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General control line discussion => Open Forum => Topic started by: Bob Hunt on August 22, 2022, 09:27:52 AM
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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
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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
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I saw one airplane at the world champs with those things.
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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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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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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.
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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.
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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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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!?
Type at you later,
Dan McEntee
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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 1/8x1/4” tapered balsa, more like a wedge than a gurney flap. After the initial test I airbrushed them black so I didn’t 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 .020” thick (if memory serves correct) and had the same effect.
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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?
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More than I ever wanted to know about Gurney flaps:
https://www.sciencedirect.com/topics/engineering/gurney-flap (https://www.sciencedirect.com/topics/engineering/gurney-flap)
Mark
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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 Cox’s .020 strips next opportunity
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I saw one airplane at the world champs with those things.
Let me guess; was it yours...? ::)
Bob
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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 Cox’s .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 can’t feel anything with them
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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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(...) 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.
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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 1/8x1/4” tapered balsa, more like a wedge than a gurney flap. After the initial test I airbrushed them black so I didn’t 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 .020” thick (if memory serves correct) and had the same effect.
Hi Matt,
Can you post a pic of your "gurney devices"?
Thanks...
Later,
Claudio.
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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
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Thanks Matt!
I'll try them on my plane too...with some double sided tape.
Cheers!
Claudio.
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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 I’ve 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
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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.
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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?
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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.
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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.
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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 couldn’t feel any difference with them so I took them off
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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
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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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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 I’ve 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
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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
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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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I have seen these on large power boats, mounted on the bottom edge of the transom.
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Them little air molecules sure are rascally little critters................... ;<)
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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...
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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.
They stay on! #^
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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?
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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
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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 it 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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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.
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Let me guess; was it yours...? ::)
I think it was, now that you mention it.
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I saw one airplane at the world champs with those things.
I also, but I affraid some judges hate them, or at least they do not give points for such model VD~
BTW I also saw another airplane on our field with them short before WCh, but owner removed them after all, because they did not work 8) ... he had also all kinds of turbulators, VGs etc and he removed them all as well and he flew WCh with nice clean model and for big surprise he also cleaned leading edges time to time ;D
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Over the weekend, I tried gorilla tape on the backup airplane to see if I got the same effect as the wedges I put on the Ferrari plane. I did three layers of the Gorilla Crystal Clear tape, approximately 1/4” wide. The difference was night and day! Airplane tracked a little better, and was much easier to find my bottoms and lock at 5ft. It worked well enough that when I build elevators to the new one, part of bench trimming will be layering the tape onto the TE of the elevator
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I also, but I affraid some judges hate them, or at least they do not give points for such model VD~
I thought judges were supposed to be looking at the geometry the plane is flying. If the judges at the FAI contests are shaving points for models that have performance enhancing parts on them, then we have reached a point where the tail is wagging the dog. Get rid of such judges. Of course it is impossible to know who is shaving points for such things... Sad day for stunt.
It is my understanding that many FAI pilots have been using vortex generators and trip tape to enhance the models' performance. Am I correct in that understanding? If so, why then are Gurney Flaps (or whatever you wish to call them) being singled out for penalty? Here in the United States at our Nationals we have seen no evidence of such behavior by the judges. Many of our top fliers' planes have doo dads stuck all over them. And even in appearance point judging the doo dads (vortex generators, trip tape, Gurney Flaps, etc.) don't seem to affect the scores one bit. And it is for certain that the flight judges don't care at all about stuff like that.
The paradigms are changing rapidly in all areas of CL Stunt. Construction is changing, the pattern is changing (for example the now well-accepted new Clover entry), and understanding of aerodynamic improvements are changing. Who's to say what the ultimate stunt model might look like? In the future I predict that there will be many more performance enhancing devices attached to the extremities of our models, and with time these now "odd looking things" will become accepted as just part of the whole Stunt Machine (sorry Gene...). Take a moment and Google Indoor RC Pattern World Championships. You will see models performing seemingly impossible maneuvers, and those models have an amazing number of doo dads stuck all over them. Yes, I know they are flying in a different aerodynamic regime than are we, but they have found ways to improve their models' performance by experimenting with new stuff. The judges at those contests don't seem to mind what odd configurations of add-ons are present; they just judge the performance.
And it's not like this stuff is kept secret so that only a select few have the advantage of the doo dads; they are there for all to see. If you think that someone is experiencing better performance than you are do to the doo dads, then start doo dading your models accordingly. It is sad to think that progress in performance is being stifled by some judges' sense of aesthetic sensibilities. Again, I'm thankful that the judges at our Nats don't seem to be thinking that way. I'm very glad in light of Igor's comment that I no longer fly in FAI contests...
