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Author Topic: Tried Gurney flaps yet? What's your conclusion?  (Read 2004 times)

Offline Bob Hunt

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Tried Gurney flaps yet? What's your conclusion?
« on: August 22, 2022, 09:27:52 AM »
At the 2021 Nats I saw two models that had vertical plates attached to the trailing edge of the elevators. There may have been others that had them as well, but the ones I saw were on Paul Walker's plane and on Dennis Nunes' plane. I didn't get the opportunity to speak with either pilot about what they were or how they affected their models' flight. But, in typical "let's try it and see what happens fashion" when I got home I made up what I thought was a representative pair of plates and attached them to the trailing edge of the elevators on my Crossfire Extreme. The result was a model that not only tracked and turned better, but also one that exhibited a much better "lock" after a corner. They stayed on the model for the remainder of the year after that, and they are still on the model to this day. I was asked at a local contest after the Nats if I liked them and I responded, "Let's put it this way; if anyone tries to remove them I'll break their arm!"

I found out that it was Chris Cox who suggested and first tried these plates (I understand that they are called Gurney Flaps; so named for Dan Gurney who supposedly used them on the rear wing of his race car - that is unconfirmed...).   

I have just put a set onto my old and trusty Genesis Extreme and intend to fly it tomorrow for evaluation (it's raining here today...). What I'd like to know is how many of you have tried these plates/flaps, and if you have, what are your findings?

I'm attaching a photo of the plates/flaps that I attached to the Crossfire Extreme for reference. One thing I did note was that I used about 3 to 5 percent more battery. That seemed logical due to the increased drag.

Later - Bob Hunt



   

Offline Gerald Arana

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #1 on: August 22, 2022, 09:56:57 AM »
Hi Bobby,

The RC pattern guys do something like that on their rudders. They have a very thick (1/2" maybe) TE.

When I saw that I wondered if it would work on elevators or flaps, but haven't gotten around to trying it.

You have made it very easy for me to do now.

Thank you, Jerry

Online Howard Rush

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #2 on: August 22, 2022, 10:28:34 AM »
I saw one airplane at the world champs with those things.
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Offline phil c

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #3 on: August 22, 2022, 10:49:31 AM »
I've read about them but not tried t hem.

I built a larger version of a combat plane- went from 430 squares to 550.  Initially it used a smaller tail, propotionately like the F2D style elevators.  Not very big.  OK performance but couldn't be trimmed to turn very tight and "pointability" was poor.

While building the bigger wing I got smart and upped the stabilator from 9" on the 43" F2D up to 16in x 3in. tapered.  The larger plane with a larger stabilator was a huge difference.  Maybe too good.  It turns promptly and stops turning immediately.  The smaller F2D planes are hard to get to perform as well in maneuvers.  Besides being fast, they have a tendency to turn before I'd like them to and then they are a bit reluctant to stop.

I can't remember any full scale with the gurney setup.  Maybe a crop duster.  Other planes need to conserve fuel.

Phil C
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Online Brent Williams

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #4 on: August 22, 2022, 11:05:24 AM »
It would be very interesting to determine where the crossover point for effectiveness is in relation to height versus drag.  The boundary layer is said to be quite close to the surface. 
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Offline Gaylord D Elling

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #5 on: August 22, 2022, 12:27:02 PM »
Hi Bob. As you may know from Frank M., I have them on two airplanes. They are staying on, and any future planes will have them as well. "Locked in" is the best way to describe them. Matt Colan has them, and that is what mine look like.

Offline Perry Rose

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #6 on: August 22, 2022, 12:54:55 PM »
I've tried Matt's style (1/8 x 1/4 strips) fastened/ double stick taped to the trailing edge and had good luck on planes that had tapered elevators. Not so much on planes with slightly or not tapered at all elevators. I removed them on planes that showed little if any improvement and kept them on the ones that showed improvement. I tried them on several planes. I found that the turn rate can be changed using strips on the top or bottom only. There's not much of a drag penalty. Matt's method is more eye pleasing as you can color them to match the plane and the plan form isn't changed. I've used composite strips and balsa both work equally well.
I may be wrong but I doubt it.
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Offline Tim Stagg

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #7 on: August 22, 2022, 01:25:25 PM »
Bob at your suggestion last fall I tried them a chipmunk of my own design and saw very little difference in how the plane flew. I tired them again this year on my Gypsy due to having less than needed thrown in my elevator due to some mechanical geometry issues...and they did a great how of increasing the amount of elevator authority i now have.

I think of them as a trimming tool. They may work for an application and they may not depending on many other factors involved on any airplane. I would give them a try, you never know how they might affect things.

