Van's Air Force
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Do 8A's tip over (flip) too?
- Thread starter N674P
- Start date
Yep. Several.N674P said:
Here's one noseover 8A that I followed while I was building Flash:
http://www.geocities.com/CapeCanaveral/Launchpad/9749/william.html
Great paint scheme.
redbeardmark
Well Known Member
N674P said:
Hey, I keep trying
: undulating gravel roads, dry lake beds, gopher-hole-pocked grass strips(there is one in ND that reminds me of a giant corncob that has been run through a corrugator), even the airport at Fort Yukon(an excellent place to chip paint off your RV and maybe even get stuck in the deep, soft gravel on the "ramp"... hint, hint... do not go there in an RV).The RV trikes DO have a weak nosegear. Anyone who has taken proper transition training would have that drilled into his/her head. As suggested, certain models may be more prone to flipping. But I don't know for sure.
Any idea of what percentage of the flip-overs had proper transition training? Is there any way to know this? Maybe not. Would it be reasonable to guestimate the number based upon the percentage of all RV pilots who took transition training prior to flying their own bird? Poll anyone?
pierre smith
Well Known Member
More practise....
Mornin' all,
Many of the guys who come here for transition training are really rusty since their time and money was/is being spent on building and buying, not flying. Often I see guys not getting the nose high enough on landings and when they do, they often also relax the backpressure immediately following touchdown and the nosewheel comes down hard.
Practise your own landings and if you'd only hold the stick in the same position it was in when the mains touch down, the nose will stay in the air for a while and come down on its own as the speed bleeds off....gently too. There is so much elevator authority that you can continue to pull back on the stick as you slow down and keep the nosewheel off even longer.....something you absolutely Must do on grass. After the nosewheel is settled, continue to hold full back stick to lighten the load on the nose. Do this taxiing as well and you'll keep a lot of weight off the nose.
Takeoffs on grass should have the nosewheel off very shortly after full throttle if you'll hold a lot of backpressure initially. Beware of the rapid acceleration and how quick the nose will come up, but this allows you to be on the mains with a nice angle of attack as you do your run on only the mains with the nosewheel maybe barely touching or off the ground altogether.
Regards,
Pierre
Mornin' all,
Many of the guys who come here for transition training are really rusty since their time and money was/is being spent on building and buying, not flying. Often I see guys not getting the nose high enough on landings and when they do, they often also relax the backpressure immediately following touchdown and the nosewheel comes down hard.
Practise your own landings and if you'd only hold the stick in the same position it was in when the mains touch down, the nose will stay in the air for a while and come down on its own as the speed bleeds off....gently too. There is so much elevator authority that you can continue to pull back on the stick as you slow down and keep the nosewheel off even longer.....something you absolutely Must do on grass. After the nosewheel is settled, continue to hold full back stick to lighten the load on the nose. Do this taxiing as well and you'll keep a lot of weight off the nose.
Takeoffs on grass should have the nosewheel off very shortly after full throttle if you'll hold a lot of backpressure initially. Beware of the rapid acceleration and how quick the nose will come up, but this allows you to be on the mains with a nice angle of attack as you do your run on only the mains with the nosewheel maybe barely touching or off the ground altogether.
Regards,
Pierre
I would like to put in an observation from my field. Every time an A model lands, well lets look at it in a broad sense here, every time a nose wheel airplane lands, it's flat landed. The last RV that I saw land, it was a 9A, it was flat landed, in fact it bounced on all three about 5 times before it finally was down. Holy ****! how is the nose wheel suppose to survive that??? I was at a fly in up north from here a couple years ago, an RV9A landed, but on the mains, beautiful landing, no front wheel shimmy on set down. Right behind him was a RV6A and it landed flat, and on role out the nose wheel shimmied real bad, recipe for desaster.
I'm a tail wheel pilot and am building a 7A, crazy, I don't think so, this bird WILL be landed like my tail wheel airplane, NOSE HIGH, which I will be keeping as well. I remember when I was in training, with a cessna, and I was always pounded with the fact that the nose wheel is for taxi not landing on. I would do touch and go's all the time with the nose wheel never touching the runway.
I think the scary part of landing nose high is you don't see down the runway, this in itself scars the bagesies out of a pilot, once you get use to looking out the left side and down, you can do it. I remember the old days of looking for a picture on flair, down to the end of the runway. In a tail wheel airplane you don't get that anymore, you have cowling in the face. I have adapted to looking left and out slightly and now I can land beautiful and land nose high. What's cool about this kind of landing is the fact that when the sun is down the runway, it's no longer an issue. I also catch myself landing and moving to the right slightly so I can follow the yellow center line as well.
I'm a tail wheel pilot and am building a 7A, crazy, I don't think so, this bird WILL be landed like my tail wheel airplane, NOSE HIGH, which I will be keeping as well. I remember when I was in training, with a cessna, and I was always pounded with the fact that the nose wheel is for taxi not landing on. I would do touch and go's all the time with the nose wheel never touching the runway.
I think the scary part of landing nose high is you don't see down the runway, this in itself scars the bagesies out of a pilot, once you get use to looking out the left side and down, you can do it. I remember the old days of looking for a picture on flair, down to the end of the runway. In a tail wheel airplane you don't get that anymore, you have cowling in the face. I have adapted to looking left and out slightly and now I can land beautiful and land nose high. What's cool about this kind of landing is the fact that when the sun is down the runway, it's no longer an issue. I also catch myself landing and moving to the right slightly so I can follow the yellow center line as well.
pierre smith said:
Sorry to disagree but holding full up elevator during taxi and idle power does virtually nothing to unload the nose gear. Like I said before, can't hurt but it mainly just makes you feel better. 10-15 lbs. of force from the elevators won't do squat when there is 300-350 lbs. on the nosewheel. Many of the flip overs have been at near walking pace.
