RFguy Posted August 31, 2023 Share Posted August 31, 2023 I'd think that you'd want it as fixed equipment. 2 2 Link to comment Share on other sites More sharing options...
facthunter Posted August 31, 2023 Share Posted August 31, 2023 As long as "Someday" it's not left out. Nev 1 2 Link to comment Share on other sites More sharing options...
RFguy Posted August 31, 2023 Share Posted August 31, 2023 (edited) 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 1 1 Link to comment Share on other sites More sharing options...
facthunter Posted August 31, 2023 Share Posted August 31, 2023 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 1 1 Link to comment Share on other sites More sharing options...
skippydiesel Posted August 31, 2023 Share Posted August 31, 2023 (edited) 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 Link to comment Share on other sites More sharing options...
skippydiesel Posted August 31, 2023 Share Posted August 31, 2023 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. Link to comment Share on other sites More sharing options...
RFguy Posted August 31, 2023 Share Posted August 31, 2023 (edited) 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 Link to comment Share on other sites More sharing options...
facthunter Posted August 31, 2023 Share Posted August 31, 2023 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 Link to comment Share on other sites More sharing options...
djpacro Posted August 31, 2023 Share Posted August 31, 2023 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. Link to comment Share on other sites More sharing options...
facthunter Posted August 31, 2023 Share Posted August 31, 2023 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 1 Link to comment Share on other sites More sharing options...
Blueadventures Posted August 31, 2023 Share Posted August 31, 2023 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. 1 Link to comment Share on other sites More sharing options...
skippydiesel Posted August 31, 2023 Share Posted August 31, 2023 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? Link to comment Share on other sites More sharing options...
Old Koreelah Posted August 31, 2023 Share Posted August 31, 2023 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. Link to comment Share on other sites More sharing options...
facthunter Posted September 1, 2023 Share Posted September 1, 2023 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 Link to comment Share on other sites More sharing options...
skippydiesel Posted September 1, 2023 Share Posted September 1, 2023 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. 1 Link to comment Share on other sites More sharing options...
facthunter Posted September 1, 2023 Share Posted September 1, 2023 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 1 Link to comment Share on other sites More sharing options...
skippydiesel Posted September 1, 2023 Share Posted September 1, 2023 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? Link to comment Share on other sites More sharing options...
spacesailor Posted September 1, 2023 Share Posted September 1, 2023 Move the ' horizontal stabiliser ' to give a better result , on the ' elevator ' incidence. IF your design allows such adjustments. spacesailor Link to comment Share on other sites More sharing options...
facthunter Posted September 1, 2023 Share Posted September 1, 2023 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 Link to comment Share on other sites More sharing options...
skippydiesel Posted September 1, 2023 Share Posted September 1, 2023 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 Link to comment Share on other sites More sharing options...
Blueadventures Posted September 1, 2023 Share Posted September 1, 2023 (edited) 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 2 1 Link to comment Share on other sites More sharing options...
Old Koreelah Posted September 1, 2023 Share Posted September 1, 2023 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. Link to comment Share on other sites More sharing options...
RFguy Posted September 1, 2023 Share Posted September 1, 2023 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.... 3 Link to comment Share on other sites More sharing options...
skippydiesel Posted September 1, 2023 Share Posted September 1, 2023 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 1 Link to comment Share on other sites More sharing options...
Blueadventures Posted September 1, 2023 Share Posted September 1, 2023 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. 1 Link to comment Share on other sites More sharing options...
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