Tim
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Offline Dan McEntee

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #8 on: August 22, 2022, 02:27:31 PM »
  I was at Oshkosh this year and one thing I wanted to look at is a new airplane being developed by Van's Aircraft, the RV-15. The prototype is a high wing monoplane, all metal, and looks to be an entry into the bush plane market. I was with one of the chairperson of the C/L area of KidVenture, who has built an RV-9 and was interested also. He was mostly interested in how the elevator functions worked so we walked around to the back of the airplane while everyone else was focused on the nose. Guess what we say on the trailing edge of the left elevator?? Yes, it was only on the one side. While we were looking at it, a representative of the company came out of the small tent they had erected, and with a Sharpie, wrote a note on the bare aluminum, "This is for experimentation purposes only !!" I think there is a YouTube tour and walk around of the airplane and if you look closely you can see the note written on the left (port) elevator!! The rep got sooooooo tired of being asked that question, that he grabbed the Sharpie and posted the note!! I guess stay tuned for further developments as they become available!!
  Interesting coincidence, isn't it!?
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Online Matt Colan

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #9 on: August 22, 2022, 03:18:32 PM »
I put them on the current airplane early in its life and the change was dramatic! I could turn the plane harder get also find a much more consistent lock on the bottom. A win-win!!  Like Perry and Gaylord posted, mine are 1/8x1/4Ē tapered balsa, more like a wedge than a gurney flap. After the initial test I airbrushed them black so I didnít have to worry about matching the paint and glued them on permanently. These will be on every future airplane in some form or fashion. Chris Cox had a new version on his Hellcat at the NATS I am planning to test on Dracula and see if I notice the difference. He had very thick tape on the elevators, about .020Ē thick (if memory serves correct) and had the same effect.
Matt Colan

Offline Motorman

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #10 on: August 22, 2022, 05:38:22 PM »
Any guidance on this, how tall and how long? Just on the elevator or flaps too? Square with the hinge line or follow the taper?

Offline Mark Mc

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #11 on: August 22, 2022, 06:21:49 PM »
More than I ever wanted to know about Gurney flaps:

https://www.sciencedirect.com/topics/engineering/gurney-flap

Mark

Online Jim Hoffman

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #12 on: August 22, 2022, 09:06:15 PM »
I tried them on one airplane and really could not discern a performance improvement in the corner exits.  I know others have been able to sense a benefit.  I did notice measurable increase in battery power consumption.  I went to partial span (1/3) doo-dads and the power issue was reduced.  Still nothing I could discern in performance.

I do have zig zag tape about 1/2 inch aft of the stab LE

I am going to try Chris Coxís .020 strips next opportunity
« Last Edit: August 22, 2022, 10:43:35 PM by Jim Hoffman »

Offline Bob Hunt

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #13 on: August 23, 2022, 06:14:45 AM »
I saw one airplane at the world champs with those things.

Let me guess; was it yours...?   ::)

Bob

Online Matt Colan

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #14 on: August 23, 2022, 06:18:25 AM »
I tried them on one airplane and really could not discern a performance improvement in the corner exits.  I know others have been able to sense a benefit.  I did notice measurable increase in battery power consumption.  I went to partial span (1/3) doo-dads and the power issue was reduced.  Still nothing I could discern in performance.

I do have zig zag tape about 1/2 inch aft of the stab LE

I am going to try Chris Coxís .020 strips next opportunity

Took this at appearance judging and this is what he had. I have trip strips on the leading edge of my stab and canít feel anything with them
Matt Colan

Offline John Park

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #15 on: August 23, 2022, 06:36:22 AM »
Two thoughts on this: 1) It is common, on free-flight models (especially rubber-powered), to make trim changes using lengths of 1/16" or 3/32" sq. balsa strip stuck above or below the TE of the relevant surface: this is simpler and neater than messing about with things like card or aluminium trim-tabs, and we all call it a Gurney Flap.  2) Many years ago, when it was normal on C/L stunters for flaps and elevators to be tapered to a knife-edge at the TE, somebody found that a thick, square TE section gave a sharper and more positive control response, especially around neutral; since when, I note, the control surfaces of many C/L aerobatic models remain untapered.  The arrangement shown above, with Gurney Flaps top and bottom on the elevators, therefore seems to be just an extension of the 'thick, square TE' principle: the next time I fly an old Peacemaker of mine (with the original, small-area tailplane), I'll add an 1/8" sq. Gurney Flap to the elevator, top and bottom, and see what difference I can detect.
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Offline Mike Alimov

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #16 on: August 23, 2022, 01:12:40 PM »
(...)  The arrangement shown above, with Gurney Flaps top and bottom on the elevators, therefore seems to be just an extension of the 'thick, square TE' principle(...)