I do agree that many people flying A models forget to to keep the nose high in the flare. You must or someday your luck will run out. Learn and retain the proper technique.
rv7boy
Forum Peruser
RV-12 Nose Gear
Just something to think about...
With the fuel tank of the RV-12 behind the CG, as the fuel is used, the CG will shift forward and there will be more nosegear loading with a nearly empty tank than with a nearly full tank. The opposite is true, I believe, with all the other RV models with the fuel tanks in the wing leading edges.
Maybe it's not much difference; I admit I haven't calculated it. But with two passengers and nearly empty fuel, an RV-12 pilot must be diligent in his/her landing technique.
Don
Just something to think about...
With the fuel tank of the RV-12 behind the CG, as the fuel is used, the CG will shift forward and there will be more nosegear loading with a nearly empty tank than with a nearly full tank. The opposite is true, I believe, with all the other RV models with the fuel tanks in the wing leading edges.
Maybe it's not much difference; I admit I haven't calculated it. But with two passengers and nearly empty fuel, an RV-12 pilot must be diligent in his/her landing technique.
Don
pierre smith
Well Known Member
Yes it does
Ross,
The nosewheel will settle at around 45 MPH and back stick does help. My 6A only has 245 lbs on the nose, not 300. Just because you don't see the nose lifting like a Cessna with an oleo strut doesn't mean it isn't unloading the nosewheel. I realize full well that it doesn't add much lift at a walk but the main point of my post was to improve pilot technique. BTW that Sube is really heavy!!
Regards,
Pierre
Ross,
The nosewheel will settle at around 45 MPH and back stick does help. My 6A only has 245 lbs on the nose, not 300. Just because you don't see the nose lifting like a Cessna with an oleo strut doesn't mean it isn't unloading the nosewheel. I realize full well that it doesn't add much lift at a walk but the main point of my post was to improve pilot technique. BTW that Sube is really heavy!!
Regards,
Pierre
rv7boy
Forum Peruser
allbee said:
What? I think you are thinking backwards. Or maybe I need another cup of coffee.
When a tricycle geared airplane is on the ground, and the CG is shifted to the rear, less force will be exerted on the nose wheel.
If you don't believe it, I can show you the results of two people standing on the steps of an RV-9A at the same time. Don't try this at home. The rudder smacked the ground.
Don
L.Adamson
Well Known Member
rv7boy said:
I think you need another cup of coffee...
If the CG is physically moved rearward, then more weight is transferred to the nose gear.
This would be different than standing on the wing steps, which is putting weight behind the prescribed CG point.
At last I think this is the technical way it is.
L.Adamson
zilik
VAF Moderator
10-15 lbs of down force on the elevator equals 10-15 lbs off the nose (equal moment arm). Now the Tail is a lot farther from the pivot point than the engine by about 3:1 so 10-15 lbs on the tail equates to 30-45 off the nose. It helps!rv6ejguy said:
Walking speed they don't flip, they just do the kneeling camel trick.
Now wait a minute. THe center of gravety that I'm talking about is if you where to pick the airplane up lets say at the main spar it should balance, if you go back lets say an inch the nose of the airplane will drop. I build and fly model airplanes and this is how we balance the airplanes out. Maybe I have the wrong terminology but I have the right idea.
mlw450802
Well Known Member
C'mon guys. Think weight and balance. We move the CG (balance point) of the aircraft all over the place when we load it. If the CG is moved forward, more weight will be on the nose wheel. If is is moved aft, more weight will be on the mains. If it is moved even a fraction of an inch behind the mains, the nose wheel will come off the ground.L.Adamson said:I think you need another cup of coffee...
If the CG is physically moved rearward, then more weight is transferred to the nose gear.
This would be different than standing on the wing steps, which is putting weight behind the prescribed CG point.
At last I think this is the technical way it is.
L.Adamson
-mike
What I'm after is the correct CG's for the A. If it's not correct than too much force on the front can happen. I have a trainer plane for remotes and if I put the cg forward than I can impress people at the field and land with nose off all the way to the pit. If I put the cg aft, forget it, can't do it.
Now my kitfox, if I have stuff in the back, luggage. Than it flies more nose high on landing. I'm sure the same is for the A models as well. Also if I don't use the flaps, it flies nose high on landings. A little increase in throttle will raise the nose up on landing. I'm sure there are many other things that will give you nose up on landing.
Just don't flat land them, recipe for desaster. I'm sure that many people end up landing flat as a rule, then when they come in for that nice main touch and let the nose down, that this is when things go wrong and blame it on the landing gear because they did land correct, but it's all those other times that put strain on the landing gear that is the cause.
Now my kitfox, if I have stuff in the back, luggage. Than it flies more nose high on landing. I'm sure the same is for the A models as well. Also if I don't use the flaps, it flies nose high on landings. A little increase in throttle will raise the nose up on landing. I'm sure there are many other things that will give you nose up on landing.
