Engineering Note from Bob - Optional Landing Gear Tube Change

[jaredyates]

Bob has released the following Engineering Note:

Engineering Note

Subject: Landing Gear Leg Tubing Optional Upgrade

For heavy duty use the landing gear legs can be changed to:
-Front Legs: .083" Wall
-Rear Legs: .095" Wall
-Axle Tubing: 1-1/2" Diameter, .156" Wall

The original size wall thickness tubing as shown on the plans has proved over the last 25 years to have worked well, but with the STOL competition, very rough ground and large tires, the heavier wall tubes may be in order. This note may be applied to the 4-Place Bearhawk, Patrol, and Companion.

http://bearhawksafety.com/4-place/june2025.html

2025-6-gearlegs.jpg 2025-6-gearlegs-text.jpg

[Nev]

What's the more detailed background to that ?

[jaredyates]

Nev, I'm speaking only for myself here, but my answer is, I don't know. You and I come from backgrounds where we have a lot of very effective and very repetitive training about safety culture and reporting. We've seen that system work and we understand why it's important.
But I have to remember that not everyone comes to aviation with the same type of mindset.
I don't know if this change is based on a specific mishap. When things happen that are undesirable, regardless of the cause, if someone wants to help others by sharing their story, I'm certainly happy to help get the word out.
But it's not universal that folks do want to communicate in those times, and I feel like I have to respect that, even if I wish it wasn't the case.

[alaskabearhawk]

This is a bit of BH history from a 20 Sept 2005 thread from the original BH Yahoo group. A builder David Mabe asked Bob to come up with some "heavy" mods for the landing gear. This is what Bob came up with for him:

Here are the mods made on my plans by Bob.

The mods Bob did for me are the following;

Lower long = 7/8 x .058 from app 6" front of sta B to app 6" aft of F/30deg.
splice
Upper longeron= T11
Diagonal sta B to S = 7/8 x .056
Vert sta C-S=7/8 x .065

Gear;

T21 change to 1 1/2"x.083
T23 change to 1 1/2"x.083
Axle = 1 1/2"x.156
Dayton Progressive EH 200-1200
Strut tube add 3.5" = 1/2" addnl preload.

I asked for these mods as i told Bob I wanted to be able to handle rough roads, gravel bars, etc. I plan on using my BH in mission aviation. I also discussed attach fittings for a lumber rack,i.e Atlee Dodge, and we decided that I could weld tubes at several stations like the ones shown for float fittings. They would also serve to anchor a pod if desired. I dont know the addnl wt. Bob wants me to get it done so we can see how the change works out.

>Reply-To: Bearhawk@yahoogroups.com
>To: Bearhawk@yahoogroups.com
>Subject: Re: [Bearhawk] BH HVY MODS
>Date: Wed, 21 Sep 2005 08:54:17 -0700 (PDT)
>
>Dayton Progressive EH 200-1200 spring is 12 inches long free length,
>860 lbs/in rate, solid length 5.47, load at solid 2,682 lbs. This
>spring is made of the same wire as the 8 inch stock spring, but because
>there is more wire in the longer spring, it is "softer".
>
>I've been looking at this spring as an alternative for the 8 inch
>spring. It will be interesting to see what Bob suggests for it's
>usage.
>
>Rob Gaddy
>BH401

Yes, Bob suggested this spring. I was concerned about the lack of travel in the 8" spring on landing with a full load on rough strips. Bob said he designed the BH as a utility plane, not a bush plane. I told him where i was going to go so we decided to use the 12" spring. Bob gave directions of increasing the strut tube length by 3.5 inches. The increase in preload is therefore 1/2". The softer, longer stroke is what we felt is needed for rough, unimproved areas. How the BH performs now is only speculation to me as I dont have any exp. in landing on rough roads etc with it. Has anyone landed on them,I dont know. I am putting the goodyear 26x6.5x6 tires on mine, a ten inch tail wheel. Between the softer tires, and longer spring, my BH should about right.

Response from Budd Davisson:

I was going to stay out of this thing but it looks as if some discussion is warranted.

First, part of what we have going on here is a matter of symantics: how are we using the words "utility" and "bush?" Most of the population would look at a Maule and say it's a bush plane, where you get up north and you won't hear "bush" and "Maule" put in the same sentence. In fact, you can get in conversations up there where it becomes very clear that even a stock Super Cub is marginally suited to the pure "bush" role. If it wasn't, F. Atlee Dodge wouldn't have such a roaring business.

I had this discussion while giving a demo just last week to a guy from Alaska. He owns an extended wing, totally "Dodged" 180 hp Super cub and wants to go the same places with the BH. I told him it wasn't going to happen and it wasn't fair to compare the two. We're talking four people, 2500 pounds and there's going to be a difference.

A Utility Airplane is something like a Cessna 180 or a Maule or, as Bob looks at it, the Bearhawk. That means it is designed for "unimproved" not "outrageously rough"field work. This is true of the other two airplanes as well. Does that mean those airplanes are weak? No, it means there are extreme uses that are outside of their design envelope.

If you're talking about flopping around in stream beds, rocky gravel bars, then there are some modifications you might want to make in a BH, some of which we're looking at. Some of which, we aren't. And not one of them is needed by the general Bearhawk population. Plus, every single thing we're discussing here adds weight, which decreases the strength and performance of any airplane.

Will it get in and out shorter than any other four place airplane. Absolutely! Will it go places you can't go with any other four-place airplane? Absolutely! Does that include plowed fields and river bottoms? Probably not. At least not in it's stock form. But, the exact same thing applies to a Super Cub. Neither were designed with that use in mind. They are both utility planes, not Bush planes.

Are there any true "bush" planes being manufactured? Again it depends on the exact definition of "bush," but I'd say the answer is no. The closest is a Husky, but the pros know that in the long term, it's not up to some of those tasks either.

The longer shock strut is going to be test flown by Mark on his airplane and I'll fly it on 509. The big question is whether it's going to let the airplane "wallow" back and forth a little on takeoff and landing, thereby compromising crosswind performance and general handling. I can't guess. As the gear is now, if you're working out of pavement or normal grass/dirt fields, you're golden. Frankly, we don't know if the longer strut is going to be an improvement or not. But, we're going to find out. We do know that it'll slow the airplane down because it'll have that much more strut hanging out in the breeze.

One thing that I want to be very clear about: I don't want discussions about mods required for extreme uses to cast a pall over the airplane in general. The problems aren't in the airplane, but in the uses a very few people are intending.

When a modification has been proven, or disproven, then we'll discuss it. Unfortunately, until then, there's nothing to discuss.

bd