Engineering Change Notice for Max Flap Speeds: 4-Place Model B, Companion, and Patrol

[jaredyates]

Bob has issued an Engineering Change Notice (this is the non-optional type of update) about the maximum flap speeds for the Bearhawk 4-Place Model B, Bearhawk Patrol, and Bearhawk Companion.

The update was originally issued in December 2022, but it has been revised/clarified as of March 2023, with the most recent language here:

Engineering Change Notice
December 2022 - Clarified March 2023

These are the maximum airspeeds for having the flaps extended, based on deflection in flight:
10 DEGREES DOWN ---100 MPH
20 DEGREES DOWN ---85 MPH
30 DEGREES DOWN ---75 MPH
40 DEGREES DOWN ---65 MPH
Deflections are in flight, with air loads. On the ground, deflections will be greater. Systems built as drawn on the plans, with flaps fully retracted on the ground, will deliver very close to these deflections. These speeds apply to the Bearhawk 4-Place Model B, Bearhawk Patrol, and Bearhawk Companion. The original Bearhawk 4-Place uses a different flap design which allows for higher speeds.

[jaredyates]

If you have something different on the first page of the plans, make it these instead. Some sets of plans for the Companion may have shown speeds for the original Bearhawk 4-Place (when they should have matched the Patrol), and some of the Model B plans only showed flap speeds for three different deflections, though most builders use a quadrant with four notches.

Note that these speeds are the same as those passed along by Nev back at the beginning of this thread:

https://bearhawkforums.com/forum/bearhawk-general-discussion-news/66471-flap-speeds-4-place-bravo

[rodsmith]

I assume these apply to the original Bearhawk as well as the Model B. In knots they are what I have printed on my panel. My plans updated 8/09 list 100mph-15deg, 85-35deg and 75-50deg. I thought there was an engineering change earlier lowering the 50deg speed, but all I could find was one dated July 2001 lowering the 35deg speed to 80mph.

[jaredyates]

I assume these apply to the original Bearhawk as well as the Model B. In knots they are what I have printed on my panel. My plans updated 8/09 list 100mph-15deg, 85-35deg and 75-50deg. I thought there was an engineering change earlier lowering the 50deg speed, but all I could find was one dated July 2001 lowering the 35deg speed to 80mph.

I'm not positive about the answer there, but I know that Bob was concerned about the Companion in particular because he had copied the 4-Place speeds when he first made the Companion plans, but the Companion has the larger flaps from the Patrol. That was what instigated the update. I don't know of any other updates related to the flap speed, which isn't to say there aren't any. The speeds in this most recent update are slightly more restrictive than those on the first page of the plans for the original Bearhawk, so there would certainly be no harm in observing the new speeds. Sometimes in flying very slippery airplanes there are times when the flaps need to go out right below the limit speed to be able to make a restriction or get slowed for pattern entry, but the Bearhawk isn't one of those kind of planes. My opinion is that the whole system appreciates deploying flaps at much lower speeds than the limits.

[Richard E]

Jared,
Thank you for posting this Engineering Notice.

I am a bit confused and concerned with the implications of this engineering notice. Our Model B 4 Place has flaps set up and placarded as per the plans.

15degrees - max 100mph - (87kts)
25degrees - max 85mph - (74kts)
40degrees - max 75mph - (65kts)
50degrees - max 65mph - (56kts)

The engineering notice requirements apply to the Model B.

10 DEGREES DOWN -100 MPH
20 DEGREES DOWN - 85 MPH
30 DEGREES DOWN - 75 MPH
40 DEGREES DOWN - 65 MPH

Is this just new Model B's built after Dec 2022 or all Model B's including ours?

If it includes ours, then it is surely not just a matter of changing the placard but also adjusting the whole flap setup, notch locations and reducing the maximum flap to only 40degrees. Following on there would have to be test flights to revise stall speeds with amendments to the approved flight manual and so on.

This seems to be be quite a major change with no reasoning or explanation. I was expecting to see more comment in the forums, as it presumably affects a number of aircraft. Hopefully I am missing something?

I am no engineer and am looking for some guidance as to what I have to do. Can you or anybody else help?