Just don't flat land them, recipe for desaster. I'm sure that many people end up landing flat as a rule, then when they come in for that nice main touch and let the nose down, that this is when things go wrong and blame it on the landing gear because they did land correct, but it's all those other times that put strain on the landing gear that is the cause.
RVbySDI
Well Known Member
I believe I understand what you are saying and what others are confused about from your post.allbee said:
You are referring to moving the point where the landing gear are attached to the fuselage. The further back the main gear are mounted the more weight the nose gear will be required to support when the airplane is on the ground. This is what I am getting from your statements. If this is what you mean, that is not necessarily a component of CG in relation to the wing and what the wing supports, which is what most people think about when discussing CG.
Harvey L. Sorensen
Well Known Member
cg
I believe you have it Steve.
The airport where I have my 9-A will close for repairs for about three months starting in June. I have my own strip at my home but it is fine for my J-4 Cub. I can check for critters homes ect and bring in my 9-A and I am thinking coming in and out of this grass strip with around 80 pounds of wieght in the luggage just to help keep the nose wheel off the ground longer. This will move the CG to the rear a lot and make the nose lighter. I have a 320 with a Hartzel CS.
Am looking for comments either for or against. I don't really like to do the grass thing but there are no hangers at any of the other local airports.
I believe you have it Steve.
The airport where I have my 9-A will close for repairs for about three months starting in June. I have my own strip at my home but it is fine for my J-4 Cub. I can check for critters homes ect and bring in my 9-A and I am thinking coming in and out of this grass strip with around 80 pounds of wieght in the luggage just to help keep the nose wheel off the ground longer. This will move the CG to the rear a lot and make the nose lighter. I have a 320 with a Hartzel CS.
Am looking for comments either for or against. I don't really like to do the grass thing but there are no hangers at any of the other local airports.
RVbySDI
Well Known Member
Well Harvey, I can see where an aft CG will help keep weight off of the nose gear when taking off. I would just make sure you are not going to load up with aft CG and fly off enough fuel that the CG will push even further aft (not saying this is what would happen with the fuel burn in the 9A but some airplanes do). As long as your CG remains within the parameters of the airplane and you can maintain full control you should be good.
These nose gear threads are very interesting to me as I am building a 9A and have a hangar on a private grass strip where I intend to fly out of. I want to do whatever it takes to assure that I can reduce my risks of a nose gear failure. If it is proven that the 9A will not perform on grass without high risk then I will be forced to re-examine my decision to fly the -A.
These nose gear threads are very interesting to me as I am building a 9A and have a hangar on a private grass strip where I intend to fly out of. I want to do whatever it takes to assure that I can reduce my risks of a nose gear failure. If it is proven that the 9A will not perform on grass without high risk then I will be forced to re-examine my decision to fly the -A.
Ok guys, you need to go back to the basics on flight. CG is the force on the underside of the airframe. This is invisible. Emagine a point that is a force on the underside of the airframe when the aircraft is FLYING. If this force is aft the nose of the airframe WILL be heavy, if this point is forward the tail WILL be heavy. The best way to understand this is to do all your computations for weight and balance and figure out your CG (center of gravity), then mark your center of gravety on the wings, then put some jacks under wings at this point and raise the aircraft, if you done things right the airframe WILL balance with no drop in the front or back, if it does something different, the weight and balance was not figured right.
Question, how many people weigh their baggage? I don't mean to put it on a bathroom scale. What I do is use a fish scale and weigh each item I put in the aircraft and note where in the aircraft I put them.
Question, how many people weigh their baggage? I don't mean to put it on a bathroom scale. What I do is use a fish scale and weigh each item I put in the aircraft and note where in the aircraft I put them.
rv7boy
Forum Peruser
allbee said:
Steve, I just returned from lunch and have read your replies and those of others, and apparently we are talking past each other. Perhaps, we are speaking a different language. Your two paragraphs above are in conflict, unless I understand you to mean you are moving your landing gear forward to impress people at the field. This is not what I call moving the CG forward. Putting weight in the nose (as I used to do on TAILHEAVY RC models) moves the CG forward and puts more weight on the nose when the model is sitting at rest.
If you can get a copy of the excellent book, "Aerodynamics for Naval Aviators" and read the section on Longitudinal Control on pages 275-278, I think you would find it an interesting read.
I do know that if I put extra weight in the back compartment of my 172, behind the mains and without moving the mains, it makes the nose wheel support less weight.
All the best,
Don
P.S. Having just read the Allbee post that was written while I was composing my post, I see we are indeed talking past each other. I too have balanced many RC airplanes, not to mention calculated weight and balance on many 150's, 172's, Warriors, etc. I have decided to not continue my end of this discourse. Again, best wishes!
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John's simple view of the world:
CG as we calculate it not the whole story when the plane's on the ground. You must also consider the location of the mains and nose gear. All things being equal, moving the CG aft will unload the nose gear. Eventually, the CG will be right over the mains and the nose gear will support exactly 0.....and move a little further than this the tail will drop and the nose will be in the air.
On the other hand, moving the CG back by adding weight will not necessarily unload the nose. Since the mains are always behind the CG, you can move the CG back with weight but actually load the nose gear MORE. Any ounce you add in front of the mains will be some fraction of an ounce felt on the nose gear.
So you're all correct....sorta.
CG as we calculate it not the whole story when the plane's on the ground. You must also consider the location of the mains and nose gear. All things being equal, moving the CG aft will unload the nose gear. Eventually, the CG will be right over the mains and the nose gear will support exactly 0.....and move a little further than this the tail will drop and the nose will be in the air.
