Discussion in 'Chevy' started by rv6ejguy, Mar 27, 2019.
Good to know. But everyone that we are familiar with, using an LS engine, has a PSRU.
That does not mean it will stay like that forever.
Today is what I am dealing with, as my plane is headed to the paint shop. My universe is very small, dealing with the T-51 Mustang.
Certainly a direct drive would be nice. Something that would produce 400+ hp, at 2600 rpm. That is what it would take to work in our application.
To quote a good friend..."Ain't gonna happen."
You realize you've gone from asking a very broad question to laser beam sharp in only a few posts, right?
It might not make any sense to put a bigger crank in your particular airplane, but there are plenty of reasons another engine developer would. Same reason Lycoming offers many different models of engine with significantly different displacement across the line.
Yes. That way anyone responding would understand what a T-51 Mustang would need. 350-400+ hp, at 2600 rpm.
No, it would not make sense for me, unless some engine guru here can tell us how to get this performance at 2600 rpm.
I'm curious what the extra $52,000 over the base cost of the engine gets you? Engine mount, PSRU, ECU and wiring?
Everything FWF. That is what they told me. Gearbox, Prop. That would be 30 Grand right there. Engine & mount, ECU, wiring harness, throttle linkage. It all adds up real fast. Plus the minor mods done to the engine, manual throttle, not the fly-by-wire version it comes with.
Just a little more than next year's second place finisher should do nicely.
A friend of mine got 2nd place at Reno, 2017. In his Glasair. Speeds around 255. Lycoming powered.
Still waiting on two questions...
1. What is the PSRU in the subject airplane?
2. Why operate as two V4's, rather than a dual ECU powered V8?
I bet Ross has the answer!
With a say.. 3500rpm redline, you can do some really stupid things with both crank and bore. Now I want to break out the engine calculator and see what that could be optimized to.
Had some of these conversations before. The thing you should consider is that one reason you need more HP out of your engine choice is that you will use a large part of that HP just to drive the reduction unit, carry the extra weight of the reduction drive, carry the weight of the extra fuel that will be needed to make the extra HP. You stated some time back that you had to upgrade your reduction drive to a both physically heavier and mechanically heavier duty unit. I suspect a minimum of 50 hp and probably a lot more than that will be used to drive the reduction drive. Any information from Titan as to actual HP required to just drive the unit ?
What you have to be cognizant of is the HP available at the propeller after you have driven the reduction drive. The Titan specs I saw say 300 HP max, but not sure whether they are talking about input to the redrive or output . VNE is about 200 mph and gross weight is 1850 with only 118 sq ft of wing with a reasonably aerodynamic shape. I struggle to understand why so much HP is needed when a Vans RV8 with comparable wing size and gross weight has a CRUISE SPEED 10 mph faster than the T51 VNE and a VNE 25 mph faster using only about 200 HP.
A direct drive is easily assembled that would provide 250 hp with little weight and less fuel burn because it isn't having to drive a reduction unit. Actually I think close to 300 HP is doable with something like an LS3 with a stroker 417 cu inches. The provided example is NOT optimized for lower rpms (camshaft choice), which should move the torque curve
lower and increase HP at the desired 2700 or close to that rpm. Minor increases in rpms with these engines can make dramatic increases in power available. At 3400 rpms, the 417 shown below produces 330 hp. Its not hard to believe that with a torque cam this engine would be near 300 HP at 2700 rpms and be a lot lighter. Seems to be about 10 HP for every 100 rpms in that lower range.
I also realize you have invested a lot of time and money into your project and at this point you are committed to the path you have chosen, so I hope that the choices you have made do work well for you.
One more thing, the LS3 crankshaft is a stout unit and probably no reason to change as long as stroke is staying the same. You can even get an LS7 factory crank to stroke with. What you will find is that the aftermarket produces even better and stronger crankshafts than the OEM units if you step up to the plate and buy the premium units.
Burning 50hp out of 350hp input to get 300hp out of the PSRU?
That is a single stage gearbox with just 0,86 efficiency? Sounds like a very low efficiency to me. I have heard 0,95 or better as a typical value for a box with gears. Maybe less with V-belts, better with chains and toothed belt in the vicinity. 50hp is 37kW, that is a mighty heater and do not sound right to me.
My statement " I suspect a minimum of 50 hp and probably a lot more than that will be used to drive the reduction drive." should have said "support" the reduction drive. As I said at the beginning of the post there are other things which have a cumulative affect requiring HP to offset their effect.Additional weight must also be offset by additional power, and running the engine at elevated rpms will generate more heat and friction within the reciprocating and revolving parts. Also the water pump , alternator, oil pump,will be turning higher rpms than they would at 2700 rpms, and it takes some power to offset that. More cycles of the pushrods and rocker arms per minute absorb power. Its a cumulative estimate
rather than a direct gear loss estimate....but it was a SWAG type of estimate based on a 10% rule of thumb with additions. Since we don't know the actual construction of the Redrive there is no way to have any really accurate number. Maybe TxFlyguy can provide some factory info on actual tests. One thing for sure is that it takes more power to use a redrive than a direct drive setup and there is less chance for harmonic issues. I just believe that if the amount of usable HP is available in the same engine type without using a redrive, to me thats a better solution. If the direct drive can't make the power, such as in a racing application, then reduction is warranted.
