IVO Prop?

[marbleturtle]

At Oshkosh, I attended 2 of the Atkins rotary forums. At one point, Mr. Atkins mentioned he was running with an IVO prop and half the room moaned. Then I just happened to walk by the IVO prop booth. While I was playing with the display, the IVO rep at the booth mentioned that the previous "problems" had been resolved.

 

Anyone know the details? How about whether or not improvements have been made?

 

Just curious...

[Jim Sower]

Ivo has a VERY bad name in the canard community - some of it deserved and some of it not. The basic problem has to do with shedding blades. Basically, the blades are not structurally connected to each other. Each blade has two bolts holding it on the airplane, and there is a gap (however small) between adjacent blades. This is a fundamentally shaky situation, that can be alleviated (if not eliminated) by meticulous and frequent torquing of the blades. To monitor blade relative movement, there is a piece of tape across the interblade gap of each blade that is to be inspected on preflight. If the tape is broken, the prop is hard down until the PROBLEM that CAUSED the tape to break (the blades to separate) is corrected.

 

The serious problems (as in accidents) have all occurred on O-360 engines that are notorious for vibration and torque reversal. These conditions are much reduced on a 6-banger, and virtually nonexistant on a rotary with redrive. Pusher applications involve much more flexing than tractor applications

 

The most infamous fatal accident involved a Velocity that had the pitch motor run away to full coarse pitch. The guy field stripped the prop, disconnected the motor, ground adjusted the prop to fine (T/O and climb) pitch [improperly I hear], reinstalled it [improperly I hear], torqued it [improperly I hear, or not at all] and launched on a longish (three hour or so) flight at night. The prop shed a blade and he and his family were killed. There is no doubt that he was flying on instruments (in the sense that there's no visual reference to the horizon when you have your head up your ass...) but the fact remains that a Performance or Catto prop CANNOT shed a blade unless you break it by passing a large, structural object (a Catto prop has survived the shedding of the lower cowl of a Long-EZ) going throuh it.

 

The design is fundamentally delicate. This can be Compensated for, but I personally would prefer a product that doesn't require so much compensation. From a performance perspective, it is pretty marginal as a "variable pitch" prop since only the outboard portion of the blade (that is physically twisted by a torque rod driven by the electric motor) changes pitch. At high/course (cruise) pitch, the inboard portion of the blade can have zero (unproductive) or even negative (counterproductive) AOA. The "magnum" prop is aleged to reduce this effect, but it's still there even if it is less prominent.

 

At this juncture, I plan to fly my rotary Cozy with the Catto prop from hell - very wide chord and pitched from here to yonder.

 

Just a theory ... Jim S.

[marbleturtle]

I was planning on the same... but in a previous post you mentioned that with the lower drag with retracts, and the higher power of the rotary (both of which I'm planning to do), you would need a adjustable prop.

 

If you go fixed, what pitch are you going to use?

[Jim Sower]

A constant speed prop sounds ideal but would be waaaay too expensive and probably too heavy. IVO is pretty much the only adjustable available and I have enough troubles without worrying about shedding blades or constantly maintaining the prop. I haven't gotten all that far in the design yet, but Greg Richter and John Slade both use performance props. I need to talk to Richter about how his worked out, and wait until John gets flying and see what his does. There will be lots and LOTS of progress in these areas long before either one of us needs to make a final decision.

[dust]

I'm buying a MT prop for only 9200

 

Just 2200 more than my engine

[marbleturtle]

I almost agree with you that we have time... but some of the decisions have a cascade affect.

 

Let's assume I decide down the road that an adjustable prop is a bad idea... okay. Did I just throw away $4000 on retracts that I installed early on? Do I now need a fixed prop so coarse (to take advantage of the reduced drag) that it cavitates on take off or climb?

 

Rats... I'm not coughing up $12k for a CS prop!

 

Now I need to rip out the gear, the center 5 gallon header gas tank, build fixed gear bulkheads (installing those after the fact should be easy!), put the foam block spacers back in the two primary gas tanks...

 

Some things should be worked out in advance!

[HM Andersen]

You might want to check this www.rospeller-aero.com .

This is a german manufacturer.Claimed to be for rotax and others,they got diameters up to 70`.It might work with other engines at a price about 4000$.

HM

[unick3]

Actually, I see little need for a constant speed prop. The only advantage of one (given you have a properly sized cruise prop) is improved performace on take off.

