speedracerntrixie

My Feedback: (29)

Rob, I'm going to pick on you for a bit. It's all in the interest of learning so I think you will be OK. From your answers this particular airplane has not been flight trimmed very well. To be fair I would not think of measuring a Parkzone Corsair for baseline either but for conversation sake lets assume that every airplane needs to be measured before a maiden flight. It's almost impossible to know what to adjust unless you know where you are starting. I am also going to assume that the heavier battery also moved the CG forward a bit thus making the elevator less effective. In the wind and especially upwind this is going to obviously seem more stable. The perception is that we are trying to maintain a constant ground speed, the reality is we are flying at a higher airspeed upwind so surfaces are more effective. Most would consider this less stable. By moving CG forward you corrected this in a round about way. The bigger point I want to make is that because the airplane is poorly set up, it reacts more to airspeed changes. Wind is nothing more then just that. Running both aileron servo ATV at 100% tells me that they are not moving symmetrical. If you had measured their throw and set them to exactly the same travel your ATVs would be at 100% for the master
channel and anywhere from about 90% to 110% for the slave channel. The result is that when you give a roll command you also get a pitch change and if the differential is wrong you will also get a yaw command. Now to CG if the CG is forward then you carry some up trim. This trim becomes more effective with speed changes. Referring back to your full scale jet, when you reduce airspeed you also have to re trim your elevator. Great practice for full scale as you need that safety margin for cargo/passengers shifting your CG. With our models we dont change wing loadings or CG positions so we can move the CG back to a more nuetral position so that we don't have to carry any pitch trim. Without that pitch trim the airplane reacts less to speed changes and will actually have a lower stall speed. Back to your Cosair, you can clearly see that we have a few forces acting against one another. these forces have different effectiveness at any given airspeed.

speedracerntrixie

My Feedback: (29)

Bottom line is that at different airspeeds ( including wind ) your Corsair is being pulled in multiple directions. This is why I am more of the opinion that a light, well trimmed airplane ( one that has all aerodynamic functions working in unison ) will handle wind better then a heavy poorly trimmed airplane.

GerKonig

Many years back (decades) we had a guy that did build and fly pattern airplanes w/retracts at our field. He built and then glassed the whole thing. The weight added was unreal. Then he primed and sanded like 10 times at least, then he did paint over and over (sanding, of course).

His airplanes were outstanding. But they had a very narrow envelope, more like Vne 80MPH, Cruising speed 79MPH and Stalling speed 78MPH. Yes a beautiful led sled! He had to come in very hot, so, his retracts would last one or 2 flight max, before being ripped off. We flew of grass. In the air, scooting around they flew nice and very fast. He needed the whole field to take off and in most instances he was able not to run off the field when landing. He was a great pilot, an his models were always correctly trimmed. The wind was on his side (making takeoffs and landings shorter), but in all, it was a clear example of what not to do, and since then, I remember Al and his models when somebody talks about heavier models fly better than light ones...

Gerry

stevegauth30

All in all, I've learned a lot from this thread. I appreciate everyone's input and experiences.

Rob2160

LOL you got me Shawn, I admit to being lazy with my aircraft set up..

Most of my BNF aircraft come out of the box, get assembled at breakneck speed and fly within the hour... This Corsair was the same.. I perhaps used 2 or 3 LiPos to adjust linkages so it flew straight, looped on-line and rolled evenly with rudder and Aileron trims neutral.

But everything you describe is 100% correct, I would probably refer to that level of adjustment as "rigging" rather than trimming..

These two articles add weight (no pun intended) to your argument and I fully concur.

https://secure.steenaero.com/Store/s...C8A8B7F7120DC9

http://www.aopa.org/News-and-Video/A...art-three.aspx

I think in my "very non scientific" assessment of the "Corsair flew better with the big battery" I was referring to how much turbulence deflected it. Eg, flying straight and level with no input, a patch of turbulence would throw it to 90 degrees angle of bank in a split second..

With the heavier battery this effect was lessened.. (more weight, more inertia) and you hit the nail on the head also.. it moved CG forward which added to dynamic stability.

The last plane I purchased, just a few weeks ago was a Parkzone SE5A and I did take the time to rig that one nicely.. It flies superbly now.. Vid below.

https://www.youtube.com/watch?v=IIcfboL7cnA

Jim Branaum

My Feedback: (3)

DUH! And I bet that is on the commercial test. The change in CG was in my oral...and you guessed it! I missed it. That is probably why I remember it so very clearly.

Pylonracr

Rob2160, his name is Shawn, and he knows a thing or two about trimming a plane. We all have our strengths, I helped him with some engine modifications for one of his race planes a while ago and I still learn from his posts about balance, CG position, and trimming planes. I would listen to him here.

To the original poster,(Bob) I build to fly. I learned long ago ( many crashes ago) planes do not survive crashes anyway, so build them to fly. I use some epoxy, laminating resin not hobby shop minute epoxy, but I always have the gram scale out when I mix it. I can feel a couple of ounces in a plane when I fly it, so I build as light as possible. The more you do it, the more weight you can take off of an airframe without sacrificing strength.

Rob2160

Its true, we remember best the things we forget in the Oral. Got this one when I did my aerobatic rating in '85. Then later worked as a part time instructor with them for 12 years. The school specialised in aerobatic ratings so we had to teach the students how 'not to' break the aircraft on their solos.

Rob2160

Thanks, I hope my post didn't come across the wrong way. the LOL was laughing at myself for being "caught out" by him... I was agreeing with Shawn that he was rignt, my Corsair probably is poorly set up if compared to his aircraft.. I took no offense at all to his comments and am happy to discuss aerodynamics all day.

Lightspeed1551

My Feedback: (4)

I do every thing in my power not to crash them, including going home if there is a small fixable malfunction or unexplained gremlin that could lead to a crash. The stuff is just to damn expensive to keep piling into the dirt.

Rob2160

HI Shawn, can I ask you to clarify this statement please I missed it on first read. At a fixed power setting in level flight, the Airspeed will remain constant regardless of flying upwind or downwind. (Power plus attitude equals performance) The only thing that changes is in fact groundspeed.

But if you are saying the pilot is "Trying to make the Groundspeed constant" then I agree fully. The airspeed will be higher when flying upwind.

speedracerntrixie

My Feedback: (29)

Rob, you are correct with that. If there are enough power reserves that would be the natural tendency. Something I see in IMAC all the time and one good reason it is important to trim the model to not have a pitch trim change with airspeed changes. Imagine trying to fly the airplane in a 10 mph wind but maintain a constant ground speed for the judges. Now throw in the mix an airplane that wants to climb when traveling upwind and wants to dive downwind. You can see how difficult it would be to score well.

Pylonracr, I have been meaning to look you up and say thanks. I took your suggestions on that engine work and ended up bringing home my second championship in two years.

Rob2160

Thanks Shawn, yes I can see in that situation the correct setup is critical. Most of my planes now are lazy sport flyers with lazy being the operative word. So I appreciate someone keeping me on my toes. Congrats on your wins and all the best.