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plane purposing badly at higher speeds

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plane purposing badly at higher speeds

Old 10-24-2014, 04:06 PM
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Default plane purposing badly at higher speeds

hey every one.......I just got back in from flying my hobbyzone corsair f4u s and super cub s . During the flights, both planes plan were purposing with up and down motion . The faster I flew
the worst it got . Both planes flew fairly well at slow speeds. I was using a dx8 spectrum transmitter with 100 high and 70 low rates with both planes. Is this movement natural ? I don't see how it isn't striping the servo
gears. Is there something I need to adjust? I'm fairly new at this so any help is appreciated.......thanks
Old 10-24-2014, 04:38 PM
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Usually it means it is tail heavy, it could be too few rubber bands holding the wing on if that is what is being used too.
Old 10-24-2014, 04:46 PM
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Both airplanes? Are you using the same receiver?
Old 10-25-2014, 05:40 AM
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Often a combination CG to far aft and to much elevator throw, sometimes either/or .

John
Old 10-25-2014, 06:35 AM
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Were you chasing the movement with your elevator stick, or were they going up and down all on their own with no input from you? What were the wind conditions like?
Old 10-25-2014, 07:28 AM
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Wind was about 8 mph, same transmitter for both planes, corsair seemed to purpose more than the cub. I have the same setup
for both planes as far as the rates go. I cg the corsair 2 1/2 inches from leading edge of wing. Would using different batteries change the cg enough to cause this? 2200mah vs 1800 mah....corsair does seemed to want to climb all the time above 1/2 trottle. The only way I can go fast is with slight pressure on down elevator. I know it's prolly simple but I haven't been doing this but about 3 months!
Old 10-25-2014, 08:17 AM
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I'm gonna check the c g with the 2200 mah and fly it this afternoon.
ill try and focus more on what I'm doing with the sticks also. I was kinda freakin out yesterday thinkin crash!!!
Old 10-25-2014, 08:20 AM
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The manual calls for the CG to be 2 1/4", not 2 1/2" so you may have balanced slightly tail heavy to begin with. Also, changing battery sizes will affect the CG. Did you balance the plane with the retracts down or up? It should be balanced with the gear up as they retract backwards and will make the plane tail heavy if you don't.
Old 10-25-2014, 08:27 AM
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If the planes have flat bottom or semi-symmetrical wings, they will climb with speed. Adding down thrust can help. The faster you move, the more lift that is generated. Porpoising - try moving the CG forward 1/4" at a time and see if that helps. The manufacturer instructions aren't always correct. You could use an online CG calculator that can provide a check on the location.
Old 10-25-2014, 08:28 AM
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ok I'll ill put the cg at 2 1/4..............the plane came with an 1800mah battery, should I use that one? and I broke my landing gear off last week on a not so good landing.
I'm using the skid plates instead of landing gear now.
Old 10-25-2014, 08:37 AM
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how do you add down thrust? not sure what you mean
Old 10-25-2014, 10:11 AM
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Originally Posted by [email protected] View Post
how do you add down thrust? not sure what you mean

I would suggest you not now at this stage add any down thrust and the reason is since you were balanced to far to the rear. The very first step is to assure that the battery is positioned so that the airplane sits level on your fingers upside down at the 2 and a quarter inch point as the manual suggested. Now since you removed the landing gear its likely you will have to add some lead or weight well forward in or around the cowling some where to get the airplane to sit level when supported at that 2 and half point

John
Old 10-25-2014, 10:33 AM
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sounds good john.........I just did a cg on the plane using a hanger nine cg machine. had to add 3 one quarter lead sticky weights to the nose to get it at 2 1/4. And im staying with the 1800amh e-flight battery. Gonna try it out when or if the wind slows down a bit......its about 10 mph
right now and I rather wait till it slows down a bit. Im on my second wing and third cowl .............starting to get expensive!
Old 10-25-2014, 11:28 AM
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Yup definitely a test flight should be in your immediate future. Extra battery is of no real importance concerning flight stability as long at it physically fits and the airplane can be balanced where it needs to be.

I actually do have some Corsair foamy but have no idea which of the 'Zones' it is, thinking maybe the Top Flite one. It came with a barter deal and I flew it quite a bit earlier this year. it was easy to throw in with other stuff to occupy quite moments at the field. I like to hand launch a lot of stuff and the technique involves using one hand and the index finger up aginst a landing gear leg. At the throw this finger gives extra control and a little push during the launch.

I found that using the hand around the bottom of the fuselage because of the wing the CG was much to far forward in the hand and made lauchs difficult. So got out the knife and carved two holes in the bottom of the fuse so two fingers can be inserted and the holes are right near the CG. This maide hand launchs an absolute piece of cake and fun.

John
Old 10-25-2014, 07:00 PM
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It worked!!! ................ you were right,.......added the weight to the cowl and the plane flew liked I hoped it would. The flybys look much better without the purposing. . I'll be sure and check the CG anytime I change something up on the
plane from now on. Didn't realize that it made that much difference. Thanks for the tip on launching the plane by hand. Im going to put me a couple of finger holes in mine too. This forum is a life saver. lots of experience in here.....Thank every one very much for their help.
Old 10-25-2014, 09:46 PM
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If you have been using 2200s in a plane and then go back to 1800s make sure the 1800s are securely fastened so they can not move around. In several of my foamies, the 2200 expanded the slot for the battery and then occasionally one the 1800s works loose. If the battery slips back, then the plane gets squirrely and your are wondering why it is no longer in trim.

