# Pulling with a Honda CRF150R with optimized prop and ReDrive

Discussion in 'Firewall Forward / Props / Fuel system' started by Shepherd Thiel, Jan 7, 2015.

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## Will this pull a Legal Eagle?

4 vote(s)
44.4%

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44.4%

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4 vote(s)
44.4%

1 vote(s)
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4 vote(s)
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8. ### I does on paper but Won't IRL, not sure why.

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1. Jan 11, 2015

### Shepherd Thiel

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I hear a lot of people who have flown both say the LE flys like a Piper Cub.

The only other gripe I here is some of the 1/2VW's feel noes heavy.

I'm making a slight change to the nose design of the Legal eagle. The nose will form a triangle from the pilot forward. Simpler, stronger and lighter than the squared nose and I don't think the engine cares if it is mounted to a square or a triangle.

The big thing will be actually reworking the stock engine. Case cutdown, balance, blueprint run on test stand.

I plan to fully break in the engine with it on the test stand. It will give me a chance to not only get real world thrust numbers but I'll know what service maint it will need to stay tip top.

In the end I should have a Engine that is 30% lighter than the 1/2VW, comparable thrust, and 1/2 the cost.

2. Jan 11, 2015

### Shepherd Thiel

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addaon, I plan on building my own version of a Legal Eagle Leonard Milholand's Better Half VW and Legal Eagel Ultralight!

I'm more or less reverse engineering the entire aircraft bit by bit, looking at the 100s of others that people have built and adding the improvements those people have made into one aircraft.

Result looks to be a Legal eagle that's dimensionally 10% larger and flys even more like a Piper Cub but with less cable/pulley and more control arm/yolk.

3. Jan 11, 2015

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The stock LE supposedly can max out Part 103 horizontal speed at 60 - 63 mph. What's the thrust of those propeller / engine combinations at 60 mph?

4. Jan 11, 2015

### Shepherd Thiel

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Your correct, the lower end (30hp) 1/2 VWs make around 150 lbs thrust and max speed at 63 or so.

Many run supped up 1/2s (45hp) and make 250lbs or better thrust. They then calibrate (De-Tune) to a 63 mph cruse and let the engine loaf along making only 35hp of the rated power.

The advantage is more takoff power and for the Legal Eagle XL (rated for a 240lb 6'4" pilot) that 45hp is needed.

The above are all based on what builder/fliers have observed in their own LE/XL builds.

The CRF250 should do everything the 45hp 1/2 VW does as the VW looses a bit of efficiency in going direct drive with a smaller prop.

1/2 VW fuel consumption is 1.8-2.1gph

The CRF250 consumes less than 1gph, although the only data I get that from is people running them hard in dirt bikes. I think at constant RPM with a constant load and leaning out the fuel it should do even better.

Part 103 is limited to 5 gallons, that fuel consumption rate (if it plays out real world) IMHO is a game changer, it takes a 2hr joy ride and gives me the option of hopping state to state with a legal amount of fuel on board.

1/3 the weight, 1/2 the cost, and twice the range of the 1/2 VW.

Also the CRF250 is water cooled. This would allow me to work out a light weight cabin heating system if I skin the cab and make zip up fabric doors. Or an even lighter way to pipe warm air into my flightsuit.

On a side note a stock CRF450 makes 62hp and is still lighter than the 1/2 VW.

If this project works out, I may be offering Honda CRF Engine/ReDrive/Prop combos converted, tuned and ready to bolt on.

5. Jan 11, 2015

### Shepherd Thiel

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I can't think of anyone who would want to fly a heated, enclosed cab Legal Eagle that can fly 5 hours on $10 worth of fuel... Especially if it's even less$ to build it than the original.

6. Jan 11, 2015

### clanon

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7. Jan 11, 2015

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Interesting motorbike air-conversion approach (I'm talking about the CRF250 variant, the 150 cc being too feable IMO) - and doable I guess, whilst some drawbacks need to be taken in calculation. And I'm not... hypothesising :gig: too much, being involved for decades in stuff related with motor(biking)sports / testing etc.

First of all: these high-tech/performance/revving 4-strokers have a very-very frequent maintenance schedule - Honda advises for example a 15-hours oil change interval for the CRF250, but most (ab)users do it every 5 (five!) hours, or even every single hour of riding.
Nothing abnormal here, as the general rule says that the piston/valvetrain wear increases 4 (four) times with every doubling of the rev-regime. And we're talking here about monocylinders able to reach 12K revs/min.

