Q-talk 78 - LETTERS, ETC.
- Category: Q-Talk Articles
- Published: Sunday, 31 October 1999 06:11
- Written by Tom Moore
- Hits: 2094
This is a continuation of Brian Martinez's article on changing the angle of incidence on the main wing that was published in Q-TALK issue #77.
Q-200 WING INCIDENCE CHANGE
This is the first flight since the change in angle of incidence on the back wing. The change was 2 degrees leading edge down. The aim of this change was to fix the tendency of the tail to lift early on takeoffs and of the aircraft to try to fly nose down. Corrections for straight and level flight required most of the reflex capability in the ailerons on the back wing for trim (i.e. trailing edge up) and several degrees of trailing edge down elevator on the front wing (canard). Moderate pilot compensation was required in order to correct for these discrepancies. Modifications took 4 weeks of off and on work which included wing de-mate, realignment, wing re-attach, surface preparation and painting. Re-assembly and preflight included the following:
(a) Corrosion inspection of all removed fasteners to include tail mounting brackets, aileron/reflexor linkage, aileron mass balances, rudder cable connections and electrical cables.
(b) Installation of ACK ELT and remote switch/sender unit.
(c) Installation of extra BNC bulkhead connector to allow use of the vertical tail, VHF COM ferrite dipole, for the ACK ELT.
(d) Re-route bundle of wiring in aft fuselage.
(e) Change linkage adjustment for aileron control up/down tubes.
(f) Clean and grease all aileron linkage.
(g) Finesse sand and polish upper surface of wing and canard.
Engine run-up was normal with no anomalies. No ballast was carried in the baggage compartment in order to get a good assessment of handling qualities. Two high-speed taxi runs were made in order to identify any hazards to safety, which might have been induced in the incidence change. No adverse changes were noted. The tail remained on the runway throughout the two test runs from 0 - 60 mph with no ballast and with the reflexor centered. This was a major improvement in aircraft handling.
Takeoff was without incident with the tail remaining on the ground for the entire takeoff run. Normal stick force was required to initiate climb. Initial climb was at 75 - 80 mph later accelerating to 90 and then 100 mph later in the climb. Aircraft rate of climb was not noted. Thumb trim switch inputs to the Stewart-Warner reflexor actuator gave immediate trim response for the climb enabling stabilized climb in the pitch axis. A slight input of elevator spring trim was used as a fine adjustment for pitch during the climb. There was a noticeable roll to the left at full power during the climbout, which marked the shortcoming in having no roll trim. This roll characteristic with no passenger or right side ballast was noted during the first flights of the aircraft with the previous wing decalage relationship. There may be a suggestion of including some form of roll trim in the design, at some point. The reflexor trim provided a strong pitch stable climb to 8,000 ft MSL.
Several straight and level runs were made at 7,500 - 8,000 ft MSL with stable indicated airspeeds of 155-159 IAS at an estimated 50-60 degrees OAT. Engine leaning and aircraft trim condition was not optimized. Trim to and stabilization at a flight attitude is significantly better. Straight and level roll trim stability is still an area for improvement.
Two attempts were made to determine pitch buck speed. Buck on-set was detected at 67 mph IAS and 8,000 ft MSL. Precise aircraft nose up pitch attitude was not noted, but was significant. The pilot could not induce a significant pitch buck on these two attempts and will revisit the issue.
Landing approaches and touchdowns were significantly improved over the previous configuration. The aircraft approach was more predictable (i.e. more Cessna-Piper like) and the fill range of reflexor settings provided for much improved trim capability over and in addition to the elevator spring trim. It is again important to note that as configured on this aircraft (N557BM), the trim switch actuated reflexor provides gross power trimming with the magnitude of a flap lever, while the elevator spring trim provides a finer, though different, trimming effect. Unlike full power on conditions, roll stability is not a factor with the power pulled back in pattern work or power pulled off for approach. Two touch and go's and a full stop landing were made. The improved handling permitted left main wheel to right main wheel to tail wheel landings. The only significant discrepancy noted during the landing is the restriction to the right toe brake pedal range of motion due to interference from the firewall stiffener. The brake pedal restriction requires moderate pilot compensation and effects initial application timing, resulting in longer landing rollout.
