FT Mini Mustang keeps climbing, even at mid throttle

[giba_fernando]

Hi folks.

I'm actually learning to fly RC with the mini mustang.. (bad choice, I know).
Well I've done a few flights, crashed in almost all of them.
I noticed the plane keeps climbing, tho' the CG is fine..
The elevator is straight along the tail, perhaps even a degree downwards.
As I'm new, I'm not quite skilled in flying pushing the nose down, and if I keep the throttle low, I end up crashing anyway..

So my question is, is it really like this or is something wrong with my mini mustang?
I found out I can mix elevator downwards with throttle increasement, but I didn't expect to have that need..

Thanks in advance for all the support!

 

[dgrigor02]

Angle the firewall down a little more should take care of it.

 

[giba_fernando]

Thanks alot, makes complete sense, with all the crashes my firewall is loosen.. :black_eyed:

 

[JimCR120]

giba,

Though you've started with a more harder airframe, it sounds like you're off to a decent start.

Though yo say the CG is good, I would consider moving it forward more. And if you can, level out your elevator and move it farther forward still. If you can make this plane fly true with balance first it will be more efficient. As you go about this effort, have you tried using elevator trim? I'm curious what kind of success you might have had if so.

How long are your flights lasting? Can you maintain the plane airborne for more than a minute?

How twitchy does the plane seem to be? Does it seem to overreact to what you want it to do?

CG's can vary so don't be surprised if yours is a little different. Warbirds are built for agility not stability. Your choice of planes to learn on sacrifices some stabiliy to achieve its agility. Flying over tall grass can help minimize damge during your pilot training. If you are growing too frustrated you could shelf the Mustang temporarily and build something easier to fly until your skills are refined enough.

Also, it would ne nice to know a little about you. Would you introduce yourself to the community?
Welcome to the forum.
—Jim

 

[giba_fernando]

Jim, thanks for the quick response and welcoming.

Looking at the plans, I don't think I have the firewall downthrust I should have. Anyway I heard it's better to have a little nose weight than tail weight so I will try that..

I did trim and it helped a bunch but not enough, after a climb and a turn, the plane loses altitude fast and that's when I screw it up. My flights won't last much more than a minute, partly cause of my noobness I guess, but I bet it can be made easier if it flies horizontally by itself..

I don't feel the plane too twitchy, the throws are as recommended.. Tho' I think I overact on my thumbs at times because of desperateness..

 

[Hai-Lee]

You sound like you know what you need to do which is, Increase the downthrust, slide the cg a little forward of the plan mark, and add about 10 to 15 degrees of Expo to the controls so that your control inputs will be a little smoother.

Have fun!

 

[Konrad]

What you describe is usually a result of upthrust and/or being NOSE heavy. I assume you are not tail heavy as you say you can fly for a minute. This indicates to you are NOT divergent in trim (tail heavy)

If you gain enough control you might want to look at this chart. I use it a lot in trimming my ships. BTW; it takes me about 10 test flights on a new model before I'm happy with its trim.
http://www.wtp.net/DBEST/trimchrt.html

You seem to be addressing the up thrust issue. But adding nose weight to control zoom or climb is often counter productive. This is because a nose heavy model needs more UP elevator to fly level. As the model gains speed (more throttle) this "up trim" cause the model to climb. I would not be surprised if the model ends up with the elevator pointed down even more than you currently show.

Now I know you aren't going to want to hear this, but I would recommend you take a step back and start with a trainer.

Now some models need the throttle elevator mix. I'm thinking high powered gliders. While I don't think your Mustang is such a model I'm happy to learn that you are aware of this mix.

All the best,
Konrad

 

[Bricks]

Might want to read this post I put up from another forum about CG

Being that this particular airplane would appeal to the older set of R/C pilots ( I too fit that catogory ) we in our earlier days were told by many instructors and fellow Modelers that nose heavy is always more stable. Well that turned into a huge wives tale. I have seen many airplanes turned into a handful by running the CG too far forward. What happens is the the forward CG is going to require two things. Up trim and more elevator throw. As speed bleeds off, the trim becomes less effective and the airplane will drop its nose. The pilot will add more elevator to compensate. Two things are likely to happen, either you are so nose heavy that you simply don't have enough elevator to land slowly and are forced to land fast or you have enough elevator but now exceed the wings AOA and boom you get hit with a tip stall. In extreme cases you can actually stall the stab and the result of that looks very much like a tip stall. Another side affect of having to use a bunch of elevator during landing is that downforce on the tail actually gives the result of adding to the wing loading thus making landings faster.

That required up trim will also make it where you will never get the airplane pitch trimmed as any change in speed will result in the trim changing. If this were an aerobatic airplane, anytime you went vertical you would have to hold down elevator to hold a vertical line whether it be an upline or downline. The up trim can in some airplane's create a pitch couple with rudder application. This can show up on landings when you use the rudder to help line up to the runway and it pitches the airplane up slightly and you loose airspeed. In that situation you are slow, lots of up elevator and suddenly climbing and loosing airspeed.