On the other hand, moving the CG back by adding weight will not necessarily unload the nose. Since the mains are always behind the CG, you can move the CG back with weight but actually load the nose gear MORE. Any ounce you add in front of the mains will be some fraction of an ounce felt on the nose gear.
So you're all correct....sorta.
L.Adamson
Well Known Member
cytoxin said:
However, adding weight in the back, means that the actual balance point, will no longer be at 27%. It would have to be moved back to compensate, and therefor add weight to the nose.
Assuming that we have fixed fore and aft points for the CG, which we do; as if the CG is the fulcrum; then adding weight to the baggage compartment does lighten the nose.
It's all in how the question is worded, I suppose.
L.Adamson
rv7boy
Forum Peruser
Now I understand...
Now I understand why we are not communicating...
If the balance point is towards the rear, I call that tail heavy and you call it nose heavy...and if the balance point is towards the nose, I call that nose heavy and you call that tail heavy.
Not where I come from...!!!
Balancing an RC airplane or balancing a full size airplane locates the point at which all the gravitational forces acting on the airplane (or any object) can be supported by a single upward force. So if the airplane balances toward the nose, there is more mass toward the nose and we call that NOSE HEAVY, NOT TAIL HEAVY!!! The weight of the airplane is a downward force acting through the center of gravity. To support the airplane, a single upward force equal and opposite can be exerted at that point...or when the airplane is flying, the sum of all forces generated by the airframe (wing, horizontal stab, fuselage, etc.) moving through the air oppose the weight of the airplane. When that sum of forces is greater than the weight of the airplane, it rises; when the sum equals the weight, the airplane flies level; when the sum is less, the airplane descends.
The balance point you are finding on the ground can be thought of as the point through which the weight is exerted DOWNWARD in a static situation. When the airplane starts flying, there is a net lift vector and it is not at the same point as the weight vector. For the airplane to fly straight and level in unaccelerated flight, the Lift Moments must balance. Does the Center of Pressure of a wing change with airspeed, angle of attack, flaps extended, etc.? Yes, in both location and magnitude, that's why the resulting forces are called vectors. The location and magnitude of the force acting through the CG (weight vector) changes in flight with fuel burn, baggage thrown out, bombs dropped, etc.
This is getting very deep. For an airplane in flight there is a lift vector and corresponding moment for the wing AND a lift vector and corresponding moment (force times distance) for the horizontal stabilizer. For a conventional airplane with the tail in the rear, the lift vector for the horizontal stabilizer is downward and balances the lift vector of the wing with a downward force (moments are equal for straight and level flight). For a canard airplane, with the horizontal stabilizer in front, the lift vector for the horizontal stabilizer is UP so it balances the lift moment of the wing with an upward force (and moment). Draw a side view cartoon of an airplane with the CG ahead of the lift vector of the wing for these two types of airplanes and it will be easier to understand.
As the CG is moved forward or back, controllability and stability are changed, and can reach the point of instability.
The book I referred to previously (Aeronautics for Naval Aviators) has some interesting reading about controllability in ground effect, at touchdown and during rollout. Too long to quote here.
(Oh, no, I'm beginning to feel like George. I think I'll go flying.)
Very interesting, indeed!
"A puzzling thread you have begun," says YODA.
Happy flying!
Don
P.S. to Steve Allbee, I read your post again. CG is not a force but the location of a force, and the total weight of an airplane acts DOWNWARD through the location of the CG. It is not an upward force on the wings as you have stated. The CG is the center of GRAVITY, the point at which total weight of the aircraft acts DOWNWARD and is balanced with LIFT, an UPWARD force. All the forces on an airplane in level flight can be reduced to four forces, lift, weight, thrust and drag. That was in the basics I studied for my Airman's Test, and it's still taught today. As the airplane maneuvers, these forces are constantly changing, some more than others, but for the pilot to remain in control, the forces and their corresponding moments must be balanced.
allbee said:
Now I understand why we are not communicating...
If the balance point is towards the rear, I call that tail heavy and you call it nose heavy...and if the balance point is towards the nose, I call that nose heavy and you call that tail heavy.
Not where I come from...!!!
Balancing an RC airplane or balancing a full size airplane locates the point at which all the gravitational forces acting on the airplane (or any object) can be supported by a single upward force. So if the airplane balances toward the nose, there is more mass toward the nose and we call that NOSE HEAVY, NOT TAIL HEAVY!!! The weight of the airplane is a downward force acting through the center of gravity. To support the airplane, a single upward force equal and opposite can be exerted at that point...or when the airplane is flying, the sum of all forces generated by the airframe (wing, horizontal stab, fuselage, etc.) moving through the air oppose the weight of the airplane. When that sum of forces is greater than the weight of the airplane, it rises; when the sum equals the weight, the airplane flies level; when the sum is less, the airplane descends.
The balance point you are finding on the ground can be thought of as the point through which the weight is exerted DOWNWARD in a static situation. When the airplane starts flying, there is a net lift vector and it is not at the same point as the weight vector. For the airplane to fly straight and level in unaccelerated flight, the Lift Moments must balance. Does the Center of Pressure of a wing change with airspeed, angle of attack, flaps extended, etc.? Yes, in both location and magnitude, that's why the resulting forces are called vectors. The location and magnitude of the force acting through the CG (weight vector) changes in flight with fuel burn, baggage thrown out, bombs dropped, etc.
