Thanks: 
Likes: Is it easier to induce a nose over due to overly aggressive braking with larger tires (say 35's) or smaller (800/850's) tires.
And why (whatever your answer may be)? I can't quite work out the mental physics with this.
Is it easier to induce a nose over due to overly aggressive braking with larger tires (say 35's) or smaller (800/850's) tires.
And why (whatever your answer may be)? I can't quite work out the mental physics with this.
I would say it's not an apples to apples comparison. Typically 850x6 class tires are used on more established runways with fewer obstacles and not as much braking needed. Bushwheels are typically used on rough ground with obstacles and typically heavy braking. The risk of nosing over then would skew towards the Bushwheel user group but not because of the tires but because typically more risky nature of the way to plane is used for the off-airport user group.
Both tire types have plusses and minuses that may cause or prevent a nose over. For example with smaller tires if you hit a relatively small pothole or land on soft ground you could nose over very easily. Bushwheels would not nose over in similar circumstances. Brakes are typically of a more powerful type and used more aggressively when used with Bushwheels which can contribute to a nose over. One thing I've heard from other pilots (never tested this myself *knock on wood*) is that it's harder to save an incipient nose over with big tires and extended gear. Once you get over center and you're up that high it's hard to save.
At the end of the day it's a poor pilot that blames either tire for causing a nose over. Good judgement on where and how you land is key.
RVBottomly thanked for this post
Thanks, but given, let's say, both on level pavement, what then?
Since you're starting to constrain the parameters - Are you starting from 3 point attitude or tail up? It makes a difference if for no other reason than the available recognition time.Originally Posted by aeroaddict
As an aside - why would anyone need to use brakes at all on a paved runway? I 3 point land about 500 ft short of my exit taxiway and just roll in.
3 point with Bushwheels and long gear the tail is heavier and brakes less effective so safer from nose over.
2 point level, there is a longer moment arm to the ground with bushwheels and long gear so less safe.
My spooky moments have all been slow with tail high, turning around with tail up in big rock, or braking hard on surfaces that slip and then grab.
Sent from my SM-G965U1 using SuperCub.Org mobile app
The heavens declare the glory of God; the skies proclaim the work of His hands. Psalms 19:1
Thanks.
Should have been more precise in the parameters. Level dry pavement, taxi (not landing) in 3 point attitude (obviously).
Again, just a general question as I could not come up with any mechanical/logical answer.
Speed, CG and inertia then rotating mass come into play. Not trying to a make a science fair here, but thought I would ask the collective/brain trust/gray beards which have more knowledge than myself.
Last edited by aeroaddict; 01-09-2022 at 07:45 PM.
If the comparison is on pavement the Bushwheels would be easier to nose over. Not only more rolling resistance which can pitch the plane forward on touchdown but also much more grip which would make braking more effective. The gotcha there would be if the brakes were the same on both setups and the Bushwheels are of the larger variety the brakes would be less effective for an equal amount of pressure at the pedal so that may even the chances of a nose over somewhat.
In regards to 3pt vs 2point I think previous posters are talking about the landing. 3 point would make it harder to nose over on bushwheels due to more weight on the tail.
With those parameters, the small tires would be more prone to nosing over. With larger tires and longer gear in a 3 point attitude, the tail gets heavier and with larger tires the brakes have less leverage.
Too many variables still in the equation. Question has to include locked brake because aggressive is a huge variable. The basic answer is if you lock the brakes even at slow speed without enough tail downforce both will put a plane on its nose in a heartbeat. Same with aggressive if you don't get off them when the tail starts to come up. Dumping flaps, full stick back, and full nose up trim in 3 point is the best you can do for keeping the tail down (not for stoping mind you) once whatever you are doing defeats that you will be heading over even at 5-10 mph.
DENNY
boarfish liked this post
Brakes are very often the precipitation of a nose over. Brakes are significantly less effective on big diameter tires. Basic physics.
