structural limitations

[flapper]

Below is an excerpt from a British aviation magazine reporter's impressions of the Sonex. The comment is provocative. My familiarity with the Sonex is not sufficient to assess the validity of the information presented. Comments would be appreciated.

Pilot Magazine (Britain)
Flight test: Sonex Aircraft LLC Sonex
PUBLISHED: 17:31 11 June 2018

However, if you plan on cruising this fast it’d better be smooth, because Va and Vno (design manoeuvring speed and structural speed) are the same at 109kt IAS. In fact, the relatively light weight (even when operating at the Utility max weight) and low wing loading mean that cruising at the sort of speeds the Sonex can achieve requires a pilot to be quite circumspect if there’s any possibility of turbulence.

[GraemeSmith]

Well simplistically - Vno - or top of the green/bottom of the yellow arcs on my bird is about 109 knots (and that is also Va). Ha - same as the Brit article.

I will say I am careful if deciding to operate in the yellow arc and keep it for smooth smooth smooth air. Slightest bit of turbulence and I back off into the green arc. That said - Va is "one full deflection of one control surface" - and if you are over 109 KIAS - it's unlikely you are going there. For sure lots of smaller inputs on all three axes is likely - but it is not like I'm slamming full aileron and elevator at the same time while up in the yellow arc.

Thus when doing acro - which requires some pretty big but SMOOTH control inputs - I do not fly acro in the Sonex in anything but smooth air. And though there may be some pretty big inputs - they are smooth and steady and you have to be ready to unload the wing is anything starts to go wrong - both to get out the probable spin and to keep the G's in limits. It's a slippy plane and can be headed to Vne awful quickly if you mess up.

I have a prohibition on snap roles. That requires an almost simultaneous stick full back and full push on the rudder (ie TWO full control inputs) - and even is started below Va - you have to be awful close to Va to get the plane to snap and it's just too big a risk. Even with the Acro G limits. That empennage is not particularly resistant to torsional loads and a snap roll is all torsion from the back end applied to the front. I'd like the tail feathers to stay on!

EDIT - and for the Waiex with a Service Bulletin to strengthen the tail feathers which were originally a bit under designed - this is probably even more important. Don't snap it!

[Bryan Cotton]

Hi flapper,
Welcome to the forum! The POH that Sonex supplied with my kit specifies Va as 125 mph (109kts) and Vc (Max Structural Cruise, top of the green arc) as 136 mph (118 kts). So, I have two observations:
1) Pilot Magazine seems to have Vno wrong. (edit: although Graeme seems to agree)
2) This is really not much different than any non-slow airplane I've flown - you have to slow down to Vno for turbulence.

My Aerovee powered Waiex cruises between 100kts and nearly 120kts depending upon how much fuel I burn. Based on this I only need to slow down for comfort. The faster guys with the nifty engines might have more to worry about. Maybe one of them will chime in.

With a 4.4G/-2.2G utility load factor, and a 6G/-3G acrobatic weight load factor rating, the airplane is pretty structurally sound. These ratings have been backed up with static tests.

[flapper]

Thanks. That is great info. I am enlightened. Fly by the numbers.

[Arjay]

Graeme/others: what speeds do you use for aerobatics? I.e. entry and never exceed speeds for loops, rolls, hammerheads, etc?

Ron j.

[Bryan Cotton]

Graeme/others: what speeds do you use for aerobatics? I.e. entry and never exceed speeds for loops, rolls, hammerheads, etc?

Ron j.

Having had the same question, there are a bunch of great youtube videos with commentary.





Here is one where Michael did a data overlay on Mike's video:

[GraemeSmith]

Graeme/others: what speeds do you use for aerobatics? I.e. entry and never exceed speeds for loops, rolls, hammerheads, etc?

I've refined it a little since I posted that. It will Aileron Roll as slow at 70 KIAS - but it is a huge, slow, messy affair! Serious nose up at start and nose down at end. I now tend to do Aileron Rolls at 110KIAS and keep the 120 for when I want to four point it.

Split S - slower is better - cause once inverted and pulling through she will quickly head for VNe. And of you pull too hard - you get an accelerated stall and a lot of mushing downhill.

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Please remember - these are for my plane. They may offer guidance for yours - but you need to experiment and find the answers specific to your plane and make the appropriate logbook entries.