This is getting very deep. For an airplane in flight there is a lift vector and corresponding moment for the wing AND a lift vector and corresponding moment (force times distance) for the horizontal stabilizer. For a conventional airplane with the tail in the rear, the lift vector for the horizontal stabilizer is downward and balances the lift vector of the wing with a downward force (moments are equal for straight and level flight). For a canard airplane, with the horizontal stabilizer in front, the lift vector for the horizontal stabilizer is UP so it balances the lift moment of the wing with an upward force (and moment). Draw a side view cartoon of an airplane with the CG ahead of the lift vector of the wing for these two types of airplanes and it will be easier to understand.
As the CG is moved forward or back, controllability and stability are changed, and can reach the point of instability.
The book I referred to previously (Aeronautics for Naval Aviators) has some interesting reading about controllability in ground effect, at touchdown and during rollout. Too long to quote here.
(Oh, no, I'm beginning to feel like George.
I think I'll go flying.) Very interesting, indeed!
"A puzzling thread you have begun," says YODA.
Happy flying!
Don
P.S. to Steve Allbee, I read your post again. CG is not a force but the location of a force, and the total weight of an airplane acts DOWNWARD through the location of the CG. It is not an upward force on the wings as you have stated. The CG is the center of GRAVITY, the point at which total weight of the aircraft acts DOWNWARD and is balanced with LIFT, an UPWARD force. All the forces on an airplane in level flight can be reduced to four forces, lift, weight, thrust and drag. That was in the basics I studied for my Airman's Test, and it's still taught today. As the airplane maneuvers, these forces are constantly changing, some more than others, but for the pilot to remain in control, the forces and their corresponding moments must be balanced.
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redbeardmark
Well Known Member
unloading nose wheel
Another observation: there is an appreciable percentage of RV'ers who taxi quite fast--just hang out at a fly-in sometime and watch. I was taught to "never taxi faster than a man can walk." But admit to violating this rule a smidge.
I agree that back-pressure on the stick defnitely unloads the nosehweel--the difference is audible and palpable. Anyone have info on what percentage of flip-overs were "heavy engine/heavy prop" combos?zilik said:
Another observation: there is an appreciable percentage of RV'ers who taxi quite fast--just hang out at a fly-in sometime and watch. I was taught to "never taxi faster than a man can walk." But admit to violating this rule a smidge.
rv7boy
Forum Peruser
L.Adamson said:I think you need another cup of coffee...
If the CG is physically moved rearward, then more weight is transferred to the nose gear.
What? Are you talking about moving a DESIGN CG, or moving the CG by moving baggage, fuel, people physically? The latter is my understanding of moving CG and obviously conflicts with your understanding.
This would be different than standing on the wing steps, which is putting weight behind the prescribed CG point.
At last I think this is the technical way it is.
L.Adamson
When two people are standing on the steps of an RV-9A, the CG IS moved rearward! Same as stuffing 350 lbs (equal to two FAA people) in the baggage compartment of an RV-9A. That would make the airplane TAILHEAVY and every pilot knows (or should know) tail heavy planes DON'T FLY!!!
Happy landings!
Don
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mlw450802
Well Known Member
It is getting a little toasty
I think some of the misunderstanding may be due to a confusion of the center of lift and the center of gravity.
If the center of lift is forward of the CG, then the aircraft will pitch up and the nose wheel will be unloaded. If the center of lift is aft of the center of gravity, the aircraft will tend to pitch downward, loading the nosewheel.
If you refer to the free body diagram of the early training aircraft where the four forces, lift, weight, thrust and drag are shown you see that the weight vector is attached to the CG and the lift vector is atached to he center of lift.
I know this won't change ingrained or incomplete understanding but it is the way of the physical universe.
mike
I think some of the misunderstanding may be due to a confusion of the center of lift and the center of gravity.
If the center of lift is forward of the CG, then the aircraft will pitch up and the nose wheel will be unloaded. If the center of lift is aft of the center of gravity, the aircraft will tend to pitch downward, loading the nosewheel.
If you refer to the free body diagram of the early training aircraft where the four forces, lift, weight, thrust and drag are shown you see that the weight vector is attached to the CG and the lift vector is atached to he center of lift.
I know this won't change ingrained or incomplete understanding but it is the way of the physical universe.
mike
n5lp
fugio ergo sum
I think we are overcomplicating this. Please review the 6A drawing at the bottom of the page from Van's website (8A is not as simple) http://vansaircraft.com/public/rv-6int.htm If we are talking about how weight is distributed on the ground, at other than high speeds, it is really simple. If weight is added in front of the main gear there is more weight on the nose gear. About the only weight that can be added ahead of the main gear is fuel weight. All other weight that can be added, like pilot, passenger and luggage weight is behind the main gear and will lessen the weight on the nose.
All talk about design CG and center of lift and center of pressure is not relevant to this discussion. It is just a big see-saw. For a flying airplane, things are different but then for a flying airplane there is no weight on the main or nose gears.
All talk about design CG and center of lift and center of pressure is not relevant to this discussion. It is just a big see-saw. For a flying airplane, things are different but then for a flying airplane there is no weight on the main or nose gears.
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John C
Well Known Member
Weight on nose gear
Larry's explaination is right on. I just added some calculations to my spreadsheet to keep a running total of weight on the nose gear. I have an O-320 and fixed pitch prop. Empty weight is 1050.