Everything else equal (which is virtually impossible), smaller tires are more likely to nose over, because brakes have more mechanical advantage.
MTV
Last edited by mvivion; 01-09-2022 at 10:04 PM.
Nose impoverished? Is that because a bent prop means an engine teardown with all the resulting red tags?
Needs to be stressed, because it is not obvious - a very low speed sudden application of brakes will have you on your nose right now! Happens to very experienced aviators (not me, so far).
I discovered it in my fiftieth year of flying - tower said “cleared for takeoff” - I answered and added power. They said “cancel takeoff clearance; hold short . . .” My tail was a foot off the ground when I got off the brakes! Had I kept the brakes on, my prop would have been toothpicks.
Let's further constrain the problem to the case of constant deceleration. That eliminates tire friction and brake effectiveness. The key factor then becomes the height of the CG above the point of rotation. Most pilots only think about the longitudinal CG position but, for this puzzle, the vertical location, and how it changes with tire size, is perhaps more important.
A few back of the envelope sketches make me wonder if the intuitive answer is the right one.
The response "Unable!" has, more than once, saved me from doing silly things with an airplane.
Small tires will be more conducive to nose over with aggressive braking on pavement.
Two reasons:
1. With big tires, the airframe is rotated nose-up, and the CG is therefore a little farther aft with respect to the tire/pavement contact point.
2. As previously stated, with big tires, the brakes have a smaller mechanical advantage (brake diameter divided by tire diameter), so that a given torque at the brake results in a greater available torque at the tire surface. Assuming non-skidding, of course.
Edit:Yep, this too, and it acts in opposition to #1. However the change in mechanical advantage between tire and brake is the greater effect because that distance ratio changes more.height of the CG above the point of rotation
Last edited by Gordon Misch; 01-09-2022 at 09:11 PM.
What do you suppose would be the answer if, as I proposed, the aircraft with the large tires was subject to the same deceleration as the aircraft with the small tires?
Last edited by frequent_flyer; 01-09-2022 at 10:58 PM.
Awesome, now we are getting somewhere. And my knowledge base has grown!
Don't forget fuel load. You have more chance of nosing over with half tanks than full tanks- the fuel sloshes froward adding to the momentum.
I don't know where you've been me lad, but I see you won first Prize!
AOA makes the tail have to travel further to go over the top with big tires. Small tires tend to skid easier so harder to grab hard enough to go over. The right pilot could flip both. A competent pilot won’t flip either. If you anticipate heavy braking be prepared to add throttle and aft stick to blow the tail down.
Momentum, huh? I cannot remember much, but wasn't that mass times velocity? Put more fuel up there, and that equation gets bigger. I really cannot remember angular momentum, but I could look it up.
I think the sloshing fuel is a closed system - net momentum probably stays the same, even given the impulse at the forward bulkhead.
By the way, the scenario is this: you are in the parking lot, see a 3 year old darting out from between the cars, and all four wheels screech. Everybody in the parking lot glares at you.
Do the same thing in a Cub, and you better get off those brakes in a big hurry. That takes lots of experience; you do not have time to think.
Mr. Aero,
I love the thinking task. And I am going to leave off all the variables that all of our thinking buddies are bringing up here and offer two thoughts to you - one is basic physics and the other is admittedly anecdotal experience.
lt is true that all the suggested variables postulated here are real and consequential. But at the end of the day all they do is moderate/change/effect the raw ruling set of physics that we must think through. If I knew how to do it, I would do as my physics professor always did - draw a vector diagram on the board - and post it as a picture. Can't do that, but can describe it. Let's say the forward momentum vector flows to our right and the tail-raising vector brought about by braking is mid-screen and pointing straight up. That vertical vector (initiated and propagated by braking) has to achieve sufficient force to not only elevate above the forward vector but begin to exceed the forward vector in forward speed. The lower that vertical vector begins in its upward and forward course the longer the impingement upon the forward vector (braking) has to occur. In other words, the increased elevation of the axle with the taller BW's requires a longer time (at the same force) of braking for the vertical vector to achieve necessary force to overcome the forward vector. That gives us more time to detect and react to the physics in play. Simply stated, in our world, all other variables being/staying equal, it is harder to nose over with the taller tires.
