Turbine Super Cub

I want to say hello. I?ve been monitoring SuperCub.Org for quite a while now and have quite enjoyed it. I especially love all of the great photos in the photos section!

I?m posting now because I?ve decided to build a Super Cub in the Experimental category. The goal will be maximum STOL performance which will mean light weight, good power and a high performance wing. I am also looking for maximum utility so multiple landing gears (tundra tyres, skis and floats). I?m leaning towards VFR but also want to look at whether IFR can be done today without too much of a weight penalty.

So here is my immediate question: I?ve read about the upcoming ATP Turbine engine:

http://www.atpcoinc.com/

And I read the discussion of it here:

http://www.supercub.org/phpBB2/viewtopic.php?t=3850

At first blush this seems an ideal engine for an experimental Super Cub (light, powerful, cheap, reliable). But the more I think about it the more I see some big problems:

1) When you fly a Super Cub you often need very quick applications of power. For example, to arrest the sink rate when coming in for a landing over an obstacle at minimum controllable airspeed. I really have my doubts whether a turbine engine can ever provide this quick goosing of power.

2) Turbine engines need careful monitoring. You really need to pay attention to the power settings to avoid overpowering the engine. There isn?t the obvious feedback you get on a reciprocating engine. With a reciprocating engine, you can basically just shove in the power and go. A turbine will just give more and more power until it destroys itself. I?m not sure a short field takeoff over an obstacle in a single-pilot aircraft is exactly the right situation for this sort of careful monitoring of the power setting.

I can imagine that technology could take care of the second problem but what about the first? Is the power availability quick enough on these engines to do the job? Or possibly are the weight savings and performance advantages enough with a turbine engine to justify putting up with these problems?

Curious what others think???

Stephen

What's it like on Mars? As far as the turbine goes Do you like the smell of raw jet fuel? I don't. I spill gas once in a while when I'm fueling the cub and it goes right down into thewing -no big deal,but jet fuel is another story. Take the same money and tweak a 180 or better yet build your plane with a 150 then after you know what there is to know about your new plane convert to jet. That will give the turbine guys time to get there stuff and kit ready. That's only if you like the smell of jet fuel. turbine is novel but for the cub it's not for me.

Stephen

Needless to say I have no knowledge about flying a turbine powered Super Cub but can pass on some thoughts about flying the P&W powered PC6 Porter.

First of all, a turbine engine, even the APU type used for the Super Cubs, are really not inexpensive. Maintenance costs are less until engine change.

When flying an aircraft with the turbine engine out front, you really get so you notice the audio at any given power setting. A person gets to understand both the engine and prop sounds real fast. Both prop and power levers on the Porter are next to each other and controlled by one hand at the same time and I would assume that would be the same in a Super Cub. Actually, I found that you can really get just as rapid power response from a turbine prop as you can with a recip prop most of the time. Power (RPM) is always maintained and than all it takes is changing the prop position. That is where a turbo prop differs from the jets on commercial airliners. I probably am not saying all this right but that is what it amounts to. Just prior to landing, power is brought back up (spooled up) and than go into ground fine setting (or more but never bata) for the prop with the same rpm setting for the engine. Talk about a speed brake. Need more power, change the prop setting, it will lay you back in the seat real fast.

What I know about flying the turbine Porter came from one of our company pilots from Kotzebue who knew everything that the Porter could do, inside and out. He did a vertical dive one time and we never got over 90 knots. What a weird feeling. All he did was put in a little bata (reverse prop) like trying to back up. Book says never to do that but what that the heck, he said he never learned how to read in school anyway.

Our Twin Otter pilots flew those aircraft, engine wise, far different than the Porter pilots did although the same basic engine, just different situations. Some of our Porter pilots may have not always understood these things.

http://www.supercub.org/gallery/view_photo.php?set_albumName=album87&id=aad

From what I have read, the turbine powered Super Cub would really be something to fly. Poor man's Porter? Those APU engines have a long history of maintenance free operations.

As with a recip engine, fuel controls the RPM of an engine and it is the same with a turbine. There is a max setting you can obtain, usually around 110% of designed limits. The N1 temperatures (operating temperatures) will go into the red real fast at that setting. Red is a no-no of course. Usually for a turbine, 90% more or less, is the normal power setting for take off. Higher if weight requires say to 93% but 98% is too normally too high. Still, to clear that 50 foot tree, you might still have 10% more power available for a few seconds without hurting the engine although it does take a second or two to spool that up. When the temps get too hot in a turbine, pulling the power back cuts back on the fuel and instant reduction in temperatures without a sudden loss in power. Gee, hope I said that right. When making a take off, just a millisecond to denote the color of the power gauge is all it takes to control power. Forget the numbers if need be, if it is red, pull the power back a fraction. Does not really distract from controlling the aircraft. Just something to get used to but normal once you have learned it.

Never any carb ice either. Word of caution, the steady sound of a turbine tends to lull a person into a dozing mode at times. Not like the hiccup from a recip to wake you up.

Keep in mind also that there is very little if any preheating needed on a turbine. Stick the heater hose under the panel and warm up the instruments and radios instead. Keep right on flying beyond 40 below zero if necessary. Just think of the cost savings too. No oil changes, jet fuel costs less than av gas. No muffler repairs and talk about no vibrations. Wow.

I suspect you could do the same thing with a turbine powered Super Cub that can be done with the Porter. Hang it on a prop just right and it will not stall but just mush forward at about 5 knots. What a feeling that is.

I had a friend from Ruby, Alaska that flew turbine powered DC-3s for a while. What an aircraft really but just not right for his operation. He was even sent a tri turbine powered 3 to tryout for a while at no charge.
If a turbine powered DC-3 is good, so would a Super Cub.

Hope this might give you some more ideas for questions.

Can't recall what the atmosphere is like on mars, maybe rocket power would be more suitable for you? This nut-job should be able to help you out http://www.rocketguy.com/oldhome.html[/url]

Phil Kite said:

Can't recall what the atmosphere is like on mars, maybe rocket power would be more suitable for you? This nut-job should be able to help you out http://www.rocketguy.com/oldhome.html[/url]

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Alas, I gave up on visiting Earth long ago. No intelligent life present. :roll:

Sorry guys. ?Mars? is just a habit I picked up from posting on some of the car related boards. Sometimes it isn?t a good idea to let people know where nice cars are located. They vanish with much greater regularity than do Super Cubs.

I travel a lot. I?m currently in Connecticut though soon I will be in Europe. My home is actually Hongkong. So Mars isn?t that far from being accurate.

Stephen

FORTYSIX12 said:

As far as the turbine goes Do you like the smell of raw jet fuel? I don't. I spill gas once in a while when I'm fueling the cub and it goes right down into thewing -no big deal,but jet fuel is another story. Take the same money and tweak a 180 or better yet build your plane with a 150 then after you know what there is to know about your new plane convert to jet. That will give the turbine guys time to get there stuff and kit ready. That's only if you like the smell of jet fuel. turbine is novel but for the cub it's not for me.

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I love the smell of Jet A in the morning! :-D

Seriously though, a turbine has a reciprocating engine beat in every way when it comes to fuel.

100LL is unreliable at this point because of the lead issue and the fact that there is only a single supplier for the additive today. Elsewhere in the world, you often need to arrange 100LL to be delivered in 55 gallon drums. On the other hand, Jet A is available absolutely everywhere that commercial jets fly.

Jet A is often much cheaper than 100LL in the rest of the world.

Auto fuel can only be used in certain engines. If using auto fuel in an aircraft is a criteria then this restricts which engines may be used. If I were to use a reciprocating engine then I would want to be able to use auto fuel so as to not to be subject to 100LL availability issues.

One of the things I?m considering on the design is how quickly and easily the aircraft can be broken down to its component parts, put in a shipping container and then reassembled in some third-world country using the available resources there.

Then the advantage of a turbine engine on an Experimental category aircraft are even greater. You can burn absolutely anything in it including auto diesel and even untaxed home heating oil.

The only down side seems to be the additional fuel that a turbine will burn and the need to carry this. But the engine weighs less and I suspect this will offset any additional weight required for the fuel (which is only necessary in any case for a long trip).

As for starting with a reciprocating engine and then converting to a turbine later, the weights of the engines will be different so the weight and balance different. Hanging the engine further off the front might not be ideal for visibility reasons. So if the aircraft was designed initially to take the turbine it might be possible to design it to reduce this overhang. Also, there will be different instrumentation and fuel needs for the two versions. So I don?t think it makes sense to start with a reciprocating engine and convert later.

Stephen

AlaskaAV said:

Needless to say I have no knowledge about flying a turbine powered Super Cub but can pass on some thoughts about flying the P&W powered PC6 Porter.

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Wow Earnie, thanx for the great post! Just reading what you say gives me goose bumps. If a Super Cub can be made to do what you say then it would be a pretty incredible flying machine. In fact, I would think even more so than the Porter due to the lower weight and therefore the quicker reaction of the aircraft to power changes.

Though it is also pretty obvious that the operator would need to learn a bunch of different procedures to really take advantage of the turbine. That should be a challenge. Also, I get the impression that it would be a lot easier to really f**k up.

But lots of smooth power, available anytime, available even at altitude, available even in the super cold, these seem to be the stuff of Super Cub fantasy. This definitely seems to be the way to go.

Stephen

FixedWing said:

AlaskaAV said:

Needless to say I have no knowledge about flying a turbine powered Super Cub but can pass on some thoughts about flying the P&W powered PC6 Porter.

Click to expand...

Wow Earnie, thanx for the great post! Just reading what you say gives me goose bumps. If a Super Cub can be made to do what you say then it would be a pretty incredible flying machine. In fact, I would think even more so than the Porter due to the lower weight and therefore the quicker reaction of the aircraft to power changes.

Though it is also pretty obvious that the operator would need to learn a bunch of different procedures to really take advantage of the turbine. That should be a challenge. Also, I get the impression that it would be a lot easier to really f**k up.

But lots of smooth power, available anytime, available even at altitude, available even in the super cold, these seem to be the stuff of Super Cub fantasy. This definitely seems to be the way to go.

Stephen

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Not as much difference than you might expect. The Porter has around 600 shaft horsepower and am not sure what the turbines for the Cubs come out at but suspect, pound to horsepower, they will be about the same. It all goes back to hp. If a turbine Cub had a turbine engine that produces only 180 hp, it will perform much the same as a recip I would think. My experience with the Porter was just after they started building them. Wien Porters started with S/N in the 50s. We had both a recip and turbine Porters and the recip was almost useless as far as I was concerned. Way under powered.
We had one Porter on amphib floats and what an aircraft properly flown. Really nice backing it up on a beach (and hope the pilot didn't forget to lift the water rudders). Full reverse props are great unless too much power is applied to back up and if that happens, it dunks the engine and prop right into the water immediately. Bye bye engine. It only happens once per pilot though.

Once a person gets checked out on turbine power, there would not really be that much difference than a recip Super Cub I would think. With either one, when you get to that bunch of trees on the departure end of the runway, it will climb like a homesick angle so to speak.

To get a good idea how far forward the engine has to be mounted on a Cub modification, take a look at the turbine modification of the Beaver and Otter. One good thing is the extra baggage compartment located behind the engine and in front of the firewall which helps on w&b.

Contrary to some comments, a person must be rather careful about the fuel that is used. They will burn regular gas of course but at a given number of hours (which is rather low), the engine has to be pulled apart and inspected. It all goes back to temperatures and sulfur content. Diesel has way too much sulfur and JP-4 is too hot. Jet A-1 and A-50 works good and probably some newer blends that I am not aware of.

I know one thing, I would love to take the stick on a turbine powered Cub.

AlaskaAV said:

The Porter has around 600 shaft horsepower and am not sure what the turbines for the Cubs come out at but suspect, pound to horsepower, they will be about the same. It all goes back to hp. If a turbine Cub had a turbine engine that produces only 180 hp, it will perform much the same as a recip I would think.

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The specific turbine engine i'm looking at is the ATP (Affordable Turbine Power) 6.5. The developer quotes:

Model 6.5 is a radial turbine in conjunction with a compound planetary gearbox. It has ram air induction and electronic fuel injection system. The Model 6.5 maintains static thrust using a NSI cap 140 propeller. The engine is capable of on-demand HP ranging from 120 HP to 240 HP. The Model 6.5 is available in a pusher or a tractor configuration. It's dimensions are : 32" in length to prop flange, 12 1/2" in diameter at the hot section and 10" diameter at the gear box, 16" in height at the accessory pad on the gear box. The Model 6.5 will burn JetA, Kerosene, Diesel and Gasoline, with JetA and Kerosene being the preferred fuel.

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http://www.atpcoinc.com/Pages/Products.html

So the available power exceeds that on almost any reciprocating Super Cub currently out there. Combine that with the under 200 lb. weight which should allow a lighter Super Cub for what should be top STOL performance!

Elsewhere I have read that they are quoting an intial cost of US$35K and a TBO of 5000 hours with a overhaul cost of $7,500 so this also beats a reciprocating engine. Fuel flow also looks good with 10.7 gph at 120 bhp which is the power I would guess would be needed to cruise a Super Cub.

Availability is said to be for AirVenture / Oshkosh 2004.

Here is a photo:



Stephen

Those numbers look real good Stephen, especially the available hp.

When they say it will burn diesel, I suspect they refer to #1 diesel which is not always available except in the winter in the northern states. Arctic grade diesel in Alaska. Big rig truckers often have to run a fuel additive to keep even #1 from jelling in the winter. I suspect the engine manufacturer would really frown on using that additive.

AlaskaAV said:

Those numbers look real good Stephen, especially the available hp.

When they say it will burn diesel, I suspect they refer to #1 diesel which is not always available except in the winter in the northern states. Arctic grade diesel in Alaska. Big rig truckers often have to run a fuel additive to keep even #1 from jelling in the winter. I suspect the engine manufacturer would really frown on using that additive.

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I agree completely. The numbers all look excellent. And now after hearing your comments I feel a lot better about the idea of operating one in a Super Cub.

I'm not too concerned about whether I need to operate JetA or can use auto diesel. Already JetA represents a savings over 100LL. And in fact, in Europe and many other places the savings can be even more dramatic as JetA is considered "international" fuel for airlines (therefore not taxed just as export booze is considered duty-free and not taxed) whereas 100LL is heavily taxes (domestic fuel for playboys).

The appeal is that in a push it will burn just about anything -- even gasoline. This is quite a feature for an airplane that you want to be able to use in unusual places. Since it will be the exception rather than the rule, I don't think the reduced life of the engine will be that big of a consideration.

Anyway, here is another interesting photo I came across which shows the ATP mounted to a Super Cub. Not a lot of room actually behind the engine:



[Photo credit: http://www.pilotlist.org/balades/oshkosh/stand_01.htm -- click on photo for full-sized version.]

Things certainly are becoming more exciting in general aviation.

Stephen

If you look real close, you will notice that with a cawling on, it will narrow down a lot near the prop. Helps cut down on drag but also helps during taxing. I really like the way the installation went in the photo. Nice and clean.

At one point in the 60s, I asked our Porter pilot (the one that taught me how to fly the Porter) for a minimum fuel flight to a town some 15 or so miles away so I could move a big backlog of mail. He took it with fuel on board. Once he got upstairs, big deal, probably 500 foot or less (he liked to fly low so he could count the sheefish in the Kobuk River enroute), he noticed the gauges were showing a little less fuel than he thought he had. Upon landing at Shungnak and offloading, he bought and paid for 5 gal of car gas just in case. He said it made him feel a little better getting back to our airport. Since it only involved just a few minutes and it was mixed probably 50% with jet fuel, it didn't require a report to maintenance.

I envy you. I would really enjoy being around a project like what you are looking at. Kind of like when I built up a big bad Chevy engine for a 1929 Ford roadster and raced it at the airbase in Lincoln, Ne back in the mid 50s.

AlaskaAV said:

If you look real close, you will notice that with a cawling on, it will narrow down a lot near the prop. Helps cut down on drag but also helps during taxing. I really like the way the installation went in the photo. Nice and clean.

At one point in the 60s, I asked our Porter pilot (the one that taught me how to fly the Porter) for a minimum fuel flight to a town some 15 or so miles away so I could move a big backlog of mail. He took it with fuel on board. Once he got upstairs, big deal, probably 500 foot or less (he liked to fly low so he could count the sheefish in the Kobuk River enroute), he noticed the gauges were showing a little less fuel than he thought he had. Upon landing at Shungnak and offloading, he bought and paid for 5 gal of car gas just in case. He said it made him feel a little better getting back to our airport. Since it only involved just a few minutes and it was mixed probably 50% with jet fuel, it didn't require a report to maintenance.

I envy you. I would really enjoy being around a project like what you are looking at. Kind of like when I built up a big bad Chevy engine for a 1929 Ford roadster and raced it at the airbase in Lincoln, Ne back in the mid 50s.

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You are totally correct about the cowling. Take a look at this photo of an RV-4 (or is it an 8?) with the ATP engine:



Now, the RV is hardly a big aircraft!

You are right about the goal. Part of it is exactly as I said, to have an aircraft which can be operated just about anywhere in the world. I really do intend to take it to places like Australia, Africa, Asia, etc. But the other part is about building ultimate hard-core machine -- just like your bad-ass 1929 roadster.

Stephen

Hey, I trashed a Chrysler Hemi powered T pickup with my good old home built Chevy the first time out on the drag strip at Lincoln. Eight thousand + RPM. Not bad for a 304 inch chev and I was working it for sure. Just had to beat that hemi because the Hemi driver knew he had me beat but I knew better. The butterflies got to me after the race and far worse than after my first solo with the J-3.

I suppose it would be fun to take a bird like you are thinking of all over the world but don't forget, you have the best country in the whole world right next door, Canada and Alaska, let alone the areas of the continental US. Well, maybe the Andes in South America would be interesting but make sure you have O2. It would take a lifetime just to explore those areas.
An airstrip just about anywhere you want to land. Stick a small mountain tent and mountain climbing survival equipment in the back along with some dehydrated food (tastes good now days) and a can or two of gel alcohol fuel to warm things up with and some water purification tablets and when you get into the mountains, you will never want to leave. Oh yes, don't forget the fishing equipment (but no firearms) and an old, well oiled cast iron frying pan, the kind that a spouse hits the other spouse with when they have been bad as seen on TV. All the animals (except bears, moose and elk) and especially the wolverine, will be just as curious about you as you are about them and with the right motions and sounds, you will become friends in no time. Been there, done that. Only thing better is sex I suppose. By the way, did I mention that a proper copilot is a must?

Ah, aviation, the only way to fly (or live).

AlaskaAV said:

I suppose it would be fun to take a bird like you are thinking of all over the world but don't forget, you have the best country in the whole world right next door, Canada and Alaska, let alone the areas of the continental US. Well, maybe the Andes in South America would be interesting but make sure you have O2. It would take a lifetime just to explore those areas.
An airstrip just about anywhere you want to land. Stick a small mountain tent and mountain climbing survival equipment in the back along with some dehydrated food (tastes good now days) and a can or two of gel alcohol fuel to warm things up with and some water purification tablets and when you get into the mountains, you will never want to leave. Oh yes, don't forget the fishing equipment (but no firearms) and an old, well oiled cast iron frying pan, the kind that a spouse hits the other spouse with when they have been bad as seen on TV. All the animals (except bears, moose and elk) and especially the wolverine, will be just as curious about you as you are about them and with the right motions and sounds, you will become friends in no time. Been there, done that. Only thing better is sex I suppose. By the way, did I mention that a proper copilot is a must?

Ah, aviation, the only way to fly (or live).

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I totally agree with everything you say and especially with your comments about exploring one's backyard first.

Thanx Ernie for all of the great input! It has cleared up a lot of doubts for me.

Thought one more photo might be useful. This is the front of the RV-4 with the ATP turbine. It really makes your point about the frontal area being so small!



Stephen

This is a J3 airframe but it will give n idea of thenose shape and length.

http://groups.yahoo.com/group/piper-cub-builders/files/Turbo-Prop/

People have said turbines were the way of the future...

John Scott

OOps....it requires a password to view. I'll try to post another way.

John Scott

Longwinglover said:

This is a J3 airframe but it will give n idea of thenose shape and length.

http://groups.yahoo.com/group/piper-cub-builders/files/Turbo-Prop/

People have said turbines were the way of the future...

