Aircraft: use of piston engine, small report

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Christophe
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Aircraft: use of piston engine, small report




by Christophe » 14/04/08, 13:20

I have uploaded a report of a small student project that I had done in 2001 on piston engines in aviation (light but not only). It is quite synthetic and will not teach anything to kk1 who knows a bit about the field. For others it will give some basics.

Download here: Aviation, aviation piston engines

Here is the summary

1. Evolution of piston engines in aviation
1.1. History engines
1.1.1. The first engines
1.1.2. Piston engines
1.1.3. Jets
1.2. The influence of the plane on auto
2. Technology existing reciprocating engines
2.1. Role of a propellant, general
2.1.1. direct drive motors
2.1.2. indirect propulsion engines
2.2. piston engines: power and performance Notion
2.2.1. engine performance
2.2.2. propeller efficiency
2.2.3. overall performance
2.3. Different types of piston engines
2.3.1. Online engines
2.3.2. Radial engines
2.3.3. Engines flat
2.3.4. V-engines
2.4. Primer on propeller
2.4.1. geometric characteristics of a propeller
2.4.2. Limits of a helix
2.4.3. The propeller with variable pitch
2.5. Variation in the power of an aircraft piston engine
2.6. Operation of propeller phasing circuit
2.7. Features of an aircraft engine relative to the automobile
2.7.1. The special components
2.7.2. Study carburetion
2.7.3. Overfeeding in aeronautics
2.7.4. The recooling
3. Replacements for aviation piston engines
3.1. Other propulsion systems
3.1.1. turboprops
3.1.2. turbojets
3.1.3. the stratoréacteurs
3.1.4. The rocket engines
3.2. The replacement of piston engines: the example of Canadair
3.3. Diesel engines: the example of Renault engine Morane


Download here: Aviation, aviation piston engines
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by Christophe » 14/04/08, 13:27

After the dissemination of this report, I received an email from Mr Paul Lucas, co-creator of the Dieselis, he made many wise comments to me. I asked him if I could put them here or better that he himself registers on the forums.
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by Christophe » 14/04/08, 14:13

Here are the remarks that I will as soon as possible, integrate in the report

Paul Lucas wrote:1.1.2

>> another type of engine, lighter and more muscular, was needed

no, it was a better designed cell which was essential: if not stable and easy to pilot, which was at least controllable, which was not the case with Ader's machines.

On the other hand its engine was clearly more powerful and lighter than that of Wright (12 cv).

The decisive contribution of the Wright is not their driving force, it is their experimental method: tests, methodical progression, learning to pilot and the controlled practice of the three-axis turn (warping).



>> a heavily modified automobile engine

an automobile type engine (4 cyl in line)



>> provide just the necessary lift

not lift, speed



>> spirit of st louis equipped with a Whirlwind

of a Wright "Whirlwind".

The company is named after the Wright brothers, but they are not part of it.



113


>> piston engines 1/2 kg of thrust for each kg of engine

Static thrust?

the thrust is about 1.5 to 2 kg per horse

the mass of piston engines from the time of the first reactors (1944) was around 0.5 to 0.6 kg / hp

which makes 3 to 4 kg of thrust per kg of engine



>> during powerful acceleration, the propellers ...

it is at the maximum continuous speed, in level (speed of rotation + speed of advance) that the speed problem at the blade tip arises.



222 Propeller efficiency

the following formula is the one we read in all the books but it is open to discussion because it does not represent physical reality.

If we set Vp = 0 (plane at stopping point), we have zero efficiency, therefore theoretically zero traction, which is not the case.

The propeller does not accelerate an airplane, it accelerates an air mass.

We should therefore consider not the plane speed but the speed of the air mass passing through the propeller, which is never zero, even with the plane stopped.

The speed downstream of the propeller is> airplane speed.



>> constant efficiency, close to 0.85

it depends on the flight regime (climb or cruise).

