# CAR-251: The Cheap Air Racer Discussion thread.

### Help Support HomeBuiltAirplanes.com:

#### bmcj

##### Well-Known Member
HBA Supporter
Could we please stop arguing about terminology and gravity, this is just silly.
But the gravity of this situation is dire!

#### nerobro

##### Well-Known Member
Log Member
But the gravity of this situation is dire!
Wait, weight, hold on a moment. Are we just going to pound this into the earth even more? We're falling down a well already.

I brought a book or two with me to work. Perhaps I can get weights and strenghts of the fuselage done today.

#### cluttonfred

##### Well-Known Member
HBA Supporter
I can't say I dislike the idea of "run any 4 cylinder you like" racing.
OK, I'll use this one, but I think I'll need a longer course, say 20 miles between pylons. ;-)

One of the largest inline-four engines is the MAN B&W 4K90 marine engine. This two-stroke turbo-diesel has a giant displacement of 6,489 L. This results from a massive 0.9 meter bore and 2.5 meter stroke. The 4K90 engine develops 18,280 kW (24,854 PS; 24,514 hp) at 94 rpm and weighs 787 tons. Source: http://en.wikipedia.org/wiki/Inline-four_engine

Of course 24,514 hp at 94 RPM is going to require a pretty big prop.

#### BBerson

##### Well-Known Member
HBA Supporter
Wait, weight, hold on a moment. Are we just going to pound this into the earth even more? We're falling down a well already.
.
At least they (we?) can't derail your project log. :gig:

#### nerobro

##### Well-Known Member
Log Member
OK, I'll use this one, but I think I'll need a longer course, say 20 miles between pylons. ;-)

One of the largest inline-four engines is the MAN B&W 4K90 marine engine. This two-stroke turbo-diesel has a giant displacement of 6,489 L. This results from a massive 0.9 meter bore and 2.5 meter stroke. The 4K90 engine develops 18,280 kW (24,854 PS; 24,514 hp) at 94 rpm and weighs 787 tons. Source: Inline-four engine - Wikipedia, the free encyclopedia

Of course 24,514 hp at 94 RPM is going to require a pretty big prop.
Throwing that motor into Raymer damned near breaks the spreadsheet. Assuming we can build an airplane that weighs 200,000lbs, that can carry the 1.5 million pounds of engine.. 70:1 power to weight.. Yeah, that's not much of an airplane. Heck, it can't even get off the ground.

A good engine for boats, not for planes. Getting 24k horsepower is something that could be done for 1000lbs... As long as you don't mind the engine poofing in 15 seconds.

#### bmcj

##### Well-Known Member
HBA Supporter
OK, I'll use this one, but I think I'll need a longer course, say 20 miles between pylons. ;-)

One of the largest inline-four engines is the MAN B&W 4K90 marine engine. This two-stroke turbo-diesel has a giant displacement of 6,489 L. This results from a massive 0.9 meter bore and 2.5 meter stroke. The 4K90 engine develops 18,280 kW (24,854 PS; 24,514 hp) at 94 rpm and weighs 787 tons. Source: Inline-four engine - Wikipedia, the free encyclopedia

Of course 24,514 hp at 94 RPM is going to require a pretty big prop.
Throwing that motor into Raymer damned near breaks the spreadsheet. Assuming we can build an airplane that weighs 200,000lbs, that can carry the 1.5 million pounds of engine.. 70:1 power to weight.. Yeah, that's not much of an airplane. Heck, it can't even get off the ground.

A good engine for boats, not for planes. Getting 24k horsepower is something that could be done for 1000lbs... As long as you don't mind the engine poofing in 15 seconds.
787 tons for 25,000 hp??? You could run 6 Pratt & Whitney R-4360's for that (4,300 hp each, 25.8K hp total) for under 24,000 lbs. Best of all, no reduction (or multiplication) redrives needed... the big diesel wouldn't need a PSRU for reduction, instead it would need a propeller multiplication system (PMS ? :mad2.

The Spruce Goose ran 8 of these 4360's for a total of 34,400 hp, yet only weighed 250,000 lbs empty.

#### nerobro

##### Well-Known Member
Log Member
787 tons for 25,000 hp??? You could run 6 Pratt & Whitney R-4360's for that (4,300 hp each, 25.8K hp total) for under 24,000 lbs. Best of all, no reduction (or multiplication) redrives needed... the big diesel wouldn't need a PSRU for reduction, instead it would need a propeller multiplication system (PMS ? :mad2.

The Spruce Goose ran 8 of these 4360's for a total of 34,400 hp, yet only weighed 250,000 lbs empty.
Or two or three top fuel motors. But you wouldn't get the same BSFC.

#### Victor Bravo

##### Well-Known Member
Of course 24,514 hp at 94 RPM is going to require a pretty big prop.
A guy named Jim Cameron has just such a propeller available for your racer, in fact it was used in a well-known speed record attempt. You have to go with him to pick it up. It's right about here...

RMS Titanic wreck featured location of Elevation Earth App for Apple and Android Devices

Now that we've solved Newtonian Physics, NASCAR engines in Hummel Birds, 220 pound iron motors in "cheap" racers, and absorbing 25,000 horsepower...

I'd like to ask that everyone interested in the entry level cheap air race idea take another closer look at the SD-1 Minisport (with its sexy new bubble canopy!), the Moni, and the MC-30 Luciole, and the Davis DA-11.

All of these airplanes are capable of well over 100 MPH on 25-35 HP, in generic non-race sport-plane configuration, and they all have more wing area on a thicker wing than a racer needs. They all weigh less than the amounts being discussed here.

The DA-11 is rather crude from a racing aerodynamics point of view. but still went pretty fast. It required a very light weight pilot,which is un-realistic for starting a new racing class, but that is solve-able with different thicknesses of metal. There's about five or six hundred dollars' worth of raw material in a DA-11, fellow cheapskates.

The SD-1 can be made slightly smaller, more reclined seating, thinner wing, and other details to yield a 120-140 MPH racer on a small block V-twin making 35HP.

#### Pops

##### Well-Known Member
Log Member
Doesn't take anymore skill to fabric cover a wing as it does to set a good rivet. Both are so easy anyone that can follow instructions can do it. Dan

#### nerobro

##### Well-Known Member
Log Member
Following instructions is hard.... (Note, I work at an ISP... and day to day I have people who should be able to follow one and two step logic trains derail, crash, and threaten me.)

Still the fact it's "different" is enough to scare people off. I want the barrier to entry to be as low as I can make it.

2