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Offline steve pennypacker  
#1 Posted : Sunday, May 5, 2019 1:12:43 PM(UTC)
steve pennypacker

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Hello everyone,

I’m preparing for my first IMAC contest in two weeks. Flying Basic and just trying to learn what it wants to teach: straight lines and arcs, wind correction, and positioning. I’m trying to set up my downline mix to work for as many scenarios as possible and wondering how people set this up.

I have a 3% idle to down elevator mix which gives me perfect vertical downlines. But that mix leads to a tuck to the wheels in the two down 45s and the horizontal line before a spin. The ideal setup would seem to be one that works for all these situations, minimizes workload and potential for point loss, and doesn’t lead to bad habits that I’ll regret later if/as I move to higher categories.

The options I can come up with are:

1. Put the mix on a switch and turn it on or off when needed for each figure. Arguably it might not seem like a lot to flip a switch 3 times through a Basic flight but looking ahead through the categories, it seems important to minimize switch flipping. I want to learn good habits that won’t come back to bite me later.
2. Leave the mix on at all times, and never throttle back to full idle except for vertical downs. It would work, but at the cost of adding both mental workload (something to think about and remember), and physical (can’t put the stick against the stops).
3. Leave the mix on (or off) at all times, and use the sticks to manually correct any pitching.
4. Move the CG aft. Not really an option.

Some of these seem better than others, but all are tradeoffs. I thought I'd look for "ideal" before accepting the need for a tradeoff.

Am I missing another option? Is there an accepted best practice? What do people recommend?

Looking forward to competing in 2019!

Steve

Edited by user Sunday, May 5, 2019 1:57:11 PM(UTC)  | Reason: Not specified

Offline Dave Dupre  
#2 Posted : Sunday, May 5, 2019 1:56:38 PM(UTC)
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Hi Steve,

Does your radio allow a curve on your mixes? Mine allows for a curve on the throttle such that the mix only happens when the throttle is all the way down. As long as I stay above about 10% power on the 45 down lines, the mix doesn’t impact things.

You can I are both in MA and have tried to connect for practice. Happy to show you if we can get some time to practice together.

Dave Dupre
Offline Mike Karnes  
#3 Posted : Sunday, May 5, 2019 2:06:16 PM(UTC)
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Make sure the throttle offset is so the down elevator does not come in play above 3 throttle clicks. If your plane is tucking on a 46 down then it should also do it on a horizontal line throttle off. If so you need to go back to step 1 and start again
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Offline steve pennypacker  
#4 Posted : Sunday, May 5, 2019 4:58:17 PM(UTC)
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Thank you Dave and Mike.

It sounds like the recommendation is to keep throttle above idle for everything but vertical downlines. That's how I've already set up my radio so now I just need to train myself to work the throttle stick accordingly.

Dave - even with the lousy weather we've had this spring I've been able to find a flyable window almost every day. I'm heading out now in fact. I'll PM you about practice. I'd love to have an experienced competitor critique my flying at least once before the BCAM contest in 2 weeks.

Steve
Offline Kevin Wilson  
#5 Posted : Monday, May 6, 2019 8:00:40 AM(UTC)
Kevin Wilson

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Hi Steve,

Nose heavy is my first thought given your description, but you say that moving the CG is not an option. Why is that? Have you gone through the Peter Goldsmith trim procedure? This will really help make your plane fly properly.

Kevin PeterGoldsmithTrim.pdf (18kb) downloaded 1 time(s).
Offline steve pennypacker  
#6 Posted : Monday, May 6, 2019 12:56:53 PM(UTC)
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Hi Kevin,

Good questions. Thanks for your input. I used the trim chart initially. I recently switched over to Bryan Hebert’s triangulation method as my primary go-to, though I’m still using both. One reason I like Hebert’s method is it’s more objective. My plane needs down elevator to fly level inverted. Is it “a lot” as the trim chart asks? I don’t know, it’s subjective and hard for someone without experience to say. It flies vertical and 45 up lines forever without correction. Down 45 and verticals pull to canopy. Knife edge pitches slightly to the belly on left rudder and to the canopy on right rudder.

I experimented a lot with CG and ultimately settled on a location that happens to be at the front of the manufacturer’s suggested range. When the CG was further back, I had other issues like a tuck to the belly in knife edge (both sides; rather pronounced on left rudder) and with precisely controlling the float at the top of looping segments. This is from memory, there was probably more than that.

My comment about not changing the CG was probably worded too strongly. It was based on my testing, my reading of both trim methods, and a desire to not introduce other problems. I’d be open to trying a different CG as long as it’s in the context of the overall big picture. I'm hungry to learn.

Steve
Offline Kevin Wilson  
#7 Posted : Monday, May 6, 2019 2:02:53 PM(UTC)
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I would tend to say that if it holds an inverted 45 upline without any down elevator, you are not nose heavy. I usually like it gradually fall out of it, meaning I need to hold just a tad of down elevator. What airplane/motor do you have?

Kevin
Offline steve pennypacker  
#8 Posted : Monday, May 6, 2019 7:54:21 PM(UTC)
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It's an AJ Laser 73" with a 12s motor. Don't laugh ;), I know this is IMAC. The shipping company trashed the 105" I ordered in Febrruary. Then they trashed the second one. Neither was AJ's fault - they're crated well. The shipper, which AJ is no longer using, was pretty abusive. Third try is somewhere on the Pacific right now.

