All credits to @FCIUSHonda RA61$H
Mclaren started developing the 2015 MP4-30 with the Size-zero concept in mind. Their partner, Honda, accepted that concept and designed the RA615H, but was forced to compromise powerto keep the PU compact. What was lost in power was supposed to be gained by aerodynamic performance, but that didn't work out; poor results persisted throughout the season.
Did they accept a lower output as inevitable given the dimension requirements? Or did they think that they could manage both, only to fail as a result?
Kakuda admits, "I don't think we fully understood how difficult it would be. "Although he is developing the PU at HRD Sakura, Kakuda nonetheless cannot be fully certain, as he joined the program in 09l'15—after the design ofthe RA615H was ﬁnalized. Thus, his explanations for the 2015 powerunit inevitably calls upon speculation based upon his expertise, in addition to his experience.
"We were starting from scratch. so we didn't fully understand the difficulty of developing a PU. This lack of understanding certainly played a part in our acceding to the chassis ' demands. when developing our first PU. However. once out on the track. we realized that there were a lot ofissues."
They had ﬁtted the turbine, compressor, and the MGU-H inside ofthe V-bank, but this decision had backﬁred.
"The turbocharger's position inside of the V-bank limited its size. It's difficult to increase its efficiency without making it larger. ”
Unless the turbocharger's efﬁciency is increased, the MGU-H cannot be utilized fully, and the thermal energy cannot be harvested enough. This lead to an insufﬁcient deployment ofthe MGU.
"Because the turbocharger was inside the V-bank. the induction system was oriented quite forcefully. When I first saw this I couldn't help but wonder. 'will this really work?' We were starting with a fresh mindset. but that resulted in us being unable to overcome reliability and performance hurdles.
New regulations in 2015 allowed for variable intake systems. Such systems are usually used to change the stroke of the intake funnel. increasing the charging efﬁciency. Combined with a turbocharged engine, simply increasing the charging efﬁciency does not necessarily increase output. so the system is sometimes manipulated to shut out air.
Either way. variable intake technology leads to an increase in output. so Honda adopted it without hesitation.
In the RA615H, packaging needs forced the plenum chamberto be ﬂat. so the intake funnel for the cylinder banks could not be extended upward. Instead. they intersected one another horizontally. like crossed arms. Honda was attempting to change the funnel length in such a layout.
“Components were moving around rapidly in such a small space. I was shocked by its complexity when I ﬁrst saw it."
That complexity may have backﬁred. as the PU struggled with sticky funnels in the ﬁrst half ofthe season.
The focus for the 2016 RA616H was the improvement ofthe cramped induction system.
“We focused our improvements to the induction and turbocharger. On one hand. we wanted to recover the inefﬁciencies ofthe RA615H by freeing up the induction, while we also wanted to enlarge the turbochargers.
Aﬂer negotiations with Mclaren. the allocated space for the engine increased somewhat. The additional space was used to raise the plenum chamber by 30mm. allowing for the branch from the plenum chamber to the cylinder head to
be a more optimal shape.
“Speaking of development for the 2016 season, we couldn‘t fully revamp the engine because ofthe Token system.
That partly led to our decision to center our development on the turbocharger and induction.
The 2017 RA617H saw widespread changes.
"I recall that the current regulations were conﬁrmed in 2009. Constructors continuously competing in F1 since then were starting development quite early. but we only resumed our involvement in 2013. when our return to F1 was made public.“
The current regulations were implemented in 2014. Honda started competing in 2015. so on the surface it may seem like a 1 year delay—but Honda was lagging years behind in development. Additionally. the disparity in the quality of the development between a team that had prepared meticulously after years of continued competition. and a team that was just starting to regain its footing in F1, was quite large. Kakuda insists. though, that “it isn‘t excusable."
“Once we stop competing. everything is reset. and we lose the ability to recognize the issues that others ﬁnd obvious.
Those issues were a revelation to us as we developed the PU, For example. the powertrain ofthe MGU-K is one example. We struggled a lotto develop it. but other constructors already had experience from developing KERS. and must have already solved a lot of issues"
One drastic change from 2016 to 2017 was the MGU—K. In the ﬁrst two years, the output ofthe MGU-K was merged into the drivetrain at the rear ofthe PU via an independent geartrain. Although this wasn‘t entirely at fault, shaft failures from vibrations frequently occurred. This issue could have been one ofthose issues that teams with KERS experience had resolved long ago.
