So I am thinking that based on your 1st post in Micromaster that it makes sense, I am thinking 550lbs for empty weight Tri-Mower, and "look" I did not completely rip off your Tri-Mow-tor name. Tri-Mower 24 foot wingspan 54" chord so 108 square feet. You were building at 7.3lbs per cubic inch this seems rational as for engine loss it would double to 14.6lbs per cubic inch. That would be like a 1430lb gross weight VP-2 on 98 cubic inches (1600cc) {Micromaster 717lbs on 49 cubic inches with one engine out} not what you normally want to do but it is do-able, that is I bet the VP-2 thing has been done though not comfortably. I am looking normally around 1100lbs or 1150lbs so losing one engine would put me at say 1150lbs on 98 cubic inches, losing two isn't a good idea as 1150lbs on 49 cubic inches direct drive you are looking for best glide.

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For a recap (not to go too far afield from your TriMower idea)

After a couple hundred posts and doing some refining, the most recent configuration of the Micromaster was (

MicroMaster thread, Post 240 ):

Span: 26'

Wing Area: 70 sq ft

Empty Weight: 450 lb

MTOW: 770 lb (450 EW + 250 lb pilot and baggage + 70 lb fuel). I'd include a bigger tank to take more gas if less cargo was aboard.

Engines: 2 x B&S 810cc (28 HP at SL, 22.5 HP at 6000'), 46" diameter props (34.6" pitch, optimized for 110 MPH).

Projected performance:

**.......Condition.............................No-lift drag........Drag due......Reqd Total Thrust..........Total thrust.............Climb **

..................................................................................to lift..........for level flight...............Available............Available
2-engines, level flight, 60 KT, SL ........... 28 lb..............16 lb.................44 lb........................168 lb..............1160 FPM

2-engines, level flight, 60 KT, 6000' MSL ...23 lb..............14 lb.................37 lb........................134 lb...............900 FPM

1 engine level flight, 60 KT SL .............37 (stopped prop). 16 lb............... 52 lb........................ 84 lb.............. 300 FPM

1 engine level flight, 60 KT, 6000' MSL... 31 (stopped prop)...14 lb.............. 45 lb.........................67 lb............... 200 FPM

2 engine cruise: 100 KT, 6000' MSL ......... 63 lb...............13 lb ............... 76 lb...................... 114 lb............... 350 FPM

---110 KT, 6000' MSL............................... 77 lb...............10 lb.................87 lb....................... 98 lb............... 100 FPM

---100 KT, sea level................................ 76 lb...............15 lb................ 91 lb.......................142 lb............... 470 FPM

---110 KT, sea level ............................... 92 lb................13 lb.............. 105 lb.......................122 lb............... 160 FPM

So, at MTOW the MicroMaster would have a wing loading of 7.7 lbs/sft.

2 engine (SL) power loading of 13.75 lbs/HP, single-engine (SL) power loading of 27.5 lbs/HP.

If the

__TriMower__ has an MTOW of 1150 lbs, then with one engine out you'd be at a power loading of 1150/56HP = 20.5 HP/lb, which is better than the situation with the MicroMaster when flying singe engine. With all engines operating the MicroMaster and the TriMower would have the same power loading = 13.7 lb/HP.

FWIW, TiPi believes pretty strongly that these engines are good for more than 28 HP in aircraft use. The MicroSport folks advertise the same engine modified to their SE33 standard as producing 33 HP. That could be handy in a pinch.

How did you estimate an 1150 lb MTOW? My back-of-the-envelope WAG:

MicroMaster EW: 450 lb (nothing scientific, just a rough guestimate based on a plussed up SD-1 (270 lb EW) with more structure/wing (90 lbs) and another engine/prop/mount (90 lbs)

+ Another engine, mount, and prop: 90 lbs

+ additional structure, landing gear, wing area, another seat, etc for the for the 33% larger MTOW: 100 lbs

Total TriMower empty weight: 640 (Sanity check: A light Sonex weighs 650 lbs, and has just 170 lbs of engine. A VP-2 is about the same. The TriMower will be carrying more engine weight. A 640 lb EW might require more a more "weight-conscious" design than we associate with the VP-2 )

2x 190 lb occupants: 380 lbs (more for baggage?)

Fuel: 100 lbs

TriMower MTOW(?): 1120 (?)

FWIW, when I was noodling around with numbers to see if the MicroMaster SE climb would work out, drag was more important than I'd first considered and weight was a

__ little__ less important than I'd thought it would be. Just 3-4 more pounds of drag had a greater impact on SE climb than 50 lbs more weight. The TriMower will have a few more ponies at work in case of an engine failure, but drag might still be an issue for you, especially if this plane looks more like a VP-2 than a motorglider. You may want to consider a bit more wingspan to reduce induced drag at climb speed if this becomes an issue. Or, give the passenger a parachute and a quick course in how to use it--there, you just reduced your engine-out climb weight considerably!