Engine Design Mystery

[Aaron]

Where are people getting this info that engines are designed based on their "Average" power output? Several times now I've been told that since auto engines are designed for only 30 hp, they wont work in airplanes.

 

???Where does this logic come from???

Let me make an engineering analogy-A footbridge.

 

Now this footbridge is only used a little a day. It's average load might only be a few pounds. Yet if we designed it for a few pounds it would fail the first time we stepped on it.

 

When designing a structure, you design it for the maximmum load, not the average load.

 

Inside the engine case-you design for 110-130% of rated power output. That's how all the bearings are sized, as well the oiling holes and cooling jacket sizes.

 

Outside the engine it's a different matter- You build capacity into the cooling systems at other than 100% power. but inside the engine case you have to design everything so that it can take full power stresses.

 

Don't get me wrong, There's nothing wrong in using an aircooled flat piston engine in aircraft, it's just not what I choose to do. I wouldn't drive an aircooled car around (not even a Porsche) so why drive an aircooled plane around.

 

just my 2 cents.

[dust]

In every plane i have seen auto engines in, the planes are heavy and the slOOOOOOOOOOOOOOOOOOOOOOOOOOOw

 

Prove me wrong and the next plane i build will have a rotary innit

 

Heck, I sell the certificated engine i'm putting in and replace it.

[Aaron]

Too bad he moved on before demonstrating the capabilities

 

I'm not trying to convince you, I'm just trying to figure out where all these misconceptions come from. If you tell me you've never seen a fast auto conversion that's fine, but have you ever seen a rotary conversion compared to the same plane with a piston engine?

[buzzard]

Check out Tracy Crook's website about his RV-4. He makes a direct comparison of his rotary installation with RV-4's with O-320 installations. http://www.rotaryaviation.com/rvotter.html

[LargePrime]

Dust;

Would you really put a auto engine in if it was proven? Most would not. Most Aviation guys dont care about facts, they just care about the facts they want to care about.

 

I think great work has been done with Subs and Rotarys. But for every great example you got 10 dozen examples of what not to do. Alot like building a plane, isn't it? The adverage plane dont get built, even the adverage cozy, yet you build one? How do you rationalize that? Wouldn't the same rationalization apply to auto engines in aircraft?

[dust]

YES. I believe in reality, not what should be, but what is.

 

Right now many are confusing what should otta be with what is.

 

An aircraft engine = lycoming,continental

 

An auto engine = subaro?, rotary, vortek

 

Whatever, I want to get into my plane and know it will go fast for a long time. When an auto engine can do that it is no longer an auto engine, it is an airplane engine, to me!!! When the rotaries are proven to be light and powerful, i will put one in, right now they are hopes and dreams.

 

I hope and dream they are right, i will install my tsio360a, and have enough experimenting getting a new airplane engine installation right.

[John Slade]

When the rotaries are proven to be light and powerful, i will put one in, right now they are hopes and dreams.

 

I think you missed something, Mike.....

 

Greg Richter's turbo 13B weighted in at less than an IO360 and got him around 250HP. He was getting airborne in < 1000 ft and decribed the take-off roll as like "setting off in a Porche". Tracy Crook's 13B RV has lots of hours on it. There were five rotary planes parked alongside each other at Sun & Fun.

[dust]

like i said, when it's proven i'll do. I know it all adds up, but the numbers and history just aren't there FOR ME yet. I think it is great that forward thinking, cutting edge, risk takers like you are out there for the backward thinking, chickens like me. I want to thank you in advance for all of your hard work. Thank you, keep it up.

[John Slade]

Ah! I understand. You're not saying that 13Bs are inherently wrong for the application, you're just saying there aren't ENOUGH flying examples yet to make you comfortable. Fair enough. IN any new market there are pioneers, early adopters and then the big crowd of followers. I guess I'm an early adopter.

 

How many Cozy's did you say were flying with turbo Continental?

[Aaron]

A race is the way to settle this

[John Slade]

Oh, you mean like the EAA Sun & Fun race last month in which a 13B powered RV won it's class with an average speed of 209mph?

[dust]

NONE, ZERO, nada, zilch, cero and no longs or others that I know of. Thats as far as I am willing to push the envelope. But hey, push away.

 

Thats why i suggested puting my turboe try info on a seperate thread, independent of what engine is being used! Maybe you will add two naca ducts to your ceiling, you know, cut through that paint and all

[John Slade]

>Thats as far as I am willing to push the envelope

Seems like you're pushing the envelope out further than me.

 

>Maybe you will add two naca ducts to your ceiling

Maybe. I've cut through the paint enough that I dont care anymore. If I need more cooling I'm thinking screw-on P51 style armpit scoops

[marbleturtle]

50 years from now you could always argue that Lyco's have 100 years of proven technology while the rotary "only" has 50... therefore the Loco is the proven technology. I guess we all push the envelope as far as we are comfortable... tin-can flyers think Dust is crazy for building an airplane, Dust thinks John is crazy for using a rotary, John thinks I am crazy for thinking about 2 duct fans and BMW motorcycle engines, I think... well... I guess I'm the last link in the crazy chain.

 

We are mission-airies in a hostile land.

[chuckthedog]

John, what P-51 Had armpit scoops? Did you know that Mazda is going to try a new Wamkel in 2004? the RX8, it is an P2 engine 1.3 liters no turbo 250bhp. They say it won't smoke like the old ones. It should only cost around $30,000.00 for the car. If it is as hot as they say you may find one in the junk yard soon after they come out.

