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US Army Advanced Composite Airframe Program (ACAP)

flateric

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Full-Scale Crash Tests of the ACAP Helicopters
Full-scale crash qualification tests were performed of the Bell and Sikorsky Advanced
Composite Airframe Program (ACAP) helicopters in 1987 [38-40]. The purpose of the Army-sponsored
ACAP was to demonstrate the potential of advanced composite materials to save weight and cost in
airframe structures while achieving systems compatibility and meeting military requirements for
vulnerability reduction, reliability, maintainability, and survivability. In 1981, the U.S. Army awarded
separate contracts to Bell Helicopter Textron and Sikorsky Aircraft Company to develop, manufacture,
and test helicopters constructed primarily of advanced composite materials. Each company
manufactured three airframes that were tested under a variety of static and dynamic conditions to
demonstrate compliance with the program objectives. In addition, one helicopter airframe from each
company was equipped to become a flying prototype. Crash tests of the Bell and Sikorsky ACAP static
test articles were conducted in 1987 at the IDRF in support of the U.S. Army AATD to demonstrate
their impact performance and to verify compliance with crash requirements. Pre- and post-test
photographs of the full-scale crash tests are shown in Figure 17. The Bell ACAP helicopter impacted
with a combined 42-fps vertical and 27-fps forward velocity, while the Sikorsky ACAP helicopter
impacted at 39-fps vertical velocity. These tests demonstrated the successful application of composite
materials to save weight and maintenance costs in rotorcraft design, while also achieving improved
crash performance.

In 1998, a research project was initiated to demonstrate the capabilities of state-of-the-art
commercial crash simulation codes in predicting the dynamic structural response of a prototype
composite helicopter, the Sikorsky ACAP helicopter, during a full-scale crash test. A crash simulation
of the full-scale crash test was developed using the commercial nonlinear, explicit transient dynamic
code, MSC.Dytran [52]. The objective of the crash simulation was to evaluate the capabilities of the
code in predicting the response of a composite airframe subjected to impact loading. An existing
NASTRAN [54] modal-vibration model of the Sikorsky ACAP helicopter was modified and converted
into a model suitable for crash simulation. The MSC.Dytran model is shown in Figure 25. A two-stage
modeling approach was implemented for the crash simulation and an external user-defined subroutine
was developed to represent the complex landing gear response. Analytical predictions of structural
deformation and failure, the time sequence of events, and the dynamic response of the airframe structure
were generated. The numerical results were correlated with the experimental data to validate the
simulation [55-58]. The level of agreement obtained between the experimental and analytical data
builds further confidence in the use of nonlinear, explicit transient dynamic finite element codes as a
crashworthy design and certification tool for aircraft.

Full-Scale Crash Test of the Sikorsky ACAP Helicopter (Flight Test Article)
A full-scale crash test of the Sikorsky ACAP helicopter was performed at the IDRF in 1999. The
main purpose of the test was to obtain experimental data for validation of a finite element crash
simulation. The helicopter was the flight test article built by Sikorsky Aircraft under sponsorship by the
U.S. Army during the ACAP. The helicopter was constructed primarily of advanced composite
materials and was designed to meet the Army's stringent MIL-STD-1290A [42] crashworthiness criteria.
For the crash test, the aircraft was outfitted with two crew and two troop seats and four instrumented
anthropomorphic dummies. The test was performed at 38-fps vertical and 32.5-fps horizontal velocity
onto a rigid impact surface [43]. Approximately 120 channels of dynamic data were collected.
Photographs of the helicopter taken just prior to and after impact are shown in Figure 22.
In addition to obtaining structural crash data for validating a nonlinear transient dynamic
computer simulation, several ancillary experiments were included. A programmable electronic crash
sensor unit (ECSU) was mounted on the cabin floor near the troop seats. The sensor was typical of the
kind that might be used to inflate an airbag. During the test, the ECSU operated successfully and was
very helpful in obtaining time synchronization between the exterior and interior cameras. In addition,
the left and right fuel tanks were instrumented with two transducers each to measure the hydrodynamic
pressure pulse during impact. The pilot and copilot dummies were seated in two military-qualified loadlimiting
seats from two different vendors. The troop dummies were seated in ceiling-suspended troop
seats, each with two wire-bender energy absorbers that were mounted in the rear cabin area of the
helicopter. The detailed seat and occupant response data obtained from the crash test were evaluated
and the occupant data were correlated with injury prediction models [44].

A History of Full-Scale Aircraft and Rotorcraft Crash Testing and Simulation at NASA Langley Research Center
http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.75.1605
 

flateric

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higher-res photos found at
A Summary of DOD-Sponsored Research Performed at NASA Langley's Impact Dynamics Research Facility
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.80.2024&rep=rep1&type=pdf
 

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Stargazer2006

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Awesome pics! Photos of the ACAP helos have always been pretty difficult to come by, especially color ones.

Perhaps the lower-res pics could be deleted from the first of the two posts??
 

Stargazer2006

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Artwork of the Bell D292 ACAP (published in Popular Science, February 1983):
 

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Stargazer2006

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Model of the Sikorsky S-75 ACAP (published in Popular Science, February 1983):
 

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Mark Nankivil

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Greetings All -

A recent donation to the Museum had a 1983/84 Bell Helicopter Textron Reference Guide which included the following page for Bell's ACAP. I also have a preliminary design report for Boeing Vertol's design which I'll scan and post shortly.

Enjoy the Day! Mark
 

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Mark Nankivil

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Greetings All -

Boeing Vertol was also involved in the initial phases of the ACAP program. I have a copy of Volume I - Preliminary Design - Part I dated December 1981 and I'll post drawings from the report in the order they are presented in the report.

