Steve King:
One way to reduce the “trim drag” is to be loaded at or close to the rear CG limit. Our planes are quite nose heavy. Without significant load in the rear seats and baggage compartment, the CG is around or forward of the forward CG limit. For my 79 Sundowner, with about 130 pounds of water ballast in the baggage area, two in the front seats, and 40 gal fuel, the CG is still near the front limit. Unbelievable? My plane’s original owner had it re-weighed right after he got it new, probably because he had a hard time believing the CG is so far forward.
I’d like to do something besides adding more ballast in the baggage area. One thing which will help some would be the replacement of the original starter with a Skytec (about 10 pounds less on the nose).
The parts book shows a ballast weight for the rear fuselage bulkhead, applicable for some serial numbers (not mine). When I checked with RAPID, the parts guy I talked to said it was approved for certain models (some model 19’s?) which were to be used in a training environment. Does anyone on our list have that ballast weight? If you don’t know, but don’t have the CG problem I’ve described, I suspect you do. Has anyone received field approval for installation on an airframe where it was not a factory option?
How about making a BAC project of helping to expedite getting field approvals? It would help if we could get pictures of original factory installations of the ballast on approved models.
Bob Steward, A&P-IA:
I’ve preached this (trim drag) relentlessly. The Musketeer is NOT a 105 mph plane, properly loaded. The Sky-Tec is a good start. The factory ballast weight weighs 22 pounds, and bolts onto the aft side of the last fuselage bulkhead, right underneath the rudder.
However, here’s something that 4 years at some “Aerospace” colleges will
not teach you: The big secret in light plane aerodynamics that no one
talks about is trim drag caused by profile drag of items below the
centerline of the plane. The further below the centerline, the larger the
arm the drag has to work on and rotate the plane nose down. This must be
reacted by the HS/Elevator to keep the plane in level flight.
Retracting the gear is a double dip of performance improvement. The first benefit is the removal of the profile drag from the air flow. This means the plane has less total drag and can fly faster on the same HP. The second benefit that you won’t hear anyone talk about is the removal of the drag below the centerline, and you can’t get much further down than the wheels and tires. This means that the stabilizer now does NOT need to pull UP on the nose as hard, because the drag on the bottom of the plane is no longer there. Thus the stabilizer is not loading the wing to carry the additional down force, and the tail is not CAUSING the drag of holding the nose up against the drag from the gear. This can have as much effect as just removing the gear from the slipstream.
Any donations that would have gone to cover the tuition no longer needed to attend 4 years of Aerospace college are gladly accepted.
Larry Perry:
Our 1983 C23 Sundowner shows a note in the airframe log of, I think, a 10# ballast weight being installed somewhere in the aft fuselage. N65503 began life as a trainer for PSA and later the Univ of Illinois.
Editor:
For what it is worth, adding aft ballast is cheap and expedient as a short-term fix when the CG is a factor. The effective payload reduction may not be an issue, if the forward loading requires aft ballast, but the resulting lower airspeed will always be in play if the ballast is permanent (hauling around more weight than required, somewhat offset by reduced pitch trim drag). As a long term project, you might want to focus on other alternatives to spending money installing permanent ballast. Some examples, as the opportunities arise, are:
The Sky-tec starter (the lightest version if it will fit, and you don’t have the IO360 engine) is a good first step, when you need a starter. You’ll be happy with it for other reasons as well.
Lighter weight avionics, and removal of undesired, unnecessary, and non-working avionics (and all related cables and antennas). This is naturally best done when other factors are driving the issue. The exception is when you have non-working equipment that is unnecessary, and which won’t get fixed. You can remove it yourself at low cost if you get the proper supervision, sign-offs, and paperwork all done. This assumes that you have the needed skills and tools to do it right.
Use of the smallest profile 600-6 tires on the main gear (mostly drag reduction; won’t have much effect on CG due to location). Here is a clip from an earlier post of mine; complete info is on BAC:
(17.5) 600×6: 17.5″ OD; 5.2″ wide;
4-ply rating max load 1,150 pounds, max inflation to 29 PSI
6-ply rating max load 1,750 pounds, max inflation to 42 PSI
Cross-sectional area comes to approximately 91 square inches, if it had a rectangular profile; slightly less due to tread curvature.
15/600×6: 15.2″ OD; 5.55″ wide;
6-ply rating max load 1,950 pounds, max inflation to 68 PSI
Cross-sectional area comes to approximately 83.25 square inches, if it had a rectangular profile; slightly less due to tread curvature, though the lower profile usually has a bit more squared shoulder.
Along the same lines, with more positive effect on CG, use a 500-5 nose gear wheel and tire. This also reduces drag, and improves the CG situation more due to its forward location. This assumes that your A&P-IA will agree with this. Many people have done it; the 500-5 is standard on the Sierras, and can certainly handle the load. Ground clearance exceeds the minimum on the Sierra with its longer prop, but you can verify it on your own plane.
One thing to keep in mind is to do a lot of number crunching prior to making changes. A key reason for the excellent loading flexibility of these planes is their forward-CG design, coupled with the stabilator. It isn’t a drawback, it’s an advantage; just like the large fuel tanks. These magazine articles that highlight the “full fuel payload” are either accidentally or deliberately misleading their readers. Calculate how much of a CG change it will make sense to achieve, that will prevent the need for ballast while preserving the loading flexibility. Calculate CG with the front seats all the way back. Keep the co-pilot’s seat that way as often as you can.
Of course, any drag reduction activities will always pay a dividend. Gaining five knots through cumulative small drag reduction efforts is like adding 20 HP to the engine, without the weight or fuel burn. Some changes may not seem to yield much per item, but they can add up. Other things make a big difference all by themselves. For example, if a Sierra nose-wheel is mis-rigged, and hangs down an extra 1/2 to 3/4 inch, it will cost close to five knots in cruise. Most people would not even notice the different appearance just by looking at the plane in flight or on jacks.
As long as you keep things logged and legal, get the proper training and oversight when it is required, and use proper and legal parts, these are the kinds of activities that can help you maximize your plane’s performance and make it uniquely yours. On the other hand, if your cobble up your plane with illegal parts and changes, you’ll make it an un-salable ramp ornament. Do things right.
Larry Perry:
I pulled out the airframe logbook, and the second item entered under “Major Alterations”, six months after N65503 left the factory, is
the following notation:
7/3/84 Install ballast weight P/N 169-44000-207 in tail.
Editor’s Note:
There is a digit missing in the part number. The correct PN is 169-440005-207. There is one available from RAPID for $149; this is the ten-pound weight. Another number is 169-440005-119 (twenty-two pounds); none available from RAPID. Beech Technical Support has told me that the -207 superseded the -119.
Both of these may well be available from salvage yards. Parts applicability is:
169-44000-119, 22 pounds: MB1 through MB557; MC2 through MC150
169-44000-207, 10 pounds: MC191 through MC536, except MC503.
If you have a demonstrable loading problem, your A&P-IA may approve installation of one of these on the M or MA series airframes, via the Form 337 route. Remember that this will require documented W&B changes; if I were the involved AI, I would require a fresh aircraft weighing for this change. Beech Technical Support has stated that neither ballast weight was ever Beech-approved for the M-series airframes. I would love to get a copy of any 337s bearing field approvals, as this would make it much easier for other members to install the weight.