| Author | Message | ||
     Bruce Newlan New member Username: Bnewlan Post Number: 5 Registered: 09-2002 |
Express Series 90 Tail (All straight tails) – Suggested Upgrade Many builders wonder why their plane “wallows” or has little stick authority at lower speeds around 80 MPH during approach. The design of the Express Series 90 aircraft as an all-composite plane results in a tail-heavy airplane with an adverse mass -distribution. The excessive tail weight results in both pitch and yaw instability. This is highly undesirable. Additionally, rudder authority is not adequate. This problem was greatly exacerbated on my plane’s tail dragger configuration. The mass distribution of this airplane appears to be way out of bounds when compared with other certified and experimental aircraft. For example, my rudder weighs 35 pounds, and each elevator 23 pounds, for a total tail control surface weight of 81 pounds. The total control surface weight of a Cessna 182 with approximately the same tail area is about 21 pounds, or 60 pounds difference. When considering the total weights of these two airplanes, the Express has a several hundred percent higher tail weight. This is very significant to flying qualities. While composites have many advantages, they have not been proven to be optimum when used for control surfaces because of their weight. An example is the composite Cirrus that was designed with all aluminum control surfaces, rudder, elevator, flaps and ailerons. Even many high-powered war-birds had fabric tail surfaces, all to reduce weight in the right places. Several options are available in refining the Series 90 tail to make the plane more stable and greatly increase elevator and rudder response. These are primarily a tail-weight reduction and a change in the elevator and rudder horn design. Neither of these should change the overall silhouette or tail appearance significantly. The amount of mass that could be reduced in the Express tail through the fabrication and installation of aluminum tail surfaces has been estimated to be at least 50 pounds. A reduction in a tail weight of 50 pounds could immensely improve the handling characteristics. Less tail inertia means better handling and more stability. Based on the extensive flight test data I have obtained during my Phase I testing, it is considered that this change could result in the single greatest handling enhancement for the straight-tailed Express. I have already invested considerable time and money investigating the feasibility of such a change, and have completed numerous hours of flight-testing using vortex generators. Qualified engineers and a highly renowned professional aerodynamicist have helped me make the design projections. Additionally, I have a gifted sheet-metal man lined up to do the fabrication. If this program works to my expectation, I would be willing to share the new design with other builders on a cost-sharing basis. While I do not have final cost estimates, I am near to having them and I feel that it could be quite reasonable if at least five or six builders participated. The package would include a new rudder and two new elevators, ready to bolt on after minor horizontal and vertical stabilizer modifications were made to accept the new parts. Or, the builder could fabricate the new parts if he wished. The cost could be proportionally lower if more builders participated. The builder would be responsible for shipping and installation. If this modification is as successful as I believe, I think there would be an opportunity for someone to make a retrofit kit for sale to the Series 90 community. I am not particularly interested in forming a business, however, I suspect others could be. If I could hear from as many interested Express builders as possible without any commitment at this time, it would be very helpful to me in planning this retrofit design. | ||
| David Frederiksen New member Username: Davidf Post Number: 1 Registered: 06-2006 |
Bruce, I am interested in your proposal. I have 30 hrs in a friends CT Express and have found it a handfull in Summer turbulance in Central Australia. I am building a Series 90 with a Vesta V8 [expecting delivery shortly]. I believe you work is spot on. My email address is david.franca@ozemail.com.au David. | ||
| James Michael Johnson New member Username: Mikej Post Number: 2 Registered: 08-2002 |
Bruce, I am just starting the tail portion of my Express and am interested in your upgrade. I do have a concern which you may be able to address. I have a Lyc IO-540 so my project is already nose heavy. I don't know whether the advantage in tail control surface lightness would 'outweigh' (pardon the pun) the additional cg issue. My email address is jmichaeljohnso@cs.com | ||
| James Butler New member Username: Jim_butler Post Number: 4 Registered: 09-2005 |
I have an IO-540 in my Express and it doesn't exhibit any of the problems Bruce seems to be having. I have excellent elevator authority and have enough rudder authority that I have landed in 21 knot crosswinds with no problems whatsoever. My nose is heavy at 700 pounds. Maybe that has something to do with it. Jim | ||
| jorge baccaro New member Username: Jabaccaro Post Number: 2 Registered: 08-2009 |
Hello Bruce I´m new in the forum and I bougth th N119NC in USA and bring to Argentina, where I live. I putted inside a container, it was modificated with a new tail. The rudder weigth is 32 pounds, and a counterbalance was put beside left motor side of 56 pounds for getting a rigth CG. I´m considering in take out the both counterbalance (in the upper part of rudder). Do you know how can affect this for control? could cause flutter? In think that your proposal is very interesting, because my CG is too aft inspite of the front counterbalance. I´m loosing a lot of cargo, because the heavy tail. Thanks for your seggestions. | ||
| Bruce Newlan New member Username: Bnewlan Post Number: 7 Registered: 09-2002 |
Hello Jorge, The weight of my aluminum tail is approximately 25 lbs elevator, and 23 lbs rudder, for a reduction of about 33lbs from the original weight, thus moving the cg forward several inches. This makes a lot of difference in the flight characteristics. If this was to be done again, a few more pounds could be saved, since it was somewhat over designed. If you or anyone else is interested in making this change, please contact me. Be careful about removing counterbalances in the control surfaces. Also, my tail dragger Express is for sale. Bruce | ||
| jorge baccaro New member Username: Jabaccaro Post Number: 4 Registered: 08-2009 |
Hello Bruce Thanks for your answer. Around how much cost your modification? because have to consider other cost, as sending and importation, and that increase a lot. For making a calculation, if I take away some weigth from back, then I habe to minus to the weigth in principal wheels? so then I can measure by calculation, how many inches CG could move. The rudder weigth is 36 pounds. | ||
| Bruce Newlan New member Username: Bnewlan Post Number: 8 Registered: 09-2002 |
Jorge, If you would email me directly, I can fill you in on many of the details of the modification and potential cost. My cg moved forward approximately 3.5 inches with the modification. Bruce bnewlanwine@earthlink.net | ||
| Shawn kelley New member Username: Skelley Post Number: 31 Registered: 01-2004 |
Everyone I have a S-90 that wieghs in at 2050lbs empty I have over 250hrs on her and have not had any the othe problems yous all seem to be having I can come in over the fence at about 75mphs and have all kinds of control some times to much. I have a IO540. That said I would like to here more about this. I think this would be great for people with smaller engine in them. Let me know what the cost are Shawn | ||
| jorge baccaro New member Username: Jabaccaro Post Number: 5 Registered: 08-2009 |
Hi everybody I have an IO360 Lycoming and the tail was change and the new one is heavier so a counterbalance of 28 kg (61,73 pounds) pounds is before firewall, for centering the CG. Yesterday I did my first fligth and it was o.k. We calculated the CG in 81", but I want to ask about the fly line, because we consider the lower contact´s door, in fuselage. But in this position (horizontal and same level), the firewall isn´t vertical; for getting this one in that way, I have to get up from principal landing wheels or get down nose wheel, and that change the CG a lot. Can anyone advice me which the correct way? Thanks. |