Now granted some of these are extreme examples but what I am getting at is that nose heavy is bad bad bad. Not as bad as being tail heavy mind you but IMO it's close.

Once CG is close to get your thrust angle correct take and fly a vertical line ( straight up ) under full power if it pulls towards the canopy then you have to much up thrust if it pulls towards the landing gear you have to much down thrust , put washers or spacer under the motor mount to correct. and try again.

 

[Hai-Lee]

The one thing barely touched upon is build. If you have different incidence angles between the tail and wing then as you fly faster, or apply more throttle, the tail incidence, (if negative WRT the main wing), would cause a pitch upwards and hence a powered climb.

Had a repair gone wrong at our club recently and he could not get stable attitude across the throttle range. A few shims under the wing TE solved his issue almost immediately and now it behaves as it did before his lawn darting episode.

 

[Konrad]

Bricks,
Can you supply us with that link?

I always say the only thing worse than being tail heavy is being nose heavy!

Being tail heavy puts you out of your misery in short order with a smoking hole in the ground! Giving you a chance to get it right with the new kit found at the end of the runway! Nose heavy leaves you with a ship that is a miserable flying machine, often for years

All kidding aside, start out on the slightly nose heavy side of things. And then move the CofG aft and if need be cut down the control throws as you move along in the test flight program. But do move it aft.

All the best,
Konrad

 

[giba_fernando]

Thanks Hai-Lee, Konrad, Bricks, I wasn't expecting so many answers, and I confess some of them are too complex for me ATM. I know they are and will be very useful 'tho.
As for my issue, I ajusted the firewall and up trim, and it flew a whole different plane.. a lot easier to control, I kept it in the air for 4 and half minutes, till I got overconfident and hit a tree.. Anyway it was awesome to try rolls and inverted for the 1st time in life

 

[Konrad]

Sounds great!
Hitting Trees it happens to the best of us. I've been fly R/C for forty years and still do that!

 

[Hai-Lee]

Hitting a tree is a good sign, it seems trees are attracted to well flown models and step forward to have a closer look!

 

[JimCR120]

Perhaps the best way to miss the tree is by trying to it it. There is a force attraction law that is inversely proportional to the wishes of the pilot.

 

[Bricks]

Bricks,
Can you supply us with that link?

I always say the only thing worse than being tail heavy is being nose heavy!

Being tail heavy puts you out of your misery in short order with a smoking hole in the ground! Giving you a chance to get it right with the new kit found at the end of the runway! Nose heavy leaves you with a ship that is a miserable flying machine, often for years

All kidding aside, start out on the slightly nose heavy side of things. And then move the CofG aft and if need be cut down the control throws as you move along in the test flight program. But do move it aft.

All the best,
Konrad

Here you go I was the one asking the question a plane I picked up used and could not find a lot about it.

https://www.rcgroups.com/forums/showthread.php?2855216-Cg

 

[Konrad]

Thanks, I guess.
I thought (hoped) it was a forum here on FT.

I try to avoid RCGoofs as they place far too much emphasis on protecting their sponsorship base, rather than the needs of the membership.

All the best,
Konrad

 

[TrentC]

Try trimming down elevator, tilting the firewall down some, or simply flying at a lower speed. Have fun and good luck!

 

[Hai-Lee]

The old saying, (Nose heavy fly poorly, BUT tail heavy only flies once!), is applicable today as it was for the Wright brothers.

To find out exactly where your CG should be you start out nose heavy, (remember "Flies Poorly"), rather than tail heavy, (only flies once), and attempt to trim the craft for level flight.

When you land it observe the elevator angle and if the elevator is trimmed to point upwards then the plane was definitely nose heavy and revise the CG point slightly rearwards, if the elevator is trimmed and pointing downwards then the tail is heavy and the CG should be revised slightly forward.

The CG has a small range over which the trim settings will not vary much and the centre of this range is the sweet spot!.

On different classes of aircraft there are slightly CG requirements as a slightly nose heavy setup is used for higher speed aircraft such a pylon racers Etc, where as a very slightly tail heavy setting is fantastic for those who like dog-fighting and other extreme, (Chuck it around the sky), flying.

Side thrust is used to compensate for Torque roll and "P" factor issues and can be extremely difficult to fine tune but as most of the issues are apparent at low speed with full throttle a little intelligent throttle use at take off and when landing can nullify the majority of the effects. As a side thrust angle can reduce the thrust rearwards a little some will keep side thrust to a minimum or lesser than would be otherwise recommended to achieve that little extra speed.

Down thrust is something that must be followed unless you like trim changes that follow throttle settings. Some even mix a little throttle into the elevator for the really high speed racing machines but this is something I would avoid as it can be extremely to quantify. Leave it to the expert high speed fraternity.

As for this site there are numerous threads discussing CG issues and some even pertinent to specific models or materials used in construction. Do a search and a lot of reading and you will find that the question no longer becomes a point of concern.

Have fun!