Clearance with an 80" Prop

[Steve W]

I gather from the drawings that with an 80" prop and 600X6 tires in a level attitude I will have about 11" of ground clearance?? Anyone swinging a similiar size prop with any issues? Thanks to those to reply and a Merry Christmas

Steve
P203

[Flygirl1]

Steve, we have 700 x 6 and the 80 in. whirlwind. In level attitude we have 10.5 in off the ground. Your welcome, happy New year. Donna P241

[Steve W]

Thanks Donna.
I am having a McCauley hub fitted with the same blades. I have 600 's on the axles but will most likely be going to 850's so shud be fine. Enjoy the test flying.

[Flygirl1]

Steve, your calculations got me thinking, ( unfortunately at 3 A.M. ). If you calculated 600x6 and 11 in. clearance and I have 700x6 and 10.5. I have a problem. We set the landing gear strut to the 1.25" called for in the plans. Looking through the comments I see a post that Bob wants the center to center tire spread to be 72" at normal flying weight and not to exceed 74" at gross. I guess I need to load her up to gross and measure. Could ruin a perfectly good day to hit a bump on a rough strip and put the tips in the ground!! The 11" I stated does not take all this into consideration. Still not a problem for you. We considered the 850's because of the 80" prop, but for other reasons, chose not to go that route. They sure look good on the Patrol!! D.

[Steve W]

Donna I wouldn't be too concerned. I think the only time you'd be close to the ground other than a nose "almost" over situation would be on a hot or fast wheel landing. 99% of the time the nose is up enough to give more than sufficient clearance. My numbers are off the plans. I haven't received my prop yet and my engine is still in the shop thus the initial query.

[Flygirl1]

You're probably right. Right now, sitting empty, center to center is at 71.5". I've seen some nose wheel guys with props that appear to be WAY too close to the earth. I've also seen them with green tips. If it appears to be a problem, I may be forced to get the 850's. Wouldn't that be a shame. ;-). D.

[JimParker256]

Flygirl1,

In evaluating prop clearance for pretty much any tire, I look for the tire's inflated diameter, subtract the 6" hub diameter, and divide by two. So a theoretical 16" diameter tire, with a 6" hub, would have a maximum "drop" of 5 inches, in the "worst case" scenario where BOTH main tires went flat and somehow rolled completely off the rim. Highly unlikely, but...

Goodyear says their 700x6 tires have a diameter of about 18" to 18.5" when inflated. In my "worst-case" scenario, your prop would still have almost 6" clearance above the turf. If just one tire went that route, you would have a couple of additional inches clearance because one side would be higher. So, even with the 8:00x6 tires, you should be OK for prop clearance.

Goodyear's says their 8:00x6 tires are 18.75" to 19.5" when inflated. That would give you 6 3/8" to 6 3/4" inches of ground clearance – only 3/8" to 3/4" more than the 7:00x6 tires – not much change for the additional weight and $$. Hardly seems worth it to me, though I do think they just "look better" on the Bearhawk and Patrol.

Goodyear says their 8:50x6 tires are 21.1" to 22.1" when inflated. This tire would give you 7.5" to 8.5" of ground clearance in that worst-case scenario. And having that much prop clearance – even in my "worst case" scenario above – would be a real comfort factor to me.

And that's why I personally decided to go with 8:50x6 tires for my Patrol. Though I did go with the Desser 8:50x6 tires that about an inch smaller diameter than the Goodyears, at about 20.6" diameter – but they are a lot cheaper. As a side benefit, I think the Patrol with 8:50x6 tires looks "just right" – not quite the "clown plane" look of a SuperCub on 31" Tundra tires... Now if I were flying in Idaho or Alaska, and was proficient enough to regularly utilize their sand bars, gravel bars, and other "unprepared" surfaces, I might want those bigger tires. But in Texas?

[Flygirl1]

Jim, WOW, thanks for all the info, really!!! I thought the 700 and 800 were the same height, only 800 were wider. Had 600 on the 7ECA and was parked next to one of "those" super cubs at Johnson Creek. Couldn't stand it and put 700's on ASAP. Still did't compare, but looked a whole lot better. Are you taking the 74" spread into consideration in your #'s? Or are these #'s at gross? I"m not sure how much clearance I would loose from a 71 & 1/2" spread to 74. Probably not 6 inches. I think my biggest problem for the 850's is the added weight. Not only from the tire itself, but also from the step stool I'd need to carry to get in and out!! Thanks again, Donna

[JimParker256]

Donna, I just used your 11" clearance numbers in my calculations, but that's why I showed you how I did it... When you determine what your "new" clearance will be with the 74" tread width, you can easily recalculate the numbers. It took longer to type it up than to do the calculations - really! And I'm rusty as heck, had to break out the calculator app to do it!

As for the height differences - it's probably BECAUSE of the added width that the 8:00-series are taller than the 7:00-series. That air just doesn''t like flat surfaces, so it tends to "round them out"...

Your Patrol has the 'step' on the gear, right? Doesn't that eliminate the need for the step-stool with the 8:50 tires? After all, it's only another 2 to 2.5 inches... LOL

[Mark Goldberg]

The 74" spread is max allowed at full gross. Normal flying weights should spread the gear to 72". If you are worried about prop clearance - bringing the tires closer together by threading in the shock strut rod end bearings would help quite a bit. I have flown my 4 place down to 69" spread. It handles fine but hurts visibility over the nose. Mark

[Flygirl1]

oops, it didn't take the post, then it did.