The efficiency varies more, depending on the regime for which the propeller is optimized, say from 0.70 to 0.85



23

>> 4 large families

2 families: star,

in line, single or double (V or flat)





132 Curtiss



>> the most powerful star engine

single star: 2100 hp, ok

two-star engines reached 3500 hp



241 a pale and not a pale



>> the twist corresponds ...

the twist is a variation of the setting to obtain an optimal lift distribution along the blade.



>> reference section

at 70 or 75%, not at 50%



27

>> the speed is around 3000 revolutions

rather 2500 - 2700



>> ... the more stable the average torque

is regular.



311

With the evolution of the price of oil (and pollution concerns), there is a lack of essential information concerning TP (turboprop): the variation of their specific consumption as a function of the% of power. I was able to establish a curve for the Cessna 208 Caravan (flight test). The ATR doc validated the shape of this curve. The sfc of a turbine at idle is very high, see attached curve (source doc ATR). High consumption in the car park (ATR in Hotel mode: the right engine replaces the APU), when driving, when going downhill. This info does not appear on any TP manufacturer site, of course. The very poor performance of reactors and TPs with low loads (and associated emissions, incomplete combustion) is responsible for very high pollution at airports. Worst of all, the Concorde: 800 kg to 1 ton of fuel for taxiing.



32

>> TP are still used in aging planes (?)

ATR 72-500, Bombardier Q-400: consume less than jets and sell very well!



>> the propeller makes it possible to reach M 0.6 to M 0.8

M 0.5, ok, M 0.6 large max. Beyond that is special transonic propeller



32 Renault Morane

designation modified thereafter SR: Snecma-Renault



>> ratio 10 between the car and the plane

I find a ratio about 3 to 5

car 40 to 80 kW / ton

aircraft 100 to 200 kW / ton



>> robust design

the engine can be robust but the design?

Reliability comes from the elimination of ignition, intake by injection pump instead of carburetor, fuel lubricating the pump, and above all from the accumulated experience of millions (or billions) of industrial and other engines. It is for this reason that an airplane diesel engine must be as close as possible to mass production and not an "ideal" engine, the development of which will inevitably be long and expensive. Developing a "new" engine costs three times more than modifying an existing engine. Order of magnitude 3 ME instead of 100 - 30 (info engine engineer from Renault). Attached is an extract from Snecma doc concerning the technical choices of the SR engine.





>> diesel engine specifications

missing a decisive criterion (respected by Thielert who uses Mercedes bases):

- the engine must be derived from an automobile engine to reduce development costs to a bearable level and integrate the know-how of the automobile industry (reliability). The block should be modified as little as possible. This implies a unit displacement <0.7 liter and water cooling. Almost all car manufacturers have given up on air cooling. In aviation, air cooling results in a limitation of the flight envelope: engine always too hot on the way up (we enrich to cool down, the top!) And too cold on the way down, thermal shock. Fast airplanes with Lycoming engines cannot climb or descend steeply.



Conclusion

What stopped the development of the piston engine in the 50s was the speed limitation (propeller propulsion), faced with the demand for high speed (long-haul transatlantic), the arrival of reliable reactors AND the minimal cost fuel. The consumption of the first reactors was very high. The last DC-7 and Lockeed Constellation had 30 and 35 liters of fuel, the B 000 capable of crossing the Atlantic 707 to 80 liters.



Reactor progress

Here are some documents:



Improvement of the performance of aircraft 1960 - 2000. See document Dgac - Snecma.

Engine manufacturers (reactors) present their technical progress with advantage by "forgetting" piston engines.

The last "compound" engines which recovered energy from the exhaust gases had a sfc of 0.175 kg / hp / h



idem, with figures since 1930.

Figures before 1960 show that progress has been made mainly in speed but not much in consumption / kilometer.

Medium-haul aircraft (A320) consume more than long-haul, not because they are less efficient, but because they spend more time at low engine load.



PROSPECTS AND ACHIEVEMENTS

Today we can make planes with diesel engines (propellers) consuming half as much as turboprop planes and three times less than jet planes.