Now the experience. 15 years ago I gave up my 4" old Piper wheels and 4x11 Goodyears that loved to spin on the rim and yank out valve stem when run at pleasingly low pressures for rough strip ops. Do not ask me how I know this. You will get an vague evasive non-incriminating answer of some sort. In the years of flying with that wheel and brake set-up, I had to constantly be on guard for the tail wanting to sneak up on me during aggressive braking. One day, intelligence exerted some influence and I changed to 6" wheels and BW tires while keeping the same brakes. I will conservatively say I elevated the forward vector plane (axle height) by 3.5 inches. I have never once in the 15 years since had the tail start to uncomfortably sneak up on me during aggressive braking. In fact, I brake as aggressive as I wish now with no worry. Guess what happens next? Better brakes. Thanks for the thinking.
It seems the better brake thing is more likely to cause a problem. I still use standard brakes with 31.s and have no need for more braking. I don't compete in STOL contests, and this setup works fine for me in grass. My 31's are only on pavement on the ramp. Certainly not opposed to landing on pavement, just haven't had to yet. I have plenty of brakes for a runup check etc.. and that's all I need. I am as guilty as anyone about wanting more and better, but not for my brakes.
Seen a lot of poor pilots blame the brakes locking up but I always find it interesting that the brakes tend to lock just before they end up in the river.
I would say with same brakes, same conditions that you described that the small tires are more prone to nose over because the brakes work better on a smaller diameter tire.
One brake is better then 2 when the river gets close. A ground loop is better than a flip over.Seen a lot of poor pilots blame the brakes locking up but I always find it interesting that the brakes tend to lock just before they end up in the river.
I would say with same brakes, same conditions that you described that the small tires are more prone to nose over because the brakes work better on a smaller diameter tire.
Glenn
"Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"
Great responses, thanks.
So I kinda hearing that it is smaller tires that would be easier to nose over?
Can I use this thread as a justification for the CFO (Chief Financial Officer) that bigger tires are safer and I should get bigger tires?
I was gonna comment that this might be a good reason for bigger tires when negotiating with the other half.
Yep, seen it done a few times and did it myself in an FX3 to keep from going off the back side of the hill.
I know two different skywagon drivers (both good sticks) who ended up upside down on paved runways,
they both said that along with goofy winds their "grabby" tires (shaved 29's) seemed to be a factor.
Those heavy tires take more spinning up when landing, I can see where that might present an issue on pavement.
Cessna Skywagon-- accept no substitute!
I think that missing picture would be useful. I think it would show that the rotation of the aircraft is around the point of tire ground contact, not around the axles. I think that picture would also show there is only one force tending to rotate the aircraft nose down. That force acts through the CG in the horizontal plane. The picture would also show there is one force resisting the tendency to nose over, That force acts vertically through the CG.
Solving the problem requires knowledge of the vertical and lateral CG position with respect to the point of tire contact with the ground.
Heard of a lot of nose overs with pilots landing on wet snow with the big tires rather than landing with skis. Just to through that into the discussion…
I’ve heard that excuse used a few times, by guys who simply didnt handle conditions. Yes, if you touch down solidly at warp speed, as some are won’t to do, those tires will grab…..a LITTLE. But, that alone should not result in a nose over. I’d bet that a bit of grab, followed by a shove on the brakes was the actual dynamic.
I really like big tires for the very reason that they grip. But I don’t touch down at 1.9 Vso. The grip is just another tool.
MTV
I'm glad I've never been put in that position but if (when) it happens to me I take it all back, it was the brakes fault!Seen a lot of poor pilots blame the brakes locking up but I always find it interesting that the brakes tend to lock just before they end up in the river.
I retract my previous answer. I have to go with small tires flipping over easier if you're talking about a taxiing incident. Lots of good points brought up in this discussion.
