The Pegasus shall have a useful load of at least four long tons.
The Pegasus shall have a high main wing.
The Pegasus shall have folding outer wings.
The Pegasus shall have a boat hull.
The Pegasus shall be corrosion resistant.
The Pegasus shall be constructed to naval aircraft survivability standards.
The Pegasus shall have a crash worthy structure.
The Pegasus shall have turboprop propulsion.
The Pegasus shall have dual pilot controls.
The Pegasus shall be easily maintained in austere locations.
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The Pegasus shall have a range of at least three and a half thousand nautical miles in ferry configuration.
The Pegasus shall have a range of at least two thousand nautical miles in patrol configuration.
The Pegasus shall have an endurance of at least eight hours in patrol configuration.
The Pegasus shall have an aircraft classification number of four or less.
The Pegasus shall be able to take off or land within half a mile on land or sea.
The Pegasus shall be able to take off or land in conditions up to Sea State Four.
The Pegasus shall be able to launch from or recover aboard a flying ship.
The Pegasus shall be able to be craned overboard from,or aboard a patrolling cutter,patrolling brig,mining sloop,hydrographing sloop,destroying frigate,flying ship,replenishing ship,icebreaking ship or depoting ship.
The Pegasus shall have a rear cargo ramp.
The Pegasus shall be able to air drop cargo and parachutists.
The Pegasus shall be able to accommodate LD3 cargo containers.
The Pegasus shall be able to accommodate passenger seats.
The Pegasus shall have under wing hard points wired for delivery of weapons and other items.
The Pegasus shall be able to accommodate the same aeromedical evacuation systems as the Centaurus and Perseus aeroplanes and the Hermes and Hercules helicopters.
The Pegasus shall be able to accommodate the same modular workstations as the Perseus aeroplane and the Hermes helicopter.
The Pegasus shall be equipped,within the boat hull,with the same Medium Range Radar as the Hermes helicopter,when in patrol configuration.
The Pegasus shall be equipped with the same camera turret as the Centaurus and Perseus aeroplanes and Hermes and Hercules helicopters,when in patrol configuration.
The Pegasus shall be equipped with the same Magnetic Anomally Detector as Perseus aeroplane and the Hermes helicopter,when in patrol configuration.
The Pegasus shall be equipped with the same communications systems as the Hermes helicopter,when in patrol configuration.
The Pegasus shall be equipped with the same Three Eighths Inch Machine Gun as the Hermes and Hercules helicopters,when in patrol configuration.
The Pegasus shall be equipped with pollution detection systems,when in patrol configuration.
The Pegasus shall be equipped with Search And Rescue equipment,when in patrol configuration.
The Pegasus shall be operated by the Royal Flying Corps.
The Pegasus shall be operated by the Royal Naval Air Service.
The Pegasus shall be chartered to Her Majesty's Waterguard Service.
The Pegasus shall be chartered to the National Health Service.
The Pegasus shall be chartered to the Foreign Office.
The Pegasus shall be chartered to the Home Office.
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The Pegasus shall be chartered to the Royal Mail.
The Pegasus shall be chartered to the Ordnance Survey.
The Pegasus shall be chartered to the Environment Agency.
The Pegasus shall be chartered to the Marine Management Organisation.
The Pegasus shall be chartered to Marine Scotland.
Picture: Grand Logistics
The Pegasus shall be used to train aircrew for the Perseus and Centaurus aeroplanes.
The Pegasus shall be used for light transport.
The Pegasus shall be used for mail delivery and collection.
The Pegasus shall be used for medical evacuation.
The Pegasus shall be used for land surveillance.
The Pegasus shall be used for sea surveillance.
The Pegasus shall be used for range safety.
The Pegasus shall be used for pollution detection.
The Pegasus shall be used for oil spill response.
The Pegasus shall be used for Search And Rescue.
The Pegasus shall patrol the United Kingdom's Search And Rescue Region.
The Pegasus shall patrol the United Kingdom's Exclusive Economic Zones.
The Pegasus shall support the United Kingdom's Overseas Territories,many of which are not accessible by fixed wing land planes.
The Pegasus shall be able to fly from Great Britain to Gibraltar.
The Pegasus shall be able to fly from Gibraltar to Cyprus.
The Pegasus shall be able to fly from Cyprus to Diego Garcia.
The Pegasus shall be able to fly from Diego Garcia to Singapore.
The Pegasus shall be able to fly from Singapore to Brunei.