The design process started with the design of three composite helicopter airframes - Best Structure, HEI-T Ballistic Tolerant and Low Radar Cross Section - and all used the Bo-105's dynamic components.

Enjoy the Day! Mark
 

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flateric

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Very interesting and rare stuff. Thanks, Mark!
 

Stargazer2006

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I second that. I had never seen Boeing's proposal for ACAP. Thank you so much!
 

Mark Nankivil

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Thanks guys - surprised me too when I saw the report. Maybe a change to the thread title then?

Some more drawings from the report - interestingly no drawing for Concept 3....

Enjoy the Day! Mark
 

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Mark Nankivil

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Stargazer2006

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Wow...

Never realized that low RCS was part of the ACAP package... Or was it just a Boeing initiative for their proposal?

Also, do you have a report number for these wonderful pics that could give us a clue as to what Boeing program number was associated with ACAP (they usually start with D***-).

Thanks again, Mark!
 

yasotay

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Absolutely fantastic. It is amazing how much work was done in the 80's and 90's. Soon to be lost in the US as the engineers who worked these efforts retire. Few aero engineers going into rotorcraft these days. Most who graduate go into other areas.

Is there any way to get access to the full report?
 

Mark Nankivil

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Hi Stargazer2006 -

I cannot find any Boeing Vertol project number assigned to the project or at least mentioned in the report. Yastotay, at some point I'll take it apart and copy/scan it. You'll be one of the first to know when I get that done.

I've attached a scan of the report description page if someone is in a position to track down Volume 2 or other documentation related to ACAP.

Enjoy the Day! Mark
 

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Stargazer2006

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Ha! Found it on the cover:

Performing Org. Report Number
D210-11672-1
One of the numerous studies under the "D210-" prefix. Used by Boeing for a whole lot of stuff I'm afraid...
 

flateric

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Renamed topic to fit Boeing ACAP entry
 

yasotay

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Mark Nankivil said:
Hi Stargazer2006 -

I cannot find any Boeing Vertol project number assigned to the project or at least mentioned in the report. Yastotay, at some point I'll take it apart and copy/scan it. You'll be one of the first to know when I get that done.

I've attached a scan of the report description page if someone is in a position to track down Volume 2 or other documentation related to ACAP.

Enjoy the Day! Mark
Mark, That is fantastic! I know some rotorcraft engineers who might really like to rediscover that report!
 

Mark Nankivil

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I guess we'll see this alongside the Stealth H-60 model in Dragon's model catalog soon ;D

Enjoy the Day! Mark
 

BillRo

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When you look at one of the Sikorsky drop test vehicles it has a noticeable chine that is not apparent in the drawings. That may be because Sikorsky would also have been asked for a design with reduced signature. It may not be a coincidence that at the time Northrop white world advanced design were asked to study a helicopter with reduced RCS for Sikorsky. We thought that an unusual request since helicopter engineers and aircraft engineers never mix. We gave the job to John B., one of our most creative configurators, and he came up with something that, although not as radical as the Boeing low RCS design, had significant shaping. It got sent off to them and we heard no more. Sorry no drawings.
 

Stargazer2006

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BillRo said:
When you look at one of the Sikorsky drop test vehicles it has a noticeable chine that is not apparent in the drawings. That may be because Sikorsky would also have been asked for a design with reduced signature. It may not be a coincidence that at the time Northrop white world advanced design were asked to study a helicopter with reduced RCS for Sikorsky. We thought that an unusual request since helicopter engineers and aircraft engineers never mix. We gave the job to John B., one of our most creative configurators, and he came up with something that, although not as radical as the Boeing low RCS design, had significant shaping. It got sent off to them and we heard no more. Sorry no drawings.
Interesting. Are you saying that the S-75 design involved Northrop at some point, or was it a separate design?
 

Triton

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deeptowild.blogspot.com
Model showing the similarities between the Sikorsky S-75 and the S-76.

Sikorsky S-75 wind tunnel model.

Three-view drawing of Sikorsky S-75.

Inboard profile of Sikorsky S-75.

Sikorsky S-75 airframe structural breakdown.

Sikorsky S-75 airframe materials.

Source:
http://www.sikorskyarchives.com/S-75%20ACAP.php
 

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Stargazer2006

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Very, very nice! Thanks a lot for sharing these pics, most of which I'd never seen before.
 

hesham

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Great find my dear Triton.
 

hesham

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From Air International magazine,


here is the Sikorsky S-75.
 

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Jemiba

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Accidentally found in the vertiflite September/October 1984 issue, a photo
of the Bell ACAP contender:
 

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Moose

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Nice find! Sadly, not as pretty as the Sikorsky bird.
 

hesham

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Hi,


here is ACAP Model;


http://www.sikorskyarchives.com/pdf/NEWS%20OCT%202009%20EG.pdf
 

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500 Fan

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Hughes Helicopters were one of the five companies who tendered a design for the initial RFPs. Does anyone have any information on their proposed design or better still, a drawing of their proposed ACAP?

The low RCS details are of interest as allegedly McDonnell Douglas Helicopter Company later flew a still-classified low RCS helicopter based on the MD500 and it would be interesting to see the Hughes/MDHC design approach to low RCS rotorcraft design.

500 Fan.
 

500 Fan

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litzj said:
Could this project affect the modified version of UH-60 for Bin Laden Hunt?
Possibly. Most low observable helicopters, real or the ones that exist only as proposals, appear to feature a fuselage with slanted sides. The aviation press seem to have concentrated on fixed-wing stealth aircraft but LO heliccopters are worthy of some investigation. Hopefully some of the older classified programmes come out of the dark soon.

500 Fan.
 
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