The Effect of Store-to-store Energy Transfers On the Global Dynamics of Aircraft

Guilherme M. Eymael Author

04/03/2021 Added

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Despite decades of innovation in aerospace engineering, wing attachments – also known as stores – still pose a serious threat to the safety and performance of modern aircraft. This research intended to understand the effect of different stores combinations on the dynamics of aircraft. More specifically, we focused on finding interactions between the stores.

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[00:00:01.170]Hello everyone, my name is Guilherme M.Eymael
[00:00:04.180]and today I'll be talking about my research
[00:00:06.710]on the effect of store-to-store energy transfers
[00:00:10.980]on the global dynamics of aircraft.
[00:00:14.130]This project was funded partly by UCARE
[00:00:16.810]and partly by the John Woollam Scholar Award.
[00:00:20.060]And it was completed under the supervision
[00:00:22.070]of Dr. Keegan Moore.
[00:00:25.880]So to give you some background,
[00:00:27.840]stores are also known as wing attachments.
[00:00:30.630]And despite decades of innovation in aerospace engineering
[00:00:33.833]wind attachments pose a serious threat
[00:00:37.060]to safety and performance of modern aircraft.
[00:00:40.440]Previous research has found that these stores
[00:00:42.690]can induce unwanted self-sustaining vibrations
[00:00:46.020]which are known as limit cycle oscillations.
[00:00:49.730]During normal flight operations,
[00:00:51.540]these oscillations produce large lateral motions
[00:00:56.380]making difficult to read displays
[00:00:58.640]and inhibiting the pilot's ability
[00:01:00.580]to effectively use the flight control mechanisms.
[00:01:06.320]Also, previous experimental results
[00:01:08.610]indicate that wink based stores
[00:01:10.900]can drastically altered the global dynamics
[00:01:12.960]of the parent aircraft,
[00:01:14.270]when the coupling mechanism between the stores and the wings
[00:01:17.980]consist of strong nonlinearities.
[00:01:21.340]So to understand how stores played a role
[00:01:24.260]in the airplane dynamics, three configurations were studied.
[00:01:28.420]A locked-locked case
[00:01:30.380]where neither store was allowed to move
[00:01:32.870]so the stores only contributed as mass effects.
[00:01:36.410]An unlocked-locked case
[00:01:38.800]where only one store was allowed to move
[00:01:42.095]and an unlocked-unlocked case
[00:01:43.720]where both stores were allowed to move.
[00:01:47.360]Furthermore, this best research found that the effect
[00:01:51.430]on airplane behavior is dramatically different.
[00:01:54.850]So when two stores are installed, instead of only one
[00:01:59.140]it was observed that the effects of the stores
[00:02:01.910]were inconsistent
[00:02:03.900]because while two stores had a bigger effect
[00:02:07.480]on the first mode
[00:02:09.120]the same two stores had no effect on the second mode
[00:02:13.600]unlike the case with one store.
[00:02:16.490]Therefore we hypothesized that two stores could interact
[00:02:21.600]with each other destructively, canceling out their effects.
[00:02:31.360]So our approach was to simplify the dynamics of the airplane
[00:02:37.390]by using a reduce or model system.
[00:02:41.570]In this case, if store to store interactions
[00:02:44.760]occur in the simplified system,
[00:02:46.930]they should also occur in the more complicated one.
[00:02:50.270]To do so, we reduced the dynamics
[00:02:53.000]to a two degree of freedom system
[00:02:55.060]that reproduced the first two flexible modes
[00:02:57.670]of the airplane.
[00:02:59.210]In this first linear case,
[00:03:01.560]each of the two masses represents a wing.
[00:03:04.700]And in the following two cases,
[00:03:07.440]when stores were added, each store when unlocked
[00:03:11.110]added an additional degree of freedom to the system.
[00:03:16.100]So part of the analysis was to simulate the response
[00:03:19.050]of the reduced or a model for 10 seconds
[00:03:22.010]by applying an initial velocity
[00:03:25.020]to the left wing for all three configurations.
[00:03:29.340]The comparison of displacements seen in this plot