Bob, I agree with John here: the Gurney flaps are a more extreme expression of essentially the same principle.  The traditional (tapered) stunt control surfaces usually have 2-3 degrees of taper, which creates a few degrees of movement range where those surfaces "drown" in the dead zone of the slipstream, blanketed by a thick wing or stabilizer ahead of them.  In order for the control surfaces to start working effectively, they need to "protrude" from that dead zone and be ready to create a cambered airfoil once deflected.
  The Gurney flaps achieve that by extending a crude lip into an energized portion of the slipstream, and have an effect of deflecting a mini-flap at the edge of a flap.  They do so, however, at a considerable cost of extra drag, which is what has been reported here in the form of greater battery consumption.  No aerodynamics textbook will advise exposing rectangular cross sections to oncoming air.

A similar, but less draggy and more aesthetically pleasing option is to reduce or eliminate flap and/or elevator taper, which has the effect of deflecting those surfaces by 2-3 degrees up and down at the same time.  If one desires, they can even produce surfaces with negative taper, although that might be excessive and result in an overly sensitive ship.

The composite Ripslinger prototype which you had a chance to fly at the last Snow contest has 1/4" thick untapered flaps and elevators.  It turns very quickly and locks solid after a turn.  We liked it enough to carry this feature into all Ripslinger series going forward.  The Ripslinger II flown by Gabe posted a high score of 516 at the 2022 Nats Finals, besting all Juniors and Seniors that day.

Offline Claudio Chacon

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #17 on: August 23, 2022, 01:32:06 PM »
I put them on the current airplane early in its life and the change was dramatic! I could turn the plane harder get also find a much more consistent lock on the bottom. A win-win!!  Like Perry and Gaylord posted, mine are 1/8x1/4Ē tapered balsa, more like a wedge than a gurney flap. After the initial test I airbrushed them black so I didnít have to worry about matching the paint and glued them on permanently. These will be on every future airplane in some form or fashion. Chris Cox had a new version on his Hellcat at the NATS I am planning to test on Dracula and see if I notice the difference. He had very thick tape on the elevators, about .020Ē thick (if memory serves correct) and had the same effect.

Hi Matt,
Can you post a pic of your "gurney devices"?
Thanks...

Later,
Claudio.

Online Matt Colan

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #18 on: August 23, 2022, 02:20:12 PM »
Hi Matt,
Can you post a pic of your "gurney devices"?
Thanks...

Later,
Claudio.

Hi Claudio, here is what I have on my plane. They run full span along the elevator
Matt Colan

Offline Claudio Chacon

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #19 on: August 23, 2022, 02:45:13 PM »
Thanks Matt!
I'll try them on my plane too...with some double sided tape.

Cheers!
Claudio.

Offline Mike Palko

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #20 on: August 23, 2022, 02:47:01 PM »
Very interesting to see the different variations and different results. Seems several variations need to be tried to find optimal results.

Bob,

Your gurney flaps are the only version Iíve seen that increase the area of the elevators. Have you tried a gurney flap flush with the elevator trailing edge? Curious if you would get different results without the added area.

Mike

Offline James H. Dean

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #21 on: August 23, 2022, 03:42:44 PM »
I use the tape style gurney flaps on my profile trivial pursuit. I used 2 layers of clear "detacked " gorilla tape. the difference was night and day. the dimensions of the taped area are 1/4" x 8", located from the inside edge of the elevators out. I know using the normal style gurney flaps if too tall, it will greatly affect battery consumption. Ask Dennis Nunes.

Online Matt Colan

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #22 on: August 23, 2022, 05:35:43 PM »
I use the tape style gurney flaps on my profile trivial pursuit. I used 2 layers of clear "detacked " gorilla tape. the difference was night and day. the dimensions of the taped area are 1/4" x 8", located from the inside edge of the elevators out. I know using the normal style gurney flaps if too tall, it will greatly affect battery consumption. Ask Dennis Nunes.

How did you de-tack the gorilla tape?
Matt Colan

Offline James H. Dean

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #23 on: August 24, 2022, 02:40:44 PM »
layed it out on my cutting mat. when pulled up off of that it was detacked enough that it didnt cause any problems when i needed to pull it off to place it where i wanted it.

