# Redrives for most commercial engines.

### Help Support HomeBuiltAirplanes.com:

#### Vigilant1

##### Well-Known Member
Did Valley Engineering provide this information??
I don't know. HBA had/has one longtime member who had a lot of experience with 100+ HP belted redrives. He reacted strongly to engineering questions/challenges, was a big fan of just running them to gain confidence. I hope I'm not mis-stating his position.

Last edited:

#### wsimpso1

##### Super Moderator
Staff member
Log Member
I haven't found this information in Type Certificate Data Sheets, Overhaul Manuals or installation manuals from Lyc or Continental. Or any PSRU manufacturer.
Oh, I agree you do not find it in the paperwork, but that is not the point.

Riddle me this, if Walter Extra waved cash for a dozen airplanes a year at Lycoming and told them you were thinking of using "this" big prop and doing snap rolls at "this" big rate with their engine, Lycoming is likely to tell him if it is a bad idea or not, because they do have some idea how much gyroscopic moment you can hang on the end of their crankshafts and have them live.

The PSRU and conversion engine makers have been getting away with selling their products with little to no evidence of suitability other than that they have been flying theirs and maybe getting some test hours off of a couple brave customer's backs. I do not expect automotive level of testing, but I sure would expect some level of analysis and reporting to make selecting or eliminating particular drives better than guesswork. If the makers do not want to answer my questions, they are only losing one sale. But if a bunch of us start asking, and one complies, market pressure may drive the rest to do their homework and start putting stuff like this in their info packages or see their business evaporate. Less BS and bluster, more facts - that is the point.

Billski

#### BBerson

##### Light Plane Philosopher
HBA Supporter
Yes, an actual customer with a custom aerobatic application should contact Ace for help with the custom application.
This was explained in post 33.
"We custom make our redrives for commercial engines as per requirement. So we cover all hp levels.
Really depends on what the customer wants. My advise is then recommended."

#### pictsidhe

##### Well-Known Member
I'm hoping m project will evolve into a kit. I could end up a competitor if I'm not a customer...

#### Factory-Fit

##### Member
Driven from this forum indeed...however now puzzled Wife is getting emails notifying posts on this forum, must be a glitch in our Outlook setup, so have had to add it to her spam filter as well as mine, as there's no means of unsubscribing.

One contributor wrote of his 'successful career in power transmission', mine's in structures, been a good money-spinner if that's how you measure success...generally use software nowadays which can make you lazy on hand calculations. Did check moments when drawing up my redrive, but discarded the design notes five years or more ago when the numbers got so high it was pointless. This isn't stressed-skin analysis but a chunk of 16mm aircraft alloy plate with a block bolted on and a 37mm eccentric shaft clamped in it, only 'hole dug' for myself is the one that bust the propeller after crash-landing and somersault in marshy ground, the redrive shrugged it off and was unharmed and reused, so building a bit of extra beef came in handy? ;-)

When designing for moments and similar it is often cheaper in man-hours to just up the section, inspecting Engineers sometimes justify their fees, play to the audience or just plain like to watch you jump hoops, material is cheap and time isn't, so provided your ego can handle the odd smug comment of 'I made them increase the section' you go heavier, finish the job, pocket the money and stroll away...
However on this occasion the critics aren't being paid, but appear to ganging up on the maker, sensing weakness and in the process potentially wrecking a useful facility making custom redrives, so I did them again:-

Side load capacity on the reduction at the propeller flange face = 28,328.5N, 2,888.703Kgf or 6,368.5 pounds, which is 2.84 imperial tons

Dynamic bearing capacity is 29,600N, 3,018.36 Kgf or 6,654 pounds, this is 2.97 imperial tons, not a bad match of capabilities eh?

Moment capacity at propeller flange is 3,121.8Nm or 2,302.518 foot-pounds; as such forces are momentary rather than applied whole life, bearings wont be troubled. If you can hang just over one ton off the tip of a foot-long bar protruding from the centre of your propeller shaft without hurting the engine mounts, excellent. 4G loads at 1.5 factor in the UK design code means a 100 kilo motor exerts 0.6 tonne on its mounts. Our code mandates 15G forward crash load too but that's axial and won't bother the redrive.

If you can be bothered with formulae, there's an interesting January 2017 paper on this subject, note the worked example numbers at the end, page 550, which are for a 210hp motor; since real world in homebuilt machinery is under 100hp the numbers tie up rather well, even for the doubled figures for aerobatic forces just before the conclusion.

http://www.arpnjournals.org/jeas/research_papers/rp_2017/jeas_0117_5652.pdf

Bye bye and fly safe, been interesting

K Armstrong

Last edited:

#### wsimpso1

##### Super Moderator
Staff member
Log Member
Side load capacity on the reduction at the propeller flange face = 28,328.5N, 2,888.703Kgf or 6,368.5 pounds, which is 2.84 imperial tons

Dynamic bearing capacity is 29,600N, 3,018.36 Kgf or 6,654 pounds, this is 2.97 imperial tons, not a bad match of capabilities eh?