Doo Dading my brains out - Bob Hunt
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Nice thread Bob! I tried my own "doo-dad's" some years ago on what was left of my first competition electric model called "Electron". I thought(?) that adding some small raised plates above and below the trailing edges of the elevators, may add some drag and smooth out the airflow. The old model had been pranged a few times so I rebuilt the fuselage with a canopy to look like it came out of a "Planes" movie. My grandson was hooked on the Planes character's so he enjoyed the face on my plane. It would not track well, so I tried this idea of those plates angled the same as the tapered elevators. Igor said that it should not work at the time, but who listens to Igor?? #^ Well.... the idea didn't work so maybe he does know a bit?
I still have it hanging on my workshop wall so I'll cut the plates off sometime soon and try these gurney doo-dad's.
Keith R
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Here is a close-up of the mods and also a photo of how it looked when I built it in 2008. I flew it in the 2008 world champs in France. I flew it in South Africa for a month or so before that and it seemed to work just fine, but it was winter out here. Then I went to stay with Uwe Kehnen in Dusseldorf, Germany, and placed 3rd in a local competition. Then it worked again in Landres in the warm-up world cup competition and in official practice. However in my first official flight the motor smoked in the vertical 8 and took out the Jeti Spin ESC. Igor had spares and gave me the same MVVS IN/OUT runner motor and a new Jeti ESC. I did a few practice rounds and all was well again, but in the next official round it smoked the motor and ESC again, and that was that. Just btw, Igor did mention that this particular motor was not big enough for my plane! (Do you see a trend here?)
When I got back home, I used a conventional out-runner but jammed the prop one day and smoked another new Jeti Spin. Now it was getting a bit expensive so I tried a few cheaper Chinese ESC's with heli governor's but none worked as well as the Jeti. It was shortly after this that I came to think that there must be another way that this whole governor could be done, and after more help from Igor, I got my KR Governor timer to work well enough to be as good or better than the stunt glow engines I was flying. In fact, the system flew as well as my own diesel conversions, and as they say.........the rest is history! It's been a good project with around 2000 systems in the field since I started.
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I thought judges were supposed to be looking at the geometry the plane is flying. If the judges at the FAI contests are shaving points for models that have performance enhancing parts on them, then we have reached a point where the tail is wagging the dog. Get rid of such judges. Of course it is impossible to know who is shaving points for such things... Sad day for stunt.
Sorry Bob, it was some "kind of humor". I see I must make the thing straight. Judges used electronic boxes to enter points and one of boxes failed in hads of one judge, he tried to make it working and during that he looked down to box and people around interpereting it as sleeping judge or something like that. And it actually happened during flight of that "model with flaps on elevator". So logic says it must be reason of that flap ... if not than what else ;D ... sorry, again kidding
... and to make the thing seriouse, I did not see any deviation of points gived "because of" ... anything else only by flight quality. Even kids (juniors) got good points if they did nice flight this time.
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It is my understanding that many FAI pilots have been using vortex generators and trip tape to enhance the models' performance. Am I correct in that understanding?
I do not thing, or at least I did not see too many. I had 3 weeks old model, and as I wrote I tested all of that during first week of trimming and after all I put them all away. Model flew well also without them. But my previouse model needed turbulators on tail. My model from Bulgaria needed turbulators on wing (and insects on leading edge ;D )
Al those models are basically the same (tey have CNCed parts like fuselage sides etc) but still all of them neded small fixes on different places. So I think it is always necessary to try them, test and see if it helps or not.
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Sorry Bob, it was some "kind of humor". I see I must make the thing straight. Judges used electronic boxes to enter points and one of boxes failed in hads of one judge, he tried to make it working and during that he looked down to box and people around interpereting it as sleeping judge or something like that. And it actually happened during flight of that "model with flaps on elevator". So logic says it must be reason of that flap ... if not than what else ;D ... sorry, again kidding
... and to make the thing seriouse, I did not see any deviation of points gived "because of" ... anything else only by flight quality. Even kids (juniors) got good points if they did nice flight this time.
Hi Igor:
Yes, it was not clear to me that you were making a joke. There are many here that do not like the look of things attached to the outside of the model, but once they fly a model that has enhanced performance due to the attached doo-dads they tend to change their minds. I know I did... The Gurney Flaps (or whatever they are...) have certainly dramatically improved the performance of both my Crossfire Extreme and my Genesis Extreme. I'm hooked on them no matter what they look like. Interestingly I did not experience much or any performance increase with the trip tape on the leading edge. Go figure.
