# Re-drives Belt or Chain ?

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#### Rik-

##### Well-Known Member
Bou

BorgWarner marine trans had bolt on reduction units that would go on the back of the FNR part of the trans. Bought many years ago, might be hard to find. I never mounted it but a simple flat plate adapter with a bearing and seal for the input shaft would do it.
These ”velvet drive” units use a planetary unit on the back of a 71 &72 models for the reduction. They still make these today. https://www.velvetdrive.com/files/7172.pdf

#### wanttobuild

##### Well-Known Member
........if the velvet drive was lighter weight

#### Rik-

##### Well-Known Member
........if the velvet drive was lighter weight
‘They have a new “Aluminum” case which drops a non reduction unit from 109 lbs to 77 lbs

#### rv7charlie

##### Well-Known Member
77 lbs is pretty reasonable for that HP rating. Is all new production aluminum, or is that an 'option'? Prowling the interwebs, I never saw any info on # of cylinders the drives are rated to operate with. Seems likely that the gas engine ratings are for V-8s, given the HP numbers, but it would be nice to have actual data.

We obviously don't need forward/reverse in an a/c (except possibly a seaplane), but there doesn't seem to be much weight penalty for having it. How is shifting accomplished? Is there an actual clutch, or just hard gear engagement/disengagement via internal oil pressure? The self-contained pressure lube/cooling system seems like a nice feature, too.

I did find one site with prices (~$5400), but no mention of whether that includes an adapter plate or coupling/damper assy to engine power to the input shaft. Anyone care to share an engineering perspective on how a large dia prop in air compares to a smaller dia prop in water, related to bending/gyro loads and torsional issues? Anyone have direct experience with one, even in a boat? #### akwrencher ##### Well-Known Member HBA Supporter I had one, long time ago. You just want the reduction part. Not the forward and reverse part. They are a hydrualic gear, oil pressure operation of forward or reverse clutch. One would need to test or reverse engineer the loading on the output. They are not designed for gyroscopic loads in particular. #### Rik- ##### Well-Known Member I had one, long time ago. You just want the reduction part. Not the forward and reverse part. They are a hydrualic gear, oil pressure operation of forward or reverse clutch. One would need to test or reverse engineer the loading on the output. They are not designed for gyroscopic loads in particular. ‘Not true, they are designed to handle direct thrust loads from a spinning propeller which exhibits far more thrust than an aircraft propeller can exert. The boat propeller has, due to the medium being over 1,000 more dense as well as the added leverage with a prop shaft being over 10’ in length for most inboard applications, a gyroscopic load in 4 axis of motion. #### Rik- ##### Well-Known Member 77 lbs is pretty reasonable for that HP rating. Is all new production aluminum, or is that an 'option'? Prowling the interwebs, I never saw any info on # of cylinders the drives are rated to operate with. Seems likely that the gas engine ratings are for V-8s, given the HP numbers, but it would be nice to have actual data. We obviously don't need forward/reverse in an a/c (except possibly a seaplane), but there doesn't seem to be much weight penalty for having it. How is shifting accomplished? Is there an actual clutch, or just hard gear engagement/disengagement via internal oil pressure? The self-contained pressure lube/cooling system seems like a nice feature, too. I did find one site with prices (~$5400), but no mention of whether that includes an adapter plate or coupling/damper assy to engine power to the input shaft.

Anyone care to share an engineering perspective on how a large dia prop in air compares to a smaller dia prop in water, related to bending/gyro loads and torsional issues?

Anyone have direct experience with one, even in a boat?
Depending upon the HP, the Mass and the Velocity, a boat propeller exerts several thousand pounds of thrust load and typical side loading is 50% of the thrust loading. Being water is roughly 1,000 times more dense than air the size of the propeller does not need to be as large in diameter, but notice the blade area of a water propeller vs. an air propeller can be similar as there are (in todays applications) 4 to 6 bladed boat propellers with a diameter in the 24-36” range for the smaller HP applications

The new versions of the aluminum housing velvet drive are called the “72-LX” series. The velvet drive transmission use an old Ford “FMX” transmission 3rd gear assembly as it’s 1:1 and for reverse they use a planetary which is 1.5:1

The velvet drives use a band to lock up the clutch drum like a normal automatic style transmission. The input shaft turns a pump which builds the pressure for the band and the clutch pressure.

In the newer designs the parasite hp loss is in the 9-11 hp range.

#### rv7charlie

##### Well-Known Member
Thrust really isn't a big deal with an a/c installation, so that should be a non-issue. But don't most of these systems use a U-joint drive shaft, with separate bearings in the hull to carry the prop shaft thrust & bending loads?

In any case, the BW website seems to indicate that only 1:1 ratio is available in the inline aluminum case. So not much use to us. Bummer.

#### akwrencher

##### Well-Known Member
HBA Supporter
I think there is some confusion regarding boat propulsion loads. There are no significant gyroscopic loads on the output bearing of an inboard boat gear. A long shaft couples the gear to the propeller and there are one or more bearings on the shaft. Normal inboards do not use u joints, those are typical on inboard/outboard drives, which don't have inboard reverse gears. The thrust loads are going to be what they are, so much hp can make so much thrust. Thats not the issue. Issue will be bending loads from gyro loads. And weight. Always weight.

