Engines. A Discussion.

Preface. I'm a believer in no replacement for displacement. Juice up a 320, a 360 still beats it. In a given displacement you can maximize fuel supply, induction, compression, and ignition but with typical opposed direct drive engine RPMs we hit a wall for max power output.

Enter the Highlanders using Yamaha's turbo Apex motor. RPMs up near 10K and gear reduction driving lightweight props. Reportedly running 300hp in a very compact and lightweight package. So far I've only seen this engine in very lightweight airplanes.

The question. Would that motor-prop combo provide good performance in heavier airframes? Would it run circles around my maximized IO-390 or does opposed-direct drive grunt spinning a beefier prop pull a heavier plane better? Is 300hp always 300hp? How about an Apex powered 185? Anyone have any wisdom to offer?

BMEP is a huge player in making power and is something lacking in the antique cylinder design in aircraft engines.

I'm from the muscle car generation. These days while I'm not a fan of the noise I am impressed by the new generation's rice rocket performance cars. But I don't see anyone dropping a piped-up Subaru motor into a Camaro chassis. There's a disconnect in my mind between the small displacement/high output engines and bigger heavier vehicles but I'm not sure why. I've had a few Yamaha 4-stroke sowgos and one outboard. Impressive engines, no question. Application of that power is part of the question. A V belt transmission allows my snowgo engine to run in the power band at all speeds. A fixed pitch prop? Interesting stuff. I hope to see more Apex powered airframes.

Horsepower equals torque multiplied by rpm, divided by a constant. Because there is generally a limit on how fast you can spin an engine, having higher torque allows for greater horsepower at lower rpms.

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I would love to see how a modern sled motor would be with it's belt transmission used in a plane. I fully expect belt life would snub that project quick though but then I do not have direct knowledge of these newest sleds. Either the new 2 smokes or the 4 strokes would be interesting with a fixed pitch and variable belt reduction.
Today's outboard motors are incredible, even my old 2.6 Yamaha Excel with 250ish HP and still has monstrous torque down low. And it is still economical on fuel burn. Packaging on the new motors may not be all that tough since they are all injected and dry sump, or call it remote sump oil re-packaging is not that tough.

In time I expect I will have a mid size 4 cyl car engine prepped for my plane, not a Subi motor. It will offer about 250+ ft Lbs down at 2500 crank with well over 300 Hp all over the place.
With a 2.3 reduction that works out in the range of 575 Ft Lbs at 1100 revs at the prop. That is 6 cyl power at big 4 cyl weight. Probably enough torque to be impressive with fixed pitch. Fuel burn at cruise will be easy on the wallet. That is on Mogas as well.
I expect I will be utilizing a ground adjustable but need to see what the market offers at that time.

At least one self launching glider uses a tooth belt to drive the prop.

I'd be leery of any aircraft engine using an untested gear box. Lots of examples of gear boxes causing problems in aircraft.

Belts in aircraft?? Look no further than the Robinson helicopters.....

MTV

The belt I am interested in is this,
https://www.continental-industry.co...Belts/Products/Product-range/CONTI-SILENTSYNC

Lets see if that link will work

On aircraft engines, I would love to see someone produce cylinder heads with D shape intake ports.
It is common to raise the floor of the port with epoxy creating a much better short side radius which would in ant plane motor greatly enhance cylinder fill.
Sure works in older bike and car motors. But every once in awhile when one goes in to inspect things the epoxy is no longer there. Never hurt anything but it just is not there.
But no matter what you do you can not fix a combustion chamber that is 80 years beyond it's engineering cycle. I am somewhat scared to improve cylinder fill unless you can improve mixture distribution so the engine does not break itself.

Innovation is awesome. But can a ''300hp'' Yamaha turn a 90'' McCauley prop like a good old Lycoming??

