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Old 06-22-2014, 03:02 AM   #1
Karnsy
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Default Did You Ever Have One Of Those Planes

I just picked up the new FMS P47 Razorback. Set it all up at neutral settings to start out / reasonable dual rates. The maiden went really bad. Not sure why but went out of control while trying to trim came nose first to the ground. Not to much bad damage. A little glue and a new prop later and time to try again. Second time up was going ok for a minute, thought I had it trimmed then suddenly it went into a spiral to the ground again. I don't get it,, I have set up other new planes and never had any big trouble. Always got them trimmed and to the ground safely but not this one. Did a range check/ receiver antennae at 90 degrees. Wonder what I am doing wrong with this one.. Puzzled ......Any Ideas ?
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Old 06-22-2014, 04:08 AM   #2
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Description of sudden departure from stable flight sounds like the typical stall of an elliptical winged aircraft. No warning just snap into a spin and if you don't know how to recover you're done.

Try cranking both ailerons up slightly. For a typical 2-56 clevise it would be about 2 turns. About 1/2 the thichness of the TE of the aileron above the surface of the wing at the end of the aileron closest to the fuselage. This will give "washout" and will make the stall less severe and recovery a bit easier.

Attempting to use up elevator in the spin for recovery before you have stopped the rotation will just lock the airplane into the spin.
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Old 06-22-2014, 04:29 AM   #3
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And don't forget the basics... CG? And how fast/slow were you going? I always keep my speed up on maidens, trim them, then get them 5 mistakes high in landing configuration, then see just how slow she'll get. I don't always get to the stall, just make sure she'll get slow enough. Then land and shake out the nerves!
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Old 06-22-2014, 07:31 AM   #4
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I think we've all had a model that has a mind of it's own !

I remember a Spitfire I had back in the 70's ... was one of the very early all foam jobs. Looked gorgeous on the ground ... Mk 5 with OS40 up front.

That ***** just would not fly nice ... didn't matter what you did - she was a pig. Gave it away in the end .. next guy couldn't sort it either ...

Nigel

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Old 06-22-2014, 08:51 AM   #5
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Originally Posted by xmech2k View Post
And don't forget the basics... CG?
Indeed. Aft CG can easily make the plane surprising and unstable.

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Old 06-22-2014, 08:57 AM   #6
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Originally Posted by fhhuber View Post
Description of sudden departure from stable flight sounds like the typical stall of an elliptical winged aircraft. No warning just snap into a spin and if you don't know how to recover you're done.

Try cranking both ailerons up slightly. For a typical 2-56 clevise it would be about 2 turns. About 1/2 the thichness of the TE of the aileron above the surface of the wing at the end of the aileron closest to the fuselage. This will give "washout" and will make the stall less severe and recovery a bit easier.

Attempting to use up elevator in the spin for recovery before you have stopped the rotation will just lock the airplane into the spin.
Good info. Something that will definitely help me out
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Old 06-22-2014, 09:27 AM   #7
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One model I had ... Zlin Akrobat by Pilot - had one habit that marred an otherwise brilliant model.



As the fuel tank went down - the CoG would shift aft slightly ... and I had to remember to NOT do full out spins at low altitude ...

With tank full - you could put nose down .. throttle and pull her out.. aileron / rudder to stop the spin. But when tank was getting empty - she would go DEAD FLAT in that spin ... and in fact was why she was removed from a Scale Comp listing ...

I'd built her and got her ready for flight testing .. couple weeks later was the Southern Area Scale Comp at Beaulieu ...

She flew a dream .. did all the manoeuvres as a Zlin Akro should ... I flew her a number of days getting used to this machine on run up to the comp.
At the field - I was comfortable with her and thought I had her just about dialled in and set. Tank was low and I thought before landing - I'd throw in one more spin .... HOLY mackerel !!

She went into a dead flat spin ... no matter what I did ... throttle, down elevator ... nothing .. she was just coming down dead flat as a pancake with no forward motion at all ...

She pancaked into the field and shoved the wing up through the seat against the servos.

Amazingly she was not so bad .. just the whole wing seat shoved up ...

I took her home and repaired her - but of course she was no longer Concourse for the comp. I rushed out and bought the Neiuport 28 of Pilots ... built that in less than 2 days ... maidened her on 3rd ... flew in comp on the 5th day .. came 8th !!

https://www.youtube.com/watch?v=kGVZbFpWGI4





But that little Zlin stayed with me till I left UK .. in fact I'm sure it's still in the garage where I lived with my Ex. I will try and find it next time home.

The Nieuport was in fact a great flyer - but what a pig on the ground !! That short nose made her vicuous ground looper ... in those days we didn't have the small electronic gyros etc. ... today I would fit a gyro for the rudder if nothing else !
I have the plans and think about building one again ... she was a real stunning static model on the ground and in the air ...

Nigel

222kph PKJ,EDF Concorde, Mini4,Mig3,T45,PKJ twin,ME109,Edge540,Cessna182,Skymaster Biplane,F15,F16,Badius,Ultimate,SE5,Qbee10,450 Heli,V911,J3 Cub Founder 9x forum: http://groups.yahoo.com/group/Flysky_RC_radio/
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Old 06-22-2014, 09:31 AM   #8
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+1 on what fhhuber said. It sounds like a classic stall/spin scenario. Hauling back on the elevator stick is the usual cause. Trick in avoiding it is to keep airspeed up and avoid use of too much up elevator, just the basics really. Adding nose weight can help but really it's just masking the problem by making the elevator less sensitive.
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Old 06-22-2014, 07:03 PM   #9
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Been following this plane on RCG. Most likely tail heavy. Not sure if you have the std or high speed version. Battery placement is critical.

