HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Nov 30, 2013, 04:52 AM
Registered User
awacsCZE's Avatar
Joined Aug 2010
305 Posts
Discussion
Facing of EDF fans under wings

Hello guys,
I am building A320 and I want to mount the engines under wings. I want to ask, how the EDF should be aligned, like if I am mounting the propeller, if it should be down, up, right, etc..
Also small question, if it is really bad, if the engines are set in V shape. Front of the engine is further from the fuselage, than the back for about 3-5mm. Somehow, during build, it moved and final thing is like this. I want to know, if it matters and should be repaired, or not

Thank you very much
awacsCZE is offline Find More Posts by awacsCZE
Reply With Quote
Sign up now
to remove ads between posts
Old Nov 30, 2013, 05:31 AM
Big gov never Works
St. Martin's Avatar
Skunk Water, Rhode Island
Joined Jul 2002
12,454 Posts
If both are equally set outward, this will not be an issue. While EDF's do have torque issues, they are minor, as compared to open props. P-factor, is non-existant. As is asymmetrical thrust.

My opinion, because of the low thrust line, some down thrust may be necessary.

Fuzz
St. Martin is online now Find More Posts by St. Martin
Reply With Quote
Old Nov 30, 2013, 05:39 AM
Registered User
awacsCZE's Avatar
Joined Aug 2010
305 Posts
Quote:
Originally Posted by St. Martin View Post
If both are equally set outward, this will not be an issue. While EDF's do have torque issues, they are minor, as compared to open props. P-factor, is non-existant. As is asymmetrical thrust.

My opinion, because of the low thrust line, some down thrust may be necessary.

Fuzz
Thank you I was worried, that it will tore the wings apart from fuse

How much down you think it should be?
awacsCZE is offline Find More Posts by awacsCZE
Reply With Quote
Old Nov 30, 2013, 09:03 AM
Registered User
Larry Dudeck's Avatar
Williamsville, NY, USA
Joined Sep 2000
4,508 Posts
The A320 is a low wing plane so the center of mass of the plane will be somewhere above the middle of the thickest part of the wing. With the fans mounted below the wing, the fan thrust will set up a moment arm, equal to the thrust multiplied by the distance between the fan's centerline and the center of mass. This moment arm will cause the front of the plane to pitch up. Further, the amount of pitch-up will increase as the thrust increases.

This can be counteracted by adding some down thrust as suggested by St. Martin. This will work perfectly a some particular throttle setting but the pitch-up, at varying degrees, will still be present at other power levels.

The more elegant, albeit more expensive, solution is to employ a gyro on the elevator. The gyro would automatically compensate for any pitch-up.

Although I haven't checked lately, Tower Hobbies as well as others used to market inexpensive gyros.
Larry Dudeck is offline Find More Posts by Larry Dudeck
Reply With Quote
Old Nov 30, 2013, 11:29 AM
It wasn't me...
DanSavage's Avatar
Trabuco Canyon, CA
Joined Nov 2000
4,572 Posts
2 degrees down when viewed from the side.

This will prevent the model from nosing up under power.

My brother Daren built a model of the Airbus A300-600ST Super Transporter (Beluga) and this is where we set the fans. Flew perfectly at all power settings with no thrust-related pitching.

Personally, I would not worry about setting out-thrust on the fans. If you lose a fan with a model that has the fans set that far out on the wings, the model is going to snap into a tight spiral and crash before you have time to recognize what's happening and do anything to stop it.

Daren Savage's Beluga Test Flight (4 min 50 sec)
DanSavage is offline Find More Posts by DanSavage
Reply With Quote
Old Nov 30, 2013, 01:26 PM
Big gov never Works
St. Martin's Avatar
Skunk Water, Rhode Island
Joined Jul 2002
12,454 Posts
Wow..that was a long time ago, Dan! Does Daren still have that? That would sound so nice with two of the high count blade fans.

Fuzz
St. Martin is online now Find More Posts by St. Martin
Reply With Quote
Old Nov 30, 2013, 05:22 PM
Registered User
awacsCZE's Avatar
Joined Aug 2010
305 Posts
Thank you very much guys, engine number one in position, number two will follow :-)

Only one small question, this thrust-related pitch, if occur, what should I expect? Some rapid stall, like bad CG, or something, that can be handled?
awacsCZE is offline Find More Posts by awacsCZE
Reply With Quote
Old Dec 01, 2013, 02:00 AM
It wasn't me...
DanSavage's Avatar
Trabuco Canyon, CA
Joined Nov 2000
4,572 Posts
If you have the fans under the wings and you don't put down thrust, the pitch trim will change with every change in power, just like the full-size.