Need to gear it for the task. A McCauley might not be my first choice though. I have not run the numbers to see if it would be logical.
That Yamaha is not a Big Torque motor although boost makes up for lack of natural torque.
Years back there was an engine block for the Hayabusa to run without the gearbox. If that were simplified for aviation use and the engine built to a 1600CC it would be impressive.
I run a turbo Busa motor in one of my cars, being the car is under #800 and with just 11# boost it has an easy 320+ Hp with monstrous torque from 2000 to 10500. Car could torque up hills at 1300rpm in top gear. That engine is stock, no reduced compression, nothing. Just some stiffer clutch springs. Great engines.

Olibuilt said:

Innovation is awesome. But can a ''300hp'' Yamaha turn a 90'' McCauley prop like a good old Lycoming??

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Charlie’s already made the point, but yes.

You’d have to add a reduction drive, but 300hp is 300hp. The RPM that power is made at only matters for the gearing required to get it to the ground (or to the prop, in this case).

On a PowerStroke forum a while back there was a great discussion about this, complete with math. The bottom line is that a 400hp v8 gas engine (when properly geared) can pull a load up a mountain equally as well as a 400hp diesel.

Wow. On that point? Disagree. I've had several GMC pickups with a few different engines and there's no way a gas engine pulls like a diesel of the same HP class. No way. I currently drive a big V8 gas truck after a couple of Duramax trucks. Hook up a heavy trailer? No comparison.

Put that into context for the Yamaha Apex? My SkiDoo Etecs are awesome sleds but they suck hind tit for torque and power compared to my Yamaha. In the snowgo example the Yamahas are HEAVY. That comes into play with sleds as much as airplanes. Go back to the Duramax? Torque conquers weight. And the confusion continues!

Some "ifs". If the "actual", not necessarily "claimed" horsepower is the same, and if they are both at their max HP RPM, and if the atmospherics and tires and such are the same, and the towing vehicle is the same gearing and weight, they would pull the same trailer the same speed up the same hill. But those are a lot of "ifs", so comparison can be deceptive. Cam Tom is right - horsepower is horsepower. 550 ft-lb per sec.

Edit: Here's a funny. Years ago I decided to measure the power required to pull a horse-drawn sickle-bar hay mower, like in my avatar. So I carefully measured the tension in the harness traces and the horses' speed, and guess what? 2 HP to pull that mower. Pretty cool, I thought.

Not many Peterbilts running 6.0 Chevy gas engines. Go figure.

Lots of reasons. None of which refute Charlie's and Tom's and my statements. Yawn.

And clearly you've never driver a gas vs equal diesel. Yawn is right. But this topic is about airplanes. High revving snowgo engine vs bigger displacement and slower revving airplane engines. Pickup trucks are the epitome of yawn.

Both, all of the Big Three manufacturers for 50 years. Horsepower is horsepower. Period. If you don't like that you shouldn't have asked. Good evening, sir.

stewartb said:

Wow. On that point? Disagree. I've had several GMC pickups with a few different engines and there's no way a gas engine pulls like a diesel of the same HP class. No way. I currently drive a big V8 gas truck after a couple of Duramax trucks. Hook up a heavy trailer? No comparison.

Put that into context for the Yamaha Apex? My SkiDoo Etecs are awesome sleds but they suck hind tit for torque and power compared to my Yamaha. In the snowgo example the Yamahas are HEAVY. That comes into play with sleds as much as airplanes. Go back to the Duramax? Torque conquers weight. And the confusion continues!

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Here’s the problem - you’ve got to optimize the gearing to take advantage of the power where it’s made.

I don’t prefer to hang out behind an engine “screaming” at 5k+ rpms while climbing a hill. I much preferred my last SuperDuty’s easy 2k-ish rpms. That’s why I owned that truck and not a gasser.

But, the truth remains that if two engines make identical power (and are optimally geared for that power band), they’ll perform identically. Regardless of what RPM that power is made at.

Personal preference doesn’t change the math.

Like I said earlier.... application. Back to airplanes, please?

stewartb said:

Like I said earlier.... application. Back to airplanes, please?

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Yeah, so here we are. Talking about the application of power to do work.