 

Our plane already have an excellent climb rate without a CS prop. In cruise there is no advantage, so you are paying LOT of $$$ for a prop which needs maintence and is heavy for more climb. In certain application such as a Cessna or a dirty plane it makes more sense, but not in our planes. I like to keep it simple, light and cheap.

[dust]

I've been told that with a turbo, which these rotery guys are also installing, that a cs prop is needed to get enough bite at altitude

 

Why spent 12000 when the mt is 9200?

 

Enjoy the build

[marbleturtle]

With some of the numbers I've been going through... a prop coarse enough to take advantage of low drag and high power would be a problem on take off at gross.

[marbleturtle]

Hey dust... has the MT been difficult to set up or work with?

[dust]

I'll tell you next year when i do it

 

Enjoy the build

[bradcrawfo]

Not really many prop options out there...Perf props have had some problems also...recently a good friends two blade wood prop came apart on his RV-4..no one is immune...the early Ivos were really ultralight props that guys put on longs and varis and low and behold they came off..go figure!...Ivo has never recommened any of his props even the newer higher horsepower ones for the higher horsepower 4 cyl engines....Yet they are recommened on the 6 cyls...and Velocity has recommended and tested them on the Franklin..with much improved takeoff performance..if you have a 4 cyl...it's all up too you...There have been no incidents with 6 cyls that I can tell..so if you have a six...it's an option...I would just follow the torque procedure and preflight it like any other prop...

[dust]

MT wrote

With some of the numbers I've been going through... a prop coarse enough to take advantage of low drag and high power would be a problem on take off at gross.

 

 

can you go through those numbers for 180 hp at 25000 feet for me and tell me anything??

 

Thanking you in advance for a very comprehensive, understandable answer.

 

 

Enjoy the build

[marbleturtle]

Dust... what weight do you want me to use?

 

Should I add 500lbs over gross for that Cozy O2 and Pressurization system?

[dust]

no need, i read that lightening holes don't decrease strength that much, so i have drilled 2" holes spaces every 4 inches in everypart

 

the wings, the fuselodge, the main spar, the seats and other bulkheads, the engine and the canopy, fuel tanks, turtle deck etc. etc.

 

the plane is now holy and quite cool on the inside when a breeze picks up and i reduces the weight to 628lbs dry.

 

Enjoy the build

[marbleturtle]

Just don't drill those holes in the speed brake! I hear that can REALLY slow you down!

[No4]

Check out these photos

 

http://www.airliners.net/open.file?id=228443&WxsIERv=TG9ja2hlZWQgQy0xMzAuLi4gSGVyY3VsZXMgKEwtLi4uODIp&WdsYXMg=RnJhbmNlIC0gQWlyIEZvcmNl&QtODMg=RmFpcmZvcmQgKEZGRCAvIEVHVkEp&ERDLTkt=VUsgLSBFbmdsYW5k&ktODMp=SnVseSAyMDAw&BP=0&WNEb25u=UGhpbGlwcGUgTm9yZXQ%3D&xsIERvdWdsY=&MgTUQtODMgKE=&YXMgTUQtODMgKERD=MzA2MzA%3D&NEb25uZWxs=MjAwMi0wNC0xMQ%3D%3D&static=yes

 

 

http://www.airliners.net/open.file?id=376950&WxsIERv=TG9ja2hlZWQgTWFydGluIEMtMTMwSi0zMCBIZXJjdWxlcyAoTC0zODIp&WdsYXMg=VUsgLSBBaXIgRm9yY2U%3D&QtODMg=WmVsdHdlZyAoTE9YWik%3D&ERDLTkt=QXVzdHJpYQ%3D%3D&ktODMp=SnVuZSAyNywgMjAwMw%3D%3D&BP=0&WNEb25u=U3ZlbiBEZSBCZXZlcmU%3D&xsIERvdWdsY=Wkg4NzY%3D&MgTUQtODMgKE=J1NwaW5uaW5nJyBhd2F5IGZyb20gdGhlIHJ1bndheS4uLiBsb29rIGF0IHRob3NlIHZvcnRpY2VzIQ%3D%3D&YXMgTUQtODMgKERD=MTI5NDQ%3D&NEb25uZWxs=MjAwMy0wNy0wMg%3D%3D&static=yes

 

The prop describes what is called a helix through the air. A fine prop the the helix is a tight coil, coarse a fat coil.

A plane with a fine prop will rev freely and climb like a mutha, a plane with a coarse pitch will bog in, take a longer take off roll, but eventualy howl past the fine pitcher.

Advance per revolution of the aircraft is a function of the length of the blades and their angle of attack to the airflow.

180 hp times prop efficiency of 75% = 135 hp

135 hp is 100 kilowatts

example weight of Cozy is 2000lbs = 910 kg = 9100 newtons

I'm guessing the cruise lift/drag ratio to 10 to 1

Drag is therefore 9100/10 = 910 N = 200 lb

A kilowatt is a thousand watts, and a watt is 1 newton metre per second

100,000 watts divided by 910 N is 110 metres per second

110 metres per second is 220 ish knots is 230 mph .

Thats at 8000 feet and matches the official figures. Up higher you can get closer to your best rate of climb speed (best lift drag ratio), and it could be worth another 50 knots.

Thats it, doesn't matter if you can make 40,000 feet you'll never go faster, unless you can reduce drag, and the only way to do that is maintain best rate of climb, but then you've to have bigger superchargers, or you could reduce weight, but all ready the Cozy's on the limit.

110 metres per second is 6600 metres per minute

rpm of lycoming at FL250 altitude 75% setting is maybe 2500 rpm

6600 divided by 2500 is an advance per revolution of 2.64 metres.

 

I initialy posted on this site touting cs props and retracts. After listening to Burt Rutan on designing the Voyager, I agree with the boss when he talks about weight and complexity. CS props are rudely expensive, require heavy maintenance , and add to weight. like wise retracts, the speeds the Cozy fly's at the decrease in drag might give a only a few more knots.

After doing my homework I say listen to Burt, listen to Nat, listen to Nick, and Go the fixed pitch prop!

The standard cozy hammers along with an O-360. Installing A TIO-360, or heavy calibre rotary will make the cozy a beast.

 

Don't worry about going fast, you'll have one of the fastest light aircraft on the planet.

 

Anyway, if you are into props, you might want to read this...

http://www.centennialofflight.gov/essay/Theories_of_Flight/props/TH18.htm

Cheers

 

PS If you are contemplating the IVO prop you are technicaly what they call a "nutter"

 

:D

[Jim Sower]

I'm not sure where you're coming from or where your figures come from ... ??

 

<... 110 metres per second is 220 ish knots is 230 mph ...>

220 kts is about 253 mph.

 

<... Thats at 8000 feet and matches the official figures ...>

Which official figures from which official?

 

<... Up higher you can get closer to your best rate of climb speed (best lift drag ratio), and it could be worth another 50 knots ...>

 

I thought best L/D speed is 80 or 90 kts. Where does this "another 50 knots" come from? What speed did you start at to approach best climb speed as you got higher?

 

<... Thats it, doesn't matter if you can make 40,000 feet you'll never go faster, unless you can reduce drag ...>

 

Never go faster than what? What about adding power?

 

<... and the only way to do that is maintain best rate of climb ...>

 

I'm completely lost now. What in the world are you talking about?

 

<... but all ready the Cozy's on the limit....>

 

The limit of what??

 

<... rpm of lycoming at FL250 altitude 75% setting is maybe 2500 rpm ...>

 

How in hell on earth are you going to get 75% power at FL250?? WOT at about 8,000' is 75% power. WOT at about 18,000' is 50% power. At FL250 you'd need about 20" (about 10 psi) of boost to get 75% power.

 

<... the speeds the Cozy fly's at the decrease in drag might give a only a few more knots ...>

How many is "a few"? Ten kts? Fifteen?

 

I'm really not sure where you're trying to go with all of this, but there's a bunch of little things left out of the math, and some rather sweeping, unsupported generalities there. Could you be a little more specific on some of these points?

 

Having trouble figuring out what you're talking about

[marbleturtle]

I was a little confused myself... then came the generalities which makes me question the math.

 

You mentioned that at the speeds the cozy flies at, the reduction in drag from retracts only increases speed minimally. But since drag resistance is geometrically related to speed, any reduction in drag at high speeds has a major affect.

 

I don't want to sound hostile... but I am curious where some of the numbers are coming from. I would like to see a few more specific calculations to compare notes.

[No4]

I apologise for my previous poorly worded post,and incorrect mph figure, I left mph on the motorway in England. It's all knots and kmh over here.

 

I agree 180 bhp at 25,000 is unlikely with a TIO-380, but those are the figures Dust asked Marble to interpolate.

When I said the Cozy was "out there" I mean't it is very light all ready, and I wouldn't know where to shave any off.

 

 

I'm currently studying my ATPL Aerodynamics and Flight systems and came across some fascinating stuff.

The basic equation I quoted is

 

Horsepower = Thrust * True Airspeed

 

I quoted it because a lot of people are speculating how fast will their Cozy go with such and such horsepower.

This is the equation at the heart of a Flight Management Computer on a Boeing or an Airbus. If you work in weights, density's, and a cosine or sine here and there it will give you rate of climb, angle of climb, fuel burn, and lots of other exciting formulae.

 

If you know your engine break horsepower and pass it through a propeller, which on average are 75% efficient, you get

 

Thrust Horsepower = Break Horsepower * 0.75

 

If you have a set of figures for your Lift/Drag ratio at an Indicated Airspeed, and you know your weight, then you can calculate the drag.

Lift must equal weight, and Thrust must equal drag for straight and level flight. So a weight of 2200lbs with a lift drag ratio of 10:1 must require 220lbs thrust.

 

So if you know your horsepower, and divide it by your thrust, that will give you your true airspeed for flight planning.

 

The numbers I quoted are from the Custom Planes magazine article that came attached to my set of plans from Nat. If I remember they are 2200lbs max take off, and 220mph cruise at 75% power, with an 0-380 180bhp motor.

180 bhp at 75% power is 135 bhp, which is 100 Thrust horsepower, which is 75 Thrust kilowatts, which is 75000 watts.

A watt is a Newton metre per second.

220 mph = 100 metres per second

75000 / 100 = 750 Newtons thrust required = 75 kg = 165 lbs

So if you are 1650 lbs heavy making 220 mph, using 75% power, you have a lift drag ratio of 10:1

 

Your best Lift Drag ratio will be at your best rate of climb, best glide Indicated Airspeed. So of course the lesser the drag the better, and the faster you will go with the same horsepower. That is all well and good, but remember you have to climb to some severe height to make 90 indicated equal 270 knots true. Whilst you've gone climbing to the flight levels the standard cozy is roaring away. If you've got a 270 knot fixed pitch prop it will climb like a dog. Ah so of course we want more horsepower, but that means a higher fuel burn, and higher engine weight. Ah and now we need to compress the thin air so we need turbo and superchargers, more weight and more fuel. So now we need more fuel to achieve the same endurance, which is now more weight still. We should probably get weather radar, nav systems, and TCAS now and the gear and brakes need upgrading, and we're starting to really need a constant speed prop.

Then we need to work in weight and balance for C of G calculations, and of course can the structure handle the increased loadings. Now we don't really have a Cozy at all, and I wouldn't know where to start with the mathematical relationships between all of the above.

That's taking things to an extreme, and I'm sure you could find many happy mediums in between. The further apart your Indicated Airspeed and True Airspeed the better.

 

I have no doubt that a cozy with retracts will have less drag than fixed, and maybe not even more weight. But certainly more cost, worry, maintenance, and complexity. For what? You can go 100 miles further than standard on full tanks, you can beat the time by 1/2 an hour A to B. Remember Marble that drag is Indicated Airspeed, if you're going to try and bust Vne, then that's silly. The Cozy is slippery all ready.

 

More horsepower? Why not? How fast do you want to go? It will cruise closer to Vne or higher and faster with altitude compensation. Props can't go much past 300 kts due to transonic flow on the blade tips.

300 knots = 150 metres per second

* Thrust 750 Newtons

=112500 watts = 112.5 Thrust kilowatts

/.75 = 150 thrust hp

/.75 = 200 brake hp

and if thats 75% then full power is 265 hp.

The props likely to be losing efficiency at that speed, so add a few hp.

So that's 190 knots Indicated Airspeed = 300 knots True Airspeed @ FL260 @ 200 hp.

200 hp is 150 kw. The Volvo diesel uses 0.25 kg/kw/hr so it will use 38 kg an hour Jet A1, or about 50 litres per hour.

If you want to go 300 knots at a lower altitude, you will have a higher Indicated Airspeed, The lift drag ratio will be worse, so you will need more hp.

You can calculate the rate of climb, using sin angle of climb times weight added to thrust required for straight and level.

I'd imagine it's not going to be worse than the already excellent 2500 feet per minute. Climb rate decreases with altitude, so give 20 minutes for the climb to FL250. You will want to descend at Vne if you are in a hurry, but adding some range again say 40 minutes.

MTO Cozy = 2050 lbs = 930 kg

Empty Standard Cozy = 1050 lbs = 477 kg

Empty Modified Cozy ( 100 kg heavy)= 577 kg

2 people at 80 kg = 737 kg

Baggage 40 kg = 777 kg

Fuel load available = (930 - 777) = 153 kg

153 kg @ 38 kg/hr = 3.5 hours endurance + reserves

range (2.5* 300) + (1 * 200) = 950 nautical miles

average speed 270 knots

 

 

 

That's as fast as you can go without losing prop efficiency, and so really having to pile on the horsepower. It is achievable with hp alone, so why make it hard and change everything else?

$10,000 on retracts = + 15 knots

$10,000 on csu = + 15 knots

$10,000 on motor = + 100 knots

 

 

 

With regard to the fixed pitch prop design. The blades will have an optimum advance per revolution.

2500 rpm = 42 revolutions per second

150 metres per second / 42 = 3.6 metres per revolution.

I don't know how to build a prop, but for a certain blade length, a corresponding blade angle will give you that advance per revolution.

Good luck working that out!

 

All considered it's pretty hard to beat the original, well done Nat.

 

It's a pleasure to chat planes with you guys

 

 

[Jim Sower]

No4,

That's all very nice. Excellent thumbnail sketch of a basic aerodynamic text. Much of that theory many of us were aware of when we were building models as a kid. Most of the rest involves high school level physics. Trouble is, it contains about disturbing number "if"'s and "average"'s that you made no attempt to resolve, until the end when you blythly assigned values that you cannot support with any kind of factual documentation. IF we could specifically quantify the if's and average's that you state, we would all know everyting and life would be perfect. If you can resolve some of these, I've no doubt you will be in great demand as a consultant.

Such as:

<... Horsepower = Thrust * True Airspeed ...>

Well, Duuuuuhh! Now if we only knew exactly what our thrust was ....

 

<... If you know your engine break horsepower ...>

HS physics again. Also, it's "brake" horsepower, and none of us know it (with any acceptable accuracy). We do know what the engine manufacturer's marketing folks claim, but we are clueless as to the actual output of our own engine in it's current state of wear. None of us owns a dyno, and nothing short of that will do.

 

<... on average are 75% efficient ...>

Does "on average" mean? Between 70% and 80%? Or between 65% and 85%? Or what? And how, precisely, do I determine where in that range my personal prop lies. Perhaps my prop is 85% efficient ... but then again, perhaps it's only 65% efficient ... but then again, guessing wrong between those two figures within the range only introduces an error of 30%, and that's pretty close

 

<... Thrust Horsepower = Break (read "brake") Horsepower * 0.75...>

True. My HS physics notes confirm this is so.

 

<... If you have a set of figures for your Lift/Drag ratio at an Indicated Airspeed ...>

And where, would you suggest, might I obtain such a set of figures for MY Cozy (with the obvious caveat that John's or Dust's or whose ever Cozy will have different figures from my Cozy)?

 

<... a lift drag ratio of 10:1 must require ...>

Wonderful. Now we're getting somewhere. What might be the L/D of my Cozy? While you're at it, grab the figures for Jonh's and Dust's. I'm sure they want to know too.

 

<... So if you know your horsepower ...>

Which or course we don't ...

<... divide it by your thrust ...>

Which, absent accurate knowlege of horsepower and prop effeciency, we have no way of knowing ...

 

<... they are 2200lbs max take off, and 220mph cruise at 75% power, with an 0-380 180bhp ...>

So now, all we have to do is poll the owners of flying Cozys to determine how many (if any) actually achieve this level of performance ... and establish how, exactly, they determined that they were at 75% power ...

 

<... _IF_ you are 1650 lbs heavy and _IF_ making 220 mph, _IF_ using 75% power, you have a lift drag ratio of 10:1 ... but IF you don't know your power, none of this means anything at all.

 

<... you have to climb to some severe height to make 90 indicated equal 270 knots true ...>

Something upwards of 60,000' as I recall (incidentally, blood at 98F boils at about 55,000' - something to consider) ...

 

<... Props can't go much past 300 kts due to transonic flow on the blade tips ...>

Unless you're a reno racer, in which case you can go about half again that fast ...

 

<... More horsepower? Why not? How fast do you want ... snip ... it will use 38 kg an hour Jet A1, or about 50 litres per hour. ...>

A lot of unsupported numbers here passed off as fact ...

 

<... You can calculate the rate of climb, using sin angle of climb times weight added to thrust required for straight and level ...>

Fantastic!! Just like my HS physics class. In the quiz, the teacher gave us the thrust required and the angle of climb ... what exactly are those items for my Cozy (Oh, and John's and Dust's ...)

 

<... I'd imagine it's not going to be worse than the already excellent 2500 feet per minute ...>

"Imagine" being the key word here ....

 

<... so give 20 minutes for the climb to FL250 ...>

In another life, I flew tactical jets. Those fighters would make FL250 in 20 minutes. Even less! I gotta' see the Cozy that does that. Cozy making 10,000' in 20 minutes it pretty good. But 10,000 instead of 25,000 '? Then again, perhaps that's within your margin of error ...

 

<... average speed 270 knots ...>

That's a damn fine average. About 100 kts better than anyone I have met.

 

<... That's as fast as you can go without losing prop efficiency ...>

Where did that come from?

 

<... and so really having to pile on the horsepower...>

From where do we get this pile of hp?

 

<... It is achievable with hp alone ...>

IS it now?

 

<... why make it hard and change everything else?

I'll need some supporting documentation on these:

$10,000 on csu = + 15 knots ... beg pardon ?...

$10,000 on motor = + 100 knots ... in your dreams ...

 

Actual tests and experience suggest that, on a given system (someone's particular Cozy) the relationship between increased horsepower and speed gain is a cube root function.

 

Like, suppose you have a really marvelous airplane, like a Long-EZ that will make 200 kts on 200 hp (a Long-EZ might, a Cozy never could).

 

Now, suppose you increase hp by 50% (to 300 hp) ...

You can expect an increase of speed factor of about 1.5^1/3 or about 1.14 which works out to about 228 kts. We can expect to see a 14% gain in speed for our investment in a 50% gain in power (and, of course, fuel burn).

 

To coin a phrase ... the devil is in the details ... or, perhaps more appropriately, ... if wishes were horses, beggers would ride ...

 

An at least nodding acquaintence with Mr. Newton would help too ... Jim S

[CBarber]

Wow, all that can really take the fun out of flying.

 

All the best,

 

 

Chris

an apparantly under educated type.

[Dave Clifford]

Gorilla'in the mist.

[No4]

Sorry Jim,

That's the formula for increasing indicated airspeed, or in other words cruising closer to Vne. Which of course means a reduced angle of attack, and a poor lift to drag ratio.

 

 

You might want to check this link

http://www.av8n.com/how/htm/power.html#sec-sketch-power-curve

May I refer you to section 7.5.4

 

I think you will find that it is the power to weight ratio that controls top speed.

Some interesting propeller driven figures

ATR-72 4000hp -20000kg-5kg/hp=250ktas

Bae Jetstream 2250hp-9000kg-4kg/hp=300ktas

Fairchild Metro-1500hp-7000kg-4.6kg/hp=300ktas

Beech King Air-1500hp-6500kg-4.3kg/hp=300ktas

Beech Starship-1800hp-6500kg-3.6kg/hp=300ktas

My Cozy TurboDiesel 2005'-300hp-1000kg-3kg/hp=300ktas

and you can eat my Kero fumes if you don't believe it.

 

By the way, it's pretty easy to take your engine when it's ready to the dyno shop and run a test on it. You could then get all tricky like the test pilots do, and weigh everything in the plane before and after the flight, record speeds, fuel flows, airspeeds. If you can't get to a dyno, the specific fuel consumption figures for most aero engines are available and measure the fuel flow.

 

 

Your right about my figures aswell Jim, I put what I like to call a fudge factor in them. My prop will actualy be 80% efficient, Gravity will be only 9.81 times mass, and the specific fuel consumption will be 0.225 kg/kw/hr or better. That figure is for an old diesel truck engine.

 

As far as reno goes, I think I said props lose efficiency after 300 knots.

Beech king Air 1500hp-9 people- 300 knots 4 hours endurance

Hawker Sea Fury 3000hp- one pilot-450 knots 30 minutes

 

You also seem to doubt the figures Nat sends out, the Cafe foundation did a very thorough testing of it

http://www.cafefoundation.org/aprs/Cozy%20IV%20APR.pdf

looks pretty close to me.

Cheers!