Post flight inspection showed no indication of delamination, flex damage or paint cracking at the structural attach points of the wing.
Based upon these observations of more satisfactory aircraft handling, we can now re-examine use and completion of the performance and flying qualities flight cards. Additionally, the improved trimming capability should allow for off design airfoil performance such as would be the case due to surface contamination and rain. Safe cross-country performance over a reasonable range of atmosphere conditions should be assured.
Brian Martinez, Quartz Hill, CA
Positive Panel Planning segments of "Cockpit Ergonomics" by Richard A. Price, CFI/PE, are reprinted with permission from Panel Planner, Inc.
Webster defines Ergonomics as "the study of the relationship between humans and machines". The objective of ergonomics is to enable people to easily and safely operate the machines they use.
Despite its importance, ergonomics seems to have been ignored by the lighter end of general aviation over the past 25 years. Compare the panel of a single engine Piper from 1970 to a new one. Other than upgraded avionics, little has changed.
This lack of progress in certified light planes can be partially blamed on certification requirements and product liability concerns. Unfortunately, ergonomically flawed cockpits are found in experimental aircraft as well. Some builders, hampered by limited panel space, place instruments haphazardly where they'll fit. Other builders skillfully mimic the style of factory-built panels, complete with scores of indistinguishable switches and controls in aesthetic but unergonomic groups.
However, with a little thought, many cockpits can be made friendlier. And since we hope to spend many hours in these cockpits, user friendliness is well worth the effort. In my opinion, one of the primary advantages of homebuilding is the opportunity to build a cockpit that fits the pilot rather than "building" the pilot, via extensive training, to fit an unergonomic cockpit.
To really understand ergonomics, a fresh, open-minded approach is necessary. We have to recognize and abandon learned biases - (i.e. The Cessna I learned to fly in was like that, so what's wrong with it?).
THE RULES OF ERGONOMICS:
Rule 1: Reduce the number of instruments, controls and switches.
Rule 2: Prioritize the placement of instruments, controls and switches so that vital components are more accessible.
Rule 3: Make switches and controls distinctive.
(The author expands on redundancy) Don't get me wrong, redundancy is not a bad thing, but unnecessary redundancy IS. Haphazard cramming of equipment makes a panel difficult to use, having two NAVCOMs from different eras makes a panel difficult to use, and installing a slick new GPS while retaining the old LORAN, each with a unique method of operation and mind numbing arrays of features, makes the panel almost impossible to use.
Why are things so bad in the homebuilt cockpit? As bad as some of those factory-built panels are, at least they have an excuse: they were designed years ago and usually have been modified. However, as mentioned earlier, a walk down the Oshkosh flight line reveals a dirty little secret. While homebuilders are innovative and forward thinking when it comes to aerodynamics, structure and engines, our panel layouts are thoroughly conventional.
Frankly, this shouldn't be happening. There should be a good reason for everything in our cockpit. And the equipment should be arranged so that flying is as simple and intuitive as possible. Our cockpits should be as functional as our designs. There is an incredible abundance of genius and inspiration in the homebuilt movement -- a testament to the American spirit. We should not be copying non-optimal cockpit designs. Remember that the ultimate goal is a panel that is easy to use and that contributes to safety and enjoyment of flight.
Panel Planner can be reached at 208-323-8724.
The above article was provided by Terry Sickler from his EAA Chapter Newsletter.
Here is the information on my auxiliary fuel tank located in the baggage compartment.
