News:


  • March 28, 2024, 09:47:22 AM

Login with username, password and session length

Author Topic: Vortex Generators - Development and Installation.  (Read 18633 times)

Offline bob branch

  • AMA Member
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 941
Re: Vortex Generators - Development and Installation.
« Reply #50 on: September 14, 2011, 05:54:49 PM »
I was installing a set of the VG's on my C-14 carbon tube fuse electric tonight and found I was out of carbon fiber sheet. Didn't feel like laying any up so I sought another material. Turns out credit card stock is about the same thickness and easily shaped with blade and sandpaper. Not brittle like plywood is either. I'll flight test on Friday and post results.

bob branch

Offline bob branch

  • AMA Member
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 941
Re: Vortex Generators - Development and Installation.
« Reply #51 on: September 16, 2011, 06:25:02 PM »
This is a flight report of my C14 carbon fuse electric profile with the vortex generators applied. I applied 2 pairs on each wing panel top and bottom. Size, shape, and spacing as PJ recommended. Details of the plane are in the build thread on it in the electric section. It utilizes Brodak P-40 wing and tail and the fuse length and moments are from the Brodak T-Rex. Flight characteristics are identical to the T-Rex except for less pull on lines due to lower weight. I fly both on 63 ft lines. Power is by axi 2826/12, phoenix 45, 3700 mah 4S pack, and APC 12X6EP prop, and hubin fm9 timer. . My normal lap speed is 5.25 seconds. The plane flies very well. Corners are very sharp and flat on exit. Rounds are smooth and require no steering to overlay on themselves. Line tension is solid thru the entire pattern except 3rd corner of the hour glass. This is the only electric with pusher prop configuration that I have not had heavy line tension at this corner. Probably because I have less motor offset than any of my other electrics. The only major thing I do not like and what I was hoping to improve is in level flight. The plane does not hunt. It locks in quite well. Not as well as my SV-11 electric but very well. Observers see no hunting but I notice I have to fly level whereas the SV I do not. I do not have to even think about level. It just stays there. BTW, my T-Rex acts identically in level flight to the C-14.

One thing about the electric is that we have accurate repeatable digitally set rpm. So I was able to quantify the drag difference quite accurately. My flying partner today was Frank Carlisle and he also flew the plane and I'll give you his input also.  First the drag issue. Temp was about 60 degrees and winds were variable 5mph or less today. Lap times initially came out to 5.45 seconds. So .2 seconds per lap slower. I increased the rpm by 60 rpm. This brought the lap time to 5.25 sec. So there is the amount of drag from the 4 VG's on each side of the wing. The level flight improved significantly. It is very locked in now. Frank in observing saw nothing he would call hunting and in his flight he felt that level was very locked in. 

The round maneuvers were easy and repeatable as they always are on this plane. I could not find any significant difference here except that in the vertical 8 I flew the best ones I have ever flown on every flight. It seemed that the top loop was much more consistent with the VG's. The overhead loops gave me the same impression. They tracked better than usual on this plane and the repeatability was right on. In the 6 flights with the wind moving around as it was there is no way I could have gotten the wind that perfect every flight. There was a difference in tracking up high.

Corners were very crisp and exits flat as always. But I felt I could repeatedly locate the corners more accurately. I got the feeling the plane responded more quickly when the control input was made. Depending on the wind I had a big tree or the sun for the vertical intersections on the square 8 and it was easier than usual to hit them. The third corner of the hour glass became more electric normal with more line tension there. I should note the governor prevents wind up or acceleration for those not familiar with it so the feeling is of the plane flying at the same speed at all places in maneuvers. This was not happening because of any airspeed change but from the VG's. Had I not installed the VG's I was going to adjust engine offset a tad more. Right now I fly with one washer of offset.

Glide did not seem appreciably different on this plane. It is a very easy plane to get a really good takeoff with and lands very nicely as well. I should note the gear are considerably longer than P-40 stock gear. In fact they are the stock gear from the T-Rex.

Later in the day I increased the line rake a quarter of an inch which slowed the airplane to 5.3 sec laps. Line tension was increased of course. But the plane still  cornered as crisply at the slower speed and there was no line tension loss at the slower speed. Later I slowed the plane to 5.5 sec lap and still no loss of line tension. The plane could be easily flown at that speed.

So I felt there was a noticeable difference in a couple of places on this plane. I will be installing them on the T Rex as well and since my SV is an arf a I feel a little heavier than it should be I will add a set there as well. It tends to develop a tad of a tip stall if I hit a corner too hard. I'd like to see if it goes away with them. That would be a very positive result from them. When I flight test them I'll post the results.

Thanks again PJ for your work on these and for sharing it. I think I finally came to understand whey the spacing being larger than in full scale planes works on a stunter. Its our circular flight path. The vorticies will not be trailing straight aft but will be sweeping outboard. This results in a longer path before intersecting the trailing edge and thus a wider vortex. If you look at it that way an look at the wing with them on you can see, it allows a much larger coverage area than if the plane was traveling a straight line path. At any rate I think this is something people would find interesting to experiment with. They certainly have the potential to solve some sticky problems with some planes. Oh, btw, I did not notice any stick force difference in my tests. Frank could not input because he has not flown the plane before. He did, however very much like the way the plane flew. He especially liked the corner.

bob branch  H^^

Offline bob branch

  • AMA Member
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 941
Re: Vortex Generators - Development and Installation.
« Reply #52 on: September 16, 2011, 06:26:03 PM »
Oh, one more thing. With electron power no issue with cleaning the plane with them on. .... sorry.....  LL~

bob branch

Offline PJ Rowland

  • AUS - 29541 AMA - 809970
  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 2058
  • Melbourne - AUSTRALIA
Re: Vortex Generators - Development and Installation.
« Reply #53 on: September 16, 2011, 07:02:23 PM »
Thanks for posting that Bob.

I would say the difference you are experience with stick force is partly due to the size of the model ( 40 size if I recall )

Compared to a full sized stunter per-say. I dont run Boost tabs on my classic model - but I certainly do on my 60 sized ships. I only notice minor stick force increase with the smaller models.


As stated earlier - one of the main reasons to run these is for precision - repeatable precsion. - you can track manouvers easier, lock in level flight, which in turn locks in round tracking. I love doing reverse wingovers, you hit the corner, and it locks in vertical tracking. Drive deeper into the corner.

Glide - I find it in windy conditions better more so than regular sessions.

It will only improve what you have, it's not going to harm any aspect of the ship. - Part of the reason to only run 1 pair is to reduce the drag but retain the charactisics of Vortex Generators.
If the model is great - it will remain great just do things better .
If the model isnt amazing - they will help but wont work miracles.

Great to hear the vertical 8's are great - Again makes everything.. better.




Id say the thinner you make them ( like with carbon ) the better the system seems to be. 
If you always put limit on everything you do, physical or anything else. It will spread into your work and into your life. There are no limits. There are only plateaus, and you must not stay there, you must go beyond them.” - Bruce Lee.

...
 I Yearn for a world where chickens can cross the road without having their motives questioned.


Advertise Here
Tags:
 


Advertise Here