Back to asking if 300hp can spin a prop the same way as 300hp can spin a prop.

Here’s where I say again: yes, it can.

On my planes the prop is what does the important work. I'm guessing the Apex motor and reduction drive have limitations for prop weight. That's probably a deal breaker for heavier airplanes. Especially where a constant speed is desired. I'm curious about the Apex and reduction for Cub types. I haven't seen or heard of one and that surprises me. Somebody must be trying it. If anyone here has some hands-on experience I'd like to talk.

Side note, Mike Patey's engine and prop choices on his new Cub are very interesting in the context of this topic.

stewartb said:

On my planes the prop is what does the important work. I'm guessing the Apex motor and reduction drive have limitations for prop weight. That's probably a deal breaker for heavier airplanes. Especially where a constant speed is desired. I'm curious about the Apex and reduction for Cub types. I haven't seen or heard of one and that surprises me. Somebody must be trying it. If anyone here has some hands-on experience I'd like to talk.

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Now that’s a good point. I don’t know the limits for the current reduction drive, but if they’re not up to spec then I don’t know why a beefier one couldn’t be engineered/built.

I’m not personally aware of any reduction drives that can take hydraulic CS props. There must be some out there though. Wasn’t the guy building the Raptor canard plane using a 300-something hp diesel car engine and a hydraulic CS prop?

Direct drive is simpler, and that’s why I’ll probably always use it. But 300hp is 300hp once you get it geared right.

stewartb said:

Side note, Mike Patey's engine and prop choices on his new Cub are very interesting in the context of this topic.

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True, but it helps to have an engine like that just sitting around the shop. Especially if the context of the build was to use scrap or previously used parts.

Balance is the challenge. A large diameter, slow prop is more efficient. The challenge is to match the engine HP to the RPM range the prop is most efficient. We used to have a Pawnee Brave (Ag Plane) that had a Continental Tiara engine. The prop turned 1/2 engine speed. Engine was 285 HP at 4000 RPM (406 cu in). Was very quiet and smooth running since the prop was turning slow. Way quieter than the Ag Wagon with the IO-520 (520 cu in).

https://en.wikipedia.org/wiki/Continental_Tiara_series

CamTom12 said:

I’m not personally aware of any reduction drives that can take hydraulic CS props. There must be some out there though.

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Lycoming built lots of GO engines in that power range, all of which used CS props. How adaptable those gearboxes might be?? Who knows?

MTV

MN_flyer1 said:

Balance is the challenge. A large diameter, slow prop is more efficient. The challenge is to match the engine HP to the RPM range the prop is most efficient. We used to have a Pawnee Brave (Ag Plane) that had a Continental Tiara engine. The prop turned 1/2 engine speed. Engine was 285 HP at 4000 RPM (406 cu in). Was very quiet and smooth running since the prop was turning slow. Way quieter than the Ag Wagon with the IO-520 (520 cu in).

https://en.wikipedia.org/wiki/Continental_Tiara_series

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Nice! Like running a turbine!

Interesting to think about. Plenty of guys getting over 200HP from skidoo 4 stroke turbocharged motor.

It's lightweight.. BUT.. if you added the weight of the required gear reduction.... would it be that great of a package?

Lots of money to find out. I love guys that like to spend money to find out. I'll sit here and watch, and dream.

JP

A friend recently got his Kitfox flying with a Yamaha RX-1 motor. He has Full Lotus floats on the plane. He de-tuned it slightly (I think he mentioned around 120-130HP). I was flying around his home the day of his trial flights and took some photos. He was taking off from a snow covered lake (MN in Dec. so frozen over), and I saw very good T/O performance. I thenk we will see a lot more of these engines flying soon. I actually bought one for one of my aircraft projects but ended up selling it due to the fact tht I already have too many projects!!!

Here's a video about the gear box. The clutch is interesting. https://m.youtube.com/watch?v=0ks9LqboEeo

I'm still curious about how mass plays into it. Mass of the prop as well as mass of the airplane.

