Weight & Balance and Fixed trim

[skippydiesel]

Just taught that I would chuck this scenario in for your discussion/debate:

 

You have an aircraft that meets its weight & balance specifications. It is fitted with a ground adjustable fixed pitch propeller.

 

Take off is normal in every respect. As is climb out.

 

When the aircraft reaches cruse altitude and levels out, the aircraft will start to accelerate, if there is no change to the engine power setting - all good so far.

 

As the aircrafts speed rises, the pilot puts in forward/down elevator trim, to counter the tendency of the aircraft to climb - still all good.

 

At some point the trim "runs out", the stick is full forward and without any reduction in prop speed the aircraft is still climbing - not so good.

 

What is your diagnosis ??

 

AND

 

What might be your solution(s) ??

[spacesailor]

Draggy high wing,

Or

Engine not inline with airfoil, pulling the fuselage into a circle climb attitude.

spacesailor

[IBob]

So, is the stick full forward...or is it forward as far as it will now go???

[Blueadventures]

Need more info re the flap setting / adjustment.

[Thruster88]

The aircraft sound like a dog, how did it get certified.  

[skippydiesel]

1 hour ago, spacesailor said:

Draggy high wing,

Or

Engine not inline with airfoil, pulling the fuselage into a circle climb attitude.

spacesailor

Way to complicated - try again.

[skippydiesel]

1 hour ago, IBob said:

So, is the stick full forward...or is it forward as far as it will now go???

Stick full forward at this point.

[skippydiesel]

11 minutes ago, Thruster88 said:

The aircraft sound like a dog, how did it get certified.  

Interesting - aircraft is a RAA 19 Rego and as engine/prop now operating as per high speed cruise I would expect the noise to be as per Rotax normal high power.

 

Perhaps you might like to elaborate

[skippydiesel]

1 hour ago, Blueadventures said:

Need more info re the flap setting / adjustment.

Flaps correctly "rigged" and at this stage fully retracted - some negative trim , as per manufactures specs.

[IBob]

Skippy, your exceedingly large packed lunch has slid to the tail of the aircraft while you were executing that blinding climbout.......)

[Blueadventures]

Unsecured mass or water in the fuse has moved aft.

[Thruster88]

46 minutes ago, skippydiesel said:

Interesting - aircraft is a RAA 19 Rego and as engine/prop now operating as per high speed cruise I would expect the noise to be as per Rotax normal high power.

 

Perhaps you might like to elaborate

If you are flying in cruise with the stick full forward something is very seriously wrong.

[skippydiesel]

1 hour ago, Blueadventures said:

Unsecured mass or water in the fuse has moved aft.

Fair guess but no - keep eliminating.

Edited August 7, 2021 by skippydiesel

[skippydiesel]

1 hour ago, Thruster88 said:

If you are flying in cruise with the stick full forward something is very seriously wrong.

Come come Thruster - if everything was as expected I would not be posting this brain teaser/conversation stimulator.

 

I would still like to understand your previous comment "The aircraft sound like a dog, how did it get certified. " 

[Blueadventures]

52 minutes ago, skippydiesel said:

Fair guess but no - keep eliminating.

Light weight pilot, weighing less than minimum seat mass and no ballast added to compensate.

[skippydiesel]

1 hour ago, Blueadventures said:

Light weight pilot, weighing less than minimum seat mass and no ballast added to compensate.

Good one Blue - the petit frame of the pilot would have been a contributing factor for sure but not the main issue. So far you are te only one who is getting "warm"

[skippydiesel]

Gentlefolk - I suggest you go back to basics.

 

What do you know;

 

This is a Rotax motivated aeroplane. Fitted with fixed pitch prop. Normal procedure is to "firewall" the throttle to give max power on take off followed by a throttle back (to stay below  continuose "redline") to max cruise power on climb out.

 

Aircraft takes off, climbs normally.

 

On reaching the pilots desired cruise altitude, the aircraft levels out.

 

Pilot choses not to reduce power. As speed increases, forward stick is applied to maintain altitude. At some point stick runs out of travel and aircraft start to climb.

 

Two more clues:

• This is a, RAA 19 register aircraft.
• Reducing power/speed, stops climb.

[Blueadventures]

Is this the aircrafts first flight? If so the engine thrust line must be a tad positive, up.

[pmccarthy]

Carrying minimum fuel. Prop pitched for max climb.

Edited August 7, 2021 by pmccarthy

[APenNameAndThatA]

It doesn’t seem possible, but I enjoy thinking about these scenarios.  

[Thruster88]

OME has returned. My answer, the aircraft has been "designed" with excessive stick position stability. It's a dog, get a different aircraft.  

[planesmaker]

Tail plane is rigged wrong, more + incidence would fix it

[skippydiesel]

10 hours ago, Blueadventures said:

Is this the aircrafts first flight? If so the engine thrust line must be a tad positive, up.

The aircraft has been flying in this "state" for many years with the pilot being content to fly at the cruise speed that did not result in a climb. Checks indicated engine thrust line within specifications

 

 

8 hours ago, pmccarthy said:

Carrying minimum fuel. Prop pitched for max climb.

Prop pitch was to facilitate short field operations but again this was discounted as the primary cause of the high speed problem. As for fuel load - made little difference full/low as main tank pretty much on C of G

 

3 hours ago, APenNameAndThatA said:

It doesn’t seem possible, but I enjoy thinking about these scenarios.  

It certainly is possible and the idea here is to stimulate conversation so my efforts are being rewarded.

 

1 hour ago, Thruster88 said:

OME has returned. My answer, the aircraft has been "designed" with excessive stick position stability. It's a dog, get a different aircraft.  

The aircraft flies very nicely as long as you stay below high speed cruise. "Throwing the baby out with the bath water" is rarely the best/most effective response

[skippydiesel]

9 minutes ago, planesmaker said:

Tail plane is rigged wrong, more + incidence would fix it

What makes you jump to this conclusion? 

 

 

[aro]

5 minutes ago, skippydiesel said:

What makes you jump to this conclusion? 

 

The description of the problem? There is nothing else it could really be based on the description you have provided.

 

If you can't stop the aircraft climbing with full forward stick, the aircraft is unairworthy and should be grounded until the problem can be fixed.