Glad we cleared this up - Bob
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Sorry Bob, it was some "kind of humor".
I thought it was very funny.
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I made a set similar to Bob's. Not as much offset. Hope to try them Thursday evening.
Tom
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I spent about 25 years prior to 1995 fighting the RC Pattern Wars. While vortex generators and "Gurney" flaps, or slats, or attachments did not exist in our conversations, we did have lots of interesting discussions concerning various unconventional shapes and setups on airplanes and control combinations programmed into our computer radios of the age that seemed to provide performance enhancement (or not). All very similar to this discussion. There was a flyer from the Louisiana area whose name is Paul Varner I think. As I recall he was quite a character (he was from Louisiana after all). He coined the phrase "Voo Doo aerodynamics" to account for the unexplainable positive (or not) effects of the various concepts. I think that is the best way to classify the effects of the devices folks are currently trying. It seems I can safely conclude that this branch of the science is still alive and well and providing us with lots of interesting discussion.
Joe
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I put 3 flights on the Crossfire and right off the bat I had the results Bob described. Locked in level flight was outstanding!
Tom
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Well guys, I dusted off my old Electron and pulled off those winglet things that did not work at all. I wrecked the covering, so it was easier to just pull it all off. I added some 3 mm x 10 mm balsa strips to the trailing edge of the elevators as shown in the pics below, and then did a quick covering with laminating film just to test it out. All I can say is......WOW! the non-existent tracking suddenly was there, and the way it comes out of the hard corners is amazing! I was really considering trashing this model because it was past its sell-by date. So now I'll give it one last re-build. I still need to do more trimming and use a better control handle but flying yesterday in windy, gusty conditions was more than manageable. Thanks to Bob for starting this thread. Now what would be nice, or should I say....GREAT, would be if one of the resident experts could explain why these "doo-dad's" work so well.
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Now what would be nice, or should I say....GREAT, would be if one of the resident experts could explain why these "doo-dad's" work so well.
y1 y1
Glad to hear that the performance in wind was great as well. I have not been able to fly mine in anything over 10mph which around here is not wind.
Your installation is the same as mine except that I went full span. I wonder if it matters. One thing I have noticed is that the ones that seem to get the best results are blunt and about 1/8" tall +-.
Ken
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Hi Ken,
So my elevator trailing edges are 4 mm thick, so top and bottom protrude 3 mm, or just less than 1/8" and like I said, the effect is amazing. I guess that this is showing up some kind of basic error on the model if it makes that much difference. I'd just like to know what is actually happening.......technically. I also want to use the Eagle Tree data recorder to check how much power a flight uses and then remove the strips again to see what the difference, if any, there is. This is so interesting!
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Hi Ken,
So my elevator trailing edges are 4 mm thick, so top and bottom protrude 3 mm, or just less than 1/8" and like I said, the effect is amazing. I guess that this is showing up some kind of basic error on the model if it makes that much difference. I'd just like to know what is actually happening.......technically. I also want to use the Eagle Tree data recorder to check how much power a flight uses and then remove the strips again to see what the difference, if any, there is. This is so interesting!
I have not logged anything, too much trouble on my ESC, and my "scientific" method is to measure battery head room after each flight. Before the strips I was averaging 30-32% remaining. With the Gurney strips on the two flights I measured, the headroom on both was 30%. I don't get concerned unless it gets under 20. Both flights were in about a 10mph wind so it will use more in really light wind but sill, I don't see any downside. My question list keeps growing. Does size matter (amount of elevator covered)? What is the optimum height? Is distance from the TE (like Bob's application) make them better? I am guessing the answer to all of them depends on the plane. In my case, how much more stable can it get? I was able to hold it steady within a couple of inches on a domed circle in wind at 4 different heights. I haven't been able to do that since I was in my 30's! Now back to the only maneuver that fails to recognize that I am the one flying the plane - the Evil Reverse Wingover. The Gurney's didn't help it at all....boo.
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Ha-ha.....the Evil Reverse Wingover! That is always the most difficult one for me too. As we follow the F2B rules here in Darkest Africa, the square eight has the highest K-factor and I've always believed that the reverse wingover should have that. It takes a lot of practice, and I have a natural aversion to that! Everything on your model must be working in sync to hit a good wingover.....including the pilot! Then too, it's the first maneuver and in a serious competition, the nerves kick in, so yes, your name of "Evil Reverse Wingover" is spot on!
