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Consequences of exceeding Vfe w/ flaps extended

jbell2355

Member
Let's say that, theoretically speaking, an RV7A pilot flew around for 10 minutes at 115 knots with 10 degrees of flaps extended. What potential damage could have occurred? What inspections should be performed?

Thank you in advance, from a non-builder.
 
I forgot to raise the flaps one time took off in my brother's RV9A with full flaps. Flew around for 15 minutes or so before realizing why the speed just didn't seem to be quite right. I raised the flaps, everything seemed fine. When I landed, we checked everything out, all was well. We even asked Van's about it. They said they doubted any damage would occur unless I had gotten into an excessive speed situation.
 
Pretty sure the VFE or flap speed is a max speed, meaning there is a sliding scale to it. I can't remember exactly, but I don't hesitate putting out 10 degrees of flaps at 110mph.
 
This isn't quite on topic, but close... On some airplanes, and I'm probably remembering one of the Cessna single engine retractables, there is a maximum gear extension speed and a maximum gear extended speed, which is higher. IIRC, the extension mechanism is to extend the gear only at or below the extension speed, but once the gear is down and held there by the down locks, the downlocks can hold the gear at a higher speed.

On the RVs, the analog would be how much force can the flap motor (or pilot's flap arm, on the older planes) exert without damaging the actuator, and how much air load can the wing structure handle with the flaps extended.

In some planes, you can use the flaps for deceleration, and there are different max speeds for flaps 10 degrees and more than 10 degrees. Sometimes I wish that RVs had considerably higher flap speeds for just that reason.
 
When I was learning how to fly my RV I extended the flaps above Vfe a couple times - a blown fuse was the only result.

I've also flown home with a blown fuse and 20 degrees of flaps - do you know how hard it is to stay below 100kts for a hour in an RV!? Pretty sure I didn't exceed 120 :p

Afterwards I did pull everything apart and checked the flap motor hinges attach point etc and everything was still normal...

So I think your good.
 
In some planes, you can use the flaps for deceleration, and there are different max speeds for flaps 10 degrees and more than 10 degrees. Sometimes I wish that RVs had considerably higher flap speeds for just that reason.
I don't know about others, but I do use my flaps for deceleration. With manual flaps it's unreasonable to pull 30 degrees of flaps at Vfe due to the force required, so I pull 10, wait for the speed to drop, pull 20, wait for the speed to drop, pull 30, etc. Usually the first notch on downwind, second on base, third on final. That makes it an easy pull to each position, which means low loading on the airframe and linkages.
 
When I was learning how to fly my RV I extended the flaps above Vfe a couple times - a blown fuse was the only result.

I've also flown home with a blown fuse and 20 degrees of flaps - do you know how hard it is to stay below 100kts for a hour in an RV!? Pretty sure I didn't exceed 120 :p

Afterwards I did pull everything apart and checked the flap motor hinges attach point etc and everything was still normal...

So I think your good.

WE have found much the same as above in testing we left them down at hi-cruse power and the aircraft just drug up to around 120-125 and would not go anything more in level flight. No we did not do it intentionally but it was nice to find out there was no damage. It just took a quick pull back on the throttle and then retract of the flaps and all was good again. I would not try to put them down at speed, that would probably hurt your feelings.
Yours, R.E.A. III # 80888
 
"FLAP SPEED: On the RV-4/6/6A/7/7A/8/8A, 110 Statute for 20? and 100 mph statute for full 40? flap deflection. On the RV-9/9A, it is 100 smph for 15? and 90 smph for 32?."

It's not the same as the diff between flap extension and flap extended speeds, but there you go...straight from the construction manual.
 
flap damage

The person I did transition training with noted both of the actuator rods attached to the flaps had a slight bow in them when they had been deployed overspeed. He replaced them with aluminum hex rod approx. 5/16" with the ends drilled and tapped for the bearings. Not recommending, just passing it on.
 