John Scott

Click to expand...

I post this photo totally without comment.



Stephen

I can maybe understand a turbine on a 18 or a 12, but on a J-3??

I think they're pulling our leg. Looks like butcher paper. :roll:

Eddy Current said:

I think they're pulling our leg. Looks like butcher paper. :roll:

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Yes, but very nicely formed butcher's paper. :lol:



Stephen

The picture you showed further up the page looks like the Smith Aviation Xp Supercub. Here's another picture (from Sun N Fun this year)



Pete

CrossedControls said:

The picture you showed further up the page looks like the Smith Aviation Xp Supercub. Here's another picture (from Sun N Fun this year)...

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The photo I posted was supposedly taken at Oshkosh 2003.

The prop in the earlier photo seems to be a variable pitch prop. But the prop on your photo seems to not be variable pitch. Is it just a mock-up? I would think a turbine engine must use a variable pitch prop.

Stephen

FixedWing said:

CrossedControls said:

The picture you showed further up the page looks like the Smith Aviation Xp Supercub. Here's another picture (from Sun N Fun this year)...

Click to expand...

The photo I posted was supposedly taken at Oshkosh 2003.

The prop in the earlier photo seems to be a variable pitch prop. But the prop on your photo seems to not be variable pitch. Is it just a mock-up? I would think a turbine engine must use a variable pitch prop.

Stephen

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It has to a variable pitch prop otherwise it would be almost impossible to fly at slow speeds. It has to keep the engine rpm up because it would take too long to spool up in an emergency (every landing). Even a full jet such as a 737 spools up maybe 25 per cent prior to the "fence" for the same reason. A turbo prop on a small aircraft is really great and as I have said before, I would love to fly a turbine powered Cub. What a pleasure that would be.

It was interesting with the P&W powered Porters where a person can hold a prop blade while the pilot spins it up and lights it up. It will actually bend the prop blade but still in place. It has to be released soon so the hub end of the prop can shove some cooling air around the engine or it will get too hot very fast.

The P&W powered Porters were always shut down in feathered position while the Astazou powered were shut down in ground fine just as the Garrets were on the Skyvans. Just the way those engines were designed.

Look at the pitch on the fixed pitch prop above... Which direction is the engine going to turn it? Also, it looks like it is on backwards. The planform shown at the prop tip shows the cambered side to the rear...

Don't you know that a TURBINE powered Super Cub will have such incredable performance that it will be able to fly BACKWARDS!!??!!

In calm wind and tailwind (up to 150kts) conditions!

John Scott

Eddy Current said:

Look at the pitch on the fixed pitch prop above... Which direction is the engine going to turn it? Also, it looks like it is on backwards. The planform shown at the prop tip shows the cambered side to the rear...

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Which is why I thought it was just a mock-up to make for a better display. Guys like looking at big props.

Stephen

My picture of the Smith Cub had the ATP turbine, don't know about the prop. Here is a pic taken at Osh 2003. The ATP turbine guys had a booth alongside Smith Aviation. Send Nick Smith an e-mail I'm sure he would fill you in with all the details.




Pete

check out the 368kb video in this link.

http://www.atpcoinc.com/Pages/Requests.html

I dont think this power plant will have trouble spooling up quick enough.

Jacob Papp said:

check out the 368kb video in this link.

http://www.atpcoinc.com/Pages/Requests.html

I dont think this power plant will have trouble spooling up quick enough.

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Yes, I saw that video. Pretty impressive. Can you imagine a Cub making a sound like that in some valley or on a small pond somewhere? Hmmm... music to our ears but I wonder if everyone will appreciate it? It might not be a good thing if too many of these turbine Super Cubs are around. In fact, I wonder if noise will be an issue?

As for the spool-up, I would think zero-load would be one thing, but how quickly will it spool up with a load? If you watch the fuel flow figures it takes a little while before those go up. I would think that is an indication of the load they are putting on the engine.

Still, it sounds like one of the design criteria for this engine is quick spool-up. I'll be very interested to hear the results once these engines are in the hands of end-users who can report their findings.

Stephen