The Pegasus shall be able to fly from Gibraltar to Ascension Island.
The Pegasus shall be able to fly from Ascension Island to Saint Helena.
The Pegasus shall be able to fly from Saint Helena to Tristan da Cunha.
The Pegasus shall be able to fly from Tristan da Cunha to South Georgia.
The Pegasus shall be able to fly from South Georgia to Adelaide Island.
The Pegasus shall be able to fly from Adelaide Island to East Falkland.
The Pegasus shall be able to fly from East Falkland to Ducie Island.
The Pegasus shall be able to fly from Ducie Island to Belize.
The Pegasus shall be able to fly from Belize to Grand Cayman.
The Pegasus shall be able to fly from Grand Cayman to West Caicos.
The Pegasus shall be able to fly from West Caicos to Beef Island.
The Pegasus shall be able to fly from Beef Island to Montserrat.
The Pegasus shall be able to fly from Montserrat to Anguilla.
The Pegasus shall be able to fly from Anguilla to Bermuda.
The Pegasus shall be able to fly from Bermuda to Great Britain.
The Pegasus shall operate from Great Britain.
The Pegasus shall operate from Gibraltar.
The Pegasus shall operate from Cyprus.
The Pegasus shall operate from Diego Garcia.
The Pegasus shall operate from Ascension Island.
The Pegasus shall operate from Saint Helena.
The Pegasus shall operate from South Georgia.
The Pegasus shall operate from Adelaide Island.
The Pegasus shall operate from East Falkland.
The Pegasus shall operate from Ducie Island.
The Pegasus shall operate from Grand Cayman.
The Pegasus shall operate from West Caicos.
The Pegasus shall operate from Beef Island.
The Pegasus shall operate from Bermuda.
The Pegasus shall replace four Beechcraft Avengers of the Royal Navy.
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The Pegasus shall replace five EMB-500 Phenom 100 of the Royal Air Force.
The Pegasus shall replace nine Britten-Norman Defenders of the Royal Air Force.
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The Pegasus shall replace six Britten-Norman BN-2 Islanders of the Royal Air Force.
The Pegasus shall replace four Vulcanair P68Rs of the National Police Air Service.
The Pegasus shall replace two Beechcraft King Air B200s of Her Majesty's Coastguard.
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The Pegasus shall replace two Cessna 404 Titans of the Ordnance Survey.
The Pegasus shall replace two Reims Cessna F-406 Caravan IIs of the Environment Agency.
The Pegasus shall replace two Reims Cessna F-406 Caravan IIs of the Marine Management Organisation.
.jpg){kind=link}
The Pegasus shall replace two Reims Cessna F-406 Caravan IIs of Marine Scotland.
The Pegasus shall replace two Beechcraft King Air B200Cs of the Scottish Ambulance Service.
The Pegasus shall replace Britten-Norman BN-2 Islanders of the Falkland Islands Government Air Service.
The Pegasus shall replace four de Havilland Canada DHC-6 Twin Otters of the British Antarctic Survey.
The distance between Cyprus and Diego Garcia is 3368.251 NM according to Google maps, which means the Pegasus wouldn't be able fly between the two with it's stated range of 3,500 NM.
ReplyDelete1. The wind could reduced range considerably below 3,500 NM.
2. Assuming favourable winds the Google distance is point to point. The plane still needs to follow flight paths into the islands. This adds to the distance flown.
3. Safety rules for civilian flights require sufficient fuel to divert at any point to an alternative airport plus 30 minutes. This plane couldn't get close to that, so it couldn't be used for civilian purposes. Even assuming it's for military purposes the lack of alternates once you get south of the Maldives means from this point on this would result in a ditching.
A range of 3,500 NM is wholly insufficient for the journey between Cyprus and Diego Garcia.
Hello fruitman,
ReplyDeletein response to your points:
1.Yes,head winds can significantly reduce range and there have been many famous hull losses as a consequence,but preventing that is what flight planning and fuel reserves are for.
2.I should be surprised if a small aircraft has to add hundreds of miles to it's journey to fly in to any of the areas mentioned.
3.This article is not referring to a civilian aircraft (the entire blog is about military and naval matters),it is about a naval and military aircraft (though a civilian variant might attract some sales),nor is it intended to routinely fly long routes,in peace time,without stops and divert locations,of which there are many along all of the longer routes mentioned,because it does not need to.
