Hey fellow aviators I need some help.. My son is into high HP little cars. Last weekend I had to listen to him tell me about the 270HP that his 2 liter subaru spits out as compared to the sluggish 300HP that my 11 liter Lyc 540 S1AD generates. Anyone know how much torque the ol turbo 540 is pumping out at take off rpm. Help me out... my ALPHA male status is on the line here. rob
Hi Rob,
My power output graphs are all out at the hangar but rather than getting into a pissing match with the lad using raw numbers as ammunition, (a battle that can't be won when fighting an uneducated opponent), why not elevate Your alpha male status instead? Explain to him (in a way he is likely to understand) that every engine is designed with a purpose that involves compromise, that's why his Subaru doesn't have nearly as much power per liter as let's say a 125cc racing kart engine (Approx. 325 HP/Liter). Then explain that Your aircraft engine is operating within 30% of it's maximum output the vast majority of the time where as on his most "enthusiastic" night of street racing he is operating his engine within that 30% of max, little more than 30% of the time. Let Tell him that there are also weight, RPM, and safety considerations to be factored in and let him take something away from the conversation that will stimulate his desire to gain knowledge. Knowledge that will elevate him above the ranks of the monkey see-monkey do crowd that frequent the street races (and at the same time let him know his old man is smarter than he initially may have given You credit for, that's the best part!) Then tell him the next time he comes to belittle Your aircraft engine, he should be sure of his numbers because by Your calculations, he dropped the ball converting cubic inches to liters!
Ya might ask him how much HP his little toy puts out at 2700 RPM. Probably idles at near that value. Also ask him to meet you at some airport say 100 miles away and then leave at the same time.
Paul Wrote:
-------------------------------------------------------
> Rob,
>
> Just compare fuel flows. That ought to do it. My
> guess is you use as much fuel in an hour as his
> tank holds ;)
>
> --paul
In very simple terms you can describe horsepower as pounds of air and pounds of fuel used.
How many hours can the Subaru engine maintain it's rated power output before it's worn out? Your Lycoming will probably travel close to 400,000 miles before it needs a rebuild. How long will the Subaru keep running if the battery fails (with it's EFI and electronic management)? Twin spark on the Subaru?
Rob T Wrote:
-------------------------------------------------------
> How many hours can the Subaru engine maintain it's
> rated power output before it's worn out? Your
> Lycoming will probably travel close to 400,000
> miles before it needs a rebuild. How long will the
> Subaru keep running if the battery fails (with
> it's EFI and electronic management)? Twin spark on
> the Subaru?
My GM truck has an hour meter incorporated. I have 85,000 miles and it is showing 2160 hours. You are correct that the Lycoming will travel way more miles in the 2000 hour TBO.
I have a turbocharged Subaru of my own. In under 10 seconds at about 70% power it's at the interstate speed limit. I can't see any (on road) condition where I'd be running that engine at 70% rated power for more than a few seconds. Most hill climbing is done at about 30% power only.
That's why I asked how long the Subaru can last maintaining it's rated output power - because most of the time that engine is probably putting out less than 50HP.
Tim, the same goes for your truck - I bet it's not been run "pedal to the metal" for those 2160 hours.
When car engines are used at high duty cycle, like F1 racing, they need to be rebuilt just about every race!
Do what his street racing crowd would do. Challenge him to a 250 mile race (preferrably with a large metropolis in the flight path), and tell him you'll take in a movie and a ball game while you're waiting for him to arrive....
Rob T Wrote:
-------------------------------------------------------
> That's why I asked how long the Subaru can last
> maintaining it's rated output power - because most
> of the time that engine is probably putting out
> less than 50HP.
The 3L H6 subaru engines are available as aircraft conversions for experimentals like the RV series. In the normally aspirated configuration, they are downrated to 200hp (from 250 in the automotive application). They also offer a turbonormalized version that is rated at 220hp.
Hey Rob,
I guess I'm responsible for getting everyone to give You answers to questions You didn't ask and in the shuffle forgot to give You an answer to the one You did (or at least tell You where to find it). About the same time there was a post regarding power settings and the merits of High vs. low RPM and MP for any given setting. Included in the discussion were several formulas for computing horsepower based on torque and RPM. Likewise You can use HP and RPM to compute the torque output of Your engine at take-off by "reverse engineering" the formula (so to speak). Since aircraft engines produce it's rated HP output at redline (Unlike automotive applications), computing torque is pretty easy. In case You're interested here is a link to a very good PPT presentation on the subject.
