# Engines: Cost and weight per HP

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#### Vigilant1

##### Well-Known Member
Looking at the various discussions here about engine weights and cost, I gathered some numbers (below) for rough comparisons.
1) I looked at engines that could be bought new and completely assembled
2) Weights and costs are from "the internet", don't include exhaust systems, and are subject to a lot of variables.
3) To some extent, none of his matters. If you've got a particular type of flying in mind, then you may need a particular engine.
4) Costs are initial purchase price. Maintenance costs and resale value may also be important factors.
Edited to add: See later post for edited chart with corrections and additions.
Numbers:

Engine.................HP.....Cost ($)....Weight (lbs)...$ per HP.....Lb per HP
Lycoming O-360.........180....27,500.(1)...305.............153..........1.69
Rotax 912 ULS/S........100....19,437.......125.............194.........1.25
Aeromomentum AM13......100....10,495.
(2)...201..(3)........105..........2.01
VW 2180cc.(4)...........76.....7,175.......167..............94.........2.20
VW 1835cc (5)...........60.....6,025.......165.............100.........2.75
VW 1835cc "basic",(6)...60.....4,750.......145..............80.........2.42
Harbor Freight670cc.....22.......584.(7)....97..............27..........4.38
"" + hub&bearing (8)....22.......734.......104..............33.........4.70

Notes
(1) Price through Van's direct purchase program. May be higher elsewhere?
(2) Price is for the Aeromomentum AM13 "low profile" version. The upright version is $8495 (3) Weight is for the AM13 engine, radiator, and coolant (4) From Hummel engine site, includes dual ignition system, starter, alternator, carb, Force One bearing and prop hub (5) As above, but simple shrink fit prop hub (no Force One bearing and hub) (6) Hummel engine site: Single ignition, hand propped, no alternator, with carb (7) With ubiquitous "20% off" coupon (8) Estimated price and weight of additional bearing and prop hub:$150, 7 lbs.

Observations:
1) Mass production does a great job in lowering prices
2) Weight: The formula for a cylinder's included volume compared to its surface area is relentless. Bigger engines generally have more HP per lb. The Rotax stands out in this regard--but they sure charge for it!

My own very subjective opinion is that, for fun flying, there's slowly decreasing utility for each HP added after we get safely airborne. More HP is almost always more fun, but the first 25 HP that may get us airborne and enjoying the magic of flight surely gets us more "fun per HP" than the 25 HP difference between a 160 HP engine and a 185 HP engine. So, in that regard, the small industrial engines that provide that first, "highest utility" 20-25 hp at a lower absolute $$/HP are very impressive standouts--if we have a plane that can take advantage of it. Luckily, if our idea of minimalist fun flying requires 60-80 HP, there are still good$$/HP (and lb/HP) choices in that range, too.

Just some not-very-original rambling on this Sunday . . ..

Last edited:

#### pictsidhe

##### Well-Known Member
Current price o the HF is $730. They have money off discounts occasionally, but not often. curently a$670 one. There was a $600 one til Feb. 20% coupons don't work on engines. The industrial V twins have a heavy flywheel that won't be needed in DD. That could be -10lb. 30hp 810cc Briggs tip the scales at 87lb out of the box. -10lb for flywheel =77lb. Price is usually around ~$100 more than HF if you look around.
23hp 627cc Briggs are 77lb out of the box. -10lb = 67lb. You'll pay maybe $1200 for one of those. There's a bit more power that can be had from the industrials, but that's either time, $$, or both. 1/2 VW, 87lb, ~32hp, #### Vigilant1 ##### Well-Known Member Lifetime Supporter Current price o the HF is 730. They have money off discounts occasionally, but not often. curently a 670 one. There was a 600 one til Feb. 20% coupons don't work on engines. The industrial V twins have a heavy flywheel that won't be needed in DD. That could be -10lb. 30hp 810cc Briggs tip the scales at 87lb out of the box. -10lb for flywheel =77lb. Price is usually around ~100 more than HF if you look around. 23hp 627cc Briggs are 77lb out of the box. -10lb = 67lb. You'll pay maybe 1200 for one of those. There's a bit more power that can be had from the industrials, but that's either time,$$$, or both.

1/2 VW, 87lb, ~32hp,
Thanks, I'll fix the chart, add a Briggs and a 1/2VW. I didn't realize the HF 20% coupons weren't good for Predator engines (and lots of other stuff, too :dis: )

#### davidb

##### Well-Known Member
Easy to see why Rotax has a monopoly with SLSA.

#### Vigilant1

##### Well-Known Member
Updated chart, includes 1/2VW and B&S 810cc engine info from pictsidhe.

Numbers:

Engine.................HP.....Cost ($)....Weight (lbs)...$ per HP.....Lb per HP
Lycoming O-360.........180....27,500.(1)...305.............153.........1.69
Rotax 912 ULS/S........100....19,437.......125.............194.........1.25
Aeromomentum AM13......100....10,495.
(2)...201..(3)........105.........2.01
VW 2180cc.(4)...........76.....7,175.......167..............94.........2.20
VW 1835cc (5)...........60.....6,025.......165.............100.........2.75
VW 1835cc "basic",(6)...60.....4,750.......145..............80.........2.30
1/2VW 37HP "basic"
(6)...37.....3,650........85..............99.........2.00
Briggs & Stratton 810cc.30.......830........87..............28.........2.90
^^ "" + hub&bearing (7).30.......980........94..............33.........3.13
Harbor Freight670cc.....22.......730........97.............33..........4.41
^^ "" + hub&bearing (7).22.......880........104..............40.........4.73