Offline Teodorico Terry

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #24 on: August 25, 2022, 05:46:36 AM »
It should also be noted that Matt's plane has end plates which will also affect how the elevator works.  It is interesting to see that some of the "tricks" used in R/C pattern are crossing over into the C/L side of things. The Gurney flaps are relative common on rudders although I have heard that they were added to increase drag and slow down the model in the downlines. They also tend to be fairly wide.  I have not seen them applied to ailerons or elevators however.

Online Matt Colan

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #25 on: August 25, 2022, 06:01:59 AM »
It should also be noted that Matt's plane has end plates which will also affect how the elevator works.  It is interesting to see that some of the "tricks" used in R/C pattern are crossing over into the C/L side of things. The Gurney flaps are relative common on rudders although I have heard that they were added to increase drag and slow down the model in the downlines. They also tend to be fairly wide.  I have not seen them applied to ailerons or elevators however.

I made a set and tried them on the rudder. I couldnít feel any difference with them so I took them off
Matt Colan

Offline Dave_Trible

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #26 on: August 25, 2022, 07:19:38 AM »
These are interesting and I will try them.  I wonder tho- these devices would cause the elevator to aerodynamically center once control pressure is released. Could this be the 'locked in' feel experienced in corners?  Would a flat plate elevator and/or a plate of the same thickness as the stab do the same?  A drag induced slowing in the dive would also feel pretty positive at the handle.

Dave
« Last Edit: August 25, 2022, 07:49:44 AM by Dave_Trible »
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Offline Steve Helmick

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #27 on: August 25, 2022, 10:29:21 AM »
It's not uncommon to see a "wedge" glued to the bottom of the TE on some HLG's, particularly indoor designs. Basically, a flat bottom airfoil with a "kicker" at the TE to effectively add some undercamber to improve the glide. Different than a Gurney Flap, however, which is normally a chunk of aluminum angle bolted to the TE of the wing or spoiler on a racecar.

As previously pointed out, sticking a wedge of TE stock to various places on AMA Gas FF models is a pretty common trimming method. IMO, the best thing about the trick is that it's more predictable than trim tabs. Kinda ugly, though they're hard to see at 500'+ AGL .  D>K Steve 
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Offline Bob Hunt

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #28 on: August 25, 2022, 11:31:55 AM »
Very interesting to see the different variations and different results. Seems several variations need to be tried to find optimal results.

Bob,

Your gurney flaps are the only version Iíve seen that increase the area of the elevators. Have you tried a gurney flap flush with the elevator trailing edge? Curious if you would get different results without the added area.

Mike

Great question and observation, Mike. I have not yet tried the GFs flush with the TE of the elevators. I have since my last post flown the Genesis Extreme with the GFs installed. These have the vertical pieces positioned about 5/32-inch behind the TE of the elevators. The result: Same as the ones on the Crossfire; lots of extra turn, great groove and amazing lock. I can't fathom that moving them closer to the TE of the elevators will improve the performance, but the only way to actually know is to remove the ones on there now and try moving them closer. Maybe I'll try that in the future; I'm having way too much fun flying this "point and shoot" airplane as it is right now! I would suggest that everyone try moving them back 5/32 to 5/16 inch and see what you get. You might like them even better.

Later - Bob

Offline Dan McEntee

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #29 on: August 25, 2022, 11:39:36 AM »
Are we all talking about the same thing here? Some are talking about simple wedges added to the trailing edges. Some are talking about additions to the trailing edge that are vertical and 90 degrees to the stab center line. More pictures please!
   I remember when these were added to the rear wing on Indy cars and were called "wickerbills" I  do believe. They were added or removed as changes in down force were required depending on the track and speeds required..
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Offline Steve Helmick

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #30 on: August 25, 2022, 11:51:13 AM »
Are we all talking about the same thing here? Some are talking about simple wedges added to the trailing edges. Some are talking about additions to the trailing edge that are vertical and 90 degrees to the stab center line. More pictures please!
   I remember when these were added to the rear wing on Indy cars and were called "wickerbills" I  do believe. They were added or removed as changes in down force were required depending on the track and speeds required..
  Type at you later,
   Dan McEntee

Talking about variations on the theme, IMO. Looks like there's a lot of potential for trying some weird stuff on the TE's...of the elevators, at this point. I'd wonder what would happen if similar things were tried on the wing flaps. As a cautionary note, remember that shedding parts in flight is a no-no!  H^^ Steve
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Offline John Carrodus

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #31 on: August 25, 2022, 04:09:56 PM »
I have seen these on large power boats, mounted on the bottom edge of the transom.

