Is the PA-28 Wing Spar really weaker compared to other designs

The wing spar attach points on PA28 series aircraft (and indeed all the aircraft based on that design) do “look” less substantial than on some other aircraft.

Worth noting I suppose that the wings on a Bonanza are held on with two bolts each.

In flight breakups are not necessarily wing spar failure either, I don’t know why everyone keeps talking about the spar only. You can have flutter leading to failure of empennage components, for example. Stabilator attachments on PA28 and TB20 look surprisingly fragile given the job they carry out.

I did look into the PA28 wing spar failures and whilst I do believe it’s less strong than some other designs, all of the aircraft which had failures in normal flight regimes are aircraft which have had very hard lives.

Finally I’d add that the PA28 fleet now probably has very few, if any, aircraft with defective spars following the inspection ADs.

Just adding a picture of the PA24 Comanche spar to the collection for debate. The structure is very noticeably thicker than the PA28 type but also keep in mind PA24 type certificate has engines up to 400hp IO720. What I find interesting however is that the PA24 spars are joint in the middle of the cockpit and the fuselage is mounted ON it via several mounting locations vs PA28 spars being mounted on the sides of the fuselage in a carry through structure. Not being a structural expert, I can only assume that the vertical bending forces on the spar is distributed over a larger area in PA24 than it is on PA28 which is essentially distributed over the spar bolts on each side.

I still don’t mean though PA28 structure is weak. It is just different and PA24 seems more obvious to be designed to carry larger loads due to aircraft being heavier, larger and it is type certificated to carry a 400hp engine cruising at 190 ktas. I think the general risk of structural failure on a PA28 is largely associated with it’s wide use as trainer and the difficulty in inspection of the spar attachments. I would generally avoid buying any a high airframe time, high cycle trainer aircraft. PA28 or not.

I think the PA24 spar arrangement is quite brilliant. It is one reason for the spacious cabin, looking at how small it is from outside.

@By9468840 What are those hoses coming from the wings? Brake fluid or fuel? It is fuel, isn’t it? And the brake fluid runs through the thinner tube further down and farther back, right?

UdoR wrote:

What are those hoses coming from the wings?

what you see in the picture are the fuel lines from the wings and below them are the push/pull cable conduits for the main landing gear.

By9468840 wrote:

are the push/pull cable conduits for the main landing gear

Ah ok understood. I haven’t had the opportunity to see this perspective, and it’s always good to understand how things work.

P.S.: Sorry for off-topic!