Tyre pressures

[skippydiesel]

We all have to land sometime so tyre pressures should be a hot topic.

 

My new Sonex is fitted with Goodyear Flight Custom, 6 ply tyres .

 

Finding the correct cold inflation pressure seems unnaturally difficult.

 

As far as I can make out, from the variose Goodyear manuals, these tyres are rated at 50 psi for a maximum load of almost 563 kg/tyre. My max Take off weight is 544 kg so the tyres are well & truly over specified (probably to get the 6 ply rating for thorn resistance).

 

My last tyres were easy - road rated wheelbarrow size, so just used 36 psi - worked for me.

 

Your advice comments, on tyre  pressure, will be most appreciated.

[Bruce Tuncks]

Skippy, the lower air pressures help to save the mainspar from landing loads. The energy to be absorbed is the landing weight times the vertical speed.  So softer tyre pressures help here.

[Thruster88]

I am guessing they are 5.00x5. For an RV (750kg MTOW)  with that size 25-35 is recommended. For 600kg MTOW 25 will give good shock absorption without risk of tyre failure. 35 will give longer time between inflation,  TBI.😄  

[Flightrite]

30psi for most applications. I’ve tried 25 to 45 on all my machines, it’s a compromise but I operate off grass most of the time.

[kgwilson]

30-40 PSI for my Mcreary Airhawk 5.00x5 mains. and 20-30 PSI for the nosewheel for my 600kg MTOW Sierra. I tend to keep them in the middle when setting pressures. I prefer to land on the grass where possible which prolongs the life of my tyres dramatically.

[skippydiesel]

Good stuff Gentlemen - I just new that there would be some real world experience/help out there.

 

Like most of you I will be operating off grass 90% of the time. Only the occasional away trip will see me venture onto sealed runway's (I forgot about Napper Field & Mittagong).

 

Sounds to me that 30psi might just be a good all round pressure.

Edited March 4, 2022 by skippydiesel

[APenNameAndThatA]

23 psi max for Foxbat “tundra” tyres. Possibly because they were originally lawn tractor tyres.  

[Kiwi]

Pa-28 140 is 24psi by the book, 975kg

Rans S6S I run 20psi

And in the Drifter I run 10psi, any lower and the tyre moves on the rim.

 

 

[IBob]

Savannah POH calls for:

11.5 - 14.5psi for 6" and Tundra tyres.

29 - 36psi for 4' tyres.

[skippydiesel]

12 hours ago, Thruster88 said:

I am guessing they are 5.00x5. For an RV (750kg MTOW)  with that size 25-35 is recommended. For 600kg MTOW 25 will give good shock absorption without risk of tyre failure. 35 will give longer time between inflation,  TBI.😄  

Thanks Thruster - I should have mentioned the size. You are correct 5.00-5, 6 ply

[tillmanr]

If you run at the lower level of recommended pressure the tyre absorbs some of the touchdown load. 

But you can get bounce/rebound while at the higher level you get harshness with less rebound and the undercarriage has to absorb the shock.

Always a trade off.

Edited March 4, 2022 by tillmanr
spelling error

[Bruce Tuncks]

Here's some trivial info...  A tyre pushes down on its surface with approximately the tyre pressure. ( the difference is what is carried by the tyre side-walls)

So a 30 psi tyre carrying 1000 lb of aircraft weight has a contact spot of 1000/30 sq inches or about 17 sq inches. At 20 psi, this will be 20 sq inches which might be noticed on a walk-around...  It is not required to check the pressures at every DI.

Oil-damped shock absorbers, like on the chipmunk, are just wonderful to land with.

One thing which puzzled me is that the 2 tug pilots who have landed my Jabiru both did bad landings. Yet a session of tugging  gives heaps of landing practice and they filled me with awe about how good they were.  One clue was how easy the chipmunk was to land compared with the SK Jabiru. I guess the other is that the Jabiru is very different to a Pawnee tug and these guys were doing their very first Jabiru landings. Personally, I have never flown a Pawnee. It does not have oleos but it does have rubber shock-cords in the landing gear.

 

[Bruce Tuncks]

Funny how we think in psi for tyre pressures.. We were supposed to go metric in 1974 but I have always thought of tyre pressures in psi.

[facthunter]

People who do a lot in one type are  "conditioned' to it and probably don't put in the right responses to something different.. IF your landings are getting crook put in more effort at responding to what the plane is doing, not just do the  same actions each time. People who fly many different planes do fairly consistent landings with a "new " one.  Nev

[Old Koreelah]

Our light little planes probably don’t need much pressure; most of our tyres seem designed for much heavier aircraft.

As Kiwi says, we need just enought to keep it on the rim and absorb landing jolts. Another bonus is low pressure tyres handle soft ground better.

[skippydiesel]

FYI

 

Sonex instructions;

 

"Inflate the tubes to approximately 50 psi. 30 psi provides a bit more "cushion" but increases rolling drag and may cause a pinched tube if flying off a hard surface runway. be if flying off a hard surface runway. "

No mention of tyre make, model or size

[spacesailor]

Or go,  OLD SCHOOL rule.

Inflate to guesstment, do a couple of high speed taxi runs, to heat those tyres.

If 4 c higher than start, they're at optimal infation, any less is over pressure,  any more is under optmal.

A word from yesterday !.

spacesailor

Edited March 6, 2022 by spacesailor
Grammer

[skippydiesel]

16 hours ago, spacesailor said:

Or go,  OLD SCHOOL rule.

Inflate to guesstment, do a couple of high speed taxi runs, to heat those tyres.

If 4 c higher than start, they're at optimal infation, any less is over pressure,  any more is under optmal.

A word from yesterday !.

spacesailor

All good suggestions Spacesailor, however its not a bad idea to start with a safe pressure - hence the question

[Roscoe]

My Jabiru 170D is placarded 45psi for the mains and 30 for the nose.

MTOW 600kg

[skippydiesel]

Thanks Roscoe - not so familiar with Jabs, to actually visualise a 170D but know the local Jabs ?? have very small wheels (tyres) so I assume that they need a pretty high inflation pressure to perform satisfactorily.

[skippydiesel]

On 05/03/2022 at 11:22 AM, Bruce Tuncks said:

Funny how we think in psi for tyre pressures.. We were supposed to go metric in 1974 but I have always thought of tyre pressures in psi.

We are a mixed up bunch for sure. PSI has always been my preferred scale for pressure - wont give you  a 0.0689476  Bar of the alternative

[Roscoe]

8 hours ago, skippydiesel said:

Thanks Roscoe - not so familiar with Jabs, to actually visualise a 170D but know the local Jabs ?? have very small wheels (tyres) so I assume that they need a pretty high inflation pressure to perform satisfactorily.

Yeah those local Jabs you refer to are the early smaller models which have smaller tyres and operate mainly from grass.

The 160, 170 and 230 Jabs have the larger tyres with higher pressures.