Offline Mel Gray

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #32 on: August 26, 2022, 11:18:33 AM »
Them little air molecules sure are rascally little critters...................  ;<)
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Offline Chris McMillin

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #33 on: September 02, 2022, 10:20:26 AM »
The homebuilt racing plane Tsunami had zero center and little feel in the rudder on the first few flights and I helped glue balsa triangle stock to the trailing edge on each side in hope of affecting more feel. As I recall it wasn't enough...
Chris...

Online Ken Culbertson

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #34 on: September 22, 2022, 02:25:06 PM »
The result was a model that not only tracked and turned better, but also one that exhibited a much better "lock" after a corner.
I was a skeptic until today.  My Trifecta is an excellent performer, but she has a wandering eye.  I practically get stopped by the game warden for hunting without a license.  I have tried just about everything and finally just gave up.  I could keep it level with extreme concentration for the judged level and inverted but I want it to simply grove in level flight between maneuvers while my focus is not on keeping the plane level.  It was beginning to hurt the maneuvers.  Yesterday out of the blue I read something about Gurney in one of the threads and decided to see what all of the fuss is about.  Cut two strips of balsa that gave me a flat plate 1/8" on each side of the elevator.  All monokoted up they don't even look that bad.  It was like someone sprinkled fairy dust on the plane.  It grooved, locked better and turned better.  And as a bonus, it now has a very small dead spot around neutral.  I was able to move the handle about 1/16" up and down (that is just a guess) with no movement of the plane!  Battery still finishes at 30% which will change since my reported lap time was up from my normal 5.4 to 5.9.  Funny thing was that it felt just as solid at 5.9. 

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Offline Crist Rigotti

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #35 on: September 22, 2022, 04:00:13 PM »
I was a skeptic until today.  My Trifecta is an excellent performer, but she has a wandering eye.  I practically get stopped by the game warden for hunting without a license.  I have tried just about everything and finally just gave up.  I could keep it level with extreme concentration for the judged level and inverted but I want it to simply grove in level flight between maneuvers while my focus is not on keeping the plane level.  It was beginning to hurt the maneuvers.  Yesterday out of the blue I read something about Gurney in one of the threads and decided to see what all of the fuss is about.  Cut two strips of balsa that gave me a flat plate 1/8" on each side of the elevator.  All monokoted up they don't even look that bad.  It was like someone sprinkled fairy dust on the plane.  It grooved, locked better and turned better.  And as a bonus, it now has a very small dead spot around neutral.  I was able to move the handle about 1/16" up and down (that is just a guess) with no movement of the plane!  Battery still finishes at 30% which will change since my reported lap time was up from my normal 5.4 to 5.9.  Funny thing was that it felt just as solid at 5.9. 

They stay on! #^

I'm wondering if this is the same effect as "slop" in the elevator push rod?
Crist
AMA 482497
Waxahachie, TX
Electric - The Future of Old Time Stunt

Offline John Carrodus

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #36 on: September 22, 2022, 04:05:44 PM »
Ken.
Sounds good.
Question
............What would happen if you did the same to your flaps?
                                       
My guess..... The turbulence produced would probably mess with the airflow over / around the tail?
Be interesting to 'prove' it.

Yeah, ok, I hear ya! y1

Online Ken Culbertson

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #37 on: September 22, 2022, 07:42:19 PM »
I'm wondering if this is the same effect as "slop" in the elevator push rod?
It didn't feel the same.  With elevator slop you actually get a reverse reaction to any movement of the flaps within the slop.  It will help grooving but if you need to make micro adjustments if can get confusing.  Actually, to me, flap slop makes more sense than elevator.  This felt more like I was towing a small streamer.  I am going to have to retrim for, or more likely adapt to the tighter turns.  The first indication that it was working was on takeoff when the plane simple stayed down.  I am eager to see how it does in wind.

Ken

 
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Offline Crist Rigotti

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #38 on: September 22, 2022, 09:53:30 PM »
It didn't feel the same.  With elevator slop you actually get a reverse reaction to any movement of the flaps within the slop.  It will help grooving but if you need to make micro adjustments if can get confusing.  Actually, to me, flap slop makes more sense than elevator.  This felt more like I was towing a small streamer.  I am going to have to retrim for, or more likely adapt to the tighter turns.  The first indication that it was working was on takeoff when the plane simple stayed down.  I am eager to see how it does in wind.

Ken

OK.
Crist
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Waxahachie, TX
Electric - The Future of Old Time Stunt

Online Howard Rush

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Re: Tried Gurney flaps yet? What's your conclusion?
« Reply #39 on: September 23, 2022, 12:49:48 AM »
Let me guess; was it yours...?   ::)

I think it was, now that you mention it.
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