Airport pollution can also be divided by 10 (LTO cycle):

. an A380 consumes 3980 kg of fuel in the LTO cycle, i.e. 7 kg for 550 passengers

. a diesel powered aircraft would consume 700g per passenger for the same cycle.

Sincerely,

Paul Lucas
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by Chatham » 14/04/08, 15:14

I generally agree with Paul Lucas' remarks, except:
The most powerful piston engine that has been in service developed 3750hp (Wright R3350 18cyl turbo compound in its latest version), but 3500hp (direct petrol injection) on the superconstellation.
The efficiency of the propeller 70 to 85% on small planes, reached 98% in the best case at the altitude and speed of better efficiency: Soviet counter-rotating propellers of transonic type: see bomber TU 95 which flies at 925km / h (235kw / ton) with 15000km of autonomy ... is much better than a B52 jet ... which is just a little faster (1000km / h)

In the 50s we also switched to reactors for other factors:
- 4 x lower maintenance cost
-weight half less at equal thrust
- less noise and no vibrations
For speed we could have made commercial propeller planes flying at 800km / h without too many problems (see TU 114 from the 50s and 60s = 770km / h when cruising ...)

In 1935, there was the Clerget star diesel engine whose consumption was 175g / cv / h, the same as the Renault Morane 60 years later, but with a much better power-to-weight ratio than the SMA which has really nothing revolutionary ... and whose development has been peppered with numerous incidents : Mrgreen:
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by Christophe » 14/04/08, 15:43

A good curve is better than all speeches as we say:

Image
Last edited by Christophe the 15 / 09 / 08, 22: 58, 2 edited once.
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by Plxdesi » 15/04/08, 19:26

> The efficiency of the propeller 70 to 85% on small aircraft, reached 98% (Soviet counter-rotating propellers)
No, certainly not: the maximum propulsion efficiency is around 0.90 for a counter-rotating, and below Mach 0.7. The total speed (airplane speed plus rotation speed) makes this Mach an absolute barrier beyond which the efficiency can only decrease because the speed at the blade tip greatly exceeds M 0.80. Airliners (soaring wings, supercritical profiles) do not exceed M 0.85 for the same reason.

> the TU 95 bomber which flies at 925km / h (235kw / ton) with 15000km of range ... significantly better than a jet B52 ... which is just a little faster (1000km / h)

Tu 95, cruising speed 720 to 750 km / h. Speed ​​record recorded in 1989: 834 km / h. The Tu 95 was able to reach this speed because it was very highly powered. Special transonic propellers (this was not the case with the Tu 95) can go up to M 0.80, but this is at the cost of a loss of efficiency, which drops to around 0.82 at Mach 0.80.
Sources "Peyrat-Armandy, transport planes", Tu-95 Bear Warbird Tech Series
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by Chatham » 15/04/08, 21:59

Christophe wrote:A good curve is better than all speeches as we say:

https://www.econologie.com/photo/puissan ... iation.gif


I know this curve, the catch is that it is skewed because in the 50s there was no charter, the plane was a luxury means of transport, and the points that are noted for recent jet planes are the high density versions (A380 with 800 seats for example ... (hello comfort ...)
Thus the most modern planes A340, B777 or A380 in normal version have a consumption in reality hardly equivalent to that of BR763 which itself was actually slightly lower than that of Loockeed 1049 Superconstellation (source Air France) which it is true was faster...

As for Plxdesi, he tends to rewrite aviation history on the basis of a single source ... I prefer to believe more serious and multiple sources, especially when the information overlaps ...
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by Christophe » 15/04/08, 22:04

Ah yes good remark Chatam ...

Besides, the A380 is missing it must be "south southeast" of the B 777 I suppose ...

