Discussion in 'Firewall Forward / Props / Fuel system' started by Dana, Jul 19, 2012.
Half as happy as this?
In case anyone isn't clear here, we're talking about a dead stock O-200 turning 2800 rpm. Yes, we all know F1 O-200s can make something close to 150hp turning 4000+ rpm...
The point being, taking half of a stock O-200 and turning it to 2900rpm isn't going to make 60hp. If you up the CR or VE with a better cam grind, yes, possible.
If Pete sees his customers racing around the pylons like that, well, they shouldn't expect much sympathy when it is overhaul time.
He did up the CR but 60 hp or even anything close to it seems doubtful.
Oldest saying in aviation.... Horsepower sells the engine but torque is what makes the airplane fly.
True, but HP quantifies the amount of work being done (work per unit time) and is how we compare different powerplants. Outside of CR increases, the only way we can make more hp is to increase the amount of mass flow through the engine. Even if a stock O-200 did put out 100hp at 2800, the best an identical O-100 could hope for would be 52hp at 2900.
Best to sell an engine on true facts rather than estimates pulled from a hat. Estimated hp and estimated TBOs on new engines are completely meaningless in my book. Prove those figures with actual running before publishing them. That gives any new engine project a boost in legitimacy and customer confidence.
Which is why I keep looking for the prop size/dyno info. Since it has flown there is should be some info available. And, no, its not early in the game. Its is in fact very late in the game so the info needs to come out.
Would you really want him to make public estimates (or even an actual dyno reading) on horsepower... to pacify all the people who are demanding information... and then have the final production engine manufactured using a different crankshaft, pistons, carburetor, and intake manifold than it had on it previously ?
Or would you all have more respect for a guy who wanted to wait until the final "frozen design" production version was tested and dyno'ed and finally (after making everyone wait for years) publish those numbers ?
Are you saying that the pre-production O-100 engine has shown 55-60hp in testing already?
Most folks, including myself, respect what Pete is doing here and how he's been doing it however projecting dubious HP numbers without a dyno test serves nobody well. Best not to say anything about this until a dyno test or club/ prop rpm test is done. I'm really not sure what point you're arguing here. Finish a final production piece (which is the version customers will be buying), then do the power test, then publish that figure. That's the sequence of events in all engine development projects which I've been involved in and how the OEMs do it too.
Claiming 60 now and ending up with 45 in reality doesn't do much for credibility.
Pegasus is making a public estimate of HP, but it's not listed as an estimate at all.
I wish Pete luck with the project, some folks definitely want this engine. BTW, I really like the design he picked on that artwork/photograph, a perfect "feel" for promoting this product.
If I was developing this engine and could prove it put out 58 hp I would be slapping that info everywhere! It would appease a lot of impatient people as well as attract even more buyers. But that is me.....
I do hope that he hits the mark as we need more options in that hp range but I'm not holding much hope for it.
The hp should be listed with the intended rpm.
Otherwise builders will be tempted to think it's an engine suited for a two place airplane. After all, the early two seat Cub had only 39hp, so 50 or 60hp should be adequate, right? But the 39hp A-40 had 1900cc. and could swing a big prop at low rpm.
It's sad and hard to honestly compete with modern market practice using these inflated hp numbers at high rpm not used in flight. Especially with VW. An industry wide system is needed to get honest numbers. The small Briggs and Hondas had to lower the hp numbers after the marketing got out of hand. Some don't post hp at all now.
I agree that HP numbers should be accompanied by an RPM. Just as important is a separate "continuous" HP rating. It's no big trick to increase the CR and optimize the camshaft to use higher RPMs to get higher specific HP for a dyno run (or for takeoff). But if the engines are ultimately limited by thermal considerations (or mechanical longevity issues, etc), it would be best to indicate that with a "continuous" HP rating.
The 2180cc VWs can make 75HP without any problem, and they can maintain 72+ output for a long time >if< careful attention is paid to cooling. I don't mind that they have to turn at 3400 RPM to do that, it works fine for clean airplanes. If thrust at lower airspeeds is the main requirement, then a longer prop with resultant lower RPM, and lower HP (due to cooling requirements and off-peak HP RPMs) may be required. That's a choice and not a problem with the engine.
Per the ad shown in post 910, the O-100 has a CR of 9:1, and is rated at 2900 RPM (per VB). The pistons are not O-200 pistons.
The O-200 has a CR of 7:1, and is rated at 2800 RPM or less. The -D has a CR of 8.5:1.
Going from 7 to 9 CR is worth about 5-6%, 8.5 to 9, practically nothing measurable.
If it runs at a higher rpm and CR it will be more like a 1/3 GO-300, which has a 1200hr TBO and is considered less reliable. I had to replace a couple of cylinders on my GO-300 in the six months I owned it. Great climb power but I didn't like the fuel consumption at that rpm. Hard to sell a GO-300 powered C-175.
You may not be wrong in your conclusion, but your logic to get there went off the rails. The 80 HP 912 runs through a 2.27 gear reduction drive, so rated power at 5800 RPM is turning the prop at 2555 RPM. Taking a prop pitched to create an 80-HP load at 2555 and and bolting it on an O-200 results in too much pitch for the Continental to reach the RPM at which it makes rated power (2750 for the -D and -X).
That's like complaining a truck isn't making rated power because it won't pull your trailer uphill in overdrive. That last 200 RPM turned loose by a pitch adjustment is a big deal when turning a prop.
Just a small bit of info, I believe that when Piper & Taylor were together there was what looked like an open cockpit
J-3, that ran a Continental A-40 which was supposed to make 40 HP. Now that plane, while lazy, still would take two people up off the ground. While that was a four cyl. The O-100 should be able to haul one or two skinny people up.
I remember that Honda M/C from from 1963 had a 50cc motorcycle(?) that had a reported 5HP. That was an ohv pushrod engine. It revved pretty well, But of course, the company may not have told the exact truth.
Don't assume things before you know all the facts.
We got 5875 rpm on the carbs and just shy of 6000 on the EFI Rotax so that's 2588 and 2643 rpm respectively at the prop. Strangely, Rotax rates TO power at 27.5 inches rather than corrected to 29.92 as we'd expect. Our tests were showing around 26.5 inches at this altitude with the EFI. If we take this into account and take the median prop rpm at around 2600 rpm (5900 crank rpm), I come up with around 79 hp from the Rotax hp chart. I'll call that 80 here for sake of discussion.
The O-200 specs say 100hp at 2750rpm, I couldn't find what MAP that is rated at. If we assume a linear increase in power, at 2600, the O-200 should be making about 95 hp. Same prop, same elevation same OAT- highly doubtful that the O-200 makes that 100hp WOT at 2750 rpm. As I said, WW ran an O-200 as well on his dyno and saw right around 80hp too IIRC. When running the same prop on his original 110hp Corvairs, they turned that prop almost 250 more RPM IIRC.
If you have some more data showing an actual dyno run on a stock O-200, that would be good to see but the two cases above don't seem to support the 100hp figure.
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