Prop diameter and ground clearance

[BC0979]

Hello to all...

What prop diameters are you turning? And do you have the required minimum 7" ground clearance with the 15x6-6 tires?

 

I just mounted my prop and discovered that I only have 3.5" of ground clearance. I think I have the wrong prop. The nose fork will not accommodate a taller tire.

 

 

 

[Marty_d]

I had this problem with the CH701 setup.  Ended up getting a larger front fork and upsizing to the 8.00-6 Carlisle Turf Glide tyres.  

The larger fork is wider too to accommodate the fatter tyre, so you need new axle bolt setup as well.  

Despite the fork being from Zenith, the larger ICP axle fits it - I got mine from Peter from Aerokits.

[facthunter]

That plane operates Beter with a nose  down on the wheels attitude.. IMHO.  Nev

[IBob]

70" is usual here. There is a 68" I think but if you visit the Stolspeed website, he's done a lot of prop comparisons, and the 68" performs less well.

[facthunter]

There's an old saying... Keep your prop as long as possible for as long as possible.  Nev

[Thruster88]

Viking engine?

[BC0979]

Yes, Viking 130.

So a 70" prop with a rotax 912 on 15x6 tires will give you how much ground clearance????

 

I fly off of a grass field so I am concerned about ground clearance.

 

[IBob]

Cutting to the chase:

The problem isn't the prop size, it's that it's attached to the aircraft lower than with a 912.

Note this will also result in a different thrust line.

 

Also, unfortunately, just jacking up the front (which would need a much bigger tyre and the forks to take it etc.) is likely to result in less than ideal takeoff and landing behaviours:

On takeoff, the aircraft is rotated from the go, so will lift off at a low speed, whether you want that or not.

On landing, gusty weather may result in multiple touchdowns, as once all wheels are on, those high lift wings are sitting in a rotated attitude.
 

 

21 hours ago, facthunter said:

That plane operates Beter with a nose  down on the wheels attitude.. IMHO.  Nev

 

[Marty_d]

To clarify,  in my case I changed all 3 tyres, not just the nosewheel. 

If that's not enough then either the prop diameter,  engine position or landing gear height would have to change,  none of which is easy or cheap. 

Edited January 23 by Marty_d

[IBob]

4 hours ago, Marty_d said:

To clarify,  in my case I changed all 3 tyres, not just the nosewheel. 

 

If increasing tyre size, I'd say that's the way to go. I was talking with a very experienced and capable Savannah owner a while back, and he was remarking on how you have to rotate the aircraft off the ground. It doesn't take much at all, but it won't lift off at lower speeds (in steady conditions)  while on all wheels.

Which is very handy for choosing your desired liftoff speed and point.

Also very handy for getting the thing to stay on the ground on landing, especially if lightly loaded.

[BC0979]

I truly appreciate all the input.

I acknowledge that I am installing a non-rotax engine and the elevation of the prop shaft may be different.

I understand the ramifications of raising up just the nose gear.

I contacted a guy that purchased all three Savannah S kits which included the 912 and prop. ICP sold him a 175cm(68.9") prop.

I received 180cm(70.9") which yields 3.5" of ground clearance.

If I convert to 22" tires(all three) from the 15" tires that would yield another 3.5" and bankrupt me at the same time 😂

 

[Thruster88]

My Thruster t500 ultralight originally had a 64 inch two blade on the 65hp rotax 582. (2500 prop rpm at full power).

A four blade ground adjustable 64 inch should work well with 130hp and would give you another 3.5 inch clearance. 

 

I would talk to Viking, they would have come across this problem before.

[BC0979]

Update:

Viking will replace the 71" with a 68" prop.

They will also supply a nose gear spacer.

I may change the main gear tires to make up for the nose gear spacer after a few crow hops. 

 

[BC0979]

I also read the Stolspeed.com prop study that you all suggested.

That guy does get work. His study uncovered that the cruise speed remains essentially the same for all props he tested but climb rate would be affected from going down to a 68 from a 71. I can live with the that since I this is not a Stol competition plane

[BC0979]

https://www.facebook.com/share/p/wr9TsRM1hdWVLSR1/?mibextid=oFDknk

 

Here's a link to what we were discussing about the nose gear and what I should not do

[FlyBoy1960]

I remember reading in the past lifetime an FAA requirement for propeller clearance.

 

An aircraft with a flat front tyre, and the suspension fully compressed, still required 6 inch clearance for it to be legal.

