Longest Prop on BH 4-place

[whee]

I'm curious what the longest prop installed on a 4-place is. I want to make sure I'm not going to run into trouble with my prop length (length currently undecided). I think Blackrock has a 84" prop that had adequate clearance on 8:50 tires. Anyone have a longer prop than that?

[Battson]

My cobber here is building with an O-470 and has an 88" Beechcraft prop mounted currently, and with 8.00's there appears to be "adequate" ground clearance. But you would not want to pole-forward too hard, you could definitely strike the prop just by pushing the stick hard foward. I can pop over and measure the clearance if you like, but there is enough to be "acceptable" in level flight attitude - maybe 8 to 10".

It also weighs a tonne, a 3 blade black mac seems to be a couple of pounds lighter.

He is not going to keep the prop, judging by how hard it is to service Beechcraft props in NZ.

[whee]

Thanks Battson. That's enough info I think.

[Mark Goldberg]

Whee, with a 540 BH that 84 inch Hartzelll is the longest I have seen. But a 86 would seem possible if you wanted to max take off and climb and sacrifice cruise. Mark

[whee]

Cool. Thanks Mark.

[whee]

, In your opinion what is the smallest tire size you'd run with an 88" prop? My plane is on 800s but if hitting the prop is possible by simply pushing the stick forward while on the roll I need to look at increasing my tire size prior to the first flight.

[Battson]

With 8.00s you would only need to push forward hard, and it would be cutting the grass *very* short. If you were on quite uneven or rocky ground, there is a chance the tip could touch.

Going up to 8.50s would buy you a couple of inches, once you consider the angles. So not much... BUT on the other hand, an 88" prop is only a 3" increase in radius over an 82" prop.

[JimParker256]

One of the considerations for me is the issue of "what happens if a main tire goes flat?" This discussion took place on another thread earlier, but if you keep the same 6" wheels, the size of the tires you run does NOT change the prop clearance when you have a flat. I personally would not want to run anything bigger than an 84" prop on a Patrol with 6" wheels. If you really think you need to go bigger, consider using 10" wheels to retain that ground clearance.

In theory, you could have a flat on landing, and either replace the tube (assuming you have a spare tube and the requisite tools) or perhaps stuff the tire with grass, leaves, etc. and make your way back to "civilization." But if you're running a really long prop, and that prop hits the ground because of a flat tire, you're not going anywhere without big-time (expensive) assistance.

Just my 3 cents worth... (Inflation)

[whee]

Your point is noted Jim. I'm using the FAA criteria for prop clearance which does consider flat main tires. The short term plan is to be on 10" wheels anyways.

[Sebastian]

Not trying to hi-jack the post, but if you go from 6" wheels to 10" wheels does that require change the whole wheel and brake assembly?

[whee]

Depends. If your starting out with ABI or Cleveland wheels/brakes then you can use the same brakes if you go with ABI 10" wheels or Gar Aero adapters. I think the new Grove wheel uses different brakes.

[whee]

Just closing the loop here. I put a 88" prop on my BH. At level flight attitude on 8.00x6 tires I have 10" of clearance. I have switched to 8.50 tires, mostly because I took so long to build my plane that the 800s dry rotted. Still have adequate clearance with a flat main. Not sure that I'll be sticking with the 88" prop. Performance and noise will determine what length I cut it down to.

[Mark Goldberg]

88" is more prop than anyone has used to my knowledge. 84" had been the max length. Let us know how it works. Mark

[yateselden]

I use an Ivo 84" paddle prop with electric pitch. My second setup like this seems to work well.

[Glenn Patterson]

It will be interesting to see how the 88" works. We went with the 82" MacCauley on the Continental IO360 as it will make max rpm and stay just under mach 1. PPonk site & others advise against going past Mach1 on prop tip speed as it reduces efficiency & affects blades stability. At some point the prop will cancel horsepower and it a is a cubic relationship the same as pumps and fans for hp. The one concern that I could not get a confident answer on was swinging a ton of prop on The Continental IO360 engine with 50 less hp than the IO-470. I talked to a couple who did longer prop mods on the IO360 that were comfortable with 84". My partner wanted to go 88" as that was what was on the Cessna 180. The concern was engine bearings as there is one version of the IO360 with heavier bearings that seems to be for larger porps and seaplanes. We compromised on 82" after extensive studying of the MacCauley application with IO360 engines. Main consideration was that we could hit max efficiency on take off with a prop that was close to max with the IO-360. The airplane is off the ground fast. On the first flight is was off really quick and over the trees. Our pilot said he went 3/4 throttle with no flaps & never opened it up on the first flight. We extended the wing skins to be gap seals, flying tail at 3 degrees and added the Hall Bros vortex generators. On the first flight he ran almost the length of the field as it did not settle in around 50 as he expected. It lands slower than expected. He is impressed with the short take offs and the low speed handling. One thing with the MacCauley C203 is that if the 88 proves to be too much that it can easily be trimmed to whatever works. I can say with confidence that the 82 allows the engine to get close to max rpm.
The exhaust is a custom dual 3 into 1 header system with equal length runners. It was our way of getting an exhaust to fit with our version of bed mount. The exhaust should net another 6 to 8hp. We were going to go with an electronic ignition for a 6% hp boost to push the engine into the 230 hp range between ignition and headers but the budget set in.