Probably most of the losses increase with rotational speed in an internal combustion engine. The question does the losses increase as a percentage? That is, is the efficiency less at a higher rotational speed?
I doubt that, a certain power to turn a propeller can be achieved with a direct drive slow turning engine or geared higher speed engine. In the end it’s the execution of the design that matter. Have a look at the Rotax and a similar powered Lycoming and other aircraft engines. Different designs for a similar mission but perform quite much the same.
Best efficiency on most SI engines occurs at an rpm about 20% under torque peak. These is where VE is still high and frictional losses are relatively low.
Traditional single mesh gearboxes have mechanical efficiencies of 97-98.5%. Very little power is lost. The biggest factor is weight and perhaps cost on aircraft applications.
Most DD auto powered aircraft are heavy dogs unless they use forced induction. The gearbox frees up 75-100% more power for a relatively small weight penalty.
I do agree that different designs change whats best for particular applications. In the distant past builders were mostly limited to heavy cast iron engines and needed to try to get more power from them to offset the weight. They added reduction drives and on smaller displacement engines there were a lot of examples that worked well...usually 4 and 6 cylinder engines. Steve Wittman took one of the first all aluminum 215 cu in Olds engines and stroked it with a 300 crankshaft. With less than 300 cu in his Tailwind flew close to 200 mph. My proposal is essentially the same idea using a newer design. Rather than use 346 or 377 cu in, my suggestion is to stroke an LS engine to 416 cu in with virtually no change in the weight of the engine and emulate certified aero engines which have proven direct drive to be very efficient and reliable at 2700 or fewer rpms. Wittman proved that it is viable, reliable, and inexpensive. Once power is coming out the end of a shaft, what matters is that someone can harness it for their application. A nominal powerplant producing 100/130 HP is readily available in the direct drive Corvair. Now the same HP can be made using a smaller engine,and spinning it faster. Questions then are: How much does it cost to build that unit and how much does it weigh ?
The Rotax 912iS weighs 140 lbs...makes 100 HP....operates at 5800 rpms ....uses a reduction gear.....and costs $22,000
The Corvair stroker 3100 weighs 200 lbs....makes 120+ HP.....operates at 2700+ rpms....doesn't use a reduction gear....and costs about $10,000 and can be homebuilt for even less
The Lycoming starts out new at $25,000 or so and goes up from there. Specs and weight depend on size . Direct Drive
The LS3 with a reduction drive purchased as a new assembly will cost about $30,000 and according to TxFlyGuy he has $52,000 in his including propellor (knock off $10K for prop)
Weight of TxFlyGuys engine and reduction drive may be around 500lbs and HP produced is apparently more than 300
(Note: Majority of Homebuilders cannot use 300+ HP, so why build more than you can use. TxFlyGuy is the exception as he is building something that apparently can use it)An LS3 480 is about $7500 before redrive and ECU )
An LS3 built with premium parts including a stroker crankshaft to 416 cu in with a direct drive should weigh in the neighborhood of 400/420 lbs with appropriate lightweight parts and properly constructed direct drive. It would target 2700 rpms but if more power is needed the rpms can be increased and prop corrected. At 2700 rpms it should easily be capable of between 250 and 300 hp depending on camshaft selection. The engine could be assembled with all premium parts for $10,000 and maybe $2000 for drive assembly.
If someone needs less than 300 HP, its available with 50+ lbs less weight, and less expense.
Now as Himat mentioned. There are other ways to get say a nominal180/200 HP by using a smaller engine than the LS but larger than the Corvair. This niche can be filled by
Turbo six engines running redrives....but you have to look at complexity vs simplicity, actual weight, and costs. Subarus have a pretty good track record in that niche, and I'm sure others can fill it also.
So I agree with you that there are differing solutions. I still don't understand why an airplane the size of the T-51 would need 350 hp when an RV8 has the same gross weight and wing area, and the wheels don't retract....yet flys faster on 200 HP. It doesn't sound very efficient even with a gearbox and a lot more horsepower on hand. How fast do the V6
Honda powered Titans fly ?
Wittmans 200mph with a small aluminum direct drive Olds engine
For those of us who don't know, please tell us how fast a 350 hp T-51 is.
Why would a ~400 cubic inch LS3 running 2700 rpm make materially more HP than a Superior IO-400 or a Lycoming IO-390, both of which are in the 210 HP range?
T51s are draggy airframes despite the retractable gear. Highly doubtful a 400 inch LS will make 300 hp at 2700 rpm, no matter what camshaft is used. 250 is more probable.
No one knows. A 350 hp version has not flown as of today. Mine will be the first, approaching 380 hp with the new HD gearbox, new propeller, and the high speed wing. Plus, we have the LS376/480 engine. It has never flown in a T-51.
A number of LS3 engines are flying in T-51's, but are limited to a max 300 hp, because of prop/PSRU limits.
On a recent test flight, the slow wing version LS3 powered T-51 had an IAS of 218, at pattern altitude, straight and level flight, normal cruise power.
Our max engine rpm is limited to 4500, as the PSRU has that limit for max continuous power.
Vne on the speed wing is 275. GW has been upgraded to 2250.
I'll take a WAG...maybe 240 IAS at max cruise power? More, less? We will know soon. My plane is going into the paint shop in about 10 days. Still waiting on the highly sought after propeller from Whirlwind. Note the new prop is 90" diameter.
Here is a very short video, slow wing T-51, with a 327 ci Chevy V8:
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