Moment capacity at propeller flange is 3,121.8Nm or 2,302.518 foot-pounds;
Now we have something! Thanks for running some numbers for us on the ACE!

Just to calibrate us, a small prop, suitable for say a 60 hp engine, will have on the order of 0.30 kg-m^2 of inertia. Rotations at 3000 rpm and in a spin at 1 turn per second - Bill Kershner published data showing the Cessna 152 at up 300 degrees per second, so 360 degrees/second seems a reasonable chinning bar. 0.30 kg-m^2 prop will make 590 Nm of prop hub bending moment, or about 435 ft-lb.

When this level of spin is applied to the ACE Factory-Fit has analyzed for us, it appears to have a pretty safe FOS of 5.2, even after derating for fatigue, etc. Factory-Fit did not indicate if this limit is due to bearings or structures, but even a very conservative derating looks pretty secure with expected props and operation in the 60 hp range. All of you thinking this is OK, had better check details for yourselves.

If you can be bothered with formulae, there's an interesting January 2017 paper on this subject, note the worked example numbers at the end, page 550, which are for a 210hp motor; since real world in homebuilt machinery is under 100hp
I would be an awful hypocrite if I was bothered by analytical rigor. I shall check out the article and see about some calcs.

I do have to quarrel with the 100 hp number. Homebuilts are running turbocharged Subaru four cylinders (150 hp and up), Subaru six cylinders (200 hp and up), Chevrolet LS V-8's (350hp and up), etc. The homebuilt community may have quite a few engines in the below 100 hp range, but we go way up from there.

Other prop sizes and their moments:

Props as used on the Rotax 912 range of engines is closer to 0.6 kg-m^2. Using 2700 rpm and 1 turn/s, 1066 Nm or 786 ft-lb. The structure of the ACE redrive might still be up to this level of power. Do your homework...

At the 200 hp level a number of props appear to be in the 2.5-4 kg-m^2 range. At 2700 rpm and 1 turn per second, these props are giving the flange, prop shaft, and bearing set 4400-7100 Nm or about 3300-5300 ft-lb. I would say PSRU do have to be designed with prop gyroscopics involved or surprises of the bad kind can come along...

Billski

#### pictsidhe

##### Well-Known Member
23.371 has a combined yaw and pitch rate of 2.7 radians per second for those who don't compute exact values, so in Billski's ball park.

#### wsimpso1

##### Super Moderator
Staff member
Log Member
23.371 has a combined yaw and pitch rate of 2.7 radians per second for those who don't compute exact values, so in Billski's ball park.
The lowly Cessna 152 has spin rates that oscillate and go as high as about 300 degrees/sec or 5.2 rad/s. Part 23 min rate is given as 2.7 rad/s? That seems a pretty low chinning bar to me... I am sticking with my 1 turn per second or 6.28 rad/s as my basis.

Billski

#### Armilite

##### Well-Known Member
We have not seen much call for redrives for these older 2 stroke Rotax engines.
When any inquiry comes into us for Rotax 2 stroke redrives. I ask for Cad drawings of the engine casework. No one has come even close to giving us those yet. I get rough drawings. Thats not good enough. Too risky for production.
Wrong Sir: We custom make our redrives for commercial engines as per requirement. So we cover all hp levels.
Really depends on what the customer wants. My advise is then recommended.
=========================================================================
GX 200
Designed for up to 24 HP <--- Thats Good. There making 15-22hp!
2.75 kg

GX 390/420 <------ A GX420 Single makes 34.83hp@5750rpm, a 460 Single makes 37.37hp@5000rpm Both more HP than your Belt Drive is rated for, per your web page. These Singles already go up to a Vegas Cart 625 (96mm x 86.5mm) 626.3cc and these can be Bored up to 100mm, giving you (100mm x 86.5mm) 679.6cc in just the Singles!
Designed for up to 32 HP
2.85 kg

Your Drive for V-Twin Engines. <--- These 993's are making 62hp@6250rpm! They haven't really started to Big Bore these yet, but they Will. A Briggs 993 is (85.5mm x 86.5) 993.6cc and Stock is up to 37hp@3600rpm. A Big Bore (100mm x 86.5mm) 1359.2cc.
Designed for up to 55 HP
623 cc = 3.9 Kg. 993 cc = 4.2 Kg

A Simple Google search "Rotax & DXF" and you will find the Provision 8 CAD Data for Rotax's, 377/447, 503, 582/617/670. That fellow who makes them for Rotax's is selling them like Hot Cakes off eBay. Both Provision 4 and Provision 8. He doesn't make one for the Rotax 277UL either. Rotax only held 80% of the World Market for Ultralights & Kitplanes. The Skidoo/Rotax 277F/277UL was made from 1980 to 2008 and many laying around in Snowmobiles, so is still a viable 26hp Engine for Part 103 Ultralights and Small Kitplanes. With a few mods it can make more hp.

