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Old Aug 22, 2014, 07:24 PM
Hugh Blackburn
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Melbourne, Australia
Joined Jun 2005
467 Posts
Quote:
Originally Posted by Bodywerks View Post
Awesome! It does show you moving the controls a lot more than is probably necessary, and if those notches are 2mm that indicates you have almost 4mm reflex and like 4-5mm camber? Seems an awful lot...
1. (Maybe the control inputs seem like over-controlling, but) I was moving the controls as much as I perceived necessary to stay in the bubbly lift I was finding. The CG was at 72mm, so the plane was less longitudinally stable than I would normally fly it in those conditions (67mm). So I'd be giving more elevator input than normal for that kind of day, and owing to elevator/flap mix (see below) that would generate more up/down camber motion than perhaps normal. That doesn't account for roll inputs, which are what I felt were required in the conditions.

I guess that was part of the point of the original question from JW: often the control inputs are larger than you might imagine, and that means the airfoil design envelope for each setting (speed, cruise, min sink) must be quite wide. The Snipe is extremely good in this regard - that is perhaps easiest to see in its acrobatic performance: energy retention is great. That's a tribute to Joe's airfoil design skills.

2. I am also a bit surprised about the amount of reflex I thought I was sometimes seeing. I thought that might be associated with parallax effects so I added some static calibration images to the original post (go back and have a look). In fact the ruler gives a reasonably fair indication, though it's probably not the best at the larger ends of the range. So then either the larger reflexes are either due to mis-perception (see LATER note below), some control blowback or to elevator/flap mixing. (Which is nominally +/- 5mm at flaps for max elevator up/down but I had paid rather more attention to the coupling to up elevator, and my max down elevator deflection (+10mm) is about double the up value (-5mm) - I will be reviewing this.) FYI the flap servos are JR285s and the linkages are nice and tight, so I think large amounts of blowback is rather unlikely, though of course possible since the flaps are supporting some of the weight of the plane.

3. As to the max down deflection: this is influenced both by slider use and elevator/flap mix. I'm rather less concerned about that, but I will be reducing my min-sink mean value from 3.5mm to more like 2mm (which is what I had thought it was - my other Snipes are set up with 2mm).

The plane has had a lot of flying (it's about 9 months old now IIRC) and I'm very happy with the basic set-up. But I will be reviewing details of elevator/flap coupling and camber slider mixes. And checking linkages!

LATER: I found that some of the "reflex" could be due to flexibility of the ruler, which will move up or down of order 1mm with a small/moderate amount of force (such as might occur at launch speeds). However, on looking again at the movies, I think the mean reflex value never goes much over -2mm which is my speed setting. I don't know where you see that "-4mm" value.

Hugh
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Last edited by floquet; Aug 22, 2014 at 08:22 PM. Reason: checked the ruler and found it could flex
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Old Aug 22, 2014, 07:48 PM
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United States, AZ, Tucson
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I don't use elevator/flap mixing. Instead, I have my flaperon mix set to about 25% of my full landing flap value in my cruise and thermal modes. So, in thermal mode, if the lift is really good and my airspeed is higher than needed, I can pull back on my throttle stick to both slow the plane down and generate more vertical lift.
I wasn't questioning your setup or flying ability(I'm in no position to!). It was just an observation.
I have deep respect for Joe Wurtz's abilities, and can appreciate his desire for the least amount of throw possible to reduce unintentionally increased drag. At the same time, I'm a 3d/IMAC pilot at heart and can't stand to not have control authority I need when I need it. So I set my throws for a good bit more than I need. But I also fly with very, very little sick movement. I'm a "fly by feel" flyer. I've never relied on letting my transmitter tell me where I need to be. I rely on the plane.
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Old Aug 22, 2014, 08:34 PM
Hugh Blackburn
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Melbourne, Australia
Joined Jun 2005
467 Posts
I didn't think you were questioning me, but they were interesting observations and I wanted to go back and give some more examination and information. My initial perception was also that I thought I was seeing more reflex than I had set the plane up with. And I was also surprised to see the size of some of the inputs I was supplying!

