Author Topic: Ratio landing / cruise speed  (Read 4023 times)

Doug Johnson

Ratio landing / cruise speed
« on: January 04, 2013, 12:03:18 PM »
Some thoughts and looking for opinions.

Just out of curiosity and because I believe the exhaust augmenters used on the H-391 should have been retained and possibly as an option for later models. I have been trying to see what I could come up with because my first main attraction to the Helio was the high ratio of Landing speed to cruise speed, the more perfect Helio would land at 25 mph (hard to do much here) not 38 mph and would cruise at 180 mph not 140 mph (maybe not 180) but a little can be done here.

Removing all those Antennas and figuring a way to bury them will give you 2 or 3 mph, I used helicopter bent whips and put them inside the wingtips.

Using LED lights would allow you to make the cowl more aerodynamic by reshaping the cowl.

I beleive that at least 10 knots increase in cruise is achievable by removing the eyebrow above the windshield burying antennas changing lights and augmented exhaust, so cowl can be reshaped, possibly Hoerner wingtips which might not help wouldn't' hurt.

Cooling drag can be 20-35% of total drag depending upon design. High performance aircraft such as the Relentless flown at Reno use exhaust augmenters. Using augmenters would allow you to decrease the inlet opening size and make the cowling more Aerodynamic.
 
A cooling system incorporating exhaust augmenters is independent of airspeed and fully dependent on power setting. This allows reduction of cooling drag without compromising the ability to cool in all phases of flight and requires no additional pilot workload. Don’t save weight at the expense of proper cooling.

An augmenter is simply a duct positioned behind the engine that allows air to be drawn into the duct where it is heated by the exhaust from the engine.
 
Because the exhaust is very hot, the cool air that was drawn into the augmenter is also heated and expands rapidly. This expansion causes an increased pressure and when properly harnessed additional thrust.

By making the duct expand towards the back, the pressure causes air to be forced out of the back to increase thrust. An augmenter can be as simple as a single divergent cone, however, to draw the largest volume of air into the engine there should be a convergent intake cone positioned in the front of the second divergent cone.

The intake angle of the first cone should be less than 45 degrees. The divergent section should be at least 3 times longer than the intake. To keep drag down, the intake and exhaust diameter should be the same, but for a static augmenter this has little impact.
Aluminum should not be used for the tailpipe, but is acceptable for making an augmenter since it will be cooled by incoming air.

Why not? Have a pair of high temp  AL/SI MSFC-398 aluminum interior/exterior ceramic-coated tailpipes http://www.appliedplastic.com/ceramicexhaust/ that runs under the plane to the back of the cabin http://www.rhinoshield.net/, inside a secondary skin also ceramic coated, exiting out where there is a good slipstream. 

Using Venturi effect to draw cooling air past the cylinders and exhaust pipes and smoothly back into the slipstream is a trick that never seems to fail.

With a smaller entrance in the front of the cowling, and dual exits around the tailpipes would create that suction (venturi) creating great airflow. The engine compartment would no longer have that raw opening for the exhaust/muffler, but rather sealed, since incoming air ducts/exits out through the back of the cabin. In addition, you would have a super quiet exhaust, and more power.

I then found this ceramic powder coat paint seems to be the latest thing on exhaust systems , exhaust manifolds and pipes it's applied inside and outside. It insulates the pipe and also smooths the interior slightly increasing hp, It reportedly (if put on a new installation) almost extends the life of the pipes indefinitely by stopping corrosion and thermal cracking, lowers the temp under the cowling by reducing radiated heat, helps keep exhaust gasses hotter which keeps oil particles suspended in the exhaust so they don't wind up caked in the pipes and would probably reduce that on the belly of the aircraft.

I spoke to Acorn welding manufactures of Helio exhaust systems and they don't recommend it especially if the system isn't brand new because once applied the pipes cannot be repaired. Also if you are installing an engine monitoring system with EGT probes you would need to use the welded on screw in type and weld them on before applying the ceramic coating. But they felt it would be perfectly legal. If you don't get a complete coat of even thickness on the inside the metal can or will erode and it can't be repaired. I think its worth trying because of the reasons in the previous paragraph.

And if you still need mufflers after the exhaust augmenter for flying a camera platform or flying in other noise sensitive areas here's some more info.

Borla Performance Systems of Oxnard, California makes exhaust systems for everything from formula racecars, Italian exotics, and high-performance motorcycles to package delivery trucks. (In one of their biggest recent contracts, Borla has replaced all the exhaust systems, from headers to tailpipes, of the entire U. S. fleet of UPS vans.) Borla also does design and consulting work for Chrysler and Ford. Alex Borla is a pilot - a Beech Baron owner - who feels that aircraft mufflers can make a big difference, and Borla is currently experimenting with such devices.

The company has instrumented the Baron so they can run muffling tests on one engine while leaving the other one stock while making simultaneous noise measurements at exactly matched power settings (confirmed through strain gauges on the engine mounts). Problem is, Borla's exhaust systems are too good. "We don't employ any baffles in our automotive and motorcycle mufflers," Alex Borla explains. "Everything is straight-through. As a result, we're able to tune the exhaust system all the way out to the tip of the tailpipe. With a baffle-type muffler, as soon as the exhaust pulse hits the first baffle, the tuning effect is over."
On an airplane, however, tuning the exhaust will buy you trouble. "If the product we make enhances the power of the engine, we can't get an STC on it," Borla points out. "I know from just looking at the manifold on the IO-520 in the Baron that I can get at least a 12 to l5 percent increase in power. Which is 30 or 40 extra horsepower, and that's a big number. I can also bring the engine internal temperatures down and convert that horsepower gain into performance and better mileage."

