weight and balance

[RFguy]

I'd think that you'd want it as fixed equipment.

[facthunter]

As long as "Someday" it's not left out.  Nev

[RFguy]

I've now read the rest of this thread

I would STRONGLY advise not adding weight to the tail ! (to get CG in right place) . no way. You will affect spin  recovery /  stall behaviour. 

 

Do what you need to do to maintain the original CG location.  add or subract  or move weight  within a meter  of the CG location ...... This may require the result to be that the outcome is heavier than original. IE sure you can put 1kg in the tail instead of 4kg behind the pilot. BUT you will change the dynamic stability of the airplane, and affect stall/spin recovery, things your aircraft was tested to . IE you are making a different aircraft and it in my mind would no longer meet the specifications of the certificate it holds. 

Edited August 31, 2023 by RFguy

[facthunter]

You will definitely affect the planes spin characteristics in an increased tendency to get into a FLAT spin which is more difficult to recover from..  Nev

[skippydiesel]

1 hour ago, Old Koreelah said:

Instead of adding lead to correct an imbalance, perhaps you could use something that could some day be useful: extra emergency gear, bottles of water,  more tools, a spare tube, etc.

For sure!

 

BUT

 

The heavier an aircraft the more energy (power/fuel) is required to keep it aloft - in the event of there being no other option (adjustments to angle of attack, engine prop angle, etc) the best weight will be the smallest (mass) placed as far out on the airframe as is practical taking into account the afromention effect on spin characteristics..

Edited August 31, 2023 by skippydiesel

[skippydiesel]

2 hours ago, Blueadventures said:

Bristelle are one example of secured 'Mass Ballast' that is bolted to the lower area of the engine mount.

Wow! I would not expect any factory built/supplied aircraft with standard fitments (engine etc) to require ballast - doesn't sound good to me.

[RFguy]

skip, you said : "taking into account the afromention effect on spin characteristics.."
and just how are you going to "take into account the effort on spin characteristics" ?

 

Going to go off and do this with a airframe parachute etc ?

Start sweating when she doesnt recover from a developed spin when you are down to 3000' ?

 

I'm not being flippant, just being real about effects and consequences ....

Edited August 31, 2023 by RFguy

[facthunter]

Engine thrust line etc is NEVER a part of W&B even though it can affect pitch up/ down  etc and the overall aircraft has to be controllable in all anticipated situations and that includes without power.. Those situations are handled by control  surface effectiveness in a dynamic situation.. W&B is done with  static Masses and gravity, (weight) Mg  and moments along the horizontal  and all falling in a "safe for flight" range. Nev

[djpacro]

2 hours ago, skippydiesel said:

Wow! I would not expect any factory built/supplied aircraft with standard fitments (engine etc) to require ballast - doesn't sound good to me.

I don't believe any have come from the factory like that. After the great crew moment arm debacle https://www.bristell.com/wp-content/uploads/2022/12/BRM-Safety-Alert-001_2020_R2.pdf Prior to that the POH had a loading example with two people of my weight shown to be within the aft limit. The revised POH omits that example as we'd be way behind the aft limit.

I wonder if they checked the strength of the engine mounting.

[facthunter]

Strange thing s happen. One of five DC-4s an airline had  on line was a bit difficult to flare when landing, compared with the others. Eventually it was found to have the Basic Index wrong. In service larger planes can have components changed without reweighing as you just calculate the changes and annotate the Airframe  Log book and it's changed on the Load sheet for that plane, subsequently. Anytime you think a plane is behaving problematically pitch wise it would be well to include some "looking at" where the C of G is.  These things do not "FIX" themselves.  Nev

[Blueadventures]

4 hours ago, djpacro said:

I don't believe any have come from the factory like that. After the great crew moment arm debacle https://www.bristell.com/wp-content/uploads/2022/12/BRM-Safety-Alert-001_2020_R2.pdf Prior to that the POH had a loading example with two people of my weight shown to be within the aft limit. The revised POH omits that example as we'd be way behind the aft limit.

I wonder if they checked the strength of the engine mounting.

[skippydiesel]

6 hours ago, facthunter said:

Engine thrust line etc is NEVER a part of W&B even though it can affect pitch up/ down  etc and the overall aircraft has to be controllable in all anticipated situations and that includes without power.. Those situations are handled by control  surface effectiveness in a dynamic situation.. W&B is done with  static Masses and gravity, (weight) Mg  and moments along the horizontal  and all falling in a "safe for flight" range. Nev

Sooo Hypothetically; we have an aircraft that flies but to do so requires unacceptable (??) elevator input (up/down). How to fi? Control surfaces are "tweaked" - some improvement but not enough. What to do? stick a bag of lead somewhere? Or might elevator issues not be helped by a small adjustment in engine/prop  thrust line? What would you do?