I was also thinking that I should try putting a triangular wedge in front of that flat 3 mm bump on each side to see if it changes anything.
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Something you might try: tape a piece of crepe paper combat streamer to the TE of each elevator- 1 foot long is probably enough. Go fly and compare. It should feel about the same.
Dave
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Something you might try: tape a piece of crepe paper combat streamer to the TE of each elevator- 1 foot long is probably enough. Go fly and compare. It should feel about the same.
Dave
Interesting because that was my reaction when I was asked how it felt. It felt like the plane was towing a streamer except the corners were better.
Ken
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Something you might try: tape a piece of crepe paper combat streamer to the TE of each elevator- 1 foot long is probably enough. Go fly and compare. It should feel about the same.
Dave
Thanks Dave, that will be interesting too, so I'll try that soon.
Regards,
Keith R
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3D printed Gunrey flaps. 5 gram each. I can go down to 3 grams I reckon. Next weekend test time!
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Hello Bob H,
I see yours are set off the TE of the elevator and others are putting theirs right onto the back of the TE. Is there a reason yours are offset and should the be or not??
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LOL! Hi Doug: No. there was no technical thought given to my Gurney Flap (or whatever they are...) installation. I just made up something that could be taped to the elevators. I had this piece of 5/16-inch thick balsa at hand and I trimmed its thickness down to the thickness of the elevators at the TE. I glued pieces of 1/64-inch thick plywood to the upper and lower faces of that piece of balsa and then attached a piece of 1/8-inch thick balsa to the rear of that assembly, letting that piece stick up proud of the plywood on either side by 1/8-inch. I attached them to the elevators using the Scotch Gift Wrapping tape (purple label on the tape...) and went to the flying field just a day before going to a local East Coast contest.
Everyone at the contest asked me what they were, and also gushed about how much better the model flew with them on. I lost that contest by a couple of points to Joe Daly...who also had them on his plane! I went on that year (last year) to win three East Coast contests, and at each one all the fliers came over to examine the plane. They were all amazed at how much more corner it had and how solid was the lock after the corner. Let's put it this way they are not coming off!
Later - Bob
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3D printed Gunrey flaps. 5 gram each. I can go down to 3 grams I reckon. Next weekend test time!
I would say keep them heavy, it can be that problem of the model is dynamic disballance of flaps to elevator making positive feedback to controls in corners (making it hard to keep straight after corner) instead of some aerodynamic black magic. Alex S. has it also on one of his models on WCh in Poland and I had also such model which I needed 5 g weight on each elevator VD~
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Something you might try: tape a piece of crepe paper combat streamer to the TE of each elevator- 1 foot long is probably enough. Go fly and compare. It should feel about the same.
Dave
Right, if stab/elevator does something wrong aerodynamically somewhere around neutral, then ANYTHiNG what can change it will help (turbulators, VGs, sharp LE, blunt LE n~ etc ...) I even know guy who makes -1 deg one left elevator and +1 on right elevator to avoid it to be "too precise" VD~ ... so that if somethig bad happens, then only on fraction of tail ;D
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Right, if stab/elevator does something wrong aerodynamically somewhere around neutral, then ANYTHiNG what can change it will help (turbulators, VGs, sharp LE, blunt LE n~ etc ...) I even know guy who makes -1 deg one left elevator and +1 on right elevator to avoid it to be "too precise" VD~ ... so that if somethig bad happens, then only on fraction of tail ;D
That's very interesting - it has the net effect of the Gurney flap or other elevator-centering/stabilizing devices, without showing it. A very long time ago, I had a problem with elevator "flutter" on a really poor design (that I came up with...) and ended up putting a prety large aluminum wedge-type device with two vanes feathered in opposite directions. This would likely do the same. It solved the flutter problem - until I folded the stabilizer in inverted level flight in extreme turbulence! No great loss, the airplane was awful otherwise, and butt-ugly.
Not to be a wise guy, but the very little experimentation I have done with elevator wedges/Gurney flaps had been very negative - the airplane felt like the elevator was frozen solid, or the controls were bound up, because it took immense effort to break it out of neutral. The issue I always fight with my airplanes (particularly the last 3, which were nearly identical), is getting it "freed up" around neutral, not getting it to track, even without any sort of centering device.
I tried running the CG back, but then the control pressure VS deflection seemed screwed up, a ton of force to get it to move at all, then, it lightened up as soon as I got any motion. I think that is the intended effect, to try to get some self-centering effect, but (again, not to be a wise guy) I haven't had that problem on any of piped-era airplanes, you let off the pressure, it stops dead, with nothing.