From an inverted 45 up at full throttle, it arcs slowly to the canopy. At half throttle it arcs a bit more. Not a strong arc but more.

Steve
Offline Dave Dupre  
#9 Posted : Monday, May 6, 2019 10:22:27 PM(UTC)
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Don’t want to do the inverted up at full throttle. These planes have so much power, it just powers through everything. What you see at half is more accurate.
Offline Kevin Wilson  
#10 Posted : Tuesday, May 7, 2019 6:39:51 AM(UTC)
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So given that, you may try strapping a half ounce or a whole ounce to the tailwheel bracket and see if there is any improvement. The fact that it pulls canopy in one knife and belly in the other concerns me that something is not straight. Have you pulled out an incidence meter to check the flying surfaces? Also check that throws are traveling evenly on all surfaces, but elevators especially. What throws are you using?
Offline Matt Komar  
#11 Posted : Tuesday, May 7, 2019 7:46:53 AM(UTC)
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I have a bit of insight when it comes to the AJ products so maybe I can lend some advise. When the CG is at the correct spot for how Andrew designed the plane, the knife edge mixing should be equal on both sides of the plane.

From your description of your current CG when flown on the 45, full power, it sound like you are ever so slightly nose heavy. If you haven't already, do multiple test passes, in multiple directions to make sure that you are not being effect effected by the wind and that your 45s are true. My preferred CG, from an inverted 45 will begin to gracefully draw an arc to the canopy.

I would definitely feel comfortable playing with the CG as our planes have a very wide comfort zone, but try moving the weight forward first.

Hopefully we can get you that 105" soon. I couldn't believe when Tim mentioned that the freight company destroyed BOTH of your models recently. Just horrible bad luck but I'm confident it will be worth the wait!!
Offline steve pennypacker  
#12 Posted : Tuesday, May 7, 2019 4:18:16 PM(UTC)
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I ran my tests at 50% throttle so the fuselage was at a significant angle of attack (top rudder) to fly level, so p-factor is significant which I expect is is why the different pitching on left vs right rudder knife edge.

I'd expect moving the CG back would require down elevator trim which would change the knife edge behavior. Not sure that would be better or worse. Just different.

The published CG range is 5.0 - 5.6" behind the leading edge at the root. I'm flying at 5.0 currently. Moving it is a simple matter of sliding the batteries back a bit on their tray.

Matt, given your knowledge of the airplane, what would you expect an optimal starting CG for Basic would be?

The one airframe issue that I know about is that the right aileron is hinged 3/32" below the centerline at the root. The way I've set it up, the aileron maintains that same 3/32" along its full chord from leading to trailing edge. In other words I did not reflex the aileron back upwards to meet the wing trailing edge.

The airplane looks and flies straight: level flight horizon to horizon or vertical upline out of sight without touching the sticks (actually there's still a very slight left yaw after climbing several hundred yards which I still need to shim out).

If there's any aileron trim at all, it's so small that I can't see or feel it. There's 1 deg. of right rudder trim.

It does have a weakness, IMO: the joiner between the two elevator halves is less than perfectly rigid so can flex a bit under load. I'm just flying Basic with low control throws. If I'm feeling effects from that, it isn't something I'm aware of. Is there something I should test to gauge its impact?

Control throws:
Elevator: +/- 13 deg. (less than this doesn't give a clean stall break - related to forward CG?)
Ailerons: +/- 9 deg. (was higher but this is helping me stop rolls at wings level at this early stage of my development)
Rudder: +/- 38 deg. for hammers, +/- 24 deg. for everything else. I could probably use much less on low rate but I sometimes forget to throw the switch and don't want to zero a figure if that happens)

As best I can measure the angles with a Robart incidence meter, averaging lots of measurements, I'm at:
Stab: 0.0 deg.
Wing: +0.5 deg.
Motor: 0.4 deg. down & 3 deg. right thrust (not stock; I've added right thrust to straighten up lines, and down thrust to both straighten up lines and to eliminate a pitch up when adding power in horizontal flight).

This is going way past my initial question but I appreciate and enjoy the feedback.
Offline steve pennypacker  
#13 Posted : Tuesday, May 7, 2019 8:11:33 PM(UTC)
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I reviewed my flight test notes and discovered that I re-ran only a very few tests after moving the CG to its current location. Doh! I know what I'll be doing my next time out...

Steve
Offline Matt Komar  
#14 Posted : Tuesday, May 7, 2019 8:28:50 PM(UTC)
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Let us know how it goes Steve!

FWIW, the GG range we list for our planes are just a starting point. Feel free to experiment little by little until you find the right setup for your flying style. I would setup the plane the same way I do for my 123" Laser, gentle arc hands off from a full power inverted 45 upline.

As far as the elevator joiner, the flex shouldn't have any effect on the plane. It's designed to to take the full abuse of all the violent 3D maneuvers out there. As long as the elevator halves are aligned you won't have any issues.
Offline Kevin Wilson  
#15 Posted : Wednesday, May 8, 2019 7:20:00 AM(UTC)
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Well that all sounds right. The only other suggestion I might offer is to set your knife mixing at whatever speed you plan on flying your base line. If it is 50% so be it, as long as you are consistent. Also, your rudder throws may be a bit high as I usually recommend +/- 17.5 degrees for normal flying.
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