# PRSU Plans

### Help Support HomeBuiltAirplanes.com:

#### whiteknight

##### Active Member
Who can tell me where I can find good plans for aircraft PRSU's? I have access to a full machine shop. How many of you have built your own PRSU? I am having difficulty seeing a reason why I should buy one when I could build one. I am currently considering using eather a 215 Buick engine or a 4.3 in a Bearhawk

Thank you.

#### GrizzlyV6

##### Well-Known Member
If you go with the 4.3, you will be time and money ahead to go with the Belted Air Power psru. It is an engineered package. They have the other parts on the shelf. It really is a plug and play set up. You will need to build your exhaust, engine mount, alternator bracket, radiator mount and some other incidentals, but not that big of a deal. Give them a call and ask for Jess.

Jim

#### whiteknight

##### Active Member
How much would that cost in the ball park?

#### GrizzlyV6

##### Well-Known Member
You would have to give Jess a call for current pricing on the redrive. You can get long block engines delivered to your door for less than 2500 bucks. A good source for those are S&S engine rebuilders in Washington state. PRE COUNTERBALANCE SHAFT ENGINES. Do the neat little mod of vortec heads on the pre-vortec block and now your over 200hp out of the little v6 at the 4000 rpmpeak. I know you can get the geared airboat redrive rated for 1000 hp for 2100 bucks.

Your Bearhawk and my Bushmaster aren't far apart as far as type. I got with Craig Catto about the prop. Craig designed a prop for me that is slightly bigger than what took first place in Valdez last year. It was an 80x37 I believe. Mine is 80x54 but has a cord of 7 1/4 inches.

Jim

#### GrizzlyV6

##### Well-Known Member
See Chevy "LS1 engine for aircraft" post #93. That is an airboat redrive on an LS engine.

#### bmcj

##### Well-Known Member
HBA Supporter
Who can tell me where I can find good plans for aircraft PRSU's?
Some might argue that there is no such thing as a good PSRU. :gig:

#### GrizzlyV6

##### Well-Known Member
Bruce - - - - now cut that out!

You and those emoticons.

delete

Last edited:

delete

Last edited:

#### Jan Carlsson

##### Well-Known Member
Some might argue that there is no such thing as a good PSRU. :gig:
He didn't ask for a good PSRU, but asked for good plans for a PSRU, Jan - :ban:

#### whiteknight

##### Active Member
He didn't ask for a good PSRU, but asked for good plans for a PSRU, Jan - :ban:
Thank you!
That is a fact. I know that someone out there must have what I an looking for. If they do I hope that they see this and speak up. Building a PRSU is not rocket science right? Should be straight forward right?

#### bmcj

##### Well-Known Member
HBA Supporter
Building a PRSU is not rocket science right? Should be straight forward right?
Actually, there is quite a bit of engineering that goes into a PSRU. I have no real knowledge when it comes to PSRU's, but I have read enough on this forum to understand that there are major hurdles in designing one, which is probably why there have been so many stories of PSRU failures.

Do some searches for the terms "harmonic" and "resonance" on this forum and you should find some of these discussions.

Bruce

#### orion

No it's not rocket science but if you want one designed for your purposes, figure conservatively at spending about $35k and up to have it properly engineered and documented. And I think that's on the low side. I've done a couple and it's actually a surprising amount of work to do it right. And I can pretty much guarantee you that few, if any, suppliers to our industry actually do it right. #### clanon ##### Well-Known Member I build my own. Cogged belt 8mm belt (powergrip2) took the info from Gates catalogs Steel drive pulley(22 tooth) Aluminum driven pulley(90 tooth) 4:1 ratio Double row angular contact ball bearing and 4140 30mm steel shaft PM if you need more info ; links ; etc #### GrizzlyV6 ##### Well-Known Member No it's not rocket science but if you want one designed for your purposes, figure conservatively at spending about$35k and up to have it properly engineered and documented. And I think that's on the low side. I've done a couple and it's actually a surprising amount of work to do it right. And I can pretty much guarantee you that few, if any, suppliers to our industry actually do it right.

Orion,
I interpret this as you had a couple of psru's engineered and doc'd. What happened to them. It's hard to imagine that much money with no product to show for it. Then there's that guarantee you put out there. That's quite a statement. I'm curious as to how you came to that opinion.

Clanon,
4:1 ratio - - - really. That means that you're turning your engine 10,000rpm to get close to a normal prop rpm of 2500rpm. Is that a typo or are you being factual.

#### whiteknight

##### Active Member
I can understand the development expenses being higher on a new concept, but not so much on preexisting technology concepts (I confess to not being a subject matter expert).
I hear that some people have used airboat PRSU's. What are the differences between the requirements for an aircraft PRSU, and an airboat PRSU if any?

#### GrizzlyV6

##### Well-Known Member
WK, check this link out, it might help. : Homepage
Give them a call, they're nice people.
Their gear drives are rated for 1000hp.
Hope that helps.

I still stand by my Belted Air Power redrive.

Jim

#### orion

##### Well-Known Member
Airboat PSRUs have been somewhat overlooked by our industry although I can't imagine why. The service the airboats are put through can be significantly more severe than anything an airplane will see and although I have not had to opportunity to take one apart and look at the details, there are a couple that show potential.

Regarding my work, I have designed four different reductions (one chain, one planetary, one spur and one internal spur) but each one was for a firewall-forward developer. The best one (I think) was for a company that wanted to produce turnkey rotary engines - the box came out great but the company did not spend enough on putting together what we might call an actual flight engine. They thought that a shiny gear box and a painted engine were enough to get customers (I didn't know that up front; they seemed sincere). But they never came out with a cowl ready engine nor what I might consider a reasonable form of mounting. In the end they spent a lot on glitz but outside of the gear box, little on substance. Too bad.

And unfortunately the other folks had similar troubles. One of my drives (an offshoot of the rotary one) was sold as a plan set to a gentleman up in Canada who was going to produce them for Subarus. I know his prototype flew but it looks like he never put it into any form of production.

Over the last fifteen years or so I've analyzed probably a dozen redrives, some for our own application and some that were part of pending lawsuits. Most were beautifully made but unfortunately had no real engineering behind them. It's really sad to see all that effort and so little substance go into products that present such a high level of risk for the buyer.

#### clanon

##### Well-Known Member
Yup , and not
I need close to 2000RPM on prop (67") and i have max hp at ~8000rpm
Lots of info here:
Redrive-design : Redrive-design
register!
And you should check Dave Blanton's design it seems to be the most reliable (over 2000hs and working)

#### Attachments

• 4.8 MB Views: 209