The person I did transition training with noted both of the actuator rods attached to the flaps had a slight bow in them when they had been deployed overspeed. He replaced them with aluminum hex rod approx. 5/16" with the ends drilled and tapped for the bearings. Not recommending, just passing it on.

So the hidden question is, if some part of the airframe is going to be overstressed, what part do you want to fail first? In the original RV design, it appears that the flap pushrods would bow before any damage was done to the wings or the flap actuator. (There's probably more to it, but I'm not up to speed on all the details.)

What this guy did with his modified pushrods might have changed things -- with stronger pushrods, maybe the flap actuator was subjected to more loads, or maybe the wing structure was subjected to more loads. Dunno.

For comparison, some (all?) of the Boeing jets have "fuse pins" on the pod mounted engines. If the G forces get too high, the fuse pins fail and the engines fall off so as to prevent the weight of the engines under excessive G forces from failing the wing structure.

And there was one guy who extended his RV wings with fuel tanks, not knowing that his design exceeded the wing bending strength not at the root (he thought he was safe there) but at the aileron mid-span.

Let's be real careful out there! It's an experimental and you can do what you want, but the laws of physics don't care what you want.
 
The person I did transition training with noted both of the actuator rods attached to the flaps had a slight bow in them when they had been deployed overspeed. He replaced them with aluminum hex rod approx. 5/16" with the ends drilled and tapped for the bearings. Not recommending, just passing it on.

The flap hex pushrods are a common upgrade and I think they are supplied in more recent kits, probably available in the Vans store.
 
The fuse pins are not sized nor designed to allow the engines to "fall off" under excessive in-flight "g" loads.

As a side note, on Boeing jets, the wing-mounted landing gears are also fused, so that they will tear off cleanly without ripping open (or punching through) the inboard wing fuel tanks for similar scenarios as mentioned above.

Hmm. The FAA has a differing opinion. "The design of the strut includes provisions to prevent fuel tank rupture in the event of an engine breakaway caused by extreme overloads from engine failure, abnormal flight, or landing."

http://lessonslearned.faa.gov/ll_main.cfm?TabID=1&LLID=38&LLTypeID=2

Let's get back to RVs, okay? That's what this website is supposed to be about.
 
Ed, I was having a nice Sunday here in your old town.... and now you made me worry an engine might land in my waffles. ****.
 
Flap overspeed consequences

Gettting back on topic - its worth considering the consequences of having a flap actuator rod buckle due to either flaps being extended above the design speeds or a straight overspeed with flaps extended. Since there is no weak link in the flap system that is common to both flaps the most likely failure would be a buckled flap pushrod connecting the flap to the weldment inside the fusalage. More likely than not only one actuator rod will fail leaving a situation with insufficient aileron roll authority to prevent roll off. I suspect it wouldnt take much flap mismatch to reach the limit of aileron authority. A single point failure with likely fatal consequences. Important to take flap speed limitations very seriously - those skinny little rods are in compression and do well when straight - not so well once they start to bow or bend with increased potential to allow one flap to retract.

KT
 
I am only aware of one (possible) instance where a push rod failure caused an asymmetric flap condition. I say possible because it was 3rd hand info with very little detail. If my memory is correct, apparently control was maintained and post inspection showed that the failure was caused by scrapes in the tube because of interference with the opening in the fuselage, AND the tubes had been purposely bent at the mid point to help them avoid rubbing on the insufficiently sized fuselage opening.:eek:

Other than this one (possible) event, I am not aware of any others and there is no accident report pointing to flap failure as a contributing factor to any RV accident.
Considering the fleet size, I would consider that a testament for the built per plans push rod design.

The only instances of bent flap push rods that I am aware of are cases where the builder bent them on purpose during the build.

For anyone not aware.... purposely putting a bend in any structural component that is intended to be loaded in compression is a very bad thing to do. (If interested, google "column load")

Here is a related old post from about 5 years ago on the subject of flap push rod strength.
http://www.vansairforce.com/community/showpost.php?p=769450&postcount=19
 
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