I note again - I am running a different tail airfoil and planform than most, it is not a flat stab with a pointy LE, it is an airfoiled stab with the high point at the hinge line, and otherwise looks like a stretched-out version of the Green Box Nobler tail airfoil. Contributor or not, I have no idea, but tracking and centering has never been a problem and all the tricky devices like trip strips, turbulators, VGs, elevator wedges, either have no effect or have negative effects.
I will freely admit that I have have not done enough testing to prove my point, and I could easily by missing something, but so far, my elevator wedge experience has been generally negative, and doesn't seem to solve any problem I have.
Brett
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Purely an educated guess on my part but I expect the problem encountered/benefit discovered is far more pronounced with ball joint "sticktion" controls and electric airplanes without the benefit of vibration to free the elevator so it can seek its own neutral in the slipstream air. It's totally up to the pilot to find the sweet spot following a sharp turn and also groove in level flight. These devices should aid the elevator lock in the right place.
Dave
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That's very interesting - it has the net effect of the Gurney flap or other elevator-centering/stabilizing devices, without showing it. A very long time ago, I had a problem with elevator "flutter" on a really poor design (that I came up with...) and ended up putting a prety large aluminum wedge-type device with two vanes feathered in opposite directions. This would likely do the same. It solved the flutter problem - until I folded the stabilizer in inverted level flight in extreme turbulence! No great loss, the airplane was awful otherwise, and butt-ugly.
Funny, exactly that was my problem, it was piped model and my flaps started to flatter at some RPM. So I installed 5g weights on both flap tips to "detune" it to lower RPM. It was sucessfull, but model did not fly well. It has mixed feeling of nose heavy/tail heavy. I tried all possible, but only the same weight on elevator helped (on trailing edge of elevator). Funny was that model after installing them (it was 10grams at tail) had feeling of more nose heavy CG position (which was actually sveral mm back).
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Good morning,
Well, I though I would add my $0.02 to this discussion and share my experience on this topic. See the attached PDF file.
Enjoy,
Dennis
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Thank you Dennis. Very informative!
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Today I tested the gurney flaps. I was disappointed. These are MY findings with MY stuntship. My findings cannot be generalised... : Although these flaps represent about half an ounce extra tailweigth, the ship felt less responsive. loops become bigger and corners need more steering. In the wingover, when there is no pressure on the elevator, some flutter was noticeable acoustically. The little slop in the elevator horn created a vibration noise. The landing was more difficult than normal and the glidepath was shorter. I removed the gurney flaps and had 7 enjoyable flights without them...
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Today I tested the gurney flaps. I was disappointed. These are MY findings with MY stuntship. My findings cannot be generalised... : Although these flaps represent about half an ounce extra tailweigth, the ship felt less responsive. loops become bigger and corners need more steering. In the wingover, when there is no pressure on the elevator, some flutter was noticeable acoustically. The little slop in the elevator horn created a vibration noise. The landing was more difficult than normal and the glidepath was shorter. I removed the gurney flaps and had 7 enjoyable flights without them...
Interesting. I wonder if the shape of your elevator with the balancing tabs has anything to do with it. I can't see the Gurney things causing flutter in a normal application.
Ken
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I think T-strips work for us. Here are some of my thoughts on the subject of T-strips and Gurney flaps.
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Thank you Frank!
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I think T-strips work for us. Here are some of my thoughts on the subject of T-strips and Gurney flaps.
Thank you SO MUCH for the technical info. After reading some of it (I am more interested in the conclusions than the math) it appears that a full span T shape that is approximately 1/8" tall, is as thin as possible and perhaps does not have a tapered ramp (no bump before the ridge) is the best starting point, and maybe ending point as well. I don't know if having it 90 degrees to the flap surface matters which would make the flap a flat "Y" shape on a tapered elevator. I read that the flap will effectively increase the moment which may explain the better corners and perhaps the better locking (Instantly Fancherized). The optimal height is probably greater than the 1/8" but the added drag would scare my batteries. They were OK with the 2% increase from the ones I put on. I suspect that the drag increase with height is not linear.
Some are trying layers of tape and having some success. One I know of uses a thick elevator TE which may contribute. Somehow, after looking at all of the examples I wonder if a couple layers of tape is producing the vortexes sufficiently large to have the necessary "wow" effect.
Ken
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I think T-strips work for us. Here are some of my thoughts on the subject of T-strips and Gurney flaps.
