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Old Dec 19, 2011, 12:58 PM
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NZ7C's Avatar
United States, AZ, Gilbert
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Kevin -
That's terrific input for me and I will enjoy experimenting - again, thanks so much for the helpful and clear explanation. I imagine there are others that will enjoy and benefit by reading your comments as well.
Tim
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Old Dec 19, 2011, 04:53 PM
Never left one up there yet...
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Canada, BC, Campbell River
Joined Jun 2009
98 Posts
I'll jump in here and add my 2 bits worth!!

I'm the guy who has been lucky enough to fly with Kevin and it has been a huge learning curve! I won't go into detail but he is a very educated man in the ways of aerodynamics. He is the one that suggested trying the airfoil "trips" and it has made a dramatic (imho) difference in the circling characteristics of the BoT. Whereas before the airplane would depart controlled flight in a rather nasty way if one was a little course with elevator control, now it is quite docile and will tolerate a goodly amount of elevator up movement without letting go. As Kevin said it is not immune to tip stalling but vastly improves the delay of it. This was not a guess on his part as he has used Dr Mark Drela's XLFR5 prgram to anaylise and plot airfoil polars while manipulating the position of the "trip". As I say, it has been a very large and interesting learning experience for me! If you look at the pics that Kevin posted a little while ago on this thread you can see where I have placed my trip tape. I went with a 30% MAC position. He suggested that after a chord length of 200mm the trip actually will turn into a bit of a detriment so on the pics if you look closely there is a little black sharpie mark of where the 200mm chordline is. This is where I started to build up the thickness and I am at about .020" which is 5 layers of automotive trim tape from that mark out to the tip. I just carried the first layer over to the already existing trim line for visual continuity.

Cheers

MJ
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Old Dec 19, 2011, 05:06 PM
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United States, AZ, Gilbert
Joined Jun 2011
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Murray -
Could you help me out a little bit? 1st - which of the two pictures represents your bird? I'm having trouble figuring out exactly where I should put these tapes from the pictures. Could you maybe provide info like how far back from the leading edge the tape crosses each rib? and what thickness the tape layers are at each rib? Literally - how did actually locate the exact placement of the tape on the model?

Kevin - Also (maybe a dumb question), but would turbulators always be the same on each tip - or does prop rotation cause one tip to be different (starting to sound like a dumb question...)...thanks guys.
Tim
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Old Dec 19, 2011, 05:36 PM
Never left one up there yet...
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Canada, BC, Campbell River
Joined Jun 2009
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Hi Tim

Glad you are so interested in this trip business!!

Mine is the second pic with the black trim tape and not the zig-zag one.....that's Kevin's.

All I did was to measure back 30% (approx 1/3rd) of the chord going across the wing. Chord on a wing is the "width" of the wing. From the tip I measured in to where the chord was at 90mm and divided it by three and then moved forward a couple of mm to get it to 30%. The leading edge of the tape is then approximately 28mm back from the leading edge of the wing at the 90mm chord line. Then I measured the chord to where it was at 210mm and then divided that by three and then moved it forward to get the 30%. At this chord position the leading edge of the tape is at approximately 66mm from the leading edge of the wing. I used 1/8 inch automotive trim tape and built up 5 layers from the 200mm chord line to the tip. Took about 15 minutes to do both tips!! You'll be very happy with the results. Be aware that not all airfoils will benefit from this tripping. If you know what airfoil you have maybe Kevin could have a look for you to see if it qualifies......there I go again volunteering Kevin's time!! On the BoT the difference is very significant.

I'll also answer your question on the symmetry. Usually all airfoil trips are the same on both tips. This is to prevent one tip stalling before/after the other one. For our modeling purposes I don't know when they would not be the same. Maybe Kevin could chime in with an opinion on this. The airfoil trip is also usually outside of the propeller arc which is the diameter of your prop in distance. You are right, there is all sorts of nasty air in that area!!

Hope this helps

Cheers

MJ
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Old Dec 19, 2011, 07:09 PM
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Old Dec 20, 2011, 09:51 AM
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Kevin and Murray - many thanks for taking the time to explain this to me. I'll maiden the model without turbulators and then try then to see the effect. Thanks much!
Now this may be taking advantage BUT since I'm talking to a man in the know - I have an unrelated question if you feel like teaching a little more :-) I'm quite fond of the Art Hobby models concept and building approach - I'm building the Odyssey starting next week. Art Hobby Models are characterized by a very narrow chord wing, extremely light weight, and most are configured with a single V-dihedral plus a dihedral in very short wing tips. Spoilerons are used in the wings. What generalizations can be made about this style of wing (narrow chord, limited dihedral) compared to more "traditional" wings on the floaters like the Ava's and Supra's etc? I ask because often in sailplane model circles you here that multi dihedral wings are much better than such V shapes and I would assume that the narrow chord gives you much less lift area......yet all reports indicate these models fly quite wll and owners are very happy with them (including me so far - the kits are wonderfully put together). If I've worn you out with questions - please pass on this one!
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Old Dec 20, 2011, 10:52 AM
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Old Dec 20, 2011, 12:46 PM
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United States, AZ, Gilbert
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Yes Kevin I did lead us astray a bit - but sure do appreciate you sharing some of this input. We CPA types know a different set of numbers and relieve stress with gliders - but have much to learn about what will preform and what won't!! Thanks so much for the knowledge sharing!!

