Prop ground clearance?

[Marty_d]

Hi all, 

 

I need some advice.

 

Starting to look at props for the 701.  At the moment looking at 3 blade 66" Bolly.

 

However I just measured from ground to centre of the prop hub, when the plane is on its undercarriage, and it's only 1040mm (41").  If there's a 66" prop on it (and if the 66" is total prop arc diameter) then there's only 8" (200mm) from the tip of the prop to the ground.

 

Is that enough?  Or do I need to extend the nosegear (not ideal) or put bigger tyres on (possible)?

 

As always all thoughts appreciated.

 

Cheers, Marty

[Old Koreelah]

I presume your 701 will be using lots of unpaved landing areas. Plenty of grass strips would give your tips a tickle up.

[walrus]

what is your engine? Read up on what other propellers 701's  with your engine use and go with the herd. No need to stress about it

[IBob]

Before settling on 66", strongly suggest you look at prop comparisons on JG's website:

https://www.stolspeed.com/

[onetrack]

Marty - Don't forget your aircraft will sit lower on the undercarriage when it's at MTOW. I presume you factored the weight of pilot, passenger, fuel and "luggage", into your calculations?

[kgwilson]

My aircraft sits low to the ground & the clearance is less that 200mm when empty as I remember. Pilot, passenger & luggage sit behind the mains so probably lift the fuselage a bit but not much. I use grass strips all the time & used to get chips on the tips of the old wooden prop all the time. After more than 100 hours with the Bolly I still don't have any. Making a bit of hay with the prop tips won't hurt it unless there is something solid you collect. My tyres are 5 inch McReary Airhawks so quite small. You could install STOL tyres to get a bit extra clearance or some balloon tyres to get a lot of extra clearance. It all depends on the type of flying you do and the depth of your pockets. Big tyres are going to affect performance as well.

[Marty_d]

Ok, just checked the plans and they state the prop centre is 1100mm off the ground, mine is 1040, so I've lost 60mm somewhere.

Possibly the best option would be to make a bigger nosewheel fork and mount the axle lower, that would then give the option to change to a bigger tyre later too.

Talking to a couple of people who have big tyres, they only lose 1-2 knots in cruise and have much better landing experience (plus an added measure of safety).  So that's probably on the cards.

 

5 hours ago, IBob said:

Before settling on 66", strongly suggest you look at prop comparisons on JG's website:

https://www.stolspeed.com/

Yep done that.  That actually encouraged me to look seriously at the Meglin.  Trouble is, the Ukraine factory want the whole price up front and then it's a 4 month turnaround before you get the prop.  That made me a bit nervous when Russia is knocking on their doorstep - I really hope there's no invasion, but there is a risk that manufacturing could be disrupted and there's no guarantees.  So going with the Bolly, they advise 70" 3 blade for STOL or 66" 3 blade for better cruise.  My initial reaction is 70", but there's another 2 inches less clearance so down to 150mm instead of 200.

 

2 hours ago, onetrack said:

Marty - Don't forget your aircraft will sit lower on the undercarriage when it's at MTOW. I presume you factored the weight of pilot, passenger, fuel and "luggage", into your calculations?

 

That's true, but there's bugger all movement in the nose suspension (rubber "puck" system) so if anything the maingear is what would settle when fully loaded, which would actually give slightly more clearance.

 

I might go over to the Zenith site and see what all the 701 users say about ground clearance.

 

12 minutes ago, kgwilson said:

My aircraft sits low to the ground & the clearance is less that 200mm when empty as I remember. Pilot, passenger & luggage sit behind the mains so probably lift the fuselage a bit but not much. I use grass strips all the time & used to get chips on the tips of the old wooden prop all the time. After more than 100 hours with the Bolly I still don't have any. Making a bit of hay with the prop tips won't hurt it unless there is something solid you collect. 

 

Thank, good to know.

[Old Koreelah]

A Cherokee is parked at our airport and it has a pronounced nose-high stance. Like a few classic low-wings with short main wheel legs, I guess that is to avoid prop strike, but it also seems to have a significant AoA just sitting there.
What impact on your flying would that have?

[turboplanner]

42 minutes ago, Old Koreelah said:

A Cherokee is parked at our airport and it has a pronounced nose-high stance. Like a few classic low-wings with short main wheel legs, I guess that is to avoid prop strike, but it also seems to have a significant AoA just sitting there.
What impact on your flying would that have?

I'd immediately disregard that and, go to the specifications and get the specified dimension (unladen to bump) for 140 or Warrior  - 30,000 students is a good start to relax the mind.

The Cherokee has  much more engineering in its suspension than the average RA machine. I've seen them sitting with a wing cocked up 150 mm and thought there was a flat tyre or a landing incident, walked over and given the wing a couple of pumps and its settled down flat, same with the nosewheel suspension; they normally sit reasonably flat. Jabs wreck wooden props if they're driven through drainage ditches. I'd be checking out other CH-701, it is a very low aircraft. I sat in one in Victoria and it felt like a go kart.

[Kiwi]

With my 140 the nose is a bit sticky and sometimes the nose comes up when you put weight on the step, and it stays up until you push it back down.

[facthunter]

Tyres can go flat also. I like to see this type of plane sitting a bit tail high on the ground.  (Most do) Reduces wheel barrowing tendencies with a nose down full flap scene and it will "pin on" better in gusts.   Nev

[meglin]

On 1/23/2022 at 5:01 AM, Marty_d said:

Before settling on 66", strongly suggest you look at prop comparisons on JG's website:

https://www.stolspeed.com/

Yep done that.  That actually encouraged me to look seriously at the Meglin.  Trouble is, the Ukraine factory want the whole price up front and then it's a 4 month turnaround before you get the prop.  That made me a bit nervous when Russia is knocking on their doorstep - I really hope there's no invasion, but there is a risk that manufacturing could be disrupted and there's no guarantees.  So going with the Bolly, they advise 70" 3 blade for STOL or 66" 3 blade for better cruise.  My initial reaction is 70", but there's another 2 inches less clearance so down to 150mm instead of 200.

 

 

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Edited July 3, 2022 by meglin