[00:03:33.820]indicates that the store's accelerate
[00:03:36.510]the decay of the vibrations.
[00:03:40.640]Resulting from energy transfers
[00:03:42.670]from the wings to the stores this increased decay indicates
[00:03:48.200]that the store has changed the global dynamics
[00:03:50.450]of the reduced order model.
[00:03:58.120]Next, to understand the energy transfers,
[00:04:01.670]we computed the energy dissipated by each mode
[00:04:05.260]for varying initial velocity.
[00:04:09.100]As observed both configurations display a similar trend
[00:04:14.010]for their first two flexible modes,
[00:04:16.870]which are represented by modes two and three
[00:04:19.770]in the left plot and modes three and four in the right plot.
[00:04:25.920]Therefore, no significant difference was observed
[00:04:29.180]when a second store is attached
[00:04:31.800]indicating that there are no interactions
[00:04:33.800]between the stores under a transient excitation.
[00:04:39.500]Then periodic forcing was used to investigate the effects
[00:04:43.450]of sustained excitation on interactions between stores.
[00:04:48.020]The left-wing was forced to using a harmonic excitation
[00:04:52.040]and the displacement response was analyzed
[00:04:55.130]for increasing forcing amplitude.
[00:04:58.110]And a strongly modulated response
[00:05:00.290]was observed for some forcing attitudes,
[00:05:03.130]which indicated strong interactions
[00:05:05.730]between the wings and the stores.
[00:05:08.560]As seen in this case, these strongly modulated response
[00:05:13.310]is periodic and regular.
[00:05:19.970]However, above a critical forcing amplitude
[00:05:23.110]this strongly modulated response behavior
[00:05:25.590]becomes aperiodic and irregular,
[00:05:28.320]due to the strong nonlinearity in the system.
[00:05:32.120]Therefore, small beats occur in the stores displacement.
[00:05:37.120]Hinting that the stores are interacting with each other.
[00:05:41.300]So to find whether this interactions occur
[00:05:44.850]and to better understand the behavior of the stores
[00:05:47.440]during the small beats
[00:05:49.220]a more detailed energy analysis was required.
[00:05:54.740]Such energy analysis can be seen this plot
[00:05:58.460]where we estimated the instantaneous total energy
[00:06:01.520]in each mass and zoomed in into a smaller beat.
[00:06:06.700]Here the total energies indicate that the small beat occurs
[00:06:11.280]when only one store interact with the wings
[00:06:15.010]and not the other store.
[00:06:16.870]By that, the total energies denied the existence
[00:06:21.550]of interactions between the stores
[00:06:23.260]and falsified our hypothesis.
[00:06:27.870]So to summarize this project,
[00:06:31.560]a reduced-order model was used
[00:06:33.670]to investigate the dynamics of a fighter jet
[00:06:36.090]with two wing attachments.
[00:06:38.350]Then we investigated the system
[00:06:40.630]for a single impulse response
[00:06:43.560]where no store to store interactions was found.
[00:06:47.580]Then we investigated a system for force response
[00:06:51.160]and even though there were indications
[00:06:54.440]about store to store energy transfers
[00:06:57.320]from the strongly modulated responses
[00:07:00.240]small beats in the displacement plot,
[00:07:03.190]the total energy analysis invalidated our theory,
[00:07:06.410]by confirming that only one story interacts with the wings
[00:07:10.510]while the other one doesn't play a role
[00:07:13.120]in the dynamics of the aircraft.
[00:07:19.970]So as a conclusion, store-to-store interactions
[00:07:22.730]do not occur in our reduced-order-model.
[00:07:27.560]And since our original hypothesis wasn't validated
[00:07:31.250]for the reduced order model,
[00:07:33.270]we will continue this study with the full-order model
[00:07:36.410]and trying to validate this conclusion
[00:07:39.240]to pursue a new hypothesis.
[00:07:42.797]Thank you very much for watching my presentation,
[00:07:47.000]and if any questions arise, I'll be happy to answer them.
[00:07:51.250]Thank you.

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The Effect of Store-to-store Energy Transfers On the Global Dynamics of Aircraft

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