Hi Frank,
You posted some excellent "thoughts" as to why Gurney flaps, T-strips, Elevator Wedges, Trip Inducing Plates or whatever you call them, do what they do. Thank you.
I was curious as to the planes you tested on. Were they IC or Electric? The plastic L-shapes of 3.2mm (.125") and 4mm (.157") sounds interesting. For my electric model the original "built-in" plates were .625" tall, with a .25" thick elevator, put the top of the plate at .188" above the surface of the elevators. But, I did put a fillet between the elevator's surface and the front of T-strip on both sides. They looked great. However, on my electric plane they produced a tremendous amount of drag and brought my remaining battery capacity to near zero.
Once I sanded the T-strip off, my lap times went from 5.35 seconds down to 5.00 seconds and the remaining battery increased to 18-20%, changing absolutely nothing, which was significant. So there is a limit one will experience with electric models if they are too tall. Where that "magical" height is I'm not sure. So far the .020" high full length strips of tape has worked remarkably well.
Dennis
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So there is a limit one will experience with electric models if they are too tall. Where that "magical" height is I'm not sure. So far the .020" high full length strips of tape has worked remarkably well.
Dennis: I am still fishing for that magic height and whether or not they need to be full span. My gut tells me that that they need to be high enough to create a vortex in front of the flap TE as well as behind it which gets better with height but not so tall as to kill the battery. I have only tested a 1/8" above the TE full span "T" so far and I did not experience the huge battery drop I was expecting. I went from 32% to 30%. My lap times went from 5.6 to 5.9 (65' lines, active timer). Aside from the expected benefits, I did not see any downside to the increased lap time. If anything, it was performing better. I can't put a finger on it but I think that the timer was reacting to the increased drag. Increasing my base RPM had no effect. What I added in base it seemed to take away in boost. My question to myself is do I need to experiment further. #1 Hunting is gone. That is why I tried them in the first place. #2 Corners are tighter with the same control input and still smooth and locked on exit even better than before and #3 I am not overtaxing my batteries. So perhaps it is time do a victory lap and recertify the pilot on his new and improved toy.
Ken
One thing I noticed in going through Frank's stuff. The flaps were always directly attached to the TE with nothing in front. No plate, no wedge. Could stuff in front of the vertical flap be breaking up the forward vortex and creating unwanted drag? Just a thought.
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again Bob Hunt leading innovation, thank you!
i tried and improved a lot indeed!
next plnae will have them bench added and painted along the finish.
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Hi Fred:
Thanks for the kudos, but this one is not my innovation. I saw these devices at last year's Nats on several West Coast airplanes and decided to try them. They have worked amazingly well for me on three of my planes, and I intend to add them to all my lanes as I am able. I believe the credit for this idea in our realm goes to Chris Cox.
Later - Bob
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Awesome work Frank! Gives a lot to ponder!
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Hi Fred:
Thanks for the kudos, but this one is not my innovation. I saw these devices at last year's Nats on several West Coast airplanes and decided to try them. They have worked amazingly well for me on three of my planes, and I intend to add them to all my lanes as I am able. I believe the credit for this idea in our realm goes to Chris Cox.
Later - Bob
Not your creation but you made it popular here in this forum and everyone that tried loved! Same thing with other developments you made like Foam Wings, Tuned Piped engines, E-Power...the list goes on. These things existed before but you put them to good use and made them user friendly by thinking outside the the narrow minded c/l "circles". Thank you for improving our sport and sharing with us.
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I experimented with this concept over the weekend by adding some 3/32 basswood square strips to the full length of the trailing edge of my elevator, top and bottom. I used rubber cement to glue the strips. It definitely helped my plane. It grooved better in level flight and it turned and locked much better. The added drag did consume more battery.
Bottom line is that the strips were a very noticeable improvement for this plane.
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Many of you likely know of Kermit Weeks, founder of Fantasy of Flight and his videos. His latest one is an update on the ME 108 Taifun restoration. There's an interesting segment on the reversed edges of the fuselage skins that could be related to this discussion. The segment starts at 3:25 and goes to 3:45. I don't know how to attach the video so if interested, go to, 'Gerd Muehlbauer visits the ME 108 at FOF' on YouTube.
Ara
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Hi Ara,
I went to the video and saw the segment you were talking about.
Very Interesting.
I assume the skin panel edges were able to perform a function like vortex generators and bring more energetic air to the surface and help prevent large scale flow separation.
That plane seemed to have very good performance for the time.
Frank