[Charles Hunt]

The Rans S7 I am purchasing has a significantly lower MTOW than others. KATI was originally Rotax 582 powered but has been upgraded (?) to a Jabiru 2200.

Most of the others are 912 powered.

Is there any LAA design code that limits mass or horsepower per unit wing area or similar that would account for the differing MTOWs?

(To those who will say 'ask the laa' I did do last February, and have chased three times in the last fortnight without success.)

[nallen]

Could the original MTOW be a function of the rate of climb with the 582? (There's a minimum rate of climb deemed acceptable -- the Jodel D9 I used to fly had a higher MTOW than all the others on the register, which seems to have been due to someone demonstrating long ago that it could achieve >300fpm at that higher weight.)

[Charles Hunt]

Thanks Nick. I do now have a reply effectively saying 'depends how it performs at the higher all up weight'. But with no fixed figures to work to.

Hopefully I can discuss with the flight test pilot and see what can be achieved.

[Bobcro]

Charles ;

You didn't state the HP of the various engines mentioned nor confirm that there is only one type of undercarriage for the aircraft. Aircraft are often recertified at higher weights if the undercarriage is strengthened, this has happened with several Cessna models.

You will need permission to fly the aircraft at weights above those stated in the permit unless you can get the LAA to agree to an increased AUW by producing evidence that there are other aircraft fitted with the same engine as yours flying at higher weights.

[Rod1]

Is there a Rans S7 on an LAA permit with a Jab engine other than yours? If so what is the MTOW. Is yours structurally identical to the Rotax version (firewall back) and can you prove it if it is?

Rod1

[Genghis the Engineer]

I would think it's based upon CS.VLA and the nature of the evidence that's actually been provided to LAA Engineering.

If you're unfamiliar with it, here is CS.VLA..

LAA tends to be somewhat relaxed about their flight testing - and usually do very little performance testing, but are very strict on structural evidence, so my guess (but it's only a guess) is that the actual structural data for your variant was at this particular MTOW and other aeroplanes have some difference of structure. But, it could I suppose be performance based.

If you have a decent store of documents for the aeroplane, particularly for the original build and flight testing I'd be happy to go through them and give a more professional opinion in exchange for an hour or two in the S7. (Or you can have such advice as I can offer here for nothing of course ).

G

[stickandrudderman]

American Falcos have a MTOW of 2100lbs whereas UK ones have 1800lbs. Go figure!

[Charles Hunt]

Rod - No, KATI is the only one.

G - Many thanks, I wondered how I was going to get a nap this afternoon.

[Genghis the Engineer]

Charles ;

You didn't state the HP of the various engines mentioned nor confirm that there is only one type of undercarriage for the aircraft. Aircraft are often recertified at higher weights if the undercarriage is strengthened, this has happened with several Cessna models.

Rotax 912 is 85hp
Rotax 582/48 (the usual model) is 65hp
Jabiru 2200 claims 80hp, but Australian horses always seem to be smaller than Austrian horses - so comparing to the two Rotax engines I'd say nearer 70hp.

With an MTOW in the range 400-600kg, the 582 is going to be a bit limiting in terms of minimum climb performance, but hard to see it being bad enough to limit MTOW.

Looking at the various examples of the type on G-INFO, what jumps out at me is that there seem to be multiple MTOWs going on here, just within the basic S7 Courier model...

G-BVNY/582/420kg
G-BWMN/912/499kg
G-CBNF/912/544kg
G-KATI/Jab2200/465kg
G-OJKM/912/545kg
G-BWKJ/582/464kg

So you've got six basic S7s, with three different engines, and 6 different MTOWs (well four, as I can't imagine that the difference between 544kg and 545kg or 464kg and 465kg is other than a typo). There are two different MTOWs with the 912, and two with the 582. That is, frankly, odd. Whether I ever get involved or not, I'd be fascinated just to learn why this is.

G

[Sooty25]

American Falcos have a MTOW of 2100lbs whereas UK ones have 1800lbs. Go figure!

something to do with their diets maybe?

[Charles Hunt]

G - Hence my confusion!

Is there any weight limit break for permitting that would explain those with a lower limit?

[Genghis the Engineer]

Not that's obvious to me. MTOW is generally defined by structural strength (main flight structure, undercarriage) and by the ability to achieve a minimum climb performance.

I can't see the heaviest of those aeroplanes struggling to achieve an "okay" if unimpressive climb rate, even with a 582.

So structural limitations seem most likely, suggesting that those six "Rans S7s" are actually several different aircraft designs.

An outside possibility is that you have different wings with different lift characteristics - CS.VLA requires a stall speed not above 45kts CAS, so maybe they all an MTOW set by stall speed. That would be unusual however, as LAA tend to be pretty relaxed about that sort of testing.

The other obvious explanation is a good old fashioned cock-up when some of the aeroplanes were approved, that's never been fixed. At the moment, I confess that seems most likely.

G

[ivor.phillips]

American Falcos have a MTOW of 2100lbs whereas UK ones have 1800lbs. Go figure!

Like wise with the Europa XS. Europe and the US it’s
1450 lbs and the UK it’s 1370lbs

[Rob L]

In the US: the builder (who is the "manufacturer") takes the build liability.
In the UK: the LAA take on the design (and build) liability for LAA-approved aircraft.

[mikehallam]

AFIR. Rans had at two different S7 air frames.
Early ones were more lightly constructed and later a more robust one with the ubiquitous Rotax 4 stroke power plant.

mike hallam.
BTW. What was your understanding of the freely available LAA TADs ?
e.g. this lifted just now:-
......"Loading Limitations
Maximum Total Weight Authorised: 545 kg (1200 lb) CG Range: 44.5” to 50.5” aft of datum Datum Point is: front face of the firewall...."