At empty weight, weight on the nose gear is 274.
With full fuel, two 180 pounds pilots, no baggage, the weight on the nose gear is about 325 pounds.
Fuel is ahead of the CG so adding fuel increases weight on nose gear.
100 pounds of fuel adds about 25 pounds on the nose gear.
The pilot and pax are over the mains, so they don't affect the weight on the nose gear much.
Baggage is 30 inches aft of the main gear.
The distance between the main and nose gear is about 60 inches.
So, 50 pounds luggage will lighten the nose gear by about 25 pounds.
Now watch it jump. A fifty-pound increase in engine weight adds about 40 to the nose gear and 20 pounds of prop add 32 to the nose gear. (I am just guessing at the O-360 and constant speed prop weights) (We have had a number of Subrus and one Chevy block go inverted, I understand that they are even heavier)
So a bigger engine and constant speed prop increase the nose gear weight from about 325 to 400 or a 25% increase, or so, or more?
Typically, we think of the airplane rotating about the CG, but in landing, main and nose gear flexures can create some dynamic motions that can exacerbate the load factor at the nose gear, and that extra 72 pounds can look a lot bigger in a hurry.
Larry's explaination is right on. I just added some calculations to my spreadsheet to keep a running total of weight on the nose gear. I have an O-320 and fixed pitch prop. Empty weight is 1050.
At empty weight, weight on the nose gear is 274.
With full fuel, two 180 pounds pilots, no baggage, the weight on the nose gear is about 325 pounds.
Fuel is ahead of the CG so adding fuel increases weight on nose gear.
100 pounds of fuel adds about 25 pounds on the nose gear.
The pilot and pax are over the mains, so they don't affect the weight on the nose gear much.
Baggage is 30 inches aft of the main gear.
The distance between the main and nose gear is about 60 inches.
So, 50 pounds luggage will lighten the nose gear by about 25 pounds.
Now watch it jump. A fifty-pound increase in engine weight adds about 40 to the nose gear and 20 pounds of prop add 32 to the nose gear. (I am just guessing at the O-360 and constant speed prop weights) (We have had a number of Subrus and one Chevy block go inverted, I understand that they are even heavier)
So a bigger engine and constant speed prop increase the nose gear weight from about 325 to 400 or a 25% increase, or so, or more?
Typically, we think of the airplane rotating about the CG, but in landing, main and nose gear flexures can create some dynamic motions that can exacerbate the load factor at the nose gear, and that extra 72 pounds can look a lot bigger in a hurry.
rv7boy
Forum Peruser
Instability
Mike, if the center of pressure is forward of the CG, for a conventional aircraft like an RV, the plane won't fly!!! It will be unstable and the wing will stall. That is the way of the physical universe.
If you are only talking about a high speed taxi where the mains don't leave the ground, and the CG is behind the Cp but in front of the mains, then you are absolutely correct, the nose wheel will see less loading for the situation you describe. (If the CG is behind the mains, the nose wheel sees no loading and the airplane becomes a real tail-dragger!)
Don
mlw450802 said:
Mike, if the center of pressure is forward of the CG, for a conventional aircraft like an RV, the plane won't fly!!! It will be unstable and the wing will stall. That is the way of the physical universe.
If you are only talking about a high speed taxi where the mains don't leave the ground, and the CG is behind the Cp but in front of the mains, then you are absolutely correct, the nose wheel will see less loading for the situation you describe. (If the CG is behind the mains, the nose wheel sees no loading and the airplane becomes a real tail-dragger!)
Don
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John C
Well Known Member
with CGs
Nose gear weight with CG
Don asked for some CGs so I?ll restructure the weight build up to be a little more meaningful when discussing changes in CG. You can see how the CG moves around.
I have an RV-9A with an O-320 and fixed pitch prop. Empty weight is 1050. The CG range is ?? to ??
At empty weight, weight on the nose gear
NGW = 274 EWCG = 76.91
With full fuel, two 180 pounds pilots, no baggage,
NGW = 325 CG = 80.38
Fuel is ahead of the CG so adding fuel increases force on nose gear. So remove 100 pounds of fuel and subtract about 25 pounds from the nose gear
NGW = 299 CG = 80.62
The pilot and pax are over the mains, so they don't affect the nose gear force much.
Baggage is 30 inches aft of the main gear.
The distance between the main and nose gear is about 60 inches.
So, 50 pounds luggage will lighten the nose gear by about 25 pounds.
NGW = 273 CG = 81.62
A fifty-pound increase in engine weight adds about 40 to the nose gear.
NGW = 312 CG = 80.86 The engine moves the CG forward about 0.76 inches.
Twenty pounds of prop add 32 to the nose gear.
NGW = 344 CG = 79.88
(I am just guessing at the O-360 and constant speed prop weights) (We have had a number of Subrus and one Chevy block go inverted, I understand that they are even heavier)
Now back to a typical weight and cg. (full fuel, two pax, no baggage)
NGW = 325 CG = 80.38
Add the 50 extra pounds for the engine, and 20 for the prop.
NGW = 397 CG = 78.45
The nose gear arm is 34.5 for the RV-9, and I wagged an arm for the prop at 28.0 and for the engine increase at 47.
The spread sheet - if you find an error (er, typo) in the basic data below, please let me know. I just wagged the engine/prop weight increases and CGs.
