# "Micromaster"-- Centerline twin using small industrial engines

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Vigilant1, Nov 13, 2018.

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1. May 29, 2019

### BBerson

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The root of a wood prop is rather blunt. It could be faired like wheels have wheel pants. Use your own inventions. I am just suggesting a prop can be optimised some for stopped lower drag.

2. May 29, 2019

### Vigilant1

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In the case of the P-3 (and the P-51, which had similar cuffs) they are designed to "increase the flow of cooling air into the engine." I wouldn't have thought that necessary with a turboprop, but how can I argue with the interwebs?

3. May 29, 2019

### BBerson

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I think the P-3 cuffs are to streamline the root when feathered. Just my assumption.

4. May 29, 2019

### blane.c

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5. May 29, 2019

### Vigilant1

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Hmm--a claimed 15% increase in static thrust from the turbocharging effect of those flaps on the prop pushing air into the engine induction system in pulses timed to coincide with the opening of valves. That seems improbable on the face of it (no spreading out of that pulse in time due to the air cleaner, bends and restrictions/expansions in the induction system, etc?). And the Micromaster would need the boost at climb speed, static thrust is relatively unimportant. But LoPresti has notoriety and credibility that I don't, so throwing stones is probably ill advised.

6. May 29, 2019

### blane.c

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Could you imagine what the prop would look like to put clocked pulses in a V-twin, lol.

7. May 29, 2019

### revkev6

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possibly but that wasn't the case for the original skymaster, the saying was that the second engine was only to get you to the ground. Plus what expense is there during normal flight modes?? we are having a discussion at this point on how to make the thing even continue to fly once the other engine quits and the prop drags it to a halt. my opinion on this has always been one similar to colin chapman of lotus fame... "Simplify and then add lightness". the most efficient solution doesn't involve doubling the sets of redundant systems. which lowers your hp/lb of the entire system. IMO you would end up with far less of a chance of an engine failure getting a decent used io-200.

to keep this on topic, if we are engineering for engineering sake, lets just throw frangible prop hub nuts on.

8. May 29, 2019

### Vigilant1

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We kinda backed into the performance goal. The original 3 goals for the Micromaster project (as ill-stated as they were):
Regarding #1, "remaining airborne" seemed a bit anemic (though the numbers indicated we might be able to maintain level flight under single-engine standard day conditions on 25 HP each). "Remaining airborne" after an engine failure immediately after takeoff--struggling around barely out of ground effect-- seems scarcely safer than no power at all. Being able to climb, under anticipated real-world conditions, is far better. The 810cc vertical shaft engines were explored as an option, and showed promise because they are:
-- Cheap compared to horizontal shaft engines of 25-30 HP
-- Light compared to horizontal shaft industrial engines of 25-30 HP
-- Already proven in other airplanes as direct-drive engines (SD-1)

Doing some rough calculations with the assumed 28 HP of these 810cc engines, it looks like* the Micromaster could achieve:
1) Sea level standard day, 2 engines: 1160 FPM climb
2) 6000' MSL, 2 engines: 900 FPM climb
3) Sea level , 1 engine and 1 stopped prop: 300 FPM climb
4) 6000' MSL, 1 engine and 1 stopped prop: 200 FPM climb.
I didn't work out a service ceiling, but at an altitude of 6000' MSL and an airspeed of 110KTS, excess thrust available would only permit a climb rate of about 100 FPM, so for practical (covering distance) purposes, that's about as high as you'd go (and it works out to 146 MPH true, which would be good on approx 4 GPH)

So, honestly, we backed in to the 300 FPM SE climb number as a result of what could be done with an attractive candidate engine. I argued elsewhere that I think this SE climb rate is satisfactory.

* The table at that link was a victim of the Xenforo migration. I'll rebuild a better one as soon as I can figure out how to build a table now--it's not as simple as it used to be.

Last edited: May 29, 2019
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9. May 29, 2019

### blane.c

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Many is the day I climbed out at 250 FPM and 100,000lbs. Sure we weren't max power (that would waste gas). And considering we were doing over 120 knots, the climb angle would be much better in a Micromaster at the same rate of climb and around 1/2 the speed. Muy' Bueno' I say. It sure beats going down hill at that rate or greater.

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10. May 29, 2019

### Vigilant1

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This is a long thread with over 800 posts, and a lot of things have been covered. I've lost track of many of them, but here are a few other posts that made your points, and some other relevant posts/points.

Yes, that is said about all twins.