Scroll down to "2-stroke ROTAX Aircraft Engines" and you will find these CAD Drawings. Never found the Rotax 277F/277UL Drawings. To make Money, sometimes you have to spend some money, like buy a cheap 277F off eBay or Craigslist to then get your own Measurements to make a Redrive, You can always resell the Engine. Like I told you, you have Half the World Population around you (India, China, and the Country's next to them, now at 4 Billion People. These Honda/Clones are just starting to catch on here for Ultralights & Kitplanes.
http://www.aviagamma.ru/draw-e.html

#### Armilite

##### Well-Known Member
These Honda/Clone Type GX420/GX460, Mods are running 11.0cr, 34mm Carb, K&N Air Filter, Tuned Exhaust, Hi-Rev Kit, a Billet Aluminum Rod, and Billet Aluminium Flywheel. There is more Nods they can do, Porting, Bigger Valves, etc.

#### cluttonfred

##### Well-Known Member
HBA Supporter
Armilite, what exactly is your beef with Ace Aviation? You are not a customer, so are you a competitor? Or just trolling?

#### pictsidhe

##### Well-Known Member
Armilite, what exactly is your beef with Ace Aviation? You are not a customer, so are you a competitor? Or just trolling?
He thinks that anyone who isn't running a drag-race tuned engine in an ultralight, should be. You dopes just don't get it, an engine that has done dozens of 1/4 mile runs should be perfectly fine for hours of high power use.

#### Armilite

##### Well-Known Member
Armilite, what exactly is your beef with Ace Aviation? You are not a customer, so are you a competitor? Or just trolling?
===================================================================
I posted my opinion on post 23. As I have stated multiple times on here, I think they're the Best Drive made for these Honda/Briggs/Clones. But Questions about Belt Life should be shown on Web Site and Answered here also. As I have shown, these Honda GX390/420 and Larger up to 625cc today Single Cylinder Engines have far Surpassed what his Web Page states his Belt Drives HP is Designed for. A Stock Honda GX390 is 13hp@3600rpm. A Stock Duromax 440 is 18hp@3600rpm. Should he change that Web Page to say as this was finally explained in Post 33. "We custom make our re-drives for commercial engines as per requirement. So we cover all hp levels." That should have been Posted in his opening Statement of this Thread and also put on his Web Page which hasn't been updated in years! These Single Cylinder Engines are not being used at 3600rpm but 5000rpm to 6250rpm. The V Twins are also being used from 3600rpm to 6250rpm!

#### Armilite

##### Well-Known Member
He thinks that anyone who isn't running a drag-race tuned engine in an ultralight, should be. You dopes just don't get it, an engine that has done dozens of 1/4 mile runs should be perfectly fine for hours of high power use.
============================================================

These Honda/Clone Type RACE ENGINES are turned 7000rpm to 12,000rpm! But we're not talking Racing here.

These Single Cylinder Honda/Clone Type Engines are not being used at Stock 3600rpm but up to 5000rpm to 6250rpm for takeoff on Airplanes. That Honda Type Stock GX390 is 13hp@3600rpm and the Stock Duromax 440 is 18hp@3600rpm. The Bigger 627cc to 993cc, V Twins are also being used from Stock 23hp to 37hp@3600rpm up to 6250rpm for takeoff on Airplanes! Since you have said in other Post, "I have never Rebuilt a Rotax 2 Stroke or a Honda/Briggs Type Engine", you sure do have a lot of opinions on How they work and their limits. I have also stated multiple times, I personally wouldn't run these Honda/Clone Type Engines higher than what the Rotax 912 80hp is run at 5500rpm!

Stock RPM for a Generator, Water Pump, Saw Mill, etc., where only 3600rpm is needed, so that's WHY they're Designed to be run at using a Low 8.0 CR for 87 Octane, use a Small 22-24mm Carb, use a Quiet but Restrictive Exhaust, A Quiet but Restrictive Air Filter, so are only Rated at 3600rpm. Even they Offer a Hi Rev kit for 4950rpm for other use Applications using Stock Parts. WHY, only 4950rpm for their Hi Rev kit, because the Factory Cast Iron Flywheel is only Good for Max 5500rpm, it will explode! So they set their Saftey margin at 4950rpm.

