Weight & Balance and Fixed trim

[spacesailor]

Is this aircraft a  'powered parachute ' ?.

" draggy high wing ".

spacesailor

 

 

[skippydiesel]

13 minutes ago, aro said:

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.

If possible, I would like a more analytical response. Planesmaker and you are on the right track.

 

The aircraft  was perfectly airworthy as long as the pilot remained within the controllable flight envelope. In the event of continuing in high speed/power cruise the aircraft was controllable in all axis, other than climb and this was easily restored by reducing power.

 

The  "problem" was recognised/diagnosed & appropriately corrected several years ago - so no need to ground/dispose of/change aircraft.

 

Edited August 7, 2021 by skippydiesel

[skippydiesel]

8 minutes ago, spacesailor said:

Is this aircraft a  'powered parachute ' ?.

" draggy high wing ".

spacesailor

 

 

No its actually a composite low wing, T tail.

[planesmaker]

If you have full forward stick in cruise your cg is out or the tailplane incidence is wrong. As you said cg was ok I would look at the tailplane. 

[aro]

14 minutes ago, skippydiesel said:

The aircraft  was perfectly airworthy as long as the pilot remained within the controllable flight envelope.

That is not a definition of airworthy. Whatever happened to "I certify that ... the aircraft is controllable throughout its range of speeds" which is required for experimental aircraft (and no less for professionally built aircraft I assume).

 

From the description it is speed dependent, what happens e.g. in a spiral dive?

18 minutes ago, skippydiesel said:

I would like a more analytical response.

We would like a more analytical question.

[aro]

51 minutes ago, skippydiesel said:

I would like a more analytical response.

An analytical response:

 

Aerodynamically, you have the wing. The horizontal stabilizer keeps the wing at the desired angle to the airflow. The fuselage is just there to join them together and provides a convenient place for payload. Then engine is there to move the wing it through the air.

 

If you do not have enough control authority to pitch the nose down at higher speed, either 

1. the horizontal stabilizer is at the wrong angle i.e. rigged incorrectly
2. the elevator doesn't have enough travel e.g. control stops
3. the weight and balance is out of range - but you said the W&B was OK and I would expect this to be a problem at lower speeds not higher

The type of engine, RPM etc are irrelevant aerodynamically.

[kasper]

Walking through the issues of Climb at power with full forward stick means the tail group is probably providing a positive lift moment in cruise.  Assuming this is not a canard I'm not happy to fly. Where do I look and why

In a  tractor aircraft where the net negative moment from the tail to balance everything is not required I'm looking for two or three areas that cause it 

a. CofG at the rear of limitations plus something else

b. Misrigged control surfaces or runs ... Or even cables that are stretching. 

C. Ridiculously overpowered airframe -prop blast over centre section providing too much lift the tail can't hold down.

d. Flaps misrigged to be deployed when in retracted position

 

any of these can provide parts of what you report. 

 

 

[IBob]

Incorrect angle of a attack on the wings would also do it....but that's pretty much the same as saying the empennage is incorrectly aligned with reference to the wings.

[skippydiesel]

2 hours ago, aro said:

That is not a definition of airworthy. Whatever happened to "I certify that ... the aircraft is controllable throughout its range of speeds" which is required for experimental aircraft (and no less for professionally built aircraft I assume).

 

From the description it is speed dependent, what happens e.g. in a spiral dive?

We would like a more analytical question.

Aro - All aircraft have a safe operating envelope. outside this , you risk nasty things happening. Anyhow this is not the the question

[aro]

1 minute ago, skippydiesel said:

All aircraft have a safe operating envelope. outside this , you risk nasty things happening.

If you are saying that it was exceeding VNE, I would say "don't do that".

[skippydiesel]

Aro, Kasper, IBob,

 

You have all jumped on Plainesmakers response - with reasonable justification.

 

The key to this is that its a 19 rego. allowing owner builder to make adjustment/errors to the aircraft ( I had thought someone would have asked this Q)

 

The problem stemmed from a factory issued  Mandatory Modification, requiring an adjustment to the horizontal stabiliser, possibly compounded by the belated fitting of, unused, factory supplied fairings around the stabilizers attachment points (fairing found in box of vendor supplied parts) 

 

Before going into that, I might mention the investigation that took place over several months;

