Wake turbulence in the Hourglass ??

[Allan Perret]

Smacked my Novar yesterday, pretty sure it was wake turbulence at the intersection of the hourglass.  Light to no winds, had completed the 3rd turn and established straight flight on the downleg.  Just above the intersection about 55~60° it rolled nearly 45° showing me the bottom of the wing.  Almost saved it but not quite. Was wondering if anyone else ever had wake issues in the hourglass.  This bird is on the heavy side, I smacked it about a year ago at the bottom of the 2nd vert.8, for sure that was a wake event; dead calm and the bottom dropped out, zero lift..  Its had more severe wake issues than any of my other birds,  and the highest wing loading by far.

[Brett Buck]

Smacked my Novar yesterday, pretty sure it was wake turbulence at the intersection of the hourglass.  Light to no winds, had completed the 3rd turn and established straight flight on the downleg.  Just above the intersection about 55~60° it rolled nearly 45° showing me the bottom of the wing.  Almost saved it but not quite. Was wondering if anyone else ever had wake issues in the hourglass.  

  Not anything interesting at the intersection. I have had issues flying through the wake of level flight in very dead calm, but not often.

    Brett

   

[Chris Cox]

I have not experienced any real wake turbulence issues on the down line of the hourglass, however I did once have an airplane (Berringer GeeBee) that had such a hard corner that if I hit the third corner in the hourglass too hard, the airplane would actually experience a stall.  This could result in an interesting view of either the top or bottom of the wing. This was at its worse when flying up in Edmonton on a warm day.  Density altitude probably between three or four thousand feet. Never crashed as a result, but it sure got my attention!

[Steve Helmick]

I haven't done as many hourglasses as Chris and Brett, but never a hint of wake turbulence problems. I would suspect turbulence off any surrounding buildings, cars, trees, bushes, or sunshades as the culprit...or a thermal. Or, maybe you just "missed the wind" a bit? Sorry about your Novar...cool paint job on that one.  Steve

 

[Allan Perret]

Leaning more towards Chris' theory, I did try to turn that corner harder than normal.   I have seen this bird stall in other corners when I forgot to fly them soft.  Guess I didnt think there was much risk in pushing it up at the top.  I could have saved it if I had bailed out the maneuver inverted instead of still try to complete the last turn.

[Bootlegger]

 Allen, sure hope that you get it flying again, nice lookin' bird..

[Randy Cuberly]

I lost my Trivial Pursuit in a stall in the third corner of the hourglass many years ago.  Flying a little slow with a heavy airplane and pulled a little too hard on that corner...
Never had any issues with wake turbulence in the hourglass however...seems possible though.

Randy Cuberly

[Allan Perret]

I lost my Trivial Pursuit in a stall in the third corner of the hourglass many years ago.  Flying a little slow with a heavy airplane and pulled a little too hard on that corner...
Never had any issues with wake turbulence in the hourglass however...seems possible though.

Randy Cuberly

I'm thinking more and more it was not wake related.  On the vertical climb up (~60°) the wing should be generating something like only 1/3 the lift of level flight, so it should be generating a minimal wake.  The 3rd corner stall seems more likely.   Decided not to fix it because it was too heavy.

[Will Hinton]

two years in a row at Dayton I had problems with getting a good(very bad) look at the bottom of my wing in the intersection of the 'glass.  Dayton is bordered by some huge trees and the wind there can be really nasty, so take it for what it's worth, but I've found it interesting that it happened both times in the same place.  It was/is a light airplane, Trivial Pursuit aerodynamics and PA's on pipe.  I was fortunate and saved the airplane both times.

[Randy Ryan]

I've experienced stuff like this in thermal conditions. They are as random as thermals of course but the turbulance generated near the ground as a thermal breaks away can be very violent. Posibility.

[Jason Greer]

Real sorry to hear about your Novar Allan.  Are you planning on making it to El Dorado in November?

Jason

[Allan Perret]

Real sorry to hear about your Novar Allan.  Are you planning on making it to El Dorado in November?

Jason

Yes, still have profile and classic birds, can fly either one in PA. 
Also need to check out that ultralite electric GeoXL of yours. 
I am planning to build an elec. PA machine over the Winter.