The tank tops and centre portions were constructed from 3/8" Clark Foam with one BID on the inside and 2 BID on the outside. The flat top was installed level with the bottom of the cutout in the existing bulkheads. I sanded the fuselage and gave it one coat of epoxy to seal it prior to installing the tank. The existing bulkheads were used for the front and back of the tank. The tank was attached using the same method as the main tank - i.e. strips of foam were first floxed to the fuselage and bulkheads in the appropriate location. They were then coated with epoxy to seal them and a bead of flox was applied to obtain a squeeze-out when the tank top/side piece was installed. The tank is really two tanks with an interconnection between them on the bottom at the front. The inner sides of each half tank are 3-1/2" high and there is about a 4" space between the two halves. The interconnection should measure about 2" by 2" or more to allow adequate flow from one side to the other during filling. The bottom of the interconnection is the fuselage and was the lowest spot in the tank in both ground and flight altitudes so that is where I located the sump drain and fuel line. The fuel line then goes to a filter and the electric fuel pump, which are both located in the space between the tanks. The pump transfers fuel to the header tank and I did not provide a return overflow to the new tank so I must watch the header tank level carefully and turn off the pump when full to prevent pumping fuel overboard through the header tank vents. I installed a separate connection into the header tank to prevent fuel being pumped from partially flowing back into the main tank through the other fuel pump (or vice versa when pumping from the main tank). The tank holds 35 liters which is 9-1/4 US gallons.
I also revised my aileron torque tube to incorporate an additional bearing in the centre armrest and a U-joint. If you do this do not use phenolic or micarta (such as used on the other bearings) directly on the aluminum torque tube because it will wear through quite quickly. I put a wear sleeve over the torque tube.
The torque tube then runs through the space between the two fuel tanks (over top of the fuel pump). A fiberglass cover Velcroed over the space between the two tanks protects the fuel lines, rudder cable, fuel pumps/filter and torque tube from being damaged or fouled by luggage.
An important consideration is venting the auxiliary tank. I ran a 1/4" vent line from the rear, highest corner of each half of the tank up the aft bulkhead about 12", then connected the two vent lines together and ran a single vent out through the fuselage into the high pressure area just under the main wing, and faced it forward into the airflow.
The fuel filler has a three-inch tall neck and is located in the baggage compartment just behind the pilot seat and very close to the side of the fuselage to put it out of the way of the baggage. Since the tanks are quite flat and the fuel must flow through the interconnection, this filler arrangement allows an easy view of how full the tank is getting so there shouldn't be any spilling during filling. However, despite this foolproof design, I have managed to soak my luggage with fuel a couple of times (the design isn't quite idiot proof). Because the tank is so flat, a fuel gauge is next to useless but in Canada a gauge must be installed to meet regulations and it must be visible from the pilot seat. My gauge is mechanical and is located behind the passenger seat cushion so it is stretching the regulation but I didn't want to get too elaborate since it is next to useless anyway. I just make sure I use up the fuel from the auxiliary tank first.
Centre of gravity is also a major concern when installing the auxiliary tank. I think the Q-200's fly better when they are forward of the aft limit and when I converted to the O-235, after test flying, I moved my forward C of G limit ahead about 1 inch and my aft C of G limit ahead 1.5-2". If your plane is near the aft C of G limit with passengers and baggage I wouldn't recommend adding the auxiliary tank unless there is something you can change (such as moving your battery ahead a few feet) to accommodate the weight of the fuel (55 pounds).
Kimbull McAndrew, DeWinton, Alberta, Canada
Some comments about Onan-powered Quickies.
Things I have changed before I flew. 20 HP heads and gaskets. This was a well documented mod most everyone had adopted.
Things I have changed during the last 380 hours. Intake guides to incorporate valve seats (the newer engines are this way), rotators on the intake valves. Before this I used to get a lot of carbon looking buildup on the valves. Stainless exhaust valves (once again, if you order new valves this is what you will get) previously I seemed to be getting more wear on the valve face than I wanted. 20 HP rods, once again used in the newer engines, I had not experienced any problems with the old ones, however the newer ones look a lot stronger (see Photos).
Things I should have done different before first flight.
1. Engine baffles to plans, I had made a minor change that didn't work as well.
2. CHT that didn't work properly in flight, vibration level in flight could not be simulated on the ground. Really no way to prevent this one.
Major screw-ups on first flight.