[jaredyates]

We would need to ask Bob, as I'm just the messenger.
Let me know if you'd like for me to call and ask or if you'd like to.
Part of the problem is that notches only loosely correspond to actual deflection degrees, with deflection at a particular notch being variable with airspeed. I don't get any impression that he is making an effort to say that the first notch must correspond to 10 degrees, and I don't see how yours could be rigged to deflect them to 15 degrees at all speeds or even the limit speed for that setting. If you are getting 15 degrees at 87 knots in the first notch, you must have something like 10-15 degrees of deflection at zero airspeed and the zero notch. This is how Russ Erb has is set up, more or less.

[schu]

Why does the airspeed change the flaps so much? The cable stretching that much? Or does the return spring not pull them tight against the cable? This sounds really odd.

[Battson]

It doesn't really vary that much with airspeed within the Vf to Vs speed range, the main point is - what you see in your hangar and what you see in flight are rather different, for the reasons explained below. It seems to be widely understood.

[kestrel]

Why does the airspeed change the flaps so much? The cable stretching that much? Or does the return spring not pull them tight against the cable? This sounds really odd.

There has been prior discussions where people have done mathematical proofs that it is cable stretch. My Bearhawk has zero cables in its flap system. I don't have any return springs either. It has an electric actuator in the ceiling where most would have the manual trim wheel. It has the same compliance as everyone else's. I believe that ~80% of the compliance is the torque tubes in the wings. I lose 10-15 degrees, even when near stall.

[schu]

There has been prior discussions where people have done mathematical proofs that it is cable stretch. My Bearhawk has zero cables in its flap system. I don't have any return springs either. It has an electric actuator in the ceiling where most would have the manual trim wheel. It has the same compliance as everyone else's. I believe that ~80% of the compliance is the torque tubes in the wings. I lose 10-15 degrees, even when near stall.

Whoa, so if the flap system is deflecting that much (torque tube or cable giving) and Bob is lowering the flap deployment speed, does that mean someone had a failure? What failed?

What about the A model? I wish the text was a little more definitive in specifically saying the A model is not affected.

[kestrel]

Mine is an A model. They have said that the A model isn't effected due to the smaller flaps that don't reach to the fuselage. I've not heard of any failures.

[Nev]

It may be relatively easy to adjust the maximum flap using the cable adjustments behind the bulkhead. But I think it's important that we get confirmation from Bob that it is his intention that the maximum deployment is now 40°, and importantly, the reason for the change. I wonder if it's possibly related to the elongated flap handle bolt holes found in one of the higher hour A models recently.

[Mark Goldberg]

My understanding is that this clarification of the flap speeds came about because of a Companion builder seeing only three flap speeds written on his plans while the actual aluminum flap guide had four positions. Bob had copied the speeds from another model on the plans and it did not correspond to the actual four positions of the flaps. This was a plans correction for that reason. Mark

[Utah-Jay]

It’s all the dude building the Companions fault

[gregc]

Well we are the black sheep of the family......

[Nev]

I think what Richard is pointing out is that the flap angles have now changed too. Instead of 50° at full flap it is now only 40°. So originally it was clarification on the flap limit speed that affected some of us, but according to the original post above it is now a reduction of flap deployment angles which would affect all of us.

[Battson]

Bob's notice describes the maximum flap speeds (Vf) and does not mention anything about maximum flap angle.

If you measure the angles on your flaps in flight, you will probably find they closely match the new angles Bob has described, assuming your system conforms to his design and hasn't been adjusted to achieve maximum flap deployment.

[Nev]

Clarification from Bob

I spoke with Bob today and got clarification on his recent engineering notice.

Bob said that originally the maximum full flap deflection was set at 50° assuming no air loads.

His intention with the engineering change is to promulgate full flap as being 40° with air loads, at the prescribed maximum speeds.

I'll check mine inflight with a marker pen and tape on the rear window, then measure the deflection on the ground.

[Richard E]

Nev,
I was just emailing Bob/Mark but you have beaten me to it. Do you know if Bob is intending to add to or amend the Engineering Change Notice? As it stands, our log entry will have to refer to your verbal clarification that you have posted above, which does seem a bit 'back door'.