#### Rik-

##### Well-Known Member
Thrust really isn't a big deal with an a/c installation, so that should be a non-issue. But don't most of these systems use a U-joint drive shaft, with separate bearings in the hull to carry the prop shaft thrust & bending loads?

In any case, the BW website seems to indicate that only 1:1 ratio is available in the inline aluminum case. So not much use to us. Bummer.
The thrust loads are directly coupled to the transmission flange which are transferred to the engine stringers.

The planetary reduction unit comes in many different ratios with some in the 2:1 to 2.5:1 ratio.

#### challenger_II

##### Well-Known Member
The thrust loads will be on the rotables. If One doesn't have a good means of transferring those loads to the case (think "thrust bearing"), the unit will destroy itself.

#### rv7charlie

##### Well-Known Member
Guys, there's likely to be more thrust load from the helical cut gears in the planetary gearset than any prop load. Bending loads due to gyro effects are *much* more significant.

Rik,
When I looked at the BW site, most versions listed multiple ratios, but the only ratio I could find listed for the *in line* 72L series was 1:1. Can you point me to the listings for other ratios?

Thanks,

Charlie

#### Rik-

##### Well-Known Member
Guys, there's likely to be more thrust load from the helical cut gears in the planetary gearset than any prop load. Bending loads due to gyro effects are *much* more significant.

Rik,
When I looked at the BW site, most versions listed multiple ratios, but the only ratio I could find listed for the *in line* 72L series was 1:1. Can you point me to the listings for other ratios?

Thanks,

Charlie

this is the planetary unit, which bolts to the tail stock of the 72C and while the website is not up to date, they offer this with the aluminum case version also.

I only use the non planetary models as mine are in the 900 to 1500 hp range applications

#### rv7charlie

##### Well-Known Member
Hi Rik,

Sorry for the late reply to this, but it raises a 'how might I use this?' question for me. As you indicate, the web site is pretty 'opaque' on how the various drives operate. Are you saying that when you order a 71 or 72 series drive with 'direct' (1:1) vs planetary reduction, there's an entire assembly that isn't on the drive? That the planetary reductions are in a separate housing that bolts to the rear of the box with the forward/reverse mechanism, the oil pump, etc? If that's true, any idea of the weight of just the planetary section?

I'm asking because having all those ratios available 'off the shelf' could be a game changer for alternative engine reduction drive availability.

Thanks for any insight you can offer,

#### Vigilant1

##### Well-Known Member

this is the planetary unit, which bolts to the tail stock of the 72C and while the website is not up to date, they offer this with the aluminum case version also.
153 lbs for the unit with the planetary gears (to provide some reduction). I'm sure the version with an aluminum case is lighter, but for practical aircraft use most folks would probably want to see considerably less weight.

#### Rik-

##### Well-Known Member
Hi Rik,

Sorry for the late reply to this, but it raises a 'how might I use this?' question for me. As you indicate, the web site is pretty 'opaque' on how the various drives operate. Are you saying that when you order a 71 or 72 series drive with 'direct' (1:1) vs planetary reduction, there's an entire assembly that isn't on the drive? That the planetary reductions are in a separate housing that bolts to the rear of the box with the forward/reverse mechanism, the oil pump, etc? If that's true, any idea of the weight of just the planetary section?

I'm asking because having all those ratios available 'off the shelf' could be a game changer for alternative engine reduction drive availability.

Thanks for any insight you can offer,
yes. If my internet wasn’t down from the rain today I’d show you a photo of the non planetary unit that is the basis for the planetary add on.

the forward/neutral/reverse (of no value in an aircraft as it only has a single clutch to absorb the power so no delta movements for a STOL competition )

it’s still to heavy for an aircraft application as one can build a simple reduction unit via a gilmer belt or even a hi vis chain ( I use a lot of these in my product) or even a geared unit for a lot less weight

#### rv7charlie

##### Well-Known Member
What interests me is whether the planetary section is effectively 'self contained' in its own housing. In the pdf linked earlier, it lists the 72 direct drive as 109 lbs and the reduction as 153 lbs and lengths as 11.44" vs 17.79". If the reduction section only weighs 44 lbs and is only 6.35" long *including its case*, that has potential; at least for bigger conversion engines like LS motors. It might mean that the entire reduction package could be in the 60-80 lb range, especially if that 44 lb number is with an iron case & there are lighter aluminum versions available. Of course, the lack of offset would be an issue with a V-engine, unless it was inverted...

#### Rik-

##### Well-Known Member
What interests me is whether the planetary section is effectively 'self contained' in its own housing. In the pdf linked earlier, it lists the 72 direct drive as 109 lbs and the reduction as 153 lbs and lengths as 11.44" vs 17.79". If the reduction section only weighs 44 lbs and is only 6.35" long *including its case*, that has potential; at least for bigger conversion engines like LS motors. It might mean that the entire reduction package could be in the 60-80 lb range, especially if that 44 lb number is with an iron case & there are lighter aluminum versions available. Of course, the lack of offset would be an issue with a V-engine, unless it was inverted...
One can, just buy a planetary and build the housing around it. They are a 1.5:1 reduction so keep that in mind