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power plant frame- is it safe? do they break?

Posted: Mon May 20, 2019 10:16 am
by ryansmoneypit
Odd airboat power plant frame question here, but first a little background..

Boat: 16x8 , not really relevant for this but whatever
engine: Caddy 500, the big one, recent rebuild, mild cam (comp cam #94-000-5), aluminum intake mani( single/ dual, IDK) HEI ignition
prop: whirl wind WhisperTip, 72"
Direct drive


I am turning an airboat that I just purchased, into a tool. I am going to be doing some hi-speed wind testing for the military, blowing various pieces of equipment with 70-110 mph wind. An airboat seemed to be the best way to jump-start the program.


I will be building a large honey comb type structure to straighten the airflow, install 20 or 30 sensors in various location, remove any non essentials, tie down the boat and let her rip.

I was really surprised to see in person, how spindly ( my words) the PPF is. looks like 1" x .095 SS tube. seems sketchy to me, to support the weight and thrust of a 500 hp engine, but I am new to aircraft/airboats..

This brings me to my questions and where I could use some guidance.

1.0 Is this seemingly under-engineered assembly safe to run up to full power while holding the boat static for 5-10 minutes at a time?

2.0 Has anyone ever seen a PPF failure

3.0 Should the unthinkable occur and we have a blade failure, where does the debris go, what directions? how far?

4.0 I want to install a remote throttle console for safety, but where is it most safe to stand? I have no idea, anywhere within 100 ft seems nuts to me.

any input or suggestions?

Thanks for reading my morning ramble.
Ryan

Re: power plant frame- is it safe? do they break?

Posted: Mon May 20, 2019 11:38 am
by OneBFC
Assuming you plan to turn the prop a max of 3000 to 3200, your not likely going to see 500hp from it.

For engine stand material I would recommend steel box tubing around 1 inch (1/8th wall) with appropriate X bracing on all sides.

Your going to support 700lbs or so and then produce around 1200lbs of thrust give or take.

Since your application isn't weight sensitive, going up on tubing size will build in plenty of safety factor. So, perhaps 1.5" would be reasonable.

My opinion on it, hope it's useful. It's just a recommendation and not official engineering advice. Use your own discretion. (yay for lawers).

Good luck with your project.

:proud:

Re: power plant frame- is it safe? do they break?

Posted: Mon May 20, 2019 1:17 pm
by unforgiven11B
Hit up Diamondback Airboats website look in the picture gallery on the webpage as well as in the gallery on this site you will see how they build wind machines basically the engine stand and cage mounted on a movable platform with a instrument panel and hand throttle mounted in front outside of cage for safe operation. IIRC it’s not built any different structurally other than being mounted on a platform instead of inside a hull.

Your power plant isn’t going to be near 500hp if it’s not tricked out. Published #’s aren’t accurate.

Also holding that engine at higher RPMs (3300-3350+) without a BUILT top end at a minimum is a fools errand. The T pedestal rockers will not tolerate it long. On an airboat the engine is rarely at WOT and when it is it's usually not for sustained periods rather few seconds at a time.

Re: power plant frame- is it safe? do they break?

Posted: Mon May 20, 2019 1:57 pm
by kwanjangnihm
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Re: power plant frame- is it safe? do they break?

Posted: Mon May 20, 2019 4:35 pm
by ryansmoneypit
excellent. Chopping down to a shorter frame mounted to a trailer, is definitely a good idea. Ill start a thread for this project as it develops.

thanks guys/girls

Ryan

Re: power plant frame- is it safe? do they break?

Posted: Mon May 20, 2019 11:25 pm
by crazycoonass
I had something go through my prop totally destroying it. Debris went in all directions [sideways and up and down. not forward or back] but the cage or prop guard contained most of it. So I would definitely not stand on the side of the boat in line with the prop. Also if you are turning the engine that fast I would certainly be concerned with the engine coming apart. If that happens it usually damages the valve train or throws a rod out of the block or oil pan. When that happens it mostly detrimental to your wallet or checkbook.

Re: power plant frame- is it safe? do they break?

Posted: Tue May 21, 2019 7:25 am
by ryansmoneypit
I will be running the engine speed in compliance with the recommendation of the prop manufacturer.