For example on the Diego Garcia to Cyprus route the aircraft might land in the Maldives,India and Bahrain for rest and refuelling (not to mention the ships this aircraft is intended to operate from).
However,it is intended that the aircraft be able to fly those long routes,as a naval aircraft,when required to do so due to urgency or denial of landing rights,both of which are important considerations for war fighting and justify the acceptance of additional risk.
Thank you for raising those points.
Grand Logistics.
P.S.If there is anything to criticise in this article,the estimated Maximum Take Off Weight might be a little optimistic.
Flight planning is about building in contingency. For a long flight, given this is a turbo prop it will be a long flight, that reduces your maximum range, it doesn't remove the problem. The fuel reserves have already been counted in your maximum range.
DeleteThe difference isn't hundreds of additional miles, it's 131nm, which is well with the additions which occur due to flight vectoring on a long flight over a number of different countries, taxiing and holding at destination.
I can't see any aircraft in the 10 tonnes category which go much further than 1,200 nm, given the other constraints from the requirements, an un-aerodynamic hull shape, bi plane and the need for STOL, a beefed up undercarriage for aircraft carrier landings and the additional sensors I would suggest 1,000 NM would be a realistic maximum for ferry range.
With regard to weight, if you are looking to achieve the total set of requirements, you are looking at two different planes, one in the > 30 tonnes category and one < 10 tonnes.
Hello Fruitman,
ReplyDeletegiven that the article made no mention of what reserves had been allowed for,how did you conclude that "The fuel reserves have already been counted in your maximum range"?
It is standard practice to include allowances for taxiing,holding and a margin for contingencies when calculating fuel reserves and,as you pointed out,this aircraft still has enough spare fuel to fly another one hundred and thirty one nautical miles past Cyprus on top of that.
The "un-aerodynamic hull shape" is not as un-aerodynamic as you might imagine,this aircraft is not intended to have a traditional boat hull with concave sections and a fixed step,it is intended to be rather more like the hull of modern planing monohull sailing boats with a tall,sharp vertical nose (or stem?) and convex "U" sections.
Similarly the sesquiplane layout,similar to a Dornier 24 or Boeing 314,is intended to reduce overall drag by using horizontal surfaces to support the stabilizing floats which generate lift in the air and on the water,allowing a reduction in main wing area,whilst also providing volume for buoyancy,fuel,sensors and undercarriage and consequently lowering the centre of mass,rather than vertical surfaces which just add more weight and drag.
This aircraft does not require "a beefed up undercarriage for aircraft carrier landings",it is not a supersonic combat aircraft with a high stall speed which needs to hook an arrestor wire at high speed to safely recover.
It is a slow flying,short take off and landing,turboprop with a low stall speed which can recover without being arrested,as demonstrated by the picture of a Supermarine Walrus in the article and many other examples including a C-130 Hercules,de Havilland Beaver,Auster Autocrat and even a U-2 Dragon Lady!
The estimated fuel consumption was based on real world figures of short take off and landing aircraft with similar cruising speeds.
What figures did you use to conclude that an aircraft with a four long ton useful load could not "go much further than 1,200 nm"?
At two hundred and fifty knots that would equate to a fuel consumption of around eighteen hundred pounds per hour,that is similar to a twenty ton class aircraft like an Antonov 24 or ATR 72.
The ferry configuration mentioned in the article includes the addition of internal ferry tanks and fuel in lieu of equipment fitted when the aircraft is in the patrol configuration,giving about fourteen hours flying time at two hundred and fifty knots.
The weight allowance made for the fuel tanks was based on the manufacturer's figures for a commercially available product.
It is not clear why you "would suggest 1,000 NM would be a realistic maximum for ferry range" of an aircraft which could,in your opinion,"go much further than 1,200 nm"?
The primary reason for the long ferry flight capability is to allow the aircraft to self deploy to it's operating areas in the United Kingdom's Overseas Territories.
When you write "if you are looking to achieve the total set of requirements, you are looking at two different planes, one in the > 30 tonnes category and one < 10 tonnes.",that suggests you are not understanding what the requirements are,unless you are thinking of something like the Short Mayo?
Thank you for the opportunity to elaborate further on the Pegasus concept.
Grand Logistics.
Ferry range is the maximum range an aircraft can fly, this is with maximum fuel load. There aren't any reserves on top of this. If the range is 3,500 NM then that is it, there aren't any extras on top by definition.
ReplyDeleteThere are four forces on an aircraft, lift, weight, thrust and drag which at constant velocity and height are always in balance. If there is an increase in drag saydsay to the body shape being less than a round cross section, then more thrust is required. The increase in thrust required increases the fuel burn, which increases the weight required, which requires more lift. An increase in lift increases drag, which etc etc.
A design optimised for STOL has a high drag coefficient due to its large aerofoil and control surfaces, likewise the turrets and other protrusions required for ASW and MR cause parasitic drag. Yes a hull shape maybe used for both floatation on water and lift, but the cost is in drag. As you increase the velocity of the aircraft the drag increases in a non linear fashion. For a cruising airspeed of 250 knots you are requiring substantially more thrust than 150 knots. This is why the amphibious aircraft you have mentioned have a speed considerable lower than 250 knots for range maximising cruise.
The requirements are fighting against each other, to get range you will need a large aircraft to carry the fuel you need. That's where two aircraft of different weights (and sizes) comes from, you can't accomplish all the requirements in one aircraft. I assume that the requirement for range to transit the Cyprus Diego Garcia hop will be the driver for the ~30 tonnes aircraft, alternatively if you compromise on the other requirements a different solution is possible.
My comment about a 1200 NM range for a 10 tonnes aircraft is from comparison with comparable aircraft, a Q200 isn't quite hitting the STOL requirements, but if we assume a bit more power, it could probably make it, so a 1,250 range there and cruise speed is 289 knots so good there. Factor in the extra drag from what ever form you are using for floatation you are losing approximately 10-15%, then the extra weight for the more powerful engines, you will be in the ballpark of 1000. This is very back of the fag packet.
Hello Fruitman,
ReplyDeleteeven aircraft manufacturers specify fuel reserves when giving the ferry range of their aircraft.
For example,the Beechcraft King Air 350ER: "Ferry Range (NBAA IFR Reserve) 2,670 nm 4,945 km".
Given that such reserves are legally required for civilian pilots operating under Instrument Flight Rules,that is hardly surprising.
At three hundred knots true that aircraft burns over six hundred pounds of fuel per hour but it burns about four hundred pounds per hour at around two hundred and fifty knots.
The Pegasus shall weigh at least a third more than a King Air 350ER and have a bigger,draggier fuselage,lower wing loading and higher thrust to weight ratio,to generate better short take off performance,all of which shall reduce fuel efficiency.
However,it shall also have a pair of modern engines like the General Electric Catalyst,modern propellers and modern aerodynamic analysis to offset that inefficiency.
The new generation engines alone are claimed to cut specific fuel consumption by around fifteen percent.
Your assumption of one thousand pound per hour would probably result in an aircraft of around fifteen long tons.
But this is where you have me confused: "you can't accomplish all the requirements in one aircraft".
The Pegasus is intended for what Americans would call Coast Guard duty,it's job is patrolling fishing grounds up to two hundred miles off shore and responding to various types of civil incidents,none of which are likely to require a thirty ton aircraft.
The aircraft would only be performing long transits in emergencies,for example when it needed to return home for depot level servicing but countries en-route had denied landing rights or if hostile forces were about to raid the Indian Ocean and it needed to leave in a hurry.
That is the raison d'etre of the long range ferry requirement,getting the Pegasus to,or back from,it's operating base in emergencies.
Grand Logistics.
Ok, I can see where the confusion had come from.
DeleteYou have assumed that the fuel burn has remained constant as you increased the range to get to 3,500 nm. But going back to the model of flight outlined above if you increase weight, you require more lift, which increases the drag, so you need to increase thrust to achieve the same velocity. Let's use the king air 350 ER as a baseline to explain where the variation has come from. Let's assume the publicly available figures, the King air gets its 2670 NM range from a cruise speed of 303 kts times 8.8 hours of fuel. But to reach 3,500 NM at 250kts requires 14 hours hours worth of fuel. Yes fuel burn will be lower at lower speed, but you need more fuel for the longer time in the air. More fuel means more weight, which means more lift is required, more lift increases the drag which means you need to increase the thrust. More thrust means increased fuel burn. You get into vicious circle where the fuel you are burning at hour 14 of the flight has required increase fuel burn during the preceding 13 hours to get it to that point. That additional burn has itself required additional fuel to be carried and burnt.
Let's look at the requirements, the King air doesn't meet the range requirement but isn't a million miles away, but it completely misses the STOL requirements. In order to achieve those you need additional lift surfaces and very importantly larger control surfaces. Those impose a drag penalty and a small weight penalty. Those drag increases mount up over the 14 hours of flight.