[Flygirl1]

Thanks for taking the time to look this stuff up Jim. Your a wealth of information and a real asset to this Bearhawk community!! My biggest complaint on these planes is that they were made for the male frame. It's a reach to the step on a good day. A real concern for me is the reach to the toe brakes. I've minimized it by raising the floor, so we'll see soon enough if that's enough. AARGH!! Pray for better WX. We want to get these birds in the air!!!!! D.

[JimParker256]

The sad thing is that I'm spending all this time online instead of building because of plantar fasciitis in one foot that is keeping me from being able to work on my plane. So this is "builder withdrawal therapy" until I can get back to it. Like you, I can't even go fly because of the weather. When it's not IFR, it's blowing 35 gusting 45... Two days ago it was 12°F for the high, and today we're at 79° (59° will be our low). Can't wait for this crazy weather pattern to cycle out...

But I know what you mean about the "standard size" being male-oriented. I have a friend who is just tiny - maybe 4'8" tall, and has to buy children's shoes to fit her feet. She has found online sources for clothes for work, but for a long time she had to buy kids clothes for that as well... Aside from the obvious challenges with reaching the pedals and seeing out of the car windows, she also had to have a footrest custom made for every car she drove, so she could reach the brake pedal without holding her leg up in the air. Imagine doing that for a 1.5 hour long commute each way, every day, in the horrible Houston traffic! She was an amazing person, though. Never complained — well except when our group started to walk too fast going back and forth between work and wherever we are lunch... She was taking at least two steps for every one we took...

[Patrol28]

Get 31" Bushwheels. Problem solved. ( I know there isn't a problem but bushwheels look cool)

[JimParker256]

Just a quick reminder that unless your bushwheels have larger-diameter hubs, they won't impact the "worst-case scenario" clearance with two flat tires...

[Sebastian]

This is a really good conversation and not that I'm close to flying my plane (4place, o-540 and 84" prop, on 800x6 tires) I thought I would take a break from the landing light work and try to figure out my prop clearance.

I started by measuring the prop from end to center (42.5"), then put my drywall square on front of the plane centering the 42.5" mark as best I could with the center of the flywheel and clamped it there. I measured from the end of the square to the floor (23"). I called this taxi position. May be a little more than that since the prop will be a little further out. See the pic.

Next I put a level on the tubing above the door (see pic) and raised the tail till it showed level bubble. Measured this time and got 10" to the floor.

I did a 3rd measurement and I called this one eyeball level since with the bubble level it looked nose low. That measured 12". See pic.

Now this may be fine "I DON'T KNOW" but as you can see in the pictures I don't even have the wings on yet so I am nowhere close to having this plane loaded. I don't think this is a problem for the test flying but as I get better and venture off airport it seems this will put my prop to close to the ground. It does have me concerned though. Any thoughts?

[Bdflies]

Well, I've got about the same (12") clearance on my Patrol. For initial and phase 1 flights, this is fine. After that, my mind is pretty much made up to get a set of 31’s. Yes, they're expensive. But, not as expensive as a MT prop!

Bill

[Flygirl1]

Bill, is that an 80" prop? What is your landing get spread as it sits now? Sebastian, nice looking start on your Bearhawk. Your working on the landing lights, must not be to far from completion!! Or as they say--90% done and 90% to go! Mark G. told me a quote that seems to be true--" Perfection is the greatest threat to completion" ;-) D. P.S. That head your holding up in your profile photo looks just like the one I feed wet cob to every day. AKA: Bucky ;-) OOPS, just took a closer look at your profile--Bucky lost his spots long ago!!

[Bdflies]

Ooohhh! CJ, I think she's saying you shot a fawn!... Granted, a fawn with a nice rack.

The MT is 205 cm, or 80.7" diameter. She's sitting on 8:50x6:00's that are aired to 25 psi (which is WAY more than I'll fly with). Center to center of the tires measures 71" right now. It'll spread more when loaded. I'm sure the 12" clearance is fine. Early on, I figured to put 31's on the plane because I kinda like the "Clown Plane" look, as Jim described it. Added insurance for the 'fragile' propellor, has furthered my intention.

Bill

[whee]

This is a really good conversation and not that I'm close to flying my plane (4place, o-540 and 84" prop, on 800x6 tires) I thought I would take a break from the landing light work and try to figure out my prop clearance.

I started by measuring the prop from end to center (42.5"), then put my drywall square on front of the plane centering the 42.5" mark as best I could with the center of the flywheel and clamped it there. I measured from the end of the square to the floor (23"). I called this taxi position. May be a little more than that since the prop will be a little further out. See the pic.

Next I put a level on the tubing above the door (see pic) and raised the tail till it showed level bubble. Measured this time and got 10" to the floor.

I did a 3rd measurement and I called this one eyeball level since with the bubble level it looked nose low. That measured 12". See pic.

Now this may be fine "I DON'T KNOW" but as you can see in the pictures I don't even have the wings on yet so I am nowhere close to having this plane loaded. I don't think this is a problem for the test flying but as I get better and venture off airport it seems this will put my prop to close to the ground. It does have me concerned though. Any thoughts?

There is a fair number of guys running a 84" prop on the 4-place with small tires...you won't have an issue from a regulatory standpoint. If you start going off airport you'll be on larger tires anyways.

The tube above the door isn't the official place to check level. You need to use the lower longeron between stations C and D.

[Sebastian]

I finally had a chance today to take Whee's advice and check the prop clearance using a bubble lever between stations C & D. I came up with 13". That's 3" difference from what I originally measured. I also put a second lever on the tubing above the door again to see what if any the difference between the levels. The level on the door was about half a bubble off (like it's owner part of the time) LOL