Notes
(1) Price through Van's direct purchase program. May be higher elsewhere?
(2) Price is for the Aeromomentum AM13 "low profile" version. The upright version is $8495 = 84.95$/HP
(3) Weight is for the AM13 engine, radiator, and coolant
(4) From Hummel engine site, includes dual ignition system, starter, alternator, carb, Force One bearing and prop hub
(5) As above, but simple shrink fit prop hub (no Force One bearing and hub)
(6) Hummel engine site: Single ignition, hand propped, no alternator, with carb

BTW, chinese scooter CV carbs of about the right size can be had for about $30-$40 each from aliexpress. So, maybe another $100 for a CV carb conversion. #### Hot Wings ##### Grumpy Cynic HBA Supporter Log Member 20% coupons don't work on engines. That is what they say but it's worth a try. All they can do is say "no". The 20% coupon I used for the one I purchased, via their web site not from a store, worked. Got the free shipping too. They may have fixed that little back door by now? #### Topaz ##### Super Moderator Staff member Log Member Pulling the flywheel altogether on any of the industrial motors is a little more involved than it sounds. Most (if not all) key the ignition off magnets on the flywheel, and use the flywheel for charging the ignition battery. Those functions would need to be replaced, somehow. For the guys who are looking at extensive modifications, EFI, etc., that's likely not an issue. For other guys (like myself) who would be interested in the most "bare-bones" conversion possible, I'd probably be tempted to swap out the steel flywheel for a lighter-weight aluminum one, should the weight reduction prove necessary. With either a no-flywheel or aluminum-flywheel conversion, some means would still need to be found to keep the battery charged. A little wind-driven generator is probably the best bet there. #### pictsidhe ##### Well-Known Member Pulling the flywheel altogether on any of the industrial motors is a little more involved than it sounds. Most (if not all) key the ignition off magnets on the flywheel, and use the flywheel for charging the ignition battery. Those functions would need to be replaced, somehow. For the guys who are looking at extensive modifications, EFI, etc., that's likely not an issue. For other guys (like myself) who would be interested in the most "bare-bones" conversion possible, I'd probably be tempted to swap out the steel flywheel for a lighter-weight aluminum one, should the weight reduction prove necessary. With either a no-flywheel or aluminum-flywheel conversion, some means would still need to be found to keep the battery charged. A little wind-driven generator is probably the best bet there. For the price of an alloy flywheel, you can probably find an electronic ignition. The standard flywheel ignition is rather heavy... A small belt driven BLDC motor seems the simple, light, cheap generator option. Add a reg-rec and Bobs your mother's brother. #### Topaz ##### Super Moderator Staff member Log Member #### Pops ##### Well-Known Member HBA Supporter Log Member Looking at the various discussions here about engine weights and cost, I gathered some numbers (below) for rough comparisons. 1) I looked at engines that could be bought new and completely assembled 2) Weights and costs are from "the internet", don't include exhaust systems, and are subject to a lot of variables. 3) To some extent, none of his matters. If you've got a particular type of flying in mind, then you may need a particular engine. 4) Costs are initial purchase price. Maintenance costs and resale value may also be important factors. Edited to add: See later post for edited chart with corrections and additions. Numbers: Engine.................HP.....Cost ($)....Weight (lbs)...$per HP.....Lb per HP Lycoming O-360.........180....27,500.(1)...305.............153..........1.69 Rotax 912 ULS/S........100....19,437.......125.............194.........1.25 Aeromomentum AM13......100....10,495. (2)...201..(3)........105..........2.01 VW 2180cc.(4)...........76.....7,175.......167..............94.........2.20 VW 1835cc (5)...........60.....6,025.......165.............100.........2.75 VW 1835cc "basic",(6)...60.....4,750.......145..............80.........2.42 Harbor Freight670cc.....22.......584.(7)....97..............27..........4.38 "" + hub&bearing (8)....22.......734.......104..............33.........4.70 Notes (1) Price through Van's direct purchase program. May be higher elsewhere? (2) Price is for the Aeromomentum AM13 "low profile" version. The upright version is$8495
(3) Weight is for the AM13 engine, radiator, and coolant
(4) From Hummel engine site, includes dual ignition system, starter, alternator, carb, Force One bearing and prop hub
(5) As above, but simple shrink fit prop hub (no Force One bearing and hub)
(6) Hummel engine site: Single ignition, hand propped, no alternator, with carb
(7) With ubiquitous "20% off" coupon
(8) Estimated price and weight of additional bearing and prop hub: $150, 7 lbs. Observations: 1) Mass production does a great job in lowering prices 2) Weight: The formula for a cylinder's included volume compared to its surface area is relentless. Bigger engines generally have more HP per lb. The Rotax stands out in this regard--but they sure charge for it! My own very subjective opinion is that, for fun flying, there's slowly decreasing utility for each HP added after we get safely airborne. More HP is almost always more fun, but the first 25 HP that may get us airborne and enjoying the magic of flight surely gets us more "fun per HP" than the 25 HP difference between a 160 HP engine and a 185 HP engine. So, in that regard, the small industrial engines that provide that first, "highest utility" 20-25 hp at a lower absolute $$/HP are very impressive standouts--if we have a plane that can take advantage of it. Luckily, if our idea of minimalist fun flying requires 60-80 HP, there are still good$$/HP (and lb/HP) choices in that range, too. Just some not-very-original rambling on this Sunday . . .. Hummel list their Basic 1835 cc engine as 135 lbs. My firewall forward weight for a Basic 1835 cc VW was 141 lbs, including prop and engine mount and exhaust system. Ready to fly. I cut some of the case round bell housing metal off to save weight. The most bang (HP) for the buck ($) in a 4 stroke, 4 cylinder engine is a 1835/1915 cc VW engine.