We get guys landing in snow with small tires also. Few years ago we had a CFI take the company plane with friend out to Lake George saw all the ski track and thinking it was OK to land (year before windblown ice and 206's brought people out for pictures) well snow was a few feet deep and he flipped it. Same year a 180 or 185 landed short on ski tracks 20R Birchwood was able to get the spinner on the tar. Then small tire 172/182 decided they would try the ski strip instead of the tar at Soldotna and flipped. About 10 years ago I found an active ELT. It was a Base Aero club small tire 172 flipped in fresh snow next to Dr Seuss house. Not to just mention small tire trikes I did have a friend a few years back flip because he landed on soft ski strip to instead of the dry runway next to it trying to save his bushwheels. Last night I slept with my brothers sister in law and her husband managed to land on a gravel bar with Federal AWB skis wheels down and dig a tip in resulting some impressive one flight prop wear and an 200 hr engine teardown. Soooo snow don't care if you got nose wheel, tailwheel, big, or small, tires if it gets it gets ya.
DENNY
Glen has a very good point. So how many note a ground loop point and side (Right vs left) when you are working a short strip? How many have practiced ground looping the plane? I want to Willow last summer and worked on it, hard to get exact speed but locking tire and hard ground loop at 15 mph was not bad at all. Get closer to 20 and you get a lot of lean. I prefer my brakes work and work well, they can save you if you know how to use them.
DENNY
Instead of being concerned with tipping on the nose due to braking and tire size under your described conditions, you should practice not using any brakes at all. Under most circumstances they are not needed for landings.
N1PA
Then the higher CG would matter (very slightly). But to obtain the same deceleration would require greater braking effort.What do you suppose would be the answer if, as I proposed, the aircraft with the large tires was subject to the same deceleration as the aircraft with the small tires?
Gordon
N4328M KTDO
Big tires really don't change the angle all that much - you can get the actual angle change by using the arctan function in your hand held. With big tires your CG goes up, with very little offset from the additional distance the tail must move to get above the CG.
It isn't the effectivity of the brakes or the size of the tires - it is the lack of flow over the stabs/elevators that will get you. It can happen - it does happen - at extremely low speeds.
We had one go over on a hot start procedure. As the engine started, the aircraft moved. Pilot of course hopped on the brakes. I don't think the aircraft moved more than three feet. Boom. Fifty grand.
My two cents: brakes are not really the reason airplanes flip, pilots are. Tire size is not really the reason airplanes flip, pilots are.
However, I will say that the biggest risk of brakes and tires contributing to this event is if the pilot does not properly plan or manage the airplane operation including to consider the differences in handling characteristics, whatever those might be, and identify those handling characteristics by doing some reasonable level of currency type work when in a new configuration. One of the areas that can be a surprise to pilots is when they buy their big new fancy tires, find the brakes are ineffective, put on more powerful brakes, then sometime in the future end up with smaller tires on the airplane. The power of those souped up brakes can be a real eye-opener on a set of small tires...
I always find braking as little as possible is the best plan, especially when you are trying out new equipment and trying to get a feel for it.
Be careful with that conversation. She might decide you are not safe in the Carbon Cub and buy you a C-150.
Do you already have 3x3 gear? That would make more difference than the tire size. So would 20 lbs of lead near the tailpost.
Sent from my SM-G965U1 using SuperCub.Org mobile app
The heavens declare the glory of God; the skies proclaim the work of His hands. Psalms 19:1
I agree it is a pilot experience issue. For new pilots one thing to remember is the plane really doesn't care it is on tar, cement, gravel or grass. So just because your CFI has claimed that the world will end if you get 3 ft from the centerline most aircraft (especially with bigger wheels) will happily leave the runway taking a light or two in the process and roll just fine as long as it does not hit some ditch or other large hard object. I had a new pilot friend that managed to get off the dirt strip and instead of just turning back on to it locked the brakes and put it on its nose. DENNY
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