No, you don't need a Drag Race Tuned Engine on an Ultralight, you need a Small Light Weight Engine with a Redrive, Built with HD Light Weight Racing parts for making 25-35hp for Endurance! You take that Duromax 440 rated Stock(18hp@3600rpm) that Cost $289 and add the HD Light Weight Racing parts to make it better so you can turn them Higher 5000rpm to 5500rpm! That means for Endurance, a HD Billet Aluminium Rod, a HD Billet Aluminium Flywheel that also Saves You Weight, use a Billet CAM, use HD Billet Needle Bearing Rocker Arms, use HD Billet Lifters, HD Chrome Moly Push Rods, a Forged Piston, HD Valve Springs (For Higher 5500rpm) & HD Keepers & HD Locks with Stainless Valves, all for Durability at your Max 5000-5500Rpm! For making way more HP, your usually going to be turning it Higher 5000-5500rpm and using a Bigger Cam, and a Higher CR than Stock, but just Bolting on a better K&N Air Type Filter, and Tuned Header Exhaust, with a Bigger 34mm Carb, will net you more HP even at Stock 3600rpm. That$289 Duromax 440 is rated 18hp@3600rpm with just them simple Bolt On Mods would probably make 20-22hp, which might work out for some Planes. With those Bolt On's and a Better CAM, it might make 25-28hp. But most Planes need more than 20-22hp. Since the Rotax 277UL was probably used on 90% of the True 254lb Part 103's ever built, it made Max 25.4hp, that's WHY I say most True Part 103's only need 25-35hp! But you would know all this if you really Built any of these Engines.

That Vegas Carts 625(\$850) is rated 23hp@3600rpm, so with just them Bolt On Mods K&N Air Type Filter, and Tuned Header Exhaust, with a Bigger 34mm Carb, will net you more probably 26-28hp@3600rpm! The only difference between the Stock GX390's(389cc) and this 625(626cc) is Bore & Stroke used. The 625 does use a 9.0cr vs all the others use 8.0-8.3cr. Same CAM & Valves. Carbs all range from 22mm to 24mm.

#### Neal Scherm

##### Well-Known Member
No. How many bits of machinery usually driven by these engines have the inertia of a prop? You need to consider the complete system. A drive system that works perfectly for a low inertia load for 10,000 hours could have a lifetime of seconds swinging a prop.
BINGO

HBA Supporter
Got it.

BJC

#### Heliano

##### Well-Known Member
A quick comment on the very interesting point brought up by wsimpso1: It seems to me that 23.371 addresses the engine mount system. The cyroscopic loads on the engine and its reduction gearbox (if any) are - correct me if I am wrong - in Part 33, more specifically Subpart D (Block Tests). Another comment: yes, spins generate high angular velocities in all axis, but there are other maneuvers that can generate even higher rates, e.g. Lonkovak. We all know how a P&W PT6 engine is reliable, right? IFSD of a low end PT6 is roughly one inflight failure each 350000 flight hours. That is amazingly good. We had a turboprop trainer designed here, equippped with P&W PT6A-25C in the early eighties which was very benign and a pleasure to do aerobatics with. We quickly found out how easy it was to do Loncovak with it. However, after one year or so of operation, a pilot of an aircraft belonging to an aerobatics demo squadron - which usually included Loncovaks in their displays - saw the prop of his plane fly away. Three months later, another aircraft used for demo by the manufacturer had the front propeller bearing desintegrated, covering the canopy with oil and the crew came close to electing to eject. After those events, Lonkovak became a forbiden maneuver. I mentioned all this to conclude: cyroscopic loads MUST be assessed. As they are related to fatigue, a generous FOS must be embedded.

#### cluttonfred

##### Well-Known Member
HBA Supporter
Armilite, I don’t know what’s going on here but your whole attitude is incomprehensible to me. You are going after a small business owner operating in another country under circumstances none of know, simultaneously outraged that he isn’t offering every option under the sun and telling him how to run his business. I am surprised he has even responded to you up until this point, and your needlessly aggressive and confrontational tone is simply going to drive him away from participating in this forum.

John Penray Evans:
We have not seen much call for redrives for these older 2 stroke Rotax engines.
When any inquiry comes into us for Rotax 2 stroke redrives. I ask for Cad drawings of the engine casework. No one has come even close to giving us those yet. I get rough drawings. Thats not good enough. Too risky for production.
Wrong Sir: We custom make our redrives for commercial engines as per requirement. So we cover all hp levels.
Really depends on what the customer wants. My advise is then recommended.
========================================

You don't have much call for Redrives for older Rotax's account hardly anybody even knows you even exist....

As a Manufacture who is making Money off these products, you need to Invest a little Time and Dollars to grow your Product Line......

Your Website still doesn't reflect what you say "We custom make our redrives for commercial engines as per requirement. So we cover all hp levels.....”

So you can make up whatever excuse you want John, you were given the Provision 8 CAD Data by me....

Last edited: