SparrowHawk performance at high density altitude

[The Rock]

I have been lurking for over a month now, and really enjoy the forum. It is time that I join in. I have been interested in gyros since RAF built the, IMHO, first attractive, enclosed gyroplane. In 1995, we flew to the PRA convention at Putnam Co to get a ride in an RAF 2000. I was appalled by the lack of pitch stability, and put aside my interest in gyros until Oshkosh last year when I saw the SparrowHawk.

From tracking this forum, it appears that the SparrowHawk resolves the pitch stability issue, but I have some questions regarding its performance at high density altitude. I live near Denver, CO where density altitudes can approach 9000 feet on the runway in mid-summer. Is it even possible for any gyroplane to provide reasonable performance at anywhere near gross weight under these conditions?

Udi, since you live in Ft Collins, you may be best able to answer this question.

The Colorado SparrowHawk distributor is building an RAF modified with the SparrowHawk kit and an EJ20 turbocharged engine. I question whether this will solve the density altitude problem, because in looking at the torque curves for this engine, it is doubtful that in the lower rpm band it has the torque necessary to get a propeller optimized for the upper horsepower band up to speed. Does anyone have any experience with either a turbocharged or supercharged Subaru engine at high density altitudes?

[Mayfield]

The SparrowHawk with normally aspirated EJ22 would not give acceptable performance at high density altitude.

We do not yet have any solid test data on the EJ20 installation.

I suspect that the minimum engine that would do the job is the FI EJ25 normally aspirated. We will offer the EJ25 as an option. Even with this engine performance would (obviously) not be as good as at lower altitudes.

One of the problems with adding more and more HP is that we feel that our 85MM belt PSRU is good to about 160 HP. To be safe with a turbocharged engine with our PSRU it would have to be turbo normalized.

We have not even begun to look at this option.

The other option is to go to a 100MM belt PSRU. This would require re-engineering of the entire drive system and the numbers of you folks that live above a significant percentage of the earth's atmosphere do not yet support the expenditure.

That being said, I believe that "acceptable" performance will best be achieved by installing the EJ25.

Jim Mayfield

[The Rock]

Jim,

Do you have anyone building a SparrowHawk with the EJ25 that will be using it in high DA? I need to be satisfied that the SH will operate effectively in my conditions before ordering a kit.

[Mayfield]

Cliff,

Not yet. We are doing the first two EJ25 installations now. Hang in there and stay in touch. We'll try to keep you informed.

Jim

[Udi]

Cliff,

I don't know much about Subaru engines, but I would think that a turbo charged EJ22 would work just fine. Colorado Component Rebuilders in Denver can probably make any SUB conversion you want.

Have you talked with Bill Clem? Bill flies a Dominator with a turbo charged Rotax 914. He gets fantastic performance, and his machine is not light.

We, who fly gyroplanes at high altitude, get penalized twice. First, we lose 20-30% of propulsion with a normally aspirated engine (just like any FW airplane) and, on top of that, we also lose rotor efficiency. The rotor has to spin faster at high DA, which means a higher rotor drag. So we have to use longer rotor blades as well.

I decided to go with a light gyroplane with adequate power. My Air Command is not as light as I would like it to be, but it is reasonable. A gyroplane that is a hot rod at sea level would have adequate performance at our altitude. I guess that's harder to do with a lead sled (i.e. a two place machine).

Udi-

[birdy]

Jim,has anyone fitted a 914 to one of your machines???

I replaced a EJ22 with a 914 on me RAF and the performance overall improved out of sight.
I'm in central Oz,at 1800' ASL and the air can get hot/thin here in summer when it's 48c and 90% humidity,and it's in these conditions that the 914 realy shines.

[KenSandyEggo]

I think a mistake a lot of us make/made is that we're getting 130 h.p. out of our injected EJ-22s. That 130 horses is made at around 5500 rpm. Most of us are only turning around 5,000 on take-off. I believe that's a significant difference. Maybe we're only cranking out about 100 at that lower rpm. That would explain Birdy getting better performance out of the Rotax, whose h.p. is figured at the usable rpm.

[mceagle]

Birdy,
Was your EJ22 a RAF modified carburettor engine with Distributor? If so they were considerably down on horsepower compared to a standard engine.

[birdy]

It had the holly carb and CTI and if it pumped 130 horses in these conditions I'm a chinaman.
The 914 has the altitude compensating waste gate on the turbo so it is the same as opperating at sea leavel,giving the true rated hp with 70kg less weight less than the EJ22.


cruise=70-80mph
@4200rpm, manifold pressure at these rpm is usually 0 or less.
Max=5600rpm,with 6psi boost.
14-15LPH with full fuel

[LARRYEBOYER]

Rock, I would be interested in you keeping an update on the EJ-20 turbocharged engine. It is my understanding the turbo can be set mechanically to come in at 3000 to start the boost. I have a EJ-20 STI FI WRX engine that was rebuilt and ported and balanced. I was going to put it on my new RAF but decided to go with the EJ-22 with a cam grind. I was concerened with to much power. I understand GATES makes a super strong 60mm belt able to handle 250+ HP. I would like to see the finished engine installation on the RAF. I may change engines later on if it works well for your friend. Parham told me he thought the EJ-20 would make an excellent direct drive. Boost it at 3000RPM andturn it to 4000. About 160hp!

[rfi]

A standard 85 MM wide HTD belt is marginal on an EJ25. The new GT-2 Gates belt which has random Aramid fibers embedded in the Neoprene teeth allow the belt to handle 70% more power than a stock belt.

In fact, a Gates engineer said, unofficially and off the record that an 85 MM wide belt would handle 270 Hp. A 60 MM GT-2 belt would be good for 170 Hp but not 270 as Larry mentioned. The EJ25 should develop adequate Hp at a mile high, especially with the Stratus cam grind which increases power from 165 to 180+.

The EJ20 is pretty much a bullet proof engine and will run wide open days on end. In 1991 an endurance test was run on a government test track near Tucson, AZ during August where temperatures reach as much as 110 degrees. Three Subaru Legacy autos with turbocharged EJ20 engines were run non-stop for 100,000 Km (62,000 Miles) in 18 days at an average speed of 130+ miles per hour. The autos were only stopped long enough to refuel and/or change drivers. All three engines completed the endurance run without a problem.

It is true that the EJ20 could be used direct drive. I have several customers that are flying direct drive EJ22 engines on gyros and fixed wing aircraft. One installation which is on a Europa airplane has over 600 hours of flight time. The only problem with direct drive is that a smaller diameter propeller has to be used which reduces efficiency and increases noise.

[Hognose]

The problem with rated horsepower is that you don't fly with rated horsepower -- you fly with thrust, and horsepower is only one piece of that puzzle (the prop's another piece, and the best prop at sea level on a standard day is a different animal from the best prop at a density altitude of 5000'.

That said, continuous rated HP of the 914UL is the same as the 912S -- 100HP. The 914 has a takeoff power setting for 115 HP, but you are limited to five minutes. So the best way of looking at a 914 is probably as a turbonormalized 912 (it is not strictly speaking, in the literal sense, turbonormalized... but that's the effect).

The 914 is about 170lb installed, complete with accessories and fluids. A soob is 200 and up.

cheers

-=K=-

[KenSandyEggo]

Speaking of Gates Belts, I just looked at a new NAPA belt I have for my alternator in my hangar, and they are made by Gates for NAPA. My NAPA prerotator belt is from NAPA and I've had it on there for several years and my prerotator gets quite a workout while waiting for takeoff at my homefield. I took off the 85mm drive belt (Gates GT2) a few weeks ago after several hundred hours for replacement, and it looked brand new. Not one sign of wear.

Speaking of Rotax, Birdy says his Rotax-equipped RAF performs better than with the Soob. I've flown 1,000+ lb. Ercoupes with a mere 85 h.p. and they've performed fine. I flew one with a 100 h.p. 0-200 and it felt like a rocketship compared to my 85 horser. I just wonder what h.p. we are really getting from the EJ-22. If a 100 horse Rotax outperforms it (according to Birdy), I'm wondering what a new 125 h.p. Continental with Fadec would do on mine.....or a Lyc 0-235. Gee, I wish I had a couple cardboard boxes of money laying around somewhere.

[Heron]

HIgh density alttitude? Or low density at high alttitude
I am confused . . .
Heron

[Udi]

Same thing, Heron.

[Envy]

Maybe there is more correct to weigh not HP but maximum statical thrust?

RAF-2000 carb EJ 22 (single CTI) with standart propeller shows 270 kg maximum thrust... (Sorry, no more details know about that.)

[Cobra]

I believe some of the rated power vs seat of the pants performance dichotomy is due to confusing torque with hp. HP is more a function of rpm- high revving engines have great hp numbers, but generally they sacrifice usable mid range torque for high rpm capability. Trouble is, torque is the more important number for spinning a propeller. Turbos normally provide a big improvement to torque output in the mid range (3000-4500 RPM) and extend the torque curve dropoff to higher rpm levels, which also yield big HP numbers.