• The W&B was checked twice, with the same satisfactory result.
• The pilot is vertically challenged and lighter than the average  person but within the factory specified weight range so as not to need "ballast". The symptoms were found to change a little with the addition of a heavy pilot./passenger.
• Wings & surfaces all as expected
• Flap & aileron movement/ settings as per factory specs.
• Elevator movement was found to operate through its correct range with & without (artificial) load.
• No loose/weak airframe  parts extended at high speed (went round pulling/pushing on bits looking for deflection/movement).
• After many flights, much discussion with other pilots and much burning of scarce brain cells - it was determined that the horizontal stabiliser (Stab) must be generating excess down forces/ negative lift ie set at the incorrect angle of attack.
• The concept being, that at lower speed operations, the Stab works just fine and within the ability of the elevator to modify its effects. As speed increases, the tail down forces would also increase - this is fairly normal. However in this case the speed/ down force would get to a point where elevator authority could no longer overcome the down force and the aircraft would begin to climb (unless power /speed reduced)
• How could this be ? - a review of the Log Book and paperwork revealed the aforementioned factory directive. The previous owner,who would have implemented the fix was dead, so no help there.
• The previous owner, a much more substantial person than the current, was known to operate the aircraft in its econamy cruise range - quite possibly did not explore its high speed performance or if he did, decided that he wasn't going to go there again.
• The horizontal stab was removed and the factory "fix" examined. Everything look OK

 

The factory fix, was a wood spacer placed such that the trailing edge of the Stab would be raised. Several readings of the (non too clear) factory instructions and a difficult (language barrier) email conversation with the factory suggested that the wooden spacer was far too thick. 

 

The factory gave the go ahead to progressively reduce the spacer thickness.

 

Many 1mm shavings and test flights later, we have an aircraft that can fly at any speed, within its capability, without the need for undue elevator trim. In flight stick position was recorded and relate back (on ground) to elevator position throughout test series .

 

For those that might be concerned - both high and low speed was checked as were stall characteristics - if anything the stall/slow speed controllability improved and the "break" may have been reduced slightly 

 

Problem solved and satisfactory result achieved.

 

[Blueadventures]

Is the air foil shape of the elevator correct; could adjust the elevator to max + limit or adjust the flap (each side) up a little.

[skippydiesel]

23 minutes ago, Blueadventures said:

Is the air foil shape of the elevator correct; could adjust the elevator to max + limit or adjust the flap (each side) up a little.

Hi Blue -  nothing wrong with the elevator (its one long elevator, reaching almost the full span of the horizontal stabilizer).

 

I would guess, that befor the factory modification was, incorrectly, applied the aircraft flew just fine - possibly a little nose heavy. The factory fix was designed to correct this but possibly due to vague instructions (transliterated into English by a less than proficient person/computer) the then owner overdid the "correction".

[aro]

1 hour ago, skippydiesel said:

You have all jumped on Plainesmakers response - with reasonable justification.

 

Because it was 100% correct, as you described in your answer. It is unreasonable to expect us to guess why the h-stab was misrigged.

 

I stand by my comment that the aircraft was unairworthy because it could not be controlled within it's normal range of speeds.

[Blueadventures]

1 hour ago, Blueadventures said:

Is the air foil shape of the elevator correct; could adjust the elevator to max + limit or adjust the flap (each side) up a little.

I hadn’t read your post when posting above.  Did you mention the breed and model of the subject aircraft. Cheers.

[skippydiesel]

1 hour ago, Blueadventures said:

I hadn’t read your post when posting above.  Did you mention the breed and model of the subject aircraft. Cheers.

No - In my view not relevant as it was a 19 and therefor had a greater potential to be mis rigged by the owner/builder.

[skippydiesel]

1 hour ago, aro said:

Because it was 100% correct, as you described in your answer. It is unreasonable to expect us to guess why the h-stab was misrigged.

 

I stand by my comment that the aircraft was unairworthy because it could not be controlled within it's normal range of speeds.

Well I had hoped for a plethora of searching questions - not guess work.

 

Miss rigging/adjustment was evident from the start - other than Planesmaker no one made a start in that direction.

 

Where were the questions into the aircrafts history - any incidents/modifications etc.

[APenNameAndThatA]

Asking a question and then whinging about the answers is *very* OME. 

Edited August 8, 2021 by APenNameAndThatA

[skippydiesel]

13 minutes ago, APenNameAndThatA said:

Asking a question and then whinging about the answers is *very* OME. 

The lack of

[APenNameAndThatA]

Someone already said “

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

 

That is EXACTLY the correct answer. They didn’t say “elevator rigged wrongly” they said “tail plane”. 

 

Not giving ant credit to a correct answer is also *very* OME. 

 

I’m going to call it. Skippy has given his account details to our mate Mark, aka OME. 

[APenNameAndThatA]

Welcome back

[planesmaker]

Does this mean I passed the test?😀😀😀😀

[pmccarthy]

The skippy and the emu, who'd have thought they would be the same animal?

[Blueadventures]

4 minutes ago, planesmaker said:

Does this mean I passed the test?😀😀😀😀

Kind of, maybe, not sure, but recon you did. What type and model was it. Tail plane would narrow things down.🤪

Edited August 8, 2021 by Blueadventures

[IBob]

1 minute ago, planesmaker said:

Does this mean I passed the test?😀😀😀😀

Yes, you did splendidly!

Though several others here are a bit hot and cross...which invariably seems to be part of these little brain teasers too.........(