Efficient hull form, more modern props and engine and devices like Coanda effect wings will take you only so far before you hit the maximum that physics allow. Actually we have hit a lot of those limits already, if a more effective propeller exists then it will be already in production and fitted, it's one of the quickest of quick wins to boost performance.
There's a reason that no aircraft designed comes close to the requirements, despite over a hundred years of aircraft development and billions spent on research, because we are hitting the boundaries of what's possible with the materials we have today.
That is why the requirements for 10 tonnes, STOL, amphibious hull, 250 kts cruise speed and 3,500NM are not possible in the same package, one or more of the requirements has to be dropped.
Hello Fruitman,
ReplyDeleteit is not clear why you "assumed that the fuel burn has remained constant as you increased the range to get to 3,500 nm".
Was the figure of one thousand pounds per hour,which you came up with,your estimate for an aircraft which could fly for fourteen hours or your estimate for a ten ton aircraft?
If the latter,then that might explain the confusion.
Would it save you a little time you omitted the explanations of the basics of flight in each post,they are not necessary.
You say "the King air gets its 2670 NM range from a cruise speed of 303 kts times 8.8 hours of fuel",but,even without allowing for reserves that would exceed the aircraft's fuel capacity as the fuel flow at that speed is seven hundred and sixty-four pounds per hour (other sources give lower figures but they are all too high to give that endurance).
The Beechcraft King Air 350ER has a claimed endurance of up to twelve hours on standard fuel tanks,in fact,notwithstanding reserves or unusable fuel,it could stay in the air for almost thirteen hours when burning four hundred and two pounds per hour at two hundred and thirty-eight knots (higher fuel consumption during the climb probably accounts for much of the difference).
There are a variety of contradictory figures published about its performance,one set gives two thousand five hundred and thirty-eight nautical miles at two hundred and thirty-eight knots true air speed with NBAA reserves and fuel to get to a one hundred nautical mile distant alternate runway.
Beechcraft says two thousand six hundred and ninety-two nautical miles with no mention of reserves.
Given a fuel consumption of four hundred and two pounds per hour at two hundred and thirty-eight knots true,it would require an additional thirteen hundred and sixty-five pounds plus reserves to reach three thousand five hundred nautical miles or just one thousand one hundred and forty-four pounds more to get from Diego Garcia to Cyprus.
In fact,as it has a payload of one thousand eight hundred and eighty-eight pounds when fully loaded with fuel,it could fly from Diego Garcia to Cyprus with an internal ferry tank and still have an hour or so of reserve fuel!
To be continued in next comment as size limit exceeded......
Grand Logistics.
Hello Fruitman,
ReplyDeletecontinued from last comment:
Let us look at another example.
The new Cessna Denali takes off in twenty-nine hundred feet,only about ten percent more than the target for Pegasus.
It also has one General Electric Catalyst engine,similar to next generation engines intended for Pegasus,and weighs about half as much.
Cessna claims a range of sixteen hundred nautical miles at a maximum cruising speed of two hundred and eighty-five knots and presumably,at the maximum continuous power output of the thirteen hundred shaft horse power engine on a fuel load of eleven hundred pounds.
They make no mention of reserves which is flattering for them and convenient for us.
That implies an endurance at maximum cruising speed of five hours and thirty-seven minutes and a fuel burn of one hundred and ninety-six pounds per hour from a modern thirteen hundred shaft horsepower engine.
It also suggests a maximum continuous power of some where around four hundred shaft horse power,assuming a published but not very specific specific fuel consumption for the Catalyst engine of around nought point five pounds per horse power per hour.
The Denali aircraft then combines both low drag,high peformance and economy with short runway requirements,as do many other aircraft.
Many modern turboprops gain performance by rapidly climbing to thinner air at higher altitudes.
Now,for something more pertinent,a flying boat.
Beriev's Be 112 is an eleven tonne flying boat concept which is intended to fly at two hundred and twenty-seven knots,at about ten thousand feet,when powered by a pair of one thousand four hundred and twenty-four shaft horsepower rated turboprop engines.
This is a very different aircraft to Pegasus,it has a conventional boat hull,vertical wing floats,a wider,taller and much longer cabin,and hence draggier and heavier fuselage and lots of seats displacing weight for fuel.