My guess: the automotive turbochargers (like the sti) will need an aftermarket adjustable boost control (or adjustable waste gate controller) when used in a constant load environment, something that will regulate the boost levels to lower levels than employed in the automotive industry (maybe 3-5 psi normal, and up to 8 psi under temporary full power conditions). The turbocharged engine will provide two improvements over naturally aspirated applications- it will provide an (adjustable) increase in the effective displacement of any engine (power when you need it, better economy than larger engines during cruise), and it will compensate for lower oxygen densities at higher atlitudes. It will provide full rated engine power at higher altitudes, but not help the lower bite of the rotor/propeller due to less dense air.

Naturally aspirated engines lose something like 20-25% of their rated output at altitudes above 5000 ft. Forceed induction can bring back that lost power safely if controlled to allow only moderate boost levels; but turbocharging can also provide much more power than needed if boost levels are not limited, which is not necessarily a positive attribute if overdone, leading to overheating or overpowering the drirvetrain.

I really feel that any high altitude engine should have some type of forced induction; and turbocharging is more efficient than supercharging, but harder to control and tune. My concern with the high output cammed engines is that they may have too high compression for forced induction (leads to detonation), and that the valve overlap is too great to allow the mid range torque improvement that a turbocharged system provides.

[PW_Plack]

Mike,

How do you and others arrive at the claim that torque is more important? The torque rating of an aircraft engine is almost meaningless unless you're forced for some reason to operate it at a specific RPM. And torque at a given RPM is what horsepower is.

Thrust is created by horsepower, not torque. Horsepower is a measure of work performed. Torque is just the measure of twisting force, independent of RPM. If you have engines with identical torque outputs at different RPM, and props chosen and pitched to load the engines fully at those RPMs, the faster-spinning engine will always make more thrust, because it makes more horsepower.

If you weigh 212 pounds, and stand on the end of a 6-inch long box-end wrench, you'll generate 106 pound-feet of torque on the nut, same as the maximum torque output of a Rotax 914. I'll bet you can't make as much thrust turning a propeller with your wrench as the Rotax can at 4900 RPM!

In cars, where the drivetrain is directly coupled to the ground, low-speed torque matters because the engine must accelerate the mass of the vehicle from a standing start, and over a wide range of RPM. It is less critical in a car with an automatic transmission, because the torque converter allows the engine to operate at higher RPMs during acceleration from a stop. In an aircraft, the engine sees very little load until it nears maximum operating RPM, and can be run to within a few per cent of redline before the aircraft even starts moving.

In theory, it would be possible to have an engine so peaky that it couldn't reach the RPM of max horsepower before prop loads held it back, but such an engine would have enough other problems you wouldn't want to fly it anyway.

[Cobra]

Paul,
I believe we are saying the same thing, but from opposite sides. HP and torque are interchangable, but only through a transmission. You are looking at the tranny output forces, Im looking at the tranny input forces. Id be happy to defer to your experience at this point, since I have no aircraft experience to speak of- but I do know a bit about engines and (I believe) the application is the same.

If you look at a dynograph chart- the torque curve rises to a peak between 3000 and 4000 rpm with most automotive engines, then drops as the engine chokes for enough air to continue the performance gain. The RPM curve slowly rises until it crosses the torque curve at 5500 rpm (by definition), then it falls off as torque crashes further. The HP curve is dependent on rpm and torque, but mostly engine speed. Dynos measure torque (through acceleration of a known mass) and then calculate HP with data from the tachometer. Because of the HP formula, you can increase HP either by building and/or extending torque output, or by increasing RPMs- these are generally mutually exclusive tasks.

The torque peak is the point where the engine produces its best abdiabatic efficiency and also, its peak combustion pressures. It is also the point where the engine produces the most twisting force on the crankshaft, but like you said, it means nothing unless the crank is spinning and doing work (adds the time element into the equasion).

We normally trade HP for usable torque with gearing, but the IDEAL scenario for any performance application is to build a torque curve that rises right up to the redline- which by the way, also assures a big HP number. My point, forced induction allows the engine to continue the peak torque peak to a higher rpm than the atmospheric-pressure inducted motor can, especially at higher altitudes when the available oxygen thins.

