Backcountry Pilot • 8.5’s. Air Pressure and The Bounce

8.5’s. Air Pressure and The Bounce

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8.5’s. Air Pressure and The Bounce

I put my Pacer in the shop to get 8.5 tires installed, went on vacation and haven’t flown in a month
Went out this morning and did 3 attempted landings
First one was fine. Second was a go around because I bounced Third attempt I parked it
Bounced on it but not bad
Tires are at 12 psi and I’m landing on pavement
Should I bump up the tire pressure until I go to dirt ?
And if doing 3 points are bounced always because the mains hit first ?
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Re: 8.5’s. Air Pressure and The Bounce

The tires don't make you bounce, regardless of air pressure. A rapid change in the angle of attack of your wing when you land too fast is what makes you bounce.
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Re: 8.5’s. Air Pressure and The Bounce

You are about to get a thousand answers to your questions. But the short of it is you are landing with too much energy, in otherwords the plane can still fly. If at touchdown all flight energy is gone at most you'll bounce an inch or two off the ground. Even a 185 won't bounce if its done flying at touchdown speed- well as long as you don't drop it in from 20 feet.
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Re: 8.5’s. Air Pressure and The Bounce

As the esteemed BCP colleagues above mentioned its all about "energy" management; WE'VE all been there and done that, practice makes perfect so get back out there and burn up some more fossil fuel. For the record I done my fair share of contributing to global warming by knocking the Earth into a new orbit on occasion :wink:
Last edited by Mapleflt on Thu Apr 11, 2019 1:07 pm, edited 1 time in total.
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Re: 8.5’s. Air Pressure and The Bounce

I will Be Out again in the morning. But do you think 12 psi is a bit low on concrete ?

And yeah. As I recall I was touching down around 65. Yikes
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Re: 8.5’s. Air Pressure and The Bounce

sierrasplitter wrote:... But do you think 12 psi is a bit low on concrete ?
...


The only issue is how the tires wear, and whether the tire will rotate on the rim and shear off your valve stem. Mark your tires and rims so you can see if there's any creep. If there is, increase tire pressure!!
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Re: 8.5’s. Air Pressure and The Bounce

sierrasplitter wrote:...As I recall I was touching down around 65. Yikes

Try flying final around that speed. I normally turn final at 70 then slow to 55-60 on short final, touchdown is much slower. If you're dropping it in, try looking at the far end of the runway; this might help judge drift and height more easily through peripheral vision.

You running the Desser 8.50s?
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Re: 8.5’s. Air Pressure and The Bounce

I ran the Pacer on Desser 8.50s @ 8 psi. 12 psi is probably perfect for what you're doing.

If you land fast, push the yoke forward. Get a low to negative angle of attack on the wing and you'll stay on the ground.

If you try to 3 point or tail low at 65, you're going to bounce down the runway for quite a while, probably just hanging on for the ride. Your two options at that point are either a go-around or push the yoke forward, close to the stop. Keep the tail up and stay off the brakes until the tail starts to sink and transition to full aft elevator and feet on the brakes.

It'll take some time to master, but you'll get there.

Go-arounds are cheap; trying to save a landing can get expensive.

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Re: 8.5’s. Air Pressure and The Bounce

Try slow flight at 6" AGL down a long runway (hover taxi.) See how slow your airplane will fly and then reduce power to touch down. Power pitch is the way to touchdown slowly and softly wherever you wish.

Rudder works fine at that speed with the prop blast. Aileron is not in the prop blast and does not work at that speed except to drag a wing and mess up longitudinal alignment.

Elevator, also in the prop blast, works fine at that speed.

A bit of rapid dynamic proactive rudder movement helps the rudder fine tune longitudinal alignment. A bit of rapid dynamic proactive elevator movement helps fine tune AGL altitude.

If longitudinal alignment is strictly maintained with rudder only, the wing stays automatically level.
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Re: 8.5’s. Air Pressure and The Bounce

I struggled with bouncing when I first got my Pacer as well. I found the the biggest issue for me was the power off sink rate of a short wing Piper seemed to be much more than the Cessnas I was flying previously and I was not arresting this sink rate in time. I started by using a touch of power held through final to touchdown. This is cheating, I know, but it does slow the sink rate. Next I transitioned into using just a dab of power just before touchdown. Now after flying the thing for a while, power off landings are smooth as I've become accustomed to the sink rate of the plane and what it takes to arrest it.

To really land a short wing Piper short, I feel power is very helpful as it allows you to really increase your angle of attack, slow the plane significantly, and still have an acceptable sink rate. But that is a different topic for a different thread!