[Old Koreelah]

7 minutes ago, skippydiesel said:

…might elevator issues not be helped by a small adjustment in engine/prop  thrust line? What would you do?

Some extreme examples allow no leeway. On some Pushers, the prop is only missing the fuselage spar by a poofteenth.

Some amphibians have the prop just above the wing.

[facthunter]

You might adjust the thrustline etc  as a change in design, but W&B is only about W&B. It has to be safe when gliding  also  so thrust can't play the full part in it  Underwing Jets need lots of forward trim on a go around . What is acceptable is up to interpretation, but I guess that's what pilots are Paid for Nev

[skippydiesel]

1 hour ago, facthunter said:

You might adjust the thrustline etc  as a change in design, but W&B is only about W&B. It has to be safe when gliding  also  so thrust can't play the full part in it  Underwing Jets need lots of forward trim on a go around . What is acceptable is up to interpretation, but I guess that's what pilots are Paid for Nev

Agreed however they way you are making your point suggests, to me, that W&B is somehow isolated from other control/ aerodynamic factors.

One thing I have learnt in my short flying experience, is that pretty much everything is interrelated ie make a small adjustment in one area (may do just what you want) may also have impacts in other areas.

[facthunter]

W&B is just one fence you must jump over and satisfy. I suggest it comes after those design characteristics have been sorted out.. You are not permitted to fly, legally if you are outside the W&B parameters specified for the Plane. IF you're designing the thing, well everything's up to you. You can as operator intentionally load the Plane towards the aft CofG limit to fly more efficiently, Your choice.. . You should also know the effects of doing so on stability.. Most planes also have a Max fuel assymetry  (control issue)  and max wt above which all extra load must be fuel/ (structural issue). Nev

[skippydiesel]

All good Nev.

 

My understanding of this conversation is, that we are considering adjustments within W&B  - so again if you have the aircraft within W&B and still feel your controls (elevator) could be brought in a neutral position (with reference to the horizontal stab) how would you seek to acheive this?

[spacesailor]

Move the ' horizontal stabiliser ' to give a better result , on the ' elevator ' incidence. 

IF your design allows such adjustments. 

spacesailor

[facthunter]

Reposition the stab to streamline with the airflow. For stability in pitch,  it's normal to have a bit more incidence on the Mainplanes than the tail feathers  Nev

[skippydiesel]

3 hours ago, spacesailor said:

Move the ' horizontal stabiliser ' to give a better result , on the ' elevator ' incidence. 

IF your design allows such adjustments. 

spacesailor

 

2 hours ago, facthunter said:

Reposition the stab to streamline with the airflow. For stability in pitch,  it's normal to have a bit more incidence on the Mainplanes than the tail feathers  Nev

 

 

Have thought of that but just seems to be in the "too hard basket" (for now).

 

Easier possible solution -  have  raised the front of the engine 1mm. Yet to fly, so assessing change (if any), to elevator position , about 2 months away

[Blueadventures]

On 31/08/2023 at 7:53 PM, Blueadventures said:

Images of mass balance on a Bristelle I took today during an annual.  Bolted to crankcase.

Edited September 1, 2023 by Blueadventures

[Old Koreelah]

2 hours ago, skippydiesel said:

Easier possible solution -  have  raised the front of the engine 1mm…

Off topic perhaps, but have you finalised your engine offset to counteract prop torque?

If not, it’s prudent to have a bit of adjustment space.

[RFguy]

Not sure how that all happened at BRM. Seems a rookie mistake having a airplane get into production and then  to need to add that mass....

 

[skippydiesel]

Wow! that's some lump of non contributing mass - Would have thought they would have done something other than that,to achieve balance - moved the engine forward.

 

Not a good look for Bristelle

[Blueadventures]

7 minutes ago, skippydiesel said:

Wow! that's some lump of non contributing mass - Would have thought they would have done something other than that,to achieve balance - moved the engine forward.

 

Not a good look for Bristelle

It's all relative to being safe for flight; my Blanik glider had shaped lead weight secured to inside the forward most frame, just inside the nose cowl to keep correct w&b. A normal practice like Jabs put lead shot in the tail etc.