Hey guys! I’ve been meaning to jump on here for awhile but haven’t gotten to it. I’m the first guy (at least in public knowledge) to mount a forced induction Apex on a super cub. To clarify, it is NOT in the air yet as my build is not completed, but I do happen to have a wealth of hands on knowledge of the subject.

To answer the original question, yes, horsepower is horsepower, but the real sex appeal of the Apex is that it can use said horsepower in a way that is SUPER conducive to our application, and in my mind at least, far superior to existing options.

Let’s make this more of a conversation about static thrust vs static thrust for a second here.
It’s not all about HP or torque. Doesn’t matter how we get there, it’s about the thrust we put out that really matters.

Hypothetically if you have an IO-390 at 200hp and say an 84/43. (I’m guessing here) but I’d imagine you’d be putting out around 775-800lbs of static thrust.

With a forced induction Apex at 300hp paired with an 82” 3 blade GA composite prop, 1000lbs static has already been made.

Sure, it takes a ton of engine rpm to reach that, but on average, how many seconds would it be necessary to hold that kind of power in a cub? You know the answer, it’s seconds. And guess what those sled engines were built for AND historically have proven to be GREAT at doing reliably? 15-30 seconds of sustained WOT, then back to normal operating rpms.

How many HP do you figure you actually utilize at cruise? It’s not all that much. So to match you performance wise, I can chop my throttle back to a pretty acceptable rpm 98% of the time.

So that’s the thrust argument. Now let’s move on to weight comparison.

My turbocharged Apex engine complete with gearbox weighs in at roughly 205 lbs.

The IO-390 is i believe something like 310lbs dry, right?

Answer me this. How many of you guys would rather fly a hopped up 320 over a 180 because of the friendlier characteristics? Or better yet, how many guys loved flying the -18 90hp because it flew SO much better? It just didn’t have the snort to be effective in our application.
A light cub is a happy cub!
We have always had to walk a fine line between “power to get you out” or a nice flying airplane. I believe that those days are over, at least for me.

As a young guy, I’m pretty apt to embrace newer technology and wonder why we as an industry are still governed by outdated technology. I mean, when is the last time you purchased a car with a magneto or a carb?
You get my drift.

Anyway, to try and keep this somewhat short and answer as many questions as I can in one shot, I’ll just throw out a quick list of a handful of reasons that I value the Apex in my build.

#1 the Apex has a long track record of being boosted and getting the absolute **** kicked out of it with great results.
They have been a hot item to builders for years because they can be built to asinine power levels. There are guys who have pushed 800hp out of Apex engines in drag sleds. Not reliable in that highly modified configuration obviously... but still, that gives a bit of context. There have been hundreds of thousands of hard sled miles on 275-400hp apex’s with a GREAT track record.

#2 My Apex is light!
205lbs with PSRU. That gives me two Huge gifts. Weight savings and the ability to add a little bit of that weight back in fuel!

#3 fuel injection.
No carb heat! Yes, more tech, more things to go wrong.... but I have taken a huge amount of time to design everything from my custom standalone ECU to my dual fuel pumps in a double redundant fashion.
I can provide more info on that end if it interests you.

#4 price
My Apex is the whole package. I went with the best of the best everything. 300hp, low comp pistons, forged rods, upgraded piston oil squirters, stand-alone ECU with a million custom parameters and safety protocols (compensates fuel maps for altitude by the way), full mil spec wiring harness, and double redundant EVERYTHING. The PRSU used by us is not your every day rotax gearbox. This thing is a work of art and has been BEAT ON by many for a lot of hours with no failures as of yet. Anyway, here’s the best selling point. I’m pretty realistically only into this engine (complete with PSRU) for around 15k. That speaks for itself.

The prop options are good and CHEAP as well. I picked up my carbon fiber 82” 3 blade ground adjust with hub and spinner for under $1200


I hope that I was able to at least answer some lingering questions and shed some light on the subject!



-Sam