Apparently FMS is sending out nose weights they forgot to include in the first production run. Read post 806 from Jim @ Diamond Hobby: http://www.rcgroups.com/forums/showt...s+p+47&page=54

Seems like some love it and some are struggling. The High Speed version( 100 + mph ) seems to have less trouble.

-Hawk
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Old 06-23-2014, 12:36 AM   #10
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I have the slower model and have been waiting for parts (new prop & spinner) so I am spending it reading your posts and making expo changes. One change I made was less responsive elevator & ailerons. All the way down to low rate of 75/40. I figure maybe it over reacted due to me. I think the cg is ok as I had it flying ok with out any hands on the tx. It was when I went to bank with ailerons she just went with a mind of its own ( I was 3 mistakes high) and still could not save it. I realize I am some what new to planes (2yrs). I think I will also give the aileron adjustment a try. Can't hurt at this point. I sure hope I figure this bird out..
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Old 06-23-2014, 01:25 AM   #11
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Karnsy
You should not assume that just because you have a plane flying 'hands off' that the CofG is automatically 'right'.
Stable flight is perfectly possible with a rearward CofG (within limits) but it is likely to be flying that much closer to the stall which when it comes is also likely to be more 'aggressive' and the recovery slower.
It really does pay to accurately determine where the CofG actually is and then compare it to what is recommended in the manual.
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Old 06-23-2014, 01:38 AM   #12
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You have to make sure airspeed is up. It may fly level at a certain speed, but then doing turns you will end up with unwanted occurrences. Balance is also important, especially if it is tail heavy.
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Old 06-29-2014, 04:04 AM   #13
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Well it turns out I did not have the cg right. So you all were right thanks . I put 1.80oz in the nose and it cg;d level. That was all the weight I had so I went with it and it made a big difference. Still had to do more expo but I could at least handle it to a point of trust. Still found I had to kind of bring it in hot to land. I fly on grass so I took out to props when she wants to nose over. They seem to snap easy. I plan on adding a little more weight and making it slightly nose heavy. Do you think I could go with a 2 bladed prop ? Anyone tried it if so what size ?
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Old 06-29-2014, 04:28 AM   #14
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3+ blade props are intended for increasing ground clearance and/or reducing tip speed. You can go to a 2 blade prop if you don't have issues with those factors.

Generally when changing from 2 blade to 3 blade we reduce diameter and/or pitch, so going from 3 to 2 you'd expect to want more diameter and/or more pitch. Its somewhat of an experiment to find how much.

I tend to go back to my glow power experience when explaining what goes on when changing prop pitch, diameter and/or blade count.
To maintain the same load you'll always change at least 2, possibly all 3.

When you have a 2 blade 10 inch dia X 6 inch pitch prop spinning appx 10,000 rpm and want to move to a 3 blade prop you reduce diameter or pitch by 1 inch and you will be spinning the 3 blade at about the same rpm. (basic rule of thumb for trading to 3 blade based on .35ci to .40ci glow engine)
Larger engines you typically need to trade MORE dia and/or pitch for the added blade even though they would tend to turn lower rpm.
(this is very "old school"... from when engines didn't turn as high rpm but gives a reasonable example of what to expect.)

Cox .049 glow which tended to turn about 15,000 to 20,000 (sometimes up to 27,000 with a racing prop) would make the 1 inch dia change, going from 6X4 2-blade to 5X4 3-blade. The tip speed being the significant load factor in making the change.

Without having experimented with your exact power system I can't make a specific recommendation on the new prop size.

The main thing you need to remember is to not overload your motor. The electric motor will want to turn the same rpm and will demand power based on the prop load. Its best to use a watt-meter and verify that you are close to the same load.

Then there's the factor of changing blade style... A wood glow style prop will load a motor far more than a thin bladed electric prop f the same diameter and blade count. Any change in the prop design or material can become a surprisingly significant factor.
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Old 06-30-2014, 11:06 AM   #15
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the guy looks like Geroge Best

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Old 06-30-2014, 05:53 PM   #16
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Originally Posted by Neilson Orlov View Post
the guy looks like Geroge Best
What guy? Like who?
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Old 06-30-2014, 05:54 PM   #17
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Originally Posted by Karnsy View Post
I just picked up the new FMS P47 Razorback. Set it all up at neutral settings to start out / reasonable dual rates. The maiden went really bad. Not sure why but went out of control while trying to trim came nose first to the ground. Not to much bad damage. A little glue and a new prop later and time to try again. Second time up was going ok for a minute, thought I had it trimmed then suddenly it went into a spiral to the ground again. I don't get it,, I have set up other new planes and never had any big trouble. Always got them trimmed and to the ground safely but not this one. Did a range check/ receiver antennae at 90 degrees. Wonder what I am doing wrong with this one.. Puzzled ......Any Ideas ?
Yeah, I had a model that will remain nameless that flew great. Until doing a simple big diameter loop. Forward speed was good, and not to much elevator was commanded.

That model snap rolled at the bottom of the loop. There was not enough altitude, or time to save the model before hitting the ground. Found out later, that was a very common problem with that model, several other club members had similar problems.

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