But to sell an aviation system, Borla would have to dumb down his product, "And that's tough to do, with the patented design that we have. But the way the FAA regs are written, I'd have to almost re-certify the airplane if I used it."

Still, Piper has contacted Borla for help in designing a muffling system for the European market. "Piper is very concerned about the European market," says Professor Patrick of Embry-Riddle, "and there's every reason to think the environmental laws in the U. S. will eventually become just as strict. All that U. S. manufacturers can do right now to meet those noise requirements is to use reduced power. Or fit mufflers, but that doesn't do a thing about propeller noise."

Whatever Borla does with his mufflers, they won't be heavy external fitments. "You see all sorts of appendages hanging out of Bonanzas and stuff in Europe," Borla says. "They're after-thoughts - basically a knee-jerk reaction to a noise problem - and I think they definitely impede the performance of the airplane substantially. You probably lose 15 percent of your performance by fitting them, but the only other choice is that you can't fly without them."
But wouldn't weight, cost and finding under-cowling space all be problems? Not necessarily: Borla Performance already manufactures compact carbon-fiber mufflers with stainless-steel end caps for motorcycles, and Borla estimates that a Baron-size installation would only add seven or eight pounds per engine using similar mufflers. "And if the motorcycle industry can handle the cost, the aircraft business certainly can.'

Doug
« Last Edit: January 05, 2013, 02:08:17 AM by Doug Johnson »
Doug

391stol

Re: Ratio landing / cruise speed
« Reply #1 on: January 04, 2013, 04:57:03 PM »
one major thing with speed is the prop size. It is hard to get a good top end cruise with a large diameter thrust circle(prop). It is hard to get low end performance with a small thrust  circle.  A 391 with 101" prop will fly much slower than a 295 with 96"prop. However the 96 will fly much faster.  Plus we are stuck with these Hartzell prop choices due to the low demand market.   The slower we go with high power settings the more cooling we need, thus larger openings. It is hard to find a happy medium which works in all aspects. Maybe helio has already found a good balance. 
I agree the coating on exhaust and internal engine components would cut down on heat this is proven in the experimental side of aviation and has become the norm.   I personally like the load noise of the helio it has a distinct sound along with the round porthole window it make my hair stand up on the back of my neck.

Doug Johnson

Re: Ratio landing / cruise speed
« Reply #2 on: January 04, 2013, 06:05:39 PM »
"The slower we go with high power settings the more cooling we need, thus larger openings."

A cooling system incorporating exhaust augmenters is independent of airspeed and fully dependent on power setting. This allows reduction of cooling drag without compromising the ability to cool in all phases of flight and requires no additional pilot workload.

I think Helio already figured that out with the 391 we just lost sight of it.

Prop diameter and airspeed are related to torque, I believe if you could come up with a lite weight variable speed reduction drive, possible a fluid drive torque converter, you could overcome some of this. I found two speed gear drives on some of the older radials to develop the torque at low speeds and more torque at higher speeds with a coarser pitch.

Doug

« Last Edit: January 04, 2013, 06:08:16 PM by Doug Johnson »
Doug

paullapoint

Re: Ratio landing / cruise speed
« Reply #3 on: January 04, 2013, 06:26:08 PM »
I was recently watching a video from one of the EAA Files. A guy with a home built , biplane I believe, was having a hard time keeping head temps down on a big lycoming. He had a custom shop that does automotive tuned exhausts in California build one that had a stinger on each side. He only gained about 7 Hp but dropped cht's by 50 degrees. It looked good under the cowl and sounds really cool.  The key was keeping the same distances from each cylinder to the stinger.  Paul

Doug Johnson

Re: Ratio landing / cruise speed
« Reply #4 on: January 19, 2013, 10:26:33 AM »
one major thing with speed is the prop size. It is hard to get a good top end cruise with a large diameter thrust circle(prop). It is hard to get low end performance with a small thrust  circle.  A 391 with 101" prop will fly much slower than a 295 with 96"prop. However the 96 will fly much faster.  Plus we are stuck with these Hartzell prop choices due to the low demand market.   The slower we go with high power settings the more cooling we need, thus larger openings. It is hard to find a happy medium which works in all aspects. Maybe helio has already found a good balance.

I found the below the 96" caught my eye, anyone have an extra 40,000 laying around and the time to go experimental for testing purposes.

Raisbeck and Hartzell have debuted a new four-blade "swept" propeller for the King Air 200 line. The design's 96-inch diameter is 3 inches greater than the B200 factory props, and 2 inches greater than Raisbeck's previous offerings. The increased diameter boosts low-speed performance and shaves 1,150 feet off takeoff, the companies said. They also said the swept-back blade design provides better high-speed performance and less noise in the cockpit and cabin. A pair of the new props costs $83,400

Doug
Doug