[JakeC]

Hey Chuck,

 

They say it won't smoke like the old ones......If it is as hot as they say....

Can we see some references? Got anything to back up your statements for some good conversation??

 

 

Mazda is going to try a new Wamkel

Is it your assertion that the 13b was not a successful engine program or it was somehow poorly designed? I'd like to hear what you have to say.

 

Jake

[chuckthedog]

Jake, Don't get me wrong. Back a few years I use to race along with RX7's. They do an outstanding job. We, meaning drivers of none rotary engine racers called them Masqito Foggers cause after a while it got hard to see behind them cause of the smoke.

Others smoked too. Nothing like the smell of Kestrol in the morning.

[chuckthedog]

Jake,

It must be a good design. Otherwise they would have quit builbing them. I guess the Japanese keep the good stuff for themselves.

Do you know why John Deere quit building them?

Why did they quit putting them in motor cycles?

Where did the engine rebuilders get all the engines to rebuild so cheep?

[JakeC]

One thing is for sure, even though the Winkle appears to be simple with its few moving parts, it is actually a very complex machine. Complex in its design, not its operation. How it works is very easy to understand, but if you told someone to go out to the shop and design and built one, that would be a very hard thing to do indeed.

 

Mazda has stuck with the design and has kept developing the concept while most everyone else has given up. I believe that they are just now starting to reap the benefits of that move with the Renesis. It's far superior power to weight ratio and it's now comparable fuel burn is going to be a huge success IMHO. The trouble is, it took them a very long time and a lot of effort to get to this point.

 

I think Detroit has too much invested in the piston to ever change the course of engine development, even if a design proved to be a better. It's simply too risky. Especially with Fuel Cell technology right around the corner. The world is full of examples of superior technology falling to the way side in favor of inferior designs because of big company influence, or public misconception. It's just a fact of life that the best designs do not always make it to the top. I'm sure someone will disagree with me but look at Microsoft Windows, VHS vs. Beta, etc...

 

The question is, which design is best suited to aircraft use. Some say Piston, some say Rotary, some say they both can make a good aircraft engine. Personally I think the last answer is closer to the truth. Both have pros and both have cons. The Rotary is tougher and more robust but has to deal with cooling issues. The Lycs have more history behind them and are air-cooled (read simpler installation) but have more catastrophic failure modes and vibration.

 

An interesting thing happened to me about 2 hours ago. I was in a cub with my new instructor and it was my first attempt at a slow pass down the runway with a go around at the end. It was also my first official lesson since I was 15 years old. I was flying down the runway at about 10 feet practicing keeping it down the centerline. I was having a great time and I was going a great job I must say . About 3/4 of the way down the runway the instructor says: "ok, let’s go around". I advance the throttle and start a climb. At about 75 feet the engine quits. Instructor takes control, switches from the left the tank to the right tank, and the engine comes to life in about 2 seconds. We land using the remaining runway and all is well. It's probably the best thing that could have happened to me on my first lesson. From this point on I will always remember that it's not my aircraft that is most likely to kill me, it’s my own stupidity and complacency!

 

Jake

 

p.s. Please remember, these are the ramblings of a Neophyte and are just meant for entertainment and discussion purposes only!

[Aaron]

Yes the RX-8 has a new version of the Wankel-Designated "Renesis" for the RX-8

 

While the published HP is 250, it's important to note thats at 8500rpm. Most aircraft-conversion guys (crook et al.) suggest not redlining the engine and running at a more conservative 6000 rpm. Unlike most piston engines the Rotary has a very sloped power curve, almost a straight line, se we can estimate at 6000 rpm the renesis makes around 176 HP (non-turbo)- not all that much more than the old school RX-7 engines at that RPM.

 

The engine is lighter, and stronger than the old engine making it an interesting candidate for an airplane. But they've made some very interesting changes in the intake of the engine, I'm concerned it will be hard to run without some special programming (as other periph. port rotaries are hard to idle)

 

As to the smoking- it wouldn't surprise me, If they've succeed in getting a harder material for apex ands housing, they could burn less oil.

[LargePrime]

No P-51's had armpit scoops. too much drag for that low flat plate drag number.

[JakeC]

not all that much more than the old school RX-7 engines at that RPM.

True, I think the number for the stock non-turbo 13b is around 150 hp at 6000 rpm. Not a huge jump by any means but not too shabby either. After mods the Atkins 13b conversion is putting out 160hp at that number. The exciting thing for me is that with a turbo, in my un-calibrated pea brain, the Renesis should be able to easily push 220-230 hp without coming close to over stressing the engine at that RPM. There is talk of Mazda coming out with a stock turbo version at 300HP in the near future so it would seem that the basic engine was most likely designed for some upward mobility in the HP department. It seems to me that once you strip the engine of the un-necessary add-ons and conservatively turbo it, the power would be quite acceptable. Then the real fun starts.....Cooling the sucker down .

 

Do you think the 6000 RPM limit should be the limit for max or continuous? I guess it would be Max considering Tracy’s redrive would put that at just under 2800 rpm at the prop. It's going to be interesting what people like Tracy and Atkins do with this new engine. I've got plenty of time to wait and see.

 

Jake