The 140 hp gap

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orion

R.I.P.
I dont think anyone could design a plane that would use either a IO390 or a 914; it would not be optimized for either. At some point the 914 will out perform in HP but it will never out perform in torque, not in practical flying. The 390 will turn a bigger prop with more pitch. The only 914 I know at my airport is in a wrecked 3/4 Storch, It is a good sized airplane and light. There is a IO-390 in the hangar next to it in a RV8A. No way the 914 would ever fly that RV unless you had 10,000 ft runway. In the summer, the density altitude at my airport can be 5000ft; still no way with the 390 handicapped. The 390 has made it the fastest RV at the field; he went from the slowest with an RV4 and 0-320. The 390s are now STCed for Mooney injected replacements. A Mooney 20E is almost 2600 gross takeoff stock. There is a Pulsar with a 912 an airport over, cool little plane; way smaller than the RV; about the same speed.
While from a practical standpoint you are absolutely right, there may be another approach. You design the plane so that it could be built with two levels of structure. An example would be to design the plane for the larger engine but then modify the design/structure for a much lighter mission. True, the savings would really be dependent on the structural type and the materials used but it may be possible to design in some flexibility so that the two airplanes could be built with exactly the same tooling, just with lighter gauges and maybe a more limited mission profile (slower speed, less range, less payload, etc.). In this way the company has two nearly identical products and is able to hit two markets with much less investment.

Well-Known Member
Overrating is effectively what I'm doing now, with the O-360, except I'm not a helicopter so why not allow all the power when available? But 140 hp is what I need for both target cruise, and 1200 fpm climb at gross weight. Climbing at 2000+ fpm is cool, sure, but not necessary. And I'd rather be able to maintain target cruise (IAS) at 14k feet than top out at 10k feet.

I like the Jabiru 3300 a lot, but it's not fuel injected, which in my very limited understanding of engines (/not/ my area of expertise, even in potentia) makes turbocharging more difficult. So assuming 120 hp is not enough (and it's really not), this drops off the board, unfortunately. A Jabiru 5100 that had finished development and had good availability might have been the answer; a 4400 at 3000 rpm max would fill the gap perfectly at ~145 hp, but apparently there really just isn't much demand between 120 hp ("powerful lsa") and 160/180 hp ("wimpy/upscale so-called-four-seater").

I've seen the "super 914" Rotax designs. I guess what I really don't understand is what the compromises are on such a design. Obviously "reliability", but in what way? Large amounts more heat generated, which means a more complicated install in terms of managing cooling. But assume you run a standard Rotax 912 and a 45-psi MAP turbo'd 912 (140 hp at same rpm?) with the same CHTs for 1000 hours, cruising at 75% of available power. What actual failure modes would you expect to see with the boosted engine? Is the answer different for boosting an IO-233 (again, given cooling, which may be harder than in the Rotax case), with lower rpm, etc?

Perhaps I have misinterpreted what you are aiming for but it reads like you are looking for an engine with a max continuous hp rating the same as your desired cruise rating. Do you plan to fly around everywhere at WOT like R/C pilots do?

Speaking of tweaked Rotax engines this Italian engine which is a reworked 912 with 130hp and fully aerobatic. This is less than what you want but is worth mentioning just because it's ace. Airframe is neat too.

http://snap.aero/04-power/power/

Well-Known Member
While from a practical standpoint you are absolutely right, there may be another approach. You design the plane so that it could be built with two levels of structure.
Indeed. C of G was of no concern to me (engine in the middle). But starting from a Rotax aircraft of roughly 650 lbs empty it's surprising how much weight you gain. Not only the engine (close to 180 lbs heavier), but 30 lbs for a stronger prop, another dozen for a stronger engine mount, by which time you desperately need a tail elongation for another 50 pounds penalty. Now to conserve our payload we need a stronger landing gear and fuselage and we're down another 50 lbs.

I ended up with 420 lbs increase in empty weight. Despite almost doubling the engine power, my power to weight ratio was only a bit higher and quickly lost to the Rotax with the thinner air. 12% extra speed was the result in doubling the horsepower. I would actually be slower with the Lyc at FL100+...

See also the LSA's. They replace the Rotax 912S with a O-233/235. Due to those being fairly massive, their power to weight ratio is actually worse than the Rotax-powered ones and they often perform worse too. "More power" isn't always the best solution.

The bottomline, sometimes less power is better, if you have a lighter engine. It might be worth it to "design down" to a 115 HP engine and buy a Jabiru 3300 or the stock Rotax 914. Power or torque at itself is a completely pointless property of your aircraft. Power to weight ratio for example is much more telling.

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Well-Known Member
Perhaps I have misinterpreted what you are aiming for but it reads like you are looking for an engine with a max continuous hp rating the same as your desired cruise rating. Do you plan to fly around everywhere at WOT like R/C pilots do?
Climb is the main driver for engine size; at 140 hp (and current weight estimates, of course) I reach my target climb of 1200 fpm at full gross; at 150 hp I have a bit of room to play.