N6699 BASIC WEIGHT DATA
WT ARM MOM PART
386 91.88 35465.68 R MAIN TARE
390 91.88 35833.2 L MAIN TARE
274 34.5 9453 N GEAR TARE
0
216 76.75 16578 FUEL - 36*6 = 216
180 92.7 16686 PILOT
180 92.7 16686 PAX
0 122 0 BAGGAGE
50 47 2350 ENGINE
20 28 560 PROP
WT / MOM = CG
1696 133051.9 78.45
1299.057 MAIN GEAR FORCE
396.9432 NOSE GEAR FORCE
1696 CHECK WEIGHT
57.38 NOSE TO MAIN
30.12 MAIN TO BAGGAGE
Nose gear weight with CG
Don asked for some CGs so I?ll restructure the weight build up to be a little more meaningful when discussing changes in CG. You can see how the CG moves around.
I have an RV-9A with an O-320 and fixed pitch prop. Empty weight is 1050. The CG range is ?? to ??
At empty weight, weight on the nose gear
NGW = 274 EWCG = 76.91
With full fuel, two 180 pounds pilots, no baggage,
NGW = 325 CG = 80.38
Fuel is ahead of the CG so adding fuel increases force on nose gear. So remove 100 pounds of fuel and subtract about 25 pounds from the nose gear
NGW = 299 CG = 80.62
The pilot and pax are over the mains, so they don't affect the nose gear force much.
Baggage is 30 inches aft of the main gear.
The distance between the main and nose gear is about 60 inches.
So, 50 pounds luggage will lighten the nose gear by about 25 pounds.
NGW = 273 CG = 81.62
A fifty-pound increase in engine weight adds about 40 to the nose gear.
NGW = 312 CG = 80.86 The engine moves the CG forward about 0.76 inches.
Twenty pounds of prop add 32 to the nose gear.
NGW = 344 CG = 79.88
(I am just guessing at the O-360 and constant speed prop weights) (We have had a number of Subrus and one Chevy block go inverted, I understand that they are even heavier)
Now back to a typical weight and cg. (full fuel, two pax, no baggage)
NGW = 325 CG = 80.38
Add the 50 extra pounds for the engine, and 20 for the prop.
NGW = 397 CG = 78.45
The nose gear arm is 34.5 for the RV-9, and I wagged an arm for the prop at 28.0 and for the engine increase at 47.
The spread sheet - if you find an error (er, typo) in the basic data below, please let me know. I just wagged the engine/prop weight increases and CGs.
N6699 BASIC WEIGHT DATA
WT ARM MOM PART
386 91.88 35465.68 R MAIN TARE
390 91.88 35833.2 L MAIN TARE
274 34.5 9453 N GEAR TARE
0
216 76.75 16578 FUEL - 36*6 = 216
180 92.7 16686 PILOT
180 92.7 16686 PAX
0 122 0 BAGGAGE
50 47 2350 ENGINE
20 28 560 PROP
WT / MOM = CG
1696 133051.9 78.45
1299.057 MAIN GEAR FORCE
396.9432 NOSE GEAR FORCE
1696 CHECK WEIGHT
57.38 NOSE TO MAIN
30.12 MAIN TO BAGGAGE
rv7boy
Forum Peruser
CG and nose gear loading
Good work! John C!
So what I understand from your calculations on your real world RV-9A is:
1) As the weight is placed forward in your aircraft, the Center of Gravity (CG) moves forward and there is MORE loading (downward force) on the nosewheel.
And
2) When the weight is placed toward the rear in your aircraft, the CG moves toward the rear and there is LESS loading (downward force) on the nosewheel.
Just as I suspected.
Thanks again for providing us some real-world numbers.
Don
Good work! John C!
So what I understand from your calculations on your real world RV-9A is:
1) As the weight is placed forward in your aircraft, the Center of Gravity (CG) moves forward and there is MORE loading (downward force) on the nosewheel.
And
2) When the weight is placed toward the rear in your aircraft, the CG moves toward the rear and there is LESS loading (downward force) on the nosewheel.
Just as I suspected.
Thanks again for providing us some real-world numbers.
Don
L.Adamson
Well Known Member
rv7boy said:Good work! John C!
So what I understand from your calculations on your real world RV-9A is:
1) As the weight is placed forward in your aircraft, the Center of Gravity (CG) moves forward and there is MORE loading (downward force) on the nosewheel.
And
2) When the weight is placed toward the rear in your aircraft, the CG moves toward the rear and there is LESS loading (downward force) on the nosewheel.
Just as I suspected.
Thanks again for providing us some real-world numbers.
Don
Which makes it, so that you can't always define CG as the balancing point, as it's often "defined".
[email protected]
Well Known Member
CG and long wind
I think this may be a small part of the flip over problem. We were told all about CG when we leaned to fly but I for one was never told about the shifting balance point when the wheels torch the ground.
CG is just that Center of Gravity, key word is Center and might also be called the balance point. The center of gravity moves depending on how you distribute the weight in the aircraft. It is a point where if you lifted the aircraft off the ground at that point it would remain level. There are two modes of operation here.
On the Ground????.
When a plane is on the ground with little or no motion we do not worry about CG . there is a pivot point, the mains. At rest or moving slowly the more weight you put in the plane the more weight on the wheels both mains and nose. The farther forward of the mains you move this weight the more is placed on the nose wheel and less on the mains. If you move the weight aft of the mains, the entire added weight will be on the mains as well as some of the nose wheel weight, and the nose will become lighter, in fact move the weight far enough back and the plane will tip backwards with no weight on the nose. (IE Tail Dragger). The total weight does not change just how it is distributed over the aircraft.
