CAR-251: The Cheap Air Racer Discussion thread.

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.

 

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.

 

At least they (we?) can't derail your project log. :gig:

 

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.

 

Or two or three top fuel motors. But you wouldn't get the same BSFC.

 

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.

The Luciole can be race-ified by using a reclined seating position, shorter wingspan allowing a shorter fuselage, and a lower drag landing gear. It does 124 miles an hour on 25HP in it's CURRENT state, and it did 137 miles an hour with a !(#*$ 26 HP electric motor.

The Moni would jump from 120 mph to 140 mph by reducing the span from 27 to 22 feet, removing the KFM engine and it's tiny propeller, bolting on a small block V-twin making 35HP with a 3 blade 42 inch propeller, and doing some easy aerodynamic cleanup, sealing, fairings, etc. They got the Mini-Moni to 140 mph on the KFM engine.

This thread should re-focus, in my sincerest opinion, on using one or more of these airplanes as the general basis for a racer, and neobro's "clean sheet" design should likewise be thinking in this area.

 

If speed of build wasn't a question in my head, I'd be pushing for a DA-11 clone. And I like the SD-1 too. Both would be great options. Neither the SD-1 or DA-11 are "a month of weekends" type build.

And it's starting to annoy me. Read my username carefully. ;-)

 

Sorry, I'm a fair writer but a horrible typist. Unintentional if there is any insult.

Pop-riveting a Moni together (using a more traditional fabricated spar instead of their proprietary extrusion) would be pretty quick. Especially after the CNC machine spits out parts with match-drilled holes

 

You left at least 3 off the list. Your sketch a few posts ago would fit right in. The Quickie would too, even though it might not be the best for a pylon race plane. There is also the Song which could conceivably fit here as well.

Also ran across this just a few minutes ago. Might be remotely related to this thread.
Ultralight Engines All Patterns All Castings All Stock Everything | eBay

 

No insult taken. Just annoyed.

If I had a CNC punch like some of the aluminum kit makers have, that would be perfect. But I don't. And that definitely fits under "special tools."

If this does get off the ground, re-engineering with aluminum to make a "even faster build." might be something. But for now.. wood and glue.

 

But it's got 2 wings! Doesn't that double the span loading? :gig:

Good span loading is going to be a problem for most anything in this class. The Song with 30 ft span is the exception in the list of planes mentioned so far.

 

The listed cruising speed of the Song is 80-110kph (49-68mph).
Made with carbon fiber. I didn't see a price.

 

You're not supposed to have a CNC punch or router... there are shops in every US city that have those. That's one of the big ideas, distributing a software file and any wannabee racer just has the parts cut locally.

The truth is, inasmuch as I've been banging a teapot about aluminum, that the first one of these can be made of wood just fine. Of course a small wooden racer can be built, been done a hundred times. When you factor in the cost and time of covering, moisture-proofing, sealing the wood against warpage, and adding carbon to the wood in two or three areas, you might find that wood is not cheaper or easier. But I'll let you find that out yourself.

The key words are small, and low-drag, and all the safety/visibility/controllability stuff.

So then still look at the Mini-Moni I posted, make it out of wood if you think you can get it light enough, but realize that like so many other airplane ideas the right engine is the key. The same designer built a VW powered racer called the Monex which did well over 200 mph.

 

I think that a 1,000 cc class is a great foundation for a racing class. 1,000 cc has a long history as a class designation in all types of racing; motorcycles were going 100 mph before WWI on 1,000 cc. There is already what amounts to a 2L and a 3.5L class - FVee and F1. If the bore and stroke were kept stock by rule, and induction kept simple, and compression limited to a reasonable number, then people could modify engines for higher rpm without spending large amounts - power limitations and prop efficiency constraints would keep the money down. 1,000 cc is a good idea, especially with the availability of the engines. It should be possible to get 50 hp or so out of them and to go 150 mph +, maybe approaching 200 mph.

 

In so many ways you're right. Aluminum is the way to go with airplanes, just in general. It's not an argument you need to win with me.

Covering is a pain. The CAR-251 won't need covering. I already thought about that The "covering" I'm intending is latex house paint. That should make it water proof enough. But this plane won't be a "tie it down outside" type plane. Covering anything with fabric takes a lot of special tools and "real technique" that I won't bet most people have.

Aluminum isn't something that's easily available everywhere. And the tools to work it, require all the woodworking tools, and then aluminum tools. (which while there aren't a lot of them.. a good rivet gun is still $300.) "maybe" we'll get to the point where having an aluminum variant makes sense. It doesn't. Yet.

 

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

 

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.