Hello trikers!
I’ve been carrying out some simple experiments in flex-wing hang gliders and would like to expand them to include a powered component. So I’m looking for a few pilots willing to carry out the series of experiments described below. The goal is to evaluate the importance of various aerodynamic effects on roll trim in turns, including roll torque from roll damping due to sink rate, roll torque from anhedral, and roll torque from sweep. I’ll be happy to discuss these ideas much more once we get some results coming in. The actual experimental protocol is quite simple and straightforward, and the whole process should only take about 5-10 minutes.
I’m primarily interested in results from flex-wing trikes. Lightly loaded (e.g. ultralight) trikes are of special interest, but data from heavier “cruisers” is appreciated as well.
I’ll give the protocol in 2 forms-- a condensed form suitable for printing out and taping to your instrument panel, and then an expanded form with more questions and more complete explanations:
First the condensed protocol:
Note, please take a moment to familiarize yourself with the expanded protocol before flying; this is highly abbreviated.
1) (skipped)
2) Left turn of 40 degrees or shallower. Pick wing reference mark. Slow to slowest comfortable airspeed while adding power as needed to hold a constant altitude. Note airspeed and bank angle. 3) Note required roll input.
4) Same bank angle, accelerate to the highest comfortable airspeed while adding power to maintain altitude. Note airspeed. 5) Note required roll input and compare to part 2.
6) Parts 7-10 are optional and best suited to aircraft with a locking hand throttle and airspeed indicator; if this is not you or if you just want to keep it simple, skip to 11.
7) Slow back to airspeed in part 2 and reduce power to hold a constant altitude.
8) Leaving throttle fixed in place, and continuing to maintain the same bank angle, pull in the bar again to accelerate to the same high airspeed used in part 4. 9/10) Note sink rate. Note required roll input and compare to parts 4 and 2.
11) Repeat the entire protocol 1-10 above, in a right turn. Use same visual reference mark on the right wing.
12) On the whole, is there any clear trend that holds true for both left and right turns, and seems independent of engine torque and P-factor? Or do the results seem dominated by engine torque and P-factor?
13) 35 to 40 degree banked left turn at low airspeed. Firmly pull in the bar while making no roll input (muscle force on the bar). Does the trike tend to roll through wings-level into a right turn? Repeat the same starting from a right banked turn. Can you find a power setting and initial airspeed where pulling in the bar while making no roll input makes the glider roll through wings-level into the opposite bank, regardless if you started in a left turn or a right turn? Can you can do a series of mild wingovers or roll reversals just by making pitch inputs alone? If so, note initial airspeed and rpm.
14) Note stall speed in a wings-level stall, with power applied as needed to maintain altitude as you approach the stall. Is this a full stall with break, or just a “mush”?
15) (skipped--Please review the expanded protocol for your post-flight debriefing)
Expanded protocol:
1) Required equipment: flex-wing trike with altimeter. Other desirable equipment-- airspeed indicator. Hand throttle with friction lock. If you don’t have an airspeed indicator, just give an estimate of the airspeeds involved. As long as you let me know that you are flying without and airspeed indicator, the data will still be useful. Likewise, even without a locking throttle you can still do the experiments, just let me know that the throttle was not really fixed in place.
2) On a calm day, enter a left turn of 40 degrees bank, or shallower if you prefer. Pick a specific reference mark where the left wing meets the horizon, so you can replicate the bank angle. It should be a reference mark that also exists on the right wing-- e.g. not some detail of the color scheme that is asymmetric between the two wings. Slow to the slowest airspeed that you find comfortable, while adjusting power as needed to hold a constant altitude. Allow a safe margin below stall, and don’t allow the wing to be wallowing in the pre-stall buffet-- you want to find the slowest airspeed where the wing flies smoothly. What is the airspeed? What bank angle are you using?
3) Take careful note of the required roll input for 2). Are you using your muscles to give a left roll input (pushing bar toward the right), a right roll input (pushing bar toward the left), or neither?
4) Maintaining this bank angle, slowly pull in the bar to accelerate to the highest airspeed that you find comfortable or feasible, while adding power to maintain constant altitude. Allow a comfortable margin below airspeed redline and below engine rpm redline. Note the airspeed. What is the airspeed? The airspeed for this portion may end up being limited by engine rpm limits, engine power output at full throttle, airspeed redline, bar pressure, room to physically pull in the bar, or some other factor. Which was it?