In the Air ???????
The pivot point is somewhere just forward of the wing spar. This is the point of max lift during flight. This is pretty much a fixed point You generally want the CG or Center of Gravity forward of this pivot point making the plane a little nose heavy, that?s why when you stall the nose moves down. Move the CG back to far and when the aircraft stalls you could find yourself in a flat spin or pitching up. Not a good thing, aircraft would also be very unstable. In flight the heavy nose is overcome by the tail pushing down via the elevators on the backside of the pivot point. Equalize downward push on the back verses nose weight and you have level aircraft, add speed to create lift and you have level flight or close to it.
Landing ?????In-between mode one and two
This is where it gets tricky. As you touch down your pivot point actually moves aft, from the wing spar to the mains which increases the nose weight because the pivot point is moved back and more of the aircrafts weight is now forward of it. Move it to fast and the nose will drop equally as fast. Now add momentum, if you drop a 1 pound block from 3 feet the ground and the block at the point of contact will momentarily see far more weigh than 1 pound, (G - Force) the faster it drops the more its apparent weight is. We are talking anywhere up to and above ten possibly twenty times or more of the nose wheel static weight . That makes your 300 pound nose weight more than 3000 pounds or more for a very short period of time. And we wonder why that nose gear flexes like that.
I have always be told the full stall landing is best???? The problem with this is when the plane stalls say with the mains just above the ground or just torching the weight of the aircraft is suddenly placed on the mains and the pivot point move aft to the mains very quickly, this makes the nose heavy fast, and if you are not quick enough with the elevator and the nose is high enough the nose will bounce, during this bounce the nose could be exerting thousands of pounds of pressure on the ground the wheel digs in and over you go. I fly to the ground (Just above stall) and very carefully place the nose wheel on the ground, if it?s a grass strip I add a little power as I break, the back wash seems to keep the nose light with full aft stick, but I am still braking. Yes it?s a little tougher on the breaks. I also find I get a bit of a nose wheel shimmy / bounce at about 15 ? 20 mph and a little power with breaks stops it instantly. I suspect my none wheel is a little out of balance.
I know ?.. Long winded But I had nothing else to do for the past half hour?
I think this may be a small part of the flip over problem. We were told all about CG when we leaned to fly but I for one was never told about the shifting balance point when the wheels torch the ground.
CG is just that Center of Gravity, key word is Center and might also be called the balance point. The center of gravity moves depending on how you distribute the weight in the aircraft. It is a point where if you lifted the aircraft off the ground at that point it would remain level. There are two modes of operation here.
On the Ground????.
When a plane is on the ground with little or no motion we do not worry about CG . there is a pivot point, the mains. At rest or moving slowly the more weight you put in the plane the more weight on the wheels both mains and nose. The farther forward of the mains you move this weight the more is placed on the nose wheel and less on the mains. If you move the weight aft of the mains, the entire added weight will be on the mains as well as some of the nose wheel weight, and the nose will become lighter, in fact move the weight far enough back and the plane will tip backwards with no weight on the nose. (IE Tail Dragger). The total weight does not change just how it is distributed over the aircraft.
In the Air ???????
The pivot point is somewhere just forward of the wing spar. This is the point of max lift during flight. This is pretty much a fixed point You generally want the CG or Center of Gravity forward of this pivot point making the plane a little nose heavy, that?s why when you stall the nose moves down. Move the CG back to far and when the aircraft stalls you could find yourself in a flat spin or pitching up. Not a good thing, aircraft would also be very unstable. In flight the heavy nose is overcome by the tail pushing down via the elevators on the backside of the pivot point. Equalize downward push on the back verses nose weight and you have level aircraft, add speed to create lift and you have level flight or close to it.
Landing ?????In-between mode one and two
This is where it gets tricky. As you touch down your pivot point actually moves aft, from the wing spar to the mains which increases the nose weight because the pivot point is moved back and more of the aircrafts weight is now forward of it. Move it to fast and the nose will drop equally as fast. Now add momentum, if you drop a 1 pound block from 3 feet the ground and the block at the point of contact will momentarily see far more weigh than 1 pound, (G - Force) the faster it drops the more its apparent weight is. We are talking anywhere up to and above ten possibly twenty times or more of the nose wheel static weight . That makes your 300 pound nose weight more than 3000 pounds or more for a very short period of time. And we wonder why that nose gear flexes like that.
I have always be told the full stall landing is best???? The problem with this is when the plane stalls say with the mains just above the ground or just torching the weight of the aircraft is suddenly placed on the mains and the pivot point move aft to the mains very quickly, this makes the nose heavy fast, and if you are not quick enough with the elevator and the nose is high enough the nose will bounce, during this bounce the nose could be exerting thousands of pounds of pressure on the ground the wheel digs in and over you go. I fly to the ground (Just above stall) and very carefully place the nose wheel on the ground, if it?s a grass strip I add a little power as I break, the back wash seems to keep the nose light with full aft stick, but I am still braking. Yes it?s a little tougher on the breaks. I also find I get a bit of a nose wheel shimmy / bounce at about 15 ? 20 mph and a little power with breaks stops it instantly. I suspect my none wheel is a little out of balance.
I know ?.. Long winded But I had nothing else to do for the past half hour?
