Understand I have no idea what I'm talking about being just a lowly Advanced flyer but I think it's more of what kind of power rather than different amounts of power. It's more about how the engine delivers the power which eludes me if I were to try and define it.

Same prop, one cross-flow, other schneurle.

I've framed the question as a hypothetical to avoid issues about particular brands, etc.

Terry

To turn a given prop at a given RPM takes the same amount of horsepower regardless of what engine is spinning it.
But it may or may not take the engine's maximum horsepower to turn the prop at that specific RPM. If a Fox 35 and a ROjett 76 both spin a 10x6 at10,000 RPM, they are putting out the same horsepower in doing so. However, the Fox will be straining, and the ROjett will be idling.

I hope there's an answer not requiring a bunch of math, but how is it that 2 same-size engines burning the same fuel, turning the same prop at the same rpm under same conditions can have different power outputs?

Terry

Simplify the question: Forget the engines (for now): So that leaves 2 identical props, spinning at the same RPM, under identical conditions, right?  Therefore the amount of power required to spin both props is identical.  But we're talking power going into the prop, not engine "power output" as in your original question.  There is one more place (at least) that power comes out of an engine.  Imagine the head of one engine is glowing red and it has flames shooting out of the exhaust port, while the other engine runs cool and burns all the fuel inside the combustion chamber, therefore no flames.  The cool engine is running much more efficiently and has a lower total power (torque plus heat) output.  The other engine is putting exactly the same amount of power into the prop (identical prop, identical RPM), but it is creating and wasting much more power as heat.  That is the only way for the two engines to have different power outputs.

I want ALL my engines to GLOW and SHOOT FLAMES!  Do you have any idea how many kids I could bring into this hobby if all my planes were fire-breathing monsters that could fly at night?!?!

Paul Wescott

I hope there's an answer not requiring a bunch of math, but how is it that 2 same-size engines burning the same fuel, turning the same prop at the same rpm under same conditions can have different power outputs?

   If it is turning the same prop at the same RPM under the same conditions, it *doesn't* have different power.

    Brett

I think an answer could be two fold.  The O&R was made in a time and at a mass-priced rate that its design is just way out of date and manufactured to very loose tolerance which makes it start and handle pretty well in inexperienced hands.  Due to those facts it's pretty easy to melt down or blow up trying to run that hard for long.  I have some of these wonderful beasts .23, .29, .33 and .60.  Lovely but delicate.  It WILL pull your Skyray but not with much macho and won't do that very long if trying to run 10k continuously.  These are more now treasured antiques to be run with care in old timers.  Their not an all day, every day slogger.

Dave

I haven't run a FRV O&R .23, but I do have two side port .23s, a blue head .29 glow, and a red head .33 ignition.  I'd estimate the .23s have about as much power as a baffled piston Fox 15.  A few years ago I built a Brodak Vampire for the .33, 24oz RTF, 40" wingspan, 353sq in.  On .012"x57' lines it flew OK when the engine ran right.  But the engine only ran right about twice in 30 flights.  It'd either be down on power or it'd sag in maneuvers.  I eventually took the O&R off the plane in favor of a Mohawk .29. 

I ran an OS 15FP on a Flite Streak ARF for awhile.  It had the power to fly the plane through the pattern on the same .012x57' lines.  I've flown an overweight TF kit built Flite Streak, and a scratch built all balsa Skyray 35 with both versions of the Fox 19 baffle.  I can't imagine an O&R .23 ever hauling a Skyray with enough power to do much more than level laps.

I'd expect ram air into the front intake would give more HP in the air, but maybe not when bench running?

For many decades, speed fliers wanted rear intake engines. Henry Nelson made some rear intake engines, but they ran slower than the FI engines.

All the best F1C engines have been front intake since the early '60's MOKI. In addition to reduced friction, the sealing is better on a FI engine, giving better pumping efficiency. 

The rear intake only seems to work better for F2C diesels, where crankcase volume improves fuel economy, and those are generally reversed drum, which reduces crankcase volume, friction and sealing problems. Of course, none are reed valve. I'm not sure what ram air would do to a reed valve, but I think it would be bad, as would vacuum. Either could happen in flight, I'd wager, depending on design details.  Steve 

Jim - I'm sure you don't intend to hijack the thread and I'd like to stay on topic - O&R .23 FRVs..
A careful read of Ty's post above may apply to your question.

Thanks.

Terry

Ha - you got me there, Brett.
I haven't flown it and don't know if I could tach it at the same time anyhoo.  

I'm certainly a newbie to c/l flying, but I thought "unloading" referred to higher rpm in the air than static.

I'm not expecting my O&R .23 to be a .25LA equivalent, just wanting to use it to it's best.

Terry

Brett, are you saying that even though the O&R may turn a given prop the same rpm on the ground as maybe a Veco .19, when it unloads in the air the Veco produces more HP at the higher rpm 'cause it breathes better?