Tim
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Old Dec 21, 2011, 06:57 PM
windyhill
United States, AZ, Kingman
Joined Jan 2009
85 Posts
arf watt bot

Hi gang, finally ran onto some one that can talk in my same terms, Nice birds, I live on a remote ranch in eastern Oregon and have been flying since the late 60s. Two years ago did a arf bird of time, converted it to an e bird with a A30-12L hacker,xb 40 pro esc,3s 30c 2700 thunder power, 12x6.5 graupner . I use a futaba 7c w/ r117 reciever. Here are a few snaps, I did an aluminum firewall. mounted the off/on switch just behind the canopy. extended the wood battery tray forward to get the battery as far forward as possiple and used stick on automotoive stick on wheel weights up under the motor as far as i could get them (less weight), Ran carbon fiber rods in the rear of the fuseloge (for strength) My cg is 3.78. Use the last hole in the rudder rod , so it goes full over. Program my tx to mix in up ele while turning and am now thinking of using a gyro for very windy flying????? It will go vertical on full throttle as i have 7 degs down and 2 deg right on the motor .

Ron
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Old Dec 22, 2011, 05:50 AM
windyhill
United States, AZ, Kingman
Joined Jan 2009
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nasa/dryfus

Here is a photo of Mike allen in 2005 launching a project sailplane and if you notice the wing tips are simmilar to the bot tips but the main wing is straight till it gets to the outer tip. Although this project is different than the tip stall you were talking about they do use the zigzag patterns.
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Old Dec 22, 2011, 11:18 AM
Never left one up there yet...
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Canada, BC, Campbell River
Joined Jun 2009
98 Posts
Nice conversion Windy!

Our's are very similar. We were just out flying yesterday and my first flight wound up being 22 minutes. It was supposed to be an ALES round but the lift I was in was too good to leave! We did 4 more rounds and between us we had 6 ten minute maxes. It was a GREAT day with temps at 5*C. All of these flights on the shortest day of the year!!

Try those turbulator strips..........you will just love them.

Cheers

MJ
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Old Dec 22, 2011, 11:29 AM
Thermal Junkie
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Now I will have to get another BOT to try this stuff. Great information in these latter posts!
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Old Dec 22, 2011, 11:34 AM
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USA, AZ, Glendale
Joined Jan 2002
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Hi,

It appears that most everyone has setup the nose with the air intake below the spinner. Other than personal choice, possibly ascetics, is there a reason why the air intake could not be on top instead ????

Landing in the desert terrain, no grass , has taught me to put the air intake on top (it doesn't scoop up the "desert terrain" ) PIC of my Mirage below is an example.

Thanks

Old_dude

ps: My BOT ARF will be tripped !
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Old Dec 22, 2011, 12:03 PM
windyhill
United States, AZ, Kingman
Joined Jan 2009
85 Posts
trying to turn in thermals

When i was 15 i ran around with a life long freind and when we got out of school we went to work for boeing , I left a year later and went to work for western skyways and he stayed there and retired and went on to design the lunar rover in the 69 moon shot. During that time i quit for a long streach but came back and have enjoying my self ever since. Of all sailplanes the bird has to be the all time classic profile and that is why i fly it. Mine flys pretty well but if i was a better pilot i could get more out of it?????. I live on a remote ranch in eastern Oregon and have lots of acres to fly in, The ranch house sits ontop of a small hill and the valley floor is in a big bowel with emense hay fields with 8 thousand ft mts in the distance with large and small foothills in front of the mts so we get boomers all the time and have large flocks of crows (as many as 100?) in the summertime that come in just to have fun and thermo.It gets very cold here in the winter 30 below but the average is 0 and i just don't like to fly much but when it warms up in the winter we do get small pockets of rising air and i get with it. My bot works ok with my setup and i have to work at it to keep it up and have found out if i do find a thermo core turning tightly to the left i loose alt it but if i turn right in wider turnes i can stay up longer? The therie is north of the equater vortexs go counter clockwise and clockwise south of the equater so if i turn right the lift flattens out my turn and i can turn tighter, But when turning left i have to go wider because of the speed.
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Old Dec 22, 2011, 12:13 PM
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