonic Engineering
GordonTarling's Avatar
UK, Greater London, Uxbridge
Joined Mar 2001
3,122 Posts
Robin - sorry to burst your bubble, but the increased outlet area is just another one of those perpetuated myths. For proof, take a look at a Spitfire's underwing coolers - you won't see increased outlet area there. Simply put, if the outgoing and expanded air is restricted, it simply speeds up and gives you a bit more thrust.
GordonTarling is offline Find More Posts by GordonTarling
Reply With Quote
Old May 22, 2013, 07:21 AM
...design-build-fly-publish...
eye4wings's Avatar
Ware, herts. U.K.
Joined Sep 2008
3,480 Posts
Gordon, whilst I appreciate the view, know the theory of how a wing generates lift and am aware that it is dangerous to take an argument to it's logical extreme I think my 'bubble' is still intact.

According to the view you stated, there should be actual benefit from restricting outlet size to a minimum - or perhaps eliminating it altogether... in which case why does the spitfire you mentioned need to open the exhaust vent for better cooling while ground running the engine?
(and why do ducted fan models not restrict their outlets to get the added push?)

Actually the flap that drops to increase the cooling for the conventional radiator cooling system adds venturi effect which deflects the outside airflow causing a lower pressure area that then encourages the airflow through the radiator to speed up to equalise the pressure.
This is equivalent to increasing the outlet area.

To take the logical extreme of closing off the outward airflow altogether there would in effect be a high pressure air dam stopping air entering the intake at all. Any air that did enter would have to back up and spill out of the sides of the intake causing only turbulence and negligible cooling effect over the heated equipment.
Again if what you say is true (I am no doubt misunderstanding the 'extra thrust' bit!) if I make a tube that is smaller at the outlet end than the intake end, put a heat source in it, mount it on wheels and give it a push it ought to accelerate?

I would hope neither of us would expect such things to work.

To talk a bit more of the Spitfire's cooling system, Mr R Mitchell would have preferred not to have needed external cooling equipment at all, designing after the Schneider trophy winner's system which ducted water heated by the engine through the wing's surface where it caused little appreciable drag, but the exigencies of wartime aircraft production (ease of manufacture and cost) and the fact that surface cooling would be more vulnerable to damage, he had to put a minimal cooling system on the outside of the aircraft - and in the higher pressure under-wing situation. The reason why the intake area is larger than the outlet (when closed) is that it had to be of sufficient size that it could still pass enough air for the aircaft's cooling needs when the exhaust flap was open.

It is of course self-evident that cooling is better when the outlet is open - and is vital when the aircraft is not travelling at sufficient speed for the airflow being forced through the system to provide adequate cooling.

One might wonder why it was not possible to partially retract the cooling sytem into the wing during flight.... but I suspect the reason is again cost (and the technical difficulty of devising such a system), but it would have given any aircraft a speed advantage by reason of decreased drag.

So while I am always open to being corrected I would like a lot more evidence before changing my view from the tried and tested rules of thumb that we apply to our hobby.

In any case most of us know that the most efficient way of coping with heat is not to put it there in the first place - and use equipment that is more than adequate to do what we need without breaking into a sweat... which is why I wondered if, in order to need more directed cooling airflow, RC Erik was running his gear close to it's limit.
eye4wings is offline Find More Posts by eye4wings
Reply With Quote
Old May 22, 2013, 10:06 AM
Registered User
RiBell's Avatar
Canada, BC, Abbotsford
Joined Jan 2003
4,756 Posts
Quote:
Originally Posted by GordonTarling View Post
Robin - sorry to burst your bubble, but the increased outlet area is just another one of those perpetuated myths. Simply put, if the outgoing and expanded air is restricted, it simply speeds up and gives you a bit more thrust.
Converging diverging duct theory and practice work in jet engine propulsion. However they are not practical methods of providing cooling for motors/ ESC's/ batteries/ or even wet fuel engines (gas/glow) in our models
Quote:
Originally Posted by eye4wings View Post

It is of course self-evident that cooling is better when the outlet is open - and is vital when the aircraft is not travelling at sufficient speed for the airflow being forced through the system to provide adequate cooling.
I agree with Robin and will always try to have an air outlet at least as big as the inlet. Even blocking off the inlet if necessary.
As a kid flying full size aircraft with my dad. We were right on the edge of having the engine overheat all the time.
All we did was fabricate a panel in from of the oil cooler. Such that the oil cooler inlet cooling air was reduced to being the size of the oil cooler. and sealed the air leaks between the inlet and outlet side of the cowl. Forcing the air to pass through the cooling fins. Net change was about 150 deg drop in cylinder temps.