1. Carburetor main mixture was adjusted too lean. It ran great on the ground, but as airspeed increased and rpm increased the engine went lean, so remember after adjusting for peak rpm on the ground richen the mixture 1/4 to 1/2 turn more. All that is said in the owners manual is don't go more than 1/2 turn more than peak.
2. Climbed at low airspeed, higher airspeed would have helped engine cooling.
Results of above mistakes, leaking exhaust valves and deformation of block around exhaust valve. So I fixed these problems and haven't had any real problems since. QAC recommended max oil temp of 275F seems too high to me, most of these engines if flown in high ambient temps will need some sort of additional oil cooling. I think an oil filter is a must-have item. Info from Onan spec sheet. These engines are designed to run at 80% continuous power max. Power decreased 3.5% per thousand feet and decreases 1% for each 10 degrees F. above standard.
Terry Crouch, Bettendorf, IA
Being 6'5" tall, I knew from the start that hanging headfirst and upside down to do the wiring wasn't an option. Necessity being the mother of invention, the following design of a swing away instrument panel was developed and works very well. This design allowed me to stand on the outside of the cockpit and complete the entire wiring of the panel. Plus I can reach the firewall while standing outside.
I placed those instruments and systems that have "plumbing" on the center pedestal, which would not be moveable. Everything on the panel wings has flexible connections (wire/tubing) allowing the opening and closing of the wing panels.
The support frame is constructed from aluminum channel 33/64 x 1/2 x 1/16 x 96" found at your local hardware store. The frame is removable. I glassed two "L" brackets to the header tank and slid the channel onto them and secured with small bolts. The same was done at the base of the main fuel tank. The middle instrument panel supports the two front, vertical supports. The cross support is pop riveted to the two horizontal arms. Look closely on the two vertical supports and you will see two hinges that hold the two wings of the panel.
The main bus (Radio Shack) is attached to the wing. Fuses are beside the main bus. The radio and transponder stack is supported by brackets from the channel frame. The ground block is bolted to one of the horizontal channels. All of this makes for shorter wire runs. The outside ends of the wings are screwed (1 each) to an "L" bracket glassed to each side of the fuselage. Simply loosen the screw and have access to the back side. Jerry Marstall, Asheville, NC This is the last issue of your 1999 subscription. All subscriptions for 1999 end with this issue. To receive the next issue you need to subscribe for 2000. I am trying to keep the subscription rate the same. Please help your editor by subscribing promptly. $20 in US, $22 in Canada and $26 for international. All US funds. The QBA T-shirts with the image seen below are now available. The image appears over the left breast. The Quickie is colored RED and the lettering is black on a white Hanes BEEFY-T that is 100% pre-shrunk cotton. They come in sizes M, L, XL. The cost is $10 per T-shirt plus $3 for shipping. Add $1 shipping for Canada and $2 for international. You can order a PDF or printed copy of Q-talk #78 by using the Q-talk Back Issue Order Page.
The main bus (Radio Shack) is attached to the wing. Fuses are beside the main bus. The radio and transponder stack is supported by brackets from the channel frame. The ground block is bolted to one of the horizontal channels. All of this makes for shorter wire runs. The outside ends of the wings are screwed (1 each) to an "L" bracket glassed to each side of the fuselage. Simply loosen the screw and have access to the back side.
Jerry Marstall, Asheville, NC
This is the last issue of your 1999 subscription. All subscriptions for 1999 end with this issue. To receive the next issue you need to subscribe for 2000. I am trying to keep the subscription rate the same. Please help your editor by subscribing promptly. $20 in US, $22 in Canada and $26 for international. All US funds.
The QBA T-shirts with the image seen below are now available. The image appears over the left breast. The Quickie is colored RED and the lettering is black on a white Hanes BEEFY-T that is 100% pre-shrunk cotton. They come in sizes M, L, XL. The cost is $10 per T-shirt plus $3 for shipping. Add $1 shipping for Canada and $2 for international.
You can order a PDF or printed copy of Q-talk #78 by using the Q-talk Back Issue Order Page.