Terry

Ty - I run all my old engines on at least 26% oil, mostly 100% castor.

Brett - I think you've answered the question I wish I'd asked in the first place, and my apologies to all for dragging you through such a circuitous route to get here.

Thanks to you and all who took time to post.

Terry

It happens that I also have a Veco .19, so I'll run them both as you suggest.
I haven't ran the Veco with the same (9x6 MAS) prop I have on the O&R, but doing so, I expect I'll find a greater percentage difference between the 2 engines with a smaller prop.

Terry

I missed the part about the thread pertaining only to O&R .23 FRVs...

My bad,
Jim

Hi Jim

I just saw this thread this morning, and no you didn't hijack the thread, so no worries, your post was perfectly acceptable . As has been pointed out , the power level on 2 given motors would be exactly the same turning props at the exact same RPMs, many people do not understand what happens when engines are unloaded in the air. Some have reserve power and are able to reach higher numbers, some are near maxed out on the power they can deliver when unloaded in the air , others have dissimilar torque curves so it , may work better for one engine to run a higher pitch and or different diameter to get more output, and run the engine in its best RPM/torque range.

Regards
Randy

Hello Terry,
I must be part of your problem, as I am the guy who called the O&R 23 Wimpy! Look, I love old spark ignition engines and must have maybe 50 or 60 of them. Apart from what are termed slag engines, the O&R engines are probably the least powerful engines you can get, capacity for capacity. They are cheaply made, the cylinders are spot welded to lugs which fit thro' holes in the case, the pistons are stamped out of flat metal and then hardened and ground. The bearing areas of the plain bearing engines are short in length and this helps to wear them out quickly. So you should by now, realise that the design is all for cheapness in building. Not for good long life!
  You seem to have an engine where all the tolerances in construction add up favourably and gives it the opportunity to run at 12,000 rpm on a 9x6 . Nome of mine will do that. So treasure your engine as a good one! If you use it as most were back in the day, then it will only run for a short period to get a free flight model up in the air and then cut to allow the model to glide. Control line usage is much more arduous as the engine will be running at full tilt for 5 minutes maybe. Do this 4 or 5 times a week all year and your engine will probably be totally worn out. In free flight applications it will last for years.
  As to power, if it is turning the same prop at the same revs as another engine then they are turning out the same power. The point being that the O&R will probably be doing its maximum revs on that prop. The other engine of similar size will have more power in hand and could be made to rev much faster on that prop by leaning out the mixture. Try leaning out the O&R and it will stop!
  So that is the difference between the two engines. After making lots of derogatory remarks about O&R engines, they are easy to handle and yes, I do fly them but not in control line models! I learned my lesson years ago when I flew an O&R60 in a control line model. At the end of the season it was worn out and I do mean worn out completely! It would still start on spark ignition, but power was woefully lacking.

Regards,

Andrew. 

Hey Terry:

It may help to understand all this engine stuff if you Google a bit for "speed torque curve".  Hopefully you'll find something informative: I know what you want, but I don't have time to sift through results.

Basically, any engine, whether it's diesel, 4-stroke, 2-stroke, 6-stroke, big, small, or whatever, tends to have a torque output that starts out moderate to low, rises as the engine speed rises, tops out at some value, then falls as the engine speed rises further yet.

The power output of an engine, or any other rotary mover, is proportional to speed times torque.  So the power* of an engine is equal to speed times torque times some constant.  This means that if you have a torque vs. speed curve, you can make a power vs. speed curve.  In all but the most obnoxious of cases, an engine's power peak happens significantly later than its torque peak.  When people talk about using different propellers, what they're telling you to do is to try to find a prop that puts the engine in a happier spot on its torque/speed curve in the air.

Two-stroke engines that are designed to handle easily tend to run out of poop (torque and power) at a lower RPM than engines designed for lots of power.  Cross-flow scavenging tends to run out of poop earlier than Schnuerle ported engines, given the same timing and intake geometry.  So its to be expected that two sport engines, one Schnuerle, one cross-flow, would behave differently at high RPM.

* What a lot of people perceive as "power" in a stunt engine can be different.  Brett buck has explained well and at great length elsewhere on Stunthanger.  It's worthwhile reading.

Hey Tim -
I'd hoped to avoid all the technicals and math - makes my head hurt.

I've seen those figures while reading reviews and simply skipped over them as being of more academic interest, 'cause I really just want to get a handle in my hands again.
But I do realize that such a mindset destroys planes and engines - ignorance would  not be bliss for long.

Actually, that sort of stuff can help you be a better "engine expert" if you're a certain kind of learner (i.e., if you don't feel you can start before you know absolutely everything).

But if you just want to fly pretty good and have fun, then look at the practical advise that's given here, and follow it.  I'm a "I want to understand it all" type, but what I actually do to succeed is to pay attention to Brett Buck, Randy Smith, and those folks who all seem to be saying the same thing and winning contests, too.