Pegasus has a much shorter,lower and significantly narrower cabin,fewer seats,a longer,sleeker tail,modern boat hull,no wing floats and,it is therefore reasonable to assume,much less drag and more weight margin for fuel.
Drag determines the power requirement which in turn dictates the fuel consumption.
The Beriev 112 is designed to sustain a maximum cruising speed of two hundred and twenty-seven knots with two Pratt & Whitney Canada PT6A-67R engines.
Though they do not state the torque conditions at maximum cruise speed,the maximum continuous rating for those engines is twelve hundred and twenty shaft horse power.
Basler,who install two of the same engines on thirteen tonne Dakotas,claim a fuel consumption of about one thousand pounds per hour at maximum cruise and ninety-five percent torque and nine hundred and sixty pounds at standard cruise and ninety percent torque.
They list long range cruise as eighty percent torque but do not give an equivalent fuel burn figure.
It would seem reasonable to assume similar figures for the Beriev 112 at maximum and economical cruise speeds respectively,given they have specified the same engines at similar altitudes.
If it were possible to find directly comparable specific fuel consumption figures for the PT6A-27R and General Electric Catalyst,this information would allow us to estimate the fuel consumption of the Beriev 112 with an engine which is not thirty years old.
If General Electric's claim of a twenty percent fuel saving (versus what?) were taken at face value,this alone would cut the Beriev 112s fuel burn to the high seven hundred pounds per hour.
Allowing for the difference in drag between the Beriev 112 and Pegasus would lower that significantly although increasing cruising speed from two hundred and twenty-seven knots to two hundred and fifty would probably add tens of pounds per hour to fuel burn at those speeds.
Of course there are other factors such as altitude to consider.
Average fuel burn in the region of six hundred pounds per hour,which would allow an aircraft of around ten tonnes to fly from Diego Garcia to Cyprus,does not appear unreasonable.
Grand Logistics.
If you have taken the figures on the Basler BT67 from their website then you might of noticed a graph below which listed the range / weight performance. For the long range variant you are able to transport 2,600lbs to 1,875NM. If you said that weight was extra fuel, that gets you to 2,619NM plus a 30min reserve. You can't go beyond this because you're at the weight limit.
DeleteThe website does give the fuel flow for 80% torque, it's 920lbs per hour. The total range ends up very similar 2,571NM.
If you want the 20% extra efficiency that the GE engine brings, that leaves you at 3,197NM.
But that's at the 200kts cruise speed. If you want 250kts cruise you state as a requirement you need to increase the fuel consumption. Given the neither the Basler nor the Beriev have a top speed of 250kts, I wouldn't guess what the fuel flow would be at 250kts, but given that the increase in fuel burn is non linear with speed, it has to be a greater than 20% increase.
You mentioned the Denali as something which could be similar to what you want to achieve by using modern design and engines. The difference is that the Denali, as you mentioned, can't achieve the STOL performance, the reason is that it's designed to achieve high speed by a low drag. Adding extra power or additional lift technology increases weight, conflicting with the range requirement. If you wanted to remove items from the Beriev 112 to make it less draggy, a less boat like hull, reduced vertical stabiliser, remove the floats from the wing end, then you conflict with the requirements for operation in sea state 5. The boat like hull is not required just to float, a perfect cylinder would achieve that, but to permit the aircraft to escape the water at speed.
Making the fuselage smaller in diameter will help, but it conflicts with the requirement for buoyancy, which other aircraft designs don't need. A high wing increases the weight of the aircraft compared to a low wing. Folding wings increases weight. Once you include all these differences an amphibious aircraft of your requirements will never achieve the same aerodynamic efficiency as a state of the art turbo prop such as Denali.
It's not possible to make the 3,500NM ferry range, even at stripped down weight, and have the cruise speed of 250kts, the STOL performance, the amphibious hull and the 10 tonnes weight in the same aircraft. The requirements are in conflict to a degree which means they can't be accommodated in the same aircraft.
There are good explanations of the Breguet range equations available on the internet, which covers the key points to consider when thinking about design and range.
Hello Fruitman,
ReplyDeleteyou appear to be going off on a tangent,do you not understand that the range performance of a Basler BT-67 is of no relevance at all to this discussion?
The Basler BT-67 is relevant only in so far as it uses the same engines as the Beriev 112 and therefore is likely to give similar fuel burn figures for any given torque setting at any given altitude.
That has got little to with the performance figures of the Basler BT-67 airframe,which weighs a third more than the proposed Pegasus.