Just keep flying and don't get discouraged, Pacers are real sweethearts once you've had a little time getting acquainted.
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Re: 8.5’s. Air Pressure and The Bounce

Gravity only thrust (power off) spot landings are good training. Giving up our best glide angle management control is not cheating any more than flying nose geared airplanes, however. If we don't use lots of power to manage the sink rate of slow approach airspeed, we may never see the slow and high sink rate necessary to get a short wing airplane into the first half of the landing zone in an engine failure.

If you don't like dragging it in, just slow up on short final enough to cause greater sink rate and add enough power to arrest the greater sink rate. Gliders have spoilers to manage sink rate. Powered airplanes don't have spoilers because the designers think pilots have enough sense to use the power to control sink when slow enough to touch down safely.

1.3 Vso is fine to get us close, but way too fast to land slowly and softly where we wish.
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Re: 8.5’s. Air Pressure and The Bounce

Are you using trim?
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Re: 8.5’s. Air Pressure and The Bounce

With airplanes as light as 170 or Pacer, and at airspeeds slow enough to land safely with little likelihood of damaging anything, trim should have little effect on control feel. Things pretty much like a wet noodle. Quite a bit of control movement with little pressure. Throttle works really good. Rudder and elevator are weak but effective. Move them until you get what you want. Aileron should be neutral with wing level or neutral with wing banked into crosswind. Yes, we can go full aileron into the crosswind when down so long as we don't try to drive with the yoke.
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Re: 8.5’s. Air Pressure and The Bounce

There's very good advice here. I'll reinforce the approach to land and not land method Contact noted can teach power and attitude control in ground effect. You loose if the plane touches the runway; you win if it flys the runway with the tires not spinning. Repeat until you can control set down at will.

Another hint is to go sit in your plane and not fly. Just look out the windshield for as long as it takes to capture a mental picture what 3-point attitude looks like. The cowl, the runway, your panel all form an image to be repeated. If you want to do wheel landings prop up the tail some and repeat the relaxation method of learning the visual picture.

Then on landing main wheels first with some speed don't relax and let the tail drop too soon. If it does you're often thrown back in space again as angle of attack and resulting lift momentarily increase when the tail drops. If you have VG's installed it's even worse as the wing can have better lift when 3-point than without them.

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Re: 8.5’s. Air Pressure and The Bounce

IMO

12 PSI is fine. More pressure = more bounce. Less pressure = less bounce. Don't believe it? Take a tire and set the pressure to 5 psi. Stand on the tail gate of your truck and drop the tire, see how high it bounces. Do the same at 50 psi, guarantee 50 will bounce a lot more.

If you're bounce/ flying again, IMO, it's not tire pressure, you are to fast, the wing still has enough lift to fly.

Don't be in a hurry to get on the ground, don't rush it. Try to hold it off the ground with the tires about 12" off. Use a little power to slow the sink rate to around 50 FPM, just above stall. It will settle softly.

Don't worry about landing short. Save that for another day.

Cheers...Rob
Last edited by OregonMaule on Sat Apr 13, 2019 8:51 am, edited 1 time in total.
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Re: 8.5’s. Air Pressure and The Bounce

MrPants wrote:….. I started by using a touch of power held through final to touchdown. This is cheating, I know, but it does slow the sink rate. Next I transitioned into using just a dab of power just before touchdown......


IMHO that's not cheating-- that's just another technique for your skill set.
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8.5’s. Air Pressure and The Bounce

Here’s a post I made on another forum about landing my Pacer. This was in response to a guy that said he lands at 80mph:

I pull the 1st notch of flaps at 95-ish and the second notch below 80 mph. This is to reduce forces on the flap handle which I assume reduces twisting loads on the false spar.

Also, landing at 80 mph seems pretty fast. What’s your plane stall at with your preferred flap setting? I usually (gradually) slow from 80 on downwind-to-base to somewhere near 50 on short final with full flaps. My plane stalls in the low 40 mph range at altitude with full flaps. I usually end up on the ground in the mid-40s in a tail-low wheel landing. All speeds here are indicated mph.

This gives me minimal ground speed which seems to be better for any of the short-coupled directional control characteristics and also for brake wear on roll-out.


I’ll also second Contact and others’ advice for slow flight work to learn technique and the advice to add VGs. They really tighten up the slow-speed control effectiveness on a shortwing.
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Re: 8.5’s. Air Pressure and The Bounce

Holy cow 80 mph YIKES, with floats on I'm happy to see that in level flight some days :wink:
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Re: 8.5’s. Air Pressure and The Bounce

Thanks for the advice gentlemen. I am able to land, just got out of practice due to just getting the plane then having it in the shop for a few weeks. Off vacation and ready to go out and beat the hell out of some runway again
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Re: 8.5’s. Air Pressure and The Bounce

Mapleflt wrote:Holy cow 80 mph YIKES, with floats on I'm happy to see that in level flight some days :wink:


Trim a couple feet off your wings. :wink:
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