In a capsule, if you want to succeed without knowing everything about engines, here's what to do:

• For a Skyray, Fright Streak, or similar-sized plane, run an OS FP 20 or LA 25.  Someone always gets on and says "Enya engines are good, too!", and someone else agrees.  I've never tried an Enya -- but I can't disagree with the group.  For that matter, there's a lot of other, more obscure engines that should work well, too -- but then you're back to needing to be an expert.
• For a plane up to about 600 square inches (give or take) use an OS LA 46.  I once asked "what size plane for an LA 46?" and got two pages of answers ranging from 550 squares up to nearly 700 -- but the weight of opinion seemed to favor 600, maybe 650 tops.
• For bigger planes -- ask.  There's a lot of good engines out there, but I've mostly ignored that whole conversation because I'm really a small-plane person at heart, being dragged kicking and screaming into the big plane arena by the fact that they just fly better.
• Run lots of oil, with lots of that castor.  22% total, with half castor seems to be a good starting point for the OS FP and LA engines.  Use more oil if you've got an iron sleeve engine.  Randy Smith has a "how to make your engine behave" or similar thread pinned to the top of the "engine set up tips" forum.  Read it, do what he says.
• If you run into trouble -- ASK.  There's a lot of subtle stuff going on that makes a good stunt run, and much of it runs against the application of simple science and even practice in other events.  That's because we want a specific run, which is by no means "best" by any yardstick other than stunt.  So when the RC guys and the team race guys and the speed guys and the combat guys say you're running your engine "too rich" with "a teeny venturi" and "the wrong propeller" you may just be out there grinning at the perfection of your engine run.

Now that's a thought provoking post for me Tim.
I must admit, I'm of the know-it-all-first school intellectually, but the lets-go-fly group emotionally.  

To be honest, I've acquired several engines (O&R, McCoy, Forster, Veco, etc.) from back in the days when/because I couldn't afford them and I really appreciate them and enjoy running them on the bench while waiting a chance to grasp that handle.
And I've had in mind seeing them in the air.
I've no delusions of someday flying against Randy, et al., so casual stunting is my goal.
It seems the .25LA is a go-to engine for such as the Flite Streak - I am a bit curmudgeonly, so, as a beginner to all intents an purposes, am I making a big mistake to think of hanging onto those old days and engines?

Terry

And for Jim Roselle -

Belated for sure, but when you posted I'd forgotten the original subject line myself, and your post was well within it's bounds.
Mea culpa for a thoughtless response.

Terry

Those old engines fly as well as they ever did -- it's just that now there's the new engines around to show us what can be done.

Glad to hear that Tim - I have a good Veco .19 and Forster .29; one or the other should do for the Flite Streak.
Flying those'd please me more than getting a new engine.

Terry

On the other hand, Bob Palmer flew a Go Devil in competition with an Ohlsson 23 after he had his accident with his hand. He said he could not stand the pull on the special glove he was using with anything larger. He also said it would do vertical 8's with ease as long as the wind was not to hard. Of course, that was Bob Palmer.

So I can still dream of the Ohlsson in the air one day. 

Terry

If you're flying for the big prize money and the gorgeous women, then stick to the top-o-the-line modern engines.  If you're flying to do what makes you happy, fly what you want.

Money and gorgeous women?! I'm calling Randy to order a PA and a pipe right now!

Glad you're asking all the questions, Terry. We all learn from reading the input they generate.
Rusty

On the other hand, Bob Palmer flew a Go Devil in competition with an Ohlsson 23 after he had his accident with his hand. He said he could not stand the pull on the special glove he was using with anything larger. He also said it would do vertical 8's with ease as long as the wind was not to hard. Of course, that was Bob Palmer.

  Supposedly, this was the result/side of a trick they played on a newbie, and led to the development of the Fox 35. At least according to Bill Winter.

   Brtt

Well, is my face red! 
I own one o' them nefarious Foxes!
Amend my previous statement to read: "...a long, long, extended education".

Terry

    Oh, you might be able to get even more opinions on the Fox than you got on the 23. Just possibly.
   
   This could be on the order of 7-th hand because it was something in Bill Winters old, quite bizarre, MA column, so bear that in mind.

    The trick was that they told some newbie to put a Ohlsson 23 in some stunter of the day, instead of the "correct" 60. This was somewhere in Southern California and Duke Fox, among other notables, was party to it. They knew for certain that this would be hopeless. So, the newbie dutifully built the airplane, and put the 23 and a bunch of lead in the engine compartment, and took it out to fly. They were all ready for the laughs, but the guys takes off, and flys it nicely, and low speed, through the pattern. Someone overcame their shock long enough to rush out and say, "hey, let me fly that airplane" and they were all amazed at the ability to fly the stunts at half-speed. Duke went off and designed the Fox 35 to do something similar.

    Brett

Brett, I've done a bunch of searching on the forum, and one thing's for sure:
I ain't askin' NOBODY what they think about the Fox .35! 

   That proves you are much wiser than I am.

    Brett