Many Japanese rev-happy perfiormance motors generate splashy peak hp numbers, similiar PEAK numbers to high displacement muscle cars. Experience will tell you that the real fun driving machines (the ones that nail your back to the seat) are the bigblocks that build big torque numbers early- and they are also more durable as well- like the huge rotary fighter engines of old.
Becuse of weight restraints, we need to use reduction drives with small engines to multiply the torque output enought to spin the propellers fast enough to create thrust. If an engine had sufficient mid range torque to cruise with, you would not need a reduction unit at all.

[TKorrison]

A question for the High Altitude group. I have installed a new 2.5 liter Subrau on my SH. This engine is rated at 165 HP at 5600 Rpm. I think this engine will put out between 175 and 180 HP with all of the extra stuff removed. I am currently running a 72" magnum prop. I am thinking about installing a variable pitch Ivopro prop to solve the altitude question.. Any thoughts about this. :rolleyes:

Tom Korrison
AAI Gyroplanes of San Diego
tomk@xmission.com

[KenSandyEggo]

Tom, we're at sea level in San Diego! What altitude question? You can fly over the mountains to Arizona by barely scraping 4,000 ft. O.K. Where you thinking of going? :cool:

[ventana7]

I am not sure of why anyone is interested in a variable prop on a gyro. In a fixed wing where you might do a climb of 5,000- 15,000 feet in one crack it makes sense. But why do you need it in a gyro?
Rob

[ventana7]

Tom,

I'm not sure if you saw my other post but last week I took a flight with Pat McNear in his RAF with the 2.5 and a 70" prop. With 2 of us at sea level we were climbing out at over 1,000 fpm without even using full power.
In my AAI modifed RAF with 2.2 and 68"WD when solo I start descending at anything under about 4200 rpm. In Pat's machine we were cruising with 2 of us at that rpm.
Rob

[Ruidoso Ron]

Rob,
What would you estimate the service ceiling to be with the 2.5, at gross ,on either the SH or the RAF?

[CLS447]

Shar & I both got a ride with Pat Mcnear at ROC. Man, is that a rocketship or what?

I believe that is a stock 2.5(no cams)? I want one!

[KenSandyEggo]

Rob, I can reduce my cruise rpm by about 1,000 rpm and increase my speed with my IVO cockpit-controlled prop. I can also pitch it to turn 5400 pm for max take-off power. Plus it wows the airport rats. I wouldn't say I "need" it, but it's nice with my 2.2. Gives me a little extra on both ends.

[TKorrison]

Ken,
We want to be able to fly demos at various airports such as Denver, Aspen,etc. and we have had a few request from Mt. Baldy and Mt. Baker in CA. Plus, I want to be able to optomize performance at any location. Additionally, as you suggested by lowering the cruse RPM the aircraft is considerably less irritating to the ground observer. A concern I have about flying California Beaches.
The Ivopro Prop " In Cockpit Adjustable" (Not Variabile Pitch as I labeled in the prior communication) doesn't cost much more than a Magnum Prop we are currently using.
We will also be doing our initial flights in Utah, where we are right up aginst 10,000 foot mountains. I don't want to spend money on one prop and turn around and buy another. Additionally, we would like to offer our customers an option that I think will improve the SH. But the main reason is QUITE!

By the way there is a new muffler system on the drawing board for the SH. I hope to see this sometime soon.

Thank you for all of your help with this. I appreciate your input and advice.

Tom Korrison
AAI San Diego

[TKorrison]

Ron,
I don't know yet. The Spanish Fork dealers have just replaced their 2.2 Liter engine with a 2.5 Liter engine. They do a lot of flying and training. I think they may have a better idea than I at this point in our limited experiance. If I were to guess I would say 10,500. I think Mike Burrton is getting alot of high altitude flying.

Tom Korrison
AAI San Diego

[KenSandyEggo]

Tom, while trying on his aluminum foil space-suit for high-altitude flying, posted: "I don't want to spend money on one prop and turn around and buy another."

Why not? I'm on my 3rd one... Warp, Prince and now IVO. :eek:

[CLS447]

Ken, don't think that I did not appreciate you evaluations, because I did!

[PW_Plack]

Rob,

"But why do you need it in a gyro?" One possible answer: Because I want to experiment in my experimental aircraft.

Following your premise through to its logical conclusion, "Why do you need to fly a gyro?" ;^)

[KenSandyEggo]

You went too far, Paul. I NEED to fly a gyro. I'd go nuts (nuttier) if I couldn't.

[TKorrison]

Ken,
I don'tnow what that means, but you must have a lot more money than I.
Tom

[KenSandyEggo]

Not any more. :( Is the gyro going to be (or is it) in San Diego yet? Will it be at Ramona? I'd love to see it.

(The aluminum suit was just a joke).