[Andrew Borgogna]

Allan
I have never had wake turbulence in the hourglass, it's always been in loops and always after doing at least one.  I was thinking about the pattern, we only do one hourglass and that comes after two judging laps so I don't think it was wake turbulence.  I would be thinking the plane stalled.  If one wing stalled before the other you can get a roll motion, in R/C land we called it a "tip stall".  The plane stalls from the tip in instead of the root out.  Tip stalls are nasty!  With the plane being heavy and in a hard corner where lots of control input is used it sounds more like a stall.

Anyway just thought I would add my two cents, really sorry about the plane we all know that pain.
Andy

[Bill Little]

It could have been one of those "micro bursts" they talk about at Huntersville.  Don't know what they are but I have seen them claim a few models!  The model is flying fine and in a millisecond they are 5' lower........

BIG Bear
RNMM/AMM

[phil c]

If the site has any trees or taller buldings withing a couple hundred feet of the circle can cause turbulence, especially if the wing is gusty.

I just had something similar happen this morning.  Gusty, 15 mph winds.  I was flying the tank out at about 30 degrees.  The plane whipped into a right roll at least 60 degrees.  Snapped back the other way, then settled down.  On the next lap, nothing.  Earlier in the flight a gust dropped the plane 10 ft. down, and then back up.  Really should not have been flying.

[john e. holliday]

Is this similar to the gravity holes I have incountered and seen while other people are flying??   Level laps at about 4 to 6 foot altitude and the bottom drops out.   Been lucky in that the plane was fast enough it missed the ground by a few inches.

[PJ Rowland]

I dont see where the "wake" would be coming from. Its unlikey any residual wake from the climb leg would be available to knock the model out. In anycase the only time you'd be flying through that "small amount" would be during the intersection.

My moneys on a thermal.

[Eric Viglione]

I've hit violent wake and flow separation at the 2nd intersection of the Vert-8 before, but I think that's more from the control reversal at the intersection leaving a big bubble.
Never had it happen on the Hourglass intersection, but I guess anything is possible.

Now, I have had some new planes so badly out of trim (excessive tip weight) that the 2nd or 3rd corner on the hourglass threw the wing so violently that everything stalled at once and it would kite away on that corner  but no intersection issues. Now that I think about it, tip weight and leadout location seem to be the biggest hourglass trim offenders for most people, assuming the C/G is even reasonably close.

Anecdotally, a couple years ago in Muncie, the air was so dead on one flight that I was hitting turbulence from a previous maneuver even after doing 2 level laps! But that seemed to be a real freak of nature kinda thing. *shudders thinking about it*. 

EricV

[Joseph Patterson]

      Allan,
             I agree that it was very likely a stall condition. You turned a very hard third corner which slowed the Novar so much it fell through the intersection.
             Doug

[Trostle]

I really do not think there is much of a wake problem at the intersection on the down side of the hourglass.  If this was a problem, this would be encountered on a fairly regular basis by most fliers.  Yes, in calm or near calm conditions, there will be some turbulence left over on the climbing leg, but on every hourglass flown (at least ones that have a real intersection), the down leg will encounter air that was "disturbed" on the up leg of that hourglass.

There are various kinds of turbulence that can upset our models.  I think that we are all familiar with the occasional thermal that will cross our circles when a model is in the air.  These can be fairly mild affairs that are barely noticeable to those that blow lawn chairs across the circle and lift weighted shade shelters off the ground.

I am convinced that there is another kind of turbulence that can be experienced both in near calm and windy conditions.  Where a thermal is basically a vertical shaft of twisting and rising air that is warmer than the surrounding air, I think that there are "rollers", or horizontal shafts of air that are rolling across the ground surface.  When one of these things move over our circles, models will do some strange things.  On several occasions with the model in level flight, not in a maneuver, that thing will be disturbed, like go loose on the lines, turn in and show parts of the airplane I do not want to see from the center of the circle.  I have not lost an airplane from this, but on one occasion recently, there was a short lived doubt a recovery could be made.

Keith