Also, I have found that my planes that came with an 1800 fly better with the 1800. There is a reason why they threw in the 1800 when you bought it. The 2200 actually increases wing loading as well as typically changes the CG, I find the 1800 planes land better with the 1800 installed.

Trim at 1/2 throttle. Then if the plane goes up at higher than 1/2 throttle on its own, then add a Throttle to Elevator mix that increases down elevator as the throttle is advanced. Put the mix on a switch and you can turn it off when you are just crusin' around and on when you are WOT.

Also, any plane with SAFE is programmed and trimmed to go up after 1/2 throttle, when in SAFE mode. I typically add significant down trim once the student is landing O.K. in SAFE mode.
Old 10-26-2014, 05:11 AM
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It worked. Good deal.

Whenever you have two entirely different airframes acting the same, it's time to focus on the one thing most apt to have affected both, the owner.

Porpoising is a lucky symptom of tail heaviness. It happens when the tail isn't large enough to operate properly as a horizontal stabilizer. That won't happen with a well designed airframe unless it's caused by misbalance. Lots of full scale planes that were well designed crashed when loaded improperly. Full scale has usually handles a wider range of balances and has an onboard monitor with a strong interest in the situation. Nowadays he usually has a lot of help from on board systems too.

When models are NOSE heavy or TAIL heavy, the horizontal tail is aerodynamically overpowered. The power of the entire tail isn't enough to keep the plane flying level AND the power of the elevator to add appropriate lift to help out is compromised.

The best and safest flying planes are ones the modeler has balanced neither nose heavy, nor tail heavy. Yeah, not nose heavy either. When it's nose heavy the tail is required to stabilize MORE than it's been designed to stabilize. You're taking away from the elevator's power. When you want your plane to fly with a less sensitive stick because you think it's more stable that way, you're fooling yourself. Want a less sensitive stick? Reduce the elevator throw by any number of ways. Best way today is to dial in exponential. Don't have exponential? Setup dual rates and use the dual rate switch. Or adjust the throw. Afraid of not having "enough" throw? Then think again about the value of exponential or properly used dual rates. And get over balancing nose heavy as a safety measure, it really takes away one "safety" while only returning something that "feels safer" but isn't.
Old 10-26-2014, 05:21 AM
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Great BGL , here are a couple of photo's of the launch holes on that old beat up Corsair I have. And forgot it took three holes. In our case the nearest grass or threes for that matter is about four hundred miles away so I keep the gear on it and can still enjoy touch and goes



John
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Last edited by JohnBuckner; 10-26-2014 at 05:23 AM.
Old 10-26-2014, 04:44 PM
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Len
thanks for the heads up! I did indeed notice some slop in the battery tray after takin the 2200 out.I had to
b a bit conscious about tightening the Velcro strips. You got me thinkin about the throttle to elevator mix.
I suppose my dx8 will do that but not sure. Haven't got that far yet. If it will , I'm gonna try it!
Old 10-26-2014, 05:11 PM
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Thanks for pictures, I see where I need to put the holes now.
Three more holes won't hurt this warbird. She's already battle ridden!
Hope nobody laughs at this but I've flew the plane about 23 times so far and crashed
11 times. As long as they keep makin planes , I'm gonna keep flying them!!!!
Old 10-29-2014, 12:06 PM
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Some porpoising is caused by an insufficiently stiff connection from the servo to the surface control horn.
Old 10-29-2014, 07:32 PM
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You shouldn't be crashing that much. If you're having a great time and not endangering anybody and your budget allows it then it's not really a problem, but anybody who crashes on half the flights he makes has a serious problem. From the sound of your posts, I'm guessing you haven't learned how to trim planes properly and also haven't learned even the basic piloting skills. That's a really bad combination- a plane that doesn't fly right and a pilot who can't compensate. It would be really smart of you to get with a seasoned pilot to at least get your planes in trim and teach you proper flying technique. That'll save you an awful lot of repairs and money, even if you have to join a club to get it.
Old 10-31-2014, 08:14 AM
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Couldn't agree more on some of those points. I'd have to admit my flying skills
leave a lot to be desired. I fly or at least try to fly in a 400 acre rice field . I fly by myself
so nobody gets hurt. Most of my flying has been trial and error until I found this wonder
forum with lots of people giving great advise. Would love to have an instructor but that prolly
is not going to happen. Club would b great also but the nearest club is about 1 1/2 hours away.
I Am making progress each time I go out. Even when I crash it's a learning experience and I get to put all
those pieces back together again! With everyone's input in this great forum and the many questions I have yet
to post , I'm hoping I'll b getting the hang of it soon. I've already learned the value of CG balancing, so maybe
theres hope for me yet!!
Old 11-01-2014, 06:42 AM
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Are you sure the nearest club is that far? Have you checked the club locator on the AMA website?
Old 11-01-2014, 08:10 AM
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thanks! I checked the AMA website you mentioned and found one about 45 miles from here. I may give them a call and check them out !!!
Right now I'm tinkering with the throttle to elevator mix on my radio......My plane will climb at a pretty good rate over 1/2 throttle. I was wanting to get a little more speed without fighting the elevator stick all the time....
On my radio display , mix 1 THR > ELE .....It wants input for rates and offset and trim inh or act . Any idea where to start ? OR should I skip this all together. I can use the little trim slider on my radio to hold the plane level at wot , but when I do that if I throttle back I have to fight the stick to
keep the plane up......... it does have the as3x SAFE receiver ar 646 and the three flight modes.... .any of this make any since ? .............Thanks again for the earlier reply.

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