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Hammer 40 length mod

Old 02-17-2020, 05:14 AM
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rgburrill
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Question Hammer 40 length mod

I just bought a Hammer 40 short kit and from the looks of it a lot of people here have had Hammers so I'm hoping I can get some advice.. One thing that surprised me since it is advertised as a pattern plane is the length is only 80% of the wingspan. I'm thinking of adding 6 to 8 inches in the fuse between the wing and the vertical stab and possibly 2 inches to the nose. Has anyone here done anything like that? Also, the plans call for some dihedral in the wings. Has anyone reduced this or taken it out?
Old 02-19-2020, 01:21 PM
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Do you want to fly a Hammer .40? If you add length to it then you're not flying a Hammer .40.

A lot of the old designs are short by today's standard, I'm not sure why? Some of the engines back then where a bit on the vibratory side so maybe they had to shorten the heavy fuse a bit to keep the weight down? Maybe they were influenced by full sized planes? Who knows, but they didn't seem to start lengthening planes until the mid 80's.

The plane won't fly "wrong" with extra length and if you build it light you may not have to add much extra to the nose as the CG will most like have to move further back too unless you make the stab area smaller.
Old 02-20-2020, 09:22 PM
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Originally Posted by rgburrill View Post
.... thinking of adding 6 to 8 inches in the fuse between the wing and the vertical stab and possibly 2 inches to the nose. .... Also, the plans call for some dihedral in the wings. ....
Increasing the fuselage length increases the polar-mass-moment-of-inertia (increased resistance to rapid changes in direction). I would expect the straight-fight to be "smoother", and the spins and snap-rolls to be "lazier" and less dramatic. (for me that would mean less "fun", cuz I like doing dramatic spins and snap-rolls)
With the low-wing configuration, the designed amount of dihedral has probably been incorporated to avoid roll-coupling when rudder is applied. (A low-wing pattern plane typically requires about 2 degrees of dihedral at each wing-half.) Accordingly, one can maintain knife-edge flight with the application of only the rudder. If you reduce the dihedral you will probably induce adverse roll when rudder is applied (i.e. right rudder => left roll; left rudder => right roll).

Last edited by gyrocptr; 02-20-2020 at 09:25 PM.
Old 02-21-2020, 05:53 AM
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Thanks guys,
Old 02-27-2020, 07:32 AM
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Originally Posted by bjr_93tz View Post
Do you want to fly a Hammer .40? If you add length to it then you're not flying a Hammer .40.

A lot of the old designs are short by today's standard, I'm not sure why? Some of the engines back then where a bit on the vibratory side so maybe they had to shorten the heavy fuse a bit to keep the weight down? Maybe they were influenced by full sized planes? Who knows, but they didn't seem to start lengthening planes until the mid 80's.

The plane won't fly "wrong" with extra length and if you build it light you may not have to add much extra to the nose as the CG will most like have to move further back too unless you make the stab area smaller.
No I don't "want to fly a Hammer .40". I want to fly a classic pattern/aerobatic type aircraft not a sport type aircraft. Trying to find one this size that is in kit form and that you aren't being ripped off by a greedy seller is a task. The Hammer 40 looks like a good one to do some toying around with. There is a single former between the wing and the stab and the fuse is solid so it should be sturdy enough to handle an extra 3 inches on both sides of that former. Only a few pieces need to be modified from the drawing and this is a short kit so I have to cut them anyway.
Old 02-27-2020, 09:24 AM
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Originally Posted by rgburrill View Post
No I don't "want to fly a Hammer .40". I want to fly a classic pattern/aerobatic type aircraft not a sport type aircraft. ....
The Hammer 40 is a “classic” style pattern/aerobatic airplane. It was built in many different sizes. (Tack Hammer— Sledge Hammer: 1/2A — gas engine). If you lengthen it as much as you plan, it will no longer perform like a “classic” pattern plane.
Old 02-27-2020, 12:38 PM
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The Hammer 40 was my second plane and my second build way back in about 88. I was serious about aerobatics more so than sport and was advised to take this plane over the Hotts. We had 3 or 4 of them in Jamaica at the time.
The Hammer flew extremely neutral and light, and I learned knife edge both ways with it. No bad habbits at all. Only downsides were the rudder Iis thinksmall ,the wing was too thick, didnt stall easily. We shaved the leading edge on one and it did better at spins etc.
With dihedral about 1/4" per wingtip there was no roll in knife edge. Mine had almost no pitch down couple...for this I would rate the Hammer higher than the ultrasports, kaos, etc.
My mods were stiffening the back end where the stab is mounted with 1/64"ply, a larger sub fin and a rudder double the size. The 46sf was a bit underpowered by today's standard for the size airframe, even with the pipe. Flew one with a 60, but prop clearance was an issue. That was eventually converted to tailwheel.
In your case I think discreetly adding 2 inches length to the hinge line, then doubling the rudder in a way to preserve the looks and shape would be very cool and give the effect you want.
I may suggest also lowering the stab about 1".
Old 02-27-2020, 12:50 PM
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Actually i meant to lengthen by 2" from back of the wing to rudder hinge line. Then a larger rudder would give you maybe 3" more. Total 5" added. Fin and sub fin can be massaged to preserve the looks.
VERY INTERESTED IN HOW IT WORKS OUT.
Old 02-27-2020, 07:56 PM
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Originally Posted by northwest View Post
.....Mine had almost no pitch down couple......I may suggest also lowering the stab about 1"....
From my experience: if the current stab position produces no pitch-down-couple with the application of rudder, then lowering the stab may induce a pitch-up couple (toward the canopy) when rudder is applied
Old 02-28-2020, 04:47 AM
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Very good information. 5 extra inches with most of it in the rudder is a good suggestion. The plans call out solid tail surfaces but if I build them up I can reduce the amount of weight gain. I'm thinking of a 46 to 60 size electric motor. I'll write what I do and post photos when I get time to do it.
Old 02-28-2020, 01:42 PM
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The Hammer would pitch down some when the rudder is hard over (but not as bad as some other hi stab designs). I can't say for sure if lowering by one inch may be too much correction.
Mine was built with a hatch under the nose to access the tank. I eventually sold my hammer. It was lost because the owner placed the battery under the tank, and the hatch somehow fell off and battery fell out.
I'm thinking that you would have your lipos inside the nose with similar access hatch.
Old 02-29-2020, 05:42 AM
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Yes the battery will go where the tank would normally go. This is another place that may grow slightly to accomodate a longer battery. I have to wait and see.
Old 03-10-2020, 08:01 AM
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Very interesting. I am almost feeling like building a Hammer, the looks and colour scheme on the box takes me way back to my teens. No extra storage space for now...
For now I am getting ready to build a Great Planes Super Aeromaster 60 from eBay, with many modifications.

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