5) Take careful note of the required roll input for 4). Are you using your muscles to give a left roll input (forcing the bar toward the right), a right roll input (forcing the bar toward the left), or neither? Are you exerting more force on the bar than you were for part 2), or less so?
6) While maintaining the same bank angle, slowly push out the bar to slow again to the same low airspeed as you used in part 2, while reducing power to hold a constant altitude, so that you end back in the configuration you had in part 2.
7) Parts 8-10 are optional and best suited to aircraft with a locking hand throttle and airspeed indicator; if this is not you or if you just want to keep it simple, skip to 11.
8) Pull in the bar again to accelerate to the same high airspeed that you used in part 4, but this time don’t advance the throttle. Leave the throttle in the same position that you had it in parts 2 and 6. You will of course be descending.
9) If you have a vertical speed indicator, what is the sink rate? Take careful note of the required roll input for 8). Are you using your muscles to give a left roll input (forcing the bar toward the right), a right roll input (forcing the bar toward the left), or neither? Are you exerting more roll force on the bar than you were for part 4 (same high airspeed, but more power, and constant altitude), or less?
10) Take a moment to summarize the trike’s roll trim at low speed and constant altitude, high speed and constant altitude, and high speed and descending. Example: “In a left turn, I had to give a mild right roll input to hold the bank angle constant when airspeed was low-- the trike had a mild tendency to roll into a tighter turn. When I increased the airspeed while advancing the throttle to maintain altitude, I now had to give a mild left roll input to hold a constant bank angle-- the trike had a mild tendency to roll toward wings-level. At the same high airspeed but a lower power setting, where the trike was descending, I had to give a much stronger (or slightly stronger?) left roll input to hold a constant bank angle-- the trike had a much stronger (or slightly stronger?) tendency to roll toward wings level.” Or-- “there wasn’t any difference between the required roll control input at high airspeed and high power setting and the required roll control input at high airspeed and low power setting.” Etc-- just describe whatever you find.
11) Repeat the entire protocol 1-10 above, but this time in a right turn. Use the same visual reference mark on the right wing, that you used on the left wing.
12) Considering the left-turn and right-turn tests as a whole, was there a clear trend in the results, independent of engine torque, P-factor, etc? E.g., at low airspeed, did the trike always tend to roll into a tighter turn? At high airspeed, did the trike always tend to roll toward wings-level? If so, was this tendency always greater at low power settings (high sink rate) than at high power settings (constant altitude)? Can you see any other clear patterns in the results, that seem independent of engine torque, P-factor, etc? I.e., trends that would likely be present even if we were running a jet engine or other torqueless power system? Or did engine torque, P-factor, etc seem to be the overwhelming factors, so that there was no near clear pattern between the left-turn tests and the right-turn tests?
13) Try the following: enter a 35 to 40 degree banked left turn at a low airspeed. Firmly pull in the bar while doing your best to make no roll input (no muscle force on the bar) either to the left or right. Does the trike tend to roll through wings-level into a right turn? Repeat the same starting from a right banked turn. Can you find a power setting and initial airspeed where pulling in the bar while making no roll input makes the glider roll through wings-level into the opposite bank, regardless if you started in a left turn or a right turn? Can you can do a series of mild wingovers or roll reversals just by making pitch inputs alone? If so, describe the starting airspeed and power setting (rpm) where this worked for you.
14) What is your stall speed in a wings-level stall, with power applied as needed to maintain altitude as you approach the stall? Is this a full stall with break, or just a “mush”?
15) That’s it for the in-flight tests. Please re-read the entire protocol and check that you have answered all the embedded questions, as best as you can. Also, please note the following: type of trike wing. Area of trike wing. Direction prop turns as viewed from rear. Estimated weight of whole aircraft and contents including pilot and fuel. Did you have an airspeed indicator, or were you just estimating? What type of airspeed indicator? (E.g. Hall type/ ultralight type of a disk in a vertical tube, or rotating wheel, or pitot tube.) Did you have a hand throttle, or were you just holding a foot throttle in constant position as best as you could? Note that even if you lack a locking hand throttle and / or airspeed indicator, you can still generate very useful data, but just let me know that you were estimating the airspeed and/or trying to hold the throttle position fixed as best you could with a foot throttle. Note-- if you reply directly by email rather than by reply to a forum or group, please let me know in what forum or group you found the survey, as I may post it to more than one and maybe in slightly different formats.
16) Can you suggest another high-traffic trike forum where I would likely get some responses to this query?
Thanks very much
Steve Seibel
Corvallis, OR
sseibelgroups at gmail dot com