Could you elaborate? Do you want a breakdown of anticipated per-hour expenses of operating two (big) lawnmower engines vs O-200 you've nominated below?
It's being discussed, but I think that's because the previous discussion has been overlooked. If you are interested, please see my post above: My calculations indicate the proposed design isn't "dragged to a stop" if an engine quits, it can stay airborne and climb. Calculations and amplification at the links in Post 808, and several preceding ones.

Your opinion is noted. Toobuilder did a good job of expressing them. Previous posts expressing similar sentiments and some back-of-the-envelope statistics are:
Here
Here
Here
Here
Here

11. May 29, 2019

### revkev6

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not all, but many. IMO it seems the aircraft that have the "remain airborne during engine out" goal tend to be the worst in those regards.

I was talking more in terms of performance and efficiency than cost. in a light craft where weight makes a large difference in performance you are adding a fair amount of complexity and weight. My mention of the O-200 is just in regards to your statement about reliability, not really cost. A proven engine that has millions of hours will more likely not have a mechanical failure and have less unknown characteristics when put in an aircraft.

the current discussion is how to keep the prop from windmilling. are your calculations accounting for a spinning prop?

sorry that I haven't fully backread, but I'm not at all surprised that Toobuilder would be able to do a better job than I at making the point. Just on a side note, i do like the idea of the industrial engine conversion in the correct applications.

12. May 29, 2019

### Vigilant1

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I was surprised that the additional weight for 58HP from 2 engines vs 60 HP from one engine does not appear to be very much. The 810cc engine, stripped of everything not needed for flight use, is claimed to weigh 71 lbs (32 kg) (source: Minisport SE33 engine spec page). That's for an engine with a starter, alternator, ignition system, etc. Apples-to-apples, a VW 1835 with an electrical system/starter and single ignition system will weigh about 160 lbs, so the two industrial engines are 18 lbs lighter. Now, after we get two (smaller) exhaust systems, two (smaller) engine mounts, two (smaller) props, etc it will probably be the same or more for the industrial engines, but it doesn't appear to be a big difference.

The biggest area of compromise for the twin surprised me. IMO (and people differ), being able to safely fly after an engine failure is a very desirable trait. But, to get that, we need to make compromises in the Micromaster design that we would not have to make if we had a single engine. To fly and climb on 1/2 of the installed HP we need a longer wing, lighter weight (even at the expense of drag/laminar flow, and at the expense of fuel/payload), and props that can produce good thrust at climb speed (sacrificing thrust at higher airspeeds). We haven't worked through the results of having to make these compromises, but they will certainly have an impact. If we just wanted to install 2 industrial engines and didn't care about flying on one, we'd have a very different airplane--faster, with more payload and range. But it would have a >much< bigger chance of an engine failure/forced landing than a SE plane because loss of either engine would put us in the trees. That's a project that wouldn't interest me at all.
No, the drag calculations are for a stopped prop. I think getting a windmilling prop to stop will be pretty simple.

Hey, go buy an 810cc engine, weigh everything, take lots of pictures, and prepare for a slew of questions. You'll be a hero!

13. May 29, 2019

### Blackhawk

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Don't know if this Italian PP aircraft has been mentioned before.

Only uses standard propellers, like the Powers-Bashforth MM-100 Mini-Master and Canadian Toucan centerline twin; no mention of prop feathering etc.

A bit heavy on fuel I think.

Tucano Delta3 VTW
Specifications
Stall speed: 30 kts (35 mph) (56 kph)
Cruise speed: 78 kts (90 mph) (144 kph)
VNE: 92 kts (106 mph) (170 kph)
Climb: 1575 ft/min (8 m/s)
Take-off distance: 197 ft (60 m)
Landing distance: 295 ft (90 m)
Engines: 2 x Rotax 582
Fuel Consumption: 16 GPH (60.6 LPH)

14. May 29, 2019

### blane.c

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They look like they would be faired into the hub feathered to me too.

15. May 29, 2019

### blane.c

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Pricey?

16. May 30, 2019

### Vigilant1

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You're not kidding. Two 65 HP 2-strokes burning a total of 16 GPH (I believe it) and cruising with 2 people at 78 Kts? Did somebody prop the doors open? Plans for the design are probably distributed at no cost by BP.

17. May 30, 2019

### BBerson

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More like $7-$8000 with the gearbox and starter for the new Rotax (each).
There is nothing bargain priced anything near to a mower engine.

18. May 30, 2019

### Tiger Tim

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A turbine only burns something like 20% of the air that goes in the intake under normal conditions. Any extra air you can cram in contributes to cooling and as most turbines are temp limited it means you can squeeze out more power.

19. May 30, 2019

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