Best cruise is in the 110 - 120 hp range, the bottom of which is 80% power on a 140 hp engine; a bit higher than normal, but not uncomfortably so.

A final constraint is that this is a low aspect ratio design, and the back end of the power curve starts to look uncomfortable at below about 90 hp; I'm a big fan of being able to climb at any non-stalled airspeed on the back of the curve, having flown a plane which couldn't and being uncomfortable with short landings in it. The low aspect ratio bit of the design is also why altitude performance is so unpleasant with a naturally aspirated engine.

I'm aware that all of these numbers lend themselves perfectly well to an O-320 or O-360, cruising at normal power ratios, and that's indeed where I'm designing right now... but it just feels like a bad match, and man would I love to save 30 lbs up front. The O-320 in particular just seems like an awful deal weight-wise, and the O-360 is so close to the top of my allowable weight range for engines that I'm going so far as to avoid the extra few pounds of fuel injection and a composite prop. It does seem odd that we're at least somewhat sanely discussing a ~150 lb Rotax 914 in the same discussion as a 250+ lb IO-360. And I'm aware that these engines are in a completely different class, but that's the frustration... the lack of a midpoint between those two classes.

Jan Carlsson

Well-Known Member
Other aspects to it, how much power is that 160-180-200 hp engine turning out? it all depends on how it is installed in the aircraft, in form of exhaust, inlet, air filter, alternator ... as have been seen when engines tested directly out of the airplane power can be down 15-20% from what it say on the box it come in from factory.
The european engines is often! tested with all apparatus on the engine. Last year I have been designing propellers for several O-200 engines, and at first using 100 hp, it was impossible to reach red line, or even take off with a high pitch prop for a fast plane, but after reading on the net, where engines was tested, and adjusted for density, 0-200 is as they sit in a Cessna a 82 hp engine, and with different equiped engines, most of the time 85 have been used in prop calculation.
The same did I read on a tuned exhaust site, testing a 320 getting something like 133 hp not the 160 it was suposed to have. after fitted with there tuned exhaust, that was tuned for 75% power 2450 rpm they got almost rated power. was it 157?

Then we have to calculate with loss of power with alt. of 3%/1000ft, (not linear) I know UL power say something different and some other, but 75% at 8000ft is what most say, I might be wrong? but that is not proved yet, but I might be humbel?

If you want to cruise at 14k´you might have just 60% power without turbo, so of you want 120 or so you need 200 SL power, if natural aspiration engine that is.
In most cases we always want more power, that help with take off and climb, safer to get over, with good margin, the line of trees at the end of the grass strip.

TFF

Well-Known Member
The 130-140 hp engine size died in the 60's. Conical mount O-320s make more hp, 20-25, for close to the same weight as the O-290s; they only made airplane 290s for 3 years before the 320 upgrade. Continental O-300s are heavier, but are about the nicest running engine. 2 extra cylinders and weight killed it. The closest things out there seem to be the O-240 Continental or the 4 cyl Franklin if you want to loose the weight and be close on HP and then turbo for altitude. About the only plane I know of that has flown with both a Rotax and a standard airplane engine is the Diamond DA20. A local airport to me was where the factory came to swap out the 912s for Continentals about 1998. No one liked flying behind the Rotax in that application, at least in the US.
Designing is academic; homebuilding is a scrounging exercise. There is only so much hardware out there that can be had at the homebuilding level. To me it has never made sense designing something that a hole cant be filled.

Well-Known Member
(Just musing to myself.) It's a pity that I'm not taking the twin engine route, as two HKS 700T would be a great fit... and as Tecnam discovered, you can build a twin with lower engine weight than a single at this point, thanks to Rotax et. al. Plus in my particular case, the strict weight limit on the engine is a moment limit, so a twin (engines mounted closer to neutral point) really simplifies things.

But darn it, I don't want a twin.

Grelly

Well-Known Member
"One quick point - the 9-cylinder R3600 is a radial engine, not a rotary".

Yup. Sometimes I use the wrong worms... I spotted my own mistake and tried to correct it, but for some reason it wouldn't take.

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Plus in my particular case, the strict weight limit on the engine is a moment limit
Would a prop extension and an aft-moved engine help there? Or does that coincide with your feet?

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Feet, unfortunately. I'm not sure what the shortest mount one can practically put on most of these engines actually is, but having looked at O-360 installed it seems like 8" (from firewall to mount points) is already pushing maintainability limits. And chopping off 3" more, say, isn't going to be that big a difference.

Well-Known Member
Is anyone familiar with Limbach engines, and in particular the DS-L2400DTX?