Fact is, our aircraft engines are designed for simplicity, longevity, and reliability. They are loafing along even at 75% power (by design). It is simple to get 1 and not hard to get 1.5 or even 2 HP per cubic inch, yet our 200 to 550 cubic inch engines are rated at only a little more than half a HP per CI. That is why they are so reliable.
If you took any of them and put in a more aggressive cam profile and installed an intake valve which was 1.5 to 2 times the size of the exhaust... and spin them up to 4 or 5000 RPM you'd see quite a difference in output...
Also, for your turbo'd engines... consider that they call them "turbo-normalized". The wastegates are set to dump over sea level pressures. As a result, a turbo puts out no more at sea level than a normally aspirated engine. All they do is put out "sea level" performance all the way up to about 25K feet which obviously gives them performance advantages at higher altitudes. Try putting in a wastegate that (and there are some STCs, but they are VERY moderate) lets you BOOST at lower altitudes and see what you get!
I agree on the American car thing... but aren't Suburus built here now anyway? Just like a Toyota? As long as they are built here by Americans and are paying Federal, State, and local taxes... they are pretty much American. Unlike anything you buy at Wal Mart which is all made in China. I pisses me off that Cessna's new 162 will have a lovely sticker in the door jam that says "made in China". Really nice.
How to Make Him AND You Look Cool while Teaching Him
Rob,
Dave and dmoser probably have the most mind grasping idea for your son, challange him to a race or either 100 miles (if you both leave from the same place at the same time) or have him drop you off at the airport and "give him a lead" and you prep and preflight and fly 250 miles away.
As a former teenage MotorHead, I know I drove my dad AND mom crazy with HP, Torque, and times - for just about anything with wheels. The car thing has been replaced by the plane thing and unless I am mistaken - about every 4-5 years the sister magazines "Road and Track" and "Flying" challange each other to duels of distance (copyright 2008 - Martin Howley) and as I remember it doesn't matter if it is a Bentley, Ferrari, Lambo, or 'Vette - the plane wins. The article and writers each contribute to eachothers magazine for that article - also. Usually a lot of fun to read. I seem to remember a hot car getting smoked by a piper cub from LA to Vegas... but that might have been a different article on the joys of GA vs Commercial Aviation.
Better yet - Have him ride with YOU and challange his friend with the hottest car to the race. He'll be on the winning team and YOU will be too cool for school to both him AND his friends. Not to mention the Old guy beating the Young Turk feeling. Then keep them at this location for overnight (yes, you pay) and go home the next day or end of the weekend. Coolness and Victory in one effort... just think of the conversation you both will have on the way home.
Having been a "Motorhead" almost since the day I disassembled a 5 HP B&S tiller engine that punched a hole in it's side with a rod, I've noticed a few things that sometimes escape the casual onlooker. During the early 80's I drove (Among others) a '69 Olds 442 that was a virtual test bed on wheels. As difficult as data logging was, My right front seat was jammed with computer equipment and several times a week the car spent several hours on a chassis Dyno. At least once every month some change was being made with induction, exhaust, compression ect. and I have had plenty of dyno hours in the years since to see a few other things. One that is unique to aircraft engines, and reinforces how detuned these engines really are, is the large gain HP increases within each "family" in relationship to it's small increase in redline RPM and/or compression. You don't have to study too many dyno charts to see these engines are operating at the bottom of their power-band potential (In common terms, they are just beginning to "Come On"). If You look at the lowly 0-540-A, B, and E-G-H's you see the relationship easily. The 0-540-B is 235 HP with a 2575 redline (I've built engines that idled around that speed) and a mere 7.2:1 Comp ratio (there was a time I didn't know if an engine would even start below 8:1!). Raise the comp ratio to an unheard of low (In the auto world) 8.5:1, change nothing else, and it's a 250. Raise redline by 125 RPM (Barely perceptible on almost any auto tach) and You have 260. The uninitiated might say "Those gains aren't that big" but in actuality they are VERY large, especially if You look at them from a percentage viewpoint or when you consider the average sedan is only putting around 40 HP to the pavement at hiway speeds.