And from this feature (high revs also needed for obtaining the max. torque) derives the need to stress the engine a lot, even for reaching that classical 75% cruise power.

Plus a third issue: the TBO of these rev-monsters is way too short (again, IMHO) for aviation use - the real-life data averaging 100 hours or even less for a not so "moderate" use.

Anyway, it would be interesting to see if someone could someday adapt a very light chain-drive PSRU for this kind of revvy engines - another feasible approach I dear to think, as "normal" motorbike chain [primary and/or secondary] transmissions CAN take plenty of abuse.

8. Jan 11, 2015

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(A short Later Edit, as I can't modify the previous post.)

1) Yes - but only in theory, since the long-term durability is what any VW conversions achieves OVER those revvy engines (addendum needed: this reliability drawback is valid mostly for the motocross hi-tech singles, other motorcycle's multi-cylinders having a much better record.)

2) ...Less than 1 gph for the CRF250? Those bikers must've been kidding - that would be sound for only 10-11 HP produced (an engine-regime slightly over the idle revs, that would lead anyway to spark-plug malfunction after much less than an hour.)

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9. Jan 11, 2015

### Shepherd Thiel

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As said maintenance schedule not a big change.

Yes TBO is shorter than a 1/2 VW, but on the CRF-250 it is much simpler and less expensive, at least simpler than the original conversion of the CRF-250 engine.

Much of the maintenance and ware on the CRFs is the trans a part I am removing. This will require an oil reservoir to be added to maintain oil volume. In my case I plan to mount an oil cooler on the nose.

The torque band on the CRF-250 is in the 70% of max RPM range @ 8500rpm, max hp @ 11000rpm redline @12500rpm

This is where I am guessing at the fuel consumption from. Honda CRF250L Mileage | Fuelly if you have a better idea of what I can expect I'm all ears.

The belt redrive I am using is a belt for a motorcycle common to home ReDrive builds, I may find off the shelf parts to get the ratio I want or I'm going out on a limb and fabricating custom ratio gears. I'm looking for 4.4/1

Based on what I got from the prop MFR the only time I should be at 11,000 RPM is on takoff

Looking at the power curve of the engine both prop thrust (tips nearing sonic) and peak engine power drop off at the same time, so unless I'm in a dive I shouldn't be able to over rev the engine.

If I only want to loaf around at 45mph I'm only turning the engine at 6,000 rpm, the effect of trying to stretch my gas should have the same effect of reducing ware.

At this point I'm willing to do a TBO every 100 hours of flight. Since this is an R&D project I'm sure I'll TBO more often than that.

Before the engine runs I plan to balance and blueprint and otherwise tame what I have heard is a fairly low vibrating engine.

I plan to rubber mount the engine to the fuse, mount the redrive to the drive shaft and the prop drive solid as possible direct to the fuse. This should help keep vibration off the prop and airframe.

The 3 blade prop should also help.

The theory should get sorted from fact as soon as I have the thing mounted to a test stand to run it through break in before install on the aircraft.

The worst thing that could happen is a really cool setup for a mini airboat where engine failure isn't such an extreme problem. As well as a proven opinion on why someone shouldn't pick up where I left off.

10. Jan 12, 2015

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Reasonable power consumption estimate for a modern four-stroke is 0.45 lbs/hp*hr; so for a 36 hp engine running at 70% peak power, you're looking at 1.9 gph as a pretty solid estimate, ±10% at most.

11. Jan 12, 2015

### JamesG

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The worst thing that can happen is that you assume everything is fine and have an engine or structure failure in flght.

12. Jan 12, 2015

### Shepherd Thiel

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Not in my mind, I know where I'm going.

Besides I plan on running many hours on the ground. Mocking up stress/breakaway parts and doing destructive testing.

Part of that will be engine mods, test stand run up and then break in, what I learn in the break in will determine my next TBO from there the idea is to mount the engine on the airframe and run it to TBO, at that point I hope any weak points will have been found.

Flight testing will be over a 2 mile level stretch of unobstructed field. I can hop or fly ground effect tell I'm blue in the face or break something.

Not a bad prospect if worst case is I'm going 30mph I'm 15 feet up and the engine falls off and wings fold up.

I may get "CRAZY" and use some of those TBO hours doing touch and go hops, adjusting controls, and putting around in ground effect.

13. Jan 12, 2015

### Shepherd Thiel

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“There are old pilots, and there are bold pilots, but there are no old, bold pilots.”

14. Jan 12, 2015

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