I've been an advocate of having enough cooling air exit ever since.
Rick
RiBell is offline Find More Posts by RiBell
Reply With Quote
Old May 22, 2013, 12:13 PM
DFC~ We Do Flyin' Right
bsbauman's Avatar
USA, GA, Atlanta
Joined Nov 2008
14,513 Posts
While I believe there might possibly be some positive affect on high performance planes, I do not think your efforts will make any difference for a J-3 Cub.

Have you taken any temp measurements from before and after your modification to see if there was any positive affect?

IMO on a Cub, I would rather it simply look right; rather than cutting all those holes... eek.
Check out how much cleaner it looks unmodified and without the big gaping hole under the spinner. Here is a 1/4 scale I just picked up
bsbauman is offline Find More Posts by bsbauman
RCG Plus Member
Latest blog entry: Snuggles Speaks
Reply With Quote
Old May 22, 2013, 11:17 PM
Registered User
RC Erik's Avatar
United States, FL, Naples
Joined Oct 2011
169 Posts
I havent taken any before and after temp readings but I did cut the large hole in front for more air since it gets pretty hot down here in the summer time.
RC Erik is offline Find More Posts by RC Erik
Reply With Quote
Old May 23, 2013, 01:33 AM
...design-build-fly-publish...
eye4wings's Avatar
Ware, herts. U.K.
Joined Sep 2008
3,480 Posts
Glad to see you're still checking out your thread Erik - was beginning to wonder if you'd abandoned us to argue among ourselves!

Any of us flying in hot weather are at a slight disadvantage from flying in cold weather so far as cooling the power train goes. If the ambient air temperature is higher there will be less cooling potential in it.

If you don't have any way of checking actual temperatures of the equipment you are carrying (most of us don't) then it is worth touching motor, ESC and batteries immediately after a test run - or after landing. If any of the three are too hot to leave your finger on them THEN you know you have a problem!

As bsbausman has said (and I agree) the apperance of a scale model is of great importance - so we would prefer to have our scale models look right and therefore use larger power components which will not heat up so badly as to be a problem.

As you have increased your cooling intake it appears that you are not that concerned about appearance, but my first point was that however big you make the INtake, without sufficient OUTlet the air is not going to flow over the heat-producing bits at all - so it's a waste of time and effort!

Robin
eye4wings is offline Find More Posts by eye4wings
Reply With Quote
Old May 23, 2013, 07:45 AM
DFC~ We Do Flyin' Right
bsbauman's Avatar
USA, GA, Atlanta
Joined Nov 2008
14,513 Posts
Quote:
Originally Posted by RC Erik View Post
I havent taken any before and after temp readings but I did cut the large hole in front for more air since it gets pretty hot down here in the summer time.
You can get a small laser pointer-like temp gauge for not much cost, but definitely use the method described by Robin as well. If you cant keep your finger on it, your cooling is still problematic or inadequate components are installed. I also fly in the southern heat and know it can be problematic.

Also take note of that last paragraph below. What we are saying is that you might have simply created an opening that no air can enter, it is affectively a speed brake.

Quote:
Originally Posted by eye4wings View Post
Glad to see you're still checking out your thread Erik - was beginning to wonder if you'd abandoned us to argue among ourselves!

If you don't have any way of checking actual temperatures of the equipment you are carrying (most of us don't) then it is worth touching motor, ESC and batteries immediately after a test run - or after landing. If any of the three are too hot to leave your finger on them THEN you know you have a problem!


As you have increased your cooling intake it appears that you are not that concerned about appearance, but my first point was that however big you make the INtake, without sufficient OUTlet the air is not going to flow over the heat-producing bits at all - so it's a waste of time and effort!

Robin
bsbauman is offline Find More Posts by bsbauman
RCG Plus Member
Latest blog entry: Snuggles Speaks
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
For Sale 90W motor and 20 AMP ESC for $25 pdansalvish Aircraft - Electric - Power Systems (FS/W) 0 Apr 04, 2013 06:24 PM
For Sale UMX BEAST 3D, DX6i, E-flite 15 Ducted Fan, Celectra Chargers, 10g motor, 6a Plush ESC Lilbanks96 Non R/C Items (FS/W) 7 Feb 16, 2013 06:51 AM
Discussion 20 To 25 cell lipo set up for ducted fan propulsion? HURRICANE FANS Power Systems 2 Jan 07, 2013 08:30 PM
For Sale WOWPLANES B-25 with SCORPION MOTORS and ESC's.LAST REDUCTION AND ADDING AIR RETRACTS! Tumbler Aircraft - Electric - Airplanes (FS/W) 6 Nov 11, 2009 06:58 PM
Sold Air Sally Ducting w/Hoffman Motor and fan for Alfa F-86 Mikemynameis Aircraft - Electric - Jets (FS/W) 4 Apr 01, 2009 06:12 PM