 

I don't think 4 inches on an inflated tire is going to be enough. You may find some hindrance to registration when the time comes.

 

[fallowdeer]

6 hours ago, BC0979 said:

https://www.facebook.com/share/p/wr9TsRM1hdWVLSR1/?mibextid=oFDknk

 

Here's a link to what we were discussing about the nose gear and what I should not do

Hi BC0979

 

Not everyone is on Facebook….. following your thread as  I’ve installed larger than standard tures on two Savannahs.

 

 

[IBob]

Yep, I would like to have read that, but am not on Facebook, and prefer not to be. Is there an alternative source?

[BC0979]

The Facebook link was just to show a pic of a Savannah with an extremely extended nose gear.

Attached is the pic.

[skippydiesel]

On 26/01/2024 at 8:59 AM, FlyBoy1960 said:

I remember reading in the past lifetime an FAA requirement for propeller clearance.

 

An aircraft with a flat front tyre, and the suspension fully compressed, still required 6 inch clearance for it to be legal.

 

I don't think 4 inches on an inflated tire is going to be enough. You may find some hindrance to registration when the time comes.

 

I doubt its a "legal"  or "registration" issue  however the common-sense requirement for clearance in the worst case scenario "...flat front tyre, and the suspension fully compressed" is, to my opinion, the only sensible way to go. It is  just a matter of deciding how much more clearance (mm) is advisable, should you encounter the worst case.

[facthunter]

Both those conditions at the same time would qualify as a 'what IF". Long U/C equals easily wheelbarrowed and hard to keep on ground with gusts. This is where a tailwheel is more adaptable for the serious operator invariable conditions. Anyone flying a glider knows how good/necessary spoilers are. Nev

[Garfly]

 

 

22 minutes ago, skippydiesel said:

...  the common-sense requirement for clearance in the worst case scenario "...flat front tyre, and the suspension fully compressed" is, to my opinion, the only sensible way to go. It is  just a matter of deciding how much more clearance (mm) is advisable, should you encounter the worst case.

This recent video from France offers timely evidence for that.

 

The relevant bit is the minute or so after 03:00 

 

Rough auto-translate is available but hardly necessary. The guy beats himself up, saying it's his habit to taxi away parallel to the hangar doors to avoid blasting prop wash inside, but then clumps of ice, I gather, have made the grassy ground unusually uneven.  Ouch.

 

 

 

[FlyBoy1960]

58 minutes ago, skippydiesel said:

I doubt its a "legal"  or "registration" issue  however the common-sense requirement for clearance in the worst case scenario "...flat front tyre, and the suspension fully compressed" is, to my opinion, the only sensible way to go. It is  just a matter of deciding how much more clearance (mm) is advisable, should you encounter the worst case.

it is a legal requirement, I found it now in the  FAA website.

https://www.govinfo.gov/content/pkg/CFR-2010-title14-vol1/pdf/CFR-2010-title14-vol1-sec25-925.pdf

it is 7 inches, not 6 inches, I did make a 1 inch mistake.

there is also a link which I can't copy to a PDF regarding LSA aircraft which you are welcome to find on Google as well.

[fallowdeer]

I’m gonna say the tail wheel vs tricycle argument for commercial utility aircraft was lost long ago in favour of the tricycle for multiple reasons.  

 

Think Quest Kodiak, PAC 750 XL, even Twin Otter. The list goes on. 
 

All aircraft you see world wide on unimproved strips.   Next thing we’ll be hearing is “Only real men (women?) fly tail wheels” and the rest of that bs.   95% of what is done these days by the hairy chested 180/185 brigade can be fine just as well much more cheaply by a 182 or 206.

 

Re the jacked up nose leg on the Savannah, yep seen that here a few places.  Just great if you want an aircraft where it’s really hard to get the nose wheel off early in your take off roll and just as hard to hold off in the flare  and with the greater leverage make it much easier to break……

[facthunter]

 IF it's hard to rotate the Mainwheels are too far back. It's nice/ necessary to be able to DECIDE when the plane is going to lift off, particularly in gusting crosswinds. You can't hold it down with an extended nose wheel  set up either.. Uncontrolled weight on the nosewheel at speed isa recipe for loss of directional control. With a tailwheel set up you can PIN it on. I'm NOT suggesting everyone should fly a tailwheel .. I doubt they will ever disappear though. No nosewheel is built to take the whole weight of the aeroplane and most of us should try harder to keep the weight OFF it. Nev