So what are they waiting for to redo the diesel then the manufacturers?
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by Other » 16/04/08, 07:04

Hello

For small aviation few small engines have been developed and succeeded well (in the range of 60hp to 180Hp) I would not speak of reliability, but of the airplane / engine / propeller adaptation.
Among the most successful the Continental 90hp the lycoming 180hp
The poorly adapted and most widespread the continental 100hp, the 85 hp, the Franklin 125hp
The worst engine propeller hitch is on the Cessna 150 and it is the best-selling aircraft…
An airplane engine must have a high torque, it has a different design from an automobile,
It must turn at 2800rpm maximum, reach its maximum torque around 2300rpm, have 75% of its power at 2400 rpm be able to provide 80% of its power continuously, and if mounted on a propeller with a fixed pitch be able to fetch 100% of its nominal power in level.
Being simple, light, robust, is reliable,
This is suitable for (large) displacement engines with a camshaft that has a parure for torque and power at low speed (all the opposite of the sharp automobile engine)

Strangely we note that these are characteristics of the diesel engine
The disadvantage in auto diesel is heavy, slowed down, needs a fairly consistent steering wheel, it will seek its maximum power at speeds of 4000 rpm, which requires the manufacturer to install a reducer, which has the disadvantage of limiting the choice in the propellers.
Metal propellers with a gear reducer pose a problem on gears
Belt reducers require belt replacement every 500 hours
A reducer is also mechanical losses, the weight gain on the motor is lost in the reducer.
Another problem on car engines is all the electronic servitude which cannot be doubled for reliability, and which is less useful on constant speed engines.

In aviation reliability comes before yield and economy.

If the car manufacturers had designed a mechanical indirect injection diesel engine, which has a fairly large displacement its full power at 3000 rpm
Its maximum torque at 2000 rpm an interesting weight, it would make the ideal candidate for an airplane.

Contrary to what many people think about propellers, a variable pitch propeller, has a perfect twist only at a certain position, when the blade turns on the hub the theoretical twist varies more quickly at the tip of the blade than at the hub
It becomes unfavorable for the big step.
A variable pitch propeller is only useful for a fast plane, installing a variable pitch propeller on a Piper J3 or an ULM which has a speed of 120 km / h uphill and a speed of 160 km / h cruising is ridiculous, a propeller with fixed pitch well proportioning is also efficient.
A good propeller has a low cruising slip around 10%
It must be of sufficiently large diameter to have a speed at the end of the blade around 750kmh (the one that turns the fastest on the Cessna 180 reaches 1050 kmh at the end of the blade at takeoff) in a cruise around 800kmh.
The trend is to install propellers of small diameter, to compensate for the lack of torque of the engines, this makes a significant slip on takeoff and mounted. (case of Cessna 150)
There are several schools of thought depending on the country
In Russia it's big propellers, pale drop, square tip
In America it is large minimum propeller 1,80m to 2,15m with medium tip, square or rounded blades. Duralumin and composite
In France it is small propellers, with narrow ends, pointed or slightly rounded generally in wood or composite.

The best propellers were designed by Lucien Chauvier in the early days of aviation, almost all the propellers were taken from his designs.
Sometimes I wonder why this knowledge is lost.

Andre
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by Plxdesi » 16/04/08, 10:56

> the points which are noted for recent jets are the high density versions (A380 with 800 seats for example ...
This figure comes from a Dgac-Snecma document from 2005. The A380 is probably not there.
> When in Plxdesi, he tends to rewrite aviation history on faith from one source ... I prefer to believe more serious sources.
1. Do you mean that Peyrat Armandy's book is not a serious source? It would be good to cite your sources.
2. The document on the Tu-95 cites 14 world records, in speed and altitude at various loads. If this plane could reach 900 km / h or more, one wonders why this record was not established.
> The efficiency of the propeller 70 to 85% on small airplanes, reached 98% in the best case ... counter-rotating propellers.
The efficiency of 0.98 that you give for a contra-rotating propeller is the theoretical value of propulsive efficiency (in perfect fluid without losses due to rotation), which is obviously better than the effective propeller efficiency, that which you gave for " small planes ". Interaction gives for the Tu-95 a propulsive efficiency of 0.988 for an effective propeller efficiency of 0.90. A "small plane" can arrive at 0.86 - 0.87 effective yield.
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