But with models, you generally want them to simply accelerate or decelerate with power changes. That's why prop-driven models have down thrust. Full-size prop-driven airplanes don't have down thrust.

Without down thrust, when you add power the model will want to climb. When you reduce power the model will descend.

Every change in thrust will require a corresponding change in pitch trim. While this works fine on full size, it's a major pain with models because you're always having to adjust the elevator trim when you move the throttle stick.

The strength of this characteristic is dependent on how much thrust the fans are producing. If you go from idle to full-power at low-speed, the model will pitch up abruptly. If you go from full-power to idle at low speed, the model will pitch down abruptly.
DanSavage is offline Find More Posts by DanSavage
Reply With Quote
Old Dec 01, 2013, 02:02 AM
It wasn't me...
DanSavage's Avatar
Trabuco Canyon, CA
Joined Nov 2000
4,572 Posts
Quote:
Originally Posted by St. Martin View Post
Wow..that was a long time ago, Dan! Does Daren still have that? That would sound so nice with two of the high count blade fans.

Fuzz
Pieces of it. On its last flight one of the fans cut out and it rolled over into a tight, nose-down spiral and crashed before we realized what was happening.
DanSavage is offline Find More Posts by DanSavage
Reply With Quote
Old Dec 01, 2013, 06:57 AM
Registered User
awacsCZE's Avatar
Joined Aug 2010
305 Posts
Quote:
Originally Posted by DanSavage View Post
The strength of this characteristic is dependent on how much thrust the fans are producing. If you go from idle to full-power at low-speed, the model will pitch up abruptly. If you go from full-power to idle at low speed, the model will pitch down abruptly.
Thank you very much But if I can have one more "annoying" question.

When you write abruptly, can I ask how much? I mean, if somehow, I will have it wrong and add the thrust on the takeoff, if I will experience rapid climb and stall and crash like here http://youtu.be/sewddfVb-ng?t=2m12s , or it will be like needing small corrections of the elevator pitch.
Sorry for so many question, but I want to figure out, what can happen


EDIT: Latest check of plane showed, that too much weight which I used to fix the plane caused, that after tooking it off the engine bounced up and now it is 5mm up, will need to redo that
awacsCZE is offline Find More Posts by awacsCZE
Last edited by awacsCZE; Dec 01, 2013 at 11:42 AM.
Reply With Quote
Old Dec 01, 2013, 05:21 PM
It wasn't me...
DanSavage's Avatar
Trabuco Canyon, CA
Joined Nov 2000
4,572 Posts
No, it's not as abrupt as a aft-CG condition seen in the video.

Small changes in throttle will require small changes in elevator trim. Large changes in throttle will require large changes in trim.
DanSavage is offline Find More Posts by DanSavage
Reply With Quote
Old Dec 02, 2013, 02:52 PM
Registered User
awacsCZE's Avatar
Joined Aug 2010
305 Posts
Thank you very much :-)
I hope it will end well :-)
awacsCZE is offline Find More Posts by awacsCZE
Reply With Quote
Old Dec 03, 2013, 11:41 AM
Registered User
Rich Uravitch's Avatar
Florida
Joined Sep 2001
361 Posts
Similar configuration. -3 degrees from fuselage reference line, no noticeable power trim change.
Rich Uravitch is offline Find More Posts by Rich Uravitch
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Sold Micro (Bat wing 30mm edf jet) Bind and fly. crispy1074 Aircraft - Electric - Micro & Indoor Airplanes (FS/W) 6 Nov 27, 2013 09:57 AM
Discussion Covering an under cambered wing modeltronics The Builders Workshop 11 Nov 04, 2013 12:42 AM
Wanted Cheap BNF flying wing under 34" wingspan andrewtexas123 Aircraft - Electric - Airplanes (FS/W) 2 Sep 20, 2013 04:55 PM
Help! Mounting (2) Ducted fans under the wings of a foamy glider??? axemanclint Micro EDF Jets and Power Systems 4 Jul 09, 2011 09:29 AM
Discussion Ducted fan under the wing? PurpleHaze The Builders Workshop 6 Mar 21, 2007 07:52 PM