To reduce weight and friction, in addition to improve reliability. the RA617H merges the output ofthe MGU-K at the front ofthe PU instead. Issues from the newly designed MGU-K haunted the team in 2017.
"We had several issues in 2017. including drivetrain issues around the MGU-K. We may havejust been lucky in ‘15 and ‘16, but attaching a gearbox to the PU changes the resonance characteristics. which in turn changes the load on the PU. We attempted to anticipate this somewhat in our dyno tests. but issues still surfaced when we took to the circuit.
The newest-spec gearbox is often unavailable until immediater before the Shakedown. However. Kakuda admits that being unable to test the PU with an actual gearbox was a mistake. The mistake will be learnt from in their partnership with Toro Rosso.
“We are being very careful of our evaluation, because the structure ofthe gearbox is changing. Toro Rosso's gearbox isn‘t changing much from ‘17. so we started testing with that gearbox from an early stage in development.“
There were more struggles. The RA617H saw a drastic change in turbocharger placement. Until then. it was situated inside the V—bank. but the turbine was now placed in the rear. while the compressor was moved to the front. At the same time. the shaft connecting the compressor. MGU-H. and the turbine was lowered. allowing for the MGU-H—still inside the V—bank—to be lowered too. Moving the compressor and turbine outside ofthe V bank opened Lip more space. and enabled the design ofthe induction system to be more ﬂexible.
"In the second half of '15. we were unable to increase power no matterwhat we did. With the basic design already in shape. there's not much room to reduce weight. or lower the center of gravity.
Reﬂecting now. our PUs Lip to the RA616H was unbeﬂtting for an F1 engine. We therefore decided to do everything we can. and moved the turbo out ofthe bank to lower the center of gravity. We also increased our ﬂexibility for the induction at the same time."
In the RA615H and the RA616H. the intake funnel faced each other horizontally in the ﬂat plenum chamber. The spec 2 engine deployed for Round 10 in 2016 featured a more vertically positioned intake funnel. so the two sides converged at an angle. Combined with a straightened branch. air now ﬂowed more smoothly.
The RA617H saw drastic redesigning ofthe intake ﬂow. The variable intake funnels were arranged longitudinally. not laterally. situated in the front and rear. Air ﬂowing in from the top now simply ﬂowed into the rear ofthe power unit.
"[The branch up to the RA616H] had to circumnavigate the turbo. In the RA617H. we made it so that the air now ﬂows from the front to back. to retain dynamic pressure. In the RA616H. the intake was sucking up turbulent air from the side. The pipes crossed when the variable intake system was active. which caused interference at times. The RA617H has a greater region ofvariablemanipulation too. We are looking to bring it to the optimal range for each revolution range.”
The protruding compressor now invaded the space for the oil tank. distorting its shape.
"Because ofthat. we faced issues at acceleration/deceleration and cornering where oil was not properly delivered. or burst out."
When a lot of oil was put in to ensure that it was delivered properly. it would ﬂow into the intake duct under certain conditions. The compressor than took in that air. resulting in MGU-H failures.
The oil damaged the bearings. scrubbed offthe lubricant. thus increasing the temperature.
"We predicted these symptoms. so we attempted to test them on the bench."
They simulated the G forces from driving. and measured the lubrication ofthe oil.
"Partly because the sensor was new. we were unable to use it when we wanted to: we ran out of time. and testing started. lssues arose at testing. which damaged Mclaren's trust in us."
Like the MGU-K issues. the oil-related issues were also resolved and Honda are prepared for 2018.
The RA617H was updated to Spec 3.8 in '17. in which Spec 3—deployed at Baku—saw major changes to the speciﬁcations around combustion. In the RA617H, a prechamber was deployed. lCEs become more efﬁcient as the air-to-fuel ratio becomes leaner. but it becomes harder to ignite.
The prechamber aims to resolve this issue. When the rich mixture around the spark plug in the prechamber is ignited. ﬂames erupt in the main combustion chamber. burning the lean air.
Spec 3 had resolved the technical issues around that process.
"Ideally this was something we must have completed before the season started. But Mclaren wasn't willing to wait that long." says Kakuta with some regret. However. a breakthrough is in sight for 2018.
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