It is the performance of it's engines (fuel burn,torque,altitude) which is pertinent to this discussion not the performance of the aircraft (range,payload,speed) which they are bolted to.
If you compare the figures quoted above to those on the Basler website,you shall see that they are for an altitude of fourteen and a half thousand feet and that there is no figure in that section for eighty percent torque.
That altitude was quoted because it is similar to the figure,rather confusingly,mentioned in the range section and therefore,presumably,economical cruise altitude and engine torque.
But if you would prefer to use figures from other altitudes that is quite acceptable,the ten thousand foot figures would probably be more pertinent to the Beriev anyway.
The Denali was mentioned because you claimed an aircraft could not have a short take off and still have low enough drag to cruise economically at high speeds.
There are dozens of other aircraft which can take off in half a mile and still cruise economically at high speed,the Pilatus PC12 for example.
Their performance has a lot to do with climbing rapidly and cruising in thinner air at high altitude.
You said: "Given the neither the Basler nor the Beriev have a top speed of 250kts, I wouldn't guess what the fuel flow would be at 250kts, but given that the increase in fuel burn is non linear with speed, it has to be a greater than 20% increase.".
As you like quoting performance figures for the Basler BT-67,let us do that,two hundred and fifty knots is twenty three knots faster than the cruising speed of a Beriev 112,a ten percent increase.
At ten thousand and five hundred feet altitude,the Basler BT-67 makes two hundred knots on one thousand pounds of fuel per hour,but at fourteen thousand and five hundred feet altitude,the same aircraft makes two hundred and twenty knots,ten percent more,on the same one thousand pounds of fuel per hour.
Both the Basler BT-67 and the Beriev 112 are bigger aircraft than Pegasus pushing their way through denser air at lower altitudes where each knot nautical mile costs more fuel.
To be continued in next comment as size limit exceeded..............
Grand Logistics.
Hello Fruitman,
ReplyDeletecontinued from last comment:
Again,you appear to be going off on a tangent with this comment: "If you wanted to remove items from the Beriev 112 to make it less draggy, a less boat like hull, reduced vertical stabiliser, remove the floats from the wing end, then you conflict with the requirements for operation in sea state 5.".
What "requirement" for "operation in sea state 5" are you talking about?
No where in this article is there any mention of operating in "sea state 5",it specifically says "conditions up to Sea State Four" and sesquiplane Dorniers were operating in Sea State Four during the Second World War,without wing end floats.
The vertical surfaces referred to were those supporting the wing mounted floats,though their elimination would likely permit a modest reduction of the vertical stabiliser area.
Previously you mentioned "requirements" for two different aeroplanes and for a thirty ton aircraft,neither of which you have yet explained.
You also said: "The boat like hull is not required just to float, a perfect cylinder would achieve that, but to permit the aircraft to escape the water at speed.
Making the fuselage smaller in diameter will help, but it conflicts with the requirement for buoyancy, which other aircraft designs don't need.".
Perfectly cylindrical section hulls are rarely seen on water craft as they offer,precisely,zero form stability,some Small Waterplane Area Twin Hull vessels have them as having two hulls mitigates that problem.
Planing boat hulls are ideally short,wide and flat to generate the lift to get on top of the water,called "getting over the hump",however this generates high accelerations when hitting waves which is why compromise designs such as shallow and deep "vee" hulls are common,not to mention the many more exotic types.
Every hull design,and every other design,is a compromise,which is why it it so amusing to see designs being criticised for being "a compromise".
Long,narrow hulls are efficient for displacement water craft as they reduce wave making resistance by increasing what is known as the "hull speed",but that is not what a flying boat needs,it needs to generate aerodynamic lift at speeds well above it's theoretical hull speed.
If it cannot reach it's "V1" speed then it cannot take off.
This is inconvenient.
For an aeroplane.
Racing mono hull sailing boats use wide "skimming dish" hulls for the same reason,that and the added righting moment given by the wider beam which allows them to extract more wind power.
A ten ton aircraft burning around six hundred pounds per hour at two hundred and fifty knots can not be described as having "the same aerodynamic efficiency as a state of the art turbo prop such as Denali" which cruises at two hundred and eighty-five knots on one hundred and ninety-six pounds per hour,albeit at about half the weight (which does not yet appear to have been published).
Thank you again for the opportunity to further discuss the Pegasus concept.
Grand Logistics.