I'm not so sure Joe's point was about desiring to have the least possible amount of throw. I think it was more that the excursions that should be taken into account for airfoil design are possibly larger than one may have imagined. The input throws are what they are!

Hugh
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Old Aug 22, 2014, 09:28 PM
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United States, AZ, Tucson
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Your aft cg was definitely a factor. I thought for sure your camera was stripped down. Even stripped down, they are close to an ounce. That's significant for a dlg.
I really appreciate the video you posted. It puts an average flight into perspective.
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Old Aug 22, 2014, 11:31 PM
launch low, fly high
New Zealand, Hawke's Bay, Havelock North
Joined Dec 2004
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floquet, thanks for the good video!

Just watched the LP version. To my eyes, the zero deflection is likely not at the center mark on the ruler as based on the reflections on the wing (zero deflection registers as a bit of negative flap on the ruler).

One thing that I tend to see is extra deflections used. It may not be excessive deflection sometimes, but instead lots of pulsed deflections where the intended result could be achieved via a smaller deflection that is held for the same time as the multiple pulsed deflections. It is important to note that the drag variance with deflection is not a linear function. For example, doing two pulsed deflections at +-4 degrees will result in a lot more overall drag than the functionally equivalent constant +-2 degrees deflection. Smooth inputs are good. Smooooth inputs are better...

Sometimes, one needs to be abrupt on the control inputs to work choppy and turbulent air. It is better to fly rough and be in the best air than to fly smooth and only be in the best air for a part of the time... For larger planes (F3J) my rule of thumb is that every movement of the stick costs a second of dead air time. So, the result of every stick movement needs to gain me at least a second in order for it to be worthwhile.

Another item to consider is the camber setting in a banked thermal turn. In order to trim the plane out in a thermal circle, the pilot will be needing to be adding some up elevator to counteract the pitch rate and its effect on the plane (that is, the pitch rate and Cmq results in a need for up elevator). As there is a mix on elevator to camber, the result is that there is more camber in a steady state thermal turn than the pilot may be intending. My 3.5 deg camber setting is mostly used for dead air or very light thermal work (low bank angles). When I am actively working thermals I tend to use maybe 2 degrees, and sometimes less. The net result when including the delta camber from the elev>camb mix may still be getting me to 3 deg of camber (if not more). I may have to do some data collection to understand this (or do some analysis and get the result numerically instead of empirically). One thing I can say is that I arrived at the lower camber settings for active air via empirical means, and sorted out the analytical rationale for doing such at a later date...
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Old Aug 26, 2014, 06:21 AM
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United States, VA, Lynchburg
Joined Jan 2012
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I saw a video a couple of months ago that I can't seen to find again. It was a Snipe (I think) being thrown in a big field of very green grass. What made this video different was the flying- no thermaling, just launch and acrobatic flying. Inverted, rolls and flips really low to the ground. Seems like there was a dirt road in the right frame of the video, and just a single guy doing the flying. Anyone remember this one?
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Old Aug 26, 2014, 06:47 AM
Hugh Blackburn
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Melbourne, Australia
Joined Jun 2005
467 Posts
You mean ...

DLG Snipe (5 min 27 sec)


Watch out for this guy at the next WC!

Both him (sorry, I don't remember his name, can anyone help out?) and Igor. Two great pilots from Ukraine.

H
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Old Aug 26, 2014, 07:10 AM
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That's the one--thanks!!
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Old Aug 26, 2014, 09:01 AM
Citizen#019
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United States, SC, Boiling Springs
Joined Dec 2011
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Oleksandr Synielytsyi- works for vladimirs models and was at the last wc.
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Old Aug 26, 2014, 12:24 PM
Location: Zurich/Sweden
United States, NC, Cornelius
Joined Jul 2012
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For your consideration:

Official Trailer: I believe it can fly (RC Modellflug) (4 min 43 sec)
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Old Aug 26, 2014, 03:26 PM
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great video funkz
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