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A record empty/MTOW ratio?

The OneAircraft ONE, for its 2+2 version, boasts empty weight of 330 kg for a MTOW of 750 kg. I can’t help feeling some skepticism, this sounds very very optimistic. Also, the 100 HP 912S might have its hands more than full with 750 kg… Would many be actually flying?

See here:

EBZH Kiewit, Belgium

The are many aircraft with MTOW 750 kg and a Rotax already flying, Aquila comes to mind.

The elephant is the circulation
ENVA ENOP ENMO, Norway

Dynaero MCR 4S has the same ratio:
https://fr.wikipedia.org/wiki/Dyn%27Aéro_MCR_4S

Jean
EBST, Belgium

Jan_Olieslagers wrote:

Also, the 100 HP 912S might have its hands more than full with 750 kg

The venerable Socata Rallye 100 has a 100-hp O-200 with a MTOW of 770 kg. Not a speed daemon, mind you, but it does what it says on the tin (pun intended).

LKBU (near Prague), Czech Republic

Jan_Olieslagers wrote:

The OneAircraft ONE, for its 2+2 version, boasts empty weight of 330 kg for a MTOW of 750 kg

It’s indeed quite an achievement from structural engineering point of view. Colomban MC100 comes into my mind as having a similar empty/mtow ratio. Certified Jodel D140 comes close. The question is what compromises have been made during design process to achieve this low empty weight?

Ultranomad wrote:

The venerable Socata Rallye 100 has a 100-hp O-200 with a MTOW of 770 kg. Not a speed daemon, mind you, but it does what it says on the tin (pun intended).

In case of the O-200 one can firewall the throttle without time restrictions, in case of Rotax it’s a different thing. 100 hp in Continental is not equal to 100hp in Rotax

Robin_253 wrote:

In case of the O-200 one can firewall the throttle without time restrictions, in case of Rotax it’s a different thing. 100 hp in Continental is not equal to 100hp in Rotax

No, it’s much less. The MCR typically has a constant speed drive, thus you will get the 100 hp when needed (not continuously though). The Ralley has fixed pitch, and will make maybe 80-90 at take off depending on propeller. I have flown the Super Dimona (a seriously big and heavy motorglider, 770 kg) with a Turbo Rotax and constant speed, I think 115 hp? If it’s a terribly good idea to extract 100+ HP out of the tiny Rotax engine, is another matter though.

Even the ancient Super Cub -95 has MTOW of 680 kg with a 90 hp engine.

The elephant is the circulation
ENVA ENOP ENMO, Norway

We are mixing apples and oranges here. An O200 will give you 100 hp for as along as you need. A Rotax 912 will give you 75 hp (Do I remember correctly?) for as long as you need. That’s the difference. Of course a variable pitch prop is more flexible in terms of efficiency, but it comes at a cost: weight, coplexity, maintainance, cost….
There are lots of variable pich props for O-200, therefore if we want to compare performance of Rotax with a variable prop let’s choose a variable prop for the O-200

Robin_253 wrote:

We are mixing apples and oranges here. An O200 will give you 100 hp for as along as you need.

Well, a 912 iS will give you 98 as long as you need, a 914 will give you 105. But, the point was that the MCR 4S is recommended with constant speed prop and a 914, and only with a constant speed prop will you achieve the needed RPM to get all available HP at any given point in time, and a turbo is needed to get that HP also at alt > 0. An O-200 will not give you 100 HP, ever, unless with a constant speed prop, and then only at sea level. A Rallye has neither turbo, nor constant speed, the MCR 4S usually do.

Apples and oranges maybe, but the MCR 4S sure has remarkable performance, the Rallye 100 not so much.

Robin_253 wrote:

The question is what compromises have been made during design process to achieve this low empty weight?

None IMO. It’s simply a well designed aircraft around the principle of using a Rotax 912/914 in a 4 seat high performance cruiser. All carbon, double fowler flaps and so on.

The elephant is the circulation
ENVA ENOP ENMO, Norway

@Robin_253, According to the operator manual, a Rotax 912ULS will give you 73.5kW (98HP) at 5800RPM for 5 min and 69kW (92HP) at 5500RPM max continuous. Consumption at max continuous is 25L/h.

The Rotax 912UL gives you 59.6kW (79.4HP) at 5800RPM for 5min and 58kW (77.3HP) at 5500RPM max continuous at 22.6L/h.

@LeSving, The ROTAX 914 has a TBO of 2000hours. It is being used in many US drones and is typically making TBO without much issues.
With a good installation (with intercooler), you get 100HP continuous till 16000ft (critical altitude) the whole day.

Belgium

The question is what compromises have been made during design process to achieve this low empty weight?

I know nothing about these types flying-wise but it takes only a casual walk around the hall at Aero EDNY to see that key components of the low weight are

  • absolutely minimal (or zero) internal trim
  • absolutely minimal seat padding
  • little or no mechanism for seat adjustment (except distance to pedals)
  • very thin body panels (1 to 1.5mm plastic)

Hopefully the structure is OK.

Empty weight is often a suspicious number. In the certified world it is often a figure which no actual flying specimen of that plane has. The reason for it is often avionics; in some cases the empty weight in the POH applies to configurations which have never existed.

Administrator
Shoreham EGKA, United Kingdom
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