I'm not yet at the point where I need to "lock in" an engine, but I need to convince myself that there'll be /some/ solution at the appropriate time, and be able to estimate the weight of that solution. This engine, plus projections of something like the HKS-700T to a four-cylinder (notional HKS-1300T), plus linear projection from the IO-233-LSA and Rotax 914 show that it /should/ be possible to put together a 140hp - 160hp turbocharged or turbonormalized package for a FWF weight of (somewhat conservatively) 250 lbs. If I really believe this, then I can figure out who will provide the actual parts when the time comes.

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Is anyone familiar with Limbach engines, and in particular the DS-L2400DTX?
I have some experience on the lower HP (NA) engines. But firstly, they've ceased operation:

And according to rumor a Chinese company took them over, so future support might become interesting.

Did you check the price? It's certified turbocharged engines ran north of 20K. Euro's

I'm not yet at the point where I need to "lock in" an engine, but I need to convince myself that there'll be /some/ solution at the appropriate time, and be able to estimate the weight of that solution.
I would size for an existing and popular engine, even if that involves major redesigns. Too many good designs have gone down by not having a suitable engine they counted on. What prop are you using for C of G? Composite fixed pitch? Battery already in the extreme rear of the airframe?

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orion

R.I.P.
BTW, that's ceased, not seized.

Jan Carlsson

Well-Known Member
BTW, that's ceased, not seized.
You guys know so many different names, Stopped, would have worked I guess.

be glad we are not Thai, where the same word can mean 4-5 different things, it just depends on the pitch and tone.
On the other hand, even me that talk far from anything that can be called good english, can laugh at there thai-english. like fryed ride!

I saw a banner in BKK, that said " Have one beer and you feel good in body, have more beer and you feel everybody"
Even in Swedish we have the same word for "feel" and "know a person", so the misstake is understandeble, still funny though.

So, on to topic, LOM have a 140 hp engine! in line also. Cz isn't more than a night fright flight away if needs parts.

Hope I make me self understood.

Well-Known Member
I have some experience on the lower HP (NA) engines. But firstly, they've seized operation:

And according to rumor a Chinese company took them over, so future support might become interesting.

Did you check the price? It's certified turbocharged engines ran north of 20K. Euro's
What were your impressions on the NA engines? Sucks that they've stopped operating, but it might still be interesting to me as one of five benchmark / proof of concept engines.

20k euro ($26k dollars?) doesn't seem unreasonable. Remember, my "fallback" engine is an O-360, which is$30k naturally aspirated and carbureted.

I would size for an existing and popular engine, even if that involves major redesigns. Too many good designs have gone down by not having a suitable engine they counted on.
For the record, I fully recognize that this is great advice and I should take it, and as such I'm going forward with the O-360 assumption.

But in practice, I'm going to have a very hard time taking this advice to heart. The trade-offs are just uncomfortably painful for this design. I'm more than willing to design around and build for an O-360 with ballast, weird battery placement, etc; but I have to believe that at some point I'll be able to re-engine it and end up happier.

That's part of why I'm hammering on different options in this thread; if I believe that there's a good chance someone like ULPower will have an engine available in five years, plus there's at least one person who's made Rotax's run in this power range, plus the Chinese might restart Limbach, plus there's always the chance of turbocharging a Jabiru 3300... none of these options would necessarily be cheap (since I'd be hiring engine expertise) or reasonable, but between all of them they show there's going to be some way to have an option besides the 360.

What prop are you using for C of G? Composite fixed pitch? Battery already in the extreme rear of the airframe?
As mentioned, assuming a two blade fixed pitch wooden prop; composite might be a better choice, but wood tends to be that much lighter. Batteries already in the back, but starter wire weight starts feeling silly...

Well-Known Member
So, on to topic, LOM have a 140 hp engine! in line also. Cz isn't more than a night fright flight away if needs parts.
Hmm, the LOM M332SH is interesting. It's not noticeably lighter that the O-360 by listed dry weight (249 lbs vs 255), but of course translating that into FWF weight takes experience with the specific engine that I don't have. Supercharger included in that weight, very nice; 140 hp max, 120 hp cruise, definitely in the target range. And the ability to pick up a mid time engine right now for \$9000 is certainly tempting. I'll keep it in the back of my mind and search for another 50 lbs, but this continues toward the examples of "things that fit my design at least somewhat better than an O-360".

Jan Carlsson

Well-Known Member
Isn't the LOM listed with all inclusiv?, (I have not checked)
the weight on O-360 seems to be low, pulled out M. Hollmann great book, have different number on all pages, he list dry weight to 290, on that add on 45-50 for starter generator carburator and things like spark plugs, harness ...

Hot Wings

Grumpy Cynic
HBA Supporter
Log Member
8" (from firewall to mount points) is already pushing maintainability limits. And chopping off 3" more, say, isn't going to be that big a difference.
Would a recess in the firewall and a swing put engine mount help any?

orion

R.I.P.
The LOM engines are usually listed with all accessories including baffles and exhaust. Weights for Lycomings are usually factory dry shipping weights, which does not include any accessories.